Distribution, population characteristics and trophic ecology of a sulphophilic hydrothermal vent tonguefish (Pleuronectiformes: Cynoglossidae)




Tyler, Jennifer

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Fish are not abundant at hydrothermal vents due to the toxicity of venting fluids. Those that are present usually roam the periphery of the vent field or visit occasionally to feed on the abundance of life supported by chemosynthesis. In the past decade, dense aggregations of a newly described flatfish, Symphurus n.sp, have been observed in association with hydrothermal vents in the western Pacific hydrothermal vent biogeographic province. In this thesis I provide evidence that Symphurus n.sp is a vent obligate and consider the ramifications that this association with hydrothermal vents may have for its distribution, population characteristics, behaviour and diet. Symphurus n.sp has a widespread but disjunct distribution throughout the western Pacific hydrothermal vent biogeographic province. Symphurus n.sp appears to be restricted to hydrothermally active, shallow, sulphur rich seamounts. Symphurus n.sp occurs on unconsolidated volcanoclastic ash and solid sulphur crusts and in close association with molten elemental sulphur. The obvious affinity that this species has for native sulphur is unusual and remains unexplained. Unlike most vent-associated fish, Symphurus n.sp occurs in close contact with point source venting and its distribution extends to the periphery of vent fields but not beyond. The density of flatfish on these seamounts surpasses density estimates of flatfish nursery grounds on the continental shelf. On Daikoku Seamount (Mariana Volcanic Arc), mean flatfish abundances were 100 and 66 individuals m-2 in 2005 and 2006 respectively. The prey items that support such high densities of flatfish vary over spatial scales. Differing prey, in turn, results in differing foraging modes. On Nikko Seamount (Mariana Volcanic Arc), Symphurus n.sp is a “sit and wait” predator that feeds exclusively on a vent endemic shrimp, Opaepele loihi. On other seamounts, Symphurus n.sp is an opportunistic forager that preys mostly on polychaetes and small crustaceans. By counting annuli on otoliths I constructed growth curves and determined that growth rates differ between seamounts. This difference in growth rates is likely due to differences in their diet and foraging strategies. Symphurus n.sp may be allocating more energy to growth when less energy is required to forage. Furthermore, size distributions also differ between populations, likely due to variability in growth rates as well as differences in strong recruitment years.



Marine Biology, Hydrothermal Vents, Flatfish