The ecology of macroalgal rafts and their associated faunal assemblages in the northeast Atlantic

SUMMARY This study describes some of the processes of macroalgal rafting important for the dispersal of benthic marine invertebrates and structuring intertidal species assemblages in Irish coastal : waters, using a combination of fieldwork and laboratory analyses. A novel method for assessing the density and distribution of seaweed rafts, which takes into consideration sea state was devised as a cost effective approach for surveying drifting algae in coastal and offshore marine environments. During the development of this surver .;, metaodotegy macroalgal rafts. were collected at various locations around the lrish coastlineand species assemblages were characterised. Species richness and abundance relationships were apparentiwhen factoring in.algal carrying capacity, and analysis indicated that rafts are most likely and opportunistic platform for species for survival and potential dispersal, rather than " assemblages where.species-specific responses to raft composition will occur. The abundance of drilling rafts in the offshore environment along with the presence of intertidal invertebrates highlights· the potential importance of such drifting habitats for the survival and movement of intertidal species across large expanses of ocean. The colonisation of Idotea species onto seaweed rafts was investigated to elucidate some of the initial smaller scale processes involved with rafting organisms and to understand some potential: behavioural associations. This was especially important, for species with direct development as they are considered to have low dispersal potential. Results indicate an activ~ colonisation of rafts by Idoteaindividuals from the surrounding water column as supposed to[ust a passive marooning along with algae detaching from the shore. Finally a comparative.analysis of shores that receive high and low levels of drift material from the ocean was undertaken to compare intertidal species assemblages, to expose anr biodiversity signatures of species colonising the shore from 1he arrival of macroalgal rafts. Abundance effects of species were clearly seen in this investigation, with some species displaying significantly higher abundances on high drift shores. These along with species richness effects indicate that.the arrival of rafts to a shore may have some effect .on . intertidal , species assemblages, although exposing any consequences of drift is difficult in such a dynamic and-complex marine environment.EThOS - Electronic Theses Online ServiceGBUnited Kingdo