An ecological baseline for Laminaria hyperborea forests in western Ireland

Abstract

AbstractThe biodiversity associated with subtidal Irish kelp forests dominated by Laminaria hyperborea has never been described. To enumerate species assemblages in these ecosystems, subtidal surveys were done throughout the calendar year to investigate species assemblages within kelp forests, composition of benthic communities, species colonizing kelp thalli, recruitment to kelp forests, and habitat recovery processes after canopy clearances. Surveys were further undertaken in maërl beds, sediment‐bottom bays, Serpula vermicularis reefs, and bedrock habitats for comparison. Across all four seasons, kelp forests harbor the richest species assemblages, second only S. vermicularis reefs in diversity, with a total of 313 unique species in the habitat (from juvenile recruits to mature macrofauna). Peak diversity in kelp forests occurred in summer and echinoderms were one of the most abundant groups, though urchins never reach densities that would threaten over‐grazing. The thalli of L. hyperborea are diverse habitats harboring many deposit feeders, filter feeders, and marine macroalgae. Epibiotic communities become more diverse with age of kelp, culminating in a maximum of 1660 individuals on stipes and 949 on holdfasts. Recruitment of crustaceans, echinoderms, and worms was high in kelp forests, but recruitment of common Irish fish could not be monitored because of unique life history stage. Habitat establishment took over a year on artificial substrata which were colonized by macroalgae and dense canopy cover inhibited growth of juvenile sporophytes. This descriptive study represents an essential baseline for kelp forest biodiversity in Ireland.