Benthic faunal response to a high energy gradient

Abstract

Macrofauna and meiofauna were quantitatively sampled along 3 transects through high energy surf zones to nearshore waters. While 1 transect included some gravel patches, the other 2 exhibited increasingly finer sand and more silt and clay fraction with distance beyond the breaker zone. Meiofaunal abundance and biomass increased beyond the breakers and then decreased again further offshore. Macrofaunal abundance and diversity increased offshore; biomass increased offshore in one case while it reached a peak a little way beyond the breakers in the other. Numerical classification revealed 3 macrofaunal assemblages. The first occupied the surf zone or inner turbulent zone and included species characteristic of the sublittoral fringe of intertidal sandy beaches. The third assemblage occupied the outer turbulent zone; it started well beyond the break point and was marked by a rapid increase in biomass and diversity. The second assemblage represents a transition zone between these 2. It had no unique species but included reduced numbers of some species typical of both inner and outer turbulent zones. This transition zone, just outside the breakers, marks the region where wave energy reaching the bottom rapidly declines from its peak at the break point. A zonation scheme for the intertidal and subtidal macrofauna of high energy sandy coasts is proposed and implications of this are discussed.

Sandy bottom communities at the end of a cold (1971-1975) and warm (1997-1998) regime in the California Current: impacts of high and low plankton production

“…Diversity, abundance, and biomass decrease from dissipative to reflective sandy beaches, another gradient in environmental stress (Defeo and McLachlan 2005). A similar general pattern was observed along the wavedisturbance gradient in both decades in Monterey Bay and in other wave-controlled environments: lower diversity, abundance, and biomass with increasing wave disturbance , McLachlan et al 1984. We documented the same decreases in the present study from a food-rich, cold regime to a food-poor, warm regime in the California Current (Figure 4).…”

The seaward limit of wave effects on coastal macrobenthos

“…The swash exclusion hypothesis (McLachlan et al 1984) and its subtidal extension, the WEH (Paavo et al 2011), predict that benthic communities increase in richness, density, total abundance and biomass with decreasing wave energy. In the south-eastern North Sea, mean shear stress velocity driven by wind-induced waves enables resuspension of particulate matter over all of our study areas during storm periods and down to approximately 10 m during calm periods (Dobrynin et al 2010).…”

“…The observation that shallow-water species were a subset of deeper living species led to the idea of a single species source pool serving reflective and dissipative shorelines, with species being excluded by harsh conditions in reflective environments (McLachlan et al 1984;McLachlan 1990). Apart from possible problems of larvae to reach the sediment in turbulent waters, recruitment limitation may not be the dominant determinant of spatial and temporal patterns in soft-sediment benthos, but postsettlement processes play a significant role in population regulation and community organisation (Olafsson et al 1994).…”

“…Quantitatively, the importance of sediment disturbance depends on wave climatology, local topography, wave exposure and sediment type (Hall 1994). Exposed sandy beaches are on the mainly physically controlled side of the spectrum where communities are structured by the independent response of species to the physical environment, with minimal biological interactions (swash exclusion hypothesis, McLachlan et al 1984;McLachlan 1990). In the surf zone next to the beach, the seabed is rather mobile (Brown and McLachlan 1990) and macrobenthic diversity attains a minimum (Janssen et al 2008).…”

Efeito do grau de exposição às ondas sobre a comunidade de peixes juvenis em praias arenosas do Município do Rio de Janeiro, Brasil

“…A ação das ondas, considerada como sinônimo de exposição, é um dos fatores primários mais importantes no controle das características físico-químicas na zona de arrebentação (McLachlan 1980). Essa variável ambiental tem uma importante contribuição na composição e estrutura da comunidade íctica (McLachlan et al 1984, Dexter 1990, Clark et al 1996, Clark 1997, devido ao estresse físico local decorrente do quebrar das ondas, afetando a modificação da estrutura do sedimento e/ou as fontes de alimentos (Bennett 1989).…”