Turbidity alters estuarine biodiversity and species composition

Turbidity is widely regarded for modulating primary production and influencing the distribution of submerged aquatic vegetation. Although less well studied, turbidity can also have significant effects on trophic interactions and food webs by modifying light penetration and scattering, influencing foraging ability of visual-hunting predators such as fishes. By interfering with visual foragers, turbidity may shift food webs towards predators that forage with other sensory modalities (e.g. chemoreception and mechanoreception), consequently altering food web structure. We analysed turbidity effects on estuarine community composition and biodiversity in the Gulf of Mexico by analysing an 18-year fisheries-independent data set and assessing communities inhabiting contemporary oyster reefs (Crassostrea virginica). In the long-term data set, elevated turbidity was associated with decreased fish species richness and diversity and higher abundances of benthic species that rely more on chemoreception for foraging and predator avoidance (e.g. crabs). High turbidity may provide a predation refuge for crabs and other benthic organisms that visually oriented fish prey upon. On oyster reefs, crabs readily consume suspension-feeding organisms including newly settled oysters and porcelain crabs (Petrolisthes armatus). Both were significantly less abundant in high turbidity. Human practices that increase turbidity may indirectly influence trophic interactions, species distributions, ecosystem function, and biodiversity.

Sex, size, and prey caloric value affect diet specialization and consumption of an invasive prey by a native predator

Escaping the control of natural enemies is thought to heavily influence the establishment success and impact of non-native species. Here, we examined how the profitability of alternative prey in combination with the presence of a competitor and predator aggressive behavior explain individual differences in diet specialization and the consumption of the invasive green porcelain crab Petrolisthes armatus by the native mud crab predator Panopeus herbstii. Results from bomb calorimetry estimates show that invasive P. armatus has high caloric value relative to alternative native prey. Laboratory assays indicated that specialization and consumption of invasive P. armatus was mostly exhibited by large, female P. herbstii, but the presence of a competitor and predator aggressiveness did not influence diet and the consumption of P. armatus. Thus, intrinsic factors (e.g., sex and body size) seem to explain consumption of P. armatus and dietary specialization in P. herbstii, more generally. Although there are still many predator individuals that do not consume P. armatus, the proportion of individuals that have begun to specialize on P. armatus suggests that for some, it has become more profitable relative to alternative native prey. Given the high caloric value of P. armatus, we suggest that it is likely that differences in the cost of its consumption, including attack, capture, and handling times relative to alternative prey, determine its net profitability to individual predators.

Chaetotaxy and setal diversity of grooming legs in species of porcelain crabs (Crustacea: Anomura: Porcellanidae)

The morphology of the fifth pereiopods was studied under scanning electron microscopy in ten species of porcelain crabs for chaetotaxy and setal diversity, namelly Megalobrachium pacificum, Megalobrachium roseum, Pachycheles grossimanus, Petrolisthes armatus, Petrolisthes tuberculatus, Pisidia brasiliensis, Pisidia longicornis, Polyonyx gibbesi, Porcellana platycheles and Porcellana sayana. Six setal types were identified: simple, pappose, sickle-shaped serrate, straight serrate, club-shaped and tooth-like cuspidate. Porcelain crabs can differ in the fifth pereiopod setal morphology, chaetotaxy and setal density, even among species within the same genus. The absence of sexual dimorphism of the grooming legs in porcelain crabs suggests that grooming eggs requires no particular grooming apparatus in females and that male and female are equal in grooming efficiency.