Valonna Baker

Status of Caribbean coral reefs in seven countries in 1986

There are few long-term datasets available to make reliable statements about trends in cover and structure in many coral reefs around the world. We present 27year old summary data of the cover of corals and other biota on Caribbean and Western Atlantic coral reefs in 7 countries collected in late 1985 and early 1986. These data were collected to support research on sponge populations and show relatively low coral cover on many of these reefs with particularly low cover of Acropora spp. We present these summaries to encourage other researchers to compare with current conditions or repeat the surveys to show long-term trends; the raw data will be supplied on request.

An attempt to locate high density populations of juvenile crown-of-thorns starfish (Acanthaster planci) on the central Great Barrier Reef

Large populat ions of juvenile crown-of-thorns starfish have eluded researchers on the Great Barrier Reef (GBR) (Moran 1986; Doher ty and Davidson 1988), in contrast to the extensive recruitment observed in Fiji by Zann et al. (1990). We surveyed 14 reefs in the central G B R during late 1989 to locate high density populat ions of juvenile crown-of-thorns starfish for proposed research. Further details of this work are presented in Johnson et al. (1991). The survey strategy was designed to maximise the chance of finding large populat ions of juvenile starfish by surveying large areas of different reefs considered likely to support populat ions of juveniles. The search was directed towards larger juveniles (5-15 cm) which were more likely to be detected than smaller individuals. All reefs surveyed were relatively small and had supported large numbers of starfish during the 1970s. They either currently supported large numbers of adult starfish or were located immediately to the south of the main concentration of reefs with outbreaks. A range of reef types, with respect to location across the continental shelf, were surveyed. The perimeter of each reef was surveyed by manta tow to identify sites with relatively high live coral cover and small areas of dead coral (caused by coral feeding juvenile starfish). Either three or six sites were selected on each reef for more intensive SCUBA swim surveys. SCUBA searches were undertaken by four divers along four depth contours at each site (reef crest, 5 m, 10 m and 15 In, where practical) for 20 rain, over approximately 100 m. Each diver scanned 1 m either side of the swim path looking for small starfish or evidence of their presence, and closely examined all areas of recently dead coral. Only 14 juvenile starfish were found, ranging f rom 5.5 to 15 cm in diameter. The gas t ropod DrupelIa was found in close proximity to 249 + (30.5%) of all small coral scars. There are 3 possible explanations for not finding high density populat ions of juvenile starfish. Firstly, there may have been no juvenile starfish on the surveyed reefs. Secondly, juveniles may have been present, but were not detected because they were too small. Finally, there may have been juvenile starfish outside the areas of the reef which were surveyed (e. g. the reef flat or deeper reef slope). Table 1. The results of SCUBA swim searches including numbers (n) of: sites surveyed, juvenile and adult starfish observed, and small feeding scars that were attributed to juvenile starfish and Drupella (+ indicates the total (n) were too numerous to be counted)

Manta tow surveys of the Great Barrier Reef

of the Great Barrier Reef Since 1985, the Australian Institute of Marine Science has used manta tows to examine changes in the distribution and abundance of the crown-of-thorns starfish and hard corals on the Great Barrier Reef. Of about 2900 reefs 331 have been surveyed, with about 57% being surveyed more than once. The photo shows a snorkeller being towed behind a small boat. at about 4 km h 1, around a reef. The boat is stopped every 2 rain to allow details to be recorded on the board. To date 40 750 manta tows have been completed, a distance of about 6860 km (equivalent to being towed from Townsville to Hawaii !) with research vessels travelling about 56000 km (equivalent to 1.4 times around the globe). The team of four spend about 450 man days p.a. at sea. The principal costs for the study have been shiptime (about US

Survey Manual for Tropical Marine Resources

52 000 p.a.) and salaries (about US

Survey Manual for Tropical Marine Resources (2nd Edition)

85 000 p.a.). A technical report detailing the methods is available on request.