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

Brachiopods are not generally considered to b e 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.