Examination of the potential relationship between boring sponges and pea crabs and their effects on eastern oyster condition.

The eastern oyster Crassostrea virginica provides a number of ecosystem services and is an important commercial fishery species along the US East and Gulf Coasts. Oyster populations have declined dramatically due to overharvesting, habitat loss, and disease. As restoration efforts and aquaculture of oysters continue to increase throughout their range, it is important to consider the impacts of a number of potential oyster pests, including the boring sponge Cliona spp. and the pea crab Zaops (Pinnotheres) ostreum, on oyster populations. Both of these have been demonstrated to reduce oyster growth, condition, and in some instances, reproductive output. Boring sponges in particular are a major concern for oyster growers and managers. Our monitoring efforts have suggested that pea crabs might be more prevalent in sponge-infested oysters; we therefore conducted an observational study to determine if there was any relationship between pea crab prevalence and sponge presence, and to examine whether the presence of both pests had synergistic effects on oyster condition. At 2 very different sample sites, North Carolina and New Jersey, oysters with 1 pest (i.e. boring sponge) were significantly more likely to have the second pest (i.e. pea crab) than the background population. Furthermore, sponge presence negatively affected oyster condition in North Carolina only, while pea crabs significantly reduced condition at both locations. When sponges and pea crabs were present together, the effects on oyster condition were additive. This study provides further evidence that interactions between an individual and a fouling/pest organism can alter oyster susceptibility to other parasites.

Morphological Variability Among Broods of First-Stage Blue Crab (Callinectes sapidus) Zoeae.

External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.