Determining coral reef impacts associated with boat anchoring and user activity

Transcription

1 Determining coral reef impacts associated with boat anchoring and user activity Protect Our Reefs Grant Interim Report October 1, 2008 March 31, 2009 Donald C. Behringer 1, Thomas K. Frazer 1, Robert A. Swett 1, Russell L. Watkins 2 1 University of Florida, Program in Fisheries and Aquatic Sciences, Gainesville, FL 2 University of Florida, Florida Sea Grant Program, Gainesville, FL Project Rationale Coral reefs around the world are under assault from innumerable threats and Florida reefs are no exception. In addition to threats from climate change (Bruno et. al. 2007), disease (Edmunds and Elahi 2007), pollution (Markey et. al. 2007), and vessel groundings (Lirman and Miller 2003) are those that arise from boating activities including anchor damage (Saphier and Hoffman 2005), habitat destruction, fishing gear damage, and recreational impacts (fishing and diving) (Barker and Roberts 2004). The 566,560 ha of coral reefs in Florida represent the only barrier reef system in the continental U.S. This exceptional natural resource, when combined with warm tropical water and favorable weather, is a consummate draw for avid boaters, fishermen, and divers from around the world. In fact, based on an analysis of Coast Guard boating statistics over the past decade, Florida has the highest number of registered boats and the sixth highest statewide rate of growth in boater registrations in the United States. This magnitude of boating and related activities has lead to intense pressure on already strained reef resources. The Florida Fish and Wildlife Conservation Commission (FWC) recognizes the importance of coral reefs by listing them as a priority habitat and designating their overall habitat threat category as very high (highest threat) in their Florida Wildlife Legacy Strategy (FWLS). Of the nearly 1000 organisms listed in the Strategy as Species of Greatest Conservation Need (SGCN) 304 of them are reef-associated animals, 88 of these are reef invertebrates, and 54 of the invertebrates are corals. One of the four highest ranking actions identified for abating the source of this stress in the FWLS is development of a vessel anchoring management plan and use of mooring buoys. Fulfillment of this action requires knowledge of vessel use patterns, associated activities, and their corresponding impacts on coral reefs. The latter is essential to validate the observations and conclusions drawn from knowledge of the former two, i.e. vessel use patterns and associated activities. Federal (NOAA), State (FDEP), and local (county) resource managers and other stakeholders have also recognized the threat that boating pressure applies to reefs. The

2 team of interagency marine resource professionals, scientists and other stakeholders who developed the Southeast Florida Coral Reef Initiative (SEFCRI) prioritized a project to evaluate the vessel use and activity patterns within the SEFCRI region (Miami-Dade, Broward, Palm Beach, and Martin counties). The project is using aerial surveys to determine use intensity, anchoring pressure, and predominant activities over the entire region and associate use level with specific areas of the reef tract. The information on use and activity patterns gained from the aerial surveys feeds directly into this project as the means for identifying reef research sites. The results of this project will give a clearer understanding of the levels and types of pressure southeast Florida coral reefs experience. Data derived from this project will allow resource managers such as NOAA, FDEP, FWC, and county governments to more effectively target conservation efforts on areas receiving the most intensive use and incurring the greatest damage. Goals This research is entirely field-based and predicated on establishment of user and activity patterns generated from aerial surveys of the entire Southeast Florida Coral Reef Initiative region. As such, the majority of the field work in the first year of this two year project was focused in the late summer/early fall to allow a satisfactory number of aerial surveys to be completed during peak boating periods which, in turn, permit identification of appropriate reef sites. Our goals for the in-water portion of this reef impact study are to determine if reef use intensity (Objective 1) or activity type (Objective 2; diving and fishing) as identified from the air correlate with impact levels measured on the reef, and if the rate of impact exceeds the rate of recovery (Objective 3). Status of objectives Our aerial surveys of use and activity patterns in 2008 were scheduled for April/May, July, and September/October to encompass many of the spring and summer holidays when boating activity is at its peak. We had initially hoped to use the early aerial surveys in April and May to establish our reef research sites, but after preliminary analysis, decided inclusion of the July surveys would add considerably greater confidence to our site selections. Therefore, we delayed our original schedule for site selection, setup, and reef data collection, from July September to September November. Site selection Following the last aerial survey at the end of July, data from all aerial surveys were compiled and entered into ArcGIS TM for analysis of use intensity by activity and timing, as well as for site selection. Data collection categories included: vessel size (< 10 m, m, >20 m), vessel activity (diving, fishing, other), vessel status (anchored, adrift, underway), and vessel type (commercial, recreational, head boat). We categorized (i.e., fishing, diving, low use) and ranked (high to low activity) all of the reefs in each county. We used the GIS data rankings to select a suite of potential sites conforming to our stratified sampling design for each county. Our goal was to establish three replicate sites for each of the following treatments: high use diving, high use fishing, low use diving, and low use fishing. Each site resembles the illustrated example in Figure 1. This design

3 will be repeated in each county, (i.e. Miami-Dade, Broward, and Palm Beach), for a total of 36 sites. We selected an overabundance of potential sites for each treatment, assuming that some would not be useful due to dramatic differences in substrate or other factors. We towed a diver at each potential site and scanned the extent of an area approximately 500 m in diameter. Our main goals were to find sites that were as homogeneous as possible in their coral cover, rugosity, and depth. Extreme heterogeneity adds a potentially confounding effect that could mask effects from the intended treatments. Stony coral cover on all sites accepted was approximately 2-5%, which is within the estimates given from prior monitoring activities (SECREMP 2005). Sites that were not accepted typically had very low live stony coral cover or were artificial in nature (e.g., rubble piles or mitigation reefs). Research activities We have completed surveys of all but the last few sites established in Broward Fig. 1. Site survey design showing three sub-samples composed of four transects each. Transects will be set in the cardinal directions for ease of relocation during subsequent surveys. County. Continuous adverse weather and dangerous sea conditions put numerous delays in our sampling plan. The National Weather Service in Jackson confirmed fall 2008 to be an unusually early and active period for cold fronts and the pattern has continued through the winter of The atmospheric pressure change associated with these cold fronts created frequent and sustained periods of high winds hazardous to boating in small vessels. These difficulties have also been experienced by many other researchers in south Florida, including our partners with the Southeast Florida Coral Reef Initiative and the Broward County Environmental Protection and Growth Management Department. Our revised plan is to have the sampling completed in all counties by May 15 th, Weather conditions have improved in the last few weeks with the onset of spring, so we anticipate more rapid progress during this period. Although logistically difficult, the delay will not greatly affect the outcome of the project. The date the surveys are initially completed is not as important as the duration between successive surveys. The initial surveys record the organisms and damage present, while subsequent surveys will give us the data necessary to determine the rate of impact and the rate of recovery. The year 2 surveys in 2009/2010 will not require pre-survey site

4 selection data, site reconnaissance, or laborious site setup, so they will begin earlier and proceed more rapidly. We are actively collecting data at this time so are not able to offer definitive results, however, our mid-study observations are intriguing. These data suggest that branching corals such as gorgonians and acroporids may act as important sentinels for reef impacts as they retain clearly visible effects of damage long after it has occurred (e.g., broken branches and dislodgement). Table 1 summarizes the data collected and entered to date. Data Category Miami-Dade County Broward County Hard corals mapped Sponges mapped Total organisms mapped (includes damaged gorgonians and all sea fans) Gorgonian count Damaged organisms marked, mapped, and photo-documented Diseased corals marked, mapped, and photodocumented 25 - Marine debris marked, mapped, and photodocumented 26 6 Partial products and other activities: 1) Advertised for and identified a masters-level technician to work on the reef impact project. She received her M.S. from Duke University and has been an asset to our reef research team. She was trained and received her AAUS certification and was subsequently trained on project methods. 2) We have entered all data collected to date into our comprehensive database which includes: all organism locations, tags (if applicable), and condition site location (latitude and longitude), rugosity, and depth gorgonian abundance per transect (tracking each would be prohibitively time-consuming) benthic substrate type and coverage 3) We have annotated all of the digital photographs taken of tagged organisms (damaged, diseased, or bleached) and tagged debris. Each photograph is now associated with the corresponding tag, county, site, transect, and survey date. Figure 2 demonstrates examples of some representative impacts.

5 A B C D E F Fig. 2. Examples of damaged organisms and debris including: (A) a dislodged and inverted coral head, (B) broken Acropora cervicornis branches, (C) rubble flipped onto a gorgonian, (D) a lobster trap weight next to an A. cervicornis clump, (E) a dislodged gorgonian, and (F) a broken branch on a gorgonian.