Settler distribution
The mean probability of one or more settlers occurring at a sponge was 0.06. Their occurrence was related to the ‘‘number of sponge tubes’’ and ‘‘maximum tube length’’ (r2 = 0.45) (Fig. 4), but not the presence or absence of residents (Table 2). The main effects indicate that the probability of settlers occurring at a sponge increased with both the number of sponge tubes and maximum tube length, with maximum tube length being a stronger pre- dictor. Considering only settler-occupied sponges, the mean number of settlers per sponge was 1.26 ± 0.44 (mean ± S.D.). The ‘‘number of settlers’’ was related to ‘‘maximum tube length’’, with the number of settlers increasing with maximum tube length (r2 = 0.18; ANCOVA: df = 1; F = 6.32; P = 0.018).