Parapholas quadrizonata (Spengler, 1792), dominating dead-coral boring bivalve from the Maldives, Indian Ocean
Endolithic bivalves were studied to establish abundance ranking and bioerosive impact on Maldivian coral reefs. In samples of dead coral, Parapholas quadrizonata(Spengler, 1792) was by far the most numerous bivalve borer. The assemblages of variously size
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Centre for Earth Sciences, University of Vienna, 1090 Vienna, Austria, ([email protected])
Abstract. Endolithic bivalves were studied to establish abundance ranking and bioerosive impact on Maldivian coral reefs. In samples of dead coral, Parapholas quadrizonata (Spengler, 1792) was by far the most numerous bivalve borer. The assemblages of variously sized and aged specimens, their spatial situation and the resulting behaviour are described and discussed. The morphology of shells and boreholes is illustrated. Intra-species competition for space may have restricted the individual growth but was not necessarily lethal. The borings show unique internal features that allow distinction from those of Gastrochaena species, whereas the borehole apertures are undistinguishable between the two genera. Keywords. Bioerosion, boring bivalve, Parapholas quadrizonata, Martesiinae, Pholadidae, coral reef, Maldives
Introduction The present paper is based on observations made in the Indian Ocean during the Coral Reef Expedition Maldives 2007, conducted from March 15 to 29, under the leadership of Karen and Wolfgang Loch (http://www.expeditionmaldives2007.org). During the cruise four atolls were examined in the central part of the republic (Fig. 1). The main goal of the expedition was to compare the state of live coral cover of the reefs of today and half a century ago and its recovery by resettlement after the severe coral bleaching event of 1998 (Scheer 1958, 1972, 1974; Pillai and Scheer 1976; Loch et al. 2002, 2004; Schuhmacher et al. 2005; Loch and Loch 2006; Wallace and Zahir 2007). The present study focused on collecting samples of endolithic bivalves and their substrate to establish a preliminary ranking of their abundance and to assess the presumed bioerosive impact on the reef frame-builders. Bioerosion is a major threat for the maintenance of stressed reefs, particularly if live coral cover drops below 50%. Therefore, a preliminary study of the present situation in the Maldivian reefs was undertaken (http://bufus.sbg.ac.at/info/Info%2037/ Info37-home.htm). M. Wisshak, L. Tapanila (eds.), Current Developments in Bioerosion. Erlangen Earth Conference Series, doi: 10.1007/978-3-540-77598-0_14, © Springer-Verlag Berlin Heidelberg 2008
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Kleemann
Fig. 1 Location of the Maldives in the Indian Ocean and the route of the expedition in the central area of the archipelago, starting from Male northwards on March 15th, 2007
Parapholas quadrizonata (Spengler, 1792) from the Maldives
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Methods Dead coral surfaces with apertures of endolithic bivalves were selected from the reef top down to 12 m depth using SCUBA. From sites of special interest, images were taken with a digital camera (Camedia 350 Zoom) in an under-water-housing before and after opening the dead coral with hammer and chisel. The coral was split open in several steps in order to preserve as many of the bivalves as possible undamaged and to observe more details of the endolithic community structure. All dislodged specimens were put into small mini-gr
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