WHY ARE SOME PRAWNS FOUND IN SEAGRASS - AN EXPERIMENTAL-STUDY OF BROWN (PENAEUS-ESCULENTUS) AND GROOVED (P-SEMISULCATUS) TIGER PRAWNS

A laboratory-based study was made of the responses of juveniles (8 to 24 mm carapace length) and adults (over 24 mm CL) of brown (Penaeus es culentus) and grooved (P. semisulcatus) tiger prawns to two habitats: simulated seagrass and bare sand. At night, the brown tiger prawns spe nt about 80% of their nonswimming time in seagrass, whereas the groove d tiger prawns spent equal amounts of time in both habitats. In daylig ht (0830 to 0930 hours), the brown tiger prawns were found mainly in t he seagrass, with most of those larger than 15 mm CL buried in the sub strate whereas smaller individuals were divided equally between standi ng on the bottom, burying in the sand, or clinging to the seagrass, ma inly to the upper half of the fronds. Grooved tiger prawns between 15 and 25 mm CL were also found mainly in seagrass in the morning, but bo th smaller and larger animals were found equally in both habitats. Mos t grooved tiger prawns found in seagrass during the day were buried; f ew were clinging to the seagrass or standing on the substrate. The res ults show that both species of tiger prawns show preferences with resp ect to structures in their environment and that these preferences are influenced by the size of the animals.