Jumars P.A.,University of Maine, United States |
Dorgan K.M.,Dauphin Island Sea Laboratory |
Lindsay S.M.,University of Maine, United States
Annual Review of Marine Science | Year: 2015
Polychaetes are common in most marine habitats and dominate many infaunal communities. Functional guild classification based on taxonomic identity and morphology has linked community structure to ecological function. The functional guilds now include osmotrophic siboglinids as well as sipunculans, echiurans, and myzostomes, which molecular genetic analyses have placed within Annelida. Advances in understanding of encounter mechanisms explicitly relate motility to feeding mode. New analyses of burrowing mechanics explain the prevalence of bilateral symmetry and blur the boundary between surface and subsurface feeding. The dichotomy between microphagous deposit and suspension feeders and macrophagous carnivores, herbivores, and omnivores is further supported by divergent digestive strategies. Deposit feeding appears to be limited largely to worms longer than 1 cm, with juveniles and small worms in general restricted to ingesting highly digestible organic material and larger, rich food items, blurring the macrophage-microphage dichotomy that applies well to larger worms. Copyright © 2015 by Annual Reviews. All rights reserved.
Prado P.,IRTA - Institute of Agricultural-Alimentary Research and Technology |
Heck Jr. K.L.,Dauphin Island Sea Laboratory
Marine Ecology Progress Series | Year: 2011
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.
Dzwonkowski B.,Dauphin Island Sea Laboratory |
Park K.,Dauphin Island Sea Laboratory
Journal of Geophysical Research: Oceans | Year: 2010
Analysis of a relatively long (3.33 years) time series of velocity in 20 m of water on the Alabama shelf of the northeastern Gulf of Mexico in conjunction with long-term records of wind stress and discharge reveal a better understanding of the seasonal currents. Analysis of the mean and seasonal signals of the depth averaged velocity shows virtually no mean flow, but a relatively small yet significant seasonal signal. The 3 cm s-1 seasonal signal is primarily rectilinear in the along-shelf direction with peak eastward (westward) flow during the late spring (late fall), consistent with the patterns reported in previous basin scale studies of the region. The two prominent regional forcing functions, wind stress and freshwater discharge, show clear seasonal signals. The seasonal vertical profiles also show two distinctively different patterns, most clearly observed in the fall with a westward maximum flow at the surface that decreases with depth and spring with a subsurface eastward flow and a reduced westward or even eastward surface flow. Separation of the current velocity into a wind-driven component and a non-wind-driven component demonstrates their counteracting influence on the mean current and maximizes seasonal effects where the minimum (maximum) seasonal wind-driven signal roughly corresponds to the maximum (minimum) non-wind-driven signal in late spring/early summer (late fall/early winter). On the basis of several sources of indirect evidence, it is hypothesized that a freshwater discharge generated barotropic pressure gradient is the primary forcing of the seasonal signal in the non-wind-driven current. Copyright 2010 by the American Geophysical Union.
Martin C.W.,Dauphin Island Sea Laboratory |
Valentine J.F.,Dauphin Island Sea Laboratory
Marine Ecology Progress Series | Year: 2012
Biological invasions are among the most pervasive yet least understood of the con sequences of the urbanization of estuarine ecosystems. In Mobile Bay, Alabama (USA), the construction of a transportation corridor, locally known as the Mobile Bay Causeway, has been hypothesized to have modified natural disturbance regimes to the point that numerous invasive species now persist in oligohaline reaches of this estuary. Here, we provide the results of field surveys and experiments designed to determine if the causeway facilitated the proliferation of the dominant invasive species, Eurasian milfoil Myriophyllum spicatum Linnaeus, 1753, throughout the Mobile-Tensaw Delta (MTD). Field surveys showed that the composition of submerged aquatic vegetation (SAV) varies greatly with location in the MTD; SAV south of the causeway is dominated by a single native species, wild celery Vallisneria americana Michaux, 1803, while milfoil and canopy-forming native species dominate areas north of the causeway. We found no evidence that the differences in species composition were related to differences in salinity, sediment grain size composition along the causeway, or competitive exclusion of the dominant native species by milfoil. We did, however, find a strong negative relationship between milfoil biomass and maximum wave force. These results suggest the causeway functions as a breakwater, reducing the penetration of large, wind-driven waves into oligohaline embayments north of the causeway. Counter to current thinking, these findings suggest that reductions in the intensity of physical disturbances will create opportunities for invasive milfoil to proliferate in the estuarine waters of the northern Gulf of Mexico. © 2012 Inter-Research.
Ajemian M.J.,University of South Alabama |
Powers S.P.,Dauphin Island Sea Laboratory
Journal of Experimental Marine Biology and Ecology | Year: 2013
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.
Horel A.,Dauphin Island Sea Laboratory |
Schiewer S.,University of Alaska Fairbanks
Chemosphere | Year: 2011
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.
Fodrie F.J.,University of North Carolina at Chapel Hill |
Heck Jr. K.L.,Dauphin Island Sea Laboratory
PLoS ONE | Year: 2011
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.
Dzwonkowski B.,Dauphin Island Sea Laboratory |
Park K.,Dauphin Island Sea Laboratory
Journal of Geophysical Research: Oceans | Year: 2012
Water column velocity and hydrographic measurements on the inner Alabama shelf are used to examine the flow field and its forcing dynamics during the Deepwater Horizon oil spill disaster in the spring and summer of 2010. Comparison between two sites provides insight into the flow variability and dynamics of a shallow, highly stratified shelf in the presence of complicating geographic and bathymetric features. Seasonal currents reveal a convergent flow with strong, highly sheared offshore flow near a submarine bank just outside of Mobile Bay. At synoptic time scales, the flow is relatively consistent with typical characteristics of wind-driven Ekman coastal circulation. Analysis of the depth-averaged along-shelf momentum balance indicates that both bottom stress and along-shelf pressure gradient act to counter wind stress. As a consequence of the along-shelf pressure gradient and thermal wind shear, flow reversals in the bottom currents can occur during periods of transitional winds. Despite the relatively short distance between the two sites (14 km), significant spatial variability is observed. This spatial variability is argued to be a result of local variations in the bathymetry and density field as the study region encompasses a submarine bank near the mouth of a major freshwater source. Given the physical parameters of the system, along-shelf flow in this region would be expected to separate from the local isobaths, generating a mean offshore flow. The local, highly variable density field is expected to be, in part, responsible for the differences in the vertical variability in the current profiles. Copyright 2012 by the American Geophysical Union.
Dorgan K.M.,Dauphin Island Sea Laboratory
Journal of Experimental Biology | Year: 2015
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.
Kim C.-K.,Dauphin Island Sea Laboratory |
Kim C.-K.,Stanford University |
Park K.,Dauphin Island Sea Laboratory
Journal of Marine Systems | Year: 2012
A three-dimensional hydrodynamic model is applied to the Mobile Bay system to study water and salt exchange with the northern Gulf of Mexico via Main Pass (MP) and eastern Mississippi Sound via Pass-aux-Herons (PaH). On average, more water leaves the Bay through MP than through PaH, and the Bay gains salt through MP and loses about the same amount through PaH. However, the volume discharge rate Q f and salt transport rate F S vary greatly in response to wind and river discharge with the range of variation 1-2 orders of magnitude larger than the corresponding mean. Stratification plays a key role for salt transport through MP. During periods of large river discharge, the landward shear dispersive transport F E peaking during equatorial tides and the landward tidal oscillatory transport F T peaking during tropic tides, respectively, balance the seaward advective transport Q fS 0. During periods of relatively weak stratification, F S at MP is almost entirely determined by Q fS 0 and its variability is well correlated with north-south (along-estuary) wind, associated with the barotropic (water level) adjustment. At the shallow, weakly stratified PaH, F S is almost identical to Q fS 0, and Q f is well correlated with east-west wind, with the correlation becoming stronger during the dry period. © 2012 Elsevier B.V.