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Many of the features that make estuaries among the most productive natural systems on earth also make them prone to acidification. Understanding the effects of estuarine acidification on different components of an ecological community is an important step in identifying indicators of ecosystem degradation. This study examined the impact of estuarine acidification, as a result of acid sulfate soil runoff, on wild Sydney rock oysters Saccostrea glomerata and their associated epifaunal communities in estuaries experiencing acid sulfate soil runoff in New South Wales, Australia. The responses of oysters and their invertebrate epifaunal communities to chronic acidification (greater than 6 mo; represented by oyster source site conditions) were assessed by examining the differences in oyster communities associated with moderate acidification (3.5 km from the source of acidification) or low acidification (8.2 km from the source). Oysters from moderate- or low-acidification sites were transplanted to a site with high exposure to acidification (less than 3 km from the source) or back to their original source sites (control) to mimic episodic acidification (2 wk). Epifaunal mussels Xenostrobus securis and limpets Patelloida mimula showed a negative association with oyster mortality, suggesting that these communities are closely tied to oyster survival. Oyster-associated epifaunal communities exposed to both chronic and episodic acidification were significantly different from communities with low exposure. Epifaunal communities exposed to episodic acidification were significantly less diverse than the control. Spionid and syllid worms were significantly less abundant and the mussel X. securis was significantly more abundant on oysters with moderate exposure or chronic exposure to acidification, as compared with communities from areas with low exposure to acidification. The mussel X. securis and the snail Bembicium auratum were significantly less abundant in oyster communities that were exposed to episodic acidification, as compared with the control. In systems where community composition depends on a single habitat-forming species, maintaining resistance may rely on the ability of that species to persist in the face of environmental stress. KEY WORDS: gastropod, bivalve, estuarine acidification, multiple stressors, diversity, INTRODUCTION Coastal ecosystems such as estuaries are some of the most productive natural systems on earth (Duarte et al. 2008). Many of the features that make estuaries so productive, including [...]

Restoring river connectivity to rebuild and sustain land is a promising restoration strategy in coastal areas experiencing rapid land loss, such as the Mississippi river delta. Results of these large-scale hydrologic changes are preliminary, and there exists limited empirical evidence regarding how benthic communities will respond, specifically in Barataria Bay and Breton Sound in southeast Louisiana. In this review, the body of existing research in this geographic region pertaining to the drivers of benthic community response that are related to restored freshwater flow and sediment deposition is examined. Overall trends include (1) potential displacement of some species down-estuary due to reduced salinities; (2) temporary lower diversity in areas closest to the inflow; (3) increased benthic production along the marsh edge, and in tidal bayous, as a result of nutrient loading; (4) more habitat coverage in the form of submerged aquatic vegetation; and (5) reduced predation pressure from large and/or salinity-restricted predators. These trends highlight opportunities for future research that should be conducted before large-scale hydrologic changes take place. [ABSTRACT FROM AUTHOR]

In Chesapeake Bay, the soft-shell clam Mya arenaria (thin-shelled, deep-burrowing) exhibits population declines when predators are active, and it persists at low densities. In contrast, the hard clam Mercenaria mercenaria (thick-shelled, shallow-burrowing) has a stable population and age distribution. We examined the potential for habitat and predators to control densities and distributions of bivalves in a field caging experiment (Mya only) and laboratory mesocosm experiments (both species). In the field, clams exposed to predators experienced 76.3% greater mortality as compared to caged individuals, and blue crabs were likely responsible for most of the mortality of juvenile Mya. In mesocosm experiments, Mya had lower survival in sand and seagrass than in shell hash or oyster shell habitats. However, crabs often missed one or more prey items in seagrass, shell, and oyster shell habitats. Predator search times and encounter rates declined when prey were at low densities, likely due to the added cost of inefficient foraging; however, this effect was more pronounced for Mya than for Mercenaria. Mercenaria had higher survival than Mya in mesocosm experiments, likely because predators feeding on Mercenaria spent less time foraging than those feeding on Mya. Mya may retain a low-density refuge from predation even with the loss of structurally complex habitats, though a loss of habitat refuge may result in clam densities that are not sustainable. A better understanding of density-dependent predator-prey interactions is necessary to prevent loss of food-web integrity and to conserve marine resources. [ABSTRACT FROM AUTHOR]

Abstract: Cultural eutrophication is a global problem that often leads to hypoxic conditions in coastal systems. Although improving, our understanding of the impacts of hypoxia on trophic interactions in pelagic and benthopelagic food webs is limited. Toward this end, we evaluated diet composition of and mass‐specific consumption by the Atlantic Bumper Chloroscombrus chrysurus, a numerically dominant planktivorous fish in the northern Gulf of Mexico, relative to dissolved oxygen concentration and fish size. Atlantic Bumper CPUE was similar in hypoxic and normoxic areas. Mean mass‐specific consumption by small Atlantic Bumpers in hypoxic areas was greater than that of both small and large individuals in normoxic areas. The most commonly ingested prey type for both large and small Atlantic Bumpers was shrimp larvae. Large quantities of fish larvae were consumed by adult Atlantic Bumpers in hypoxic regions. These findings demonstrate that hypoxic conditions can alter feeding of dominant fishes in the northern Gulf of Mexico, which may influence energy flow in the region. [ABSTRACT FROM AUTHOR]

Acidification due to anthropogenic CO 2 pollution, along with episodic or persistent acidification that occurs in coastal environments, will likely result in severe seasonal acidification in estuarine environments. Acidification decreases the fitness of individual species, but the degree to which predator-prey interactions will be impacted is largely unknown. This mesocosm study examined the effect of CO 2 acidification on crab-bivalve predator-prey interactions involving two commercially important Chesapeake Bay species, the blue crab Callinectes sapidus and the soft-shell clam Mya arenaria . In particular, the direct effects of CO 2 acidification on clam growth and behavior, and the indirect effects of CO 2 acidification on interactions between crabs and clams were examined. Mya arenaria were grown in CO 2 -acidified water (pH 7.2) or ambient conditions (pH 7.8) for 30 days. To determine the effect of acidification on clam responsiveness to mechanical disturbance, a probe was slowly moved towards clams until they ceased pumping (a behavior to avoid detection by predators), and the distance between the probe and the clam's siphon was noted. Clams were exposed to predation by C. sapidus , which were held under acidified or ambient conditions for 48 h. Callinectes sapidus handling time, search time, and encounter rate were measured from video. Acidified clams had lighter shells than ambient clams, indicating that shell dissolution occurred. Acidification reduced the responsiveness of M. arenaria to a mechanical disturbance that simulated an approaching predator. As compared to ambient trials, crabs in acidified trials had higher encounter rates; however, this was offset by crabs taking longer to find the first clam in trials, and by increased occurrence of crabs eating only a portion of the prey available. As a result, there was no net change in predation-related clam mortality in acidified trials as compared to ambient conditions. Understanding how acidification will impact food webs in productive estuarine environments requires an examination of the direct impacts of acidification on organism behavior and physiology, as well as indirect effects of acidification mediated through predator-prey interactions. [ABSTRACT FROM AUTHOR]

Studies of long-term exposure tomultiple stressors on predator-prey interactions are necessary to determine the effect of coastal degradation on organisms that have had generations to adapt and acclimate to change. In New SouthWales, Australia, a natural gradient of multiple stressors produced by acid sulfate soil effluent was used to determine the impact of exposure to multiple stressors on predator-prey dynamics between mud crabs Scylla serrata and Sydney rock oysters Saccostrea glomerata. Wild oysters were collected from two polluted and two reference sites that varied in their distance away from a flood gate that acted as a point source of water with low salinity, low pH and low alkalinity. Oysters from sites affected by multiple stressors and those from reference sites were offered to mud crabs in 48-h laboratory no-choice feeding trials. Oysters from affected sites had lower mortality than those from a reference site that was farthest from the source of polluted water. Linear models containing distance from flood gate best explained oyster mortality. Differences in rates of mortality were due to the decreased time crabs spent foraging on affected oysters. Long-term exposure to acid sulfate soil effluent alters trophic dynamics between predators and prey, which may have consequences for coastal food webs. [ABSTRACT FROM AUTHOR]