MEPS 182:109-118 (1999) - doi:10.3354/meps182109
Assemblages of sessile marine invertebrates: still changing after all these years?
A. J. Butler1,*, R. M. Connolly2
ABSTRACT: The fouling organisms on Port Bonython pier, South Australia, had previously been monitored for 6.5 yr after initial immersion of piles using photographs of fixed positions and direct observation by divers. Up to that date it appeared that predictions based on experiments at more sheltered sites had not been fulfilled. In particular, the assemblage had not become dominated by modular organisms. The rate of change seemed to be slowing after 6.5 yr but this could not be tested. The assemblage on the piles was re-examined in December 1995, after a further 7 yr. Faunal composition differed at sites along the pier throughout the study, and still did so after 13.5 yr, but the composition at all sites tended to change in a similar way through time; positions differed in a consistent way at 6.5 and 13.5 yr, probably reflecting consistent environmental differences between sites along the pier. Abundances of key taxa fluctuated markedly from site to site at any one time, and through time. As originally predicted, after 13.5 yr much of the pile surface area had become covered by encrusting or mound-forming modular animals (54%), especially sponges, and by foliose red algae (25%); unitary organisms such as bivalves and solitary ascidians had become greatly reduced in abundance. It is now clear that the overall composition of the assemblage had not converged to a 'stable' condition by 6.5 yr; more sampling dates would be needed to determine whether it had done so by 13.5 yr.
KEY WORDS: Assemblage · Dynamics · Fouling fauna · Modular organisms · Ascidians · Sponges · Octocorals · Bivalves
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