MEPS prepress abstract  -  doi: 10.3354/meps07416

ABSTRACT: Knowledge of their population structure and feeding capabilities is critical to evaluate the influence of herbivores on energy flow and community structure in their habitats. We tested for patterns in abundance (24 reefs) and size (12 reefs) of turbinid gastropods across four locations spanning >6^o latitude (~1,000 kilometres) in Western Australia, and we tested the effect of density (1-5 individuals) and size (38.8 – 747.1 gWW) of Turbo torquatus on consumption of macroalgae with different thallus structure (functional groups 3-5). Turbinid gastropods were found at all locations (up to 2.4 ind m^-2). 82.4% of all individuals were T. torquatus. One location (Marmion, Perth) had considerably higher abundances than all other locations. Populations of T. torquatus at the two southern locations had a broad range of sizes (9 - 119 mm TSL), although one location was dominated by small, and the other by large, individuals. In contrast, both northern locations were strongly dominated by one size-class (40-60 mm TSL). T. torquatus consumed Ulva lactuca, Hypnea valentiae, Hennedya crispa and juvenile Ecklonia radiata at rates of 150 - 450 mg FW day^-1 depending on density of gastropods and species of algae. There was a positive relationship between the rate of consumption and size of T. torquatus when fed U. lactuca and H. valentiae. This study has produced three main insights: (1) densities of turbinids on offshore, wave exposed, subtidal reefs are similar to those in other coastal habitats; (2) patterns of abundances and sizes are consistent with broad-scale processes, such as ocean climate, fishing pressure, and eutrophication; (3) T. torquatus can consume a variety of macroalgae at rates which suggest it has the potential to exert top-down control of macroalgae, although low densities of gastropods preclude strong effects.