Competitive interactions in the epifaunal community at Portsea, Victoria.

The resource provides information on the rates of growth, competitive ability and life spans of species in the epifaunal community at Portsea.

Estimates of rates of growth for all species were collected from panels immersed on 16/11/1977 except for the common barnacle (Elminius modestus) and ascidian (Didemnum augusti) which were collected from panels immersed on 24/10/1975. Length and average width of colonies or individuals and maximum height of arborescent bryozoans were made at regular intervals during the time of immersion. Colonial ascidians were the most rapid occupiers of space. In general, colonial ascidians and sponges attained a larger size and occupied space more rapidly than encrusting bryozoans.

Competitive interactions between species were examined using the same panels as described in the record 'Patterns of development in the epifaunal community at Portsea, Victoria' (File identifier: a88f2d70-ebf6-11dc-a93a-00188b4c0af8). These panels had been immersed for 2 to 42 months and fixed in formalin-sea water solution. Approximately 5500 interactions were recorded between 52 species. An interaction was defined as the overgrowth or smothering of an organism by another organism of the same or different species. For each interaction the species involved were identified, the sizes of the interacting organisms were measured and the percentage of overgrowth, if any, was estimated visually in increments of 5% overgrowth of the colony or individual. There was no single competitively dominant species in the marine epifaunal community at Portsea. The competitive ability of a species depended on the rate of growth of the species and the maximum size they could attain. The relative size of interacting colonies was often important in determining the outcome of an interaction with larger colony generally winning.

The maximum life span for each species was estimated from observations of communities on panels and on pier pilings over the 4 year period of the study (October 1975 to November 1979). The life spans of the major groups of epifauna on panesl at Portsea followed the order sponges (>24 months) > ascidians (~ 12 - 20 months) > bryozoans (~ 8 - 20 months) > barnacles, polychaetes, tubicolous amphipods and hydroids (4 - 12 months).