Kochzius, M.

Moreels, N.

Open Marine Archive

 103 
Abundance of giant clams (Tridacna sp.) on protected versus 
unprotected coral reefs in the Western Indian Ocean 
Moreels Nele and Kochzius Marc 
Marine Biology, Ecology and Biodiversity, VUB, Pleinlaan 2, 1050 Brussel, Belgium 
E-mail: nele.moreels@gmail.com  
 
Along the East African coast, we encounter three species of giant clams Tridacna sp. in marine 
protected areas (MPAs) as well as non-protected areas. The studied species are T. maxima, T. 
squamosa and T. squamosina (previously known as T. costata). 
 
Giant clams are mixotrophic, being capable of generating biomass through both primary and 
secondary production. Primary production is controlled by Symbiodinium microadriaticum, their 
symbiotic photosynthetic zooxanthellae algae. Thus giant clams are susceptible to stress-induced 
bleaching (expulsion of their symbiotic zooxanthellae) often associated with increased sea surface 
temperatures. 
 
Furthermore, has the abundance of giant clams been greatly reduced due to overfishing and loss of 
habitat. Four main reasons for giant clam overfishing are increased human population, improved 
technology available to fishermen, expanded international/ inter-island trade and poaching of giant 
clam meat and expanded international trade in shell specimens as ornaments. 
 
Besides it is important to know that tridacnids are vulnerable species to stock depletion, because of 
their late sexual maturity, sessile adult phase and broadcast spawning strategy. Fertilization success 
requires sufficient numbers of spawning individuals. Low densities result in reduced (or zero) 
recruitment and eventual population collapse in the long-term. 
 
Free-swim surveys have been conducted in the Western Indian Ocean in order to estimate abundance. 
By using multivariate statistics, we aim get an answer to the question if there is a significant difference 
between the abundance of giant clams in MPAs and non-protected areas. 
 
Keywords: Western Indian Ocean; Marine Protected Areas; Tridacna sp.  


Abundance of giant clams (<i>Tridacna sp.</i>) on protected versus unprotected coral reefs in the Western Indian Ocean

http://www.vliz.be/imisdocs/publications/311646.pdf

Abundance of giant clams (<i>Tridacna sp.</i>) on protected versus unprotected coral reefs in the Western Indian Ocean

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