Contribution of mussel fall-off from aquaculture to wild lobster Homarus americanus diets.

Anthropogenic subsidies to natural systems can influence the diet of mobile omnivore species and co-occurring species. This study assessed if fall-off from mussel aquaculture subsidized wild populations of mobile scavengers and predators, such as the commercially important lobster Homarus americanus. A Bayesian stable isotope-mixing model with parameters determined from the literature and from a 105 days laboratory feeding experiment was applied to wild lobsters to determine how important the various food sources were in these lobsters, especially mussel fall-off. Isotopic values were mainly affected by lobster size with model outputs indicating that large lobsters (>80 mm cephalothorax) fed mainly on mussels from the mussel farm (46% of the diet) while small ones fed mostly on the rock crab Cancer irroratus (99%). The contribution of mussel subsidies to the lobster's diet was thus size-specific and direct (i.e. through mussel fall-off and not through co-occurring species such as rock crab). The absence of a link between food sources and lipid energy content in lobsters suggested that the reduction of rock crab consumption would have to be more drastic to affect the general health of large lobsters in the short term.

Free-living bacterial communities associated with tubeworm (Ridgeia piscesae) aggregations in contrasting diffuse flow hydrothermal vent habitats at the Main Endeavour Field, Juan de Fuca Ridge.

We systematically studied free-living bacterial diversity within aggregations of the vestimentiferan tubeworm Ridgeia piscesae sampled from two contrasting flow regimes (High Flow and Low Flow) in the Endeavour Hydrothermal Vents Marine Protected Area (MPA) on the Juan de Fuca Ridge (Northeast Pacific). Eight samples of particulate detritus were recovered from paired tubeworm grabs from four vent sites. Most sequences (454 tag and Sanger methods) were affiliated to the Epsilonproteobacteria, and the sulfur-oxidizing genus Sulfurovum was dominant in all samples. Gammaproteobacteria were also detected, mainly in Low Flow sequence libraries, and were affiliated with known methanotrophs and decomposers. The cooccurrence of sulfur reducers from the Deltaproteobacteria and the Epsilonproteobacteria suggests internal sulfur cycling within these habitats. Other phyla detected included Bacteroidetes, Actinobacteria, Chloroflexi, Firmicutes, Planctomycetes, Verrucomicrobia, and Deinococcus-Thermus. Statistically significant relationships between sequence library composition and habitat type suggest a predictable pattern for High Flow and Low Flow environments. Most sequences significantly more represented in High Flow libraries were related to sulfur and hydrogen oxidizers, while mainly heterotrophic groups were more represented in Low Flow libraries. Differences in temperature, available energy for metabolism, and stability between High Flow and Low Flow habitats potentially explain their distinct bacterial communities.