Some direct observations on the ecology and behaviour of the Norway lobster Nephrops norvegicus

A detailed investigation of a small area of sea bed occupied by the Norway lobster Nephrops norvegicus (L.) was carried out by diving and television observations at depths of 30 m in Loch Torridon, Scotland. The density of burrows was 1/2 m², but only a proportion of these were occupied by N. norvegicus. Although about 70% of the larger burrows were occupied by N. norvegicus, giving a density of 1 lobster/8 m², very few juveniles (carapace length less than 30 mm) were found in the area. Many of the small burrows were occupied by the gobiid fish Lesueurigobius friesii (Collett). There was evidence that N. norvegicus frequently change their burrows, and fighting for burrows was observed. N. norvegicus remain within their burrows during the day, emerge around sunset to forage for food during the night, and then return to their burrows at dawn. This, and other aspects of their burrowing behaviour, have a marked effect on the commercial trawl catches of N. norvegicus which show large seasonal and diurnal variations in size and sex composition.     

Observations on the burrows and burrowing behaviour of two mud-dwelling decapod crustaceans,Nephrops norvegicus and Goneplax rhomboides

The burrows of the Norway lobster Nephrops norvegicus (L.) and of the crab Goneplax rhomboides (L.) were studied in Loch Torridon, Scotland. Polyester resin casts of burrows in the sea were made by divers to reveal their subsurface form. Tunnels made by N. norvegicus were usually simple, with two or more openings on the mud surface, and penetrated to a depth of about 30 cm. G. rhomboides burrows did not descend more than about 15 cm beneath the surface, but were usually more complex than the lobster burrows and had several openings. The methods of burrow construction used by the two crustaceans are described from aquarium observations. Neither N. norvegicus nor G. rhomboides show obvious morphological adaptations for burrowing, and it is suggested that the fossorial habit was adopted very early by decapods. The burrows of N. norvegicus do not seem to have assumed any functions in addition to the original one of providing refuge from predators. There is not sufficient known of the biology of the crab to indicate whether the same is true in its case.     

Survival and growth of the Norway lobster Nephrops norvegicus in relation to light-induced eye damage

 The long-term survival and growth of Norway lobsters, Nephrops norvegicus (L.), were examined in relation to light-induced retina breakdown. The incidence of eye damage was first assessed in tagged N. norvegicus released in Loch Torridon, on the west coast of Scotland between 1978 and 1983. Of 34 recaptures examined, all but four showed evidence of eye damage, varying in extent from 1 to 63% of the retina. Additional tagged N. norvegicus were released in Loch Torridon in 1984 and 1985 in order to compare recapture and growth rates in lobsters with and without eye damage. Three groups of N. norvegicus were released; normal sighted, partially sighted (median retina damage = 68%) and fully blinded (retina damage = 100%). From 1217 lobsters released, 235 were recovered by September 1992, when the experiment was concluded. The final proportions of N. norvegicus recaptured were found to be independent of eye-damage condition, and there was no evidence that growth rate was affected by eye damage. Combining all categories of releases, the overall proportion of females recaptured (0.244) was significantly greater than the proportion of males (0.145), suggesting better long-term survival in females than in males. At the time of release, ∼80% of the females were carrying recently spawned eggs. Although the proportion of berried females in the recaptures was slightly reduced in the two eye-damaged groups compared with the normal sighted group, the difference was not statistically significant. It is concluded that light-induced eye damage in N. norvegicus is irreversible, but such damage does not seem to influence their long-term survival, growth or reproduction. Received: 21 October 1998 / Accepted: 26 October 1999     

Small-scale spatial and temporal interactions among benthic crustaceans and one fish species in the Bay of Biscay

In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasière) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus suggested reduced competition for food but also space as both are burrowing species. The observed temporal and spatial activity patterns may contribute to regulating assemblage structure as competing species may be actively foraging at different times and locations thus reducing direct competition.     

Effect of unfavorable trophic scenarios on amylase and protease activity of <Emphasis Type="Italic">Nephrops norvegicus</Emphasis> (L.) larvae during their first vertical migration: a laboratory approach

In Portuguese waters, Nephrops norvegicus larvae hatch at 400–800 m depth and need to perform a vertical migration to food-rich shallower waters to find suitable prey. The effect of suboptimal feeding on digestive enzymes activity of N. norvegicus larvae during this early period of their larval life remains unknown. Protease and amylase activities were investigated ex situ using flurometry in laboratory-hatched larvae exposed to different feeding and/or starving scenarios in the 24 h following hatching, the period during which they typically accomplish their upward vertical migration. Amylase activity was very low in comparison with protease activity, indicating that carbohydrates are not a primary energy reserve. Larvae starved for 12 h and subsequently fed displayed no increase in amylase activity, which suggests that feeding may be required before 12 h post-hatch to trigger amylase activity. Protease activity was high under all feeding conditions, and the increase in protease activity under sustained starvation indicated the catabolism of protein reserves. The ability of first-stage N. norvegicus larvae to metabolize protein reserves may play a decisive role for their survival during their first vertical migration, as it enables them to overcome the deleterious effects of short-term starvation and/or suboptimal feeding.     

Between-individual variation in haemocyanin concentrations in the Norway lobster<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> following exposure to hypoxia and manganese

Environmental hypoxia and the release of reduced manganese (Mn) are often combined stress factors in marine sediments. Previous investigations have shown that hypoxia induces variable responses in the concentration of the respiratory pigment haemocyanin (Hc) of crustaceans. A recent study demonstrated that the magnitude and direction of the changes was dependent on the initial level of Hc in individuals of the Norway lobster Nephrops norvegicus. The changes also took place within 24 h rather than days as suggested by previous studies. In this present study we investigated changes of Hc in individual N. norvegicus in uncontaminated sea water after exposure to and release from realistic hypoxic stress (PO ₂=6.0 kPa). Furthermore we investigated how concomitant exposure to realistic concentrations of manganese (20 mg l ^-1) modified the responses we observed. We confirmed a between-individual variation in response and a change in Hc towards an optimum level after hypoxia, but also showed that changes that took place post-hypoxic exposure occurred over a timescale similar to that of the hypoxic response itself. Manganese exposure resulted in no significant changes in Hc whereas Mn exposure combined with hypoxia resulted in a significant decrease (15%) in all individuals independent of initial Hc. N. norvegicus was thus unable to compensate for the effects of hypoxia by synthesis of Hc after exposure to naturally occurring Mn concentrations.     

Locomotory behaviour and swimming performance of the Norway lobster,Nephrops norvegicus,in the presence of an acoustic tag

Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman     

Biochemical composition of Nephrops norvegicus : changes associated with ovary maturation

Changes in the biochemical composition of the ovary of Nephrops norvegicus (L.) were examined throughout maturation at stations with fast and slow growing individuals in Scottish waters and in the Mediterranean. Ovary index (ovary wt:total body wt) increased significantly with maturation. Lipid, protein and water content of the ovary increased with maturation, while carbohydrate content decreased. Similar changes were also identified in the hepatopancreas. Significant spatial differences in ovary and hepatopancreas composition were identified, which may be related to whole-body growth rate. The ovary maturation scale commonly used for N. norvegicus was shown to reflect biochemically distinct stages in ovary development. Received: 7 February 1997 / Accepted: 25 February 1997     

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     

The eye and some effects of light on locomotor activity in Nephrops norvegicus

The compound eye of Nephrops norvegicus (L.) is of the superposition type, well-adapted to the low levels of light prevailing at the sea bed during the activity periods of the species. Only the proximal retinal shielding pigment responds to light, the distal retinal shielding pigment being in the dark-adapted position at all times. The response of the proximal pigment appears to vary seasonally. Field observations compared light intensity at the sea bed with the numbers of N. norvegicus caught by trawl at various times of day in the Irish Sea in summer and winter. Laboratory experiments were combined with these field data to indicate that light is an important modulator of locomotor activity in this species.     

Fécondité de Nephrops norvegicus dans le golfe de Gascogne

Females of the Norway lobster Nephrops norvegicus (L.) incubate their eggs under the abdomen for a period of several months. We estimated the individual fecundity of N. norvegicus (1) before spawning, and (2) at the end of the incubation period. From these two relationships, we then calculated the average egg loss. Egg loss seems to be relatively higher for small females than for large ones. The mean egg loss estimated for the Bay of Biscay (45%) differs from the only other existing value (75%) calculated by other authors for Portuguese waters. Egg loss may regulate stock-density, and may be a mechanism intervening in stock-recruitment. In order to estimate the fecundity per recruit, fecundity at the end of the incubation period must be used: this takes into account the rate of egg loss as a function of female length.

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Contribution No. 721, du Centre Océanologique de Bretagne     

Swimming performance and endurance of the Norway lobster Nephrops norvegicus

The swimming behaviour of the Norway lobster, Nephrops norvegicus (L.), was studied in the laboratory. The lobsters were stimulated to swim repeatedly until they failed to respond to a single tactile stimulus. The position of the initiating stimulus on the body determined the height of the escape path above the bottom of the tank. A stimulus to the rostrum resulted in a low swimming trajectory, rarely exceeding a height of 0.1 m. A similar tactile stimulus to the abdomen produced higher mean swimming trajectories up to 0.5 m. Several parameters of swimming performance and endurance were measured for each swimming sequence, including distance, duration, mean and maximum velocities and the frequency and number of tail beats. Results showed no significant differences in the average swimming performance and endurance of males and females, but there was a sex difference in the relationship between swimming performance and N. norvegicus size.     

Effect of aerial exposure on concentrations of selected metabolites in blood of the Norwegian lobsterNephrops norvegicus (Crustacea: Nephropidae)

The Norwegian lobsterNephrops norvegicus (L.) collected from Firth of Clyde, Scotland between December 1987 and March 1988, was unable to survive longer than 18 h experimental emersion at 10°C. During this time the partial pressure of oxygen (P O₂) in the venous blood decreased rapidly and the lobster supplemented cellular energy requirements by anaerobic metabolism. This was indicated by the rapid accumulation ofL-lactate in the blood. Although the survival rate increased (to ca 36 to 48 h) if lobsters were kept on ice, the accumulation ofL-lactate in the blood was not significantly different from lobsters at 10°C, despite the temperature difference. There was no indication thatN. norvegicus was able to further metabolize circulatingL-lactate during emersion. On emersion there was also a marked hyperglycemia in the blood due to the stress of handling and asphyxiation. There was fairly good agreement between results obtained during laboratory studies and simulated fishing activity in the Firth of Clyde. Both sets of results are discussed in the context of adaptation to air breathing within the Crustacea and an assesment of post-harvest treatment of lobsters.     

Investigations of carotenoids in some fauna of the Adriatic Sea. III. Leander (Palaemon) serratus and Nephrops norvegicus (Crustacea: Decapoda)

Investigations have been carried out on the carotenoids in Leander (Palaemon) serratus (Pennant) and Nephrops norvegicus (L.) (Crustacea: Decapoda) from the Adriatic Sea. The presence of the carotenoids was determined by means of columnar and thin-layer chromatography. The following carotenoids were found: Leander serratus: -carotene, echinenone, isocryptoxanthin, cryptoxanthin, canthaxanthin, lutein, isozeaxanthin, zeaxanthin, astaxanthin, and astacene; Nephrops norvegicus: -carotene, lutein, zeaxanthin, astaxanthin, and astacene.     

Effects of hypoxia on the respiratory and circulatory regulation of Nephrops norvegicus

The burrowing decapod Nephrops norvegicus (L.) was kept under various degrees of hypoxia in order to measure respiration, heart rate, scaphognathite rate, haemolymph oxygen content and pH. An emergence reaction to hypoxia occurred only in dim light (<10^-2 m-c) or darkness, but after 10 d of moderate hypoxia the decapods showed no emergence response at all. The weight specific respiration of quiescent individuals was relatively low and increased only slightly in hypoxia (P_wO₂=40 torr). Heart rate, about 50 beats min^-1, changed little during hypoxia, down to P_wO₂=40 torr, whereas scaphognathite rates rose from about 60 beats min^-1 at normoxia to peak at 120 beats min^-1 at P_wO₂=40 torr. The oxygen extraction efficiency (E) remained at 20 to 30% during the first hour of hypoxia then rose gradually to maximum values of 30 to 40%. A small respiratory alkalosis of the blood became evident only after 4h of hypoxia (P_wO₂=50 torr). Normoxic postbranchial O₂ tensions (P_aO₂) were low (25–30 torr) and showed only a small decline during hypoxia. Over 10 to 13 d in moderate hypoxia an effective biosynthesis of 0.024 mM haemocyanin individual^-1 d^-1 occurred in fed decapods, whereas controls (normoxic) showed no significant change in pigment levels. A linear relationship between oxygen carrying capacity and haemocyanin concentration was found. It is contended that N. norvegicus is better able to cope with periodic exposure to hypoxia when food of sufficient quantity and quality is available.     

Gender- and oxygen-related irrigation behaviour of the decapod Nephrops norvegicus

The Norway lobster Nephrops norvegicus (L.) inhabits burrows in muddy clay sediments (e.g. on the Swedish west coast), where an autumnal oxygen deficiency in the bottom water can occur. Our experiments investigated whether the irrigation of the burrows would reflect a behavioural adaptation to hypoxia, and whether any gender differences of such behaviour exist. Irrigation is performed by the pleopods which may compensate for a decreasing oxygen tension. Pleopod activity (total number of strokes per sampling time), associated with oxygen concentration and gender, was studied in N. norvegicus kept in artificial burrows resembling their natural habitat. Male and female lobsters were separately exposed to either normoxia (70% oxygen saturation) or hypoxia (30% oxygen saturation). A sexual difference in behaviour was found, where females irrigated the burrow less than males during normoxia. Females showed a significant increase of pleopod activity in hypoxia compared with normoxic conditions, which was not displayed by the males probably due to the degree of individual variation found. However, when only males were studied during progressive hypoxia (from 60 to 5% oxygen saturation), following any changes of irrigational behaviour, a significant increase of accumulated pleopod activity occurred. A major increase of pleopod activity appeared between 60 and 50% oxygen saturation, below which the activity remained high until a critical point (<10% saturation, 11 °C, 33 psu) where irrigation dropped to a level close to that of normoxic values. Activity sessions during hypoxia were longer and had a higher stroke rate than during normoxia. Received: 22 October 1997 / Accepted: 26 February 1998     

Host feeding and nutrient sufficiency for zooxanthellae in the sea anemone Aiptasia pallida

Nutrient sufficiency of zooxanthellae in the sea anemone Aiptasia pallida cultured in low nutrient seawater depends on the availability of particulate food to the host. Zooxanthellae in anemones unfed for 20 to 30 d exhibited the following characteristics of nutrient deficiency: cell division rates decreased; chlorophyll a content gradually decreased from 2 to <1 pg cell^–1; and C:N ratios increased from 7.5 to 16. Over a 3-mo period, algal populations in unfed anemones gradually decreased, indicating that zooxanthellae were lost faster than they were replaced by division. The mitotic index of zooxanthellae in unfed anemones was stimulated either by feeding the host or by the addition of inorganic N and P to the medium. Whether algae are nutrient-limited in hosts under field conditions has not been examined fully; however, C:N ratios in zooxanthellae from field-collected hosts are slightly higher (9.4 vs 7.5) than in hosts fed to repletion in laboratory cultures. This observation might indicate N limitation in the field.     

Mechanism of toxicity of ionic copper and copper complexes to algae

The mechanism of toxicity of ionic copper and copper complexes to growth, photosynthesis, respiration, ATP levels and mitochondrial electron-transport chain-activity in two marine diatoms, Nitzschia closterium (Ehrenberg) W. Smith (Hasle, 1964) and Asterionella glacialis Castracane, and one freshwater green alga, Chlorella pyrenoidosa Chick was investigated. Copper ions depressed both cell division and photosynthesis in A. glacialis and C. pyrenoidosa, whereas ionic copper concentrations which were inhibitory to cell division in N. closterium had no effect on photosynthesis, respiration, ATP production, electron transport or membrane ultrastructure. This suggests that in N. closterium, copper does not act on the chloroplast, the mitochondrion, or the cell membrane, since if it did, the above parameters should be affected. Copper-ethylxanthogenate was exceptional amongst the copper complexes in that it stimulated respiration, mitochondrial electrontransport and ATP formation in N. closterium under conditions of strongly inhibited cell division and slightly stimulated photosynthesis. Ionic copper toxicity may result from an intracellular reaction between copper and reduced glutathione (GSH), leading to a lowering of the GSH:GSSG ratio and suppression of mitosis. In addition, copper inhibits the enzyme catalase and reduces cell defence mechanisms against H₂O₂ and oxygen-free radicals. Lipid-soluble copper complexes are more toxic than ionic copper because both the metal and the ligand are introduced into the cell. Toxicity of ionic copper is ameliorated by trivalent metal ions in the growth medium, including those of Mn, Co, Al, Fe and Cr which form a layer of metal (III) hydroxide around the algal cell, adsorb copper and reduce its penetration into the cell. The degree of insolubility of the metal (III) hydroxide is related to its ability to protect against copper toxicity. In addition, manganese and cobalt catalytically scavenge damaging H₂O₂ and superoxide radicals, respectively, produced by the cell.     

Mechanism of toxicity of zinc to the marine diatomNitzschia closterium

The effect of zinc on cell division, photosynthesis, ultrastructure, respiration, ATP levels, mitochondrial electron-transport chain (ETC)-activity, total thiols and glutathione in the marine diatomNitzschia closterium (Ehrenberg) W. Smith was investigated. Although 65µg Zn 1^–1 halved the cell division rate, photosynthesis and respiration were unaffected by zinc concentrations up to 500µg Zn 1^–1. Most of the zinc associated with the cells was bound at the cell surface, with only 3 to 4% of this extracellular zinc penetrating the cell membrane. Once inside the cell, zinc exerted its toxicity at a number of sites. Increased ATP production and ETC activity were observed in zinc-treated cells. Zinc also enhanced cellular thiols (SH) and total glutathione, and zinc toxicity was reversible by the addition of thiol compounds such as cysteine. Zinc-thiol binding may be a detoxification mechanism for the cell. It is suggested that increased ATP production may provide the energy required for increased glutathione synthesis at the expense of other energy-requiring processes including cell division. The mechanisms of toxicity of ionic zinc and copper toN. closterium were compared.     

Effects of ambient ammonia levels on blood ammonia, ammonia excretion and heart and scaphognathite rates of Nephrops norvegicus

During commercial handling of Nephropsnorvegicus (L.) there are a number of situations when the prawns may be exposed to very high ambient ammonia levels. These experiments evaluated the effects of increased levels of ambient total ammonia (TA = NH₃ + NH₄ ⁺) on␣blood ammonia, ammonia efflux rates and on the cardio-ventilatory performance of N. norvegicus. When prawns were taken from <1 to 2000 μmol TA l⁻¹ medium, blood TA concentrations increased rapidly for the first 2 h but tended to drop thereafter. Original blood TA levels were restored 6 h after the prawns were transferred back from seawater containing 2000 to <1 μmol TA l⁻¹. Sudden exposure to 500, 1000, 2000 or 4000 μmol TA l⁻¹ medium induced blood TA concentrations to increase respectively to 50, 30, 33 and 36% of external concentrations (normally, internal TA values are much higher than external levels). Immediately after transfer back to seawater with low ammonia concentration ( <1 μmol TA l⁻¹), excretion rates were higher than those of control prawns, and the absolute amounts of TA excreted were considerably higher than those calculated to have accumulated in the haemolymph. Heart rate (HR) and scaphognathite rate (SR) were not altered when prawns were subjected to sudden alterations in ambient ammonia ( <1 to 2000 to <1 μmol TA l⁻¹). When water ammonia concentrations were altered more gradually, both rates increased, but only at 4000 μmol TA l⁻¹. These results show that N. norvegicus is able to remove ammonia from the haemolymph and/or transform ammonia into some other substance when subjected to increased levels of ambient ammonia. Possible mechanisms involved (e.g. active transport across the gills; storage in some other tissue; glutamate synthe sis) are discussed. Received: 20 May 1996 / Accepted: 1 July 1996