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     

The burrows and physiological adaptations to a burrowing lifestyle of Natatolana borealis (Isopoda: Cirolanidae)

The isopod Natatolana borealis Lilljeborg constructs U-shaped burrows in soft mud, the bore of which closely approximates the width of the occupant. Within artificial burrows, the isopods are largely quiescent and often adopt a position close to one of the burrow openings. Conditions within burrows constructed in the laboratory are moderately hypoxic [11.7 to 14.9 kPa (88 to 112 torr)], with isopods showing discontinuous irrigation behaviour (pleopod beating). Rates of oxygen consumption (measured at 10°C) are maintained approximately constant over a wide range of oxygen partial pressure (P_{O 2}) due, in part, to a pronounced increase in pleopod beat rate. Values for the critical partial pressure of oxygen (P_c), the P_{O 2} at which can no longer be maintained independent of P_{O 2}, were 2.0 to 3.3 kPa (15 to 25 torr). N. borealis can survive lengthy periods (65 h at 5°C) of anoxia, during which there is a significant reduction in the carbohydrate concentration and an increase in the l-lactate concentration of the tissues. The oxygencarrying capacity of the haemolymph of N. borealis was low. The haemocyanin showed a relatively high oxygen affinity [P₅₀=0.39 kPa (2.99 torr) at 10°C at the in vivo pH of 7.80] and a pronounced Bohr effect (-1.22). These characteristics may be advantageous to a burrowing mode of life and also for the conditions likely to be encountered in fish carcasses into which they burrow en masse to feed.     

Larval development of Euphausia nana (Crustacea: Euphausiacea)

The larvae of Euphausia nana Brinton in Sagami Bay and Suruga Bay, Central Japan, are described and illustrated. The furcilia stage is separated into six stages on the basis of the form of the pleopods and the number of terminal telson spines. Furcilia I, no pleopod or non-setose pleopods and seven terminal telson spines. Furcilia II, nonsetose and setose pleopods and seven terminal telson spines. Furcilia III, five pairs of setose pleopods and seven terminal telson spines. Furcilia IV, five pairs of setose pleopods and five terminal telson spines. Furcilia V, five pairs of setose pleopods and three terminal telson spines. Furcilia VI, five pairs of setose pleopods and one terminal telson spine. Segmentation of the antennal endopod and mandible palp occurred at the furcilia V stage. The dominant forms of early furcilia larvae of E. nana differed during different seasons of the year. The total lengths of calyptopis III and furcilia I to VI larvae also showed seasonal changes; they were largest in May and smallest from September to December.     

A stereoscan electron microscope study of male reproductive characters in the Jaera albifrons group of species (Crustacea: Isopoda)

The male secondary sex characters of Jaera albifrons Leach, Jaera ischiosetosa Forsman, Jaera praehirsuta Forsman and Jaera forsmani Bocquet are described with the Stereoscan electron microscope (S.E.M.). These characters, which are present on the peraeopods, are the only means of identification for these Jaera species which together form the Jaera albifrons group (Isopoda, Asellota). The male praeoperculum (modified, fused, first pair of pleopods) and appendix masculinae (modified endites of the second pair of pleopods) have also been studied with the S.E.M. and possible functions of the various sex characters are discussed. Both the male operculum and appendix masculinae are similar for each species, suggesting that copulation with females of a different species is anatomically possible. The fact that hybrids are rarely collected in ecological investigations is discussed with reference to the present known information. Two methods of copulation for the members of this group have been proposed and these are discussed. A method of sperm transfer along the male operculum is outlined.     

Effect of temperature and food on the heart beat,ventilation rate and oxygen uptake of Mytilus edulis

The heart beat, ventilation rate and oxygen uptake of Mytilus edulis L. were measured simultaneously, in response to changes in temperature and food level. There was no thermal acclimation of heart-beat frequency or amplitude to temperatures from 5° to 25°C. Oxygen consumption and ventilation rate acclimated to 10°, 15° and 20°C, but not to 25°C. Starvation reduced the rate of oxygen uptake and heart-beat frequency to a standard level and, in response to food, the ventilation rate and oxygen consumption immediately increased to an active level. Feeding was maintained after the initiation of active metabolism, and during the following 10 days the heart-beat frequency gradually increased to the level characteristic of fed individuals. There was no direct correlation between the rate of oxygen consumption and heart rate, and an apparent absence of a close nervous coupling between ventilation rate and heart rate in M. edulis.     

Calorimetric studies on the energy metabolism of an infaunal bivalve,Abra tenuis,under normoxia,hypoxia and anoxia

Direct calorimetry was employed to measure the energy metabolism of infaunal bivalves, Abra tenuis, collected from a tidal lagoon in the Fleet, southern England, in June 1989, at various oxygen partial pressures. A significant anaerobic component (i.e., 20% of total metabolic rate) was detected under normoxia, presumably brought about by the intermittent ventilatory activity of this bivalve under these conditions. Under hypoxia (2.3 to 10 kPa, or 11 to 48% of full air saturation), however, the energy metabolism was maintained fully aerobic; the measured heat equivalent of oxygen uptake was not significantly different from the theoretical ranges for fully aerobic catabolism. Under anoxia, the rate of heat dissipation was reduced to 5–6% of the normoxic rate of heat dissipation. This conserves energy expenditure and would thus increase resistance of A. tenuis to anoxia or emersion. Physiological compensation by A. tenuis under conditions of declining oxygen tension involved a marked increase in ventilation rate. Comparison between fed and starved individuals indicated that costly physiological processes, such as digestion, absorption and growth declined at 10 and 5 kPa and were arrested at P_{O 2} (oxygen partial pressure) levels below 2.3 kPa. The present study provides evidence that there are no major differences between the metabolic responses of epifaunal suspension-feeding (eg. Mytilus edulis) and infaunal deposit-feeding (eg. A. tenuis) bivalves when exposed to environmental hypoxic stress.     

Simultaneous hermaphroditism in the marine shrimp Lysmata wurdemanni (Caridea: Hippolytidae): an undescribed sexual system in the decapod Crustacea

Simultaneous hermaphroditism with outcrossing, a previously unconfirmed sexual system in decapod crustaceans, is documented in the shrimp Lysmata wurdemanni (Gibbes), using time-lapse video observations on mating in pairs of “female-phase” (FP) individuals. Copulations between FPs resulted in successful spawning and development of embryos. However, female-phase hermaphrodites maintained in isolation were unable to self-fertilize spawned eggs. All smaller individuals possessed characters typical of caridean males, including male gonopores, appendices masculinae, ejaculatory ducts, and cincinnuli on the first pleopods. However, the gonad of these male-phase (MP) individuals was an ovotestis with an undeveloped ovarian portion. FPs, which spawn eggs and incubate embryos, also had male gonopores and an ovotestis terminating in ejaculatory ducts containing sperm. In FPs, male pleopod characters were absent or reduced, and a female incubatory character, expanded pleopod flanges, showed a greater relative size. Smaller size classes of the population were composed only of MPs while larger size classes consisted of both MPs and FPs. “Transitionals,” individuals with MP characters but an ovotestis containing vitellogenic oocytes, were rare and overlapped completely in size with FP and larger MP individuals. It is suggested that not all MPs transform into FP hermaphrodites. Social interactions may mediate MP change into FP hermaphrodites in L. wurdemanni. The social system of L. wurdemanni and other Lysmata spp. may determine the exact form of the sexual system in these species. Received: 26 October 1997 / Accepted: 21 April 1998     

Direct measurement technique for determining ventilation rate in the deposit feeding clam Macoma nasuta (Bivalvia,Tellinaceae)

An exposure chamber, the clambox, was developed to measure ventilation rate, sediment processing rate, and efficiency of pollutant uptake by Macoma nasuta conrad, a surface deposit-feeding clam. Clams, collected from Yaquina Bay, Oregon, USA, were cemented into a hole in a piece of rubber dental dam so that the inhalant and exhalant siphons were separated by a membrane. The dental dam was then clamped between two glass chambers. The inhalant and exhalant siphons were thus directed into separate chambers of the device so that the amounts of water or feces discharged into the exhalant chamber provided direct measures of ventilation rate and sediment processing rate, respectively. Clams exhibited no stress from the procedure. Ventilation rate was not affected by the imposition of a 5 mm hydraulic head in the exhalant chamber, by having sediment only in the inhalant chamber, or by exposure to organic-free sediment. The mean weight-specific ventilation rate for M. nasuta was 7.3 ml g^-1 h^-1 on a wet-flesh basis. This low rate, compared to rates for filter-feeding bivalves, supports the contention that deposit-feeding is the dominant feeding mode for M. nasuta. The short-term pattern was for ventilation to be intermittenly interrupted, essentially ceasing for 12 to 120 min, followed by a short period of active ventilation and then a resumption of the normal rate. Less than 3% of the total water flux could be attributed to water which entered the body cavity across the mantle margin. Water exhaled from the inhalant siphon during the ejection of pseudofeces was <10% of the ventilation rate. The clambox technique should be adaptable to studies on other tellinid bivalves.     

The ecophysiological complex of Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda). I. Respiration rates

The metabolic rates of high and low shore estuarine populations of Bathyporeia pilosa Lindström and an open coast population of B. pelagica (Bate) have been determined over a range of temperatures during January and February, and June and July, 1968. Changes in oxygen uptake have also been measured monthly at 15°C. During the winter, oxygen uptake was in the order: high shore B. pilosa>low shore B. pilosa>B. pelagica. During the summer, high shore B. pilosa and B. pelagica had similar metabolic rates, but both were significantly higher than low shore B. pilosa. Both populations of B. pilosa had lower metabolic rates in summer than in winter, whereas the metabolic rate of B. pelagica remained much the same. Seasonal changes in metabolic rate are closely correlated with reproductive cycles. The possible influences of environmental parameters are discussed.     

Electrocardiogram of a marine fish,Pagrus major,exposed to red tide plankton,Chattonella marina

Examinations of the electrocardiogram of Pagrus major exposed to Chattonella marina, a planktonic organism causing red tide, were made to determine the physiological effects on fish. The heart rate decreased as a result of the extention in the interval between T and P waves. The decrease in heart rate with the extended intervals between T and P waves was also recognized in the condition of decreased dissolved oxygen. Also, the decrease in heart rate of the fish exposed to the red tide occurred while the fish was struggling. This reduction seems to be caused by the strong tension of the vagal nerve. Upon exposure to C. marina at high cell concentration, the heart beat at a very low frequency after 30 min. The very low heart rate is expected to limit seriously the oxygen uptake by the gill, because the cardiac output is probably very low in this situation.     

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.     

Effect of low dissolved oxygen concentrations on behavior and predation rates on red sea bream Pagrus major larvae by the jellyfish Aurelia aurita and by juvenile Spanish mackerel Scomberomorus niphonius

A shift in outcomes of predator-prey interactions in plankton community may occur at sublethal dissolved oxygen concentrations that commonly occur in coastal waters. Laboratory experiments were conducted to investigate how a decline in dissolved oxygen concentration alters the predation rate on fish larvae by two estuarine predators. Behavior and consumption of larval fish by moon jellyfish Aurelia aurita (103.1±12.4 mm in bell diameter) and by a juvenile piscivore, Spanish mackerel Scomberomorus niphonius (30.1±2.1 mm in standard length: SL), were observed under four oxygen concentration treatments (1, 2 and 4 mg l^–1 and air-saturated: 5.8 mg l^–1). Larvae of a coastal marine fish species, red sea bream Pagrus major (7.21±0.52 mm SL), were used as prey for the experiment. Bell contraction rate of the jellyfish did not vary among the oxygen concentrations tested, indicating a tolerance to low oxygen concentration. Gill ventilation rate of the Spanish mackerel increased and swimming speed decreased as the oxygen concentration decreased, indicating that oxygen concentrations 4 mg l^–1 are physiologically stressful for this species. The number of larvae consumed in 15 min. by jellyfish increased whereas those consumed by Spanish mackerel decreased with the decrease in oxygen concentration. Low oxygen concentrations that are commonly observed in coastal waters of Japan during summer have the potential to increase the relative importance of jellyfish as predator of fish larvae and to change the importance of alternative trophic pathways in estuarine ecosystems.Communicated by T. Ikeda, Hakodate     

Factors influencing the gas composition in the vesicles of Sargassum

The composition of gas in the vesicles of Sargassum cf. leptopodum Sonder has been investigated. The oxygen content depends upon the oxygen partial pressure of the surrounding medium. It does not depend upon the photosynthetic activity of the vesicle. Evidence is provided that the lower limit of the vertical distribution zone of Sargassum cf. leptopodum Sonder is not controlled by the vesicles' capability of resisting hydrostatic pressure.     

Effects of receptive females' secretion on some male reproductive behaviors in the amphipod crustacean Microdeutopus gryllotalpa

The use of a choice test apparatus has shown that receptive females of the tube-building amphipod crustacean Microdeutopus gryllotalpa (Costa) secrete a waterborne substance which attracts males. This substance (1) increases the level of activity of males, and (2) orients the males' movements towards its source. Males do not secrete this substance. In this species, females tend to remain inside their residential tubes, and males generally travel from receptive female to receptive female. Thus, in the field, the attractant may stimulate the male to accelerate his movements toward, and guide him directly to a receptive female. On the other hand, at the concentration tested, the substance alone does not elicit intermittent pleopod beats, a male-specific behavior that only occurs in a reproductive context. The expression of intermittent pleopod beats is shown to require the presence of a female plus its tube.     

Potential impact of a toxic dinoflagellate (Alexandrium excavatum) bloom on survival of fish and crustacean larvae

During the last 20 yr the western half of the Dutch Wadden Sea has undergone significant eutrophication: concentrations of P and N compounds and planktonic algae have roughly doubled, as has primary production. Though oxygen levels are often low in summer, anoxic areas are small and rare due to strong tidal mixing. During the 1970 to 1990 period, macrozoobenthos was sampled annually at 15 stations at Balgzand, a 50-km² tidal-flat area in the westernmost part of the Wadden Sea. Not only did the estimates of total numbers, biomass, and production double during these two decades, but significant changes in the composition of the benthic community were observed, too: (1) the numerical proportion of polychaetes increased at the expense of molluscs and crustaceans, (2) the overall mean weight per individual of the macrozoobenthos decreased (numbers of individuals of small-sized species increased more rapidly than those of large-sized species), and (3) though absolute numbers and biomass of all feeding types increased, the share of carnivores declined and that of deposit feeders increased; the proportion of suspension feeders showed little change. This study refers to true macrobenthos only (1-mm sieve) and further excludes two taxa (Corophium spp. andHydrobia ulvae) which occasionally exercised an undue influence on numbers. Mass mortalities caused by low oxygen concentrations were of a small-scale nature only. Total number of species fluctuated without a clear trend. As a consequence of the increasing numerical densities, trends in species numbers were slightly increasing when expressed per unit of area and slightly decreasing when estimated per 100 individuals (by rarefaction).     

Respiratory dynamics of the starry flounder Platichthys stellatus in response to low oxygen and high temperature

Starry flounder (Platichthys stellatus Pallas) were fitted with masks for measurements of ventilation volume and post-gill oxygen tensions, and with arterial and venous cannulae. They were then subjected to periods of low oxygen levels and high temperature. Pre- and post-gill oxygen tension, blood oxygen tension and content, oxygen uptake, and ventilation volume were measured. Effectiveness of gas exchange across the gills, cardiac output, and transfer factor were calculated. A series of blood-oxygen dissociation curves were also constructed at two pH's and temperatures. The data suggest that flounder are able to regulate oxygen uptake down to an environmental oxygen tension of at least 50 mm Hg by increasing ventilation volume and transfer factor while not changing blood flow rate or pattern. Also, the flounder's response to temperature increase is similar to the expected response to exercise, with the exception of an increase in gill diffusion resistance.     

Photosynthesis and ion loss in the brown algae Dictyopteris membranacea and Fucus virsoides

The sublittoral brown alga Dictyopteris membranacea (Stackhouse) Batters is very sensitive to low salinities. A one minute exposure to distilled water causes total breakdown of photosynthesis and respiration. The breakdown phenomena were studied as after-effects following re-exposure to sea water. Since rate of ion loss is highest during the first minute of osmotic stress, the irreversible metabolic depression appears to be due to fast ion loss. Photosynthesis of Fucus virsoides J.Ag is not affected by distilled water, even over very long periods of time.     

Tail beat frequency as a predictor of swimming speed and oxygen consumption of saithe (<Emphasis Type="Italic">Pollachius virens</Emphasis>) and whiting (<Emphasis Type="Italic">Merlangius merlangus</Emphasis>) during forced swimming

Oxygen consumption and tail beat frequency were measured on saithe (Pollachius virens) and whiting (Merlangius merlangus) during steady swimming. Oxygen consumption increased exponentially with swimming speed, and the relationship was described by a power function. The extrapolated standard metabolic rates (SMR) were similar for saithe and whiting, whereas the active metabolic rate (AMR) was twice as high for saithe. The higher AMR resulted in a higher scope for activity in accordance with the higher critical swimming speed (U _crit) achieved by saithe. The optimum swimming speed (U _opt) was 1.4 BL s⁻¹ for saithe and 1.0 BL s⁻¹ for whiting with a corresponding cost of transport (COT) of 0.14 and 0.15 J N⁻¹ m⁻¹. Tail beat frequency correlated strongly with swimming speed as well as with oxygen consumption. In contrast to swimming speed and oxygen consumption, measurement of tail beat frequency on individual free-ranging fish is relatively uncomplicated. Tail beat frequency may therefore serve as a predictor of swimming speed and oxygen consumption of saithe and whiting in the field.     

Effects of dieldrin-contaminated food on the development of Leptodius floridanus larvae

Leptodius floridanus (Rathbun) (Decapoda: Xanthidae) larvae were fed dieldrin-contaminated Artemia nauplii throughout their development to megalopa. Sublethal effects were noted at dieldrin concentrations as low as 5.49 ppm, and no larvae completed their development when fed Artemia containing 33.0 ppm dieldrin. Organochloride pesticide residues were measured in zooplankton collected from Onslow Bay, North Carolina, USA. These residue levels were found to be much lower than those found to affect Leptodius larvae in the laboratory.     

Respiration,pumping activity and heart rate in Ciona intestinalis exposed to fluctuating salinities

Specimens of Ciona intestinalis L. were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and the changes in pumping activity and oxygen sonsumption monitored. Heart rate was monitored under steady state conditions using a new in vivo method, and pumping activity was monitored as spontaneous squirting by use of a pressure transducer. Oxygen consumption was also monitored under steady state conditions and under conditions of declining oxygen tension. It was found that during periods of regular beating the mean heart rate for 5 ascidians was 13.2 beats min^-1 for the branchial pacemaker and 32.6 beats min^-1 for the visceral pacemaker. Regular periods of beating lasted for approximately 1 min, followed by periods of irregular activity prior to heart beat reversal. The heart beat became irregular and reversal occurred sporadically when the ascidians were exposed to dilute seawater. The ascidians showed a pumping rate of 14 squirts per hour in full-strength seawater. This rate declined during decreasing salinity and ceased entirely when the external seawater concentration reached approximately 60% seawater (100%=32% S). During periods of decreased salinity, the siphons were tightly closed and oxygen consumption was zero. The rate of oxygen consumption by C. intestinalis decreased during decreasing salinities and there was no evidence of an oxygen debt. Oxygen consumption under steady state conditions varied with body weight according to the following: oxygen consuption =0.515 W ^0.831 (where W is body weight). The rate of oxygen consumption was found to be dependent on the external oxygen tension.