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Dauphin Island, AL, United States

Prado P.,IRTA - Institute of Agricultural-Alimentary Research and Technology | Heck Jr. K.L.,Dauphin Island Sea Laboratory
Marine Ecology Progress Series

Consumers of seagrasses are increasingly recognized for their ability to shape landscape features and regulate energy flux in coastal ecosystems. To date, however, the nutritional characteristics and morphological features by which herbivores and omnivores make feeding decisions are poorly understood. To elucidate how consumers of marine vascular plants discriminate among different food resources, we conducted food-preference assays with seagrass leaves and seagrassincorporated agar diets of the 3 most common seagrass species of the Gulf of Mexico (Thalassia testudinum, Halodule wrightii and Syringodium filiforme). These 3 species were offered simultaneously to the most abundant local consumers: the omnivorous pinfish Lagodon rhomboides and filefish Stephanolepis hispidus, the herbivorous emerald parrotfish Nicholstina usta, and the herbivorous sea urchin Lytechinus variegatus. Consumption rates (g fresh weight [FW]) of leaves or seagrass-incorporated agar diets were estimated over 24 h periods. Measured plant properties included C:N, N:P, total carbohydrates, protein and lipid concentrations, caloric content, percentage of organic matter, water and ash. Results showed that S. filiforme was preferred by all fish species (81, 60.2 and 59% of total leaf consumption of pinfish, filefish and parrotfish, respectively), whereas sea urchins consumed the highest amounts of H. wrightii (71.2% of total). However, when leaf structure was removed, by incorporating ground leaf tissue into agar matrices, pinfish and filefish did not show any significant dietary preference. In contrast, parrotfish and sea urchins maintained their preferences for S. filiforme and H. wrightii, respectively. Parrotfish preference for S. filiforme coincided with highest lipid and carbohydrate contents, whereas the preference of sea urchins for H. wrightii could be explained by higher levels of the percentage of organic matter and caloric content. Our results suggest that structural plant features (e.g. leaf manipulability and/or visual recognition of resources) are the most important factors driving discrimination between seagrass species by omnivorous fish, whereas strict herbivores make feeding decisions that are highly influenced by nutritional characteristics, presumably as recognized by both olfaction and gustation. © Inter-Research 2011. Source

Ajemian M.J.,University of South Alabama | Powers S.P.,Dauphin Island Sea Laboratory
Journal of Experimental Marine Biology and Ecology

Large mobile predators are hypothesized to fulfill integral roles in structuring marine foodwebs via predation, yet few investigations have actually examined the foraging behavior and impact of these species on benthic prey. Limited studies from the Cape Lookout system implicate large schooling cownose rays (Rhinoptera bonasus) in the devastation of patches of commercially harvested bay scallop via strong density-dependent foraging behavior during migrations through this estuary. However, despite the extensive Atlantic range of R. bonasus, the pervasiveness of their patch-depleting foraging behavior and thus impact on shellfisheries remains unknown outside of North Carolina waters. To further understand the potential impacts of cownose rays on benthic prey and the role of bivalve density in eliciting these impacts, we conducted exclusion and manipulation experiments at two sites in the northern Gulf of Mexico frequented by rays during spring migrations. Despite a correlation in ray abundance with haustorid amphipod (primary natural prey) density at our study sites, we were unable to detect any effect of rays on amphipod densities. In addition, through manipulation of predator access, we determined the main cause of mortality to manipulated patches of hard clams was predation by smaller predators such as Callinectes sapidus and not cownose rays. While cownose rays consume hard clam in other parts of their range, we suggest rays along northern Gulf of Mexico barrier islands may prefer foraging on smaller and thinner-shelled bivalves (e.g., Donax sp.), as well as more abundant amphipod crustaceans. We caution that these preferences may have reduced our ability to detect effects of rays on manipulated prey, and thus future impact experiments should strongly consider the local diet of these predators and explore novel techniques to estimate effects on small crustaceans. Further synchronized experimentation along basin-wide scales may elucidate the environmental factors that determine the severity of cownose ray foraging impacts across their range. © 2012 Elsevier B.V. Source

Horel A.,Dauphin Island Sea Laboratory | Schiewer S.,University of Alaska Fairbanks

Bioremediation of sandy soil contaminated with fish-biodiesel, conventional diesel, and blends of both was studied in microcosm experiments at different temperatures, simulating the subarctic environment. While distinct lag, exponential, and stationary phases were observed at 20. °C, degradation at 6. °C was slow and the lag phase continued throughout the 4-week experiment. A three-phase 1st order kinetic model successfully described respiration at 20. °C, a one-phase model was sufficient at 6. °C. For temperatures fluctuating between ∼6 and ∼20. °C, higher than expected microbial activity persisted at 6. °C for several days, due to the presence of active cultures, even though the soil temperature closely followed the air temperature. At 20. °C, respiration peaked already after 1 week, and 18-51% of the initially added fuel was mineralized within 4 weeks, whereby degradation was higher at higher biodiesel percentages. Biodiesel addition accelerated mineralization of blends with regular diesel beyond expectations. In blends with 20% biodiesel, the degradation rate constant was twice as high as for conventional diesel. These synergistic effects are likely due to an active microbial population. Addition of biodiesel to conventional diesel could reduce the impact of diesel spills. © 2011 Elsevier Ltd. Source

Dorgan K.M.,Dauphin Island Sea Laboratory
Journal of Experimental Biology

Burrowers and borers are ecosystem engineers that alter their physical environments through bioturbation, bioirrigation and bioerosion. The mechanisms of moving through solid substrata by burrowing or boring depend on the mechanical properties of the medium and the size and morphology of the organism. For burrowing animals, mud differs mechanically from sand; in mud, sediment grains are suspended in an organic matrix that fails by fracture. Macrofauna extend burrows through this elastic mud by fracture. Sand is granular and non-cohesive, enabling grains to more easily move relative to each other, and macrofaunal burrowers use fluidization or plastic rearrangement of grains. In both sand and mud, peristaltic movements apply normal forces and reduce shear. Excavation and localized grain compaction are mechanisms that plastically deform sediments and are effective in both mud and sand, with bulk excavation being used by larger organisms and localized compaction by smaller organisms. Mechanical boring of hard substrata is an extreme form of excavation in which no compaction of burrow walls occurs and grains are abraded with rigid, hard structures. Chemical boring involves secretion to dissolve or soften generally carbonate substrata. Despite substantial differences in the mechanics of the media, similar burrowing behaviors are effective in mud and sand. © 2015. Published by The Company of Biologists Ltd. Source

Fodrie F.J.,University of North Carolina at Chapel Hill | Heck Jr. K.L.,Dauphin Island Sea Laboratory

The ecosystem-level impacts of the Deepwater Horizon disaster have been largely unpredictable due to the unique setting and magnitude of this spill. We used a five-year (2006-2010) data set within the oil-affected region to explore acute consequences for early-stage survival of fish species inhabiting seagrass nursery habitat. Although many of these species spawned during spring-summer, and produced larvae vulnerable to oil-polluted water, overall and species-by-species catch rates were high in 2010 after the spill (1,989±220 fishes km-towed-1 [μ ± 1SE]) relative to the previous four years (1,080±43 fishes km-towed-1). Also, several exploited species were characterized by notably higher juvenile catch rates during 2010 following large-scale fisheries closures in the northern Gulf, although overall statistical results for the effects of fishery closures on assemblage-wide CPUE data were ambiguous. We conclude that immediate, catastrophic losses of 2010 cohorts were largely avoided, and that no shifts in species composition occurred following the spill. The potential long-term impacts facing fishes as a result of chronic exposure and delayed, indirect effects now require attention. © 2011 Fodrie, Heck. Source

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