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close this section of the library Sharma, Ashishika D.

View the PDF document A study of the Benthic Foraminifera of Laucala Bay, with special focus on Marginopora vertebralis
Author:Sharma, Ashishika D.
Institution: University of the South Pacific.
Award: M.Sc.
Date: 2007.
Call No.: pac In Process
BRN: 1156242
Copyright:This thesis may be copied without the authors written permission.

Abstract: Foraminifera (often abbreviated to "forams") are acellular organisms (protists) that form shells (tests) of calcium carbonate or cemented grains of sand or other material which, when the animals die, may form calcareous sand. The purpose of the study was to determine the species of benthic foraminifera present in Laucala Bay, and to investigate the role of large foraminifera, especially the soritid Marginopora vertebralis (Quoy & Gaimard, 1830) in supplying carbonate sediments to a lagoonal sedimentary system in Fiji, namely the Nukubuco Reef flat in Laucala Bay. A total of 68 different species from 48 different genera were identified from the 13 sites sampled and the species classification and taxonomy were determined. Synonyms for each species were found and recorded. Plates were made showing the photographs and the species details. It was assumed that the species live close to where their tests were found and so were mapped accordingly. Generally, it was seen that the sites around Makuluva Island, Nukulau Island and the "Fish Patch" showed high diversity of species, while the sites on the Nukubuco Reef and on the northern edge of Makuluva Island showed fewer species. The sites in the middle of Suva Harbour and Laucala Bay as well as off the Laucala Island showed a considerably fewer species. However, the least number of species were to be found on the Nasese Tidal Flat and in the Vatuwaqa River estuary. A multidimensional scaling map divides the 13 sites into 3 clusters based on the presence of similar species. It appears that all the sites on or near the reefs consist of similar species, while the sites toward the middle of the bays have similar species and those sites close to the mainland have similar species. The general trend in the study area was a greater abundance of species in sediments from the sites outside the reef boundary on the lagoon: that is, the sites around Makuluva Island. The abundance of foraminifera in the sediment samples decreased towards the mainland, becoming the least near the Nasese Tidal Platform and Vatuwaqa River estuary. Three separate large colonies of Marginopora vertebralis were found on the seagrass beds off the Sandbank Island. The largest colony was located on the south of the Sandbank Island and the colony was spread out to the southeastern part. Two other smaller colonies were found on the northeastern side and the southwestern side of the southern end of the island. M. vertebralis seems to prefer to live on the bilate, flattened fronds of Halodule uninervis than on the cylindrical blades of Syringodium isoetifolium. This may be due to the density of the different seagrass species populations. Culture of M. vertebralis in the laboratory showed that the group of M. vertebralis larger than or equal to a diameter of 1 cm showed a growth of 0.1307 grams/month while the group of M. vertebralis bigger than a diameter of 0.5 cm and smaller than or equal to a diameter of 0.7 cm showed a growth rate of 0.0632 grams/month. However, if the weight grown relative to size of organism (percentage growth) is considered then the smaller group has a much faster growth rate. The smaller organisms show a growth rate of 7.7277% of their initial body weight while the larger organisms show a growth rate of 1.8727% of their initial body weight. The growth rates obtained from this culture allowed calculation of the approximate rate of sediment production from the three M. vertebralis colonies from the Sandbank Island: 35.9304 kg of sediments each month and 431.1648 kg of sediments each year, at an average of 0.1274 kg/m2/yr. Future studies may seek to identify all species of Foraminifera from around Viti Levu and compare distribution over greater distances.
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