Over 60% of the Earthís surfaces lie beyond the continental shelves, mostly in waters deeper than 2 km. These so-called abyssal plains are areas of ~2ļC water temperature with no light and no seasonality. They are amongst the smoothest surfaces on the planet, with less than 1m of vertical variation for every kilometer. This under-sampled environment has for a long time been regarded a stable desert with consequently very little diversity and biomass . In recent years other authors published work that refutes the stability and homogeneity of the deepsea . The discoveries of unique deep-sea habitats such as hot-vents, cold seeps, methane ice, and whale carcass falls challenge the desert-analogy. These ecosystems (reviewed in ) house specialized groups of animals that thrive in the deep, displaying high species richness (compared to the common deepsea) as well as high biomasses, in certain places exceeding terrestrial biomasses . Furthermore, a study that assessed deep-sea species richness through extrapolation suggested that the common seafloor (abyssal plains) is extensively colonized by arguably millions of species .
Questions arising from these findings are: Why are there such ranges in the species richness and biomasses in different locations in the deepsea? What factors drive speciation in the deepsea? What factors dictate the carrying capacity (biomass) of an environment?
Ecological studies that could answer these questions are inherently difficult due to the remote nature of the study sites, the technical difficulties in manipulating scientific contraptions at the sites as well as the challenges of controlling the environment.
Deep-sea wood-boring clams from the subfamily Xylophagainae (Bivalvia: Mollusca) represent an ideal deep-sea invertebrate model system due to their wood dependency. The wood habitat can be controlled by choosing a specific type of wood, which in turn can be deployed in pre-determined locations and exposed to the deep-sea environment for specific amounts of time before retrieval.
We discovered eight new morphological taxa of deep-sea wood-boring clams on experimental woodblocks deployed in the NE-Pacific at depths between 100 and 3700m, increasing the total number of known taxa from one to nine. I used the 18S-rRNA gene sequence to explore the genetic relatedness among these taxa to test whether the newly discovered taxa are more closely related to each other than to taxa from outside the NE-Pacific and whether the morphological taxon classifications can be corroborated by genetic data from the 18S-rRNA gene. A neighbour-joining tree based on the alignment of 45 individual sequences of woodborers from the NE-Pacific and Atlantic reveals multiple clades. Two of the clades include taxa from both the NE-Pacific region and the Atlantic. Consequently, some newly discovered taxa are more closely related to taxa from the Atlantic than to the NE-Pacific. Three distinct morphological taxa share 100% sequence identity in the 18S-rRNA gene. The 18S-rRNA gene cannot confirm morphological taxon classifications for these taxa. Additional genes are being explored.
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References:Corliss, J. B., J. Dymond, et al. (1979). "Submarine Thermal Springs on the Galapagos Rift." Science 203(4385): 1073-1083.