Effects of sulfide exposure history and hemolymph thiosulfate on oxygen-consumption rates and regulation in the hydrothermal vent crab Bythograea thermydron

The hydrothermal vent crab Bythograea thermydron is exposed to high environmental concentrations of sulfide and low levels of oxygen for extended periods of time. It has previously been shown that hydrogen sulfide is oxidized to the relatively non-toxic thiosulfate (S₂O ₃ ^2– ), which accumulates in the hemolymph. Hemolymph thiosulfate levels in freshly captured crabs vary significantly among crabs from different hydrothermal vent sites as well as between crabs from different microhabitats within the same site. Hemolymph thiosulfate concentrations were not significantly different between crabs captured at the same site 6 mo apart. Hemolymph thiosulfate concentrations ranged from 66 mol 1^–1 in a crab captured at a site with relatively low sulfide venting, to 3206 mol 1^–1 in an individual that was netted from an active smoker vent with much higher sulfide exposure. The differences in hemolymph thiosulfate between sites and the stability of hemolymph thiosulfate in crabs captured at the same site at different times suggest that sulfide exposure is significantly different between sites and that this exposure may not vary significantly over the course of a few months. B. thermydron experimentally exposed to sulfide had high levels of thiosulfate in their hemolymph and increased abilities to regulate oxygen consumption in conditions of low oxygen. This enhancement of regulatory abilities suggests that the previously demonstrated increased hemocyaninoxygen (Hc–O₂) affinity due to elevated thiosulfate may be adaptive in vivo. Average oxygen-consumption rates were much higher in crabs experimentally exposed to sulfide than in unexposed crabs. Crabs injected with isosmotic thiosulfate did not have increased oxygen-consumption rates as did the sulfide-exposed individuals, but did show a similar reduction in P _c (the critical partial pressure of oxygen at which crabs can no longer regulate oxygen consumption). This suggests that it is the sulfide exposure and/or detoxification rather than the elimination of thiosulfate that causes the increase in metabolic rate. Thiosulfate diffuses into dead crabs and into live crabs exposed to 15 mmol S₂O ₃ ^2- l^–1, indicating substantial permeability, and yet live crabs are able to eliminate thiosulfate when incubated in sea water containing 1.5 mmol S₂O ₃ ^2- l^–1, suggesting a process that has an active component.     

Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi

Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi Bernard was studied in native hemolymph samples. Clams were collected from two different reducing environments, beneath log booms in Alberni Inlet, British Columbia, Canada, and from the sewage effulent in Santa Monica Bay, California, USA. The hemocyanin concentration in a pooled hemolymph sample (n = 10 individuals) was 33.5 mg ml⁻¹. The mean hemolymph pH of five Alberni clams maintained for 3 wk in mud was 7.96 ± 0.06. No significant variation in hemocyanin oxygen-affinity or cooperativity was found for hemocyanin in whole hemolymph samples from these five individually studied clams. There was a significant difference only at 15 °C in the oxygen affinity of hemocyanin in pooled whole-hemolymph samples from S. reidi collected from Alberni Inlet compared with clams collected from Santa Monica Bay. Little effect of temperature on hemocyanin oxygen-affinity was found for temperatures below 20 °C; above 20 °C, the oxygen affinity was reduced for clams from both sites. Temperature and pH had no apparent affect on hemocyanin cooperativity. Moderate Bohr shifts were found at all temperatures examined. The presence of physiologically relevant concentrations of thiosulphate in hemocyanin samples resulted in a decrease in hemocyanin oxygen-affinity, opposite to the effect on hemocyanin found for the hydrothermal vent crab Byth-ograea thermydron, but thiosulphate had no effect on hemocyanin cooperativity. Received: 2 September 1997 / Accepted: 6 February 1998     

Effects of three different nanoparticles on bioaccumulation,oxidative stress,osmoregulatory, and immune responses of Carcinus aestuarii

Abstract

In this study, the toxicity of CuO (40?nm), α-Al₂O₃ (40?nm), and α-Fe₂O₃ (20–40?nm) nanoparticles was comparatively investigated on Carcinus aestuarii. Crabs were semi-statically exposed to 1?mg/L of each for 14?days and their accumulation and distribution in tissue and hemolymph, potential oxidative stress mechanism, total hemocyte counts and types, and the osmoregulatory and ionoregulatory responses were determined. The tissue distribution of CuO nanoparticles was hepatopancreas?>?hemolymph?≥?gill?> muscle, for α-Fe₂O₃ gill?>?hepatopancreas?>?muscle?> hemolymph, and for α-Al₂O₃ gill?>?muscle?≥?hemolymph?> hepatopancreas. While α-Al₂O₃ and α-Fe₂O₃ NPs, induced lipid peroxidation and changes in antioxidant enzyme activity in the hepatopancreas tissue, the oxidative damage caused by the CuO nanoparticles was minimal. All three nanoparticles, copper in particular, elicit osmoregulatory and ionoregulatory toxicity at this concentration, due to the inhibition of Na⁺, K⁺-ATPase activity in the gill and depletion of hemolymph and carcass ion concentrations.     

Behavioural and physiological responses of the Norway lobster,<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> (Crustacea: Decapoda), to sulphide exposure

The Norway lobster, Nephrops norvegicus, is moderately tolerant of sulphide [the lethal time to 50% mortality (LT₅₀) was 22.5 h when exposed to 500 M sulphide] but, whenever possible, it attempts to avoid the presence of sulphide in its immediate vicinity. Any sulphide entering the animal is oxidized to thiosulphate, which accumulates in the haemolymph and in the tissues. During exposure to low concentrations of sulphide, the rate of oxygen consumption is maintained or even enhanced even though the lobsters become quiescent. The apparent increase in oxygen consumption is probably due to the oxidation of sulphide to thiosulphate. At higher concentrations, oxygen consumption decreases, perhaps because of the inhibitory effect of sulphide on electron transport, and N. norvegicus resorts to anaerobic metabolism as indicated by the accumulation of lactate in the haemolymph and in the tissues.Communicated by L. Hagerman, Helsingør     

Metabolic disposition of lactate in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria

The metabolism of ¹⁴C-labelled lactate was investigated in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria. When a bolus of (¹⁴C-U)-D-lactate was injected into L. polyphemus, there was substantial release pf ¹⁴CO₂ into the medium. In the case of M. mercenaria, ¹⁴CO₂ release was also observed after injection of (¹⁴C-U)-L-lactate into experimental individuals. Analysis of the distribution of radioactivity in whole body extracts of both species revealed easily detectable amounts of radioactivity in the glycogen fraction, although the bulk of the radioactivity was in the cation, anion/neutral and CO₂ fractions. To investigate the metabolism of lactate further, ¹⁴C-labelled lactate was injected into large individuals of L. polyphemus and M. mercenaria, and the distribution of radioactivity was determined in the hemolymph, muscle and hepatopancreas. Utilization of (¹⁴C-U)-D-lactate by L. polyphemus resulted in the accumulation of significant amounts of labelled glucose in all three body compartments as well as the production of labelled glycogen in the telson levator muscle and hepatopancreas. Utilization of (¹⁴C-U)-L-lactate resulted in a similar pattern of glucose and glycogen labelling in the hemolymph, cheliped muscle and hepatopancreas of M. mercenaria. These studies demonstrate that both L. polyphemus and M. mercenaria have the capacity for glyco- and gluconeogenesis using lactate as the substrate.     

Fungicidal activity and molecular modeling of fusarubin analogues from Fusarium oxysporum

Abstract

Fusarubin analogues of Fusarium oxysporum f. sp. ciceris were investigated for antifungal activity in vitro against five soil borne phytopathogenic fungi. 3-O-Methyl-8-O-methyl-fusarubin was inhibitory towards S. sclerotiorum (EC₅₀ 0.33?mmol L^?1) and Sclerotium rolfsii (EC₅₀ 0.38?mmol L^?1). A structure–antifungal activity relationship of fusarubin analogues was established from their activity performance. Possible mechanism of action of these compounds was studied using molecular docking and simulations against three target enzymes which revealed receptor ligand binding affinity. Docking of 3-O-methyl-8-O-methyl-fusarubin into the succinate dehydrogenase site revealed formation of salt bridge, hydrogen bond, π–anion, π–alkyl, and Van der Waals interactions.     

Photosynthetic utilization of CO2(aq) and HCO 3 - in Thalassia testudinum (Hydrocharitaceae)

The effects of total dissolved inorganic carbon (DIC), free carbon dioxide [CO_2(aq)], and bicarbonate (HCO ₃ ^- ) concentrations on net photosynthetic oxygen evolution of the marine angiosperm Thalassia testudinum Banks ex König collected from Biscayne Bay (1988) and from Tampa Bay (1990), Florida, USA, were examined. Rates of photosynthesis declined by 85% from pH 7.25 to 8.75 in buffered seawater media with constant DIC concentration (2.20 mM), suggesting a strong influence of CO_2(aq) concentration. A plateau in the pH-response curve between pH 7.75 and 8.50 indicated possible utilization of HCO ₃ ^- . Responses of photosynthesis measured in buffered seawater media of varying DIC concentrations (0.75 to 13.17 mM) and pH (7.8 to 8.61) demonstrated that photosynthesis is rate-limited at ambient DIC levels. Photosynthesis increased in media with increasing HCO ₃ ^- concentrations but near-constant CO_2(aq) levels, confirming HCO ₃ ^- assimilation. Calculated half-saturation constants (K _s )for CO_2(aq) and HCO ₃ ^- indicated a high affinity for the former [K _s (CO₂)=3 to 18 M] and a much lower affinity for the latter [K _s (HCO ₃ ^- )=1.22 to 8.88 mM]. Calculated V _max values for HCO ₃ ^- were generally higher than those for CO_2(aq), suggesting relatively efficient HCO ₃ ^- utilization, despite the apparent low affinity for this carbon form.     

Inhibitory effect of the iron chelator desferrioxamine (Desferal) on the generation of activated oxygen species by Chattonella marina

Recent studies demonstrated that the toxic red tide phytoplankton Chattonella spp. produce activated oxygen species such as superoxide anion (O ₂ ^- ), hydrogen peroxide (H₂O₂), and hydroxyl radicals (·OH), which may be responsible for the toxicity of this flagellate. However, the mechanism behind the production of these oxygen radicals and H₂O₂ by Chattonella spp. is largely unknown, and the physiological significance of activated oxygen species for Chattonella spp. is also unclear. In the present study, we investigated the involvement of iron in the generation of O ₂ ^- and H₂O₂ by C. marina. The generation of O ₂ ^- by C. marina was related to the growth phase; the highest rate of O ₂ ^- production was observed during the exponential growth phase. However, no such increase during the exponential growth phase was observed in C. marina growing in an iron-deficient medium, even though the growth of C. marina was not significantly affected by iron-deficiency during the first 4 d. In addition, the iron chelator desferrioxamine (Desferal) strongly inhibited the generation of both O ₂ ^- and H₂O₂ by C. marina in a concentration-dependent manner. The growth of C. marina was also inhibited by Desferal. Furthermore, in the presence of 500 M Desferal, C. marina-induced growth inhibition of the marine bacteria Vibrio alginolyticus was almost completely abolished. These results suggest that iron is required for the generation of activated oxygen species by C. marina, as well as for its own growth.     

Absence of sterol synthesis in larvae of the mud crab Rhithropanopeus harrisii and of the spider crab Libinia emarginata

A dietary requirement for sterols in crustacean larvae was established by the use of isotopic tracer techniques. Larvae of the mud crab Rhithropanopeus harrisii and larvae of the spider crab Libinia emarginata were exposed to acetate-¹⁴C or mevalonate-¹⁴C. Radioanalysis of the fatty acids of each species indicated sufficient incorporation of acetate for lipid synthesis. No radioactivity was detected in the sterols of animals exposed to either acetate-¹⁴C or mevalonate-¹⁴C. It was concluded that R. harrisii and L. emarginata larvae are unable to synthesize sterols from acetate or mevalonate and, therefore, require them in their diet.     

Bioturbation effects of the amphipod Corophium volutator on microbial nitrogen transformations in marine sediments

Microcosms containing different densities of Corophium volutator, ranging from 0 to 6000 ind m^-2, were incubated in a flow-through system. Benthic fluxes of CO₂, O₂, NO₃ ^- and NH₄ ⁺ were measured regularly. Thirteen days after setup the microcosms were sacrificed and sediment characteristics, pore water NO₃ ^-, NH₄ ⁺ and exchangeable NH₄ ⁺ concentrations, and potential nitrification activity were measured. The presence of C. volutator increased overall mineralization processes due to burrow construction and irrigation. The amphipods increased the ratio CO₂/O₂ fluxes from 0.73 to 0.86 in microcosms inhabited by 0 and 6000 ind m^-2, respectively. Burrow ventilation removed NH₄ ⁺ from the sediment, which was nitrified in the oxic layer and transported NO₃ ^- to the burrow sediment, where denitrification potential was enhanced. Nitrification and total denitrification rates (denitrification of NO₃ ^- coming from the overlying water and of NO₃ ^- generated within the sediment) were calculated and discussed. Bioturbation by C. volutator increased both nitrification and denitrification, but denitrification was stimulated more than nitrification. Denitrification of NO₃ ^- coming from the overlying water was stimulated 1.2- and 1.7-fold in microcosms containing 3000 and 6000 ind m^-2 relative to control microcosms. The presence of C. volutator (6000 ind m^-2) stimulated nitrogen removal from the system, as dinitrogen, 1.5-fold relative to non-bioturbated microcosms. C. volutator individuals used in our study were collected from Norsminde Fjord, Denmark, in 1990.     

Life on the edge: physiological problems in penaeid prawns <Emphasis Type="Italic">Litopenaeus stylirostris</Emphasis>, living on the low side of their thermopreferendum

The underlying physiological mechanisms explaining why the adult penaeid prawn Litopenaeus stylirostris cannot successfully face heavy stressful events on the low edge of its thermopreferendum (20–22°C) were studied during the austral winter. Prawns were studied during recovery from net fishing and rapid transfer from outdoor earthen ponds into indoor facilities. This was assimilated to a predator–prey interaction. O₂-consumption, hemolymph osmotic pressure (OP_h), arterial O₂ partial pressure (PO₂), a–v O₂-capacitance and mortality rates were analysed. Data were compared to similar challenges performed at 28°C during the austral summer. At 20–22°C, mortality of up to 70% was observed after 2 days whereas at 28°C, maximum mortality was 3–5%. Mortality occurred when OP_h shifted towards equilibrium with seawater, the resting O₂-consumption, the a–v O₂-capacitance and the arterial PO₂ went down to minimal values. These events can be counterbalanced by transiently hyper-oxygenating the hemolymph or by blocking the OP_h shift in isosmotic water (Wabete et al. in Aquaculture 260:181–193, 2006): both led to a dramatic decrease in mortality. It is concluded that in penaeid prawns L. stylirostris, a mismatch between O₂-demand and O₂-supply contributes to setting the geographical limits for this animal species through an impairment of their hemolymph O₂-carrying capacity during heavy stressful events like chasing by predators.     

Physiological role of branchial carbonic anhydrase in the shore crabCarcinus maenas

Excretion of total CO₂ and uptake of sodium and chloride ions across the branchial epithelium of the posterior gills of the shore crabCarcinus maenas, collected from Kiel Bay (Baltic Sea) in 1989, were measured using isolated perfused gill preparations. Total CO₂ effluxes depended on the HCO ₃ ^- concentration of the internal perfusate in a saturable mode and were inhibited by internally and externally applied acetazolamide at 10^–4 M. Potential differences between hemolymph space and medium did not change significantly during experimental treatments. Neither a bicarbonate gradient (6 mM) directed from the internal perfusate to external bath solution nor symmetrically applied 10^–4 M acetazolamide significantly influenced the influxes of Na⁺ and Cl^–. Results confirmed the role of carbonic anhydrase in CO₂ excretion but called into question the assumed functioning of the enzyme in branchial ion transport processes.     

Effect of copper on ion- and osmoregulation in the shore crab Carcinus maenas

The uptake and effect of dissolved copper on regulation of hemolymph osmolality and Na⁺, K⁺, Cl^-, Ca⁺⁺, and Mg⁺⁺ concentrations in the shore crab Carcinus maenas (L.) were determined at 400 mOsm (=14 S) ambient salinity. One mg Cu l^-1 resulted in 50% mortality in 11 to 22 d; the highest sensitivity was observed around the moulting period. 0.25 and 0.5 mg Cu l^-1 were not lethal after a onemonth exposure. Ten, 1, and 0.5 mg Cu l^-1 altered regulation of osmolality, Na⁺, K⁺, and Cl^- concentrations, while 0.25 mg Cu l^-1 did not. Exposure to 1 mg Cu l^-1 reduced hemolymph osmolality and Na⁺, K⁺, and Cl^- concentrations to 80 to 90% of controls within 4 to 6 d and no further reduction was observed during a 21-d exposure. The effect of various copper concentrations on these four parameters were almost identical and the highest sensitivity was observed around the moulting period. Hemolymph calcium levels increased 20 to 80% in crabs exposed to 1 mg Cu l^-1, while they decreased 20 to 30% in crabs exposed to 0.5 mg Cu l^-1. Prolonged exposure to copper caused 20 to 70% reductions in hemolymph magnesium levels. Crabs exposed to 0.5 mg Cu l^-1 for 29 d accumulated copper in hepatopancreas, gills, carapace, heart, testes, and hypodermis, but not in muscles and hemolymph. Increased copper levels in crabs exposed to 0.25 mg Cu l^-1 were observed in hepatopancreas, gills, and carapace only. The present results suggest that effects of copper on ion regulatory processes in part explain why the toxicity of copper towards euryhaline invertebrates increases at low salinities.     

Acid–base regulation in the Dungeness crab (Metacarcinus magister)

Homeostatic regulation allows organisms to secure basic physiological processes in a varying environment. To counteract fluctuations in ambient carbonate system speciation due to elevated seawater pCO₂ (hypercapnia), many aquatic crustaceans excrete/accumulate acid–base equivalents through their gills; however, not much is known about the role of ammonia in this response. The present study investigated the effects of hypercapnia on acid–base and ammonia regulation in the Dungeness crab, Metacarcinus magister on the whole animal and isolated gill levels. Hemolymph pCO₂ and [HCO₃ ^?] increased in M. magister acclimated to elevated pCO₂ (330 Pa), while pH remained stable. Additionally, hemolymph [Na⁺], [Ca²⁺], and [SO₄ ^2?] were significantly increased. When challenged with varying pH during gill perfusion, the pH of the artificial hemolymph remained relatively unchanged. Overall, ammonia production and excretion, as well as oxygen consumption, were reduced in crabs acclimated to elevated pCO₂, demonstrating that either (amino acid) oxidation is reduced in response to this particular stress, or nitrogenous wastes are excreted in an alternative form.     

Photosynthetic carbon acquisition in the red alga Gracilaria conferta

In this continuing study on photosynthesis of the marine red alga Gracilaria conferta, it was found that ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in crude extracts had a K _m (CO₂) of 85 M. Since seawater contains only ca. 10 M CO₂, it appears that this alga must possess a CO₂ concetrating system in order to supply sufficient CO₂ to the vicinity of the enzyme. Because this species is a C₃ plant (and thus lacks the C₄ system for concentrating CO₂), but can utilize HCO₃ ^- as an exogenous carbon source, we examined whether HCO₃ ^- uptake could be the initial step of such a CO₂ concetrating system. The surface pH of G. conferta thalli was 9.4 during photosynthesis. At this pH, estimated maximal uncatalyzed HCO₃ ^- dehydration (CO₂ formation) within the unstirred layer was too slow to account for measured phostosynthetic rates, even in the presence of an external carbonic anhydrase inhibitor. This observation, and the marked pH increase in the unstirred layer following the onset of light, suggests that a HCO₃ ^- transport system (probably coupled to transmembrane H⁺/OH^- fluxes) operates at the plasmalemma level. The involvement of surface-bound carbonic anhydrase in such a system remains, however, obscure. The apparent need of marine macroalgae such as G. conferta for CO₂ concentrating mechanisms is discussed with regard to their low affinity of Rubisco to CO₂ and the low rate of CO₂ supply in water. The close similarity between rates of Rubisco carboxylation and measured photosynthesis further suggests that the carboxylase activity, rather than inorganic carbon transport and intercoversion events, could be an internal limiting factor for photosynthetic rates of G. conferta.     

Respiration as a function of oxygen concentration in intertidal barnacles

Respiration as a function of oxygen concentration was studied in two species of intertidal barnacles: Balanus amphitrite amphitrite ¹ (Darwin) and B. tintinnabulum tintinnabulum (L.). A critical oxygen tension was observed in both species below which the respiratory regulation broke down. In B. amphitrite amphitrite the critical oxygen tension was 2.5 ml O₂/l, and in B. tintinnabulum tintinnabulum 3.5 ml O₂/l. Species differences and habitat relations were observed in both species in their respiratory adaptation to oxygen concentration. B. amphitrite amphitrite which inhabits oxygen-deficient areas was able to regulate to much lower concentrations than B. tintinnabulum tintinnabulum which inhabits oxygen-rich open intertidal regions.     

Carotenoids indicate differences in diet of the hydrothermal vent crabBythograea thermydron (Brachyura)

Carotenoid pigments were used as markers to investigate the sources of energy to two deep-sea hydrothermal vent communities. Specimens of the hydrothermal-vent brachyuran crabBythograea thermydron were collected at 2 500 m depth from the Rose Garden vent site in the Galápagos Rift Valley in February, November and December 1979, and 2 600 m depth on the East Pacific Rise at 21°N in May 1982. Four carotenoids (astaxanthin, canthaxanthin, echinenone and beta-carotene) have been identified as the pigments responsible for the red color of the eggs of the crabs from the Galápagos Rift site. Consistent with the fact that animals are unable to synthesize carotenoidsde novo, precursors were not present in the crabs' tissues, affirming that these pigments are of dietary origin. The number of ovigerous female crabs and the concentrations of carotenoids in the eggs suggest a readily available source of these pigments in the Galápagos vent environment. In contrast, the developing eggs ofB. thermydron from the 21°N vent site were cream-colored, with only trace quantites of carotenoids and fewer types of carotenoids. Analysis of carotenoid distribution in both females and males in these two populations indicates a very low level of carotenoids in the diet of the 21°N vent crabs, and reflects differences in trophic interactions and primary production at the two vent sites. The few types and low concentration of carotenoids inB. thermydron indicate a diet that is different from non-vent, deep-sea crustaceans. We hypothesize that the source of carotenoids are bacteria within the vent community, and not ultimately from photosynthetic production.     

Functional morphology and significance of the circulatory system of Ostracoda,exemplified by Vargula hilgendorfii (Myodocopida)

Combined high-resolution video-recordings of live specimens, SEM and serial microtome sections were used to document the morphofunctional aspects of blood (hemolymph) circulation in Ostracoda, exemplified by the nektobenthic myodocopid Vargula hilgendorfii from Japan. The circulatory system is comprised of a single-chambered dorsal heart (pericardium, myocardium with two ostia), efferent vessels (aorta and secondary arteries) and an integumental afferent network of sinuses radiating from the adductor muscle area to a peripheral channel leading to heart. The heartbeat and the linear velocity of hemolymph in sinuses range from 0.5 to 6 times s^-1 and 200 to 1000 m s^-1, respectively. Hemocytes (10 to 17 m) of irregular shapes occur within the circulating hemolymph. This typical open circulatory system is found in most myodocope ostracodes and other crustaceans. It is totally absent in small (mostly <2 mm) ostracodes such as Podocopa. We conclude that the fluid convection of hemolymph augments the diffusion process of O₂ in larger animals. Oxygen uptake is assumed to occur preferentially through the inner (posterior) surface of the carapace where hemolymph sinuses are best developed and in close contact with sea water. Hemocytes may be involved in coagulation processes as in other crustaceans (e.g. Decapoda). Integumental circulation, preserved as anastomosing features in fossil Ostracoda, is known from the early Palaeozoic through to the Recent.     

Influence of the polychlorinated biphenyl preparation Aroclor 1242® on color changes of the fiddler crab Uca pugilator

The melanin in the melanophores of specimens of the fiddler crab, Uca pugilator, exposed to 2, 4, and 8 ppm solutions of the polychlorinated biphenyl (PCB) preparation, Aroclor 1242^®, became less dispersed than in untreated specimens. This effect was dose-dependent. It was probably due to the PCB itself and not to polychlorinated dibenzofurans which are contaminants of commercial PCBs. The decreased melanin dispersion appeared to be related to a decrease in the rate of release of melanin-dispersing hormone from eyestalk neuroendocrine cells into the hemolymph. Eyestalks of crabs kept for 4 days in Aroclor 1242 contained 4 times as much melanin-dispersing hormone as did control crabs. When injected into isolated legs, did hemolymph from control crabs. Aroclor 1242 did not appear to have a direct effect on the pigment-dispersing mechanism of the melanophores.     

Natural food,foregut clearance-rate and activity of the crab Scylla serrata

The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e^0.033x , where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved.