Differential patterns of distribution of limpets on intertidal seawalls: experimental investigation of the roles of recruitment, survival and competition

Abstract

On artificial surfaces (seawalls) in Sydney Harbour (Australia), local biodiversity of grazers differs between sandstone and concrete constructions because limpets Siphonaria denticulata are more abundant on sandstone, while Patelloida latistrigata are more abundant on concrete walls. Competition between siphonarian and patellid limpets is unstudied on artificial structures, although the limpets are common and are known to compete in natural habitats. We tested hypotheses that the substratum (concrete or sandstone), intra-and/or interspecific competition, or a combination of factors, influence recruitment, survival, rates of grazing, or the quantity and types of algal food to explain the observed patterns. Such analyses enable better understanding of the processes influencing diversity. Both species recruited more to concrete than to sandstone plates. S. denticulata recruited more in the presence of conspecifics and slightly less in the presence of P. latistrigata. Results varied between locations and experiments, but each species survived better on concrete, which had more macro-and micro-algal food. Increased densities of P. latistrigata reduced survival of conspecifics and of S. denticulata. S. denticulata had no effect on survival of P. latistrigata, but reduced amounts of macro-algae. P. latistrigata did not affect macro-algae. Initially, there were more micro-algae on concrete and a minor effect of large densities of S. denticulata. After 95 d, differences between habitats decreased and P. latistrigata were more strongly associated with reduced amounts of micro-algae. Neither substratum, density, nor mix of limpets affected rates of grazing. Thus, interspecific interactions were similar to predictions from knowledge of natural habitats, despite the different characteristics of artificial habitats and the reduced intertidal area available for grazing. Recruitment and competition were important in explaining different densities of these limpets on sandstone and concrete walls. Increasing urbanization requires more experimental tests to identify how well current theories of intertidal ecology and of the processes maintaining local biodiversity can apply to artificial shorelines.

Urban structures provide new insights into interactions among grazers and habitat

“…During this period, a few Patelloida and Cellana were added to prevent extensive growth of macro-algae (Ivesˇa et al 2010).…”

Impacts of a ‘black tide’ harmful algal bloom on rocky-shore intertidal communities on the West Coast of South Africa

“…obs.). The net increase in biomass likely reflected a reduction in competition with other grazers, as siphonariids are known to be inferior competitors to other limpets (Creese and Underwood, 1982;Lasiak and White, 1993;Iveša et al, 2010). Greater availability of food in the form of ephemeral algae may have been a contributory factor, as these algae were strongly correlated with the biomass of S. capensis.…”

Quantifying scales of spatial variability in algal turf assemblages on coral reefs

“…Grazing and competition (Steneck & Dethier 1994) are two of the most dominant processes that drive succession and thus heterogeneity in community structure. However, the effects of grazing are widely variable at scales ranging from meters (Iveša et al 2010, Poray & Carpenter 2014 to local (Fletcher 1987) and regional scales (Foster 1990). Disturbance has long been known to play a major role in driving variability among communities separated by several meters in the rocky intertidal and subtidal habitats (Sousa 1979, Smale et al 2010, and large-scale disturbances such as storms, fires, or El Niño events can create heterogeneity over a scale of 10s or 100s of meters (Kennelly 1987, Collins 1992, Dayton et al 1992.…”