Volume No. 5 Issue No.: 3A Page No.: 741-748 January-March 2011

 

STUDY OF PHYSICO - CHEMICAL PARAMETERS AFFECTING THE DISTRIBUTION OF SPONGE XESTOSPONGIA EXIGUA (PHYLUM PORIFERA, CLASS DEMOSPONGIAE) IN A NORTHERN LAGOON OF MAURITIUS

 

Chandani Appadoo, Sandeep Shivram Beepat*1 and Daniel Marie2

1. Department of Biosciences, Faculty of Science, University of Mauritius, Reduit (Mauritius)
2. Mauritius Oceanography Institute, France Centre, Quatre Bornes (Mauritius)

 

Received on : October 20, 2010

 

ABSTRACT

 

Sponges are very important in the marine ecosystems and also represent organisms known for producing a diversity of chemicals. The present study was performed from September 2009 to February 2010 and aimed at making a mapping of the sponge Xestospongia exigua in the lagoon of Trou aux Biches. This research is a first in the lagoons of Mauritius and it gives indication of sponge distribution and the physico-chemical parameters affecting their abundance. Such knowledge adds to the lack of information on the biology of these marine invertebrates in Mauritius. Visual censuses were made along the 2.5 Km lagoon during fifteen snorkeling sessions (15 days) covering a snorkeling distance of approximately 500 m per session. The distribution and mapping of sponge was done following surveys and recording of GPS positions of the sponge patches present. Abundance of sponge was assessed by random throws of 1.0 m2 quadrats (n = 30). Moreover, physical and chemical parameters such as depth, pH and salinity were also recorded. The sponge size and the immediate habitats of sponges living in Trou aux Biches were assessed by random throw of 900 cm2 quadrats. Observations showed that the sponge species Xestospongia exigua were distributed in six different patches of different sizes with a largest patch of 48922 m2. From aerial maps, it was also observed that the distribution of sponges was not uniform (patches were of irregular forms) within the lagoon of Trou aux Biches. From statistical analysis (ANOVA), it has been observed that water depth, pH and salinity have an effect on the sponge abundance within the lagoon. The study shows that increasing depth is favorable to sponge abundance (8.0 specimen/m2 at a depth of 3.0 m). Sponges were also observed to be abundant in water of higher pH (5.6 specimens/m2 at pH 8.27). However, with increasing water salinity, a decrease in sponge abundance was observed. The study also showed that Xestospongia exigua sponges in Trou aux Biches were more abundant in habitats of dead corals.

 

Keywords : Sponge distribution, Physico-chemical parameters, Lagoon, Sponge, Xestospongia exigua

 

 

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