Information for restocking is needed on habitats of trochus in Western Australia (W.A). An investigation into the habitat preferences of trochus on reefs in King Sound W.A. was conducted, in two parts, on a macro-habitat and micro-habitat scale. Broad-scale surveys were done on four reefs in King Sound, W.A. Surveys along transects were used to examine the density and size distribution of juvenile (<50 mm) and adult (>50 rnm) trochus among 4 intertidal reef habitats: reef platform, patch reef, sand/seagrass, and rocky/boulder. No single habitat was preferred exclusively by juvenile or adult trochus. A two-factor ANOV A showed that the distribution of juvenile trochus on these reefs was highly patchy at scales within habitats (predominantly), among habitats and among reefs. Trochus rarely occurred in habitats dominated by sand. Analyses suggest that greater sampling effort (15 to 30 transects) is required to increase precision of abundance estimates to a level of 0.2 or 0.1. High densities of larger size classes in the rock habitat indicate its suitability for translocation of large juveniles. Higher abundances of smaller juveniles in the reef platform and patch reef habitats, occupying most reef area, indicate that both habitats are suitable for seeding of small juveniles. Fine scale surveys were conducted on 3 reefs. Sampling rings (paired) were used to examine differences of percentage abiotic and biotic area cover around juvenile trochus and in random areas, among 2 intertidal habitats: reef and rock. Frequency distributions of juveniles (mouthparts) in contact with substrates and biota were calculated. Randomised block univariate and multivariate ANOV As showed juveniles preferred different substratum and algae in different habitats but this was similar among reefs. Juvenile trochus were selecting micro-habitats within macro-habitats with substrates that offered refuges and abundant crustose algae. Juvenile and adult trochus broad-scale and fine-scale habitat preferences relate to preferred stock enhancement habitats and improved stock assessment methods.
|Date of Award
|Penny Wurm (Supervisor)