Marine Biological Survey Report of the Fiji Great and North Astrolabe Reef, Ono Kadavu - WWF South Pacific - 2001

Marine Biological Survey Report of the Fiji Great and North Astrolabe Reef, Ono Kadavu – WWF South Pacific – 2001

Executive Summary

Marine biological surveys of coral reefs of the Great Astrolabe Reef (GAR) and North Astrolabe Reefs (NAR) were conducted from the 29 April- 3 May, 2001.

The GAR and AR are found on the northeast and northern end of the Kadavu island group, within the Ono tikina, or customary fishing area, situated approximately 70km south of Viti Levu, the main island of Fiji.

The surveys were conducted for the World Wide Fund for Nature’s (WWF) South Pacific Programme, as a component of the development of community-based management of the reefs.

A separate study commissioned by WWF, on the first marine protected area in Kadavu, the Yavusa Ulunikoro Marine Conservation Area, run by Waisomo village on Ono Island, was conducted immediately preceding this study, and the results are incorporated here.

All surveys were undertaken on SCUBA using standard long term monitoring techniques to sample benthic cover, coral diversity and condition, invertebrate abundance and diversity and fish abundance and diversity.

Two survey teams of 4-5 divers each operated from the 120-foot vessel MV NAI’A, focusing on the 12-15 m depth zone and covering 47 sites.

The GAR and NAR have a classic barrier reef and lagoon structure with four reef zones being identified, namely eastern (windward) barrier reefs, western (leeward) barrier reefs, lagoon reefs and channels.

The blue hole and backreef sites comprising the Waisomo village protected area were treated as separate habitats.

The barrier reef and bommie complexes of the windward reefs had the highest cover (>25%) and most diverse coral communities, providing extensive habitat for invertebrate and fish populations. Leeward barrier reefs showed less topographic complexity.

Lagoon patch reefs, back reef slopes and blue holes had the lowest topographic complexity, with low coral cover «10%) and high abundance of turf and fleshy algae (20-30%).

Coral communities ofthe GAR and NAR showed significant evidence of bleaching related mortality during the 2000 La Nina phenomenon, with a low average coral cover of 12%, and abundant evidence of newly dead colonies.

Many surfaces were covered with an early successional filamentous algae/microbial mat assemblage. The eastern barrier reefs were least affected, probably due to upwelling of cooler oceanic water during the bleaching in 2000, resulting in lower stress.

Lagoon and leeward reefs had extremely low coral cover, with higher mortality during the La Nina as calmer conditions in these zones and higher water residence time would have allowed greater heating of the water.

Affected coral communities were dominated by massive corals, as branching corals tend to be more vulnerable to bleaching and mortality.

Low levels of coral bleaching were observed, though at the time of surveys, in June 200 I, it was common in other parts of Fiji.

Crown-of-thorns starfish were common on windward and channel sites of the NAR, with high numbers of feeding scars seen. Coral species richness was recorded as 148 species, compared to a national list for Fij i of21 0 species.

The algae community was taxonomically typical of Fijian reefs with all 46 species previously recorded for Fij i.

Mobile invertebrate populations were low reflecting the impact of intense harvesting of once-abundant resources.

Bivalves and sea cucumbers were the most abundant invertebrate groups, and found primarily in lagoon sites with high runoff and/or sediment bottoms. Fish populations were low throughout the study sites (116±10 I per 250m 2, mean±stdev), though highest on the NAR, and on leeward and windward reefs.

Evidence of fishing was seen in the generally low populations and small fish sizes, the scarcity of preferred fish such as snappers (Lutjanidae) and rabbitfish (Siganidae) and the high abundance of fish such as fusiliers (Caesionidae) and surgeonfish (Acanthuridae).

Sharks and other large predatory fish targeted by fisheries were scarce, and found mostly on channel and windward sites due to their low accessibility. Fish species richness was recorded at 249 species, in 24 families and 3 higher level groups.