Abstracts
(alphabetical by author)
A comparison of acoustic techniques, videography, and quadrat sampling for mapping and characterizing subtidal oyster reefs
Jamie Adams,1* Raymond Grizzle,1 Larry Ward,1 Semme Dijkstra,2 and John Nelson.3 1Jackson Estuarine Laboratory, University of New Hampshire, Durham, NH 03824, USA; 2Center for Coastal & Ocean Mapping, University of New Hampshire, Durham, NH 03824, USA; 3New Hampshire Fish & Game Department, Marine Fisheries Division, Durham, NH 03824, USA.
Acoustic techniques, videography, and quadrat sampling were used to characterize several subtidal oyster reefs in the Great Bay Estuary in New Hampshire and to compare their effectiveness, with the long-term goal being a general protocol for reef mapping and monitoring. The acoustic techniques consisted of a hull-mounted Klein 5000 sidescan sonar system, a Knudsen 320P, 50-200 KHz dual frequency sounder, and a Navitronic Seadig 210 KHz multi-channel sounder. Videography was conducted by systematically imaging each of 40 sampling cells in a grid covering the approximate area of each reef. A single drop was made in each cell and a 5 to 10-s recording made of a 0.25 m2 area. A still image was produced for each of the 40 cells and all were combined into a photomontage that revealed the approximate boundaries of the reef. Five to ten cells on each reef were randomly chosen and sampled by divers using a 0.25 m2 quadrat; all live oysters were measured (shell height) to nearest mm using calipers. The same quadrat area was also video-imaged. Preliminary analyses showed good correlations between the quadrat counts and counts made directly from the video images only when densities were relatively low. Preliminary analysis of the acoustics data indicated that reef boundaries could readily be mapped, and some differences possibly related to shell density variations also detected. Overall, our results to date indicate that acoustic techniques generally can delimit the boundaries of oyster reefs, as has been demonstrated in other studies. The potential for acoustically inferring other reef characteristics (e.g. oyster densities), however, remains to be fully tested. Videography also may be a powerful and relatively inexpensive tool for detailed reef mapping, including inferring oyster densities and perhaps other characteristics.
Fiddler crab fitness: exercise and the cost of sex
Bengt J. Allen* and Jeffrey S. Levinton. Department of Ecology and Evolution, State University of New York, Stony Brook, NY 11794, USA.
Fiddler crabs (genus Uca) exhibit extreme sexual dimorphism. The major claw comprises as much as 40% of the male’s total body mass. Male’s with larger claws have an advantage in male-male competition, and are often preferentially chosen as mates by females. Sexually selected characters may have associated costs, and it has been suggested that the presence of the major claw might result in reduced foraging efficiency or increased risk of predation for male crabs. Empirical support for these hypotheses, however, has been mixed. Using a simple measure of performance efficiency, we tested the hypothesis that carrying the major claw represents an energetic cost to male fiddler crabs.
We ran male sand fiddler crabs (Uca pugilator) on a motorized treadmill at a constant velocity, and measured time to fatigue. Crabs with a major claw tired significantly sooner than crabs without a major claw (which can be autotomized by the crab, and subsequently regenerated). Similarly, crabs carrying added weight tired sooner than crabs without an additional load. The relationship between weight and endurance is complex, and there appears to be a threshold weight associated with a marked decrease in crab performance. Crabs without a major claw crossed a threshold of endurance and could run for much longer periods of time. There also appears to be a postural cost associated with holding the claw away from the body. Our results suggest that claw size must be a reliable indicator of male fiddler crab quality, as only crabs in good condition would counteract the energetic cost of bearing such a large major claw.
Effects of hemichordate bioturbation on infaunal abundance and composition on a sandflat in southeastern North Carolina
Troy Alphin,* Martin Posey, and David Wells. University of North Carolina at Wilmington, Center for Marine Science, Wilmington, NC, USA.
The acorn worms, Balanoglossus and Saccoglossus, are large infaunal bioturbators, commonly found on sandflats in southeastern North Carolina. These organisms deposit large amounts of sediment on the substrate surface in the form of castings. In addition to the physical disturbance of sediment deposition and reworking caused by these organisms, they also produce halo-organic compounds that have been proposed to act as a predator deterrent. We present here the results of two studies evaluating the infaunal community impacts of high-density assemblages of these infaunal bioturbators. The first study evaluated functional guild responses through defaunation and recovery experiments as well as seasonal comparisons of the ambient community within the acorn worm assemblage compared to adjacent areas with few of these bioturbators present. The second study focused on recruitment (both immigration of adults and larval recruits) into the hemichordate assemblage compared to adjacent areas, as well as targeting the effects of halogenated compounds on infauna through chemical infusion experiments.
De-coupling of top-down and bottom-up regulation due to hypoxic disturbance in Narragansett Bay, Rhode Island
Andrew H. Altieri* and Jon D. Witman. Department. of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA; e-mail .
Predation pressure (i.e. top-down control) has been shown to control the lower depth distribution of the blue mussel (Mytilus edulis) in many areas of the world. Moreover, in many of these systems the distribution and abundance of many predator species are trophically dependent on availability of the highly productive mussels (i.e. bottom-up control). The opportunity to test the generality of these interactions arose in the spring of 2000, when a pulse of blue mussel recruitment covered large areas (over 7,200 m2) of the benthos in Narragansett Bay to depths exceeding 7 m. The following spring we initiated a series of surveys and experiments at 3-16 subtidal sites on a scale of tens of kilometers designed to elucidate the relative importance of top-down and bottom-up interactions between blue mussels and their predators, with particular attention to the seastar Asterias forbesi. Here we present several lines of evidence that suggest blue mussels did exert strong bottom-up control of predator distribution and abundance as predicted by previous studies. However, during the period of our study we observed a massive die-off in the blue mussel population of Narragansett Bay that appeared to be of a strong and pervasive abiotic origin. Our results suggest that an intense period of oxygen depletion (hypoxia) in Narragansett Bay waters was responsible for this control of the blue mussel populations. In sum, it appears that while blue mussels can play an important role in the bottom-up structuring of the benthic community in Narragansett Bay, environmental stress in the form of hypoxic disturbance, rather than predation, drives the dynamics of the blue mussel population.
Effects of disturbance on invasion success in marine communities
Safra Altman,* Jeffrey Terwin, and Robert Whitlatch. Department of Marine Sciences, University of Connecticut, Avery Point, 06340, USA.
Introductions of non-indigenous species have resulted in many ecological problems including the alteration of ecosystems, reduction of biodiversity, and decline of commercially important species. The question of how disturbance affects invasibility has been examined through theoretical and correlative terrestrial studies. While theory repeatedly predicts that increased disturbance leads to increased invader success, results from empirical studies do not always support theory. The link between disturbance and potential invasion has rarely been studied in the marine environment where dominance hierarchies, dynamics of larval supply, and resource acquisition may differ greatly from terrestrial systems. In this study, marine fouling communities of Long Island Sound were used as an experimental system to assess the effect of mechanical disturbance on invasion success. Experiments consisted of manipulating disturbance in fouling communities that were grown on 100cm2 PVC panels. Treatments began after a five-week development period, when fouling communities covered 100% of the possible primary substrate. Disturbance treatments were characterized by frequency (single, biweekly, monthly) and magnitude ( 20%, 48%, 80%). Disturbance was created by removing all organisms from a randomly distributed area corresponding to treatment value and thus providing primary substrate, a limited resource. Frequency and magnitude of disturbance had a significant effect on both natives and invaders, although their responses to these factors differed. The impact of disturbance treatments was significantly different from the control for natives and invaders in the single and biweekly frequencies as well as the 20% and 80% treatments. The direction of deviation from the control demonstrates a positive effect of disturbance on invaders coupled with a negative effect on natives. Disturbance, by creating available space, may facilitate the success of invasive species in subtidal fouling communities.
Scientific diving
American Academy of Underwater Sciences. 430 Nahant Road, Nahant, MA 01908, USA; telephone (781) 5581-7370 x 334; fax (781) 581-6076; e-mail ; URL
The American Academy of Underwater Sciences (AAUS) is a non-profit, self-regulating corporation composed of active diving scientists dedicated to the establishment and maintenance of standards of practice for scientific diving. The AAUS has been serving the scientific diving community for over 20 years.
The mission of the AAUS is:
1. Develop, review and revise standards for safe scientific diving certification and the safe operation of scientific diving programs. These standards were developed and written by the AAUS by compiling the policies set forth in the diving manuals of several university, private, and governmental scientific diving programs. These programs share a common heritage with the scientific diving program at the Scripps Institution of Oceanography (SIO). Adherence to the SIO standards has proven both feasible and effective in protecting the health and safety of scientific divers since 1954.
2. Collect, review and distribute statistics relating to scientific diving activities and scientific diving incidents.
3. Conduct symposia and workshops to educate the membership and others in safe scientific diving programs and practices.
4. Represent the scientific diving interests of the membership before other organizations and government agencies. AAUS has established relationships with the following organizations: Occupational Safety and Health Administration (OSHA), National Oceanographic and Atmospheric Administration (NOAA), University-National Oceanographic Laboratory System (UNOLS), Association of Diving Contractors, Inc. (ADC), Divers Alert Network (DAN), Undersea and Hyperbaric Medical Society (UHMS), Recreational Scuba Training Council (RSTC), National Science Foundation (NSF), National Association of Marine Labs (NAML), Diving Equipment and Marketing Association (DEMA).
5. Fund research, education and development of safe scientific diving programs and practices. AAUS has established scholarships awarded annually to graduate students engaged in, or planning to begin, a research project in which diving is/will be used as a principal research tool. AAUS also funds workshops on topics of interest to the scientific diving.
Are we chronically underestimating the abundance of lobster postlarvae?
Eric R. Annis,* Ruth Howell, and Robert S. Steneck. Darling Marine Center, 193 Clark’s Cove Rd., Walpole, Maine 04573 USA.
Larval abundance drives the abundance of the American lobster, Homarus americanus. To understand the pelagic to benthic coupling of this species we need quantify the abundance of settlement-competent postlarvae. Lobster postlarvae were thought to reside primarily in surface waters, and past studies using plankton net samples estimate 75-95% of the population occurs in the top meter of the water column. Accordingly, most research on the distribution and abundance of postlarvae has been based on surface samples. We examined the vertical distribution of postlarvae using direct observation of individuals in situ with SCUBA to determine the proportion of time postlarvae spend within our normal plankton net sampling depth(00.5m). Our results indicate that proportion of the population at the surface may be considerably lower than previous estimates with individual postlarvae spending only 35% and 50% of the time in the top 0.5m and 1.0m respectively. The proportion of the postlarval population represented in surface samples is critical to estimates of total abundance which are used to determine distribution patterns, and estimates of production, mortality, and percent settling to the benthos. Our findings indicate that fewer postlarvae are represented in surface samples than previously thought and suggest that estimates of total abundance and subsequent calculations may be in need of reevaluation.
The coral that dies beneath the waves: species turnover on Caribbean reefs during the last 3,000 years
R. B. Aronson,1* W. F. Precht,2 I. G. Macintyre,3 T. J. T. Murdoch,1 and C. M. Wapnick.1 1Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island, AL 36528, USA; 2Ecological Sciences Program, PBS&J, 2001 NW 107th Avenue, Miami, FL 33172, USA; 3Department of Paleobiology, Smithsonian Institution, Washington, DC 20560, USA.
Most ecologists suspect that the ongoing degradation of Caribbean reefs is unprecedented on a millennial time scale. If this surmise is correct, then the spatial extent of species turnover must have increased greatly, from localized areas of coral mortality and species replacement before the late 1970s to recent changes in biotic composition that transcend reefs and even reef systems. Analysis of 36 reef cores, extracted according to a hierarchical sampling design from 20 stations in a 375-km2 area of the central shelf lagoon of Belize, showed that the staghorn coral Acropora cervicornis dominated continuously for at least the last 3,000 yr. The lettuce coral Agaricia tenuifolia occasionally grew in small patches until the late 1980s. Within a decade, Ac. cervicornis was virtually eliminated by white-band disease and Ag. tenuifolia recruited to and grew on the dead coral branches. The scale of species turnover increased from tens of square meters or less to hundreds of square kilometers or more. Likewise, during the 1970s much of the open space on fore reefs in Jamaica, Belize, St. Croix, Florida and elsewhere was covered by living populations of Ac. cervicornis interrupted by damselfish territories and other small areas of dead Ac. cervicornis covered with fleshy and filamentous algae. Macroalgae now predominate because the scale ofmortality of Ac. cervicornis and its replacement by algae has increased enormously. The expanding scale of species turnover events is rooted in the accelerating pace of ecological change at the regional level.
Green crab (Carcinus maenas) situation in the southeastern Gulf of St. Lawrence, Canada: the Prince Edward Island situation
Dominique Audet,1* Gilles Miron,1 and Mikio Moriyasu.2 1Départementde biologie, Université de Moncton, Moncton, N.B., E1A 3E9, Canada; 2Departmentof Fisheries and Oceans Gulf region, Moncton, N.B., E1C 9B6, Canada.
The green crab Carcinus maenas was accidentally introduced on the eastern coast of the United States in the 19thcentury. It has since migrated northward from New Jersey and was officially observed off the coast of Prince Edward Island in 1998. A two year field project was conducted from June to November 2000 and from May to December 2001 on the southeast coast of P.E.I. to characterise the demographic profile and life cycle of C. maenas at the northern end of its range on this side of the Atlantic. Bated eel traps were used as fishing gear. Fyke nets and juvenile collectors were also deployed to capture crabs. Results obtained will be shared to describe seasonal variations of various population characteristics (e.g. seasonal dynamics of cohorts, size, sex ratio). The moment of different life cycle events such as period of molting, copulation and egg laying were also established. In the south of the St. Lawrence Gulf, crabs bearing eggs occurs from July to November. The peak last two weeks at the beginning of July. Water temperature varied between 16.5 and 20.0°C at that time of the year. Mature males are molting from June to December, but mainly in July before copulation, which begins in August just after larvae are released. In general, life history events of C. maenas seems to occur slightly later in P.E. I. than what is observed in Maine. The arrival of C. maenas in P.E.I. is of particular concern to the shellfish culture industries and commercial inshore clam fishers. Its interactions with other coastal species may also have a great ecological impact. The 1998 incursion of C. maenas in P.E.I may represent the early stages of a booming population. The long-term status of the green crab in the southeastern Gulf of St. Lawrence is, however, still uncertain.
Assessment and restoration of mangrove impacts: a case study from Grand Cayman, B.W.I.
Timothy Austin,1 Kirsten Luke,1 Beth Zimmer,2* Adam Gelber,2 Martin Heaney,3 William Precht,2 Mark Henry,2 and Cindy Savage.4 1Department of Environment, P.O. Box 486 GT, Grand Cayman, Cayman Islands B.W.I.; 2PBS&J, 2001 N.W. 107th Ave., Miami, FL 33172, USA; 3PBS&J, 1880 South Dairy Ashford Street, Suite 300, Houston TX 77077, USA; 4Caribbean Utilities Company, P.O. Box 38 GT, Grand Cayman, Cayman Islands B.W.I.
Coastal mangrove ecosystems are among the most productive systems in the tropics. Mangroves provide a variety of intrinsic ecological benefits including the nursery grounds for a number of commercially important finfish and shellfish. Accordingly, mangroves form an important part of the economic resource base of the Caribbean. In addition, they are important as geologic agents, providing a coastal buffer against waves and storms. Although this ecosystem is highly resilient in the face of natural stressors, they are extremely vulnerable to a number anthropogenic impacts. To this end it is imperative to protect this resource and where possible to restore disturbed areas. At Rum Point in northeastern Grand Cayman, unavoidable impacts related to the construction of the Islands power infrastructure consumed an area of red and mixed mangrove habitat totalling 0.24 and 0.68 acres, respectively. An assessment of these impacts, including a GPS base map was prepared detailing the type and amount of mangrove loss. A restoration plan was developed in accordance with this assessment. The first phase of restoration included the physical grading of the site to appropriate mangrove elevations and was completed within a few weeks of the initial impacts. Phase two included the collection of some 5,500 red mangrove propagules that were planted in pots, and reared in a nursery for about six weeks until leaves emerged. These were planted on 0.5 m spacing throughout the 0.92-acre area. Follow-up monitoring shows this planting effort to be extremely successful with <14% prop mortality in the three months since transplantation. It is anticipated that as these red mangroves become well established, natural recruitment of black mangroves will occur in areas of slightly higher elevation and/or in areas of higher soil salinity. A long-term monitoring effort is underway to evaluate the efficacy of this restoration effort over time.