Sentinel Species - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 166

- Accumulation of carbonates (consequences over a long period?)

- Structural instability of reefs

- Change in community structure
(i.e., increase of species with fast growth and resistance to grazing)

Decrease of bioerosion

135 t ha -1 y -1 living coral

Coral

Bolbometopon muricatum

279.3 t ha -1 y -1 carbonates

Roles in the ecosystem

- reef stability

Redistribution of carbonates

fitness

-

Colony shape

- growth rate

- distribution of corals

FIGURE 7.2
Impacts of the bioerosion by Bolbometopon muricatum on the coral ecosystem and the consequences of its deple-
tion. (After Bellwood, D.R. et al., Ecol. Lett ., 6, 281-285, 2003.)

it intervenes in the growth of reefs and their spatial distribution, on the shape of
coral colonies and their fitness, and on their stability in case of storms or of cyclones
(Bellwood et al. 2003). The humphead parrotfish is also a major factor in the redis-
tribution of carbonates in the ecosystem. According to these authors, its depletion
because of pollution and overexploitation is one of the reasons that can explain the
regression of coral reefs and the observed changes in the structure of coral communi-
ties. These same authors are also concerned, in the longer term, about consequences,
which could be dramatic, of the accumulation of carbonates in the reef system.
• In northwest European estuarine areas, the endobenthic annelid Nereis diversicolor
(Figure 7.3a) represents an important biomass; according to the environmental
conditions, its biomass can vary from 39 to less than 1 g m -2 (Scaps 2002). In the
same manner, the infaunal tellinid bivalve Scrobicularia plana (Figure 7.3b) plays
a key role in the structure and the functioning of estuarine and coastal mud-
flats because of its density of up to 2000 ind m -2 (Orvain 2005). Both species are
common prey for numerous predators (crabs, fishes, birds), and so they are par-
ticularly important food reserves, the rarefaction of which can have important
consequences for all the species for which they constitute the basic food source.
• The work of Weis et al. (2001, 2011) has shown the cascading effects of imbalance
that can result from the decrease in the density of a population of predators and/
or of prey species, and from any decrease in their capacity, respectively, to carry
out predation or to escape from predators.