Wave action limits crowding in an intertidal mussel

JORGE LUIS CEFERINO GUTIERREZ; PALOMO, M. G.; BAGUR, M.; ARRIBAS, L. P.; SORIA, S. A.

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2015 vol. 518 p. 153 - 163

0171-8630

Intraspecific competition for space is generally invoked as the chief process limitingcrowding in sessile or highly sedentary marine invertebrates. However, the mechanisms by whichhigh conspecific density induces individual removal or mortality, in turn restraining crowding inthese organisms, generally remain uninvestigated. Here we illustrate that mussel crowding in asouthwestern Atlantic rocky intertidal shore is limited by a combination of wave action and spacelimitation. Brachidontes rodriguezii mussel beds at this site occur primarily as a single layer ofindividuals because wave forces remove multilayered mussel hummocks quickly after theydevelop. Mussels in hummocks show lower attachment strength than those in the single-layeredmatrix. Accordingly, wave conditions associated with the passage of cold fronts (i.e. transitionzones from warm air to cold air accompanied by moderate to strong winds and wave action, with7 d average recurrence times based on historical weather data) cause detectable mussel dislodgmentin a high proportion of hummocks but have virtually no impact on single-layered areas.Since wave action is the proximate cause of mussel dislodgment, upper limits to crowding in thisspecies would not be fixed to a particular level of space occupation (i.e. as predictable from interindividualinterference alone) but would be variable in space and time depending on wave exposure.This example suggests a mechanism of population control where the impact of a physicalfactor on population size is larger at higher population density and supports early hypothesesabout the occurrence of density-dependent population control by physical factors when the availabilityof safe sites is limiting.