title: Gradients of intertidal primary productivity around the coast of South Africa and their relationships with consumer biomass.
abstract: The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly "connected" to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.
authors.affiliation: Coastal Ecology Unit, Zoology Department, University of Cape Town, 7700, Rondebosch, South Africa. rbustama@fedarwin.org.ec.
authors.forename: Rodrigo H
authors.initials: RH
authors.lastname: Bustamante
authors.affiliation: Coastal Ecology Unit, Zoology Department, University of Cape Town, 7700, Rondebosch, South Africa.
authors.forename: George M
authors.initials: GM
authors.lastname: Branch
authors.affiliation: Coastal Ecology Unit, Zoology Department, University of Cape Town, 7700, Rondebosch, South Africa.
authors.forename: Sean
authors.initials: S
authors.lastname: Eekhout
authors.affiliation: Botany Department, University of Port Elizabeth, Port Elizabeth, South Africa.
authors.forename: Bruce
authors.initials: B
authors.lastname: Robertson
authors.affiliation: EMETEK, CSIR, Stellenbosch, South Africa.
authors.forename: Peter
authors.initials: P
authors.lastname: Zoutendyk
authors.affiliation: Oceanographic Research Institute, Durban, South Africa.
authors.forename: Michael
authors.initials: M
authors.lastname: Schleyer
authors.affiliation: Zoology Department, University of Transkei, Umtata, South Africa.
authors.forename: Arthur
authors.initials: A
authors.lastname: Dye
authors.affiliation: Tsitsikamma National Park, Storms River, South Africa.
authors.forename: Nick
authors.initials: N
authors.lastname: Hanekom
authors.affiliation: Botany Department, University of Western Cape, Cape Town, South Africa.
authors.forename: Derek
authors.initials: D
authors.lastname: Keats
authors.affiliation: Botany Department, University of Western Cape, Cape Town, South Africa.
authors.forename: Michelle
authors.initials: M
authors.lastname: Jurd
authors.affiliation: Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa.
authors.forename: Christopher
authors.initials: C
authors.lastname: McQuaid
keywords: Community; Consumers; Intertidal; Nutrient gradients; Productivity