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Effects of oxygen depletion on the ecology, blood physiology and fishery of the Norway lobster Nephrops norvegicus

1990; Inter-Research; Volume: 67; Linguagem: Inglês

10.3354/meps067141

1616-1599

Susanne Baden, Leif Pihl, Rutger Rosenberg,

Crustacean biology and ecology

Biomass, population structure, food selection and blood (haemolymph) physiology of the Norway lobster Nephrops norvegicus (L.) were investigated in SE Kattegat, an area where low oxygen concentrations (t 2 m1 1-', 30 % 02-saturation) have occurred in the bottom water for 1 to 3 mo periods in most years in the 1980's.During the study period (October 1984 to September 1989) lobster biomass decreased in the area from 10.8 kg h-' (catch per u n ~t effort) to zero (estimated during the last 12 nlo of the investigation).Males contributed on average 78 % of the population density, except in September 1988 during severe hypoxia when a reversed sex ratio was found and females (even berried) dominated (75 % of density).The food of N. norvegicus belonged to 4 major groups; crustaceans, echinoderms, molluscs and polychaetes.The dominant species eaten within these groups were also found to be dominants in the benthic infauna.This suggests that N. norvegicus are not feeding selectively but taking available organisms indiscriminately.In the field and in laboratory experiments N. norvegicus increased blood pigment (haemocyanin, Hcy) concentration in moderate hypoxia (20 to 40 '10 0 2saturation), and reduced it in severe hypoxia (10 to 20 % 02-saturation).At 02-saturations below 15 % N. norvegicus ceased feeding and had empty stomachs.Thus in low oxygen concentrations the lobsters suffer from hypoxia-induced starvation rather than lack of food.Survival of N. norvegicus exposed to 15 and 10 % 02-saturation was 4 wk and 2 to 4 d, respectively.After return to normoxia recovery of blood Hcy concentration was slow, probably due to lack of copper in the diet, which is essential for Hcy synthesis.We consider blood Hcy concentration to be a promising 'in situ' biomarker with ecological relevance.O Inter-Research/Printed in Germany Investigations on the effects of eutrophication on Nephrops norvegicus were carried out between 1984 and 1989.The aims of these investigations were to (1) make field observations on changes and interactions in lobster biomass, population structure and feeding, (2) study changes in blood (haemolymph) pigment concentration in response to hypoxia (02 < 20 % saturation) in the SE Kattegat and, (3) evaluate the use of blood haemocyanin concentration of lobsters as an 'in situ' biomarker of hypoxia in the Kattegat and Skagerrak and in experimental studies. AREA INVESTIGATEDA 3000 km2 area in the SE Kattegat at 25 to 50 m depth and with a soft sediment bottom was investigated (Fig. 1).The sediment structure in the area is silty-mud with a content of organic matter (ignition loss) of about 13 to 15 % (Rosenberg & Loo 1988).The