The effect of Gracilaria verrucosa on the growth rate of Pacific oyster (Crassostrea gigas)

Abstract

Abstract by author:

In natural aquatic systems, there are ecological balances between different species of organisms and individuals. However in culture conditions the systems are usually meant to favour the preferred organisms, but still other organisms might invade and share in the utilization of resources. Gracilaria verrueosa is an unwanted plant that grows in marine cultured beds along the Namibian coast and this experiment showed that it adversely affects the growth performance of the Pacific oyster (Crassostrea gigas). The decrease in growth of the oyster in rafts was directly linked to the presence of Gracilaria verrucosa. This experiment quantitatively showed that invasion quantities of Gracilaria verrucosa influences the percentage growth reduction rates of oyster. The various seeding rates (O, 400, 800 g) of Gracilaria verrucosa resulted in significantly (P0. 05) reduced growth rates of oysters by 21 percent and 37 percent in medium and high seeding rates of the seaweed, respectively. This was shown to be significant using the t-test and Wilcoxon Sum Rank Test (P0. 05). Although conducted over a short growing period of 6 weeks, the experiment demonstrated detrimental invasion of Gracilaria verrucosa in oyster rafts