Pilot assessment of depth related distribution of macrofauna in surf zone along Dutch coast and its implications for coastal management

Abstract

ProblemDunes, beaches and surf zones have always protected the land against flooding by the sea. However, a sandy coast is more than just a pile of sand providing a natural defence against the sea. The protection of the Dutch coastal environment is laid down in (inter)national legislation and regulations, such as the EU Water Framework Directive (WFD), the EU Bird and Habitat Directive, and in international treaties and recommendations. Moreover, in 2006, the European Commission adopted the Marine Strategy Directive to protect the marine environment; it states that management of coasts should be based on an ecosystem approach (http://ec.europa.eu). To protect the coastal environment, one has to know what to protect and (i) what are its characteristics (ii) which organisms inhabit it and (iii) which functions does it fulfil? The surf zone of beaches is, however, rarely accessible for faunal sampling because of harsh and dynamic wave climate.On the Dutch coast, we assume that the main shortterm threats are sand nourishment to counter erosion, the mechanical cleaning of beaches, and disturbance by vehicles and tourists -all consequences of increasing recreational pressures, pollution and fisheries. Important Abstract Surf zones are highly dynamic, physically stressful parts of sandy beach ecosystems. The high wave energy of surf zones has in the past severely hampered ecological surveys of these systems. Here we used a novel technique to collect fauna from this environment along the Dutch coast. A large vehicle in the form a tripod that drives along the sandy seafloor and supports a sampling platform 11 m above the water line can collect both infaunal (grabs) samples and pull beam trawls for epibenthos. The distribution and diversity of macrofauna were studied at different depths in the surf zone along the Dutch coast. Species diversity and abundance increased with increasing depth of the water column. This increase was especially noticeable on the seaward side of the outer breaker bar. Within the surf zone, in the trough between the two breaker bars, there were spots of high diversity and abundance of macrobenthic infauna. Moreover, the area is also important for epibenthic and fish species, like the commercially important flatfish sole. Spatial patterns of species richness and abundance across an onshore-offshore gradient from the beach to seawards of the breakers suggest the presence of faunal zonation in this environment. The high abundance recorded in troughs was primarily caused by patches of juvenile Sand mason Lanice conchilega. The management implications of these results are that we suggest to protect the surf zone, including the trough between the two breaker bars, as a potential area of high diversity and abundance and to reconsider the objectives of the EU-Habitat Directive and the Water Framework Directive for the coastal area.

The ecology of fish in the surf zones of ocean beaches: A global review

“…gutters, runnels, sandbars), which experience different wave energy conditions and consequently may support distinct fish assemblages (Layman, ; McLachlan & Brown, ). Fish diversity and abundance can be greatest in gutters or runnels (but see Borland et al., ), which are areas of deeper and less turbulent water that occur away from breaking waves (Janssen, Kleef, Mulder, & Tydeman, ; Watt‐Pringle & Strydom, ). Shallow turbulent waters over sandbars also provide foraging areas for juvenile fishes (Able et al., ), support large elasmobranchs that are of conservation concern (Vargas‐Fonseca et al., ) and sustain high functional diversity (Borland et al., ).…”

The seaward limit of wave effects on coastal macrobenthos

“…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). With decreasing wave energy, sandy beach communities increase in richness, density, total abundance and biomass (Defeo and McLachlan 2005).…”

Habitat type and beach exposure shape fish assemblages in the surf zones of ocean beaches

“…whiting; Sillaginidae); conversely, certain piscivores (e.g. tailor; Pomatomidae) forage in the white water associated with waves that break over bars (Layman 2000, Watt-Pringle & Strydom 2003, Janssen et al 2008. Thus, habitat type (i.e.…”