Geographic variability in the utilisation of biogenic habitat: a South African perspective

Ecological engineers have important effects on biodiversity for two reasons: they increase habitat complexity and they moderate environmental conditions, implying that the influence of biogenic habitats on associated fauna... [ view full abstract ]

Ecological engineers have important effects on biodiversity for two reasons: they increase habitat complexity and they moderate environmental conditions, implying that the influence of biogenic habitats on associated fauna will vary across gradients of environmental stress. Mussel beds increase biodiversity on rocky intertidal shores and play an integral role in the proper functioning of coastal ecosystems. We investigated the positive effects of mussel beds on rocky intertidal benthic communities around the entire South African coastline (~3500 km) during both summer and winter. We hypothesised that benthic communities would show stronger responses to the presence of mussel beds under thermally stressful conditions. Solitary mussels experienced significantly greater daily maximum temperatures than mussels within beds across all locations. However, this difference was generally greater during the summer months and on the warm temperate east coast than on the cool temperate west coast, confirming that the thermal buffering properties of mussel beds vary between seasons and among biogeographic regions that reflect a gradient of temperature stress. Differences in the abundance, diversity and community structure of molluscan invertebrates within and outside of mussel beds also showed similar biogeographic and seasonal variability. Molluscan diversity and abundance were consistently greater within mussel beds across all locations within each of the three biogeographic regions. However, these differences were greatest during summer and on the east coast of South Africa. The results support the prediction that benthic communities show greater affinity to mussel beds within biogeographic regions that experience greater heat-stress and under warmer conditions. This research highlights that the ecological value of biogenic habitat is largely dependent on geographic context and environmental conditions.