Scaling the influence of topographic heterogeneity on intertidal benthic communities: alternate trajectories mediated by hydrodynamics and shading

Abstract

Scale-dependent influence of environmental complexity has become a central issue in ecology. We quantified the impact of artificial reefs on community characteristics (biomass, density) and on individual mussel growth, and we tested the relative importance of physical processes (i.e. flow velocity, substratum temperature) as intermediate factors mediating the scale-dependent influence of topographic heterogeneity on benthic communities. Twelve concrete reefs (cylinders) of 3 different sizes (52, 76 and 115 cm) were placed on randomly selected sites along a rocky intertidal platform. The area around each reef and 4 control sites were divided into 24 sampling cells (6 orientation and 4 distance categories). Hydrodynamic patterns around reefs and control sites were determined using the dissolution of plaster cylinders. Flow velocity was simulated around reefs using a finite-element hydrodynamic model. Substratum temperature was also measured. The biomass and density of benthic community adjacent to the reefs was sampled using 10 × 10 cm quadrats before and 1 yr after installation. Growth of individual Mytilus edulis attached to experimental panels was measured. A flow index revealed a strong scale-dependent gradient of decreasing water motion intensity with distance from the reefs, and the hydrodynamic model showed a reduction of flow velocity on the downstream side of large reefs. Substratum temperature was lower closer to reefs, and shaded areas increased with reef size. Maximum M. edulis biomass was around large reefs, while the biomasses of other dominant species were not positively influenced by reef size. Biomass and density patterns close to the reefs were significant only around large reefs, with the downstream side having the lowest M. edulis biomass. Growth of M. edulis decreased significantly with distance away from the reefs. Biomass patterns were best explained by the flow velocity around the large reefs (R 2 = 0.27), while mussel growth was best correlated with substratum temperature close to the medium reefs (R 2 = 0.66). Our study shows that the spatial structure of the benthic community studied and its scaling with topographic heterogeneity depends on dominant mediating physical factors (i.e. hydrodynamic processes or substratum temperature).

Contribution of environmental and spatial processes to rocky intertidal metacommunity structure

“…Rock surface rugosity Provides refuge from predation or desiccation stress (e.g., Guichard et al, 2001). …”

Zonação de comunidade bêntica do entremarés em molhes sob diferente hidrodinamismo na costa norte do estado do Rio de Janeiro, Brasil

“…Ao longo do eixo horizontal do costão, a variabilidade espacial tem sido um tema vastamente citado na literatura (UNDERWOOD 1981, UNDERWOOD & CHAPMAN 1998a, b, BENEDETTI-CECCHI & CINELLI 1997, GUICHARD et al 2001, ARAÚJO et al 2005, estando relacionada a uma escala específica de observação. UNDERWOOD & CHAPMAN (1998a, b) observaram uma variabilidade espacial considerável em todas as associações de organismos examinadas em diferentes escalas (i.e.…”

“…A heterogeneidade do substrato pode modificar o padrão hidrodinâmico específico durante a maré alta e influenciar no sombreamento e na intensidade de vento durante a maré baixa (GUICHARD et al 2001).…”

Epibenthic colonization of concrete and steel pilings in a cold-temperate embayment: a field experiment

“…However, there are few experimental that use standardized units of diVerent materials to evaluate the eVect of diVerent substrates on the development of the epibenthic assemblage (but see Chapman and Clynick 2006). The current regime around a cylindrical structure is diVerent from commonly used panels or complexed constructed artiWcial reefs in colonization studies and will inXuence the epibenthic development (Mullineaux and Garland 1993;Lemire and Bourget 1996;Guichard et al 2001). In addition, diversity in marine invertebrate assemblages has been shown to be scaledependent (Keough 1984;Sousa 1984;Eggleston et al 1999).…”