Feeding selectivities of the marine cladocerans<Emphasis Type="Italic"> Penilia avirostris</Emphasis>,<Emphasis Type="Italic"> Podon intermedius</Emphasis> and<Emphasis Type="Italic"> Evadne nordmanni</Emphasis>

We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm³ l^–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm³ l^–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.^–1 day^–1, respectively. Ingestion rates at similar food concentrations (0.4 mm³ l^–1) were 0.6, 0.8 and 0.9 g C ind.^–1 day^–1.Communicated by O. Kinne, Oldendorf/Luhe     

In vitro reproduction of the turbellarian<Emphasis Type="Italic"> Urastoma cyprinae</Emphasis> isolated from<Emphasis Type="Italic"> Mytilus galloprovincialis</Emphasis>

Urastoma cyprinae is a species infecting the gills of several marine bivalves. Although there is some literature on this turbellarian, its life cycle remains unknown. In our work we have demonstrated that reproduction of U. cyprinae can be completed out of its host. More than 50% of turbellarians isolated from mussels (Mytilus galloprovincialis) secreted and cemented a cocoon to the well bottom during the first 72 h of incubation in seawater (34 salinity) at 14°C. Oviposition started at days 1–18 (average 4.8 days) and occurred in most cases inside the protective cocoon. Each Urastoma laid an average of 2.9 egg capsules (range 1–10) and 3.9 embryos were developed inside each egg capsule (range 1–11). Hatching started at days 20–43 (average 24 days). An average of 12.8 juvenile forms (range 1–64) escaped from the cocoon after hatching. The free-swimming juveniles showed a positive phototactic response and survived about a month after hatching. On the basis of our results, we propose a life cycle for U. cyprinae involving a sexual maturation parasitic period in the bivalve gills and a reproduction period including cocoon secretion, egg laying, and hatching that is entirely completed in the external environment.Communicated by S.A. Poulet, Roscoff     

Reproductive strategy of<Emphasis Type="Italic"> Calanoides carinatus</Emphasis> and<Emphasis Type="Italic"> Calanus helgolandicus</Emphasis> during a summer upwelling event off NW Spain

Reproductive activity and production of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were measured during a summer upwelling event off the coast of NW Spain. The upwelling pattern affected the distribution and fecundity of both species in the study area. The demographic composition of both populations and the stage of gonad maturation (e.g. the high abundance of fertilised females with mature ova) indicated active reproduction. C. carinatus, a highly fecund species associated with the African upwelling zones and considered as an upwelling specialist, showed low production rates (overall means of 15 eggs female^–1 day^–1 and 3% body C day^–1), despite the fact that the food conditions (high phytoplankton biomass dominated by diatoms) seemed to be optimal for this species. By contrast, C. helgolandicus, a temperate species that shows a strong link between spring phytoplankton blooms and reproduction time, seems to be flexible enough to take full advantage of shorter-term, enhanced feeding conditions associated with the pulsed nature of the summer coastal upwelling. Both the egg and carbon-specific production rates attained by this species (overall means of 26 eggs female^–1 day^–1 and 12% body C day^–1) were similar to values reported for a spring bloom situation. This high production would imply a long spring–summer recruitment event of C. helgolandicus in these waters. For both species the stage of gonad maturation was significantly correlated with their egg production rates and likely influenced by the food conditions; a species-specific nutritional requirement for final oogenesis is suggested. The carbon condition factor (carbon weight/prosome volume) of C. carinatus females was higher than that of C. helgolandicus, suggesting differential use of the carbon ingested; C. helgolandicus seems to use all ingested carbon to produce eggs at a high rates, whereas C. carinatus seems to store part of the ingested carbon as lipid reserves to ensure female survival and to support production during subsequent unfavourable food conditions.Communicated by S.A. Poulet, Roscoff     

Characterization of urease activity in three marine phytoplankton species,<Emphasis Type="Italic"> Aureococcus anophagefferens</Emphasis>,<Emphasis Type="Italic"> Prorocentrum minimum</Emphasis>, and<Emphasis Type="Italic"> Thalassiosira weissflogii</Emphasis>

The availability of different forms of nitrogen in coastal and estuarine waters may be important in determining the abundance and productivity of different phytoplankton species. Although urea has been shown to contribute as much as 50% of the nitrogen for phytoplankton nutrition, relatively little is known of the activity and expression of urease in phytoplankton. Using an in vitro enzyme assay, urease activities were examined in laboratory cultures of three species: Aureococcus anophagefferens Hargraves et Sieburth, Prorocentrum minimum (Pavillard) Schiller, and Thalassiosira weissflogii (Grunow) Fryxell et Hasle. Cultures of P. minimum and T. weissflogii were grown on three nitrogen sources (NO₃^m, NH₄⁺, and urea), while A. anophagefferens was grown only on NO₃^m and urea. Urease was found to be constitutive in all cultures, but activity varied with growth rate and assay temperature for the different cultures. For A. anophagefferens, urease activity varied positively with growth rate regardless of the N source, while for P. minimum, urease activity varied positively with growth rate only for cultures grown on urea and NH₄⁺. In contrast, for T. weissflogii, activity did not vary with growth rate for any of the N sources. For all species, urease activity increased with assay temperature, but with different apparent temperature optima. For A. anophagefferens, in vitro activity increased from near 0-30°C, and remained stable to 50°C, while for P. minimum, increased in vitro activity was noted from near 0-20°C, but constant activity was observed between 20°C and 50°C. For T. weissfloggii, while activity also increased from 0°C to 20°C, subsequent decreases were noted when temperature was elevated above 20°C. Urease activity had a half-saturation constant of 120-165 wg atom N l^у in all three species. On both an hourly and daily basis, urease activity in A. anophagefferens exceeded nitrogen demand for growth. In P. minimum, urease activity on an hourly basis matched the nitrogen demand, but was less than the demand on a daily basis. For T. weissflogii, urease activity was always less than the nitrogen demand. These patterns in urease activity in three different species demonstrate that while apparently constitutive, the regulation of activity was substantially different in the diatom. These differences in the physiological regulation of urease activity, as well as other enzymes, may play a role in their ecological success in different environments.     

Comparing biochemical changes and energetic costs in gastropods with different developmental modes: <Emphasis Type="Italic">Crepipatella dilatata</Emphasis> and <Emphasis Type="Italic">C. fecunda</Emphasis>

The Chilean gastropods Crepipatella dilatata and C. fecunda have different development modes: brooding and direct development in C. dilatata and brooding and planktotrophic development in C. fecunda. Unlike many other congeneric invertebrate species pairs, recent genetic evidence suggests that C. fecunda may have evolved from C. dilatata. To explore the changes involved in this unusual evolutionary path, this study examined the biochemical, energetic, and morphological characters during early development of both species. Mean egg size was slightly smaller for the direct-developing species C. dilatata, and initial energy content was lower—by about 27%—for eggs of that species. In both species, protein content in the eggs was the principal biochemical component. Although females of C. fecunda produce 180 times more eggs than C. dilatata, females of C. dilatata invest 20 times more energy in each of their offspring, through nurse eggs; their embryos have approximately eight times more energy at hatching and about 5 times more energy when they enter the benthos, despite a long planktonic feeding period in the larvae of C. fecunda. Evolutionary switching between modes of development in these species is reflected in shifts in maternal energy investment.     

Otolith microstructure and daily increment validation of marbled sole (<Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis>)

We examined the daily deposition of otolith increments of marbled sole (Pseudopleuronectes yokohamae) larvae and juveniles by rearing experiments, and estimated the growth pattern of wild larvae and juveniles in Hakodate Bay (Hokkaido Island, Japan). At 16°C, prominent checks (inner checks; ca. 19.8 µm in diameter) were observed on the centers of sagittae and lapilli extracted from 5-day-old larvae. On both otoliths, distinctive and regular increments were observed outside of the inner checks, and the slopes of regression lines between age and the number of increments (n_i) (for sagittae: n_i=0.98×Day–5.90; for lapillus: n_i=0.96×Day–5.70) did not significantly differ from 1. Inner check formations were delayed at lower temperature, and the inner checks formed 13 days after hatching at 8°C. Over 80% of larvae, just after their yolk-sac has been absorbed completely (stage C), had inner checks on both their otoliths. On the lapilli, other checks (outer check) formed at the beginning of eye migration (stage G). To validate the daily deposition of increments during the juvenile stage, wild captured P. yokohamae juveniles were immersed in alizarin complexone (ALC)-seawater solutions and reared in cages set in their natural habitat. After 6 days, the mean number of rings deposited after the ALC mark was 5.7. The age–body length relationship of wild P. yokohamae larvae and juveniles caught in Hakodate Bay was divided into three phases. In the larval period, the relationship was represented by a quadratic equation (notochord length=–0.010×Age²+0.682×Age–2.480, r²=0.82, P<0.001), and the estimated instantaneous growth was 0.38 mm day^–1 at 15 days, 0 mm day^–1 at 34 days and –0.12 mm day^–1 at 40 days. The age–body length relationship in the early juvenile stage (<50 days) and the late juvenile stage (>50 days) were represented by linear equations (standard length=0.055×Age+5.722 and standard length=0.345×Age–9.908, respectively). These results showed that the growth rates in the late larval periods and the early juvenile stage were lower than those in the early larval stage and late juvenile stage; during the slow growth period, energy appears to be directed towards metamorphosis rather than body growth. This study provided the information needed to use otolith microstructure analysis for wild marbled sole larvae and juveniles.Communicated by T. Ikeda, Hakodate     

Effects of temperature on activity,food consumption rates,and gut passage times of seaweed-eating<Emphasis Type="Italic"> Tegula</Emphasis> species (Trochidae) from California

Previous feeding studies on herbivorous marine snails rarely have focused on temperature effects on food intake. If temperature affects food intake, ectothermic snails may experience difficulty obtaining sufficient nutritional resources, limiting their ability to sustain populations at suboptimal temperatures. We hypothesized that the feeding responses of Tegula species would correspond with temperatures characteristic of their geographic distributions. We determined activity, consumption rates, and gut passage times at 11°C, 15°C, 19°C, and 23°C for three Tegula species with distinct thermal distributions: T. brunnea (cold water), T. aureotincta (warm water), and individuals from warm- and cold-water populations of T. funebralis, a broadly distributed species. Activity and consumption rates of T. aureotincta increased with increasing temperature, but were highest for T. brunnea at 19°C, a temperature rarely achieved in habitats occupied by this species, and lowest at 11°C. Warm-water T. funebralis showed significantly lower activity and consumption rates at 11°C, whereas cold-water T. funebralis consumed food fastest at 15°C and were most active at 23°C. Temperature affected gut passage time only in T. aureotincta. These data suggest that temperature might influence the northern limit of T. aureotincta by affecting activity and food consumption rates. T. brunneas activity and ability to consume food were not hindered by warmer temperatures despite the present day restriction of this species to colder waters. Also, widely separated (>300 km) T. funebralis populations may be adapted to regional conditions based on the different temperature responses of northern and southern snails.Communicated by P.W. Sammarco, Chauvin     

Embryogenesis and larval biology of the ahermatypic scleractinian<Emphasis Type="Italic"> Oculina varicosa</Emphasis>

The ivory tree coral Oculina varicosa (Leseur, 1820) is an ahermatypic branching scleractinian that colonizes limestone ledges at depths of 6–100 m along the Atlantic coast of Florida. This paper describes the development of embryos and larvae from shallow-water O. varicosa, collected at 6–8 m depth in July 1999 off Fort Pierce, Florida (27°32.542 N; 79°58.732 W). The effect of temperature on embryogenesis, larval survival, and larval swimming speed were examined in the laboratory. Ontogenetic changes in geotaxis and phototaxis were also investigated. Embryos developed via spiral cleavage from small (100 µm), negatively buoyant eggs. Ciliated larvae developed after 6–9 h at 25°C. Embryogenesis ceased at 10°C, was inhibited at 17°C, and progressed normally at 25°C and 30°C. Larval survival, however, was high across the full range of experimental temperatures (11–31°C), although mortality increased in the warmest treatments (26°C and 31°C). Larval swimming speed was highest at 25°C, and lower at the temperature extremes (5°C and 35°C). An ontogenetic change in geotaxis was observed; newly ciliated larvae swam to the water surface and remained there for approximately 18 h, after which they swam briefly throughout the water column, then became demersal. Early larvae showed no response to light stimulation, but at 14 and 23 days larvae appeared to exhibit negatively phototactic behavior. Although low temperatures inhibited the development of O. varicosa embryos, the larvae survived temperature extremes for extended periods of time. Ontogenetic changes in larval behavior may ensure that competent larvae are close to the benthos to facilitate settlement. Previous experiments on survival, swimming speeds, and observations on behavior of O. varicosa larvae from deep-water adults indicate that there is no difference between larvae of the deep and shallow populations.Communicated by J.P. Grassle, New Brunswick     

Predation on egg capsules of <Emphasis Type="Italic">Zidona</Emphasis><Emphasis Type="Italic">dufresnei</Emphasis> (Volutidae): ecological implications

Among the diverse patterns of energy allocation to the offspring of gastropods, the presence of egg capsules to protect embryos is common. Females of the edible snail Zidona dufresnei attach egg capsules to hard substrates in shallow Argentine Patagonian waters (40°45′S, 64°56′W) during spring-summer. Embryonic development takes about 30 days at 22°C. In this study, three likely capsule predator species and the marks left by each on egg capsule walls were identified in laboratory experiments in February 2010. Abundances of predators and egg capsules with evidence of predation were assessed in the field in the summers of 2010 and 2011. Under laboratory conditions (N = 10 replicates per treatment and control), the predation rate by the chiton Chaetopleura isabellei was the highest (up to 90%), followed by the gastropod Tegula patagonica and the crab Neohelice granulata (~20% each). Nearly 60% of 41 capsules found in the field showed signs of predation. According to the marks identified in the laboratory, C. isabellei was responsible for 79% of this predation, and T. patagonica for the rest. Predation appears to be important during the encapsulated early life and could be an agent for selecting for resistant capsule walls and a relatively shorter development time.     

Intraspecific competition in<Emphasis Type="Italic"> Fucus serratus</Emphasis> and<Emphasis Type="Italic"> F</Emphasis>.<Emphasis Type="Italic"> evanescens</Emphasis> (Phaeophyceae: Fucales) germlings: effects of settlement density,nutrient concentration,and temperature

Survival and growth of early post-settlement stages are critical for the development of seaweed populations. Fucoid germlings commonly settle in dense monospecific aggregates, where intraspecific competition and environmental variables (e.g. nutrient concentration and temperature) may affect survival and growth. Using factorial experiments, we determined the effects of settlement density (~10, ~50 and ~250 germlings cm^–2), nutrient enrichment (from ~10 to ~40 µM N and from ~0.5 to ~2.5 µM P), and temperature (7°C and 17°C) on Fucus serratus and F. evanescens germlings in laboratory cultures over 3 months. Settlement density, nutrient concentration and temperature interactively affected growth of germlings, and the magnitude of this interaction varied between the two species. This represents the first record of such factorial interactions in Fucus spp. germlings. Intraspecific competition, estimated as the relative reduction in germling growth and survival from low to high densities, increased with decreasing nutrient concentration and increasing temperature in both species. While temperature and nutrient concentration had little effect on germling size distributions, size inequality and skewness generally increased with germling density, indicating that a few large individuals gained dominance and suppressed many smaller ones at high density. Self-thinning increased with settlement density and depended on nutrient concentration and species at high density. At high density, self-thinning increased with decreasing nutrient levels in F. evanescens, but not in F. serratus. At low density, nutrient enrichment increased germling growth in F. evanescens, but not in F. serratus, whereas growth in both species was stimulated by nutrient enrichment at higher densities. These results suggest that germling growth and self-thinning are more sensitive to variation in nutrient concentration in F. evanescens than in F. serratus. The potential implications of our findings for the understanding of eutrophication-related abundance changes in both species in southern Norway are discussed.Communicated by L. Hagerman, Helsingør     

Energy content at metamorphosis and growth rate of the early juvenile barnacle<Emphasis Type="Italic"> Balanus amphitrite</Emphasis>

The energetic cost of metamorphosis in cyprids of the barnacle Balanus amphitrite Darwin was estimated by quantification of lipid, carbohydrate and protein contents. About 38–58% (4–5 mJ individual^–1) of cypris energy reserves were used during metamorphosis. Lipids accounted for 55–65%, proteins for 34–44% and carbohydrates for <2% of the energy used. Juveniles obtained from larvae fed 10⁶ cells ml^–1 of Chaetoceros gracilis were bigger (carapace length: 560–616 µm) and contained more energy (5.56±0.10 mJ juvenile^–1) than their counterparts (carapace length: 420–462 µm; energy content: 2.49±0.20 mJ juvenile^–1) obtained from larvae fed 10⁴ cells ml^–1. At water temperatures of 30°C and 24°C and food concentrations of 10⁴ and 10² cells ml^–1 (3:1 mixture of C. gracilis and Isochrysis galbana) as well as under field conditions (26.9±3.1°C and 2.2±0.8 µg chlorophyll a l^–1), juveniles obtained from larvae fed the high food concentration grew faster than juveniles obtained from larvae fed low food concentration until 5 days post-metamorphosis. Laboratory experiments revealed a combined effect of early juvenile energy content, temperature and food concentration on growth until 5 days post-metamorphosis. After 10 days post-metamorphosis, the influence of the early juvenile energy content on growth became negligible. Overall, our results indicate that the energy content at metamorphosis is of critical importance for initial growth of juvenile barnacles and emphasize the dependency of the physiological performance of early juvenile barnacles on the larval exposure to food.Communicated by O. Kinne, Oldendorf/LuheAn erratum to this article can be found at     

Patterns of gamete incompatibility between the blue mussels<Emphasis Type="Italic"> Mytilus edulis</Emphasis> and<Emphasis Type="Italic"> M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis>

Previous research on gametic incompatibility in marine invertebrates suggests that for highly dispersive marine invertebrate species, barriers to fertilization among closely related taxa are often incomplete and sometimes asymmetric. The nature of these barriers can dramatically affect the patterns of gene flow and genetic differentiation between species, and thus speciation. Blue mussels, in the genus Mytilus, are genetically distinct in allopatry yet hybrids are present wherever any two species within the group co-occur. The present study sampled M. edulis (L.) and M. trossulus (Gould) in May and June 2001 from the East Bay section of Cobscook Bay, Maine, USA (latitude 44°56′30″N; longitude 67°07′50″W), where the two species are sympatric. Gamete incompatibility was investigated in a series of laboratory fertilizations carried out in July 2001. The proportion of fertilized eggs typically exceeded 80% at sperm concentrations of 10³–10⁴ ml^?1 among intraspecific matings (n=18), but was <30% even at sperm concentrations in excess of 10⁵–10⁶ ml^?1 for interspecific matings (n=13). Further analysis indicated that approximately 100- to 700-fold higher sperm concentrations were required to achieve 20% fertilization in interspecific matings relative to intraspecific matings, indicating strong barriers to interspecific fertilization. The proportion of fertilized eggs did not follow this general pattern in all matings, however. The eggs from two (out of five) M. edulis females were almost as receptive to M. trossulus sperm as they were to M. edulis sperm. In contrast, the eggs from all M. trossulus females (n=3) were unreceptive to M. edulis sperm, suggesting that fertilization barriers between these species may be asymmetric. Given the experimental design employed in this study, the results are also consistent with a strong maternal or egg effect on the level of interspecific gamete compatibility in M. edulis.     

Spawning and development in <Emphasis Type="Italic">Osedax</Emphasis> boneworms (Siboglinidae,Annelida)

We report observations on spawning and early development in bone-eating worms of the genus Osedax. Individual females of Osedax rubiplumus were observed at 1820 m depth freely spawning hundreds of oocytes, and females of an undescribed species, Osedax “orange collar”, were observed spawning in laboratory aquaria. Cytological and molecular analysis of the spawned oocytes of two Osedax species revealed no evidence for the bacterial endosymbionts that the female worms require for their nutrition, suggesting that the bacteria must be acquired later from the environment, as they are in other siboglinids. Individual O. “orange collar” females released an average of 335 (±130) eggs per day, but the number of oocytes spawned per day varied greatly, suggesting that not all the females spawned daily. Fertilization rates of the spawned oocytes varied from 0 to 100%, though most females showed nearly 100% fertilization rates. Oocytes spawned in the laboratory at 4–6°C were negatively buoyant. If fertilized, these oocytes extruded polar bodies and then after at least four hours cleaved unequally. Subsequent cleavages occurred in a spiral pattern at roughly 2-h intervals, resulting in free-swimming trochophore larvae after 24 h. These lecithotrophic trochophores swam for 9–16 days before settling with several hooked chaetae, similar to those of dwarf Osedax males. The larval life span of the Osedax species studied in the laboratory appears to be shorter than in closely related Vestimentifera. Osedax rubiplumus, on the other hand, has much larger oocytes and so may have greater dispersal potential than these other Osedax species. The high fecundity and apparently continuous reproduction of Osedax boneworms permits the opportunistic exploitation of sunken vertebrate bones. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of dietary fatty acids on the reproductive success of the calanoid copepod<Emphasis Type="Italic"> Temora longicornis</Emphasis>

Egg production and hatching success of the copepod Temora longicornis were measured in laboratory experiments and in the field (North Sea). In the laboratory, ingestion of four algal species (Thalassiosira weissflogii, Phaeocystis globosa, Isochrysis sp. and Dunaliella tertiolecta) was followed and the content of fatty acids in the algae was determined. The two food types (T. weissflogii and Isochrysis sp.) that provided the highest ingestion of carbon and long chain fatty acids also resulted in the highest egg production rate (E_r) and hatching success (H%). In contrast, D. tertiolecta led to both low ingestion of carbon and long chain fatty acids, resulting in low reproductive success. There was a positive relationship between the amount of eicosapentaenoic fatty acid [20:5(n-3), EPA] ingested and E_r and H%, and of the ratio between docosahexaenoic and eicosapentaenoic fatty acid [22:6(n-3)/20:5(n-3), DHA/EPA] in the ingested food and H%. In the field, chlorophyll a and specific fatty acids were measured and protists were enumerated, in order to investigate the link between these factors and the reproductive success of T. longicornis. Hatching time was found to be related to temperature and exceeded 120 h at 6°C. No relationship was found between chlorophyll a and reproductive success (E_r or H%). E_r correlated with the concentration of diatoms and ciliates, which were the dominating protists in early spring, indicating that food quantity was the limiting factor for E_r. As in the laboratory experiments, H% was dependent on the fatty acid DHA and the ratio of DHA/EPA, which indicates that the quality of eggs (H%) is linked to the quality of food.Communicated by M. Kühl, Helsingør     

Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). I.<Emphasis Type="Italic"> Mysis mixta</Emphasis> (Mysidacea)

Seasonal population dynamics of Mysis mixta Lilljeborg were studied from December 1998 to November 2000 at a 240 m deep site in Conception Bay, Newfoundland. At this depth, temperature was <0°C and salinity between 32.0 and 34.0 psu year-round. The spring phytoplankton bloom began in early or late March and reached a maximum in late April to mid-May. M. mixta exhibited a highly synchronised life cycle, with spawning and mating occurring in October to November, embryos brooded for ~5 months, and juveniles released during spring bloom sedimentation in April and May. Females were semelparous and died at age 2.5 years, following release of juveniles in spring, whereas the majority of mature males died at age 2 years, following mating in November. The biennial life cycle of this population resulted in the presence of two cohorts in the hyperbenthos at any given time. Variation in density and biomass was low among cohorts but high within cohorts, the latter probably due to the high motility of mysids. Densities in 1999 and 2000 were 242±379 and 544±987 ind. per 100 m³ (mean±SD), respectively. Although growth rates were similar between years, rates measured from changes in dry mass differed both seasonally and among life-history stages (range from –4 to 7 mg month^–1). Annual secondary production was estimated at 29–73 mg C m^–2 in 1999 and 53–205 mg C m^–2 in 2000. The annual P/B ratios were 1.62 and 1.19 in 1999 and 2000, respectively.Communicated by J.P. Grassle, New Brunswick     

Classification of juvenile rockfish,<Emphasis Type="Italic"> Sebastes inermis</Emphasis>, to<Emphasis Type="Italic"> Zostera</Emphasis> and<Emphasis Type="Italic"> Sargassum</Emphasis> beds,using the macrostructure and chemistry of otoliths

Young-of-the-year (YOY) Sebastes inermis use Zostera and Sargassum beds as nursery grounds, although it is not known which habitat YOY prefer. In this study, YOY S. inermis were accurately assigned to Zostera or Sargassum beds by two approaches: the width and length of the otolith nucleus and the composition of trace elements in otoliths. The otolith nucleus was initially opaque and then showed a marked shift to hyaline deposition once YOY settled in the nursery grounds. The first hyaline zone (FHZ) was deposited earlier in Zostera beds (from mid-May to early June) than in Sargassum beds (around mid-summer). Likewise, irrespective of settlement year, the FHZ was formed at both significantly younger ages and shorter back-calculated sizes (total length, TL) in the Zostera bed (overall mean: 131±3 days; 2.5±1.7 mm TL) than in the Sargassum bed (overall mean: 158±12 days; 61.3±1.00 mm TL). YOY collected in the Zostera bed were born earlier (mainly in January) than YOY from the Sargassum bed (mainly in February). In addition, a significant linear relationship was found between the age at formation of the FHZ and nucleus dimensions, suggesting that nucleus dimensions were a reliable macroscopic indicator of the time of formation of the FHZ and, consequently, also an indicator of the nursery where YOY grew. Linear discriminant function analysis (LDFA) based on the width and length of the otolith nucleus could distinguish juveniles from Zostera (88–96%) and Sargassum (96–97%) beds with a high degree of accuracy. In the other approach, six detectable trace elements (Li, Mn, Ni, Cu, Zn, and Ba) in otoliths of YOY collected in the nursery grounds were measured by high-resolution, inductively coupled mass spectrometry. LDFA based on the trace elemental composition separated YOY from three nurseries with 100% of accuracy. Findings suggest that both the trace elemental composition and nucleus dimensions of otoliths can be used as natural tags of the nursery grounds of S. inermis, offering a considerable potential for answering questions on habitat use and the contribution of nursery grounds to the adult stock.Communicated by T. Ikeda, Hakodate     

Early life history of two closely related gastropods,<Emphasis Type="Italic"> Rissoa auriscalpium</Emphasis> and<Emphasis Type="Italic"> Rissoa italiensis</Emphasis> (Caenogastropoda: Rissoidae)

A comparative analysis of the early life history of two common gastropod forms living on the leaves of the Mediterranean seagrass Posidonia oceanica has been carried out, taking into account timing and phases of development. The forms have a different distribution along a depth transect at Ischia Island (Gulf of Naples, Italy), the more squat and ribbed being mainly present between 1 and 15 m depth, with a maximum density at 3 m, the other, between 10 and 30 m. They were distinguished as sibling species, Rissoa italiensis (Verduin, 1985) and Rissoa auriscalpium (L., 1758), on the basis of protoconch size. However, to date, the systematic relationship between them is still unclear. Electrophoretic studies showed lower genetic distance between the two forms along the transect, than among populations from other locations in the Mediterranean Sea. R. auriscalpium have planktonic development, with a higher number of smaller eggs, while R. italiensis have an intracapsular veliger, with hatching juveniles. As for the patterns of development, while the same stages are recognizable in the two gastropod forms up to the formation of the veliger, several differences in timing occur, along with differences in growth and death rates of the embryos. R. auriscalpium hatches as a veliger at the first phase of torsion, about 10 days after spawning, while R. italiensis completes its torsion and metamorphosis within the capsule, and then hatches as a juvenile about 18 days after spawning. The time of encapsulation is what seems to lead to similar developmental sequences with different reproductive patterns and ecological roles, depending on the organization of the elements in the capsule.Communicated by R. Cattaneo-Vietti, Genova     

Seasonal variations in the growth rates of euphausiids (<Emphasis Type="Italic">Thysanoessa inermis</Emphasis>, <Emphasis Type="Italic">T. spinifera</Emphasis>, and <Emphasis Type="Italic">Euphausia pacifica</Emphasis>) from the northern Gulf of Alaska

The euphausiids Thysanoessa inermis (Kroyer 1846), Thysanoessa spinifera (Holmes 1900), and Euphausia pacifica (Hansen 1911) are key pelagic grazers and also important prey for many commercial fish species in the Gulf of Alaska (GOA). To understand the role of the euphausiids in material flows in this ecosystem their growth rates were examined using the instantaneous growth rate (IGR) technique on the northern GOA shelf from March through October in 2001–2004. The highest mean molting increments (over 5% of uropod length increase per molt) were observed during the phytoplankton bloom on the inner shelf in late spring for coastal T. inermis, and on the outer shelf in summer for T. spinifera and more oceanic E. pacifica, suggesting tight coupling with food availability. The molting rates were higher in summer and lower in spring, for all species and were strongly influenced by temperature. Mean inter-molt periods calculated from the molting rates, ranged from 11 days at 5°C to 6 days at 8°C, and were in agreement with those measured directly during long-term laboratory incubations. Growth rate estimates depended on euphausiid size, and were close to 0 in early spring, reaching maximum values in May (0.123 mm day⁻¹ or 0.023 day⁻¹ for T. inermis) and July (0.091 mm day⁻¹ or 0.031 day⁻¹ for T. spinifera). The growth rates for E. pacifica remained below 0.07 mm day⁻¹ (0.016 day⁻¹) throughout the season. The relationship between T. inermis weight specific growth rate (adjusted to 5°C) and ambient chlorophyll-a concentration fit a Michaelis–Menten curve (r ² = 0.48) with food saturated growth rate of 0.032 day⁻¹ with half saturation occurring at 1.65 mg chl-a m⁻³, but such relationships were not significant for T. spinifera or E. pacifica.     

Egg survival,embryonic development,and larval characteristics of northern shrimp (<Emphasis Type="Italic">Pandalus borealis</Emphasis>) females subject to different temperature and feeding conditions

Laboratory experiments on ovigerous females of northern shrimp (Pandalus borealis) were used to assess the effects of temperature and food ration on female condition during incubation and examine how combined effects of temperature and female condition influenced egg survival, embryonic development, and larval characteristics. Ovigerous females were maintained at 2°C, 5°C, and 8°C and fed on a low (three times/week; 2–2.7% W/W) or high ration (five times/week at satiation). The increase in temperature accelerated the developmental time of the eggs but their survival at 8°C was reduced. Conversion efficiency of yolk reserves in developing embryos was significantly reduced at elevated temperatures and larvae hatching at 2°C and 5°C were significantly larger and heavier than those hatching at 8°C. The experimental design did not result in any effect of food ration on the energetic condition of females or on egg characteristics and their biochemical composition. However, lower energy reserves were observed for females held at 8°C.     

Adaptations of subtropical Venus clams to predation and desiccation: endurance of<Emphasis Type="Italic"> Gafrarium tumidum</Emphasis> and avoidance of<Emphasis Type="Italic"> Ruditapes variegatus</Emphasis>

Intertidal endobenthic bivalves are often dislodged from sediments by hydrodynamic forces. As a result, they encounter the dangers of predation and desiccation, which are generally harsh near the sediment surface. To cope with such dangers, the bivalves possibly possess: (1) a strong body to endure predation and desiccation stress, (2) quick mobility to avoid the stresses, or (3) a high growth rate for attaining a size refuge. The present study examined which of these modes are adopted by the subtropical cobbled-shore Venus clams Gafrarium tumidum (Röding, 1798) and Ruditapes variegatus (Sowerby, 1852), revealing the following interspecific differences. (1) G. tumidum survived better than R. variegatus did in harsh experimental conditions, namely: the experimental cages exposed to predation and desiccation on a cobbled shore; a laboratory aquarium with a predatory crab Scylla serrata; and ovens with high temperatures (27°C and 34°C). (2) R. variegatus was more mobile than G. tumidum was, digging into the sediment on a cobbled shore more rapidly at both high and low tides. (3) The two species with shell lengths 20–30 mm showed similar growth rates (median: –0.2 to 44.5 m day^–1) in seasonal mark–recapture surveys over 2 years. Overall, to cope with the dangers of predation and desiccation G. tumidum appears to have a strong body, while R. variegatus displays rapid mobility, and neither species seems to attain a size refuge through rapid growth. Such species-specific modes are discussed in relation to the interspecific differences found in shell morphology.Communicated by T. Ikeda, Hakodate