EASTERN OYSTER (Crassostrea virginica) AQUACULTURE AND DIVERSITY OF ASSOCIATED SPECIES

Transcription

1 P a g e 1 EASTERN OYSTER (Crassostrea virginica) AQUACULTURE AND DIVERSITY OF ASSOCIATED SPECIES Gulnihal Ozbay, Brian Reckenbeil, Frank Marenghi, and Patrick Erbland Delaware State University, Department of Agriculture and Natural Resources, 1200 North DuPont Highway, Dover, Delaware USA Table of Contents Page# Foreword 3 A. Eastern Oysters 4 B. Habitat and Biodiversity 7 C. Oyster Restoration 11 D. Oyster Aquaculture 14 E. Case Studies 18 E.1. Diversity in Relation to Man-Made Oyster Habitats: 20 Aquaculture Gear vs. Created Reef E.2. Diversity in Relation to Floating Aquaculture Gear 26 E.3. Diversity in Relation to Rip-Rap Stocked with Cultured 33 Oysters F. Final Remarks 40 G. Acknowledgments 45 H. Literature Cited 46

2 P a g e 2 Common Abbreviations and Definitions CIB DIB RB IRB LAB RRO RR NS bu. Rack and Bag Taylor float Riprap Habitat Biodiversity Ecosystem Hypoxia Macrofauna Infauna Epifauna Meroplankton The Center for the Inland Bays Delaware Inland Bays Rehoboth Bay Indian River Bay Little Assawoman Bay Riprap stocked with oysters Riprap with no oysters Natural Marsh Shoreline Bushel (35.24l) Aquaculture technique using gear (rack or table) to hold shellfish in containment gear (bags) off of the benthos (Figure 9.a) Floating aquaculture gear, PVC holding a wire gauge basket (Figure 14a) Rocks randomly placed along the shoreline for erosion control (Figure s 5, 21a, 23) an area with the prevailing range of conditions in which an organism is able to survive and reproduce. refers to the degree of variation of life forms within a given population or ecosystem a community of living and dead organisms interacting in the same physical environment water conditions with limited dissolved oxygen (<5.0mg/l) invertebrates that live on or in sediments or are attached to hard substrates macrofauna which live within a substrate organisms living on or just above the benthos substrate organisms that are planktonic for only a part of their life cycles, usually the larval stage

3 P a g e 3 FOREWORD The eastern oyster, Crassostrea virginica, is a keystone species with the welldocumented ability to provide ecological services, environmental enrichment, and commercial value. Oyster reefs provide valuable habitat for many ecologically and economically important species, as well as stabilizing benthic and intertidal habitats. Oysters drive benthic-pelagic coupling as they filter suspended particles from the water and their deposits enrich benthic communities and increase carbon sequestration. Their bioactivity and structure creation leads to a greater abundance and diversity of other aquatic species. A dramatic decline in the eastern oyster populations of the Mid-Atlantic and Gulf Coast of the United States has been well documented since the late 1800s. This decline is often attributed to anthropogenic actions including overharvesting, habitat degradation, and reduction in water quality. Everincreasing land use and development have impacted the eastern oyster throughout their range. Dermo and MS diseases caused massive mortality in the past and continue to suppress recovery of eastern oyster populations. Diminished oyster abundances and the critical ecosystem services they provide may lead to a negative cascading effect on the entire estuarine environment. The culture of the eastern oyster in containment gear has become a valuable tool not only of commercial aquaculture but also for restoration programs throughout many states along the East Coast of the United States. Oysters grown in aquaculture gear provide many of the same ecological services as natural or restored reefs. The cultured oysters and gear may also provide important habitat for fish, mobile crustaceans, and a variety of other species. A number of studies have demonstrated a positive correlation between oyster aquaculture and the presence of infaunal and epifaunal communities, including populations of ecologically and economically important fauna. In response to the drastic decline in oyster populations, conservation organizations in the coastal eastern states have developed community culturing programs, commonly referred to as oyster gardening, to help mitigate the loss of oyster populations. Oyster gardening instills in the community a strong sense of environmental stewardship while locally providing the ecological services of the oyster stocks. As enhancement and restoration of the eastern oyster move forward, it is important to understand the overall contributions and impacts that oyster aquaculture may impart in the surrounding environment. As wild oyster stocks continue to dwindle, research focusing on the ecological effects of commercial oyster aquaculture is being carried out with greater urgency.

4 P a g e 4 A. Eastern Oysters (Crassostrea virginica) The eastern oyster (Crassostrea virginica) is classified under Phylum Mollusca, Class Bivalvia (Pelecypoda), Order Mytoloida (Pleriodea), and the Family Ostereidae. It inhabits the benthos of coastal waters of eastern North America from Canada to the Gulf of Mexico (Figure 1) and it is one of the oldest species of extensively cultured bivalves (Sellers and Stanley 1984, Lorio and Malone 1995). C. virginica is adapted to a wide range of environmental conditions and can thrive in areas with notably different salinities and temperature. This ability to withstand stress and physical disturbance is vital and allows them to survive even after being frozen and subsequently thawed. Shumway (1996) reports intertidal oysters in the Gulf of Mexico survive after being exposed to high air temperatures of o C for 3 hours. Although they normally reside in salinities from 5-40 ppt, ppt is widely considered optimal for eastern oysters (Shumway 1996). As Wells (1961) discussed, C. virginica distribution in low salinities may be physiologically limited because they are better suited to marine conditions and are also limited to intertidal areas due to predation. In 1996 Kennedy issued a report based on historical records which stated that the average size of individuals and their densities on reefs have been greatly reduced from historic levels. Historically, these oyster populations were so healthy and large in size that there are accounts of oysters that had to be bisected or trisected before they would fit in the mouth. In addition, oyster reef formation presented a significant navigational hazard, often grounding ships (Kennedy 1996). Ingerssol (1881, cited in Kennedy 1996), discussed shell middens left by Native Americans, confirming oyster shells greater than 30 cm in height. These historic populations apparently represented the capital or breeding stock and provided the habitat for subsequent generations (Kennedy 1996).

5 P a g e 5 Figure 1. Oyster reefs habitat range. Purple regions on the east coast of U.S. show the range for eastern oysters. Image courtesy of Chesapeake Bay NOAA Office ( Overharvesting and habitat destruction since the mid-19 th century has resulted in a dramatic decline of the oyster populations and oyster reefs in the Mid-Atlantic region (Kennedy 1996). Oysters were harvested for consumption while shell from reefs had been utilized for home and road construction and even for the liming of farm fields (Kennedy and Breisch 1981, Rothschild et al. 1994). Eastern oysters are gregarious reef builders with young planktonic larvae requiring shell, or cultch, for settlement and metamorphosis (Smith et al. 2001). The loss of live oysters and their cultch equates to a quantitative habitat loss for oysters and the surrounding environment. Blanketing sedimentation due to erosion or re-suspension also decreases cultch availability for settling larvae (Smith et al. 2001) (Figure 2). Figure 2 summarizes some of the ecosystem benefits provided by eastern oysters as well as ecosystem stressors which inhibit oyster growth and survival. Figure 2. Ecosystem benefits oysters provide and ecosystem stressors oysters are threatened by. Image courtesy of Chesapeake Bay NOAA Office ( Within the last five decades two diseases, Haplosporidium nelsoni (MS) and Perkinsus marinus (Dermo), have had a devastating impact regionally and continue to be bottlenecks in oyster recruitment and restoration efforts (Ewart and Ford 1993, Ford and Tripp 1996, Mann and Powell 2007). MS disease was a leading factor in the decline of oysters in the Delaware Inland Bays (DIB) in the 1950s (Scotto et al. 1983). MS infects and causes oyster mortality predominately in young oysters (Ewart and Ford 1993, Wilberg et al. 2011) whereas Dermo often harms older oysters due to an increase in susceptibility to parasite exposure in subsequent years (Ewart and Ford 1993). Dermo and MS cause greater oyster mortalities in high salinities and high temperatures (Ewart

6 P a g e 6 and Ford 1993, Ford and Tripp 1996, Mann and Powell 2007, and Vølstad et al. 2008). Dermo disease spreads from one oyster to another when parasites are transmitted from an infected to uninfected host (Cook et al. 1998). This may eventually result in a large mortality event. Kendall et al. (2007) reported that Dermo is active within the DIB waters yet has remained at concentrations too low for outbreaks to occur. Considering the limited natural oyster populations in the DIB, other shellfish populations may act as secondary hosts for P. marinus (Kendall et al. 2007). Mortality rates may rise quickly after being infected for two years from both diseases (Coen et al. 1999) and different strains of pathogens may occur between regions (Bushek et al. 2004). According to Mann and Powell (2007), remaining stocks of oysters in the Delaware Bay are offspring from the oysters that survived the epizootic MS disease in (Mann and Powell 2007). The Rutgers University Haskins Shellfish Research Laboratory (HSRL), in Port Norris, NJ, has been culturing these MS-resistant high performance strains of oysters. Delaware s oyster gardening program in the DIB currently purchases its oyster larvae from HSRL biennially. Using disease resistant broodstock, it is expected that reproductive failures from low population growth and natural recruitment will be prevented (Brumbaugh et al. 2000). Historically, the eastern oyster was the dominant suspension feeder in Mid-Atlantic estuaries. Newell (1988) calculated summer filtration rates of eastern oysters based on the historical and present population levels. The findings showed that the oyster populations in Chesapeake Bay prior to 1870 could filter its entire volume in 3 to 6 d versus 325 d for the 1988 stock. According to Newell (1988), if the historical population was same in 1988 as in 1870, the oysters would have removed 23-41% of that year s phytoplankton produced carbon versus 0.4% of the phytoplankton produced carbon for 1988 at its phytoplankton density. Eastern oysters persist in various environmental conditions and their feeding mechanism is especially adapted for turbid environments (Rhoads 1974, Boynton et al. 1980, Newell 1988). Newell (1988) found subtidal oysters in Chesapeake Bay feeding for 23 h a day with no diurnal rhythm but with seasonal variation and average summer filtration rate of L/kg/d. Their filtering activities are extremely efficient and they have the ability to capture bacteria and both organic and inorganic particles down to 3 µm (Haven and Morales-Almo 1970). Filtering rates of this species are not reduced during an increase in food availability, but their selectivity for ingesting food particles increases (MacDonald 1998). This feeding mechanism, coupled with constant feeding and high filtering efficiency, results in clearance rates much greater than most other suspension feeders (Newell et al. 2005). More specifically, food particles that are captured are bound into mucous strands of feces and pseudofeces limits particle re-suspension and increases benthic-pelagic food web coupling (Newell 1988). As the concentration of particles in water increases, the concentration of particulate organic matter (POM) in pseudofeces also increases (Newell et al. 2005). Peterson and Heck (1999) and Newell et al. (2005) summarized that oyster biodeposits yield 2-3

7 P a g e 7 times the amount of C, N, and P by weight compared to unprocessed settling particles. As stated by Newell et al. (2005), bivalve feeding enhances nutrient loss through sedimentation, bacterial denitrification, and trapping of nutrients by the microphytobenthos. Newell et al. (2002) studied enriched sediment cores with simulated oyster biodeposition using pelletized phytoplankton in a controlled laboratory environment and found that in anoxic sediments nitrogen is released solely as ammonium ion but when coupled with nitrification/ denitrification between aerobic and anaerobic sediment zones a 20% loss of nitrogen as nitrogen gas (N 2 ) was observed. He exposed core samples to a 12:12 h light cycle which supported sufficient microphytobenthos to sequester additional nitrogen. As he hypothesized, oyster biodeposits served to enhance system-wide denitrification; 17-24% of particulate organic nitrogen (PON) deposited in aerobic sediments was denitrified and was unavailable to phytoplankton. The biological processes of filtering sediments and algae from the water column reduces turbidity and allows for greater light penetration in shallow coastal bays and estuaries, which in turn facilitates the growth of submerged aquatic vegetation (SAV) such as eelgrass (Phelps 1994, Peterson and Heck 1999, Newell 2004, Caraco et al. 2006, Cerco and Noel 2007). B. Habitat and Biodiversity Environments and ecological communities are dynamic aspects of the ecosystem and need to be considered accordingly. Habitat may be considered as an area with the prevailing range of biotic and abiotic factors which support a population s ability to survive and reproduce. The estuarine environment is a stressful and rigorous habitat for many species due to dynamically shifting environmental conditions. Survival and colonization within this ecosystem requires particular adaptations, such as morphological adaptations for attachment to the substrate and physiological adaptations to endure fluctuations in salinity or turbidity (Cognetti and Maltagliati 2000). Oysters possess such adaptations, which give them exceptional advantages to overcome the demanding conditions of their habitat. Biodiversity, or biological diversity, refers to the degree of variation of life forms within a given population or ecosystem. The three concepts involved in biological diversity include: 1. genetic diversity which refers to the number of genetic characteristics within the same species, 2. ecosystem/habitat diversity which is the diversity of habitat in relation to the specific area, and 3. species diversity which is the number of species within a collection (Nybakken and Bertness 2004). However, Botkin and Keller (2011) make a further distinction in species diversity by defining species richness as the total number of species in an area while species evenness is the relative abundance of the species. Species diversity may help maintain or enhance the stability of an ecosystem as well as helping a system recover from disturbances. As Cunningham and Cunningham (2011) noted, biological communities with high species diversity endure

8 P a g e 8 environmental stress and recover much better than the communities with fewer species. Biodiversity is threatened by habitat loss and degradation, overexploitation, and competition from invasive alien species (UNEP-WCMC 2011). Responses to mitigate these threats are increasingly required to protect and maintain biodiversity. Oyster aquaculture demonstrates potential to restore and enhance species diversity; mitigate the damage caused by habitat loss and degradation, and the over-exploitation of fishery resources in estuarine habitats. Oyster bioactivity implies greater positive services in the habitat than just the provision of structure (Jackson et al. 2008). The eastern oyster has a long history of being studied but an even longer history of being exploited (Kennedy 1989, Hargis and Haven 1988, MacKenzie 2007). Despite the early observations around 1877, it was only within the second half of the last century that the ecological benefits of oyster reefs have been realized. This keystone species adds ecological, environmental, and commercial value to areas with established oyster populations (Coen et al. 2007). Oyster reefs provide services to the ecosystem create conditions required for the settlement of other species. Those services include water filtration (Figure 3), benthic-pelagic coupling, carbon sequestration, and stabilization of benthic and intertidal habitats. Oysters provide habitat in a variety of ways, especially in otherwise softbottom environments. Their biogenic reefs supply a hard substrate for sessile invertebrates to settle on, provide refugia from predation within their complex three dimensional structures, enrich the benthos with biodeposits, and provide structure and forage species for predatory fishes, many of which have value to recreational or commercial fisheries (Kennedy 1996). The presence of oyster reefs also affects other portions of the estuarine ecosystem including the shoreline. Oysters, like all filter-feeders, may increase photosynthetically active radiation penetration by filtering phytoplankton and other particles from the water to the point where submerged aquatic vegetation can become reestablished and may help to remove excess nutrients in anthropogenically eutrophied estuaries and bays (Newell 2004).

9 P a g e Figure 3.. Visible differences in water transparency due to oyster filtration occurring within a flow-through system. Tanks 1 & 4 provide neither structure nor bioactivity. Tank 2 oyster shells provided structure. Tank 3 live oysters provide structure and bioactivity. Photo courtesy of Jackson (2003). Oyster reefs are complex systems on the benthic landscape. Wells (1961) surveyed aquatic species in and around a single oyster reef supporting over three hundred species. Greater fish species diversity is associated with restored oyster reefs than with artificial fishing reefs (Harding and Mann 1999). Harding and Mann (2001) further reported increases in size and abundance of transient fish along a gradient from sand flats to oyster reefs, thus indicating increasing habitat quality and productivity with proximity to oyster reefs. Not only are oyster reefs essential for commercial species, they are essential to many species, the values of which have yet to be discovered. Oyster reefs are important nursery habitat for juveniles, some of which are economically important. This is especially important in regions where seagrass beds are absent or disappearing due to environmental degradation like in the Mid- Atlantic (Posey et al. 1999). In Virginia, areas with shell substrate supported fish densities 14 times greater than areas lacking shells (Harding and Mann 1998). This increase is attributed, in part, to the use of oyster reefs as feeding grounds for various finfishes including weakfish (Cynoscion regalis), Atlantic croaker (Micopogonius undulates), Atlantic menhaden (Brevoortia tyrannus), Blueback herring (Alosa aestivalis), cobia (Rachycentron canadium), and Spanish mackerel (Scomberomorus maculates) (Harding and Mann 1998). A few other important species that are either growth or recruitment enhanced through the southeast are bay anchovy (Anchoa mitchilli), spotail pinfish (Diplodus holbrooki), gray snapper (Lutjanus griseus), inland silverside (Menidia beryllina), gag grouper (Mycteroperca microlepis), pigfish (Orthopristis chrysoptera), southern flounder (Paralichthys lethostigma), and tautog (Tautoga onitis) (Lenihan and Peterson 1998).

10 P a g e 10 Eastern oyster reefs are the primary source of hard bottom structure in estuaries of the eastern seaboard of the United States, yet natural reefs are currently absent from the DIB (Erbland and Ozbay 2008, Marenghi and Ozbay 2010a). Oyster shells serve as the foundation and anchor of an entire ecological community (Kennedy 1996). Oyster reefs form over time as existing oysters and shell provide substrate for continual recruitment, settlement, and survival of successive generations (Dame 1996). These reefs trap and incorporate shell, sediment, algae, and other floating particles that is colonized by tube-builders, bacteria, microalgae, invertebrates, and other benthic species (Cocito 2004) and varied additional fauna utilize reefs for refuge and resource acquisition (Wells 1961; Dame 1979; Breitberg 1999; Luckenbach et al. 2005). Oyster reefs have higher species richness than adjacent oyster-free areas, and may serve as essential habitat for fish and invertebrates (Coen et al. 1999, Lenihan et al. 2001, Tolley and Volety 2005, Plunket and La Peyre 2005). Bahr (1974) estimated that every 1 m 2 of intertidal Georgia oyster reef provides an entire 50m 2 of surface area. Taylor and Bushek (2008) saw rapid development of a diverse ecological community on constructed intertidal oyster reefs in the Delaware Bay which were similar to the natural sub-tidal oyster community described by Maurer and Watling (1973). The presence of oyster reefs can indirectly affect other landward portions of the estuarine ecosystem. Oyster reefs reduce the impact of wave action on the shoreline, reduce erosion in coastal wetlands, and stabilize sediments (Piazza et al. 2005). Oysters can affect the dynamics of other nearby habitats such as salt marshes by protecting it from the influences of wave energy. A study in Louisiana found that shoreline retreat was significantly lower at sites with a constructed intertidal reef only 0.7 m tall in areas of low energy (Piazza et al. 2005). Suspension feeders and the bio-deposits they produce are an important source of nutrients for seagrasses, which absorb nutrients through the rhizomes, rather than surrounding water, as in algae (Peterson and Heck 1999). Both low and high energy sites had good oyster growth and recruitment (4.9 spat per shell) and showed potential to help stabilize sediments, reduce erosion, and enhance the longevity of nearby salt marsh structure and habitat (Peterson and Heck 1999). Oyster reefs in salt marshes trap sediments as they grow and can eventually become colonized by Spartina spp. and other grasses. Oyster reefs once dominated the Chesapeake Bay; these reefs controlled the trophic interactions from the based up and enhanced the overall water quality, which facilitated the development of complex benthic communities (Mann and Harding 1997). Floating aquaculture gear has the capacity to provide many of the ecosystem services that a natural oyster reef provides (O Beirn et al. 1994, Dealteris 2004, Erbland and Ozbay 2008, Marenghi and Ozbay 2010a). Oysters and the fauna of their associated communities will continue to be an essential area of study as restoration efforts continue all along the east coast of the United States and will be important indicators of environmental quality as humans continue to develop, modify, and manipulate coastal environments.

11 P a g e 11 C. Oyster Restoration Peterson and Lipcius (2003) stated that restoration attempts may fail to restore ecosystems to pristine conditions due to shifting baselines and this should be taken into account when any restoration practice is planned. Mann and Powell (2007) summarized oyster restoration programs in the western Mid- Atlantic and came up with four challenges to overcome: 1) habitat degradation, 2) impacts of disease, 3) low population size, and 4) infrequent and unpredictable periods of natural recruitment. Knowledge of pre-existing reef conditions is needed before large scale restoration efforts are implemented (Grosholz et al. 2008). One common species-specific restoration technique is to improve a species habitat. For oysters, this is a very unique and difficult problem to overcome because oysters and oyster habitat are one and the same, thus creating a positive feedback relationship (Bushek et al. 2004, Mann and Powell 2007, Wilberg et al. 2011). Restoration and preservation of natural oyster reef habitats are essential for the long term survival of the species (Mann and Powell 2007) and such efforts necessitate an understanding of the eastern oyster s life cycle (Figure 4). Oyster larvae settle on benthic surfaces within coastal bays and accumulate into large reefs which consist of both male and female oysters. During the spring and summer months, oysters broadcast spawn, releasing gametes into the water column. External fertilization occurs, and larvae begin to grow for several weeks as meroplankton. The planktonic veliger develops a foot to become a pediveliger, and seeks a hard substrate to attach to. While adult oysters are the ideal habitat, these pediveligers can attach to anything hard, including rocks (Figure 5), metal cans, wooden docks, etc. When the larvae settles, it is referred to as a spat (<30mm) (Figure 4). The oysters begin to feed and grow, creating dense oyster reefs in the process. To sustain an oyster reef, two things need to occur: 1) the recruitment rate of spat must be higher than the natural mortality rate, and 2) the growth rate of oysters must be faster than the sedimentation rate. To achieve this, both a sufficient supply of larvae must be present, as well as adequate high quality substrate (Brumbaugh et al. 2000, Wilberg et al. 2011).

12 P a g e 12 Figure 4. The oyster life cycle. Individual adults broadcast spawn releasing gametes. Weeks after fertilization the pediveliger larva has developed, is ready to settle, and attaches itself to hard substrate (e.g., other oyster shell). The juvenile oyster, now called a spat, grows into an adult oyster. Diagram courtesy of South Carolina Department of Natural Resources

13 P a g e 13 Figure 5. Natural settlement of oysters on riprap in DIB. Photos courtesy of Reckenbeil. Substrate limitations and successful spat recruitment are major factors that larval oysters need to overcome before recolonization of the DIB can be efficacious (Roegner and Mann 1995, Brumbaugh et al. 2000, Schulte et al. 2009, Brumbaugh and Coen 2009, Wilberg et al. 2011). Oyster populations rely upon living and dead oysters to sustain oyster beds through shell accretion, where the rate of larval settlement is just slightly higher than the rate of death (Mann and Powell 2007, Schulte et al. 2009). Population persistence is limited for two reasons; oysters recruit poorly in most years and oysters are an r- selected species with an extremely low fertilization rate (10-5 ; Mann and Powell 2007). Reef height significantly influences the longevity of an oyster reef (Schulte et al. 2009). High relief promotes growth, recruitment, and access to water flow (i.e., food and oxygen; Lenihan 1999). Low relief reefs are much less successful due to poor habitat quality (anoxic or hypoxic conditions), low settlement rates, small population sizes (Schulte et al. 2009), and increased siltation (Lenihan 1999, Wilberg et al. 2011). Destructive oyster harvesting practices physically remove shell from naturally growing oyster beds which negatively impacts the entire population since the shell is not retained in the system (Powell et al. 2006, Schulte et al. 2009, Wilberg et al. 2011). Larger oysters tend to have higher fecundity than small oysters, and a higher proportion of large oysters tend to be female (Wilberg et al. 2011). This is because the eastern oyster is a protandric hermaphrodite, which normally spawns first as male, and changes gender to become female later in life (Thompson et al. 1996). The market for oysters generally revolves around oysters >75 mm in length for human consumption, thus effectively eliminating many females from wild harvested populations. To mitigate shell loss, many restoration programs add cultch (sun dried bivalve shells) to rebuild reefs, and subsequently encouraging population expansion on clean substrate (Bushek et al. 2004, Mann and Powell 2007). Shell used for reef supplementation should be dried on land for one month or longer to substantially reduce the risk of spreading Dermo disease (Bushek et al. 2004). The main purpose of adding shell to the benthos is to provide potential settling grounds for naturally occurring oyster larvae (Brumbaugh et al. 2000, Brumbaugh and Coen 2009). Ecologically, most fish species do not discriminate between habitat comprised of live oyster clusters or clean articulated shell (i.e. oyster boxes) on created reefs; however some species do prefer oyster boxes to live oysters, which is likely due to the shelter and substrate provided by the boxes (Tolley and Volety 2005). Marenghi and Ozbay (2010b) also determined that species assemblages were similar between live oyster clusters and loose shell in floating aquaculture gear. Plunket and La Peyre (2005) surveyed benthic trays and found fish populations residing more often in oyster cultch than over mud bottoms in Louisiana. Therefore, restoration efforts which add loose shell not only increases habitat for potential oyster settlement, but for various other reef residents and transient species. Although a strong demand

14 P a g e 14 for habitat restoration places a spotlight on the impoverished state of oyster reefs in the Mid-Atlantic, these restoration attempts are not novel due to the fact that enhancement through shell planting has occurred since the 1850s (Mann and Powell 2007). Adding shell as substrate (large programs) and increasing broodstock through plantings (often smaller programs) are two strategies used to restore oyster populations (Brumbaugh et al. 2000). When comparing the total planted bushels of oyster shells per year within the DIB to the restoration activities occurring in the Delaware Bay, it is clear that oyster restoration in the DIB is a small fraction of the overall restoration activities. During 2005, 2006, and 2007, a total of 118,810, 182,724, and 370,836 bu. of cultch were planted, respectively, at various natural seed beds in Delaware Bay, totaling 672,370 bu. across all three years (Greco 2008). Alternatively in the DIB, Delaware s oyster gardening program aims to increase broodstock by growing 150+ bu. of live oysters in floating cages for two years, and then planting these various sized oysters around the DIB for restoration purposes (E.J. Chalabala, Delaware Center for the Inland Bays (CIB) Restoration Coordinator, pers. comm.). Other small programs try to increase broodstock by placing bags of cultch in areas with high concentrations of oyster larvae, and then moving the recruited spat on shell to restoration locations (Brumbaugh and Coen 2009). Growing oysters on vertical relief structures off the bottom of the bay may increase survival by allowing settled spat to grow higher in the water column than they normally would on a reef (Erbland and Ozbay 2008). Case studies in the following section provide in-depth discussion on how man-made reefs, aquaculture activities, and oyster bioactivity have contributed to habitat enhancement and species diversity in the Delaware Inland Bays. D. Oyster Aquaculture Aquaculturists employ a broad range of techniques and equipment to grow and harvest a diversity of aquatic species under different environmental conditions. The tremendous growth of the aquaculture industry has been accompanied by growing public concern over possible environmental impacts resulting from these activities. In the United States, the Sustainable Fisheries Act (1996) has restricted activities in areas considered to be essential fish habitat including oyster reefs and other estuarine environments. Bivalve aquaculture is, in general, one of the most benign, even beneficial sectors of the aquaculture industry. Specifically, oyster aquaculture in the Mid-Atlantic is largely a passive operation using a native species grown without supplemental inputs (food, medicines, etc.). These culture operations provide many, if not all, of the same ecosystem services of their wild counterparts. Filter feeding by bivalves in sufficient abundance can exert control over phytoplankton communities. Bivalve aquaculture is now commonly used in conjunction with finfish aquaculture to mitigate environmental impacts of the fish farm, by

15 P a g e 15 utilizing wastes from other species as a food source in a process called Integrated-Multi-Tropic Aquaculture (Chopin et al. 2006). The eastern oyster is central to the physical, chemical, and biological health of Mid-Atlantic estuaries. Its associated fishery has historically been an important regional food source and economic driver. Over the past 200 years, populations of C. virginica have declined greatly with significant ecological and economic repercussions. Culture of C. virginica in the Mid-Atlantic may partially restore ecosystem services while also providing an important source of income to watermen. The ecological benefits provided by naturally occurring C. virginica have been well documented and many are similarly provided by oyster culture operations, i.e. filtration, nutrient removal, and benthic deposition. However, the habitat value of oyster aquaculture in the Mid-Atlantic United States remains to be studied extensively. Reef creation and enhancement is a critical part of ecological restoration in these estuaries, through oyster aquaculture may also provide a valuable contribution, specifically in the provision of habitat for estuarine macrofauna. Farmed oysters can reduce estuarine nitrogen and phosphorus as effectively as their wild counterparts however high densities may lead to anaerobic sediments which inhibit denitrification and release phosphorous and hydrogen sulfide (Newell 2004). Newell (2004) predicts that cultured oysters in an environment with sufficient nutrients will not compete with other suspension feeders, but that in oligotrophic waters, or when aquaculture is intensive, cultured bivalves may compete with the surrounding ecosystem for limited food resources. Bivalve feeding activity decreases turbidity and encourages the growth of microphytobenthos that absorb additional nitrogen from the system. Oyster and other suspension feeders may control phytoplankton populations from the top-down (Newell 1988). Non ingested plankton and detritus particles decay in the benthos, consuming valuable oxygen in the decomposition process. A reduction in the dissolved oxygen content can lead to hypoxia, or even worse anoxic dead zones, inhibiting aquatic organisms to thrive on the bottom of the bay. Oyster cages provide hard substrate for colonization by fouling organisms which become the foundation of productive habitats for a diversity of species. Kilpatrick (2002) compared the habitat value of oyster aquaculture cages, an eelgrass (Zostera marina) bed, and non-vegetated bottom and found macrofauna diversity to be higher for oyster cages than the other two habitats. Oyster aquaculture cages provided 60 times the surface area of a nearby seagrass bed in summertime with continuous year-long habitat as compared to ephemeral sea grass (Kilpatrick 2002). Breitberg et al. (1995) showed that larval fish and other zooplankton demonstrate a preference for down-current eddies created behind rocks and other structures which are abundant on oyster reefs and even more so around oyster cages. Increased mortality of oysters and associated fauna at deeper portions of reefs was reported to be due to hypoxic conditions near the benthos (Lenihan

16 P a g e 16 and Peterson 1998). Subtidal oyster cages provide shallow water refugia from the hypoxia that is prevalent in Atlantic estuaries during the summer months (Officer et al. 1982). Lenihan and Peterson (1998) partially attributed increased deep water hypoxia and mortality of C. virginica and associated fauna in these waters to dredging by fishermen and the subsequent leveling of reefs. Oyster aquaculture would relieve dredging pressure on natural reefs allowing them to re-grow into shallow water with higher levels of dissolved oxygen providing additional refugia from hypoxia (Lenihan and Thayer 1999). A study by Harding and Mann (1998) demonstrated a preference by striped bass (Morone saxatilis) and bluefish (Pomatomus saltatrix) for three dimensional oyster shell reefs over sand bar and shell bar type habitats while Harding and Mann (2001a) observed increased concentrations of the recreationally and commercially important bluefish over reefs compared to sandy bottom. Gut content analysis revealed a greater diversity of prey was consumed by bluefish caught near reefs (Harding and Mann 1998). This higher prey diversity may improve survival in adverse conditions when certain prey species may be reduced (Harding and Mann 2001b). Oyster cages create an artificial reef and elevate abundances of forage organisms for predatory fish while providing nursery habitat for their young (Harding and Mann 2001b). The culture of eastern oysters in containment gear has become a viable industry in many states on the east coast of the United States. As naturally occurring populations of oysters decline, aquaculture and reef creation/restoration efforts are increasingly important to maintain oyster populations and the reef communities they create. Oyster aquaculture can remove nutrients from the water column while enriching sediments initiating a trophic cascade across the epifaunal and infaunal community (Jackson et al. 2008). Oyster reef restoration is central to recovering ecosystem health (Figure 6a). Oyster aquaculture provides limited but similar services, as oysters still function the same in an aquaculture environment, thus they can still remove nutrients and control phyoplankton. (Figure 6b). Sport fish such as striped bass (Morone saxalis) and bluefish (Pomatomus saltatrix) that frequent oyster reefs may also be attracted to and forage within the habitat that oyster farms create (Harding and Mann 2001b). a b Figure 6. a. Restored intertidal oyster reefs ( Figure 6. b. Oyster aquaculture using Taylor floats (

17 P a g e 17 Measuring biodiversity in and around aquaculture gear is a means to evaluate the impact of these culture operations on their host ecosystem, holistically. Unlike some finfish farming, rearing shellfish in high densities in shallow water can have positive environmental effects such as increased biodiversity and improved water quality. O'Beirn et al. (2004) recorded 45 species of macrofauna were recorded inhabiting one commercial oyster farm that used floating aquaculture gear. Species richness was significantly greater in submerged aquaculture equipment than in a nearby seagrass bed or an unvegetated sand flat, especially for juvenile fish and invertebrates in their early life stages (Dealteris et al. 2004). Such studies are critical to understanding these complex ecological interactions and will allow shellfish farmers, managers, and regulators to fully appreciate and best manage the influence of oyster aquaculture activities. The DIB oyster gardeners grow roughly 200 oysters per float at their docks (Ozbay et al. 2013). A single adult oyster has the capability of filtering up to 9.62 l (2.5 gallons) per hour under ideal summer conditions (Gadwa 1995, Newell 1988). Under poor conditions, they may only be able to filter 2 l (~0.5 gallons) per hour (Mann & Powell 2007). Oysters grown in this program may collectively filter about 7.6 million l of water per day during ideal summer conditions. The DIB have a surface area of 8,288 hectares and averages 1.2 m in depth (Martin et al. 1996) for a volume of over 100 million l. Filtering the entire volume of the Inland Bays on a daily basis will require just over half a billion additional oysters. The oyster gardening project s estimated 40,000 oysters are a great step forward, but large-scale oyster aquaculture in combination with restorative efforts will be needed to generate a measurable positive impact on the health of the DIB.

18 P a g e 18 E. CASE STUDIES Overview All three case studies were conducted within the three Delaware Inland Bays: Rehoboth, Indian River, and Little Assawoman (Figure 7). Oyster gardening sites occurred in State waters closed to shellfishing. These oysters were grown only for research, restoration, and education. Figure 7. Map of Delaware s Inland Bays showing oyster gardening locations, riprap planting locations, and known wild oyster locations (Marenghi 2009).

19 P a g e 19 In the study by Erbland and Ozbay (2008) discussed below, modified rack and bag method of oyster aquaculture supports additional populations of ecologically and economically important macrofauna compared to a created oyster reef, with minor impact on sediments and infaunal communities. This study further demonstrates that off-bottom oyster aquaculture operations in the US Mid-Atlantic can be beneficial addition to host estuaries and associated natural communities. Erbland and Ozbay (2008) monitored 18 species showing significantly greater abundance and richness in and around the oyster cages than in adjacent low-profile oyster shell reefs and natural shorelines. One of the most recent types of oyster mitigation is known as "oyster gardening" by using floating cages. Marenghi and Ozbay (2010a) found 15 species around Taylor float oyster gardens including three species that require oyster shells for spawning substrate: naked goby (Gobiosoma bosc), oyster toadfish (Opsanus tau), and striped blenny (Chasmodes bosquianus). They monitored the commercially valuable blue crab (Callinectes sapidus), American eel (Anguilla rostrata), and mummichog (Fundulus heteroclitus) species utilizing floating oyster aquaculture gear as habitat in a eutrophied, turbid, periodically hypoxic coastal lagoon during the first year of their study. In the second year, over 57 taxa of fishes and invertebrates and 8 species of macroalgae were recorded within a few canals in one of the DIB. Many of the species in the Inland Bays estuary system have commercial or recreational importance and are habitat-limited due to the direct and indirect loss of tidal wetlands, oyster reefs, and seagrass beds (Marenghi and Ozbay 2010b). Floating aquaculture gear seems to have the ability to provide many of the ecosystem services a natural oyster reef provide (Newell 2004, Erbland and Ozbay 2008, Marenghi and Ozbay 2010b). According to Rossi-Snook et al. (2010), it is important to consider that oysters grown in aquaculture gear or floats are restoring habitat for a variety of species before they are planted for restoration in the bays as long as the culture operations are continuous. Based on these studies, even at small scales in eutrophied, turbid, and occasionally hypoxic conditions, oyster aquaculture can encourage native estuarine fauna more than an abiotic floating structure or loose oyster shells used as substrate in oyster restoration programs. These floating structures are in no way, however, intended to replace natural reefs or replicate all of the ecosystem services reefs provide. Enhanced habitat is one of the many positive environmental impacts of shellfish aquaculture and may be incorporated into a larger-scale restoration strategy. In a substrate-limited estuary, riprap also has the ability to be used as a restoration tool for enhancing oyster populations. Oysters show a 50% survival rate after one year when placed between crevices within riprap in Delaware (Reckenbeil 2013). Efforts to stock oysters in locations where riprap already exists is more economical and less time consuming than constructing an artificial oyster reef. However, all riprap does not provide the same habitat value. Reckenbeil (2013) and Ozbay et al. (2013) focused on utilizing riprap as potential hard substrates for oyster stocking and monitoring species in and

20 P a g e 20 around those riprap crevices. Due to difficulty capturing species in and around riprap crevices, their research resulted in less species diversity within riprap than at natural shorelines. However it is most likely the resulting catch did not fully represent the community living within the riprap crevices (Ozbay et al. 2013). Oysters may have increased demersal species abundances, but it is near impossible to measure such in a riprap environment in brackish waters. Although the number of species captured in and around the riprap crevices was less than the other habitat studied, species distribution overall was more even for riprap stocked with oysters as compared to riprap without oysters or the natural marsh shorelines. 10 species were captured in and around the riprap crevices with oysters (Reckenbeil 2013). Mummichogs, Fundulus heteroclitus, represented 81.4% of all catch of the 15 species collected, and were found in significantly greatest abundance at the natural shorelines. Cyprinodon variegatus, sheepshead minnow, also was found most frequently at the natural shorelines. Grass shrimp Palaemonetes pugio and Palaemonetes intermedius showed prevalence along the riprap shorelines, as well as rainwater killifish, Lucania parva. E.1. Diversity in Relation to Man-Made Oyster Habitats: Aquaculture Gear vs. Created Reef Summary This study compared the macro-epifaunal communities associated with two oyster habitats: a created oyster reef and oyster aquaculture cages. Both habitats were sampled with lift nets, during the summer and fall months, and habitats were compared over time. A significantly greater (P <0.05) total abundance and species richness was found in the oyster cages, but significantly greater (P <0.05) species evenness was found on the reef. Species diversity was similar between habitats. Juveniles of four reef-oriented fish species (gag grouper, grey snapper, sheepshead and tautog) were found only in the cages. Blue crabs were also found only in the cages and were composed of molting adults and hard-shelled juveniles. Mud crabs and naked gobies were the most abundant species throughout the study and were similar in both habitats. Grass shrimp and oyster drills were significantly (P <0.05) more abundant in the cages; their presence was variable, spatially and temporally with large numbers appearing in October.

21 P a g e 21 The task of increasing oyster abundance in the DIB is an extremely difficult due to current low population densities that preclude any significant level of natural recruitment by C. virginica (Rossi-Snook et al. 2010). Historic populations of oysters in the DIB are questionable due to very limited documentation (Rossi-Snook et al. 2010). Knowledge of pre-existing reef conditions is needed before large scale restoration efforts are implemented (Grosholz et al. 2008). Oysters grown in aquaculture gear create habitat for a variety of species before they are planted for restoration in the bays (Rossi- Snook et al. 2010). Several demersal fishes such as blennies, gobies, and skilletfish utilize oyster shell as spawning substrate (Saksena and Joseph 1972) however when oyster restoration efforts are attempted, it is unclear how restoring oysters in various habitats influences community structure (Grabowski et al. 2005). Murray et al. (2006) suggested that structure- forming biota is valuable because bioengineered habitats, like oyster reefs, are vulnerable to impacts. A Restoration effort with native eastern oyster in the DIB (Figure 8a) has been limited and challenging but progress is being made. To facilitate oyster population expansion, The Delaware Center for the Inland Bays (CIB), with help from the Delaware Sea Grant Marine Advisory Program, started Delaware s oyster gardening program in In 2005, staff and students from Delaware State University joined in research efforts as well as program development and implementation. According to Brumbaugh et al. (2000) oyster aquaculture through community based restoration programs can be an effective small scale restoration technique and measuring biodiversity in and around oyster aquaculture gear. This allows a holistic understanding of the impact of culture operations on their host ecosystem. Figure 8b show the pictures of the fishes recorded in and around oyster gears in James Farm. Figure 8. a. Map showing Delaware Bay and Delaware Inland Bays, Map courtesy of Erbland (on the left).

22 P a g e 22 a Figure 8. b. Pictures of some of the species collected in and around oyster aquaculture gear, Picture courtesy of Erbland; from Erbland (2007) (on the right). b Erbland and Ozbay (2008) compared the species diversity and abundance of sub-tidal C. virginica rack and bag type gear with an adjacent created C. virginica reef over the summer months. This project was also designed to examine the impacts of oyster aquaculture on infaunal community structure. The objective was to compare the diversity, evenness, abundance, and biomass of macro-infaunal communities of a sub-tidal oyster cultivation area with those occurring in adjacent open sand flat. a Figure 9. a. Rack and bag oyster gear. Picture courtesy of Erbland. Figure 9. b. created oyster reef. Picture courtesy of Erbland. b Indian River Bay is one of the three Inland Bays of southern Delaware and is approximately 3.2km wide by 9.7km long with a surface area of 3800 hectares (Scotto et al. 1983). Its main tributary is Indian River as well as Pepper and White Creeks (Scotto et al. 1983). The research was conducted at the James Farm Ecological Preserve in the southeast corner of Indian River Bay along the

23 P a g e 23 east side of Pasture Point near Ocean View, Delaware (Figure 10). Average water depth is about 1.66m with tidal amplitude generally of 1.25m in this area (Smullen 1992). Because of existing five year old created oyster reef and ongoing research demand by the CIB, this study location was selected for this research. According to the National Oceanic and Atmospheric Administration s Chesapeake Bay Program Classification Scheme, Indian River Bay is classified as highly to very highly enriched (Scotto et al. 1983); however this study location is close to the ocean and is therefore well flushed. Figure 10. The research site at the CIB James Farm Ecological Preserve (left, Erbland 2007) and location of oyster reef and layout of experiment (right, Erbland and Ozbay 2008). The reef is enclosed within a designated research area denoted by poles and signs and the protective nature of the cove and associated hydrology reduce the risks of losing gear due to storms. The bottom characteristics composed of open sand/ mud. During the warm months, at low tide, water temperatures ranged from C, salinity 28-32ppt, and dissolved oxygen was 7-12mg/L. Study sites were monitored sampled for species in and around the gears and created oyster reefs over a five month period (June - October). Sediment grain size and macro-infauna were examined directly beneath oyster cages and at a nearby control site consisting of open sand/mud bottom. Greater total abundance and species richness (P < 0.05) was found below the oyster gear, but greater species evenness (P < 0.05) was found on the reef (Figure 11). Samples were dominated by naked goby (Gobisoma bosci) and Atlantic mud crab (Panopeus herbstii). Gobisoma bosci were significantly (P < 0.05) larger but less abundant on oyster reefs compared to oyster gear but overall biomass was not significantly different between sites. Panopeus herbstii were significantly larger (P < 0.05) and more abundant in oyster gear than on the reef, while the oyster reef supported a greater biomass. Four-eye butterfly fish (Chatedon capistratus), feather blenny (Hypsoblennius hentzi), and oyster toadfish (Opsanus tau) were common to both habitats. Blue crab (Callinectes sapidus), tautog (Tautoga onitis), American eel (Anguilla rostrata), sergeant

24 P a g e 24 major (Abudefduf saxatilis) and gag grouper (Mycteroperca microlepis) were unique to the oyster gear while skilletfish (Gobiesox strumosus) was only found on oyster reefs Cage Reef Abundance N/m Panopeus herbstii Gobisoma bosc Palaemonetes vulgaris Urosalpinx cinerea Nereididae Callinectes sapidus Chatedon capistratus Ampharetidae Archosargus probatocephalus Opsanus tao Hypsoblennius hentzi Mycteroperca microlepis Species Ilyanassa obsoleta Lutjanus griseus Tautoga onitis Arbacia punctulata Anguilla rostrata Gobiesox strumosus Figure 11. Mean species abundance (N) averaged during the four months (June, August, September, and October) for all species in cage (rack and bag) or reef habitat with standard deviations (Erbland 2007). Silt and clay formed a slightly smaller fraction of sediments below oyster cages than control site sediments and, of the seven most abundant infaunal taxa, Streblospio benedicti (under family Spionidae) was the only species significantly different (P < 0.05) in abundance between treatments (Figure 12) and was possibly reduced under cages by being flushed away along with sediment silt and clay during disturbance from oyster culture activities.

25 P a g e Treatment Control 1600 Abundance N/m Gammaridean Spionidae Orbiniidae Bivalvia Capitellidae Oweniidae Spirorbidae Taxon Figure 12. Mean abundance (N) (+ standard deviation) of the seven most abundant infaunal taxa averaged during the four months (June, August, September, and October). Treatment was the oyster cage and a nearby control site was the open sand/mud bottom (Erbland 2007). This study suggests rack and bag type oyster culture support greater populations of ecologically and economically important macrofauna compared to a created reef, with little impact on sediments and infaunal communities. This style of oyster culture is largely sustainable and may play a significant role in restoring the oyster resource and associated industry in the Mid-Atlantic. The results of this study show that this method of oyster aquaculture supports additional populations of ecologically and economically important macrofauna compared to a created oyster reef. This might mainly due to availability of larger spaces in gears therefore better refugia for the aquatic life. Furthermore this study demonstrates that off-bottom oyster aquaculture operations in the Mid-Atlantic are a beneficial addition to host estuaries and associated natural communities. Further examination of the effects of various forms of oyster culture on estuarine ecosystems will guide future shellfish aquaculture operations in the state of Delaware and other Mid-Atlantic states. In-depth information will enable decision-makers, interest groups and the general public to formulate science-based opinions and policies regarding this industry.

26 P a g e 26 E.2. Diversity in Relation to Floating Aquaculture Gear Summary Floating aquaculture gear is utilized worldwide to farm shellfish, yet the habitat value provided by increasingly popular oyster gardening programs has received very limited attention, particularly in degraded coastal bays like those found in southern Delaware. In the 2007 study, 14 species were captured in floats from the three embayments that comprise the DIB, while 57 species were captured from one specific embayment in This study examined species assemblages utilizing floating aquaculture gear containing live oysters, oyster shell, or empty baskets (no oysters) as habitat. Delaware s oyster gardening program started in part to locally promote public awareness about the importance of oysters in estuaries. Few studies have explored whether or not oyster gardening can provide any of the ecosystem services that natural oyster reefs provide. It was hypothesized that even at small scales, in eutrophied, turbid, and occasionally hypoxic conditions, oyster aquaculture activities can support and encourage native estuarine fauna. The research focus was narrowed to one embayment within the DIB (part of Little Assawoman Bay, the canal system of Fenwick Island, DE; Figure 13) to conduct a finer-scale assessment of floating oyster gardens as habitat for fishes and macro-invertebrates (Figure 14a). With no natural reefs remaining in the DIB for which to compare with, species composition and diversity was compared in Taylor floats with live oysters, loose oyster shells, or empty baskets without oysters or shells. From these comparisons we could infer which habitat was preferred by each species in the oyster garden assemblage.

27 P a g e 27 Figure 13. Study sites in Fenwick Island canal system in Little Assawoman Bay. Numbers label study dock locations (Map courtesy of Marenghi). Sampling protocols included lowering a net slowly beneath each float to collect species residing within the floating gear (Figure 14b). Together, the float and net were raised out of the water, effectively trapping animals >3mm inside. Water from a garden hose was then utilized to wash off the oysters, thus dislodging other species from the float into the net. A total of 49 species of fishes and invertebrates and eight species of macroalgae were collected from floating oyster gardens. Nine commercial or recreational fished species use these semi-artificial habitats and include blue crab (Callinectes sapidus), American eel (Anguilla rostrata), mummichog (Fundulus heteroclitus), summer flounder (Paralichthys dentatus), spotted seatrout (Cynoscion nebulosus), black sea bass (Centropristis striata), sheepshead (Archosargus probatocephalus), bay anchovy (Anchoa mitchilli), and oyster toadfish (Opsanus tao). Figures 15 and 16 illustrate the abundance of the ten most conspicuous species by substrate. For most of the common species, significantly greater abundance was found in floats with live oysters or oyster shells. Only a few species (e.g., the ubiquitous F. heteroclitus) were found in equal abundance in the empty floats. Examination of taxa accumulation curves

28 P a g e 28 conveys two critical concepts. The first is that sampling was most likely adequate to estimate the true richness of oyster float communities. This is clearly seen in the overall curve, which seems to approach an asymptote at 25 motile species (Figure 17). a b Figure 14a. Taylor floats were used for the oyster gardening program. Photo courtesy of Marenghi. Figure 14b. Net lowered underneath the float for collecting samples. Photo courtesy of an oyster gardener. Accumulation curves for each assemblage according to shell treatment are given for motile and sessile fauna in Figures 18 and 19. Not only does each curve reach an asymptote, comparing these curves visually indicates that for motile fauna, floats with live oyster clusters had the richest assemblage and empty floats had the least rich, with the loose shell assemblage intermediate (Figure 18). Regarding sessile fauna, the oyster cluster assemblage was richer than that of the loose shell initially; however the same number of species was detected by the end of the sampling period (Figure 19). Indicator species analysis isolated four species that are indicative of a particular substrate. Naked goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus), and clam worm (Neanthes succinea) were all indicative of oyster cluster floats and American eel (Anguilla rostrata) was indicative of loose shell floats (Table 1). Many of these species are habitat-limited in the Inland Bays due to the direct and indirect loss of tidal wetlands, oyster reefs, and seagrass beds, all of which are particularly important as juvenile feeding and staging areas. Floating oyster gardens are also habitat for important forage species. Furthermore, newly settled juvenile oysters were found for the first time within floating oyster gear in the man-made, residential canal systems of the Inland Bays.

29 P a g e 29 Measurable effects like these, coupled with continuing community involvement, make oyster gardening a significant oyster habitat component in the DIB. Mean abundance (+ SD) Oyster Clusters Loose Shell Empty Float C. sapidus G. bosc L. parva N. succinea F. heterclitus G. strumosus Species Figure 15. Mean abundance (+ standard deviation) for six species collected from Little Assawoman Bay study floats by substrate type, oyster clusters, loose shell, and empty float, pooled across months (Marenghi 2009). Mean abundance (+ 1 SD) Oyster Clusters Loose Shell Empty Float A. rostrata O. tau C. bosquianus anthidae Species Figure 16. Mean abundance (+ standard deviation) for four species collected from Little Assawoman Bay study floats by substrate type, oyster clusters, loose shell, and empty float, pooled across months (Marenghi 2009).

30 P a g e Cumulative Number of Motile Taxa Detected Observed Number of Taxa Michaelis-Menten Curve Asymptote Number of Samples Figure 17. Taxa accumulation curve showing the cumulative number of motile taxa detected as the number of samples increased. Blue dots represent observed taxa, the solid red line is the Michaelis-Menten Curve fit to the data, and the dotted line is the asymptote representing the total number of taxa sampled from the assemblage (Marenghi and Ozbay 2010). Cumulative Number of Motile Species Detected Clusters Shell Empty Number of Samples Figure 18. Taxa accumulation curves showing the cumulative number of motile taxa detected as the number of samples increased for each substrate type, oyster clusters, loose shell, and empty float (Marenghi 2009).

31 P a g e 31 Cumulative Number of Sessile Species Detected Oyster Clusters Loose Shell Number of Samples Figure 19. Taxa accumulation curves showing the cumulative number of sessile taxa detected as the number of samples increased for each substrate type, oyster clusters, and loose shell (Marenghi 2009).

32 P a g e 32 Table 1. Results of Indicator Species Analysis (PC-ORD) by substrate. Indicator species value range from 0 100, 100 being a perfect indicator. Max group is the group with the highest mean abundance (1 oyster clusters, 2 loose shell, 3 empty float). Significant results are in bold (Marenghi 2009). Taxa Max group Indicator species value Mean St Dev p-value Palaemonetes spp Chrysaora quiquecirrha Fundulus heteroclitus Gobiosoma bosc parva Chasmodes bosquianus Opsanus tau Anguilla rostrata anthid crabs Callinectes sapidus Gobiesox strumosus Apeltes quadracus Lagodon rhomboides Menidia menidia Paralichthys dentatus Neanthes succinea Cynoscion nebulosus Eucinostomus argenteus Syngnathus fuscus Archosargus probatocephalus Nassarius vibex Hippolyte sp Orthopristis chyrsoptera Anchoa mitchelli Alpheus heterochelis

33 P a g e 33 Marenghi and Ozbay (2010a) found conditions in at least some of the canals in the Inland Bays are adequate for oyster settlement and spat growth as a small amount of recruitment was recorded on loose shells held in floats. Although this is the first documentation of oyster recruitment in the Inland Bays' canals, and area with heavy residential pressure, results of this study provide a strong baseline for the ecological effects of oyster gardening. It is expected that much longer time scales (perhaps decades) will be necessary to know if restoration of the near-extirpated oyster population is achievable in this heavily degraded estuary. Successful restoration will require a sciencebased strategy implemented at a large scale, thorough and periodic assessments, long-term commitments in labor and finances, and continued public engagement to ameliorate the factors hindering natural recovery. E.3. Diversity in Relation to Rip-Rap Stocked with Cultured Oysters Summary Riprap was stocked with oysters in order to assess potential improvement in species diversity in a tidal marsh creek system in Delaware. Minnow traps were utilized to collect transient species from three shoreline environments, riprap stocked with oyster (RRO), riprap with no oysters (RR) and natural marsh shoreline (NS). Seine nets, modified lift nets, and cast nets proved ineffective in sampling the riprap habitat. Species richness and abundance was highest at the NS, but evenness and diversity indicated that RRO habitat was most diverse. Mummichogs, Fundulus heteroclitus, represented 81.4% of all catch of the 15 species collected, and were found in significantly greatest abundance at the NS. Sheepshead minnows, Cyprinodon variegatus, also were found most frequently at the NS. Grass shrimp Palaemonetes pugio and Palaemonetes intermedius showed prevalence along the riprap shorelines, as well as rainwater killifish, Lucania parva. Riprap is a combination of various sized rocks and boulders used to armor shorelines. The literature provides conflicting results as to whether or not riprap increases or decreases species abundance and richness (Sobocinski 2003, Toft et al. 2004, Eros et al. 2008, Pister 2009). Some studies show higher abundance of organisms at armored shorelines when compared to natural shorelines nearby (Shields et al. 1995, Barko et al. 2004, White et al. 2009), while some studies show no difference in community structure or species diversity (Sobocinski 2003, Toft et al. 2004, Chapman 2006, Eros et al. 2008, Pister 2009), and other studies indicate lower diversity along riprap when compared to natural shorelines (Peterson et al. 2000, Moschella et al. 2005). These conflicting results are potentially due to biogeographic variation (Pister 2009). Locally in the Chesapeake, nekton communities are similar among riprap and natural shorelines, but different from bulkhead shorelines (Bilkovic

34 P a g e 34 and Roggero 2008). Riprap may increase diversity for some taxa but not others (Toft et al. 2004, Eros et al. 2008), since habitat requirements differ among taxonomic groups. To date, no published research has studied the impacts of adding oysters to an artificially constructed shoreline. However, it is well documented that oysters are a keystone species, benefiting local environments on numerous fronts. Most notable is the oyster s ability to provide essential fish habitat, thus increasing the number of species of reef residents, as the empty shell is often utilized for protection and as a surface to lay eggs (Schwartz 1964, Coen et al. 1999, Tolley and Volety 2005). Oysters in low abundance (<200 oysters per floating aquaculture gear) can benefit local fauna, allowing an increase in species diversity (Marenghi 2009). Therefore, it was assumed that planting oysters into the rocky shoreline would increase species diversity in that particular environment since larger nekton (transient species) are attracted to smaller prey (reef residents), which are attracted to the clusters of oysters between the rocks. In Jefferson Creek South Bethany, Delaware, two volunteer residential oyster gardening properties were chosen as study sites to compare shoreline environments. Each site is comprised of three sub-sites/habitats: riprap stocked with oysters (RRO), riprap vacant of oysters (RR), and natural marsh shoreline (NS) (Figure 20). The RRO shoreline at site Fifi (high density oyster) was stocked with 30 bushels of oysters (Figure 21a) in 2009, 2010, and 2011 and 15 bushels of oysters stocked at site GD (low density oyster). No preference was given to planting only live oysters, as dead oyster boxes are known to provide shelter and substrate (Figure 21b). Biweekly, three un-baited rectangular minnow traps (Minnie Large Minnow Trap, Memphis Net and Twine Co.) of dimensions 45.7 cm x 40.6 cm x cm (18 in. x 16 in. x 8 in), were set by kayak (Figure 22) at low tide (Rozas and LaSalle 1990) for one hour (Kneib and Craig 2001) at each sub-site to collect nekton from each shoreline habitat (Figure 23). Three other collection techniques (seine netting, modified lift nets, cast netting) all proved unsuccessful in collecting specimens from Jefferson Creeks shoreline habitats.

35 P a g e 35 Figure 20. Shoreline locations utilized in Jefferson Creek, South Bethany, Delaware. Purple markers indicate riprap with oysters (RRO), red markers indicate riprap vacant of oysters (RR), and green markers indicate natural marsh shoreline (NS) (Map courtesy of Reckenbeil). a b Figure 21. a. Planting oysters in rip-rap crevices. Photo courtesy of Nathan. Figure 21. b. Blenny utilizing an oyster box as habitat. Photo courtesy of Janiak.

36 P a g e 36 Figure 22. Student researcher collecting a minnow trap from the NS by kayak. Photo courtesy of Reckenbeil. Figure 23. A minnow trap placed along the rip-rap shoreline. Photo courtesy of Reckenbeil.