A. Migne et D. Davoult, MACROBENTHIC METABOLISM AS CARBON AND NITROGEN FLUXES IN A COASTAL AREA EXPOSED TO STRONG TIDAL CURRENTS (DOVER STRAIT, EASTERN ENGLISH-CHANNEL), Hydrobiologia, 376, 1998, pp. 307-315
In view of recent studies of a Dover Strait macrobenthic community (ea
stern English Channel), an annual budget of carbon and nitrogen fluxes
is proposed and discussed in order to understand the contribution of
macrobenthic metabolism in this productive coastal area (phytoplankton
ic production = 336 g C m(-2) y(-1)). In this area typical of coarse s
ediments which are exposed to strong tidal currents in the English Cha
nnel, the macrobenthic compartment is suspected to be responsible for
the major part of exchanges at the bottom-boundary layer. The macroben
thic biomass is high (mean annual biomass = 281 g afdw m(-2)) and domi
nated by three species (98.5%): the ophiurid Ophiothrix fragilis and t
he two cnidarians Urticina felina and Alcyonium digitatum. Carbon and
nitrogen budgets including ingestion, production, respiration, excreti
on and egestion allow the estimation of annual fluxes from the water c
olumn to the benthic compartment (Ingestion = 820 g C m(-2) y(-1) and
130 g N m(-2) y(-1)) and from the benthic compartment to the water col
umn (Respiration + Egestion = 710 g C m(-2) y(-1) and Excretion + Eges
tion = 100 g N m(-2) y(-1)). The net metabolism, as the difference bet
ween primary production and consumption of organic matter, shows that
this coastal ecosystem is heterotrophic. Its functioning is based on a
llochtonous material and advection and it appears to be an important s
ource of carbon dioxide.