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Reaugh-Flower K.,University of Cape Town | Branch G.M.,University of Cape Town | Harris J.M.,University of Cape Town | McQuaid C.D.,Rhodes University | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

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 recruitlimited. This has important management implications because low-recruitment and recruit-limited locations in southern Africa occur where human exploitation is most intense. © Inter-Research 2011.

Reaugh-Flower K.E.,University of Cape Town | Branch G.M.,University of Cape Town | Harris J.M.,University of Cape Town | McQuaid C.D.,Rhodes University | And 3 more authors.
Marine Biology | Year: 2010

Quantifying sessile marine invertebrate recruitment often requires destructive sampling or extrapolation from artificial substrata, the latter introducing the danger of artifacts. We measured intertidal mussel recruitment into mussel beds and into brushes at three-month intervals for five years across 3,200 km of southern Africa and determined substrata effects on recruitment rate. Recruitment into mussel beds showed a strong, coast-wide gradient, with high recruitment on the West coast, diminishing on the South coast, and increasing slightly on the East coast. At scales of 10 s of km, brushes reflected natural temporal recruitment variability, with a strong significant linear correlation between recruitment into brushes and into mussel beds. However, the relationship became semi-logarithmic when comparing among locations at a scale of 100 s of km. Artificial substrata thus reflect local natural settlement well but may be a poor indicator of it when spatial scales are large, particularly when mussel bed topography is complex, or localities have very different recruitment densities. © 2010 Springer-Verlag.

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