Respiration By the Opportunistic Spionid Polychaete \u3ci\u3eStreblospio gynobranchiata\u3c/i\u3e During Adjustment To and Recovery From Moderate Hypoxia

Understanding the capacity of estuarine organisms to acclimate to stressful conditions provides insights into how communities cope within fluctuating environments. The opportunistic spionid polychaete, Streblospio gynobranchiata Rice and Levin, 1998, regularly experiences intermittent moderate hypoxia within shallow sedimentary habitats. To better understand fine-scale adjustments by this opportunistic species to short-term moderate hypoxia, the aerobic respiration response of three size classes was examined over a 12 h period and after 24 h of exposure to moderate hypoxia (i.e., 20% air saturation) at 25 °C. In addition, the capacity to resume standard respiration was examined over a 12 h period following a 24 h period of exposure to moderate hypoxia. Mass-specific respiration varied with body size during both exposure and recovery from hypoxia. Small worms switched from an oxyregulating to an oxyconforming strategy within 6 h of exposure to moderate hypoxia at 25 °C. After 24 h of hypoxia exposure, small worms hypo-regulated at 81% of the preceding 24 h normoxic reference level. By contrast, medium and large worms hyper-regulated during the first 12 h exposure period, but hypo-regulated at 70% and 79% of the preceding 24 h normoxic reference levels after 24 h of hypoxia exposure. Fluctuations in respiration levels during the recovery period revealed a temporal recovery pattern implying cycling energetic processes. The recovery pattern also indicated some respiration overshoot to compensate for oxygen debt. The timing of the cycling recovery pattern also differed with body size. The ability of S. gynobranchiata to dynamically adjust its metabolic response to low oxygen stress underscores the ecologically important role of tolerant organisms within estuarine benthic habitats subject to recurrent diel or intermittent hypoxia. View Full-Tex

Destabilizing Effects On a Classic Tri-Trophic Oyster Reef Cascade

How interactions among multiple predators affect the stability of trophic cascades is a topic of special ecological interest. To examine factors affecting the stability of the classic tri-trophic oyster reef cascade within a different context, configurations of three predators, including the Gulf toadfish, Gulf stone crab, and oystershell mud crab, were manipulated together with either oyster shell or limestone gravel substrate within a multiple predator effects (MPE) experiment. Additionally, a complimentary set of trait-mediated-indirect interaction (TMII) experiments examined the inhibition of oyster consumption relative to mud-crab size and top predator identity in the absence of other cues and factors. The classic tri-trophic cascade formed by the toadfish-mud crab-oyster configuration was potentially weakened by several interactions within the MPE experiment. Consumption of oysters and mud crabs by the intraguild stone crab was undeterred by the presence of toadfish. Although mud crab feeding was inhibited in the presence of both toadfish and stone crabs, estimated non-consumptive effects (NCEs) were weaker for stone crabs in the MPE experiment. Consequently, the total effect was destabilizing when all three predator species were together. Inhibition of mud crab feeding was inversely related to direct predation on mud crabs within the MPE experiment. Complimentary TMII experiments revealed greater inhibition of mud crab feeding in response to stone crabs under sparse conditions. TMII experiments also implied that inhibition of mud crab feeding could have largely accounted for NCEs relative to oysters within the MPE experiment, as opposed to interference by other mud crabs or top predators. An inverse relationship between mud crab size and NCE strength in the TMII experiment disclosed another potentially destabilizing influence on the tri-trophic-cascade. Finally, although habitat complexity generally dampened the consumption of oysters across MPE treatments, complex habitat promoted mud crab feeding in the presence of toadfish alone. This study underscores how ecological interactions can mediate trophic cascades and provides some additional insights into the trophic dynamics of oyster reefs for further testing under natural conditions

Flexible Feeding Strategies of Juvenile Gray Triggerfish (Balistes capriscus) and Planehead Filefish (Stephanolepis hispidus) Within Sargassum Habitat

Sargassum-associated juvenile gray triggerfish and planehead filefish exhibited flexible feeding strategies in terms of their use of epifauna or pelagic zooplankton. Four diet samples represented instances of co-occurrence and segregated occurrence. Co-occurring gray triggerfish had the most specialized diets consisting mainly of pelagic copepods and hyperiid amphipods. Conversely, segregated triggerfish as well as both co-occurring and segregated filefish had broader diets mainly consisting of Sargassum epifauna, such as bryozoans, portunid crabs, and hippolytid shrimp. Still, co-occurring planehead filefish also consumed somewhat more zooplankton than segregated planehead filefish. Ontogenetic diet transitions were not as distinct for gray triggerfish as for planehead filefish. Our study demonstrates that juvenile tetradonts can be flexible in their use of benthic versus pelagic feeding strategies. Consequently, the influence of these key consumers on Sargassum food webs may vary spatiotemporally

Temperature-Modulated Expression of Allometric Respiration Strategies Supports a Metabolic Scaling Rule

A model based on the mass-specific oxygen consumption rate of the tolerant polychaete, Capitella telata, related meaningfully to a novel metabolic scaling rule as applied to the infaunal size spectrum. Depending on temperature, C. telataexpressed divergent oxyregulating or oxyconforming strategies relative to oxygen availability. A non-linear response surface fitted to the allometric exponents of a family of VO2 curves for 12 treatment combinations of DO saturation and temperature was used to project oxygen consumption rates across the infaunal size spectrum. Plasticity in respiration strategies was evident, based on four simulated dynamic 32 d oxygen-temperature exposure scenarios and on simulated static oxygen-temperature exposures. The oxyconforming strategy of C. telata expressed under hypoxia near the upper thermal limit agreed with a hypothesized allometric scaling rule based on metabolic ecology. Conversely, an oxyregulating respiration strategy was expressed at cooler temperatures under low oxygen concentration, except organisms hyper-regulated relative to normoxic conditions. At warm temperatures, small organisms exhibited relatively greater metabolic depression than large organisms; whereas at cool temperatures, small organisms hyper-regulated relatively more than large organisms. Dichotomous shifts in respiration strategies likely reflect a breakdown in the functioning of special adaptations, and reliance on alternative coping mechanisms. Divergent temperature-dependent respiration strategies illustrate how responses to multiple stressors can be synergistic. Moreover, results imply that population responses to hypoxia may differ, depending on prevailing temperature regimes

Destabilizing Effects On a Classic Tri-Trophic Oyster Reef Cascade

How interactions among multiple predators affect the stability of trophic cascades is a topic of special ecological interest. To examine factors affecting the stability of the classic tri-trophic oyster reef cascade within a different context, configurations of three predators, including the Gulf toadfish, Gulf stone crab, and oystershell mud crab, were manipulated together with either oyster shell or limestone gravel substrate within a multiple predator effects (MPE) experiment. Additionally, a complimentary set of trait-mediated-indirect interaction (TMII) experiments examined the inhibition of oyster consumption relative to mud-crab size and top predator identity in the absence of other cues and factors. The classic tri-trophic cascade formed by the toadfish-mud crab-oyster configuration was potentially weakened by several interactions within the MPE experiment. Consumption of oysters and mud crabs by the intraguild stone crab was undeterred by the presence of toadfish. Although mud crab feeding was inhibited in the presence of both toadfish and stone crabs, estimated non-consumptive effects (NCEs) were weaker for stone crabs in the MPE experiment. Consequently, the total effect was destabilizing when all three predator species were together. Inhibition of mud crab feeding was inversely related to direct predation on mud crabs within the MPE experiment. Complimentary TMII experiments revealed greater inhibition of mud crab feeding in response to stone crabs under sparse conditions. TMII experiments also implied that inhibition of mud crab feeding could have largely accounted for NCEs relative to oysters within the MPE experiment, as opposed to interference by other mud crabs or top predators. An inverse relationship between mud crab size and NCE strength in the TMII experiment disclosed another potentially destabilizing influence on the tri-trophic-cascade. Finally, although habitat complexity generally dampened the consumption of oysters across MPE treatments, complex habitat promoted mud crab feeding in the presence of toadfish alone. This study underscores how ecological interactions can mediate trophic cascades and provides some additional insights into the trophic dynamics of oyster reefs for further testing under natural conditions

Selected Life-History Observations on the Cayman Gambusia, Gambusia xanthosoma Greenfield, 1983 (Poeciliidae)

The Cayman gambusia (Gambusia xanthosoma Greenfield, 1983) is an uncommon species within the G. punctata species group, endemic to North Sound, Grand Cayman Island, BWI. Since the original description (Greenfield 1983) only phylogenetic information has been published and little is known of its habitat, feeding ecology, or reproductive life history (Wildrick and Greenfield 1985, Rauchenberger 1988). Originally described from a brackish-water (30 psu) mosquito control ditch, the species also occurred throughout marine mangrove habitat and inland saline ponds adjacent to North Sound, Grand Cayman Island. Here we present information on the habitat, diet, reproduction, life history, and parasites of the Cayman gambusia

Early Growth of Three Kingfish (Menticirrhus) Species Found in Coastal Waters of the Northern Gulf of Mexico

Southern kingfish (Menticirrhus americanus), gulf kingfish (M. littoralis), and northern kingfish (M. saxatilis) are members of the drum family (Sciaenidae) that are widespread in coastal habitats of the western Atlantic, including in the Gulf of Mexico (GOM). Despite their economic and ecological importance, little is known about growth of young kingfish. Young kingfish were collected from four different Mississippi shoreline habitats in 2005 and 2006; two associated with barrier islands and two along the mainland. Barrier island habitats included surf zones on the south shore and grass beds on the north shore. Mainland habitats were located along marsh-edges and sandy shorelines. Kingfish growth comparisons were made using analysis of covariance (ANCOVA) on 194 aged fish (127 M. americanus, 54 M. littoralis, and 13 M. saxatilis). Growth rates for all three species were generally similar ranging from about 0.7mm/day at 4-6 mm standard length (SL) to 1.9mm/day at 55-60mm SL. In 2005, M. americanus from marsh-edges grew significantly faster than those from sandy shorelines. Size-at-age of M. americanus and M. littoralis was significantly smaller in the spring than in the summer and fall, while both growth rate and size—at—age were similar in the summer and fall

Soft-Sediment Recruitment Dynamics of Early Blue Crab Stages in Mississippi Sound

In order to understand the recruitment dynamics of early blue crabs, it is necessary to sample quantitatively across early stages and habitats at appropriate spatio-temporal scales. Few studies of early blue crab recruitment have considered the potential role of soft-sediment habitat or directly related megalopal supply to local densities of early stages. During a 7-wk peak recruitment period, fluctuations in early stages of blue crabs from settlement collectors were significantly cross-correlated between two sites separated by 7.5 km, showing connectivity on this large spatial scale. Moreover, numbers of megalopae from settlement collectors were directly correlated with densities of early juveniles from nearby soft-sediment, showing that settlement collectors may reflect local recruitment intensity. Significant habitat variables included depth and salinity (i.e., water mass) for small post-settlement juveniles (CW), and substrate type for large juveniles ( greater than or equal to6 mm CW). Early juveniles from soft-sediment habitat were spatially aggregated at relatively low densities; although initial rates of loss may not be as high there as in structured habitats. Thus, soft-sediment habitat may subsidize the supply of early juvenile stages to structured habitats

Benthic-Pelagic Coupling in Northern Gulf of Mexico Estuaries: Do Benthos Feed Directly on Phytoplankton?

Few of the dominant benthic taxa of the northern Gulf of Mexico feed directly on phytoplankton. Rather, most of them feed on near-bottom seston and detritus. This is in contrast to models for Chesapeake Bay and San Francisco Bay. We found that detritivores represented over 80% of the macrobenthic organisms and over 90% of the biomass in Gulf of Mexico estuaries. The paucity of benthos that consumed phytoplankton led us to hypothesize that macrobenthos in Gulf of Mexico estuaries had less effect on plankton communities than was documented in U.S. east coast and west coast estuaries, where benthic communities consumed much of the water-column production. We provided as evidence gut-contents analyses of dominant taxa, the feeding morphology of suspension feeders (especially clams), and the lack of vertical mixing or strong turbulent flow that is necessary for benthos to remove substantial portions of the phytoplankton