Wave action limits crowding in an intertidal mussel.

JORGE L. GUTIÉRREZ; M. GABRIELA PALOMO; MARÍA BAGUR; LORENA P. ARRIBAS

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2014

0171-8630

Intraspecific competition for space is generally invoked as the chief process limiting crowding in sessile or highly sedentary marine invertebrates. However, it generally remains uninvestigated how high conspecific density induces individual removal or mortality in turn restraining crowding in these organisms. Here we illustrate that mussel crowding in a Southwestern Atlantic rocky intertidal shore is limited by a combination of wave action and space limitation. Mussel (Brachidontes rodriguezii) beds at this site occur primarily as a single-layer of individuals because wave forces remove multilayered mussel hummocks quickly after they develop. Mussels in hummocks show lower attachment strength than those in the single-layered matrix. Accordingly, wave conditions associated to the passage of cold fronts (i.e., transition zones from warm air to cold air accompanied by moderate to strong winds and wave action; 7-day average recurrence time based on historical weather data) cause detectable mussel dislodgement in a high proportion of hummocks but have virtually no impact on single-layered areas. Since wave action is the proximate cause of mussel dislodgement, upper limits to crowding in this species would not be fixed to a particular level of space occupation (i.e., as predictable from inter-individual interference alone) but variable in space and time depending on wave exposure. This example suggests a mechanism of population control where the impact of a physical factor on population size is larger at higher population density and supports early hypotheses about the occurrence of density-dependent population control by physical factors when the availability of safe sites is limiting.