Short-term effects of sessile organisms on colonisation of intertidal boulders

Keith Mcguinness

Research output: Contribution to journalArticlepeer-review


This study examined how the sessile organisms on boulders (algae on the tops; polychaetes, bryozoans, ascidians, and sponges on the undersides) influenced the rates of colonization of other species. Experiments showed that the sessile organisms occupying space on the undersides of boulders reduced the rate at which other sessile species recruited. This was true for rocks in their normal orientation and for those which had been experimentally overturned and disturbed. This preemption of space reduced diversity on the undersides of boulders low on the shore where space was in short supply. Grazers and predators (primarily molluscs) moved more quickly onto rocks with sessile organisms than onto those without and the rate of recolonization also varied with rock size. Thus, observed patterns in number and abundance of species with rock size were at least partially due to selection among rocks by these species. High on the shore rocks of medium size (300–600 cm2 in surface area) had more species. This pattern is often explained by the intermediate disturbance model (as the result of the interaction of disturbance and competition) but here it resulted from selective colonization of different sized rocks. Overall, the sessile organisms on boulders influenced their colonization by other species. This influence is important since these communities are often disturbed and frequently recovering from disturbance.
Original languageEnglish
Pages (from-to)159-175
Number of pages17
JournalJournal of Experimental Marine Biology and Ecology
Issue number2
Publication statusPublished - 28 Apr 1988
Externally publishedYes


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