Observations of Flatfish "Spas" From Three Hydrothermally Active Seamounts in the Mariana Arc
Abstract
During a cruise to the Mariana Islands in spring 2004, dense aggregations of small flatfish were recorded from areas of diffuse flow on two hydrothermally active seamounts known as Kasuga-2 and Daikoku. This is quite novel, as flatfish are not known to be part of vent faunas elsewhere. Based on a single specimen, it was determined to be a new species of tonguefish in the genus Symphurus, and is currently under description. In October 2005, we returned to the Mariana Arc and collected about 60 specimens from Kasuga-2, Daikoku, and a third site, Nikko Seamount. Interestingly, the Nikko specimens were about twice as large as the flatfish from Kasuga-2 and Daikoku. Current molecular work (using the Barcode of Life Data System) will determine the relationship among these populations, and verify whether they are the same species. Under the microscope, the sandy sediments from the flatfish habitat were found to be full of tiny nematodes and polychaete worms. Our current hypothesis is that the fish are feeding on both and, thus, are ultimately supported by chemosynthesis, since the worms likely feed on bacteria in the sediments. However, during our most recent cruise in May 2006, we also observed several instances in which dead (or nearly dead) mid-water fish and shrimp fell out of the water column onto the bottom, after which they were almost immediately fed upon by the flatfish. This suggests that there may also be an additional energy subsidy to the seamount benthos from the water column. We hypothesize that sulfite (or some other toxic chemical) in the plume overlying these active volcanoes either kills or anesthetizes small pelagics that get advected over the seamount summit while feeding in near-surface waters at night. Stable isotope and lipid analysis of samples from these "fish spas" are currently underway to establish trophic relationships. We hope to use otolith microstructure analyses to quantify individual growth trajectories and population age structure of the flatfish from the three sites. The observed size differences of the fish from the three seamounts may reflect differences in food availability, as Nikko Seamount appeared to be a far more productive environment. Alternatively, the smaller average size of flatfish on Kasuga-2 and Daikoku may indicate fairly recent colonization events.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.V32A..05D
- Keywords:
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- 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460);
- 4804 Benthic processes;
- benthos (0408);
- 4817 Food webs;
- structure;
- and dynamics (0491);
- 4832 Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 8135;
- 8424);
- 8400 VOLCANOLOGY