Changes in the abundance and distribution of sav along Florida’s springs coast: a comparison based on aerial photography acquired in 1992 and 1999

D. Morales,¹* E. Irlandi,¹ W. Arnold,² and S. Herber.^{1 1}Department of Marine and Environmental Systems, Florida Institute of Technology, Melbourne, Florida, USA; ²Florida Marine Research Institute, St. Petersburg, Florida, USA.

The hard clam, Mercenaria mercenaria, is an important fisheries resource along the east coasts of the USA. In the Indian River Lagoon along the east central coast of Florida, clam populations have been significantly reduced by overfishing and altered salinity regimes due to water-management strategies. A variety of restocking efforts are being investigated by the State to re-establish hard clams in the lagoon. We have been evaluating the potential of direct larval injection as a means of restocking. Initial studies indicate that mortality at settlement and early recruitment stages may be limiting successful establishment of hatchery-reared eggs and larvae that have been released directly into the lagoon. To further examine the role of predation, we enclosed a ca. 10-m-diameter area of water column and seafloor with a sediment-retention screen that extended from the sediment to the water surface. Three plot types (1-m² plots) were established within each enclosure: oyster shell hash, vexar mesh screens, and natural bottom. The shell hash and vexar were used to examine if different methods of predator exclusion influenced settlement and recruitment. Hatchery-reared competent larvae were released into the enclosure. After 24 hours the sediment curtain was removed to allow predators access to the plots and the newly settled clams. Sediment cores were taken after removal of the curtain and monthly thereafter to monitor larval settlement and survival. After 4 months we have not recovered any M. mercenaria in the samples. Potential explanations for lack of successful settlement include: predation, sediment type, water temperature at time of release, and insufficient time to allow settlement before removal of the retention screen resulting in transport of larvae out of the sampled area. Additional experiments are planned to continue the evaluation of this method as a means to create localized patches of clams to contribute to a spawning population.


Green turtle grazing: effects on structure and productivity in seagrass beds

Kathleen Moran* and Karen Bjorndal. Archie Carr Center for Sea Turtle Research, Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611, USA.

Seagrass beds are important and productive habitats in Caribbean marine ecosystems. Seagrass blades serve as surfaces for epibionts and traps for detritus, while seagrass pastures are nurseries for many juvenile organisms. Thalassia testudinum is the most robust Caribbean seagrass, often forming extensive, monospecific pastures. Green turtles (Chelonia mydas) are the primary herbivores in many Caribbean Thalassia beds. They can maintain grazing plots for a year or longer, in which they re-crop seagrass blades near the substrate. Today, green turtles are endangered throughout the Caribbean and represent perhaps 1% of historical populations, which numbered in the tens of millions. Productivity and structure of seagrass habitats are undoubtedly different today than when they were grazed by millions of green turtles. Green turtle grazing was simulated in Thalassia plots from July 1999-November 2000 at Lee Stocking Island, Exumas, Bahamas. Seagrass blade structure, productivity, and nutrient composition were quantified initially and at intervals during the grazing experiment. Some of these parameters changed, as re-cropping stressed the plants. As efforts are made to increase green turtle populations, realistic goals of population size are needed for management programs. Incorporating grazing-induced changes in Thalassia productivity and nutrient composition can improve current estimates of seagrass carrying capacity for green turtles.


Infaunal colonization and succession in a 21-acre disturbance: the creation of the Friendship marsh

S. Moseman,* C. Forder, and L. Levin. Biology Department, University of California, San Diego, Ca 92122, USA.

The destruction of wetland habitats, particularly in southern California, has spawned efforts to artificially create salt marshes. While artificial marshes are often intended to compensate for lost habitat, they may also be viewed as large-scale disturbances for the purpose of ecological studies. The 21-acre Friendship marsh in Tijuana Estuary provides a unique opportunity to examine infaunal response to disturbance at a scale that far surpasses those often studied in manipulative experiments. This study characterizes the early colonists of mudflat and S. foliosa habitat within the Friendship marsh. In the early months of marsh establishment, dipteran larvae and the naidid oligochaete, P. litoralis, dominated the infaunal community. These taxa were shown to arrive into the marsh via algal rafts and passive transport. Comparison of samples from algal rafts and larval/bedload collectors revealed that both modes of introduction were utilized by infaunal taxa during the first 6 months of marsh establishment. This study also characterized the successional trajectory of the macrofaunal assemblage, which transitioned from insect domination to increased representation of spionid polychaetes, during the marsh’s first 2 years. There was no influence of vegetation on infaunal trajectories. Rather, similar sediment organic matter and salinity between the created marsh and an adjacent natural S. foliosa habitat more directly influenced the early infaunal community. By 14 months of age, the Friendship marsh achieved comparable species richness and density to that of the natural habitat, although infaunal density declined at 21 months. These results suggest that environmental parameters and life-history traits may particularly govern successional trajectories and limit recovery rates when the scale of disturbance is large.


Shifts in wetland community composition across estuarine salinity gradients: physical and biological determinants

Caitlin Mullan,* Mark Bertness, and Brian Silliman. Department of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI 02912, USA; e-mail [e-mail].

Elucidating the mechanisms that generate species distribution patterns is critical to preserving landscape community structure and to predicting the effects of anthropogenic change to the environment. In estuaries, plant community composition changes dramatically from salt marshes near the coast to tidal freshwater marshes upriver. Current models of coastal marshes assume that salinity stress alone dictates the zonation of species along this environmental stress gradient, but this hypothesis has never been tested. We conducted reciprocal transplant experiments between salt and fresh-tidal marsh dominant plants with and without neighboring native vegetation to investigate the roles of physical stress and biotic interactions in controlling species distribution in a Rhode Island estuary. After one growing season, the salt marsh grasses Spartina patens and Spartina alterniflora transplanted into a fresh-tidal marsh with neighboring vegetation removed were performing as well as, or better than, in their native habitat, but were etiolated and dying when neighbors were included. Fresh-tidal marsh dominants, Typha angustifolia and Scirpus americanus, died within weeks of transplanting into a salt marsh regardless of neighbor treatment. These results indicate that competition for resources, in addition to physical factors, regulates the distribution of wetland plants across salinity gradients. In addition, results from this study suggest that the theory developed along vertical gradients in the intertidal, that superior competitors dominate physically benign habitats and displace weaker competitors to physically harsh habitats, may be generalizable to horizontal environmental gradients.


Pen shell community patterns and assemblage: local and regional dynamics

Pablo Munguía.* Department of Biological Science, Florida State University, Tallahassee, FL 32306-1100, USA.

The interaction between local and regional diversity patterns has been a major focal point in ecology. Theory predicts one of two outcomes: (1) diversity at the local scale is a constant proportion of diversity at a regional scale. (2) Local diversity saturates at higher regional richness. The second outcome has been difficult to observe in nature due to three main reasons: problems in delimiting a species pool, pseudoreplication, and assuming that communities are at some equilibrium. Here I incorporate the relative abundance of species and assembly time to show how the relationship between local and regional diversity develops during different colonization times. At St. Joe Bay, Florida, the pen shell (Atrina sp.) is one of the few sources of hard substrate, serving as a habitat for sessile and mobile invertebrates and fish. During the summer of 2001 I placed empty pen shells spread among different plots within the bay and removed them at different time intervals. The results showed that with time, species richness increases significantly while evenness indices saturate. Initially a local-regional plot of species richness shows that few species are present at the local scale, regardless of the species pool size. With time the slope between local and regional richness increases, presenting unsaturated communities. Rarefying the number of species at the local scale and comparing them to the regional species pool shows a different pattern. With rarefied richness there is a positive linear relationship between local and regional richness initially, but at subsequent times the curve saturates. These results suggest two things: (1) the degree of species saturation will depend on the colonization stage of a community. (2) Incorporating species abundances (i.e. through rarefaction or other techniques) demonstrates the role of species commonness or rarity in determining patterns of community diversity at different scales.


Predation on seeds of seagrasses by a tanaid crustacean Zeuxo sp.: impact on seed production of Zostera marina and Zostera caulescens

Masahiro Nakaoka.* Graduate School of Science and Technology, Chiba University, Inage, Chiba 263-8522, Japan; e-mail [e-mail].

I report the first evidence of seed predation by a tanaid crustacean on seagrasses Zostera marina and Zostera caulescens in Otsuchi Bay, northeastern Japan. A tanaid Zeuxo sp. was found to live in spathes of the seagrasses. Spathes with the tanaid were observed to have bored seeds. Laboratory observation revealed that the tanaid consumes seeds by drilling a hole. For both seagrass species, tanaids and bored ovules were not observed for spathes before anthesis, whereas spathes with bored seeds and density of the tanaid increased from June to August after anthesis. In August, 14% and 27% of seeds were found bored in Z. marina and Z. caulescens, respectively, suggesting that seed predation by the tanaid has considerable negative impact on seed production of the seagrasses. The seed predation was also observed in another seagrass bed at Funakoshi Bay, adjacent to Otsuchi Bay, where the tanaid consumed ca 30 % of seeds of Z. caulescens. Some adult individuals of Zeuxo sp. in spathes had brood pouches containing eggs and juveniles. A large number of juveniles were found in spathes in August. Thus, the tanaid utilizes seagrass spathes not only as feeding site, but also as place of reproduction and a nursery.


A probabilistic assessment of benthic condition of California estuaries: results from the National Coastal Assessment 1999

Walter G. Nelson,* Henry Lee II, and Janet Lamberson. National Health and Environmental Effects Research Laboratory, Pacific Coastal Ecology Branch, Western Ecology Division, US EPA, Newport, OR 97365, USA.

As part of the National Coastal Assessment, the Environmental Monitoring and Assessment Program of EPA is conducting a three year evaluation of benthic habitat condition of California estuaries. In 1999, probabilistic sampling for a variety of biotic and abiotic condition indicators was conducted at eighty stations in all California estuaries except San Francisco Bay, which was sampled in 2000. Assessment results indicate that only a small percentage of the total area of these estuarine systems has levels of sediment contamination of either metals or organic compounds potentially toxic to benthic organisms. These results were confirmed by a general absence of elevated mortality in sediment bioassays conducted with two amphipod species. Nonindigenous species were present at many sites and were the numerical dominants at several, but overall constituted only ~2% of the total fauna compared to 11% in highly invaded San Francisco Bay (previous studies). Within California’s small estuaries, nonindigenous species may be a more widespread form of disturbance to benthic communities than sediment chemical contaminants.

Recovery of a U.S. Virgin Islands red hind spawning aggregation following protection

Richard S. Nemeth, Adam Quandt, and Laurie Requa.* Center for Marine and Environmental Studies, University of the Virgin Islands, #2 John Brewers Bay, St. Thomas, USVI 00802, USA.

The Red Hind Marine Conservation District is an important grouper spawning aggregation site that was heavily fished for many years during the annual spawning season (December through February). The Red Hind Bank was closed seasonally in 1990 in response to the declining size and number of spawning red hind (Epinephelus guttatus). In 1999, this area was designated a Marine Conservation District (MCD), which prohibits all fishing year-round. To document the recovery of the red hind spawning aggregation, 1800 fish were captured, measured, tagged with numerically coded anchor tags, and released over a two year period. Length measurements and visual counts of spawning fish were compared to historical data. Our data indicate that the size of red hind increased from 29.5 cm (11.6 in.) in 1988 to 38.8 cm (15.4 in.) in 2000. The average number of spawning red hind increased from 5 to 25 fish/ 100m², between 1997 and 2001. The increase in the size and number of red hind indicates that the MCD has provided adequate protection to reverse the negative population trend for this species. During the study 21 tags were returned for a reward and catch information was documented. Results show that the majority of tagged fish migrated 10 to 30 km to the west of the spawning ground to an area between St. Thomas, USVI and Culebra and Viequez, Puerto Rico. Continued protection of the red hind spawning aggregations will mean greater reproductive output for this population and better catches in the near future for commercial fishermen of the Virgin Islands. This protection will also mean an increase in other species within the MCD. It is predicted that if we set aside 20% of our marine resources as marine protected areas we will gain the greatest benefit to maintaining sustainable fisheries.


Settlement and survival of the oyster Crassostrea virginica on constructed oyster reef habitats in Chesapeake Bay: how does reef architecture and construction material influence habitat restoration success?

Janet Nestlerode,¹* Mark Luckenbach,² and Robert Diaz.^{1 1}Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, USA; ²Virginia Institute of Marine Science, Eastern Shore Lab, Wachapreague, Virginia 23480, USA.

The objectives of oyster reef habitat restoration in Chesapeake Bay are not only the enhancement of oyster stocks, but also to restore the physical structure and ecological services provided by these systems. Restoration efforts have focused on reconstructing 3-dimensional reef habitats, yet a shortage of sufficient volumes of oyster shell for creating large-scale reefs has lead to an evaluation of alternative base materials. Recent evidence has revealed the importance of two components of reef architecture--vertical relief and interstitial space--on the development of oyster populations on restored reefs and we will present data which show that oyster populations vary between reefs built using different construction configurations and base materials. Oyster recruitment, survival, and growth are compared among intertidal and subtidal reef mounds built with oyster (Crassostrea virginica) shell or surf clam (Spisula solidissima) shell. Results indicate that intertidal oyster shell mounds support greater oyster growth and survival, offer the highest degree of structural complexity, and maintain a more diverse and abundant macrobenthic community. The patterns observed give context to the importance of substrate selection in similar restoration activities.


Oyster reef health in selected southeastern North Carolina tidal creek estuaries

Bethany Noller,* Jacqueline Horner, Martin Posey, and Troy Alphin. Department of Biological Sciences, University of North Carolina at Wilmington, Wilmington, NC 28403, USA.

Due to impacts from various sources, such as increased development, declining water quality (caused by high sedimentation and eutrophication,) and over-harvesting, the health of the oyster population in many areas along the Atlantic and Gulf coasts is in question. Oysters have been identified as critical habitat for juveniles of many important fisheries as well as having significant effects on water quality. They provide a key refuge and foraging habitat for many estuarine residents, transient fish and decapods. However, the habitat function of the oyster reefs may vary with reef structure, especially vertical relief, density, and edge characteristics. This study focuses on the structural characteristics of oyster reefs found in the tidal creeks of New Hanover County, NC. The study was conducted at Howe, Whiskey, Pages, and Hewletts creeks. Within each of these four creeks three oyster reefs were selected. The percent coverage of shell hash and live or dead oysters was measured using ten replicate 30-cm by 30-cm quadrats. Vertical relief was measured on each reef using ten meter square quadrats. We found strong variation in reef morphology and extent among creeks emphasizing the need to examine habitat quality in addition to reef area when comparing even closely spaced estuarine systems.

Effects of the invasion of the Asian shore crab Hemigrapsus sanguineus on resident crab populations

N. J. O'Connor.* Department of Biology and School for Marine Science and Technology, University of Massachusetts Dartmouth, No. Dartmouth, MA 02747-2300, USA.

The Asian shore crab Hemigrapsus sanguineus is becoming established along the rocky intertidal coastline of New England, reaching densities greater than in its native habitat. H. sanguineus occurs throughout the rocky intertidal zone, overlapping in distribution with resident crab species such as green crabs (Carcinus maenas, another non-indigenous species) and mud crabs in the family Xanthidae. The objective of the study was to determine whether populations of green and mud crabs are affected as H. sanguineus populations become established and increase in size. Crab populations in several localities in Narragansett Bay, Vineyard Sound, and Cape Cod Bay were sampled for 3-6 years, usually in the spring (May-June) and fall (September-October), to examine temporal changes in crab populations and to determine whether any changes observed were similar at different locations. Three to five replicate 2m² square quadrats were randomly placed on rocky areas low in the intertidal zone during low tide. All crabs in quadrats were identified, counted, measured in most cases, and then returned to the sampling site. Results to date suggest that the establishment of H. sanguineus has negatively affected the abundance of xanthid crabs, although the mechanism is unknown. H. sanguineus may also be impacting C. maenas, because densities were low where H. sanguineus was abundant. Future sampling where C. maenas currently dominates is necessary to determine whether C. maenas densities decline as H. sanguineus populations grow in size.


Vanadium in sea squirts: is heavy metal in bad taste?

Shobu Odate* and J. R. Pawlik. Center for Marine Science Research, University of North Carolina at Wilmington, NC 28409, USA.

Ascidians may defend themselves from fish predators by producing secondary metabolites or sequestering acid, but many species also accumulate heavy metals, most notably vanadium. The possible defensive function of heavy metals in ascidians is unclear. Past studies have demonstrated that vanadium salts deter fish feeding, but our preliminary results suggest that the same salts are not deterrent in fish feeding assays with the bluehead wrasse, Thalassoma bifasciatum. However, vanadium occurs as haemovanadin in biological systems. We will assess the effects of naturally occurring vanadium complexes and valences in assays testing anti-predator, anti-fouling and anti-microbial effects.

“Where’s my sea whip?” Are defenses in Caribbean gorgonians physical or chemical?

William O’Neal* and Joseph R. Pawlik. Biological Sciences and Center for Marine Science, University of North Carolina at Wilmington, Wilmington, NC 28409, USA.

Previous investigations have shown that gorgonians are defended from generalist fish predators by secondary metabolites and calcitic spicules, but feeding assays in most of those studies were performed on the basis of tissue mass, not volume. We re-evaluated chemical and physical defenses and examined the nutritional quality of 32 species of Caribbean gorgonians on the basis of tissue volume. Crude organic extracts from 100% of the gorgonian species were deterrent toward the bluehead wrasse, Thalassoma bifasciatum, in laboratory feeding assays. Natural volumetric concentrations of spicules from only two species (6.3%) were deterrent. There was no relationship between gorgonian nutritional quality and the presence of chemical or spicule defenses. These results demonstrate that chemical defense is the primary means by which gorgonians protect themselves from generalist fish predators and that assay techniques may greatly influence the results of feeding experiments.

Distribution and abundance of zooplankton at three depth increments over a Florida coral reef

K. L. O’Neil,* K. B. Heidelberg, and K. P. Sebens. Department of Biology, University of Maryland, College Park, College Park, MD 20742, USA.

Benthic suspension feeders and planktivorous fishes rely on zooplankton as a primary source of food. The zooplankton found above coral reefs is made up of holoplankton, meroplankton, demersal and epibenthic plankton. Zooplankton may be residents of the reef or pelagic plankton supplied to the reef by oceanic processes such as internal waves. The majority of research on reef related zooplankton has focused on demersal forms, although pelagic holoplankton can make up a significant portion of the zooplankton. In this study, a specially designed plankton pump system was used to test for differences between the zooplankton population near the substratum, two meters above the reef, and at the surface. Samples were collected six times daily for one week at all depths simultaneously. Copepods were the most abundant group, primarily Oithona spp., nauplii, and Acartia spp.. No difference in total zooplankton density was found with time of day, with high densities frequently occurring during daytime hours at all depths. Temora spp, Calocalanus spp, and Corycaues spp. copepods were all found to be significantly higher at the surface than at the substrate. Acartia spp. density was greatest at two meters and Oithona spp. had equal density at all depths. All rare zooplankton taxa showed significant differences in density between depths. The study discusses the importance of delivery processes and oceanic migration patterns on vertical distribution of zooplankton in coastal areas. Our data shows that certain zooplankton taxa are more or less available to benthic suspension feeders due to varying patterns of vertical distribution.


Estuarine infaunal responses to food enhancement: do patterns indicate specialist or generalist strategies?

M. Owens,* M. Posey, and T. Alphin. University of North Carolina at Wilmington, Center for Marine Science, 5600 Marvin K. Moss Lane, Wilmington, NC 28409, USA.

Studies of the effects of eutrophication on estuarine systems have focused on nutrient inputs and factors structuring estuarine communities. We previously conducted a study examining the effects of bottom-up (resource) and top-down (predation) controls in benthic communities in four tidal creeks in southeastern North Carolina. Short-term experiments and comparative studies were used to examine microalgal biomass, infaunal composition and abundance, predator effects and nutrient variations among four estuaries that varied in background nutrient loadings. The results from these studies were mixed and weak, showing few individual effects of nutrient enhancement and no interactions between predation and nutrient inputs, in contrast to the predictions of a simple cascade model. Possible explanations point to the opportunistic life histories of resident fauna and a lack of strong linkages between specific food resources and infaunal growth and reproduction. We are initiating a series of experiments to determine the relative growth, reproduction and survivorship of three infaunal species common in southeastern North Carolina in response to varying levels of microalgal and detrital food resources, with objectives of determining resource quality/quantity effects as well as understanding whether these species are specialist or opportunistic consumers. Reliable information on the feeding habits of common infauna, including the degree to which they are opportunistic, is essential to predicting and interpreting effects of bottom-up control in benthic communities.


Predatory-induced variability in the composition of decapod crustacean assemblages in the subtidal of central Chile

Alvaro T. Palma,¹* Mauricio Arriagada,² Cael Orrego,² and Anna Astorga.^{2 1}Departamento de Ecología Costera, Facultad de Ciencias, Universidad Católica de la Ssma. Concepción, Paicaví 3000, Casilla 297, Concepción, Chile; ²Departamento de Ecología, P. Universidad Católica de Chile, Alameda 340, Casilla 114-D, Santiago, Chile.

Although common, and in some cases of commercial value, little is known about the mechanisms and processes that affect the distribution and abundance of several decapod crustaceans along the coast of Chile. All these species have planktonic larvae that must undergo settlement and recruitment before becoming part of the adult segments of their populations. For several of these species, we detected the existence of newly settled individuals that display a diverse degree of color polymorphisms. This pattern appears to be more pronounced in those species that are detritivorous and is less evident in the carnivorous ones. Through the implementation of a meso-scale predator-exclusion experiment we were able to quantify the degree of relative protection that such cryptic coloration confers. Our results suggest that the more cryptic species are more susceptible to be preyed upon by “blind” predators such as other crabs, compared to the higher susceptibility of the less cryptic species to visual predators, such as demersal fish.