Growth morphology and succession in a temperate marine fouling community

Marine fouling communities contain a plethora of sessile colonial invertebrates. These invertebrates come in many different shapes which occupy space and compete for resources in different ways. It has been theorized that these organisms be placed into morphological categories based on the way in which they utilize the environment around them. Studying the interactions between these various colonial forms can give us a better idea of the mechanisms that drive succession. Few studies, however, have taken colony morphology into account when studying fouling communities. This study examined three morphologies. Two of these forms were, 'Sheets' (e.g. colonial ascidians), which occupy large areas of substrate, and 'Trees' (e.g. erect bryozoans), which are upright branching forms. A third form not previously considered, 'Clonal Polyps', are represented by sea anemones. Experimental panels containing these three morphologies were placed in Humboldt Bay and the effects of these organisms on the developing fouling community through time were assessed. The morphology of fouling organisms had profound effects on patterns of succession. The structure created by resident organisms increases larval recruitment into the community. Biotic interactions with resident adults may also alter recruitment patterns. Over longer time periods the 'Sheet' morphology was able to occupy more substrate than the other forms, although spatial dominance may be dependent on suitable conditions for growth. However, experimental communities containing the dominant 'Sheets' had no fewer species communities containing the spatially restricted 'Trees'. Finally, the anemones contained in the 'Clonal Polyp' treatment maintained large areas of free space within their communities.