Increased energy differentially increases richness and abundance of optimal body sizes in deep-sea wood falls

Sunken trees in the deep sea link terrestrial and marine biodiversity

Wood in the deep sea serves as a substantial food source in an otherwise barren environment, forming specialized, endemic, and diverse community assemblages. This biodiversity reliance on a terrestrial source creates a linkage by which anthropogenic impacts on land can alter the deep oceans. Knowledge of the alpha- or beta-diversity of entire wood-fall communities, and wooden drivers of each would elucidate the terrestrial and deep-sea linkage. We report on a multifactorial experiment in the deep ocean in which alpha- and beta-diversity of 43 wood falls and 11 tree species are quantified over time, wood density, and wood size. We tested multiple hypotheses seeking to link how biodiversity on land may impact the biodiversity in the deep oceans. A tremendous biodiversity occurred among these wood falls in the deep Gulf of Mexico; 114 invertebrate species from 10 phyla. Time, wood hardness, and wood size all impacted various components of community structure. In many cases, these effects were additive. Species occurring on softwoods versus hardwoods and small versus large wood falls were compositionally different. Although various processes can control community structure, this experiment suggests a strong influence of environmental filtering and host specificity of wood-fall invertebrates suggesting an intimate coupling to tree biodiversity and biomass on land.

Energetic constraints on body-size niches in a resource-limited marine environment

Body size of life on the Earth spans many orders of magnitude, and with it scales the energetic requirements of organisms. Thus, changes in environmental energy should impact community body-size distributions in predictable ways by reshaping ecological and niche dynamics. We examine how carbon, oxygen and temperature, three energetic drivers, impact community size-based assembly in deep-sea bivalves. We demonstrate that body-size distributions are influenced by multiple energetic constraints. Relaxation in these constraints leads to an expansion of body-size niche space through the addition of novel large size classes, increasing the standard deviation and mean of the body-size distribution. With continued Anthropogenic increases in temperature and reductions in carbon availability and oxygen in most ocean basins, our results point to possible radical shifts in invertebrate body size with the potential to impact ecosystem function.

Deep-sea benthic communities in the largest oceanic desert are structured by the presence of polymetallic crust

Based on the specimens collected during three deep-sea cruises, and deposited at the Muséum National d'Histoire Naturelle (MNHN) in Paris, we analysed the diversity of benthic communities within the EEZ of French Polynesia. The literature and the MNHN database allowed us to inventory 471 species of invertebrates, among which 169 were newly described. We mainly found data for Mollusca, Crustacea, Brachiopoda and Crinoidea. We also found samples from other taxa, which still remain unidentified within the collections of the MNHN. Although this inventory is incomplete, we demonstrate that the deep waters of French Polynesia host unique benthic communities and endemic species. Using diversity and multivariate analyses, we show that the deep-sea benthic communities are structured by depth, habitats, geography and also by the presence of polymetallic crust. Furthermore, by focusing on the molluscs of the central area of French Polynesia, we show that the spectrum of shell size differs among deep-sea habitats. Specifically, shells tend to be smaller on encrusted seamounts than on island slopes. Together with the size range of organisms, low abundance, rarity and endemism designate these habitats as sensitive. These results should thus be taken into account in the evaluation of the expected impact of mining activities on biological communities.

Energetic increases lead to niche packing in deep-sea wood falls

Mechanisms leading to variation in diversity over energetic gradients continue to challenge ecologists. Changes in diversity may reflect the environmental capacity to support species' coexistence through increased niche packing or niche space expansion. Current ecological theory predicts that increases in energy may lead to both scenarios but not their relative strengths. We use experimental deep-sea, wood-fall communities, where energy supply can be controlled, to test for the importance of niche expansion and packing in functional space over an energetic gradient. Invertebrate communities were identified and counted from 16 Acacia sp. logs ranging in size from 0.6 to 20.6 kg in mass (corresponding to energy availability) deployed at 3203 m in the Pacific Ocean for 5 years. We use four fundamental energetic species-level functional traits-food source, trophic category, motility and tiering-to characterize species niches. Increases in energy on wood falls lead to increases in species richness. This higher species richness resulted from a substantial increase in mean niche overlap, suggesting that increases in energy may afford reduced competition.