Nitrogen excretion by the Cape rock lobster Jasus lalandii and its possible contribution to the inshore Benguela System |
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| Abstract: | The Cape rock lobster Jasus lalandii is a major predator in the inshore Benguela system. The mean density and biomass at Oudekraal is 0,48 individuals ·m?2 or 49,75 g dry mass ·m?2. The main component of its diet is Aulacomya ater, the ribbed mussel, which has a mean biomass of 1,15 kg dry mass ·m?2. Daily consumption of carbon and nitrogen from this source reaches a maximum in summer and, when J. lalandii feed on mussels, 14,1 per cent of the flesh is lost to the environment as a result of "messy feeding". The absorption efficiency of ingested nitrogen is 86,2 per cent. Ammonia and urea excreted in the first 12 h after feeding represent 6,7 and 1,6 per cent respectively of the nitrogen ingested. Endogenous nitrogen excretion has a mean rate of 1,9 μg N·g (dry mass)?1·h?1 The range of estimates for combined figures of kelp and phytoplankton nitrogen requirements are 76,4 – 86,7 g N·m?2·year?1 J. lalandii returns 6,3 g N·m?2·year?1 to the system, accounting for 7,2 – 8,2 per cent of annual kelp and phytoplankton requirements. This could be of particular importance during downwelling when the supply of new nitrogen is limited. |
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