Food Quality Affects Secondary Consumers Even at Low Quantities: An Experimental Test with Larval European Lobster

The issues of food quality and food quantity are crucial for trophic interactions. Although most research has focussed on the primary producer – herbivore link, recent studies have shown that quality effects at the bottom of the food web propagate to higher trophic levels. Negative effects of poor food quality have almost exclusively been demonstrated at higher food quantities. Whether these negative effects have the same impact at low food availability in situations where the majority if not all of the resources are channelled into routine metabolism, is under debate. In this study a tri-trophic food chain was designed, consisting of the algae Rhodomonas salina, the copepod Acartia tonsa and freshly hatched larvae of the European lobster Homarus gammarus. The lobster larvae were presented with food of two different qualities (C∶P ratios) and four different quantities to investigate the combined effects of food quality and quantity. Our results show that the quality of food has an impact on the condition of lobster larvae even at very low food quantities. Food with a lower C∶P content resulted in higher condition of the lobster larvae regardless of the quantity of food. These interacting effects of food quality and food quantity can have far reaching consequences for ecosystem productivity

The time course of early post-mortem biochemical processes in the abdominal muscle of a commercially important decapod crustacean (Nephrops norvegicus) : implications for post-catch processing

The post-mortem processes in the fast abdominal muscle of the Norway lobster Nephrops norvegicus have been investigated by simulating the first 24-h post-harvest in a controlled experiment. Tissue pH and the concentrations of arginine phosphate, glycogen, L-lactate, ATP, ADP, AMP, IMP, HxR, and Hx were measured at the time of sacrifice and 3, 6, 12 and 24 h thereafter. Additionally from the nucleotide values the corresponding adenylate energy charge (AEC) was calculated. The results reveal that the post-mortem biochemical processes in the abdomen of the Norway lobster after sacrifice and during storage at 10°C are comparable to those of vertebrates. It was found that arginine phosphate was depleted from 38.5 ± 5.2 to 10.9 ± 2.9 µmol g−1 within 3 h, and anaerobic glycolysis was enhanced, so that glycogen was depleted and L-lactate accumulated. The muscle pH decreased significantly from 7.6 ± 0.1 to 7.0 ± 0.15 within 20 min and then continued to decrease at a slower rate. Most interestingly, the ATP concentration was maintained at approximately 3.5 ± 0.3 µmol g−1 for up to 12 h post-mortem. This is unusually long and indicates a special characteristic of this fast-type crustacean muscle. AMP accumulated to a maximum after 12 h and was then slowly transformed into IMP. The AEC fell from an initial value of 0.88 to only 0.17 after 24 h. When viewed in context with the fishing industry the results demonstrate that when the product is tailed (removal of the cephalothorax) upon catch, as is common practice in this industry, the result will always be an extensive post-mortem glycolytic response that will lead to an unavoidable and rapid depletion of the energy reserves resulting in a product of lesser quality