Coastal and Estuarine Research Federation

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1 Coastal and Estuarine Research Federation Epibenthic Fishes and Decapod Crustaceans in Northern Estuaries: A Comparison of Vegetated and Unvegetated Habitats in Maine Author(s): Mark A. Lazzari Source: Estuaries, Vol. 25, No. 6, Part A (Dec., 2002), pp Published by: Coastal and Estuarine Research Federation Stable URL: Accessed: 19/02/ :42 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Coastal and Estuarine Research Federation is collaborating with JSTOR to digitize, preserve and extend access to Estuaries.

2 Estuaries Vol. 25, No. 6A, p December 2002 Epibenthic Fishes and Decapod Crustaceans in Northern Estuaries: A Comparison of Vegetated and Unvegetated Habitats in Maine MARK A. LAZZARI* Maine Department of Marine Resources, PO. Box 8, West Boothbay Harbor, Maine ABSTRACT: Species richness and abundance of epibenthic fishes and decapod crustaceans were quantified with daytime beam trawl tows and throw traps to provide information on nekton assemblages in Zostera marina and unvegetated sandy habitats in northern latitudes. Sampling at randomly selected stations with a 1.0-m beam trawl occurred in eelgrass (Zostera marina) and unvegetated sandy substrates of two mid-coastal Maine estuaries: Casco Bay and Weskeag River. Random 1.0-m throw trap samples were collected in Zostera and adjacent unvegetated sandy substrates in Casco Bay and Weskeag River as well. Species richness and faunal abundances were positively associated with the occurrence of Zostera within Weskeag River and Casco Bay estuaries using both gear types. A total of 17 species of fishes and 6 species of decapods were collected in the two estuaries using both gears. Populations of most species were dominated by youngof-the-year and juvenile life history stages. Number and densities of fishes were higher in Zostera, due primarily to the abundances of eelgrass residents such as threespine, Gasterosteus aculeatus, and fourspine sticklebacks, Apeltes quadracus, grubby, Myoxocephalus aenaeus, and cunner, Tautogolabrus adspersus. Crangon septemspinosa dominated decapod catch per unit effort and density in both estuaries and habitats. Introduction Information on the nearshore distribution of epibenthic fishes and decapod crustaceans is critical due to the importance of shallow inshore habitats as nurseries and feeding grounds, the environmental variability of these areas, and the potential for anthropogenic impact (Warfel and Merrimen 1944; MacDonald et al. 1984; Brown and McLachlan 1991). Beds of eelgrass, Zostera marina, represent a valuable habitat for shallow water fishes and decapods (Briggs and O'Conner 1971; Heck and Orth 1980; Raposa and Oviatt 2000) with numerous studies in more southerly locations (Huh 1984; Sogard et al. 1987; Heck et al. 1989; Sogard and Able 1991). No such studies exist for coastal waters north of Massachusetts (Heck et al. 1989). The role of eelgrass beds as nursery habitat for newly settled juvenile fishes and decapods has been documented (Adams 1976; Heck and Thoman 1984; Orth and van Montfrans 1987; Heck et al. 1989) as have higher faunal densities in seagrass relative to unvegetated sand or mud substrates in estuaries (Orth et al. 1984). Habitat value of seagrasses is often compared with unvegetated areas, macroalgae, and salt marsh creeks (Briggs and O'Conner 1971; Weinstein and Brooks 1983; Sogard and Able 1991), and nekton abundance is of- * Tele: 207/ ; fax: 207/ ; mark. lazzari@state.me.us. ten highly variable between different beds of seagrass when multiple sites are sampled (Heck et al. 1989; Sogard and Able 1991; Raposa and Oviatt 2000). Adjacent salt marsh habitats and distance from shore can also affect nekton abundances in eelgrass in temperate areas (Weinstein and Brooks 1983; Connolly 1994; Raposa and Oviatt 2000). Other studies have documented the value of seagrass as a refuge from predation (Heck and Thoman 1981; Stoner 1982; Leber 1985; Heck and Wilson 1987; Wilson et al. 1987). Comparison of recruitment patterns suggested that young-of-year of many species do not begin exploiting estuarine habitats until relatively late in the summer, perhaps as a result of peak spawning in mid-summer (Bigelow and Schroeder 1953; MacDonald et al. 1984; Sogard and Able 1991; Lazzari et al. 1999). This paper describes results of an intensive seasonal survey of shallow water habitats in two Maine estuaries during August through November The study objectives were to describe the shallow water fish and decapod crustacean communities, to relate variations in species richness and abundance to the presence of eelgrass (Z. marina) in two northern estuaries, and to latitudinally compare nekton use in Maine eelgrass habitats to other geographic areas of the northeastern U.S. and Canada. Study Locations Two estuaries (Casco Bay and Weskeag River) located in mid-coastal Maine were selected for study? 2002 Estuarine Research Federation 1210

3 Maine Estuarine Fauna 1211 TABLE 1. Sampling effort, species richness (Jackknife estimate (SE); Heltsche and Forrester 1983), mean (SE) species tow-', and CPUE (mean (SE) number tow-1) for each station in Casco Bay and Weskeag River in Maine. E = eelgrass, Zostera marina. 7, Number Mean of Species Species Mean Estuary Station Tows Richness per Tow CPUE Casco Bay (1.8) 1.7 (0.2) (56.2) (0.9) 2.0 (0.3) (50.2) (0.9) 2.5 (0.3) 53.5 (21.1) (2.2) 2.9 (0.4) 38.7 (7.1) 5 (E) (0.9) 3.4 (0.6) 95.8 (28.8) 6 (E) (1.5) 3.5 (0.4) 59.7 (8.3) 7 (E) (1.5) 3.6 (0.8) (48.7) Weskeag River 8 (E) (0.8) 2.8 (0.6) (76.9) (1.3) 1.9 (0.2) 45.0 (15.1) (1.8) 2.0 (0.2) 65.2 (35.4) (0.9) 2.4 (0.2) 25.1 (7.0) (1.8) 2.2 (0.3) 22.9 (6.8) 5 (E) (1.3) 3.4 (0.5) (20.3) 6 (E) (0) 5.0 (0.5) 37.3 (3.7) 7 (E) (1.3) 3.1 (0.3) 69.0 (15.5) 0 50 Kilometers 70? 69? I l Fig. 1. Map of the southern Maine coast showing the locations of Casco Bay and Weskeag River. Trawl stations are numbered from 1 through 8 in Casco Bay and 1 through 7 in Weskeag River. The throw trap sites are shown by V in the two estuaries. based on the presence of large areas of eelgrass and nearby unvegetated areas (Fig. 1). The Cousins Island area of Casco Bay (70?15'N, 43?78'W) was characterized by low relief, expansive eelgrass beds, and adjacent mussel areas. Some Spartina alterniflora marsh bordered the lower intertidal area near stations 1 and 2, but tows at both stations occurred more than 50 m from the marsh. The remaining six stations were located at least 100 m from rocky intertidal areas where Ascophyllum and Fucus algaes occurred. Subtidal habitat near Cousins Island is dominated by eelgrass beds, mussel bars, and adjacent sandy areas. Tow depths at all stations were between 3 and 6 m at mean low water (MLW). Freshwater input from the Royal River was moderate though salinities were high at all stations with the exception of station 1 following rainfall. Tides were semidiurnal and in the m range. The Weskeag River estuary (69?20'N, 43?98'W) was distinguished by moderate relief, minimal salt marsh but expansive mudflat and mussel areas. A narrow S. alterniflora marsh bordered the lower intertidal near stations 1-3, but the stations towed were all greater than 100 m from shore. Algae, Ascophyllum and Fucus, occurred on the rocky intertidal areas more than 100 m from the four other stations. Freshwater input was minimal and salinities were high. Tides were semidiurnal and range from about m and eelgrass was present. Surface water temperatures in both estuaries were consistently above 15?C from August until the end of September before dropping steadily during the fall. By November, temperatures averaged about 9?C. Surface salinities differed little among sites in Weskeag River ranging from 29 to 32 psu (practical salinity units) over the sampling period. Salinities in Casco Bay were more variable, ranging from 18 to 32 psu over the sampling period. On average, the salinity across all sites within Casco Bay was above 27 psu with the exception of station 1 following a rainfall event in September (18 psu). Epiphytic fouling of Zostera blades with Chaetomorpha algae and Microciona sponge was noted in several tows in both estuaries. Materials and Methods BEAM TRAWL SAMPLING Randomly selected shallow subtidal (3-6 m) stations (Fig. 1, Table 1) were sampled biweekly for organisms during daylight hours from August-November 1999 in Casco Bay and Weskeag River estuaries. Eight stations were sampled in Casco Bay and seven stations in Weskeag River. Zostera occurred at four stations in Casco Bay and at three stations in Weskeag River. At each location, three 2-min tows were made with a 1.0-m beam trawl (3 mm cod-end mesh) in either continuous eelgrass coverage or unvegetated sandy areas. Three short

4 1212 M.A. Lazzari tows were collected to minimize the potential for mixing habitat types during a tow. Each sample was sorted live and discarded. All fishes and decapod crustaceans were identified and counted; fishes were measured for total length and decapods for carapace width and length in mm. Surface water temperature and salinity by refractometry were recorded at each site on every sampling trip. A total of m beam trawl tows was made in Casco Bay (n = 102) and Weskeag River (126) between August 17 and November 19, 1999 (Table 1). In Casco Bay, 48 tows were made in Zostera and 54 tows in unvegetated sandy habitats. Fifty-one tows were made in Zostera and 75 tows in unvegetated sandy habitats in Weskeag River. THROW TRAP SAMPLING Epibenthic fishes and decapod crustaceans also were collected with a throw trap (Kushlan 1981), an open aluminum frame 1 m2 in area and 20 cm in height. The height of the trap was increased to 1 m with a band of 3-mm mesh netting attached to a hollow PVC frame that prevented escape over the top of the trap. Following a short waiting period, the trap was thrown far enough (> 3 m) to minimize avoidance. The trap was thrown on to the desired substrate and immediately pushed into the sediment. Animals were removed with a 1-m wide framed net with 3-mm mesh until three consecutive net passes produced no fish or decapods. Large beds of Z. marina with adjacent isolated patches of unvegetated sand were selected in each estuary. Both vegetated and unvegetated sites were similar in depth, averaging 30 to 60 cm MLW. The Casco Bay site was about 50 m from a S. alterniflora marsh while the Weskeag River site was a similar distance from a rocky intertidal area with Ascophyllum and Fucus present. Three throw-trap sampling trips were conducted on a biweekly basis at one site in Weskeag River and one site in Casco Bay (Fig. 1) during daylight hours from August 17 to October 5, Samples were collected beginning 1 h before low tide and continuing until 1 h after. Six to 10 randomly selected samples were collected from vegetated and adjacent unvegetated substrates at a throw trap site during each 2-h period. In the two estuaries, m throw trap samples were collected. This gear provided quantitative 1-m samples, allowing direct comparison of different habitats. Decapods and fishes were identified and measured in mm (total length for fishes and carapace length/width for decapods). Following sampling in August, Zostera shoot density was quantified with six 40 cm2 quadrats at each sampling site and the shoot density m-2 was calculated from the quadrat density. STATISTICAL ANALYSES Fish catches are expressed as number tow-1 for beam trawl samples and number m-2 for throw trap samples. All statistical testing used SYSTAT statistical software (Wilkinson 1996). To compare species number and catch per unit effort (CPUE)/ density of the fishes and decapods across the various estuaries and habitats for each gear type, twoway nested ANOVAs using location and habitat type as main effects followed by a priori least significant difference multiple comparisons tests were used when the data met the assumptions of normality and heterogeneity of variance, following the method of means testing outlined by Sokal and Rohlf (1981). All numbers were log10 transformed prior to analysis. Although concerns for experimentwise error rate exist when multiple comparisons are made in a given study, the objective of this study was to make a series of individual comparisons by estuary and by vegetated and unvegetated sandy habitats within Casco Bay and Weskeag River. Due to the robustness of ANOVAs and highly significant differences among groups (p < for most tests), results of the statistical tests could be interpreted reliably. CPUEs and densities (including all sampling dates) were compared for the two estuaries and the two habitat types: Zostera and unvegetated sandy substrates in Casco Bay and Weskeag River. Two-sample t-tests for unequal variances (Sokal and Rohlf 1981) were also used to compare the CPUE of individual species of fishes and decapods between tows in vegetated and unvegetated sandy habitats within each estuary. Species richness for each station was estimated using the jackknife method detailed by Heltshe and Forrester (1983), which takes into account rare species and sample size. Estimated mean species richness was compared using two-sample t-tests for the two estuaries and for vegetated and unvegetated sandy habitats within each estuary. Mean shoot density in August at the two throw trap locations was compared using two-sample t-tests for the two estuaries. Coefficients of Jaccard (Krebs 1989) were prepared for comparing the similarity of the fish fauna collected in this study with comparable studies from estuaries from North Carolina to the Bay of Fundy. These comparisons were designed to determine the relative value (in terms of mean CPUE or density) of the different habitats for the common epibenthic fishes and decapods. These multiple comparisons only provide a general view of habitat relationships because the same substrate types did not occur at all sites making it impossible to directly compare habitats without some influence of site location in each estuary.

5 Maine Estuarine Fauna 1213 TABLE 2. Catch per unit effort (mean (SE) number per tow) of fishes and decapod crustaceans in vegetated and unvegetated habitats in Casco Bay and the Weskeag River, Maine. Vegetation is eelgrass, Zostera marina. t-test results for eelgrass versus unvegetated sandy habitats, *** = p < 0.001, ** = p < 0.01, * = p < Casco Bay Weskeag River Species No. Eelgrass Sand Eelgrass Sand Tows Apeltes quadracus (1.2) *** 0.2 (0.2) 0 0 Gasterosteus aculeatus (0.8) (0.1) 0 Fundulus heteroclitus (0.5) Myoxocephalus aenaeus (0.2)* 0.2 (0.1) 0.6 (0.1)** 0.2 (0.1) Tautogolabrus adspersus (0.2) (0.2)** 0.1 (0.1) Pleuronectes americanus (0.1) 0.3 (0.2) 0.1 (0.1) 0.1 (0.1) Urophycis tenuis (0.1) 0.1 (0.1) 0.4 (0.1) 0.1 (0.1) Syngnathus fuscus (0.1) <0.1 <0.1 0 Cyclopterus lumpus (0.1) (0.1) <0.1 Microgadus tomcod 1 < Pholis gunnellus <0.1 0 Menidia menidia Liparis coheni <0.1 0 Cryptacanthodes maculatus I < Decapoda Crangon septemspinosa 18, (14.2)** 67.2 (24.8) 70.3 (10.4)** 38.5 (11.9) Carcinus maenas (0.2) 0.7 (0.3) 1.7 (0.3) 1.8 (0.4) Cancer irroratus (0.1) 0.2 (0.1) 0.1 (0.1) 0.1 (0.1) Pandalus montagui 168 < (0.1) 1.6 (0.4)** 0.5 (0.2) Homarus americanus (0.1) (0.1)** 0.1 (0.1) Lebbeus groenlandicus (0.1)** <0.1 Species number Fishes Decapods Total Results Seventeen species of fishes and six species of decapod crustaceans were collected with beam trawling and throw traps in Casco Bay and Weskeag River over the study period. For the fishes, the most abundant species were threespine, Gasterosteus aculeatus, and fourspine sticklebacks, Apeltes quadracus, grubby, Myoxocephalus aenaeus, cunner, Tautogalabrus adspersus, and small schooling species, such as mummichog, Fundulus heteroclitus. White hake, Urophycis tenuis, and winter flounder, Pleuronectes americanus, also were common. Together these species represented 83% numerically of the total fishes collected. Only three decapod species were abundant, sevenspine bay shrimp, Crangon septemspinosa, green crab, Carcinus maenas, and northern shrimp, Pandalus montagui. These species comprised 99.5% of the total decapods. BEAM TRAWL OVERVIEW A total of 20,309 organisms including 855 fishes (14 species) and 19,454 decapod crustaceans (6 species) were collected with the beam trawl (Table 2). In Zostera, 11 fish species occurred in tows in Casco Bay and 9 species in Weskeag River. Five fish species occurred in sandy habitats in both estuaries. The total number of decapod species was gen- erally similar (n = 4-6) between habitats in Casco Bay and Weskeag River. The most commonly occurring species in the estuaries was C. septemspinosa followed by C. maenas. A. quadracus, P. americanus, and M. aenaeus occurred at five or more stations in Casco Bay. In Weskeag River, M. aenaeus, P americanus, U. tenuis, T. adspersus, American lobster (Homarus americanus) and P montagui, all occurred at seven or more stations. Four fish species (T. adspersus, Atlantic tomcod, Microgadus tomcod, Gulf seasnail, Liparis coheni, and wrymouth, Cryptacanthodes maculatus) were only captured with the beam trawl. The most abundant organism collected in beam trawl tows was C. septemspinosa, followed distantly by C. maenas and A. quadracus. C. septemspinosa comprised at least 92% of the decapod abundance in both estuaries. Dominant fishes varied by estuary with A. quadracus, G. aculeatus, and M. aenaeus, comprising about 79% of the fishes collected (n = 678) in Casco Bay. In Weskeag River, M. aenaeus, T. adspersus, and U. tenuis made up about 76% of the fish abundance (n = 167) collected there. ESTUARY COMPARISONS Slightly greater overall species richness of fishes occurred in Casco Bay (n = 12) than in Weskeag

6 1214 M. A. Lazzari River (n = 10). More decapod species were collected in Weskeag River (n = 6) compared with Casco Bay (n = 5). Greater species richness tow-1 occurred with beam trawl in Casco Bay than in Weskeag River (Table 2). Catch per unit effort (number tow-1) for all species was greatest in Casco Bay (96.7) than in Weskeag River (52.4) with C. septemspinosa being the most abundant organism (Table 2). Fishes were much less common ranging from about 7 tow-1 in Casco Bay to 1 tow-1 in Weskeag River. An analysis of species richness tow-1 and CPUE for fishes and decapods with nested ANOVA did reveal significant differences by location and habitat within location. Significantly more fish species tow-1 (F1224 = 11.9, p < 0.001) and higher CPUE (F1,224 = 28.9, p < 0.001) occurred in Casco Bay than in Weskeag River. Higher decapod CPUE (F1,224 = 11.9, p < 0.001) occurred in Casco Bay as well, but more decapods species tow-1 = (F1, , p < 0.001) occurred in Weskeag River than in Casco Bay. Overall species richness estimated by the Jackknife method (Heltshe and Forrester 1983) was not significantly different (two sample t- test, df = 13, t = 1.2, p > 0.05) between the Casco Bay (mean = 12.1 species, SD = 3.9) and Weskeag River (mean = 10.1 species, SD = 5.1). EFFECTS OF VEGETATION Species richness tow-1 and CPUE were positively associated with the occurrence of Zostera. In Casco Bay and Weskeag River tows tested with nested AN- OVAs (Fig. 2), areas with Zostera had significantly more fish species tow-~ (F2,224 = 17.6, p < 0.001), higher fish CPUE = (F2, , p < 0.001), and decapod CPUE (F2224 = 16.2, p < 0.001) than unvegetated habitats. Fish species tow-1 and CPUE were significantly greater in Zostera in Casco Bay than Weskeag River which in turn was greater than sandy areas in both estuaries. Significantly lower decapod CPUE occurred in Weskeag River sandy habitats than all the other habitats. Significantly more decapod species tow-1 occurred in Weskeag River Zostera habitats (F2,224 = 15.1, p < 0.001) than in Zostera in Casco Bay and sandy habitats in the two estuaries. While there was a trend toward greater overall species richness (Heltshe and Forrester 1983) in Zostera compared with sandy areas in Casco Bay (mean = 11.5 versus 8.8, SD = 4.7 versus 5.2) and Weskeag River (mean = 12.9 versus 11.3, SD = 2.7 versus 4.4), the variability was high enough to limit significance in both estuaries (two sample t-tests, df > 5, t < 1.0, both p > 0.05). In individual species testing, two fishes (T7 adspersus, M. aenaeus) and four decapods (C. septemspinosa, Lebbeus groenlandicus, H. americanus, P montagui) all had higher CPUEs in tows in Zostera with U) 2 _ u t 80-.Q E 60- = o? I'_l l N GCB SCB GWR GCB I Site rt I I ~ -I SWR SCB GWR SWR Site Fishes El Decapods E Fishes ElDecapods Fig. 2. Top: Mean number of fish and decapod species tow-1 collected in eelgrass (GCB) and sandy (SCB) habitats in Casco Bay, and in eelgrass (GWR) and sandy (SWR) habitats in Weskeag River. Bottom: Mean CPUE (number tow-1) of fishes and decapods collected in eelgrass (GCB) and sandy (SCB) habitats in Casco Bay, and in eelgrass (GWR) and sandy (SWR) habitats in Weskeag River. in Weskeag River (two sample t-test, t > 2.4, df > 53, all p < 0.01) than unvegetated sandy habitats. Four additional species (G. aculeatus, rock gunnel, Pholis gunnellus, northern pipefish, Syngnathus fuscus, L. coheni) only occurred in Zostera. In Casco Bay, CPUE of two fishes (A. quadracus, two sample t-test, t = 5.2, df = 82, p < 0.001) and M. aenaeus (two sample t-test, t = 2.4, df = 98, p < 0.05) were higher in tows in Zostera than unvegetated tows. Six other fish species (G. aculeatus, F heteroclitus, lumpfish, Cyclopterus lumpus, M. tomcod, T adspersus, C. maculatus) and H. americanus only occurred in tows in Zostera. THROW TRAP OVERVIEW A total of m throw trap samples were collected in this study. In Casco Bay, 52 throw trap samples were collected in shallow habitats with Zostera present and adjacent unvegetated areas (26 in each habitat) and 60 samples (30 in each habitat) were collected in Weskeag River (Table 3, Fig. 1). Fifteen species (12 fishes and 3 decapods) occurred in the throw trap collections from the two estuaries. Eight fish species occurred in Zostera in both Casco Bay and Weskeag River with either two or three additional decapod species, respectively.

7 Maine Estuarine Fauna 1215 TABLE 3. Mean density (maximum) of fishes and decapod crustaceans (no. m-2) collected in eelgrass (Zostera marina) vegetated and unvegetated habitats in Casco Bay and Weskeag River, Maine. Mean shoot density (SE). Effort = number of throw traps at each habitat type. t-test results, *** = p < 0.001, * = p < Casco Bay Weskeag River Species No. Eelgrass Sand Eelgrass Sand Shoot density m-2 (SE) (22.3) (28.6) Effort Pisces Clupea harengus 1 0 (0) 0 (0) <0.1 (1) 0 (0) Apeltes quadracus (13) 0 (0) 0 (0) 0 (0) Gasterosteus aculeatus (6) 0 (0) 0.5 (3) 0 (0) Fundulus heteroclitus (14) 0.7 (11) 0 (0) 0 (0) Fundulus majalis (16) 0.1 (1) 0 (0) 0 (0) Myoxocephalus aenaeus (1) <0.1 (1) 0.1 (2) 0 (0) Pleuronectes americanus (1) <0.1 (1) <0.1 (1) 0.3 (1)* Urophycis tenuis 5 0 (0) 0 (0) 0.2 (1) 0 (0) Syngnathus fuscus (1) 0 (0) <0.1 (1) 0 (0) Cyclopterus lumpus 3 0 (0) 0 (0) 0.1 (1) 0 (0) Pholis gunnellus 2 0 (0) 0 (0) <0.1 (1) <0.1 (1) Menidia menidia (2) 1.0 (19)* 0 (0) 0 (0) Decapoda Crangon septemspinosa 2, (111) 15.2 (30) 13.6 (38) 14.5 (34) Carcinus maenas (4)*** 0.2 (3) 2.4 (6)*** 0.6 (4) Cancer irroratus 1 0 (0) <0.1 (1) 0 (0) 0 (0) In unvegetated throw trap samples, five fish species occurred in Casco Bay and two in Weskeag River with three and two additional decapod species, respectively. A total of 2,508 organisms (275 fishes and 2,233 decapods) were captured with throw traps. Two fish species, Atlantic herring, Clupea harengus, and striped killifish, Fundulus majalis, only occurred in throw trap samples. Density of fishes and decapods averaged about 22 organisms per 1.0 m2. As with the beam trawl samples, C. septemspinosa generally dominated density in both habitat types in the two estuaries. Shoot density m-2 of Zostera during August was significantly greater (two sample t-test, df = 10, t = 5.8, p < 0.001) at the throw trap location in Casco Bay (364 m-2, SE = 20.3) than at the Weskeag River site (198 m-2, SE = 28.6). ESTUARY COMPARISON AND EFFECTS OF VEGETATION Differences existed in both fish and decapod densities by habitat within each system. In Zostera, fish densities within Casco Bay were about 3.7 times higher than in adjacent unvegetated areas (7.1 versus 1.9 fishes m-2) and 3.3 times higher within Weskeag River (1.0 versus 0.3 fishes m-2). Decapod density was 2.4 times higher in Zostera in Casco Bay (41.7 versus 17.3 decapods m-2) but about the same (16.0 versus 15.1 decapods m-2) in Weskeag River. The number of fish species m-2 and fish density in throw traps was significantly greater in Casco Bay than in Weskeag River (F1,108 > 36.7, p < 0.001) and were significantly greater from areas of Zostera than adjacent sand areas (F2,108 > 25.9, p < 0.001). The number of decapod species m-2 was significantly greater in Weskeag River (F1, 108 = 8.7, p < 0.01) and was significantly greater in throw traps from eelgrass vegetated areas than adjacent sand areas in both estuaries (nested ANOVAs, F2,108 = 12.4, p < 0.001). Decapod density (F = 58, t = 1.8, p > 0.05) was similar between the two estuaries (F1,108 = 0.7, p > 0.05) and habitats (F2,108 = 0.8, p > 0.05; Fig. 3). In species comparisons, six fishes (M. aenaeus, C. harengus, G. aculeatus, C. lumpus, U. tenuis, and S. fuscus) occurred only in collections in Zostera in Weskeag River (Table 3). Density of C. maenas (two sample t-test, df = 58, t = 5.1, p < 0.001) was significantly greater in Zostera while P americanus density was higher (two sample t-test, df = 38, t = 2.6, p < 0.05) in sand collections. In Casco Bay species comparisons, three fishes (G. aculeatus, A. quadracus, and S. fuscus) occurred only in Zostera while rock crab, Cancer borealis, occurred only in sand. Density of C. maenas (df = 36, t = 4.6, p < 0.001) was significantly greater from Zostera and Menidia menidia (df = 32, t = 2.2, p < 0.05) from sand collections. Discussion Fish and decapod species richness and abundances were closely linked to the occurrence of Zostera in northern estuaries. Both beam trawl and throw trap sampling in two Maine estuaries revealed that most fish and decapod species in Casco Bay and Weskeag River preferred Zostera since they

8 1216 M.A. Lazzari 0) CO, 0 a, (1) 0 Q Fishes E Decapods GCB SCB GWR SWR Site Fishes _E Decapods GO I O I L- I n I GCB SCB GWR SWR Site Fig. 3. Top: Mean number of fishes and decapod species m-2 collected in throw traps in eelgrass (GCB) and sandy (SCB) habitats in Casco Bay, and in eelgrass (GWR) and sandy (SWR) habitats in Weskeag River. Bottom: Mean density (number m-2) of fishes and decapods collected in eelgrass (GCB) and sandy (SCB) habitats in Casco Bay, and in eelgrass (GWR) and sandy (SWR) habitats in Weskeag River. more abundant than on unvegetated sandy substrates. This finding was expected since it has been shown to occur repeatedly in more southerly estuaries (Nixon and Oviatt 1973; Orth et al. 1984; Heck et al. 1989; Szedlmayer and Able 1996; Raposa and Oviatt 2000), but this study was the northernmost to date. The occurrence of commercial or recreationally important fishes (C. harengus, M. tomcod, U. tenuis, T. adspersus, P americanus) and decapods (H. americanus, P. montagui, Cancer irroratus) reinforces the nursery role of Zostera and other shallow nearshore areas observed in Maine (Ayvazian et al. 1992; Lazzari et al. 1999) and elsewhere in the western (Pearcy and Richards 1962; Nixon and Oviatt 1973; Keats et al. 1987; Heck et al. 1989; Sogard and Able 1991) and eastern North Atlantic (Edwards and Steele 1968; Daan 1978; Gibson et al. 1993). With Zostera generally thought to be on the increase in Maine coastal waters (Maine Department of Marine Resources unpublished data), increased habitat will be available for many of these important species. Fish and decapod species richness and abundances differed between areas of Zostera in the two estuaries. Casco Bay supported significantly more fish species and greater fish and decapod abundances than did Weskeag River, while decapod species richness was greater in Weskeag River. Vari- ability in species associations and abundances has often been noted when multiple beds of Zostera were sampled as replicates (Heck et al. 1989; Sogard and Able 1991; Raposa and Oviatt 2000). These variations have been attributed to a more extensive nature of habitats vegetated with Zostera, greater shoot density/biomass, and an increased area of salt marsh (Sogard and Able 1991; Connolly 1994; Raposa and Oviatt 2000). Any of these factors could account for the differences observed between Casco Bay and Weskeag River collections. Individual fish species differed in their habitat utilization. G. aculeatus was limited to Zostera, where they were present in high numbers and densities but absent at the sandy sites. A. quadracus, S. fuscus, T adspersus, M. aenaeus, and C. lumpus were highly dependent on Zostera but were also present at the unvegetated sandy sites. Several other species (i.e., P. americanus, C. maenas) occurred in Zostera, but were also common in other habitats. No fish or decapod species were limited solely to unvegetated habitats. C. septemspinosa was a habitat generalist, abundant at all sites and in all habitats. The fish and decapod densities observed in Zostera within Casco Bay and Weskeag River were comparable to previously reported densities from seagrasses using similar sampling methods in Texas (Huh 1984), Florida (Sogard et al. 1987), New Jersey (Sogard and Able 1991), and New York (Raposa and Oviatt 2000). Capture efficiencies of enclosure traps for epibenthic species were known to be very high on both vegetated and unvegetated substrates (70% to nearly 100%; Kushlan 1981; Pihl and Rosenberg 1982), but were probably lower for active water column species. Quantitative studies of fish and decapod communities for U.S. east coast estuarine habitats include those from Zostera in North Carolina (Adams 1976), Zostera and tidal creek habitat in Virginia (Weinstein and Brooks 1983), Zostera, Ulva, and tidal creek habitat in New Jersey (Sogard and Able 1991), and Zostera and unvegetated habitat in New York (Raposa and Oviatt 2000). In order to increase similarity comparisons for the fishes, I included studies using seining and trawling methods in Zostera in Virginia (Orth and Heck 1980) and Delaware coastal bays (Derickson and Price 1973), in Zostera and unvegetated areas in New Jersey (Szedlmayer and Able 1996), in Zostera and unvegetated areas in New York (Briggs and O'Connor 1971) and Long Island Sound, Connecticut unvegetated shallows (Richards 1963), Zostera and unvegetated areas from Massachusetts (Heck et al. 1989), and shallow habitats in Maine (Ayvazian et al. 1992; Lazzari et al. 1999; Lazzari and Tupper 2002) and New Brunswick, Canada (Tyler 1971; MacDonald et al. 1984). The Maine fish fauna was

9 Maine Estuarine Fauna 1217 TABLE 4. Coefficient of Jaccard for fish species (n = 17) in Casco Bay and Weskeag River compared with other shallow water and estuarine systems along the northeast coast of North America from Canada to North Carolina. * = shallow stations only. Gears used in the various studies are: drop net (D), fyke net (F), beach seine (S), trawl (T), and throw trap (Tt). Total Species in Coefficient Estuary Species Common of Jaccard Gear Source Passamaquoddy Bay, NB 35* T MacDonald et al Passamaquoddy Bay, NB T Tyler 1971 Penobscot Bay, ME T Lazzari and Tupper 2002 Kennebeck Point, ME F, S Lazzari et al Wells Harbor, ME T, S Ayvazian et al Nauset Marsh, MA T Heck et al Waquoit Bay, MA T, S Ayvazian et al Mystic River, CT T, S Pearcy and Richards 1962 Long Island Sound, CT* T Richards 1963 Great South Bay, NY S Briggs and O'Connor 1971 Great South Bay, NY Tt Raposa and Oviatt 2000 Little Egg Harbor, NJ T Szedlmayer and Able 1996 Little Egg Harbor, NJ Tt Sogard and Able 1991 Delaware coastal bays T, S Derickson and Price 1973 Chesapeake Bay, VA T Orth and Heck 1980 Vaucluse Shores, VA T Weinstein and Brooks 1983 Bogue Sound, NC D Adams 1976 most similar to Massachusetts and intermediate in composition between Canada and more southern areas (Table 4). The fish community in Maine shallow waters consisted primarily of cold temperate species and few of the southern species that add to the faunal richness of New Jersey, Virginia, and North Carolina estuaries occurred here. Gadoids occurred from New York to Canada. Species common in Maine but rare in Massachusetts included P. gunnellus, C. lumpus, and T. adspersus. The dominant Maine species of A. quadracus, G. aculeatus, M. aenaeus, and E heteroclitus were common from Virginia northward. The summer-autumn fish fauna in shallow Maine habitats was dominated by cold temperate species, those with relatively wide geographic ranges, and included few southern species. Studies on decapod communities include those from North Carolina (Weinstein 1979), Virginia (Heck and Orth 1980), New Jersey (Wilson et al. 1990; Sogard and Able 1991), New York (Raposa and Oviatt 2000), and Massachusetts (Fiske et al. 1967; Teal 1986; Heck et al. 1989). Green crab, Carcinus maenas, and rock crab, Cancer irroratus, were common in Maine and Massachusetts but relatively rare to the south. P montagui and L. groenlandicus occurred only in Maine and were absent from Massachusetts, New York, and New Jersey. New York and New Jersey estuaries supported high densities of Callinectes sapidus, Palaemonetes vulgaris, and Hippolyte pleuracanthus, which were rare in Massachusetts and absent in Maine. C. septemspinosa was a dominant faunal component from Virginia northward. Areas of Z. marina in northern estuaries function in the same manner as more southerly ones with a generally richer and more abundant nekton community than in adjacent unvegetated areas. This study represents the northernmost detailed assessment of nekton community structure associated with Zostera in the western Atlantic Ocean to date. The observed fish fauna was similar to other Maine and Massachusetts estuaries, but the importance of Zostera to the overall abundance of many commercial and recreational species will require more research, particularly on the relationship to Zostera biomass and shoreline type. ACKNOWLEDGMENTS I would like to thank K. Kanwit and three anonymous reviewers for helpful comments made to an earlier version of this manuscript. LITERATURE CITED ADAMS, S. M The ecology of eelgrass, Zostera marina (L.), fish communities. I. Structural analysis. Journal of Experimental Marine Biology and Ecology 22: AYVAZIAN, S. G., L. A. DEEGAN, ANDJ. T. FINN Comparison of habitat use by estuarine fish assemblages in the Acadian and Virginian zoogeographic provinces. Estuaries 15: BIGELOW, H. B. AND W. C. SCHROEDER Fishes of the Gulf of Maine. Fishery Bulletin 53: BRIGGS, P. T. AND J. S. O'CONNOR Comparison of shorezone fishes over naturally-vegetated and sand-filled bottoms in Great South Bay. New York Fish and Game Journal 18: BROWN, A. C. AND A. McLACHLAN Ecology of Sandy Shores. Elsevier, Amsterdam, The Netherlands. CONNOLLY, R. M A comparison of fish assemblages from seagrass and unvegetated areas of a southern Australian estuary. Australian Journal of Marine and Freshwater Research 45: DAAN, N Changes in cod stock and cod fisheries in the North Sea. In North Sea Fish Stocks-Recent Changes and Their Causes. Rapports et Process-Verbeaux des Reunions Conseil Internationale pour l'exploration de la Mer 172: DERICKSON, W. K. AND K. S. PRICE, JR The fishes of the

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