Characteristics of faecal and dissolved nitrogen production from tropical spiny lobster, Panulirus ornatus

Abstract

Spiny lobster aquaculture in sea-cages produces both particulate (faeces and waste feed) and soluble wastes [dissolved inorganic nitrogen (DIN)] that have the potential to degrade the environment. To begin to understand the environmental impacts of tropical spiny lobster aquaculture, the waste products of these lobsters were quantified, including the settling velocity of faecal material and DIN output from lobsters of a range of sizes and fed two dietary treatments (seafood and artificial diet), as well as determining the nitrogen leaching from faeces and diets for lobsters. The mean faeces settling velocity of lobsters fed with seafood was significantly higher than those from lobsters fed with artificial diet (0.30 ± 0.01 and 0.22 ± 0.01 cm s−1, respectively, mean ± SE), but the settling velocity of faeces did not differ among the lobsters of different sizes for each diet. The settling velocity of faecal material showed a positive relationship with faeces weight, volume and density but not length. Both carbon and nitrogen content in faeces showed no significant differences between the two diets. Feeding activity doubled the DIN output from lobsters consistently for both dietary treatments compared with unfed lobsters. Nutrient leaching from samples of faeces and diet was highly variable and did not differ among lobsters of different sizes or between the two dietary treatments. Overall, while faecal material, waste feed, as well as DIN excretion by lobsters in aquaculture operations could potentially negatively impact the environment, their faeces settling velocity and DIN output is markedly lower than fin-fish. Thus, the environmental impact from lobster aquaculture is unlikely to be as intensive as for fin-fish aquaculture.