Kiskaddon, E., Kiskaddon E, Chernicky, K., Chernicky K, Bell, S., & Bell S. (2019). Resource use by and trophic variability of Armases cinereum (Crustacea, Brachyura) across human-impacted mangrove transition zones. PLoS One, 14(2), e0212448.
Abstract: In Florida, resource use patterns by Armases cinereum (Armases), a highly abundant crab in coastal habitats, may serve as important indicators of habitat condition. Here we investigated feeding patterns of Armases in coastal palm scrub forest to intertidal mangrove forest transition zones (transitions) as well as the relationship between habitat disturbance and Armases' trophic position across three pairs of geographically separated populations in Tampa FL, USA. Each pair of sites represented an unmodified "natural" location as well as a "disturbed" location lacking upland terrestrial palm scrub forested habitat. Laboratory experiments established a baseline understanding of feeding preference of Armases offered strictly mangrove material as well as sources abundant at the transition. In-situ feeding behavior was examined using MixSIAR mixing models with delta13C and delta15N stable isotope tracers. Armases showed a strong preference for consuming partially-decomposed mangrove material from Avicennia germinans and an equally strong preference for Iva frutescens. Armases also displayed predatory behavior under laboratory conditions, confirming omnivory in the presence of mangrove material. Stable isotopes revealed a pattern of elevated trophic position of Armases in disturbed habitats over paired natural locations. Diet reconstruction provided coarse resolution of in-situ feeding and results show high spatial variation: in natural habitats, Armases appears to rely heavily upon upland plant material compared to disturbed habitats where it may consume more animal prey. Combined, these findings support that Armases trophic position and diet may indicate habitat quality in mangrove transitions in the southeastern United States.
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Pusack, T. J., Kimbro, D. L., White, J. W., & Stallings, C. D. (2019). Predation on oysters is inhibited by intense or chronically mild, low salinity events: Low salinity stress reduces predation. Limnol Oceanogr, 64(1), 81–92.
Abstract: Environmental stress gradients can affect species distributions and interspecific interactions. Because environmental stress depends on both intensity and duration, understanding the consequences of stress requires experiments that simultaneously manipulate both dimensions. In Apalachicola Bay, Florida (U.S.A.) the southern oyster drill (Stramonita haemastoma) is a major predator of the eastern oyster (Crassostrea virginica). Drill predation appears to be salinity-dependent: in a recent field study, predation rates were positively correlated with salinity. Salinity in the bay is typically high (> 20) during the dry summer months, conditions that favor both oysters and the drill. However, periodic freshets can dramatically reduce salinity, which inhibits (or kills) drills, but not oysters. In this study, we used field measurements of salinity and drill densities to inform mesocosm experiments. We investigated the specific combinations of intensity and duration of low-salinity stress that inhibit drill predation. In these experiments, more intense salinity reductions reduced feeding both during and after the low-salinity stress event. During the event, longer durations (15 d) were necessary for mild salinity reductions (-5) to reduce the feeding rate by the same amount as a short (5 d) exposure of more intense (-10 or -15) salinity reduction. Both conditions may create a predation refuge for oysters, consistent with field observations. Given that the recent collapse of the Apalachicola Bay oyster population was preceded by several years without low-salinity events to inhibit predation, our results provide a mechanism by which a predator may have contributed to the loss of a historically productive and sustainable fishery.
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