The fish assemblage using shallow nursery habitats in the Ogeechee River-Ossabaw Sound salt-marsh estuary, Georgia, was investigated during the winter and spring of two successive years. High river discharges during these periods produced fully freshwater conditions (all tidal stages and amplitudes) in the upper portion of the study area for up to 4 months. Abundances of Atlantic croaker Micropogonias undulatus, southern flounder Paralichthys lethostigma, silver perch Bairdiella chrysoura, and hogchoker Trinectes maculatus recruits were highest in the upper estuary. Spots Leiostomus xanthurus were more evenly distributed, but continued to use upper-estuary nursery areas during periods of high river discharge. Although the recruitment of several species likely was inhibited during discharge peaks, only striped mullet Mug//cephalus avoided freshwater conditions. Spots, southern flounder, Atlantic menhaden, and silver perch utilized shallow nursery areas on a size-specific basis. Recruitment and utilization patterns of fishes spawned in deeper areas generally were maintained throughout prolonged periods (up to 100 days) of freshwater conditions. The precise function of upper-estuary nursery areas is governed by the timing and magnitude of discharge events, but remains essentially intact through the seasonal encroachment of fresh water. Extensive and highly productive salt-marsh estuaries are a dominant feature along much of the Atlantic and Gulf of Mexico coasts of the southeastern United States. Shallow areas within estuaries provide habitat for fish assemblages that are highly dynamic both spatially and temporally. Some species are resident year-round, but an important component of these assemblages is a transient group of young-of-the-year clupeiform, perciform, and pleuronectlform fishes that are spawned in deeper estuarine, nearshore, and offshore waters (Turner and Johnson 1973). These species enter the shallow portions of estuaries primarily in the winter and early spring, occur in very high densities during their recruitment and residence periods, and leave the shallows as they grow or as the water begins to cool in late summer and early fall (Herke 1971; I Present address: University of Delaware, College of Marine Studies, Lewes, Delaware 19958. • Present address: South Carolina Wildlife and Marine Resources Department, Post Office Box 12559, Dean 1980; Weinstein2 et al. 1980; Weinstein and Brooks 1983). Comparisons of their spatial and temporal nursery use between studies are complicated by differences in habitats sampled, timing of sampling with respect to tidal-lunar cycles, and gear design and efficiency. However, it is apparent that fishes generally exhibit similar patterns throughout the region. "Waves" of recruitment and peaks of abundance unique to each species are separated through time during the late fall, winter, spring, and early summer (Weinstein2 et al. 1980). Each species associates with particular ranges of physicochemical and biotic factors, including salinity, substrate composition, veget...

Ocean acidification is an altering marine carbonate chemistry resulting in potential effects to marine life. In this study, we determine the effects of decreased pH on the morphology, growth, and survival of juvenile blue king crab, Paralithodes platypus. Crabs were reared at three pH levels: ambient (control, pH ∼8.1), pH 7.8, and pH 7.5, for 1 year and monitored for morphological changes, survival, and growth. Exposure to seawater at pH 7.8 had no effect on morphology or mortality and had only a minor effect on growth compared with the ambient treatment. However, exposure to seawater at pH 7.5 substantially increased mortality and decreased growth compared with the ambient treatment. The best fit model of mortality rate at pH 7.5 showed an initially high mortality rate, which dropped to become comparable to the mortality rate in the other treatments. This suggests phenotypic variability or plasticity in juveniles and may indicate acclimation by blue king crab to ocean acidification. As such, blue king crab may have scope for evolutionary adaptation in response to gradually changing pH levels. However, effects on other life-history stages, sub-lethal effects, carryover or transgenerational effects, and interactions with other stressors, such as increased temperature, still need to be investigated.

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