14.1 Abstract
The present chapter is devoted to the role played by benthic
suspension feeders in ecosystem functioning, through their importance
in a coastal silicate pump. Following a brief review of
pelagic-benthic coupling and eutrophication (Section 14.2,
based on the recent review of Grall and Chauvaud [185]),
the focus is placed on the Bay of Brest, an eutroph macrotidal
ecosystem of Western Europe subject to both excessive N inputs from
the watersheds and the proliferation of an invasive suspension feeder.
N river inputs have led to reccurent limitation of diatoms by silicic
acid availability. At the same time, C. fornicata has been
proliferating, constituting today the main benthic suspension feeder
in the Bay. There exist in the literature only few examples of a
direct interaction between suspension feeders and the Si cycle. Such
an interaction is described in Section 14.3 of this chapter,
based on a working hypothesis described by Chauvaud et al.
[84] and tested by Ragueneau et al.
[382]. Suspension feeder activity, stimulated by the
proliferation of the invasive species Crepidula fornicata, would be
the driving force of a biologically active silicate pump which would
- retain Si within the bay during spring and
- provide the Si necessary for diatoms during summer
During the year 2000, this hypothesis was successfully tested. Direct
evidence of DSi limitation has been provided, and during summer,
benthic fluxes measured at a site with high density of C.
fornicata are one order of magnitude higher than those measured at
the site with no C. fornicata. Seasonal budgets of Si inputs
and diatom demand demonstrated that diatom production during summer
depends strongly upon Si recycling at the sediment-water interface.
In the last section of this chapter, the short-term (seasonal)
consequences are explored from an ecological viewpoint, with a major
emphasis on the role played by invasive species. The long-term
(interannual) consequences are also explored but from a more
biogeochemical viewpoint, based on Ragueneau et al.
[383]. It is suggested that enhanced biodeposition,
through the proliferation of invasive species (both accidental or for
aquaculture purposes), could constitute a third means (beyond
eutrophication and river manipulation) by which the Si cycle may be
perturbated along the land-ocean continuum.
