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

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 2008• Sheltered reefs situated within and near the mouths of land-enclosed estuaries whererun-off of freshwater and particulate matter from the land does not inhibit coralgrowth;• Narrow fringing reefs less than 50 m across located on protected leeward coastswhich are exposed to relatively light wave action; and• Reefs on south-facing coasts, which are regularly exposed to wave action and surgegenerated by the prevailing onshore winds.Morton (1974) considered that the sheltered reefs within land-enclosed waters were the mostcomparable in terms of exposure regime and coral composition to the reefs associated withatoll systems. The sheltered reefs studied were located at Honiara and Paruru Bay inGuadalcanal, Banika Island in the Russell Group and Marovo Lagoon, New Georgia.The following description of the lagoon complexes in New Georgia is based on thedescription given in Wells and Jenkins (1988), which in turn was derived from Stoddart(1969c). Marovo, Gerasi and Togavai lagoons on the north-east coast and Roviana Lagoonon the south-west coast are enclosed by raised barrier reefs. The north-eastern lagoons forma shelf with a total surface area of 700 km 2 . Marovo Lagoon, the largest system, is 35-55 kmlong and 500 m to 8 km wide. The main body of this lagoon is 25 m deep, but the bottomdrops to 50-60 m in some of the inshore passages between the eastern barrier islands. Njaepassage, for example, is about 40 m deep and the area of the lagoon to the west of this is 50-60 m deep, but the depth drops to 80 m at the entrance to the ocean. The maximum depth inthe eastern part of the lagoon is 25-30 m, but the water is shallower on the east coast. Thelagoon contains numerous sand cays, mangrove islets, raised reef islands and some smallvolcanic islands. The lagoon has three major habitats: sand cay complexes consisting ofsand islets on patch reefs with a thin fringe of mangroves; estuarine complexes with shallowwater, muddy bottoms, variable salinity and freshwater inputs rich in organic detritus; andbarrier islands with markedly different environments on their ocean-facing and lagoon sidereefs (Baines 1985 in Wells and Jenkins 1988). Coral reefs are found throughout the lagoon,but their growth is poor at the surface.The partly submerged barrier reef that extends from the south to the north coast fringingreef on Guadalcanal encloses a 1000 km 2 area known as Marau Sound. The depth of waterwithin the channel of the sound varies from 20-60 m and increases from west to east andtowards the barrier entrances. The reef flats in the sound cover an area of 25 km 2 and wereraised 0.6 m in 1961 by an earthquake. The flats on the barrier reef are up to 2 km wide, buthave little living coral, probably because they dry out at low tide.A recent report on the status of coral reefs in the Solomon Islands (Sulu et al. 2000), indicatesthat some of the largest areas of coral reef are found in association with large lagooncomplexes and lists the following as significant areas:• around the Shortland Islands near Bougainville;• inside the barrier reefs along the northeastern shore of Choiseul;• on either side of the Manning Strait between Choiseul and Santa IsabeI and along thesouthwestern shore of Santa Isabel;• in the Ghizo–Vonavona lagoonal area on New Georgia’s southern shore;• encircling Vangunu in southeastern New Georgia and along the northeastern coastarea past Ramata almost to Lever Harbour (Marovo Lagoon);• in the north at Lau Lagoon and west at Langalanga Lagoon in Malaita;The Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 18