Are perspex panels suitable surrogates for natural hard substrates in coastal ecological studies? An example from the...

Different eco-engineering methods have strived to mimic benthic processes in natural habitats by providing functionally similar conditions and consistent topographic features on artificial structures. Evidence of the applicability of man-made constructions for ecological studies is unambiguous and varies across environmental conditions, topographic complexity and location of a substrate. This study was set up to verify the use of Perspex panels as a substitute for natural hard bottom (rocks) in investigating the settlement and development processes of benthic assemblages. During a one-year field experiment, principal community measures (species richness, density and biomass of dominant fouling species) were compared between the horizontal panels and cobbles in two shallow benthic habitats in the southern Baltic Sea: (1) sheltered sandy and (2) more exposed gravelly-sandy sediment. The panels and cobbles supported communities of similar taxonomic richness (sessile and associated fauna) and biomass (sessile fauna). Dissimilarities were observed for the density of the fouling fauna and its dominant species, the barnacle Amphibalanus improvisus, which can be attributed to differences in hydrological conditions and substrate texture. At a more sheltered site, transport of sediment particles adversely affected the settlement on cobbles, though panels favoured the settling of planktonic larvae. At a more exposed gravelly-sandy site, wind-induced currents likely dislodged established individuals from the smooth panels, while rougher cobbles enhanced colonisation by creating micro-habitat heterogeneity. The Perspex panels proved to provide a consistent and uniform experimental apparatus with good mimicry of a complex natural substrate.