Stimulating investment in pearl farming in ... - World Fish Center

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 2008Friedman et al. (1998) examined the availability of wild spat in seven habitats across sevenregions (Gela, Seghe, Noro, Gizo, South Malaita, Ysabel and Shortlands) of the SolomonIslands:• inner lagoons with low water movement and periodic run-off from land masses;• mid lagoon in shallow areas or close to reefs, where there was either low, some ormoderate water movement;• mid lagoon near channel flows, where there was moderate water movement;• the outer edge of lagoons, near channel flows with moderate water flow; and• outside barrier/fringing reef, near channel flows with moderate waterflows).They showed that reasonable quantities of spat could be collected from some habitats within“open” reef systems, particularly from sites with clear water and moderate currents thatwere at least 35 m from the nearest reef. The inner lagoon habitats at Seghe, Noro, Gizo andSouth Malaita yielded the smallest numbers of spat, which is in contrast to the situation inPolynesia. Friedman et al. (1998) noted that these lagoonal sites differed from the atollsystems in Polynesia in that they were smaller, shallower, had soft rather than firmsubstrata, and were more turbid due to runoff of sediment and nutrients from their adjacentland masses. They suggested that collectors were less effective at these sites, because theybecame clogged with particulate matter and overgrown with epiphytic algae, particularlyduring the rainy season. Sites that were located near extensive reef systems with clearwater, had moderate current flow, depths > 15 m and were at least 35 m from the nearestreef generally yielded the most spat, with the greatest numbers being collected at midlagoon sites at Nusa Tupe, Gizo and an outside barrier/fringing reef site at Noro. Theirstudy also showed that the collectors attracted predatory gastropods and crabs and that alarge proportion (42%) of the oyster spat collected was dead. Friedman et al. (1998)concluded that there is potential for black-lip pearl cultivation in these “open” reef systemsbased on collection of wild spat, provided that the high rate of mortality can be reduced.Friedman and Bell (1999) subsequently examined seasonal differences in the availability ofspat in offshore and inshore zones of “open” reef systems in two contrasting geographicregions bordered by major landmasses, an embayed lagoonal system at Gizo and anenclosed sound at Noro. They predicted that more spat would be collected from offshorethan inshore zones and that spatfall in the offshore zone would be similar in “wet” and“dry” seasons, but greater during the “dry” than in the “wet” season in the inshore zone.In both seasons, significantly more spat were collected in the offshore zone than in theinshore zone at both locations (Friedman and Bell 1999). The offshore-inshore pattern ofabundance could be due to environmental conditions suitable for the settlement of spatbeing less suitable inshore than offshore because of the greater influence of runoff from theland masses, greater flows offshore may result in more water and larvae coming into contactwith the collectors, differential predation after settlement or differential supply of larvaebetween zones. Although the influence of these factors was not determined, Friedman andBell (1999) concluded that differential predation after settlement was unlikely to be a majorfactor because the variation in abundance of living spat was similar to that for total numberof spat. In the offshore zone, similar numbers of spat were collected at Gizo during bothseasons, but at Noro significantly more spat were collected during the “dry” than the “wet”season. The seasonal decline in abundance of spat in the offshore zone at Noro may havebeen due to greater than average runoff resulting from cyclone activity being channelledthrough the sound further offshore than usual. At Gizo, the runoff is more likely to haveThe Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 22