Brachiopod populations : distribution in fjords of British Columbia ( Canada ) and tolerance of low l oxygen concentrations

نویسندگان

  • Verena Tunnicliffe
  • Kerry Wilson
چکیده

Brachiopods are not generally considered to be important components of modern communities, especially in comparison to their Paleozoic heyday. By using a submersible to examine the deep walls of 4 fjords in British Columbia (Canada), the abundance of 3 brachiopod species was documented. Laqueus californlanus is ubiquitous from 50 to 700 m water depth being found in conditions of high turbulence, h ~ g h suspended sediment load and low oxygen concentrations. Terebratulina unguicula is most common in a fjord that shows annual upwelling of anoxic waters; it is one of the few animals found in areas with oxygen levels frequently below 0 1 m1 1-l. The inarticulate Crania californica has a restricted distribution that may be a function of low dispersability. Over a number of years, one monitored brachlopod population was stable although a gradual retreat from the low oxygen waters was observed. Size-frequency examinations of in situ brach~opods revealed no distinguishable size classes: the death assemblage resembled the in situ population but a dredged collection did not. Brachiopods are common in all British Columbian fjords; we measured an average density of 190 m-' while maxima ranged up to 945 m-2. Bivalves, commonly cited as ecological replacements of brachiopods, are virtually absent. Two features of the brachiopods stand out: they withstand prolonged periods of low oxygen stress, and they remain a consistent part of the deep-water, hard-substratum habitat.

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تاریخ انتشار 2006