The effect of predator/prey density and water dynamics on feed intake and growth in spiny lobster larvae (Jasus edwardsii)

Abstract

Consumption of Artemia by phyllosoma of the spiny lobster Jasus edwardsii was examined under static and turbulent conditions. Phyllosoma larvae were stocked at two densities (2 or 4 phyllosoma container -1; 2P or 4P) and fed juvenile Artemia (1.6mm total length) at two feed rates (1.5 or 0.75 Artemia ml-1; 1.5A or 0.75A) in 50 ml of seawater. This provided a combination of 4 treatments (2P/1.5A, 2P/0.75A, 4P/1.5A, 4P/0.75A). Daily intake of Artemia by phyllosoma was monitored and assessed relative to moult size and intermoult duration at differing predator-prey densities. Phyllosoma numbers were held constant; in the event of mortality, animals were replaced with others from the same cohort cultured under similar conditions. Phyllosoma endogenous reserves at hatch combined with the lowest ration of 0.75 A was sufficient to ensure normal growth and intermoult duration until Stage II. When phyllosoma were fed for an extended period (several moults), low ration and high phyllosoma density resulted in smaller size and extended intermoult duration. Fluctuations in the feeding pattern of phyllosoma were evident between treatments during the experiment. Phyllosoma with access to more Artemia consumed more, and consumption was reduced prior to a moult, even during early stages of development. The second phase of the study examined the intake of 1.7 mm juvenile Artemia by phyllosoma and their response to flow-induced turbulence with a combination of two water exchange rates (2.5 or 5 times h-1) and two inlet positions (2 cm above the water surface or 0.5 cm above the culture vessel bottom and parallel to it). Larvae exposed to slow flow were larger and had a shorter intermoult duration associated with an increased ability to capture and consume more Artemia. Similar numbers of Artemia were consumed during the intermoult in high flow treatments compared to the low flow, albeit over a longer duration. Phyllosoma development between moults required less Artemia to be consumed under static conditions.