Satellite to Seafloor - The Global Biogeography of the Elasipodid Holothurians

Abstract

Knowledge of the environmental factors driving species distributions in the deep-sea is essential for a better understanding of the biogeography of the abyssal benthos. Differences in the niches of elasipodid holothurians appear to exist at the level of species, genera and family. This study analysed the global distributions of elasipodid holothurians from records collected from online Natural History Collection databases, cruise reports and published literature.

A comparison of the distribution of four families of elasipodid holothurians, in relation to seven abiotic environmental factors found the families Psychropotidae and Elpidiidae to have the most different environmental distributions. POC flux, intra-annual seasonality and inter-annual variability in POC flux were the best explanatory factors for differences between the families. The Elpidiidae were generally found in areas with greater temporal variability. The potential for biogeographic schemes based upon the ecology of the upper ocean to inform management decisions for the deep sea was also investigated. Results suggest that Longhurst’s ‘case models’ are more closely linked to the distribution of species and genera than Longhurst’s biomes. Results also confirmed that provinces from the same ocean and latitude were more similar in terms of species composition, but that historical factors were equally capable of explaining the observed patterns and must be taken into account.

Population genetic studies of two species of Elasipodida; Psychropotes longicauda and Oneirophanta mutabilis were conducted using CO1 and 16S molecular markers. Multiple sympatric lineages were found in the Indian, Pacific and Atlantic Oceans in both species. Differences between sympatric lineages were greater than geographic differences within lineages. The potential for speciation in the Antarctic or Southern Ocean before multiple northwards dispersal events is considered the most plausible explanation for the observed patterns. Oceanic gyres therefore do not appear to be barriers to dispersal in these species.

The distributions of the elasipodid holothurians are therefore thought to be controlled by a combination of life-history, dispersal ability, temporal and quantitative variations in food supply and competitive interactions as well as historical processes relating to centres of origin for particular genera.

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