The influence of temperature on the development of Baltic Sea sprat (Sprattus sprattus) eggs and yolk sac larvae

In spring 2004 and 2005 we performed two sets of experiments with Baltic sprat (Sprattus sprattus balticus Schneider) eggs and larvae from the Bornholm Basin simulating ten different temperature scenarios. The goal of the present study was to analyse and parameterise temperature effects on the duration of developmental stages, on the timing of important ontogenetic transitions, growth during the yolk sac phase as well as on the survival success of eggs and early larval stages. Egg development and hatching showed exponential temperature dependence. No hatching was observed above 14.7°C and hatching success was significantly reduced below 3.4°C. Time to eye pigmentation, as a proxy for mouth gape opening, decreased with increasing temperatures from 17 days post hatch at 3.4°C to 7 days at 13°C whereas the larval yolk sac phase was shortened from 20 to 10 days at 3.8 and 10°C respectively. Maximum survival duration of non-fed larvae was 25 days at 6.8°C. Comparing the experimental results of Baltic sprat with existing information on sprat from the English Channel and North Sea differences were detected in egg development rate, thermal adaptation and in yolk sac depletion rate (YSDR). Sprat eggs from the English Channel showed significantly faster development and the potential to develop at temperatures higher than 14.7°C. North Sea sprat larvae were found to have a lower YSDR compared to larvae from the Baltic Sea. In light of the predictions for global warming, Baltic sprat stocks could experience improved conditions for egg development and survival.     

Spread and potential impact of the recently introduced European green crab,Carcinus maenas,in central California

Our study examines the potential impact of the European green crab Carcinus maenas on communities of coastal embayments of western North America. We document the current distribution and range expansion of this species beyond San Francisco Bay, where C. maenas first became established along this coast in 1989–1990, and we test the effect of C. maenas predation on different species and sizes of infaunal invertebrates in field and laboratory experiments. In our samples from eight coastal locations in central California collected between June 1993 and May 1994, we found no green crabs at the two closest embayments south of San Francisco Bay and found the crabs in all four embayments sampled within 120 km north of San Francisco Bay, up to and including Bodega Harbor. C. maenas was not present in samples from sites farther north. This northward range expansion is apparently the result of larval recruitment by a single cohort, corresponding to the predominant northern transport of surface waters and the approximate distance water moves during larval green crab development. At Bodega Harbor, the current northern range limit, the C. maenas population is now well established and reproducing. Females and males became sexually mature within their first year at 40 mm carapace width, molting approximately monthly from summer through fall, and females were ovigerous in late fall of their first year at 50 mm. We expect larvae from this population to recruit locally and to the north, promoting episodic range extensions as new populations are established and reproduce. Enclosure experiments conducted during the summer of 1993 at the intertidal sandflats of Bodega Harbor showed that C. maenas significantly reduced densities of the most abundant taxa, including the bivalves Transennella confusa and T. tantilla, the cumacean Cumella vulgaris, and the amphipod Corophium sp. Furthermore, Carcinus maenas selectively removed larger (>3 mm) rather than smaller (<1 mm) Transennella spp. in both field and laboratory experiments. Based on the available data from this and other studies of green crabs, and our 10 yr study of community dynamics at Bodega Harbor, we predict C. maenas will significantly alter community structure, ecological interactions, and evolutionary processes in embayments of western North America.     

Potential impact of climate warming on the recruitment of an economically and ecologically important species, the European lobster (Homarus gammarus) at Helgoland, North Sea

A laboratory-based study was performed to assess the impact of climate warming on the recruitment of the endangered population of the European lobster (Homarus gammarus) at Helgoland (North Sea, German Bight). Egg-bearing females collected in situ just after spawning in late summer were subjected to various seasonal temperature regimes. Regimes with elevated temperatures (mild winters) resulted in a strong seasonal forward shift of larval hatching. Hatching took place at significantly lower temperatures than under regimes with normal winters. Experiments on larval development across a range of constant temperatures showed that no successful larval development occurred at temperatures below 14°C. Larval survival increased from 9% at 14°C to 80% at 22°C, while duration of larval development decreased correspondingly from 26 to 13 days. We hypothesize that an ongoing warming of the North Sea will strongly affect the recruitment success of the Helgoland lobster, mainly resulting from a decoupling of the seasonal peak appearance of larvae from optimal external conditions (temperature, food availability) for larval development.     

Elevated temperature impairs onset of symbiosis and reduces survivorship in larvae of the Hawaiian coral, <Emphasis Type="Italic">Fungia scutaria</Emphasis>

Many corals obtain their obligate intracellular dinoflagellate symbionts from the environment as larvae or juveniles. The process of symbiont acquisition remains largely unexplored, especially under stress. This study addressed both the ability of Fungia scutaria (Lamarck 1801) larvae to establish symbiosis with Symbiodinium sp. C1f while exposed to elevated temperature and the survivorship of aposymbiotic and newly symbiotic larvae under these conditions. Larvae were exposed to 27, 29, or 31°C for 1 h prior to infection, throughout a 3-h infection period, and up to 72 h following infection. Exposure to elevated temperatures impaired the ability of coral larvae to establish symbiosis and reduced larval survivorship. At 31°C, the presence of symbionts further reduced larval survivorship. As sea surface temperatures rise, coral larvae exposed to elevated temperatures during symbiosis onset will likely be negatively impacted, which in turn could affect the establishment of future generations of corals.     

Viable embryogenesis of the winter flounder Pseudopleuronectes americanus from - 1.8° to 15°C

Pseudopleuronectes americanus spawns in late winter near New York, and its eggs may be found in shallow water under ice at temperatures below the usual freezing point of vertebrate tissues. Survival and duration of development at a variety of constant temperatures were recorded for artificially fertilized eggs in the laboratory. Many eggs hatched into normal larvae after 2 months at the lowest temperature tried,-1.8°C. The upper lethal temperature was about 15°C. There was a linear relation between log time and temperature in the minimum mortality range (0° to 10°C), with a Q₁₀ of about 4.8.     

Impacts of temperature and acidification on larval calcium incorporation of the spider crab <Emphasis Type="Italic">Hyas araneus</Emphasis> from different latitudes (54° vs. 79°N)

The combined effects of ocean warming and acidification were compared in larvae from two populations of the cold-eurythermal spider crab Hyas araneus, from one of its southernmost populations (around Helgoland, southern North Sea, 54°N, habitat temperature 3–18°C; collection: January 2008, hatch: January–February 2008) and from one of its northernmost populations (Svalbard, North Atlantic, 79°N, habitat temperature 0–6°C; collection: July 2008, hatch: February–April 2009). Larvae were exposed to temperatures of 3, 9 and 15°C combined with present-day normocapnic (380 ppm CO₂) and projected future CO₂ concentrations (710 and 3,000 ppm CO₂). Calcium content of whole larvae was measured in freshly hatched Zoea I and after 3, 7 and 14 days during the Megalopa stage. Significant differences between Helgoland and Svalbard Megalopae were observed at all investigated temperatures and CO₂ conditions. Under 380 ppm CO₂, the calcium content increased with rising temperature and age of the larvae. At 3 and 9°C, Helgoland Megalopae accumulated more calcium than Svalbard Megalopae. Elevated CO₂ levels, especially 3,000 ppm, caused a reduction in larval calcium contents at 3 and 9°C in both populations. This effect set in early, at 710 ppm CO₂ only in Svalbard Megalopae at 9°C. Furthermore, at 3 and 9°C Megalopae from Helgoland replenished their calcium content to normocapnic levels and more rapidly than Svalbard Megalopae. However, Svalbard Megalopae displayed higher calcium contents under 3,000 ppm CO₂ at 15°C. The findings of a lower capacity for calcium incorporation in crab larvae living at the cold end of their distribution range suggests that they might be more sensitive to ocean acidification than those in temperate regions.     

The invasive gastropod Crepidula fornicata: reproduction and recruitment in the intertidal at its northernmost range in Wales, UK, and implications for its secondary spread

The establishment and spread of a non-native species in an introduced range depends to a large extent on the performance of the species under the prevailing environmental conditions. The spawning, larval and spatfall periods of the invasive gastropod Crepidula fornicata were monitored in the intertidal zone at its northernmost range in Wales, UK, between February 2010 and January 2011. The duration of the reproductive season was similar to that recorded from more southerly European populations. Spawning and larval release occurred throughout most of the year even at low seawater temperatures of <7 °C, but benthic recruitment was observed over a much shorter period at seawater temperatures >16 °C. Recruitment was low and likely controlled by post-settlement mortality. These observations suggest that C. fornicata’s northwards spread in Welsh waters will not be limited by seawater temperature negatively affecting reproduction, but by processes acting after larval release. These data show the importance of incorporating settlement and post-settlement processes into studies on recruitment success when aiming to predict the potential spread of a potentially harmful invader such as C. fornicata.     

Neue ergebnisse über die aufzucht von Carcinus maenas im laboratorium

The shore crab Carcinus maenas was reared in the laboratory from egg deposition to sexual maturity. Special enclosures were developed for cultivation of the larvae. Food and temperature proved to be the most important exogenous factors for rearing success. Fresh Artemia salina nauplii were the only food suitable for all larval stages. The following rearing temperatures proved most successful during larval development: (1) embryonic development, 10°C; (2) zoea stages, 15°C; (3) megalopa stage, 17.5°C. The larvae hatch preferably in darkness when reared under short-day conditions.     

Comparison of somatic growth and otolith increment growth in laboratory-reared larvae of Pacific saury, Cololabis saira, under different temperature conditions

The relationship between somatic growth and incremental growth of otoliths of Pacific saury, Cololabis saira (Brevoort), larvae under different temperature conditions was studied in the laboratory for three age groups (0 to 9, 10 to 20 and 20 to 30 d posthatch). Larvae were incubated from hatching to 9 d at 24, 20, and 16 °C. Further, larvae initially reared at an ambient temperature of 21.7 °C were transferred to experimental temperatures of 22, 18, and 14 °C on Day 10 and reared to Day 20 and similarly from Day 20 and reared to Day 30 posthatch. Growth trajectories of larvae sampled at the end of the three experiments were back-calculated using the biological intercept method and compared to the measured values 0 and 5 d after the start of each experiment. Back-calculated knob length at the different temperatures indicated no significant difference to the measured knob lengths except for the cases at 20 °C from hatching to 9-d-old larvae and at 14 °C from 20- to 30-d-old larvae. The close correlation between somatic and otolith growth shown in this study indicated the feasibility of estimating the growth history of Pacific saury larvae using otolith readings. Received: 14 April 1999 / Accepted: 27 October 1999     

Temperature ecotypes near the southern boundary of the kelp Laminaria saccharina

Effects of temperature on survival, growth, and photosynthesis were compared for two USA populations of Laminaria saccharina Lamour. One population was located in New York State, near the southern latitudinal boundary of the species in the western North Atlantic. This southern boundary population was exposed to ambient temperatures 20°C for about 6 wk each summer. The second population was located in Maine, toward the center of the latitudinal range of the species, and was rarely exposed to temperatures>17°C. sporophytes from the New York (NY) population exhibited greater tolerance of high temperature than plants from the Maine (ME) site. Juvenile sporophytes from the two sites had similar rates of survivorship and growth at temperatures below 20°C, but showed different responses at 20°C in laboratory experiments. NY plants survived and grew for 6 wk at 20°C. ME plants showed negative growth during wk 2 and 100% mortality during wk 3. NY and ME plants held in situ at the NY site during June to September, 1985, also exhibited differential survivorship when ambient temperatures exceeded 20°C. Results of photosynthesis and dark respiration measurements on NY and ME plants grown at various temperatures suggested that the high-temperature tolerance of NY plants was attributable to their ability to maintain positive daily net C-fixation at 20°C. The high-temperature tolerance of the NY plants appeared to be due to genetic adaptation and is probably crucial to the persistence of the species near its southern boundary.     

Effects of elevated temperature on larval settlement and post-settlement survival in scleractinian corals, <Emphasis Type="Italic">Acropora solitaryensis</Emphasis> and <Emphasis Type="Italic">Favites chinensis</Emphasis>

We examined the effects of elevated temperature under different exposure periods on larval settlement and post-settlement survival in scleractinian corals, Acropora solitaryensis and Favites chinensis. In the first experiment with the subtropical coral, A. solitaryensis, the numbers of larvae settling and those dead were examined daily for 5 days at 20, 23 (ambient), 26 and 29°C conditions. Larval settlement of A. solitaryensis was initially greater at higher temperature conditions, but the peak in number of settled larvae shifted from 29 to 26°C by day 5, due to ca. 90% post-settlement mortality at 29°C condition. In order to determine the effects under short-term exposure, larvae of F. chinensis were exposed to 27 (ambient), 31 or 34°C only for one hour in the second experiment. The number of larvae settling for 24 h after the exposure and their survivorship over subsequent week was monitored in the ambient temperature condition. Larvae of F. chinensis exhibited greater settlement at higher temperature treatments and constantly low post-settlement mortalities (< ca. 17%) in all temperature treatments, resulting in the highest number of settled larvae at 34°C treatment. These results suggested two different effects of elevated temperature on the early stages of recruitment process of scleractinian corals; (1) the positive effect on larval settlement and (2) the negative effect on post-settlement survival under prolonged exposure.     

Latitudinal patterns of shell thickness and metabolism in the eastern oyster Crassostrea virginica along the east coast of North America

The goal of this study was to quantify growth and metabolic responses of oysters to increased temperatures like those that will occur due to global warming. Impact of temperature on eastern oyster (Crassostrea virginica) shell growth and metabolism was investigated by sampling 24 sites along the eastern North American seaboard ranging from New Brunswick, Canada, to Florida, USA, in March and August 2013. There was a positive correlation between oyster shell thickness and site temperature. At southern sites, shells were up to 65 % thicker than at the northernmost site, likely due to higher precipitation of CaCO₃ in warmer water. This was supported by laboratory experiments showing that thicker shells were produced in response to temperatures 2, 4, and 6 °C above ambient seawater temperatures (8–14 °C) in Connecticut, USA. Field experiments with oyster respiration were conducted during winter and summer at 13 sites to compare responses to thermal stress with latitude. Respiration rates were much higher during summer than winter, but the combination of summer and winter data fell along the same exponential curve with respect to temperature. At all sites, temperature-specific metabolic rates at elevated temperatures were lower than predicted, indicating significant seasonal acclimatization by C. virginica.     

Effect of temperature on viability and axial muscle development in embryos and yolk sac larvae of the Northeast Arctic cod (Gadus morhua)

Cod (Gadus morhua L.) eggs may develop and hatch within temperatures of −1.5 to 12 °C, but little is known about the effects of very low temperatures on larval characteristics. Eggs of the Northeast Arctic cod (Gadus morhua) were incubated at 1, 5 or 8 °C from Day 1 after fertilisation until hatching, and transferred to 5 °C after hatching. Histological samples of the axial musculature were taken at hatching and 5 d after hatching, and the data on muscle cellularity from these samples were related to survival and hatching, size, developmental data and viability of the yolk sac larvae. All larvae hatched at the same developmental stage. Incubation of eggs at 1 °C produced shorter larvae with a larger yolk sac and more, small deep fibres at hatching than larvae from eggs incubated at 5 or 8 °C. The larval size difference was still present 5 d after hatching, a time at which the larvae from 1 °C-incubated eggs were less developed and less resistant to an acute viability stress test (65 ppt salinity). Although there were no differences between temperature groups in number and size of muscle fibres 5 d after hatching, the deep fibres of the 1 °C-group contained less myofibrils than the two other groups. The phenotype of the larvae at hatching was thus affected within these incubation temperatures. Although all groups were transferred to the same temperature after hatching, the lowest egg incubation temperature (1 °C) still had a negative effect 5 d after hatching, as these larvae were both smaller, less resistant to stress and had less functional muscles at the time of first feeding. Our conclusion is therefore that 1 °C is close to, or below, the lower thermal tolerance limit for normal functional development of Northeast Arctic cod. The results are discussed in relation to larval viability and recruitment of this species in the wild. Received: 4 February 1998 / Accepted: 10 July 1998     

Facultative lecithotrophy during larval development of the burrowing shrimp Callianassa tyrrhena (Decapoda: Callianassidae)

Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae, hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations (19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d⁻¹). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures: compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy, more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food density combinations encountered in the wide geographical range of their natural habitat. Received: 28 February 1998 / Accepted: 21 October 1998     

Female adaptation to developmental plasticity in male calling behavior

The katydid Neoconocephalus triops exhibits in North America substantial developmental plasticity of male mating calls. The AM rate of the summer calls is significantly faster than that of the winter calls at the same temperature. In the tropics, where N. triops originated, males express only the fast summer-call phenotype. We tested two alternative hypotheses: (1) call plasticity in the population from North America evolved in response to selection by female preference after N. triops colonized North America, or (2) call plasticity evolved before N. triops expanded into North America and its expression in the novel environment led to adaptive change of female preferences. First, we tested whether call plasticity was present in tropical populations of N. triops. Tropical males expressed the winter-call phenotype when reared under winter conditions, indicating that call plasticity did not evolve in response to temperate climates. Second, we compared female preferences among temperate and tropical populations. We found that the temperature dependence of preferred AM rate was significantly steeper in temperate N. triops than in a tropical population of N. triops. Third, we compared temperature dependence of female preference of the N. triops populations to three Neoconocephalus species without call plasticity. Only temperate N. triops had significantly steeper temperature dependence than the other species. This steeper temperature dependence matched female preference to the fast summer call at high temperatures and to the slow winter call at low temperatures in temperate populations. These results support the hypothesis that female preference changed in N. triops in North America to compensate for the plasticity of male calls.     

New insights into temperature-induced white muscle growth plasticity during Dicentrarchus labrax early life: a developmental and allometric study

Dicentrarchus labrax is a major finfish of interest in Mediterranean aquaculture. As the development of its hatchery production had gone with an increase of its larval rearing temperature, we studied the effect of a constant high (20°C) and two lower (13 and 15°C) temperatures on its early white muscle growth, with developmental and allometric approaches. D. labrax, sampled at hatching and at three developmental stages corresponding to main events in fish early life (first exogenous feeding, notochord flexion and completion of fin ray counts), were histologically processed in order to follow changes in the white myotomal muscle size, cellularity and localisation of proliferative nuclei. Morphometric analyses showed that, for 13, 15 and 20°C incubated/reared D. labrax, the total cross-sectional area of white muscle increased slowly in eleutheroembryos shorter than 5.2 mm, and four times faster in longer fish (free-swimming larvae). White muscle growth occurred both by hypertrophy (increase in muscle fibre size) and hyperplasia (increase in total number of muscle fibres) in all sampled fish, but both processes were higher in free-swimming larvae than in eleutheroembryos. The morphometric establishment of a higher hyperplastic growth of white muscle in free-swimming larvae was confirmed at immunological level by a high occurrence of proliferative nuclei. Early thermal environment was demonstrated to affect the growth process of white muscle on a different way in eleutheroembryos and free-swimming larvae: in the former, white muscle hypertrophy was stimulated at 20°C and hyperplasia at lower temperature, whereas in the latter, both white muscle hypertrophy and hyperplasia were more stimulated at 20°C than at lower temperatures. This was verified at once when the fish length and the white muscle total cross-sectional area were used as explicative variables.     

Genetic evidence for the occurrence of a cryptic species with the littoral nemerteans Lineus ruber and L. viridis (Nemertea: Anopla)

Lineus ruber and L. viridis are common intertidal heteronemerteans found on the coasts of northern Europe and the east coast of North America. The two species resemble each other morphologically and were synonymised for many years prior to being separated on the basis of larval development. In this study, specimens of L. ruber and L. viridis were collected from sites along the west and southwest coast of Britain, northern France and the east coast of North America. The external morphology and allele frequencies of isozymes of the two species were compared from all sites. The external morphology of L. ruber and L. viridis was similar but they could generally be separated by colour. Allele frequencies for up to 13 enzyme loci between sympatric populations of L. ruber and L. viridis indicated that these two species are genetically very different (Nei's genetic identity=0.090 to 0.083). Allele-frequency data also indicated the presence of a third genetic type occurring sympatrically with populations of both L. ruber and L. viridis on the coasts of Britain and France but not on the coast of North America. Fixed differences in allele frequencies between populations of the third genetic type and sympatric populations of L. ruber and L. viridis were observed across multiple loci. Genetic identity between the third genetic type and sympatric populations of L. ruber and L. viridis were extremely low (Nei's genetic identity =<0.078). Such large genetic differences between populations indicate a barrier to gene flow and reproductive isolation. The aberrant type, which exhibits sufficient morphological variation to prevent individuals being distinguished from those of both L. ruber and L. viridis, therefore represents a separate species. The low genetic identities found in intrageneric comparisons of species found in this study have been found in other studies on nemerteans. They may indicate systematic problems within these groups or other phenomena such as morphological stasis.     

Effect of development rate on the swimming, escape responses, and morphology of yolk-sac stage larval American plaice, Hippoglossoides platessoides

To examine the impact of development rate on swimming performance, escape response, and morphology, yolk-sac larvae of American plaice (Hippoglossoides platessoides, Fabricius) were reared at two temperatures (5 and 10 °C). Videomicroscopy and silhouette collimation videography were used to examine swimming, escape behaviour, and morphology (standard length, finfold area, and yolk-sac area) of individual larvae. Larvae were examined from 0 d post hatch (dph) to 14 dph for the 5 °C treatment group and from 0 to 6 dph for the 10 °C treatment group (3 August to 17 August 1996). Since larvae were not fed, yolk-sac reserves were essentially exhausted by 14 and 6 dph for the 5 and 10 °C treatment groups, respectively. To control for the effect of testing temperature on behaviour, larvae from each temperature treatment were tested at both 5 and 10 °C. Testing temperature had an effect on some swimming parameters but not on escape response. Swimming performance, escape response, and morphology varied with age, while only morphology and escape response varied with development rate. Morphology and swimming performance, and morphology and escape response were found to be correlated as determined by canonical correlation. This study suggests that both types of swimming behaviours should be examined when developing models of the impacts of predation on the early life history of larval fish. Received: 13 September 1999 / Accepted: 21 June 2000     

Intraspecific physiological variability of the gastropod Littorina saxatilis related to the vertical shore gradient in the White and North Seas

 Physiological responses to desiccation and temperature stress as well as behavioural responses to fast and abrupt environmental changes were investigated in high- and low-shore Littorina saxatilis (Olivi) from several populations from the White and North Seas. Variations in evaporation rates, resistance to air exposure and to acute and chronic temperature stress between animals from different shore levels were similar in White and North Sea periwinkles, consistent with the adaptive nature of these variations. High-shore snails were found to be able to conserve body water reserves better, to resist higher temperatures and to survive longer under conditions of combined temperature and desiccation stress than their low-shore counterparts. In a temperature range of 25 to 35 °C, the rate of evaporative water loss was positively correlated with temperature in low-shore snails while being largely temperature-independent in high-shore snails. Median lethal time during air exposure in L. saxatilis was negatively but not linearly related to the temperature of exposure. In a temperature range of 30 to 38 °C, the resistance to heat exposure in air was only slightly dependent on the temperature, with Q ₁₀ = 1.4 for the median lethal time; the heat resistance dropped drastically at temperatures above 38 °C, with Q ₁₀ = 593.8. This suggests different mechanisms of temperature resistance in different parts of the studied temperature range. In contrast, behavioural response to extreme salinity fluctuations was not uniform in the high- and low-shore periwinkles from the White and North Seas, which may reflect specific environmental conditions at different shore levels in the two areas studied. Observed physiological and behavioural variations are discussed from the viewpoint of different adaptive strategies employed by eulittoral and eulittoral-fringe animals within populations of a single species. Received: 13 December 1999 / Accepted: 11 April 2000     

Temperature and salinity tolerances of embryos and larvae of the deep-sea mytilid mussel ��Bathymodiolus�� childressi

We examined temperature and salinity tolerances of early embryonic and larval stages of the deep-sea, cold-seep mussel ??Bathymodiolus?? childressi to determine whether they may control the dispersal depth of larvae. Salinity and temperature tolerances increased with developmental stage, but tolerance ranges were not as wide for the larvae of ??B.?? childressi as for the larvae of the related shallow-water mussel Mytilus trossulus. Normal development occurred in ??B.?? childressi from 7 to 15°C and at salinities of 35 and 45. Greater tolerance of ??B.?? childressi embryos to high than low salinities may aid development of negatively buoyant early embryos at brine seeps. Although there was a decreasing trend in survival of ??B.?? childressi larvae with increasing temperature, survival of ??B.?? childressi trochophores was not significantly different at 20°C than at the adults?? ambient temperature. Since larvae tolerate increasing temperatures as they age and seawater temperatures at 100?m depth do not exceed 20°C in months following the mussels?? spawning season, we suggest that temperature would not limit vertical migration of the veliger larvae of ??B.?? childressi into even the uppermost layer of the water column above the cold seeps in the Gulf of Mexico.