Decreased lipid storage in juvenile Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) during settlement in cold-water eelgrass habitat

We characterized the prey field and the lipid classes/fatty acids in the flesh of age 0 juvenile cod (Gadus morhua) during their late-summer/fall arrival and settlement into eelgrass (Zostera marina) in coastal Newfoundland. Examination of available prey demonstrated a high abundance of small zooplankton (Acartia, Microsetella and Oithona sp.) with no larger Calanus sp. prey. Breakpoint analysis showed significant changes in the accumulation of relative (mg g⁻¹ wet weight) and absolute (μg fish⁻¹) amounts of lipid with standard length at the time of settlement (~60 mm standard length). Settling juvenile cod showed an alternate lipid utilization strategy where they catabolized phospholipids (PL) to a greater extent than triacylgylcerols (TAG). Polyunsaturated fatty acids (PUFA) content in cod flesh decreased as fish grew indicating that nearshore zooplankton quality was not optimal for PL formation. The dramatic reduction in cod PL was likely due to both catabolism of muscle and a lack of dietary PUFA suitable for PL synthesis. However, juvenile cod continued to grow, leading to decreased lipid stores and suggesting that cod settling into eelgrass are under intense selection pressure for growth prior to the onset of winter, possibly as a means of escaping gape-limited predation. These data contrast better-studied freshwater and estuarine systems in which lipid storage is critical for successful overwintering.     

Fine-scale observations of the predatory behaviour of the carnivorous copepod <Emphasis Type="Italic">Paraeuchaeta norvegica</Emphasis> and the escape responses of their ichthyoplankton prey,Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and quantitative measurement) of predator–prey interactions between these two species in 3-dimensions. Tail beats, used by cod larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are used to estimate the hydrodynamic signal strength of the cod larva’s tail beats and the copepod’s perceptive field for larval fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva’s capture. These observations can serve as input to the predator–prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae.     

Energy content and fecundity of capelin (<Emphasis Type="Italic">Mallotus villosus</Emphasis>) along a 1,500-km latitudinal gradient

Capelin is a planktivorous key fish species in many subarctic ecosystems representing the link between lower trophic levels and apex predators. Little is known, however, of capelin in Greenland waters, but it has been suggested that size and growth increases due to difference in food availability and temperature conditions along a 1,500 km south–north gradient on the west coast. It is presently unknown how the qualitative state of capelin energy content is affected along this gradient. Based on 2007 and 2008 samples, we show that energy content increases with capelin length in both spawning and non-spawning fish and that it varies with latitude in spawning fish along West Greenland (60–71°N). Combining our results on energy content with information on capelin growth along the same latitudinal climate gradient demonstrates that less and lower-quality food is available to capelin predators in the south than in the north.     

Inverse vertical migration and feeding in glacier lanternfish (<Emphasis Type="Italic">Benthosema glaciale</Emphasis>)

A bottom-mounted upward-facing 38-kHz echo sounder was deployed at ~400 m and cabled to shore in Masfjorden (~60^°52′N, ~5^°24′E), Norway. The scattering layers seen during autumn (September–October) 2008 were identified by trawling. Glacier lanternfish (Benthosema glaciale) were mainly distributed below ~200 m and displayed three different diel behavioral strategies: normal diel vertical migration (NDVM), inverse DVM (IDVM) and no DVM (NoDVM). The IDVM group was the focus of this study. It consisted of 2-year and older individuals migrating to ~200–270 m during the daytime, while descending back to deeper than ~270 m during the night. Stomach content analysis revealed increased feeding during the daytime on overwintering Calanus sp. We conclude that visually searching glacier lanternfish performing IDVM benefit from the faint daytime light in mid-waters when preying on overwintering Calanus sp.     

Foraging behaviour of larval cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) at low light intensities

The ability to forage at low light intensities can be of great importance for the survival of fish larvae in a pelagic environment. Three-dimensional silhouette imaging was used to observe larval cod foraging and swimming behaviour at three light intensities (dusk ~1.36 × 10⁻³ W/m², night ~1.38 × 10⁻⁴ W/m² and darkness ~3.67 × 10⁻⁶ W/m²) at 4 different ages from 6 to 53 days post-hatch (dph). At 6 dph, active pursuit of prey was only observed under dusk conditions. Attacks, and frequent orientations, were observed from 26 dph under night conditions. This was consistent with swimming behaviour which suggested that turn angles were the same under dusk and night conditions, but lower in darkness. Cod at 53 dph attacked prey in darkness and turn angles were not different from those under other light conditions. This suggests that larvae are still able to feed at light intensities of 3.67 × 10⁻⁶ W/m². We conclude that larval cod can maintain foraging behaviour under light intensities that correspond to night-time at depths at which they are observed in the field, at least if they encounter high-density patches of prey such as those that they would encounter at thin layers or fronts.     

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod <Emphasis Type="Italic">Rapana</Emphasis><Emphasis Type="Italic">venosa</Emphasis> (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female⁻¹ week⁻¹. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Lyngbya majuscula</Emphasis> blooms and the diet of small subtropical benthivorous fishes

Increasing concerns about the ecological impacts of ongoing and possibly worsening blooms of the toxic, carcinogenic cyanobacteria Lyngbya majuscula in Moreton Bay, Australia, led us to assess differences in meiofaunal prey assemblages between bloom and non-bloom substrates and the potential dietary impacts of dense L. majuscula blooms on the omnivorous benthivore, the Eastern Long-finned Goby, Favonigobius lentiginosus and the obligate meiobenthivorous juveniles of Trumpeter Whiting, Sillago maculata. Marked differences in invertebrate communities were found between sandy and L. majuscula bloom foraging substrates, with copepods significantly more abundant (18.49% vs. 70.44% numerical abundance) and nematodes significantly less abundant (55.91% vs. 1.21% numerical abundance) within bloom material. Gut analyses showed that bentho-planktivorous fishes exposed to L. majuscula in captivity had consumed a significantly greater quantity of prey by both total number (P < 0.0019) and volume (P < 0.0006) than fish exposed to sand treatments. Thus, it is likely for such fishes that L. majuscula blooms increase rates of prey encounter and consumption, with consequent changes in trophic relationships through shifts in predator–prey interactions between small benthivorous fishes and their meiofaunal prey.     

Auditory defence in the peacock butterfly (<Emphasis Type="Italic">Inachis io</Emphasis>) against mice (<Emphasis Type="Italic">Apodemus flavicollis</Emphasis> and <Emphasis Type="Italic">A. sylvaticus</Emphasis>)

Morphological and behavioural traits can serve as anti-predator defence either by reducing detection or recognition risks, or by thwarting initiated attacks. The latter defence is secondary and often involves a ‘startle display’ comprising a sudden release of signals targeting more than one sensory modality. A suggested candidate for employing a multimodal defence is the peacock butterfly, Inachis io, which, by wing-flicking suddenly, produces sonic and ultrasonic sounds and displays four large eyespots when attacked. The eyespots make small birds retreat, but whether the sounds produced thwart predator attacks is largely unknown. Peacocks hibernate as adults in dark wintering sites and employ their secondary defence upon encounter with small rodent predators during this period. In this study, we staged predator–prey encounters in complete darkness in the laboratory between wild mice, Apodemus flavicollis and Apodemus sylvaticus, and peacocks which had their sound production intact or disabled. Results show that mice were more likely to flee from sound-producing butterflies than from butterflies which had their sound production disabled. Our study presents experimental evidence that the peacock butterfly truly employs a multimodal defence with different traits targeting different predator groups; the eyespots target birds and the sound production targets small rodent predators.     

The role of fecundity regulation and abortive maturation in the reproductive strategy of Norwegian spring-spawning herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

This study investigates the reproductive strategy, an important component in the estimation of stock reproductive potential, in Norwegian spring-spawning (NSS) herring (Clupea harengus), an iteroparous, extreme capital spawner, through the estimation of fecundity over a period of 3 years including two complete maturation cycles and three spawning seasons. NSS herring have an ‘optimistic’ strategy, with almost all adult herring caught in August being in the vitellogenic stage of ovary development, despite overwintering energy levels not being determined at this time. Fecundity in the summer, i.e., more than half a year before spawning in spring (February–April), was also much higher than could be supported by an individual’s concurrent energy levels. Consequently, fecundity was later reduced through atresia with the majority of this occurring before overwintering. The total reduction and the length of the time period in which the reduction took place appeared to vary between years. During the spawning season, atresia was mostly prevalent in small first-time spawners <180 g and several individuals aborted ovary development at this time. Final fecundity varied between years with a difference of up to 18% and was linked to annual variations in condition. In conclusion, this extensive field study has demonstrated that each individual herring can display a suite of size-specific reproductive tactics to fine-tune oocyte production in response to fluctuating levels of planktonic prey.     

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.     

Reproductive periodicity,spawning and development of the deep-sea scleractinian coral <Emphasis Type="Italic">Flabellum angulare</Emphasis>

Increasing threats to deep-sea corals highlight the need to expand knowledge of these taxa so that conservation measures can be developed. The present study focused on the reproductive patterns of the deep-sea solitary coral Flabellum angulare. A series of samples (n = 398) collected in 2006–2008 in the northwest Atlantic at depths of 925–1,430 m revealed that gametogenesis was synchronous among males and females and fluctuated seasonally. Initiation of gamete synthesis was estimated to be in August–September and spawning in June. Further analysis and daily monitoring of 30–60 individuals maintained in a flow-through mesocosm showed that gamete release occurred in March–June with a peak in May. Release of oocytes coincided with rising seawater temperatures and high deposition rates indicative of elevated water column productivity. Oocytes (900–1,200 μm diameter) were released through the oral cavity, generally in bundles of 3–5 surrounded by mesenterial filaments and attached to a thread (30–50 mm long). As oocytes became free in the water column, ovulation occurred followed by fertilization. Eggs/embryos initially remained on the tentacles of the spawner before either falling onto the substratum or floating to the surface. The embryos developed into planula larvae measuring 2–3 mm in length within about 24 h. Together, these findings shed new light on the strategies used by deep-sea corals to maximize their reproductive success.     

Dissolved saxitoxin causes transient inhibition of sensorimotor function in larval Pacific herring (<Emphasis Type="Italic">Clupea harengus pallasi</Emphasis>)

Herring (Clupea harengus pallasi) spawning sites in Puget Sound, Washington overlap spatially and temporally with blooms of Alexandrium catenella, a toxic dinoflagellate species responsible for paralytic shellfish poisoning. Consequently, newly hatched herring larvae may be regularly exposed to the suite of dissolved paralytic shellfish toxins that are released into the water column from toxic cells during blooms. To date, virtually nothing is known about the impacts of these neurotoxins on early developmental stages of marine fish. In the present study, herring larvae at three ages, 0 days post hatch (dph), 4 dph, and 11 dph, were exposed to dissolved saxitoxin (STX) in 24-h and multi-day exposures. All larvae were examined for sensorimotor function (i.e. spontaneous swimming behavior and touch response). Significant reductions in spontaneous and touch-activated swimming behavior occurred within 1 h of exposure. EC₅₀s at 1 h of exposure were 1,500, 840, and 700 μg STX equiv. l⁻¹ for larvae introduced to STX at 0, 4, and 11 dph, respectively. This progressive age-specific increase in STX-induced paralysis suggests that older larvae were more sensitive to the toxin than younger larvae. Interestingly, herring larvae at all ages exhibited a significant degree of neurobehavioral recovery within 4–24 h of continuous exposure relative to the 1-h time point. This recovery of normal motor behaviors was not observed in previous studies with freshwater zebrafish (Danio rerio) larvae under the same continuous exposure conditions, suggesting that an adaptive detoxification or toxin sequestration mechanism may have evolved in some species of marine fish larvae. Our data reveal that (1) dissolved STX is bioavailable to marine finfish larvae, (2) the toxin is a paralytic agent with potencies that differ between developmental stages, and (3) STX-induced sensorimotor inhibition occurs rapidly but is transient in marine larvae. Collectively, these results suggest that dissolved algal toxins may have important sublethal effects on marine fish populations.     

Comparative life-history study on sympatric hyperiid amphipods (<Emphasis Type="Italic">Themisto pacifica</Emphasis> and <Emphasis Type="Italic">T</Emphasis>. <Emphasis Type="Italic">japonica</Emphasis>) in the Oyashio region,western North Pacific

Life-history features of the sympatric amphipods Themisto pacifica and T. japonica in the western North Pacific were analyzed based on seasonal field samples collected from July 1996 through July 1998, and data from laboratory rearing experiments. T. pacfica occurred throughout the year, with populations peaking from spring to summer. In contrast, T. japonica were rare from autumn to early winter, but became abundant in late winter to spring. Mature T. pacifica females and juveniles occurred together throughout the year, indicating year-round reproduction. Mature T. japonica females were observed only in spring, and juveniles occurred irregularly in small numbers, suggesting limited, early-spring reproduction in this study area. Size composition analysis of T. pacifica identified a total of eight cohorts over the 2 years of the study. Due to the smaller sample size and rarity of mature females (>9.6 mm) and males (>7.1 mm), cohort analyses of T. japonica were not comparable. Laboratory rearing of specimens at 2°C, 5°C, 8°C and 12°C revealed that a linear equation best expressed body length growth by T. pacifica, while a logistic equation best expressed body length growth by T. japoncia. Combining these laboratory-derived growth patterns with maturity sizes of wild specimens, the minimum and maximum generation times of females at a temperature range of 2–12°C were computed as 32 days (12°C) and 224 days (2°C), respectively, for T. pacifica, and 66 days (12°C) and 358 days (2°C), respectively, for T. japonica. The numbers of eggs or juveniles in females marsupia increased with female body length and ranged from 23 to 64 for T. pacifica and from 152 to 601 for T. japonica. Taking into account the number of mature female instars, lifetime fecundities were estimated as 342 eggs for T. pacifica and 1195 eggs for T. japonica. Possible mechanisms for the coexistence of these two amphipods in the Oyashio region are also discussed.Communicated by O. Kinne, Oldendorf/Luhe     

Intraguild predatory interactions between the jellyfish <Emphasis Type="Italic">Cyanea capillata</Emphasis> and <Emphasis Type="Italic">Aurelia aurita</Emphasis>

While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range of prey concentrations (0.38–3.8 m⁻³) in large containers (2.6 m³) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations. Ingestion rates increased linearly up to prey concentrations of 1.92 m⁻³, yielding maximum clearance rates of ∼2.37 ± 0.39 m³ predator⁻¹ h⁻¹ for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m⁻³) was 4.01 ± 0.78 prey predator⁻¹ h⁻¹. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested prey was often discarded when fresh prey was encountered.     

Irradiance-induced changes in the photobiology of <Emphasis Type="Italic">Halophila johnsonii</Emphasis>

The endangered seagrass Halophila johnsonii Eiseman, exhibits high-light adapted photophysiology consistent with its distribution in intertidal and shallow subtidal (0–3 m) coastal-lagoon habitats along 200 km of southeastern Florida. To examine the short-term responses of this seagrass to three controlled-irradiance treatments (PAR + UVA + UVB [full spectrum], PAR + UVA, and PAR only), greenhouse-acclimated plants were transferred to outdoor mesocosms during July–August 2002. Chlorophyll fluorescence, UV fluorescence, and samples for pigment extraction were collected in the greenhouse, prior to moving the plants outside and on days 1, 2, 3, 4, 6, 10, and 21 of the 24-day experiment. Typical of sun-adapted plants, effective quantum yields measured by pulse-amplitude modulated (PAM) fluorometry were relatively low in all treatments, ranging from 0.46 ± 0.09 (PAR only) to 0.58 ± 0.08 (PAR + UVA + UVB). In the PAR only treatments, there were strong effects on days 1 and 4, presumably because the irradiance in the greenhouse not only lacked all λ<400 nm, but also had low irradiance maxima (∼700 μmol photons m⁻² s⁻¹, compared with ∼1,500 μmol photons m⁻² s⁻¹ outside at midday). There were few treatment differences between PAR only and PAR + UVA treatments indicating little effect of UVA radiation on this species. Differences in effective quantum yields and relative electron transport rates between the PAR only and PAR + UVA + UVB treatments on day 4 indicated rapid acclimation to UVB radiation. Tissues of H. johnsonii contained compounds that absorbed strongly in the UV, with a λ_max at ∼345 nm (depending on the extraction solvent). Absorption peak maxima and minima changed over the course of the experiment but there were no significant light-treatment differences in any pigment parameters. Percent UV shield values, measured using a newly developed UVA PAM fluorometer, were highest the day after plants were transferred from the greenhouse to the outdoor mesocosms and declined significantly to pretreatment levels in all treatments by day 21. Percent UV shield exhibited a significant positive relationship with UV-absorbing pigment (UVP) absorbance, however, the absence of treatment effects suggests that the wavelengths inducing pigment synthesis must lie between 400 and 700 nm (PAR). The results indicate that H. johnsonii rapidly acclimates to high UVB and PAR which may largely explain its distribution in intertidal and shallow subtidal areas.     

Spatio-temporal variations in the diet and stable isotope composition of the Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 of the continental shelf of southeastern Brazil

The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m). The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio. δ¹⁵N and δ¹³C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7 for M. hubbsi was estimated using δ¹⁵N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels.     

Age and growth of the naticid gastropod <Emphasis Type="Italic">Polinices pulchellus</Emphasis> (Gastropoda: Naticidae) based on length frequency analysis and statolith growth rings

In Red Wharf Bay, UK the naticid gastropod, Polinices pulchellus, was more abundant and more highly aggregated during the summer months (June–August 2001) than during the winter (December 2000). Whilst small numbers of juvenile P. pulchellus (4–6 mm shell length) were present throughout the year the population consisted mainly of individuals of 12–14 mm shell length. Juvenile snails grew rapidly in size during the winter and early spring; growth then virtually ceased between May and June, following which there was a further period of rapid growth between August and February. Densities ranged between 57 and 4,073 ha⁻¹ and the largest individual collected during this investigation measured 16.2 mm in shell length. Statoliths from adult P. pulchellus revealed the presence of a settlement ring and two prominent growth rings (rings 1 and 2). A curvilinear relationship exists between statolith diameter and shell length in snails up to 16 mm in length. Settlement rings ranged in diameter from 19.7 to 45.2 μm (mean 29.8 μm; SE=0.41) giving an estimated shell length of the settled juvenile of 1.1 mm. The diameter of ring 1 and ring 2 were significantly correlated indicating that rapid growth during the first year is maintained during year 2. Shell lengths estimated from the diameters of the prominent statolith rings and those obtained from length frequency data analysis (LFDA), were broadly congruent strongly suggesting an annual periodicity to the statolith rings. The largest snails (>15 mm) present within this population were estimated to be between 2 and 3 years old. Von Bertallanfy seasonal growth curves obtained from the LFDA predicted values of L∞, K and t ₀ of 14.32 mm, 1.54 and −0.14 years, respectively, suggesting that P. pulchellus rapidly attains its maximum asymptotic size.     

Life history and production of the mysid <Emphasis Type="Italic">Orientomysis robusta</Emphasis>: high <Emphasis Type="Italic">P/B</Emphasis> ratio in a shallow warm-temperate habitat of the Sea of Japan

Although mysids play important roles in marine food chains, studies on their production are scarce, especially for warm-water species. We investigated life history and production of Orientomysis robusta in a shallow warm-temperate habitat of the Sea of Japan. Its spawning and recruitment occurred throughout the year; 19 overlapping cohorts were recognizable over an annual cycle. The summer cohorts recruited in July–September exhibited rapid growth, early maturity, small brood size, and small body size. A converse set of life history traits characterized the autumn–winter cohorts recruited in October–March. The spring cohorts recruited in April–June had intermediate characteristics of both cohorts. Life spans were 19–33, 21–48, and 69–138 days for summer, spring, and autumn–winter cohorts, respectively, and mortality rates were high for spring and summer cohorts, especially during June–August but were low for autumn–winter cohorts. Production calculated from the summation of growth increments was 488.8 mg DW m⁻² year⁻¹ with an annual P/B ratio of 21.26. The short life span seems to be responsible for such an extremely high P/B ratio. A method not requiring recognition and tracking cohorts gave similar values (534.0 mg DW m⁻² year⁻¹ and 20.49). The close agreement in production values between the two methods indicates our estimates are valid.     

Emergence of an oocytic circumnuclear ring in response to increasing day length in Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

Understanding physiological and environmental variables that initiate sexual maturity would provide fundamental information on life history dynamics. The aim of this study was to test the usefulness of the common circumnuclear ring (CNR), an oocytic structure similar to the Balbiani body, which appears just prior to oocyte development as a predictor of first maturation in Atlantic herring (Clupea harengus). The relative roles of physiology (e.g. fat) and photoperiod as triggers of maturation were also investigated. Samples were collected in May 2008 (72°26′–73°84′N/11°26′–18°40′E) and February 2009 (56°12′–59°45′N/00°25′–03°06′W). These data suggested that thresholds in body size may influence the decision to mature. We also found that short days (winter solstice) may be the photoperiod trigger for a first-decision window for both Norwegian spring-spawning (NSS) and North Sea autumn-spawning (NSAS) herring. The second-decision window for NSAS herring maturation appears to be triggered by longer days (spring equinox), while a decreasing rate of day lengthening may trigger NSS herring maturation. So, photoperiodic cycle is a key determinate of the timing of maturation in Atlantic herring.     

Feeding behavior of the ctenophore <Emphasis Type="Italic">Thalassocalyce inconstans</Emphasis>: revision of anatomy of the order Thalassocalycida

Behavioral observations using a remotely operated vehicle (ROV) in the Gulf of California in March, 2003, provided insights into the vertical distribution, feeding and anatomy of the rare and delicate ctenophore Thalassocalyce inconstans. Additional archived ROV video records from the Monterey Bay Aquarium Research Institute of 288 sightings of T. inconstans and 2,437 individual observations of euphausiids in the Gulf of California and Monterey Canyon between 1989 and 2005 were examined to determine ctenophore and euphausiid prey depth distributions with respect to temperature and dissolved oxygen concentration [dO]. In the Gulf of California most ctenophores (96.9%) were above 350 m, the top of the oxygen minimum layer. In Monterey Canyon the ctenophores were more widely distributed throughout the water column, including the hypoxic zone, to depths as great as 3,500 m. Computer-aided behavioral analysis of two video records of the capture of euphausiids by T. inconstans showed that the ctenophore contracted its bell almost instantly (0.5 s), transforming its flattened, hemispherical resting shape into a closed bi-lobed globe in which seawater and prey were engulfed. Euphausiids entrapped within the globe displayed a previously undescribed escape response for krill (‘probing behavior’), in which they hovered and gently probed the inner surfaces of the globe with antennae without stimulating further contraction by the ctenophore. Such rapid bell contraction could be effected only by a peripheral sphincter muscle even though the presence of circumferential ring musculature was unknown for the Phylum Ctenophora. Thereafter, several live T. inconstans were collected by hand off Barbados and microscopic observations confirmed that assumption.