Resident distribution
The mean probability of one or more residents occupying a sponge was 0.32. The probability of occupancy was related to ‘‘depth’’, ‘‘number of sponge tubes’’, ‘‘maximum tube length’’ and the interaction between ‘‘depth’’ and ‘‘maximum tube length’’ (r2 = 0.36) (Fig. 3; Table 1). The interaction indicates that the relationship between the probability of occupancy and maximum tube length varies with depth (Fig. 3a). Specifically, the initial rate of increase in the probability of occupancy with maximum tube length was much lower at depths less than 10 m than at all other depths. In addition to the interacting effects of depth and maximum tube length, the probability of resident occupancy increased with the number of sponge tubes (Fig. 3b).