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

Heather Harwell,* Martin Posey, and Troy Alphin. Department of Biological Sciences, University of North Carolina at Wilmington, Wilmington, NC, USA.

The blue crab Callinectes sapidus is a euryhaline estuarine species that copes with rapidly changing environmental conditions including varying temperatures and salinities. Although settlement may occur predominantly in euryhaline areas, juvenile and adult blue crabs are found across the estuarine gradient. Potential osmoregulatory costs of occurring in low salinity water raises questions about potential effects on growth. This question may be particularly important for juveniles that have high surface area to volume ratios and that receive decreasing predation pressure with increasing size. We conducted a field experiment measuring growth rates of juvenile blue crabs across the estuarine gradient examining effects of salinity and covariant factors on growth and survival. Five sites along the Cape Fear River in southeastern North Carolina were selected. Those sites represent salinity ranging from full strength seawater to oligohaline regions of the upper river. Juvenile crabs (15-30 mm CW) were placed in individual cages at each location for a twelve-week period, in summer and again in fall during which carapace width measurements were made weekly. Infaunal and sediment cores were also taken at each site in order to examine possible food availability and grain size distribution. Crabs placed at the low salinity site (0 ppt) suffered high mortality and could not be used for growth evaluation. Percent growth was similar at all other sites, although the average period of intermolt was 14 days at sites of lower salinity (5.3 and 14.4 ppt) and 24-27 days at higher salinity sites (18.2 and 22.1 ppt). Fall results for percent growth were similar to those of summer. There was, however, an overall increase in intermolt period and mortality in fall compared to summer.


Utilizing a seabed classification system, RoxAnn^TM, to monitor changes in a biologically created benthic habitat

Olivia A. Hauser* and Douglas C. Miller. University of Delaware, Graduate College of Marine Studies. 700 Pilottown Rd. Lewes, DE 19958, USA; e-mail [e-mail].

RoxAnn, a seabed classification system, has the power to map various bottom types by interpreting the strength and shape of a sound signal echoed from the bottom. This system plots the first and second echoes (E1 and E2) on a Cartesian graph and classifies bottom types by E1 and E2 combinations. E1 is a proxy for bottom roughness while E2 is a proxy for bottom hardness. A 5-km² area of Delaware Bay, Delaware was surveyed in once in September 2000 and again in January 2001 and the resulting images compared. The five bottom types (tubeworm nodules, mussels, gravel, fine sand and coarse sand) were identified and ground truthed with sixteen sediment grabs in the first survey and three grabs in the second survey. The distribution of RoxAnn classified bottom types was not notably altered between surveys, which was confirmed with the sediment grab samples. While consistency in classification indicates a stable benthic habitat, the individual plots of E1 and E2 values indicated changes in the bottom properties. Bottom roughness (E1) stayed relatively constant while bottom hardness (E2) differed between the two survey dates. Since the ground truthing confirmed the bottom types stayed the same, we have concluded that seabed roughness (E1) was a better proxy for benthic bottom type than seabed hardness (E2). Overall, RoxAnn was found to be an effective technique to map this benthic hard bottom habitat found in Delaware Bay.


Tough decisions—having sex or being dinner: the dilemma for some tropical seaweeds

Mark E. Hay* and Julia Kubanek. School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA.

When tropical green seaweeds in the genus Halimeda become reproductive, both generalist herbivorous fishes and specialist ascoglossan gastropods begin consuming reproductive plants at rates of 5-10 times the rates that they consume vegetative plants. These seaweeds appear to invest about 1/3 of their total ash-free-dry-mass in reproduction over a period of several hours, and then die. During the time that they are maturing gametes on their surface, they contain higher concentrations of secondary metabolites that have previously been identified as feeding deterrents, but they are none-the-less consumed at higher rates than are vegetative plants. Rapid field bioassays of lipid extracts from vegetative versus reproductive plants show that vegetative plants are more chemically resistant to fishes, but this chemical difference is lost if extracts are held for more than a few hours, suggesting rapid degradation of active metabolites. Follow-up efforts to stabilize activities and specific compounds using different extraction solvents and procedures were unsuccessful at determining which chemical changes were affecting differential palatability of vegetative vs. reproductive plants, but did indicate that methodologies did strongly affect the secondary metabolites obtained. Maturation of gametes, chemical changes of defenses within the plant, and susceptibility to herbivores all change rapidly throughout the afternoon and evening immediately before synchronous release of all gametes at about sunrise. Following gamete release, the white, apparently dead, skeletons of Halimeda are immediately consumed by fishes. The tremendous rates of grazing on reproductive plants may have selected for Halimeda to allocate all mobalizable resources to reproduction, even though this leads to plant death.


The effect of prey density on zooplanktivory by the burrowing ophuiroid Hemipholis elongata (Say, 1825)

F. C. Helies* and S. E. Stancyk. Marine Science Program and Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.

The ophiactid brittlestar Hemipholis elongata readily captures brine shrimp and copepods from the water column with its extensible, sticky tube feet. To develop a feeding response curve, we tested the effect of prey density on the rate of prey capture by individual brittlestars. Following acclimation, brittlestars of approximately the same size were allowed to bury, each in individual 6 cm diameter plastic cores filled with muddy sand. Each core was placed in a separate battery jar containing 4000ml of 35 ppt seawater and a bubbler. Over several trials, each individual was given 50, 100, 200 and 500 brine shrimp (Artemia salina) and allowed to feed for half an hour. In each trial, control battery jars were run for each prey density. The brittlestars were then removed and the remaining Artemia were collected on sieves, preserved and enumerated. The data were compiled to determine consumption rates and the type of feeding response curve the brittlestars demonstrated.


Star-crossed sponges: the sponge-brittlestar association between Callyspongia vaginalis and Ophiothrix lineata

Timothy P. Henkel* and J. R. Pawlik. Biological Sciences and Center for Marine Science, University of North Carolina at Wilmington, Wilmington, NC 28409, USA.

On coral reefs cryptic species form regular and intimate associations with sessile benthic invertebrates for refuge from predation in a space-limited environment. In a recent survey of sponge-dwelling ophiuroids in the Florida Keys, the deposit feeder Ophiothrix lineata was found to occur almost entirely in the common tube sponge Callyspongia vaginalis. Local abundances of O. lineata increased with the presence of C. vaginalis, and brittlestars were partitioned by size class on individual sponges, with large individuals (> 5 mm oral disk diameter) only occurring inside sponge tubes. In field manipulations, O. lineata actively selected C. vaginalis over non-living refuge or the sponge Niphates digitalis. Large O. lineata remained in an individual sponge for up to 3 months, and abundances of large individuals never exceeded the number of tubes per sponge. This study provides evidence that O. lineata may be a species-specific sponge commensal, and suggests that access to feeding surfaces and refuge from predation may regulate habitat partitioning in O. lineata.


Emergency restoration of significant seagrass injuries: a case study from North Sound, Grand Cayman, B.W.I.

Mark Henry,¹* Adam Gelber,¹ William Precht,¹ Martin Heaney,² Lisa Vitale,³ and Beth Zimmer.^{1 1}PBS&J, 2001 N.W. 107th Ave., Miami, FL 33172, USA; ²PBS&J, 1880 South Dairy Ashford Street, Suite 300, Houston TX 77077, USA; ³PBS&J, 206 Wild Basin Road, Suite 300, Austin, TX 78746, USA.

In North Sound, Grand Cayman, large monospecific beds of Thalassia testudinum abound. During the installation of a series of submarine power cables, localized patches of this seagrass were injured by the mechanical operations. In all, four scars each measuring approximately 1 m in width by 1 m depth by 50 m in length were identified and assessed using standard scientific diving techniques. Where sufficient substrate has been removed in such a disturbance event, the natural recovery of the T. testudinum is usually small or nonexistent. The inability of this seagrass to re-colonize a deep trench or depression is due to the vegetative propagation of the rhizomes. These creeping rhizomes extend horizontally through the sediment with new leaf-bearing shoots growing off the apical meristems. If no sediment is present where the rhizome extends, the rhizome stops growing, failing to reorient into the depression. If this sediment is not replaced, these depressional scars remain as permanent features over temporal scales of multiple decades or longer. To prevent this protracted recovery, an emergency restoration plan was implemented within 72 hours of the actual injury. Using a team of commercial divers, inert fill (clean sand) was placed in the elongate troughs, followed by the replacement of sediment and seagrasses that had been pushed up in berms along the edge of the scars. Within two weeks, the outline of the original injury was almost indistinguishable from the surrounding unimpaired seagrass meadow. Follow-up monitoring of multiple biotic indices some nine months after the original injuries shows complete restoration. This project highlights the importance of early intervention in seagrass restoration and the need for replacement of lost sediment to accelerate the recovery process.


Do sediment disturbance processes structure estuarine soft sediment communities?

Elizabeth K. Hinchey* and Linda C. Schaffner. School of Marine Science, The College of William and Mary, Virginia Institute of Marine Science, Gloucester Point, VA 23062, USA.

We are investigating the role of sediment disturbance processes in structuring low diversity soft sediment benthic communities. Field studies conducted in two Chesapeake Bay tributaries examined effects of sediment disturbance events on seabed dynamics and associated macrobenthic recruitment success and community structure. The York River, characterized by relatively high tidal energy, experiences deep sea-bed mixing over various time scales due to erosion and deposition processes. Multi-year comparisons at the York River study region revealed that more severe sediment disturbance events were observed during a high discharge, wet year vs. low discharge, drought conditions. During the drought, effects of sediment disturbance were most pronounced in deep channel environments where tidal currents are strongest, as opposed to wet years when sediment disturbance was observed in channel, flank and shoal environments. Sites demonstrating evidence of recent reworking of near-surface sediments exhibited depressed abundances of sedentary infaunal organisms and were dominated by motile fauna. The Patuxent River experiences minimal sea-bed mixing as a result of an order of magnitude lower tidal energy; sites in this system were populated by a combination of sessile tube builders and motile fauna. Effects of sediment deposition on estuarine macrobenthic organism growth and survival were further investigated in laboratory experiments. We tested response to overburden stress due to burial for a sedentary tube-dwelling species (Streblospio benedicti) and motile shallow burrowing species (Leptocheirus plumulosus) and motile deep burrowing species (Macoma balthica). Mortality was correlated with motility mode, with Streblospio benedicti and Leptocheirus plumulosus exhibiting significant, but differential, mortality. Macoma balthica did not suffer any burial-induced mortality at the levels of overburden stress tested. Our results suggest that tidal flow-mediated disturbance can be a strong structuring force in energetic estuaries, at sites where tidal currents are strongest and during events when fine-grained sediment input via the spring freshet is enhanced.


Analysis of Biscayne Bay sediments: do benthic Foraminifera of the bay reflect trace metal contamination?

A. M. Hoare,¹* P. Hallock,² B. H. Lidz,³ C. D. Reich,³ and E. A. Shinn.^{3 1}College of Marine Science, University of South Florida, 140 7th Ave. S., St. Petersburg, FL 33701, USA; ²College of Marine Science, Faculty of Marine Science, University of South Florida, 140 7th Ave. S., St. Petersburg, FL 33701, USA; ^cU. S. Geological Survey, 600 4th St. S., St. Petersburg, FL 33701, USA.

The human population explosion in South Florida over the past hundred years has brought significant changes to Biscayne Bay, many of them detrimental to the coastal ecosystems. The construction of bridges, canals and causeways degraded shorelines and altered benthic communities. Raw sewage effluent and chemical pollutants have also degraded the bay. Although discharge of untreated sewage has been addressed and the Toxic Substance Control Act was enacted, trace metal pollution remains an issue of concern. Numerous studies carried out in both temperate and tropical regions have shown that benthic foraminiferal assemblages are efficient indicators of trace metal pollution. In addition, shell aberrations typically occur in sediments that are highly contaminated with trace metals. The objectives of this study were to analyze sediments of Biscayne Bay for trace metal contamination and determine whether benthic foraminiferal assemblages reflect contamination and indicate hotspots of pollution. Thirty-eight sites in Biscayne Bay were sampled for surficial sediments. Analysis of the sediments consisted of geochemical assessment for 30 chemical parameters, grain-size analysis and micropaleontological assessment of foraminifera at the genus level. Geochemical analysis revealed that effects range low (ER-L) values, and in some cases, effects range median (ER-M) values for several trace metals were exceeded at several nearshore sites in the upper bay. Three assemblages of foraminifera were identified. Sediments of finer grain size were dominated by opportunistic taxa, whereas those of large grain size consisted of other smaller foraminifera. Sites farthest offshore from Black Point had higher percentages of symbiont-bearing foraminifera. Although shell aberrations were present in several samples, the percentages of deformed specimens were low and deformations were not concentrated near or at the hotspots of chemical contamination.


Growth and survival costs of aggression in juvenile Hemigrapsus sanguineus crabs

Niels-Viggo S. Hobbs.* Biological Sciences Department, University of Rhode Island, Kingston, RI 02881, USA.

Aggression in decapod crustaceans is well studied but the associated long-term costs have yet to be fully explored. Costs are a critical component of any analysis of risk assessment in the decision-making process of animals. To identify how aggression impacts growth, survival and injury, and thus presumably affects behavior, a long-term growth study was done of juvenile Hemigrapsus sanguineus crabs. treatments were comprised of individuals paired together for different lengths of time each day (simulating actual encounters rates) from post-settlement to the onset of maturity. In treatments with higher encounter rates, H. sanguineus showed a significant decrease in survival and a greatly increased injury rate. In addition, growth was significantly slowed in these same groups, further indicating clear costs of agonistic behavior. Analysis of how aggression affects timing of maturity and fecundity is presently underway for this and other decapod species, and should provide a more complete picture of the toll aggression can take on fitness and growth.


Invasive green porcelain crabs, Petrolisthes armatus, on oyster reefs in the South Atlantic Bight: friend or foe?

Amanda L. Hollebone¹* and Mark E. Hay.² School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, Georgia 30332-0230, USA; ¹e-mail [e-mail]; ²e-mail [e-mail].

Biological invasions can be a threat to natural communities and a major force in determining ecosystem structure and function. The recent invasion of Petrolisthes armatus into southeastern oyster reefs raises questions concerning the crab’s impacts on non-native habitat and reasons for its abundance and success. Our research addresses the ecological implications of the invasion as well as the ecosystem’s susceptibility to invasion. Habitat choice assays with live and dead oyster clumps, single live and dead oysters, and combinations thereof, indicate that P. armatus significantly chooses to associate with clumped live oysters over all other options. This choice appears to be guided, in part, by chemical and/or visual cues. Crabs significantly choose oysters with a biofilm over those where it is mechanically removed; this distinction disappears as the biofilm reforms over time. Tethering experiments suggest that predation pressure on adult crabs can be intense (0-10% survival in mud flats without shelter, both day and night, 0-10% survival within live oysters during the day, and 20-67% survival within live oysters at night, depending on crab size), and laboratory assays suggest that P. armatus is palatable to native predatory crabs. Despite their relatively small size, reproductive females (5-10 mm carapace width) brood tens to hundreds of large, spine-bearing larvae (8-10 mm). Laboratory assays suggest that neither filter-feeding adult crabs nor oysters feed on these larvae. Initial mass spectrometry data (¹³C and ¹⁵N) indicate that the crabs do not consume crude seawater filtrate, oyster feces, or oyster biofilm. Thus, they may be actively distinguishing between food particles in the water column. Because we do not know much about the crab in either its historic range (tropical Atlantic - eastern Pacific) or recently expanded range, we cannot predict possible impacts on temperate oyster reefs unless we begin to understand the crab’s life history and ecology.

The influence of Diadema antillarum recovery on the growth and survivorship of scleractinians on a Jamaican coral reef

Joshua A. Idjadi¹* and Nick Haring.^{2 1}University of Delaware, Newark, DE, USA; ²California State University, Northridge, CA, USA.

Since the late 1950’s, the cover of reef building corals on many Caribbean reefs has sharply declined in favor of high macroalgal cover. These changes probably were caused by multiple natural and anthropogenic disturbances including, perhaps most importantly, the region-wide mortality of Diadema antillarum. However, after nearly two decades there are signs of Diadema recovery in Jamaica. Diadema can now be found on the forereef in dense “zones” (~ 5 urchins/m²) characterized by low macroalgal cover and increased numbers of juvenile corals (< 4 cm in diameter): the presence of Diadema is associated with an increased density of scleractinians. In this study, we addressed two hypotheses to explain this relationship: (1) can juvenile coral success in urchin zones be attributed to higher growth rates, or (2) is increased success of juvenile corals driven by reduced mortality in these zones? To test these hypotheses, juvenile corals were tagged in urchin and algal zones at three locations at Discovery Bay, Jamaica. Coral growth rates were determined by measuring the change in major diameter between January of 2001 and January of 2002, and coral mortality was determined by counting the number of corals that died from one year to the next. Standardized growth rates (using z transformations) for 7 scleractinian genera were significantly higher in urchin zones when compared to algal zones (ANOVA, F_1,2= 51.160 , p< 0.02). In addition, juvenile corals were less likely to experience mortality in urchin rather than algal zones (chi-square, df=1, ²=6.257, p< 0.02). The results indicate that corals are more successful in terms of growth and survivorship in the presence of Diadema. Thus, this study underscores the potential importance of Diadema in the recovery of Caribbean coral reefs and provides more “good news” for these coral communities.


Anthropogenic impacts and plant/plant interactions

E. Irlandi,* M. Reiber, and K. Taplin. Department of Marine and Environmental Systems, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA.

The seagrass, Halodule wrightii, and the alga, Caulerpa prolifera, naturally co-occur in the Indian River Lagoon, FL. Long-term monitoring, conducted by the St. Johns River Water Management District (Palatka, FL), indicates shifts in abundance of the two species occurring over 6-month periods. In addition, Caulerpa often occurs in higher abundance at greater water depths while Halodule is more common in shallower areas. We conducted field and mesocosm experiments to evaluate the influence of light on potential competitive interactions between the two species. Neighbor-removal experiments were conducted in the field at shallow and deep water depths as a proxy for light. Removal of Caulerpa resulted in higher shoot densities and greater above-ground biomass of Halodule in deep-water plots, while there was no effect of removal at shallow water depths. Caulerpa, however, showed no difference in density or biomass in the presence or absence of Halodule in shallow- or deep-water plots, and it occurred in greater abundance in deep water plots than in shallow. Mesocosm studies manipulating light regime corroborated the results of the field experiment. Halodule grown alone under low light conditions demonstrated higher shoot densities than when grown in combination with Caulerpa under low light conditions. Caulerpa frond density was unaffected by the presence of Halodule regardless of light condition, and showed an inverse relationship with light. These results suggest that anthropogenic effects that reduce water clarity and increase light attenuation will produce conditions less favorable for Halodule than for Caulerpa