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A New Species of Hydrothermal Vent Sponge from the Galapagos Rift
Waller, Buckman, Shank and Pomponi
Deep-sea hydrothermal vents were first discovered on the Galapagos Rift at 86°W in 1977. A NOAA Ocean Exploration Program expedition in May-June 2002, utilizing the RV Atlantis and DSV Alvin, was the first expedition to the area since 1990. A large clam field, named Calyfield, was discovered along the rift during this cruise. It is the most westerly of the known active vent sites on the Galapagos Rift. Calyfield is a large pillow lava field (approximately 60m x 60m), characterised by the large Calyptogena magnifica clams that inhabit the margins of the pillows. Clumps of Bathymodiolid mussels and swarms of amphipods around the areas of active venting were also abundant. The most unusual of Calyfield's inhabitants was the large grey mats of biological material, what appears to be an encrusting sponge, covering the basaltic pillow lavas.
The encrusting sponge is grey in colour, and forms large mats containing 0.2 to 0.5 mm-long spicules. Small white ovoid masses at the base of the sponge resemble invertebrate (e.g., gastropod) egg masses. If these masses are not eggs, it is thought that they may be bacterial clusters within the sponge tissue.
Typical habitat areas covered by sponge ranged from 0.5m2 to 1m2. The sponge only appeared within the vent site, reducing in coverage towards the periphery of field.
In order to taxonomically identify the grey sponge, we examined a 500 base pair portion of the mitochondrial Cytochrome Oxidase subunit I (COI) gene. Whole genomic DNA was extracted from both the 'egg' masses and the complete sponge tissue and was subsequently amplified using the COI primers LCO1490 and HCO2198 (Folmer et al., 1994).
A preliminary GenBank Blast of the sequenced COI portion of the DNA indicated that it is most closely related to Placospongia sp. (with ~16% sequence divergence). Placospongia are marine sponges, at least one species of which may be circumequatorial (De Laubenfels, 1954). Members of the family Placospongiidae have encrusting to lobate-digitate growth forms, often with a grooved surface (Hooper, 2000).
Although sponges have been found in association with hydrothermal vent areas (Morri et al., 1999; Tarasov et al., 1999; Pansini et al., 2000) this particular species has not been observed at any other vent site around the world. There are also no known species of sponge endemic to hydrothermal vents.
Planned genetic comparisons of "egg" and sponge DNA will provide a first order assessment of whether or not these "egg-like" bodies belong to the sponge. If they are eggs of another invertebrate, then a new ecological relationship at vents will have been discovered, and new hypotheses for testing. For example, the sponge may provide predation protection for these eggs that would otherwise be exposed on the basaltic surfaces. Developing juveniles may also utilize the sponge as a food source.
Molecular analysis will continue through examination of the COI portion of the mitochondria as well as the 18S and 28S ribosomal genes. The goal of these analyses is not only to provide a better perspective of the molecular taxonomy, but the evolutionary history of deep-water sponges and their relationship (e.g., invasion into) to hydrothermal vent environments.
This work is funded by NOAA Ocean Exploration grant no. NA16RP2390. We would like to thank the captain, crew and scientists of RV Atlantis cruise AT7-13, as well as the pilots and technicians of DSV Alvin.