Partial protection disallowing trawling has conservation benefits in a subtropical marine park

Multiple-use Marine Protected Areas are typically predominantly zoned for partial protection, allowing 'acceptable' exploitation activities. However, biotic responses to Partially Protected Areas (PPAs) are varied, and the effectiveness of this approach in relation to management objectives can be ambiguous. Few studies have compared different levels of partial protection to provide insight into this issue. Using remote underwater video methods (stereo baited video, drop-camera) we compared fish and invertebrate assemblages between two PPA types with differing levels of protection (Habitat Protection - HP; and General Use - GU) on unconsolidated substrata in the subtropical Solitary Islands Marine Park, Australia. While both Management Types are fished, trawling is only allowed in GU. Despite high levels of spatial variation across the scales of investigation, we found fish and invertebrate assemblages differed significantly between the two Management Types. The abundance of two fish taxa and low-mobility and sessile benthic macro-invertebrates, and the mean size of the commercially targeted bluespotted flathead PlatycephaIns caeruleopunctatus, were each significantly greater in the un-trawled HP. Contrary to expectations, abundance of a conspicuous habitat former (pennatulacean seapens) and elasmobranchs did not differ significantly between Management Types. While unconsolidated sedimentary habitats are more homogenous than reef, our study revealed high assemblage diversity at a range of scales. Although assemblages and some individual taxa benefitted from a higher level of partial protection, the broader merit of this management approach remains unclear. Globally, PPA benefits likely depend on social, regulatory, environmental, and site-specific ecological factors.