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Ecosystem Monitoring of Subtidal Reefs in the Jervis Bay Marine Park
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 macro-algal abundance.
Baseline surveys were conducted in 1996 (18 replicate sites), 2000 (24 sites) and 2001 (25 sites). Since establishment of the JBMP zoning plan in October 2002 five surveys in 2003, 2004, 2005, 2006 and 2007 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 in excess of 220 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 yellowfin bream Pagrus auratus were highly variable between sites and between years. Newly-recruited juveniles of tropical species, which usually 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 grandis) 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 population numbers of two species, red morwong and grey nurse shark, diverged between “no take” sanctuary zones established in October 2002 and fished reference sites, and the abundance of “large fish” also diverged through time. Both recovering species exhibited trends for population increase in sanctuary zones, with statistically significant bay-wide increases in abundance for red morwong and a strong single site response for grey nurse sharks. While shark numbers were variable, 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. The trend for increasing numbers of large fish (300 mm length or greater) within sanctuary zones also indicates that these zones are affording protection to a number of species, and that this change may continue into the future as protected resident species grow.
The other notable pattern observed over the monitoring period was a significant decline in abundance of all common macro-invertebrates, including the common turbo (Turbo torquatus) the gastropods Astraea tentoriformis and Astralium squamiferum, and red-throated ascidians (Herdmania grandis). While more time is required to properly determine the biological significance of this trend, it comprises a significant directional response that represents a major shift in the invertebrate assemblages on JBMP reef systems, with substantial ecosystem consequences likely if the trend continues.
Detection to date of relatively few changes related to protection from fishing is not surprising given that sanctuary zones in the JBMP have only been protected for 4.5 years and, following a one year advisory phrase, prohibitions strongly enforced for only 3.5 years. A more realistic and biologically meaningful timeframe to detect change will be 5-10 years, as resident species recruit to reefs and grow in size. Hence we recommend that annual surveys continue to the five year post protection stage, and then continue at intervals no longer than two years to ten years post protection, when the frequency of the MPA monitoring program should be reviewed. We also note that the value of the monitoring program for coastal management is considerably greater than its value for assessing MPA effectiveness. The annual time series has proved highly useful for detecting significant regional shifts in marine assemblages, and thus represents a critically-important management tool in an era of climate change. For this reason, annual surveys are recommended through the long term, particularly if the evident decline in macro-invertebrate populations is sustained.
Publication titleReport to Jervis Bay Marine Park
PublisherTasmanian Aquaculture and Fisheries Institute