Ecosystem monitoring of subtidal reefs in the Jervis Bay Marine Park 1996-2005.

Abstract

Surveys of subtidal rocky reefs were conducted in the Jervis Bay Marine Park (JBMP) as part of a broader study into the effectiveness of marine protected areas (MPAs) in Australian temperate waters. The study used the same standardised methodology used in baseline and long-term monitoring programs in Western Australia, South Australia, Tasmania and Victoria. Surveys assessed fish size, diversity and abundance, as well as macro invertebrate and algae abundance. Baseline surveys were conducted in 1996 (18 replicate sites), 2000 (24 replicates) and 2001 (25 replicates). Since establishment of the JBMP zoning plan in October 2002 three surveys in 2003, 2004 and 2005 have been completed at 27 sites. Sites were chosen to allow an approximately balanced design between treatments with 14 sites in sanctuary "no-take" zones and 13 reference sites where fishing is still permitted. Sites were also stratified by wave exposure between sheltered and exposed locations. A diverse fish fauna totalling 216 species has been recorded. Site attached species such as wrasse, damselfishes, red morwong Cheilodatylus fuscus and rock cale Crinodus lophodon, provided the most temporally and spatially stable components of the fish assemblage. More mobile and schooling species such as the snapper Acanthopagrus australis, and the bream Chrysophyrs auratus were highly variable between sites and between years. Newly-recruited juveniles of tropical species, which presumedly die each winter, also added considerable variation between years. The invertebrate fauna was dominated by the long-spined urchin Centrostephanus rodgersii, while other species such as Turbo snails and red-throated ascidians (Herdmania momus) were locally abundant. Commercially and recreationally important abalone and rock lobster species were extremely rare. Algal diversity was relatively low compared to other temperate Australian study locations, with the kelp Ecklonia radiata the most common species. Results from surveys showed little divergence between "no take" sanctuary zones established in October 2002 and fished reference sites. Two exploited fish species, the red morwong and bream, and one threatened species, the grey nurse shark, exhibited trends for population increase in sanctuary zones; however, longer-term trends will be required before the significance of these observations can be reliably assessed. While numbers were low, the re-establishment of grey nurse sharks within a sanctuary zone in Jervis Bay was certainly an encouraging sign that general protection from fishing may help protect this threatened species. Other patterns observed over the monitoring period included divergence between fished and unfished zones for the abundance of invertebrate gastropod Astralium tentoriformis and the total cover of the common kelp Ecklonia radiata. As for the fish results, more time is required to properly determine the biological significance of these trends. As the JBMP has only been protected on paper for 2.5 years, and due to a one year advisory phrase strongly enforced for only 1.5 years, it is not surprising that few changes have been detected as yet. A more realistic and biologically meaningful timeframe to detect change will be 5-10 years, hence it is recommended that annual surveys continue over this period. Due to the broad scale of the survey the current design should be able to detect changes at all levels of species interaction. Ideally surveys will continue to be repeated at the same time each year. This will produce a time-series of data documenting changes in the abundance and size distribution of species of interest, allowing clear trends through time in sanctuary zones to be differentiated from chance divergence and natural levels of inter-annual variability.