Landscapes and life-histories influence colonisation of polychaetes to intertidal biogenic habitats

Patches of biogenic habitats created by algae, tubeworms and bivalves are common on intertidal rocky shores and are used as habitat by many different invertebrates. Invertebrates in mosaics of different habitats must colonise different patches either by moving from an adjacent patch of a different habitat or by dispersal through the water-column. Using polychaetes as model organisms, we tested how different biogenic habitats influence patterns of colonisation to standardised units of habitat, plastic pot-scourers placed in the biogenic habitat. In general, colonisation by polychaetes was strongly influenced by the surrounding biogenic habitats; patterns of colonisation to identical patches (i.e. scourers) differing according to their surrounding matrix. Using fences (to exclude lateral movement from the surrounding habitat) and roofs (to restrict colonisation from the water-column), different pathways of colonisation are distinguished. Due to lack of information about specific life-histories of many species of polychaetes in the Southern Hemisphere, we used 2 broad groups based on their mobility as adults (i.e. highly mobile “Errantia” or “Sedentaria” which have limited mobility). “Errant” polychaetes colonised scourers from the water-column, but also moved in from the surrounding habitat. “Sedentary” polychaetes were unaffected by restrictions on lateral movement because they mostly entered scourers from the water-column. Differences in and changes to the distributions, presence and relative covers of these intertidal biogenic habitats can therefore have large effects on organisms living in these patchy habitats.