Pergamon 0025-326X(94)00257-6 Marine Pollution Bulletin, Vol. 31, Nos 1-3, pp. 93-102, 1995 Copyright O 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0025-326X/95 $9.50+0.00 Uptake, Accumulation and Regulation of Manganese During Experimental Hypoxia and Normoxia by the Decapod Nephropsnorvegicus (L.) S. P. BADEN*, S. P. ERIKSSON* and J. M. WEEKSt:~ * Gi~teborg University, Kristineberg Marine Research Station, S-45034 Fiskebiickskil, Sweden t lnstitute of Biology, Odense University, Campusvej 55, DK-5230 Odense M, Denmark ~:Present address: Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE 17 2LS, UK. A consequence of eutrophication in marine coastal waters is the increased oxygen demand of the sedi- ments. This has resulted in repeated autumnal hypoxia of the bottom waters in many areas and an enhanced flux of manganese (Mn) from the sediment to the overlying waters. Manganese accumulation, subsequent uptake and regulation in the Norway lobster, Nephrops norvegicus, have been investigated. Nephrops norvegicus were continuously exposed for 2 weeks to 555, 1755 and 5555 ttg 1-1 manganese in combination with hypoxia (2.8-3.2 kPa) or normoxia. Net accumulation occurred in animals exposed to concentrations of 1755 jig !-1 Mn and higher. Accumulation was greatest in gills and haemolymph and least in muscle tissue. The oxygen level had no effect on the accumulation of bioavailable manganese or copper distribution in any tissue of N. norvegicus. In short term experiments using labelled manganese (54Mn) lobsters were exposed to 100 jtg Mn !-t for up to 72 h. The results confirmed that haemolymph and gills were the main target tissues. Urine Mn excretion after pre-exposure to 100 ttg Mn !-1 was constant in animals allowed to excrete into clean water for an additional 5 days. Manganese is an essential trace metal involved in many metabolic functions of both plants and animals (Johnson & Nielsen, 1990). In excess, however, manganese is a neurotoxin (Hille, 1992). In the marine environment increased concentrations of bioavailable manganese often result from anthropogenic activity. The reduced and solubilized manganese (Mn(II)) released from the sediment surface result in an exponential increase in This article is dedicated to the late Dr G. W. Bryan, whose article in 1965 with E. Ward on the absorption and loss of radioactive and non- radioactive manganese to the lobster Homarus gammarus (as Homarus vulgaris) published in the Journal of the Marine Biological Association UK was a major influencing factor on the following work. manganese concentration in the overlying water. The process is initialized with increasing temperature, decreasing oxygen concentrations (resulting from organic detritus undergoing microbial oxidation) and an upward movement of the redox cline (Balzer, 1982; Hunt, 1983; Sundby et al., 1986). Reoxidation of Mn(II) is a slow process compared to reduction and is catalysed on the surface of particles (Balzer, 1982; Santschi et al., 1990). Eutrophication-induced hypoxia in the sediment-water interface reduces the manganese (Gavis & Grant, 1986; Hall et al., 1989) and the reduced form of manganese (Mn(II)) is bioavailable (Baden et al., 1994). Hypoxic concentrations < 16% saturation (3.2 kPa) can increase the concentration of bioavailable manganese above that normally found in seawater (1 ~g Mn 1-1) to concentrations approaching 1500 Ixg Mn 1-1 (Balzer, 1982). Increased concentra- tions of manganese and low concentrations of copper were found in the Norway lobster, Nephrops norvegicus, exposed to hypoxia in the Kattegat, Sweden (Baden et al., 1994), as well as in blue crabs, Callinectes sapidus, from a metal contaminated area in North Carolina, USA (Weinstein et al., 1992). In both areas the incidence of shell disease in the animals was higher than in reference areas (Baden et al., 1990; Weinstein et al., 1992). Shell disease in crustaceans has also been reported from the sewage sludge and dredge spoils dumping grounds of the New York Bight where the sediments contain high concentrations of heavy metals (Gopalan & Young, 1975; Young & Pearce, 1975). Any link between shell disease and metal accumulation (especially manganese) has still to be proven. The literature on routes of uptake and the sub- sequent effects of manganese in crustaceans and other invertebrates is very sparse. One of the few investiga- tions was carried out by Bryan & Ward (1965). From their work on absorption and loss of manganese by the lobster Homarus gammarus (as H. vulgaris), they concluded that lobsters were efficient body content regulators of manganese, and accumulation even at water manganese concentrations up to 1000 ~g Mn(II) 93