Effects of inorganic and organic phosphates on feeding, feeding absorption, nutrient allocation, growth and righting responses of the sea urchin Lytechinus variegatus

The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l⁻¹, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l⁻¹. However, chronic exposure to low (0.8 mg l⁻¹ inorganic and 10 mg l⁻¹ organic phosphate), medium (1.6 mg l⁻¹ inorganic and 100 mg l⁻¹ organic phosphate) or high (3.2 mg l⁻¹ inorganic and 1,000 mg l⁻¹ organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate. Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only, while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues. Received: 10 April 2000 / Accepted: 2 October 2000     

Effects of temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis

To assess the effects of both temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis (O.F. Müller), individuals collected December 1996 (winter experiment) and June 1997 (summer experiment) were maintained for 3 months in one of four experimental treatments: (1) 3 °C and fed ad libitum (high ration), (2) 3 °C and fed one-seventh of the maximum ration (low ration), and (3) 12 °C and fed the high ration; (4) 12 °C and fed the low ration. All individuals were fed an artificial diet and exposed to only 1 h of light every day. At the end of both experiments, mean gonad indices of sea urchins fed the high ration had increased significantly (11–24% and 6–19% in the winter and summer experiments, respectively), while the gonad indices of individuals fed the low ration did not change. At the high ration (both experiments), the increase in gonad index of sea urchins occurred primarily as the result of a significant increase in the mass of nutritive phagocytes, as revealed by histological analyses. Primary oocytes were significantly larger in individuals held at 3 °C than at 12 °C throughout the winter experiment, regardless of food ration; during the summer experiment, primary oocytes were significantly larger in individuals receiving the high ration, regardless of the temperature at which they were held. These results suggest that: (1) food availability is the most important factor regulating energy storage and the relative size of gonads throughout the year, (2) temperature affects the rate of growth and maturation of primary oocytes during the later stages of oogenesis, and (3) once gametogenesis has been initiated, mature ova will be produced, even under conditions of low food availability. Conditions of high food availability in summer and low temperature in winter would thus favor reproductive output in sea urchin populations. Received: 1 March 2000 / Accepted: 4 October 2000     

Effect of diet on growth rate and reproductive fitness of Turbo sarmaticus (Mollusca: Vetigastropoda: Turbinidae)

Experiments were conducted to determine the effect of four algal diets (Corallina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture of these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12 months), reproductive fitness of mature specimens (gonad index up to 33%) and energy reserves (up to 4.76 mg glycogen/100 mg foot tissue) were achieved when T. sarmaticus was fed U. rigida or a mixed diet. In addition, the gonad index of individuals fed these diets was almost twice that of similar-sized field specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reproductive fitness of adults fed on such a diet was also poor (gonad index <4.5%) and energy reserves were low (<3.5 mg glycogen/100 mg foot tissue). Along the southeastern coast of South Africa, T. sarmaticus has a distinct reproductive cycle with gametogenesis occurring from March/April until August/September, whilst maturity (gonad index = 15%) was maintained until December, after which spawning occurred until March. Received: 6 July 1998 / Accepted: 8 March 1999     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Arm regeneration in the field in Ophiocoma echinata (Echinodermata: Ophiuroidea): effects on body composition and its potential role in a reef food web

Eighteen percent and 47% of two populations of Ophiocoma echinata in the Florida Keys were undergoing regeneration. An individual would take approximately 720 days to completely regenerate three arms. Regeneration of three arms had a greater effect on gonad production in females than in males, and reduced storage material in the stomach of both. Regeneration in O. echinata was estimated to be 0.07 kJ m^-2 day^-1, which could provide the equivalent of 0.07% of primary production on a reef to higher trophic levels per day.     

Damage, autotomy and arm regeneration in starfish caught by towed demersal fishing gears

Arm damage and loss were examined in the starfish Asterias rubens that had been caught in a variety of towed commercial fishing gears deployed on different sea bed types. Between 7% and 38% of the starfish in each catch lost one or more arms, and arm loss was positively correlated with the volume of the catch for two of the fishing gears examined. Subsequent monitoring of damaged animals showed that arms were autotomised for at least 3 weeks following capture. Mortality was highest in starfish with damaged or missing arms, compared with those that appeared intact after fishing. Arm regeneration was delayed in a small proportion of the animals caught by commercial gears. In a parallel study, 17% of starfish caught by a 4 m beam trawl had a damaged ambulacral ossicle at the point of autotomy (cf. none from a control group that were induced to autotomise under controlled conditions). There was no difference in regeneration rates between the animals caught by commercial gears and a control set (caught by a small trawl and forced to autotomise an arm in the laboratory) once the animals that delayed regeneration were excluded from the dataset. After 1 year under laboratory conditions the starfish had, on average, regenerated the missing arm to 75% of the length of the other four arms. During this time period the lengths of the undamaged arms increased by ca. 50%. The implications of this study for using arm loss in starfish as an indicator of fishing disturbance are discussed. Received: 16 August 2000 / Accepted: 20 October 2000     

Density-related reproductive trade-offs in the green sea urchin, Strongylocentrotus droebachiensis

Green sea urchin, Strongylocentrotus droebachiensis (O.F. Müller), populations are being depleted rapidly in the Gulf of Maine and there is justified concern that the potential of this free-spawner to produce larvae may be severely inhibited. We evaluated the opposing effects of different population densities on gonad development and fertilization success, using population surveys and fertilization experiments. We determined gonad indices (gonad mass/body mass) over a range of population densities (0.1 to 250 ind. m⁻²) at seven sites in coastal Maine, USA, sampled at two depths (5 and 15 m). At shallow sites, we found that gonad indices declined by 50% over the 1500-fold range in adult population density. At 15 m deep locations, gonad mass was consistently low and did not vary significantly with density. Patterns of macroalgal abundance suggest urchins at high density and in deeper water were food limited. Because macroalgal cover co-varies inversely with sea urchin density, we designed field experiments to determine the interaction between sea urchin density and kelp canopy on fertilization success. On square arrays we manipulated the spacing of simulated urchins, but held their numbers constant (five sperm-filled syringes interspersed with four Nitex mesh egg containers permeable to sperm). These experiments, simulating the observed range of natural density, suggested that (1) fertilization rates decreased many times faster than individual gamete production increased over the same range in density, and (2) kelp increased fertilization success at high density when eggs were within 25 cm of a sperm source, but not when spaced 1 m apart. Additional laboratory fertilization experiments at ambient temperatures (3 to 5 °C) indicated that diluted sperm were viable for <1 h, but egg viability was virtually unchanged for >8 h. In short, to the individual the reproductive benefits of aggregating appear to outweigh the costs; and while sperm may be limiting at low population density, eggs may remain viable long enough to be fertilized by sperm from more distant males. Received: 10 February 1998 / Accepted: 22 January 1999     

Feeding, metabolism and growth in the Antarctic limpet, Nacella concinna (Strebel 1908)

Post-prandial increases in metabolism, the specific dynamic action of feeding (SDA), were evaluated in the Antarctic limpet Nacella concinna. O₂ consumption rose to a peak value 2.3 times higher than pre-feeding standard metabolic rates. This peak rise is low for marine ectotherms, but is typical of polar species. There were three peaks in the SDA, the first lasted only for the 1st day, was caused by handling, and was minor. The second was the major peak. It lasted from post-prandial days 4–9 inclusive, and accounted for around 70% of the SDA response. The third peak lasted from day 11 to day 15 and accounted for 30% of the total SDA. A 15-day SDA is much longer than values for temperate species, but is again typical for polar marine ectotherms. NH₃ excretion declined post-prandially from around 0.4 μmol animal⁻¹ h⁻¹ to values between 0.025 and 0.223 μmol animal⁻¹ h⁻¹ throughout the SDA. The total O₂ consumed in the SDA was 90.2 μmol O₂, which converts to 44.7 J of energy. This was 45–50% of the energy consumed in the meal (93.5 J). Pre-feeding O:N ratios, after 26 days without food, were around 1, indicating protein as the sole metabolic substrate prior to initiating the SDA. After feeding, O:N ratios rose to between 2.5 and 19, indicating significant use of lipid or carbohydrate from the food. Experiments were conducted in ambient seawater with enhanced levels of Sr (SrCl added at 800 mg kg⁻¹), and limpets were fed microalgal films also grown in enhanced Sr media. Sr incorporated in the shells during the experiment allowed the measurement of shell increments deposited during the SDA. Between five and eight microgrowth bands were present in the Sr-enhanced increments, which was similar to the number of days in the second SDA peak. The mean shell increment laid down was 17.6 μm. Estimating tissue deposition from measured growth increments and published ash-free dry mass (AFDM) to length relationships produced a value of 0.81 mg AFDM, which converted to 26.4 J of energy, or 25–30% of the energy ingested in the meal. Estimates of growth increments associated with a single SDA have not previously been possible. Overall energy used in the SDA and tissue deposition accounted for 75–80% of the energy ingested; the remainder was probably accounted for by unmeasured costs such as mucus production. Received: 6 June 2000 / Accepted: 20 September 2000     

Effects of food ration and feeding regime on growth and reproduction of the sea urchin Strongylocentrotus droebachiensis

To determine the effects food ration and feeding regime on growth and reproduction of Strongylocentrotus droebachiensis (Müller), sea urchins in laboratory aquaria were fed kelp (Laminaria longicruris) supplied at either a high (H, ad libidum daily) or a low (L, ad libidum 1 d wk⁻¹) ration in two successive 12-wk intervals during the reproductive period. After 24 wk, urchins fed the high ration continuously (HH) or for the last 12 wk only (LH) had a significantly greater mean gonad index [(gonad weight/total body weight) × 100] and body weight than urchins fed the low ration continuously (LL) or for the last 12 wk only (HL). Urchins in the HL treatment had a significantly greater gonad index than those in the LL treatment; there was no significant difference in gonad index between the LH and HH treatments. Females had a greater gonad index than males in the low ration (LL and HL) treatments at the end of the experiment; there was no significant difference between sexes in the high ration (LH, HH) treatments. Gametogenesis proceeded to maturation in all treatments and some individuals spawned at the end of the experiment. Females in the high ration (HH and LH) treatments had a greater proportion of nutritive phagocytes in their ovaries than females in the low ration treatments, but there was no effect of feeding treatment on oocyte or ovum size. Feeding treatment had no effect on the relative abundance of nutritive phagocytes in the testes, although the proportion of spermatocytes was higher (and that of spermatozoa lower) in the high ration than in the low ration treatments. Urchins in the high ration treatments had a lower mean jaw height index [(jaw height/test diameter) × 100] and greater mean test diameter than those in the low ration treatments at the end of the experiment, although these differences were not statistically significant. Feeding rate on kelp at the end of the experiment was significantly greater for urchins in the low ration than in the high ration treatments. Our experimental results show that even relatively low rations of kelp support somatic and gonadal growth in S. droebachiensis. Increasing the supply of kelp, particularly during the period of active gametogenesis, results in maximal rates of growth and reproduction. These results suggest that populations of S. droebachiensis in barrens may derive a substantial proportion of their nutrition from drift kelp, which may contribute to their persistence in these habitats. They also explain the large body size, high reproductive effort and fecundity of urchins grazing on kelp beds. These findings have important implications for understanding the dynamics of natural populations of S. droebachiensis and for development of effective aquacultural practices. Received: 17 February 1997 / Accepted: 5 March 1997     

Feeding ecology and evolutionary survival of the living coelacanth Latimeria chalumnae

One concept of evolutionary ecology holds that a living fossil is the result of past evolutionary events, and is adapted to recent selective forces only if they are similar to the selective forces in the past. We describe the present environment of the living coelacanth Latimeria chalumnae Smith, 1939 at Grande Comore, western Indian Ocean and report depth-dependent cave distribution, temperature, salinity and oxygen values which are compared to the fish's distribution and its physiological demands. We studied the activity pattern, feeding behaviour, prey abundance and hunting success to evaluate possible links between environmental conditions, feeding ecology and evolutionary success of this ancient fish. Transmitter tracking experiments indicate nocturnal activity of the piscivorous predator which hunts between approximately 200 m below the surface to 500 m depth. Fish and prey density were measured between 200 and 400 m, both increase with depth. Feeding tracks and feeding strikes of the coelacanth at various depths were simulated with the help of video and laser techniques. Along a 9447 m video transect a total of 31 potential feeding strikes occurred. Assuming 100% hunting success, medium-sized individuals would obtain 122 g and large females 299 g of prey. Estimates of metabolic rates revealed for females 3.7 ml O₂ kg⁻¹ h⁻¹ and for males 4.5 ml O₂ kg⁻¹ h⁻¹. Today coelacanths are considered to be a specialist deep-water form and to inhabit, with their ancient morphology, a contemporary environment where they compete with advanced, modern fish. Received: 5 July 1999 / Accepted: 11 November 1999     

Feeding biology of a predatory and a facultatively predatory nematode (Enoploides longispiculosus and Adoncholaimus fuscus)

This paper reports on the feeding biology of a predatory and of a facultatively predatory nematode, Enoploides longispiculosus and Adoncholaimus fuscus, respectively. Both species represent genera which are common and abundant in the littoral of the North Sea and in adjacent estuaries. Observations on the foraging behaviour of both species are given, and for the former species, a range of prey from its natural habitat is identified. Respiration was determined using a polarographic oxygen electrode technique and compared to consumption determined as predation rates on the monhysterid nematode Diplolaimelloides meyli. The daily C-loss due to respiration accounted for 15% of the measured C-consumption in E. longispiculosus and for 111% in A. fuscus, proving the observed feeding rates in the latter species to have been inadequate for the maintenance of its aerobic metabolism. Daily respiration rates at an average environmental temperature were 219 ng C ind⁻¹d⁻¹ for adults of A. fuscus and 21.9 ng C ind⁻¹ d⁻¹ for adults of E. longispiculosus. Using radiotracer techniques, no uptake of bacterial cells or of organic matter in the dissolved phase was demonstrated for E. longispiculosus. In A. fuscus, however, a significant drinking of label in the dissolved or volatile fraction occurred; bacterial cells were taken up at a level insignificant to the nematode's daily C-ration. It is concluded that E. longispiculosus has a fairly strict predatory feeding strategy, while A. fuscus gains a majority of C from additional foraging strategies, among which the uptake of dissolved material and scavenging on macrofauna carcasses (as reported in the literature) may be of particular importance. Received: 28 August 1998 / Accepted: 8 March 1999     

Free amino acids and energy metabolism in eggs and larvae of seabass, Lates calcarifer

Contents of free amino acids (FAA), protein and ammonium ions together with rates of ammonia excretion and oxygen consumption were measured in order to study the role of FAA as an energy substrate in developing eggs and larvae of seabass (Lates calcarifer) maintained in seawater (30 ppt) at 28 °C without feeding. Initially eggs contained 25.3 nmol ind⁻¹ of FAA of which 21.5 nmol was rapidly utilised by the developing eggs and larvae during the period up to 40 h post spawning (PS) when nearly all the yolk had been resorbed. During the same period, a net increase in protein content of 1.7 μg ind⁻¹ was observed, indicating that the major part of the amino acids lost from the free pool had been polymerised into body proteins. Assuming that the balance of the FAA after protein synthesis was used entirely for energy metabolism, FAA appeared to be an important energy substrate during the embryonic stages (2 to 16 h PS); after hatching, the contribution of FAA to energy metabolism was less significant. From 50 h PS until the end of the study period at 100 h PS, amino acids derived from somatic protein were used for energy metabolism. For the overall period from just after spawning up to 100 h PS, the data indicate that ca. 14% of the total aerobic energy metabolism was derived from amino acid catabolism. Received: 26 September 1997 / Accepted: 1 April 1998     

Growth, carbon, nitrogen and caloric content of Solea senegalensis (Pisces: Soleidae) from egg fertilization to metamorphosis

Eggs and larvae of the Senegal sole, Solea senegalensis Kaup, were reared from fertilization until the end of metamorphosis, which occurs by Day 17 after hatching at 19.5 °C. Changes in energy content and biomass quality were studied in terms of dry weight and of carbon, nitrogen and energy content. S. senegalensis spawned eggs of about 1 mm diameter which hatched 38 h after fertilization. Average dry weight of individual eggs was 46 μg, the chorion accounting for about 18% of total dry weight. Gross energy of recently fertilized sole eggs was approximately 1 J egg⁻¹. From fertilization to hatching, eggs lost 8% of their total energy (chorion not included). After hatching, larvae lost 14% of their initial energy until the start of feeding which occurred about 48 h afterwards. The principal components catabolized during embryogenesis were carbon-rich compounds that decreased by 26%, while nitrogen-rich compounds decreased by only 10% and were practically unaltered from hatching to the start of feeding. Feeding larvae displayed constant growth during the period studied (specific growth rate on a dry weight basis was 0.26 d⁻¹). The relative proportion of carbon and nitrogen content revealed an accumulation of high energy compounds in the days before metamorphosis. By Day 14, the energy content reached values similar to those of recently hatched embryos, but decreased again during metamorphosis. Received: 10 June 1998 / Accepted: 28 January 1999     

Importance of food quantity to structural growth rate and neutral lipid reserves accumulated in Calanus finmarchicus

 Growth and developmental rates were determined for copepodids of Calanus finmarchicus (Gunnerus) from experimental seawater mesocosms in a western Norwegian fjord. The instantaneous growth rates (g) from copepodid stage I (CI) to adult ranged from 0.08 to 0.10 d⁻¹. Daily per capita mortality rate of the cohorts was as low as 0.012 d⁻¹ (1.2% d⁻¹). At local increasing temperatures (5.1 to 8.3 °C), development was equiproportional, and the cumulative median development time from egg to CV was approximately 65 d. CV moulted to males and females, and egg production was initiated. Enhancement of food resources by nutrient addition caused a 23.4% increase in growth rates from CI to adult. Additionally, copepodid stages showed a generally larger body size, carbon and nitrogen content and total storage lipid content (wax esters + triacylglycerols) in response to enhanced resources. Our data support an elsewhere proposed exponential-growth hypothesis; growth of the structural compartments and store lipids (mostly wax esters) was exponential during the copepodid stages. However, a sigmoidal pattern of growth best described growth of adult stages if reared at high resources, and depot lipid accumulation in late CVs and adults at high resources. Body nitrogen growth increased exponentially, however, no significant changes in nitrogen specific growth rates were found between individuals from low and high resources. CV and adults seem to have reached near-maximal weights at high resources, whereas structural weight continued to increase at low resources. Despite the differences in structural growth dynamics, cohort development was similar until the end of CV. During the onset of sexual differentiation, the male:female ratio and the adult:CV ratio were highest at high food resources, suggesting that the time used for the final moult depends on the feeding history of the copepods in relation to food quality and quantity. It appears that relatively small changes in food availability strongly influence the biochemical composition of C. finmarchicus copepodids. Received: 28 May 1999 / Accepted: 10 February 2000     

Effects of food type and ration on reproductive maturation and growth of the sea urchin Strongylocentrotus droebachiensis

We investigated the effects of food quality and quantity on reproductive maturation and growth of juveniles of Strongylocentrotus droebachiensis (Müller) in a 22 month laboratory experiment in which we fed sea urchins four diets: (1) kelp (Laminaria spp.) for 6 d wk⁻¹ and mussel (Mytilus spp.) flesh for 1 d wk⁻¹ (KM); (2) kelp for 7 d wk⁻¹ (high ration, KH); (3) kelp for 1 d wk⁻¹ (low ration, KL) and (4) no food other than encrusting coralline algae (NF). At their first and second opportunity for reproduction, all sea urchins in the KM and KH treatments, and most in the KL treatment were reproductively mature, whereas all sea urchins in the NF treatment remained immature. Gonad index differed significantly among all fed treatments at first and second reproduction, and was highest in the KM and lowest in the KL treatment. Gonad index was similar in both sexes at first reproduction, but it was higher in females than in males at second reproduction. Diet had little or no effect on the relative abundance of spermatocytes, spermatozoa, or nutritive phagocytes in testes at first and second reproduction. In ovaries, nutritive phagocytes were significantly more abundant in females in the KM and KH treatments than in the KL treatment at first reproduction, and significantly more abundant in unfed (NF) than fed (KM, KH, KL) females at second reproduction. Mean oocyte size was similar in all fed females at first reproduction, but significantly larger in fed than unfed females at second reproduction. Mean ovum size was similar in all fed females in both reproductive periods. Increase in test diameter was greatest in the KM treatment and smallest in the KL treatment; sea urchins in the NF treatment decreased slightly in size. Survival was 95 to 100% in all fed sea urchins but significantly lower in unfed ones. The feeding rate on kelp was significantly greater in the KL than the KM and KH treatments. In the KM treatment, the feeding rate on kelp increased significantly over a 6 d period after mussel flesh was provided. Our results demonstrate that a diet of high food quality and quantity accelerates reproductive maturation and growth rate, and enhances gonad production and survival in juvenile and young adult S. droebachiensis. These findings contribute to our understanding of the reproductive ecology of S. droebachiensis in habitats with differing food supplies (e.g., kelp beds and barrens). Our results also can be used to improve aquacultural practices for sea urchins. Received: 3 June 1998 / Accepted: 2 February 1999     

Responses of ovaries and testes of Lytechinus variegatus (Echinodermata: Echinoidea) to dietary administration of estradiol, progesterone and testosterone

 In many vertebrates, environmental factors influence gamete differentiation and growth of the mature gonad through alteration of sex steroid production or action; however, it is unclear how gamete differentiation and gonadal growth are regulated in echinoids. The purpose of this study was to examine the influence of dietary administration of estradiol (E2), progesterone (P4), testosterone (T) and finasteride (F, a 5α-reductase inhibitor) on the ovaries and testes of mature Lytechinus variegatus (Lamarck) during gonadal growth. Echinoids were fed a formulated diet supplemented with steroids or steroids in combination with finasteride for 36 d. The effects of dietary administration of steroids on L. variegatus were both steroid- and sex-specific. The mean ovary index was 54% greater in individuals fed E2 than from individuals fed the control (C) diet (10.0 ± 1.1 vs 6.5 ± 0.7, respectively; P < 0.05). Individuals fed E2, P4, E2/P4, and P4 in combination with F had significantly smaller oocytes (P < 0.005) than individuals fed C. The volume fraction occupied by nutritive phagocytes in ovarian tubules from individuals fed E2/P4 or P4 were significantly larger than the volume fraction occupied by nutritive phagocytes from individuals fed C, indicating that E2 and 5α-reduced progestins may promote nutrient allocation to nutritive phagocytes. Although oocytes from the individuals fed T alone were significantly smaller than those fed T in combination with F, oocytes from individuals in both treatments were significantly larger compared to oocytes from individuals fed C. These data suggest that upon removal of 5α-reduced androgens, T is able to promote an increase in oocyte diameters. In contrast, the mean testis index was 56% greater in individuals fed P4 than in individuals fed C (8.9 ± 0.6 vs 5.7 ± 0.9, respectively; P < 0.05); the testis index did not increase in individuals fed P4/F, suggesting that 5α-reduced progestins stimulate testicular growth. Testes growth in the presence of 5α-reduced progestins was accomplished by significant increases in the volume fraction occupied by nutritive phagocytes and by a significant reduction in the volume fraction occupied by spermatogenic columns in testicular tubules. These data further indicate that 5α-reduced progestins (or 5α-reduced androgens) may inhibit spermatogenic column formation. In conclusion, E2 stimulated ovarian growth but inhibited oocyte growth, whereas T had no affect on ovarian growth but promoted oocyte growth in L. variegatus. We hypothesize that the E2 (or E2 metabolites) and/or 5α-reduced androgens in combination with T regulate oocyte growth in the echinoid L. variegatus. In addition, 5α-reduced progestins promoted nutrient accumulation in nutritive phagocytes within the ovaries and the testes. Furthermore, 5α-reduced progestins stimulated growth of the testes and inhibited spermatogenic column formation, suggesting that 5α-reduced progestins regulate nutrient accumulation into nutritive phagocytes and spermatogenic column formation in L. variegatus. The differences in estrogen effects between echinoids and asteroids may be related to differences in gonad morphology and, ultimately, the differences in cellular signalling pathways (paracrine vs endocrine). Received: 22 May 1999 / Accepted: 24 May 2000     

Feeding and assimilation kinetics of Artemia franciscana fed Isochrysis galbana (clone T. Iso)

Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l⁻¹) for 11 d at 26 to 28 °C, and 34 ppt salinity. Three groups of brine shrimp were used in the feeding experiments: metanauplius III and IV (Group 1), post-metanauplius II and III (Group 2) and post-metanauplius VIII (Group 3), corresponding to 4-, 7- and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages at different concentrations of ¹⁴C-labeled I. galbana ranging from 0.05 to 30 mg C l⁻¹. The handling time of algae was determined for all three groups. The ingestion rate (I, ng C ind⁻¹ h⁻¹) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maximum level (I _max) and remained constant at food concentrations ≥10 mg C l⁻¹ (saturated food concentrations). The clearance rate (CR, μl ind⁻¹ h⁻¹) increased with increasing food concentration up to a maximum rate (CR _max), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consistent with Holling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2 and 3) differed significantly from a Type 2 response (p < 0.05). The gut passage time for the three groups of A. franciscana, feeding on saturated food concentration (20 mg C l⁻¹), varied between 24 and 29 min. As the nauplii developed to pre-adult stage the handling time of the algae increased as a function of animal size. The assimilation rate (ng C ind⁻¹ h⁻¹) in the youngest stages (Group 1 and 2) increased with increasing food concentrations, reaching a maximum level close to 10 mg C l⁻¹. At higher food concentrations the assimilation rate decreased, and the proportions of defecated carbon increased, reaching 60 to 68% in the post-metanauplius stages (Group 3). The assimilation efficiency (%) was high at the lowest food concentrations in all three groups (89 to 64%). At higher concentrations, the assimilation efficiency decreased, reaching 56 to 38% at the highest concentrations. Received: 2 February 2000 / Accepted: 25 March 2000     

Fluoride in Antarctic marine crustaceans

The concentration of fluoride in the body parts of a range of Antarctic crustaceans from a variety of habits was examined with the aim of determining whether fluoride concentration is related to lifestyle or phylogenetic grouping. Euphausiids had the highest overall fluoride concentrations of a range of Antarctic marine crustaceans examined; levels of up to 5477 μg g⁻¹ were found in the exoskeleton of Euphausia crystallorophias. Copepods had the lowest fluoride levels (0.87 μg g⁻¹ whole-body); some amphipods and mysids also exhibited relatively high fluoride levels. There was no apparent relationship between the lifestyle of the crustaceans and their fluoride level; benthic and pelagic species exhibited both high and low fluoride levels. Fluoride was concentrated in the exoskeleton, but not evenly distributed through it; the exoskeleton of the head, carapace and abdomen contained the highest concentrations of fluoride, followed by the feeding basket and pleopods, and the eyes. The mouthparts of E.␣superba contained almost 13 000 μg F g⁻¹ dry wt. Antarctic krill tail muscle had low levels of fluoride. After long-term (1 to 5 yr) storage in formalin, fluoride was almost completely lost from whole euphausiids. Received: 1 April 1998 / Accepted: 29 July 1998     

Egg production of Calanus finmarchicus : effect of temperature, food and season

The use of the egg production rate of herbivorous copepods as an important parameter for understanding population dynamics and as an index of secondary production requires knowledge of the regulatory mechanisms involved and of the response to changes in food concentrations and temperature. Furthermore, the effects of season and generation on egg production have to be studied. In this context data are presented for Calanus finmarchicus from the northern North Atlantic. Prefed and prestarved females were exposed to different concentrations of the diatom Thalassiosira antarctica over 1 to 2 wk at 0 or 5 °C, and egg deposition was controlled daily. Egg production increased with higher food concentrations, but much less when prestarved. The effect of temperatures between −1.5 and 8 °C on egg production was studied in females maintained at optimum feeding conditions. Egg production rate increased exponentially over the whole temperature range by a factor of 5.2, from 14.2 to 73.4 eggs female⁻¹ d⁻¹, and carbon-specific egg production by 4, from 2.1 to 8.5% body C d⁻¹. The response to starvation was also temperature dependent. In both the temperature and feeding experiments egg production rate was regulated mainly by changes of the spawning interval, while changes of clutch size were independent of experimental conditions. Different responses to optimum feeding conditions were observed in females collected in monthly intervals on three occasions between March and May. The March females deposited more clutches than the April and May females. In May, >50% of the females did not spawn at all. Maximum egg production rates were never >25% of the rate expected at 5 °C, indicating endogenous control of egg production in addition to food and temperature effects. Received: 4 August 1996 / Accepted: 11 September 1996     

Physiological and behavioral aspects of Calanus euxinus females (Copepoda: Calanoida) during vertical migration across temperature and oxygen gradients

 In the Black Sea, during summer stratification, Calanus euxinus (Hulsemann) undertakes diel vertical migrations with an amplitude of about 117 m from oxygenated, warm (18 °C) surface layers to hypoxic (∼0.8 mg O₂ l⁻¹) zones with lower temperature (7.9 °C). When such changes in temperature and oxygen concentration are reproduced in the laboratory, total metabolism, basal metabolism and scope of activity of copepods decrease 7.2, 7.8 and 6.7 times, respectively, while the frequency of locomotory acts and mechanical power decline 3.4- and 9.5-fold, respectively. These changes allowed the copepods to conserve a significant portion of food consumed near the surface for transformation to lipid reserves. Diel respiratory oxygen consumption of migrating individuals, calculated so as to include actual duration of residence in layers with different temperature and oxygen concentrations, is estimated at 17.87 μg O₂ ind⁻¹. The net energy cost of vertical migration made up only 11.6% of the total. Copepods expend 78.6% of diel energy losses during approximately 10 h in the surface layers, while about 5.4% is required during about 9 h at depth. Hypoxia is shown to have a significant metabolic advantage during diel vertical migrations of C. euxinus in the Black Sea. Received: 1 October 1999 / Accepted: 11 July 2000