Habitat Type and Light Affect Sheltering of Juvenile Tiger Prawns (Penaeus Esculentus Haswell) and Success Rates of Their Fish Predators

Abstract

The burying and sheltering behaviour of two different sizes of juvenile tiger prawns (shrimp) Penaeus esculentus Haswell was studied during light and dark periods, in three habitats: bare silt substratum; short, thin-leaved seagrass (Halodule uninervis Aschers.); and tall, broad-leaved seagrass (Cymodocea serrulata Ashers & Magnus). Relative predation rates by the sand bass Psammoperca waigiensis Cuvier were also studied in these three habitats and in an additional seagrass with tall, thin leaves (Syringodium isoetifolium Ashers). Burying behaviour differed with prawn size, seagrass habitat and exposure to light. Small prawns (2.5 to 3.5 mm carapace length [CL]) rarely buried, even on bare substratum, whereas large prawns (11 to 13 mm CL) buried often and in all habitat types. However, large prawns buried in the substratum less often in tall, broad-leaved seagrass than in short, thin-leaved seagrass. Small prawns remained emerged in both the light and dark, whereas large prawns spent more time above the substratum in the dark than in the light. Small prawns perched on all types of seagrass leaves, whereas large prawns perched only on the broad-leaved seagrass.

Fish detected juvenile P. esculentus (4 to 5 mm CL) more quickly in narrow-leaved seagrasses than in broad-leaved seagrass, and more quickly and more often, on bare substratum than in narrow-leaved seagrasses. More juvenile prawns were detected in bare substratum and the thin-leaved seagrasses, S. isoetifolium and H. uninervis, than in the broader-leaved C. serrulata. More prawns were caught and eaten on bare substratum than in the broad-leaved seagrass. These results indicated that small juvenile tiger prawns would suffer higher rates of predation in short, thin seagrass and unvegetated habitats, and this would lead to a decrease in abundance in these habitats. In the field, observations of the abundance of prawns in seagrass habitats of different structural complexity suggests post-settlement processes such as predation may explain prawn distribution.