MEPS 434:101-119 (2011)  -  DOI: https://doi.org/10.3354/meps09169

ABSTRACT: Different processes shape ecological communities at different physical scales. Their relative importance is central to ecology, particularly in the case of foundational species like mussels. For 5 yr at 8 locations across 5 bioregions spanning 3200 km of the southern African coast, we monitored recruitment and adult populations of 4 intertidal mussel species. At most locations, mussel bed width and percent cover were surprisingly constant, but declines did occur at 3 locations. Recruitment rates displayed a strong geographic gradient: exceptionally high on the West Coast, low on the South Coast and intermediate on the East Coast. At a regional scale, significant positive relationships existed between the magnitude of annual recruitment maxima and (1) adult abundance, (2) intertidal primary productivity and (3) the magnitude of upwelling. Recruitment was highest at locations with large adult populations, high productivity and more upwelling. Within locations, recruitment varied inconsistently among sites, years and seasons. Sea temperature and recruitment were seasonal at all locations except in the southern Benguela, suggesting they are linked. At the medium scale (<1 km), at which local hydrology is believed to be important, relationships between recruitment and adult abundance were observed at only 2 locations, while at the smallest scale (<1 m), significant positive relationships were more common. Two of the 3 locations with lowest recruitment were recruit-limited. This has important management implications because low-recruitment and recruit-limited locations in southern Africa occur where human exploitation is most intense.

KEY WORDS: Mytilid mussel settlement · Supply-side ecology · Large-scale coastal processes · Mytilus galloprovincialis · Perna perna · Semimytilus algosus · Aulacomya ater