Effects of temperature and delayed feeding on growth and survival of larvae of three species of subtropical marine fishes

In larvae of the bay anchovy Anchoa mitchilli (Valenciennes), the sea bream Archosargus rhomboidalis (Linnaeus), and the lined sole Achirus lineatus (Linnaeus), growth, survival, and starvation times were investigated at temperatures of 22° to 32°C. The rate at which hours after hatching until starvation decreased in relation to temperature for unfed larvae did not differ significantly among the 3 species, ranging from-5.4 to-6.3 h per degree increase in temperature. The total number of hours until starvation did differ for all 3 species: lined soles survived longest, bay anchovies were intermediate, and sea bream survived the least time. At 28°C, unfed sea bream could survive 90.1 h, bay anchovy 102.3 h, and lined sole 119.8 h. The eyes pigmented at nearly the same time after hatching for sea bream and bay anchovy, but took about 20 h longer at all temperatures for lined sole. Quadratic equations best described the relationship between hours after hatching when the eyes became pigmented and temperature. Eye-pigmentation times became nearly constant for all 3 species at temperatures above 28°C. At 28°C, eyes pigmented about 27 h after hatching for bay anchovy and sea bream but not until 47 h for lined sole. Hours after eye pigmentation when unfed larvae starved was a measure of the effective time that larvae had to commence feeding. Bay anchovies and lined soles were nearly alike in this respect, but sea bream starved at tewer hours after eye pigmentation. Slopes of regressions representing decrease in times to staration for increasing temperatures ranged from-3.7 to-4.4 h per degree increase in temperature, and were not significantly different among the 3 species. At 28°C, unfed lined soles starved at 70 a after eye pigmentation, bay anchovies starved at 72.5 h, and sea bream at only 62 h. Yolk absorption was most rapid for all species during the first 20 h after hatching, and was faster at higher temperatures. Amounts of yolk remaining at the time eyes became pigmented were less at higher temperatures for bay anchovy and lined sole, but were greater for sea bream, suggesting that sea bream used yolk more efficiently at higher temperatures. Either no yolk or small traces (>0.20%) remained at 24 h after eye pigmentation in all 3 species. Feeding was delayed for periods of 8, 16, 24, 32, 40 and 48 h after eye pigmentation for all species at a series of experimental temperatures from 24° to 32°C. Growth and survival were affected when food was withheld for more than 24 h at 28°C, but survival did not decrease markedly until food was withheld at least 8 h longer. At lower temperatures food could be withheld longer and at higher temperatures for less time. Feeding can be initiated by most larvae for several hours after all visible yolk reserves have been exhausted. All species tested can survive for 24 to 40 h after eye pigmentation at 24° to 28°C without food and still have relatively good growth and survival when food is offered. If the “critical period” is considered relative to time of hatching, lined soles need not find food for 3 to 3.5 days after hatching, but bay anchovy and sea bream must feed within 2.5 days of hatching.     

Food concentration and stocking density effects on survival and growth of laboratory-reared larvae of bay anchovy Anchoa mitchilli and lined sole Achirus lineatus

Bay anchovy (Anchoa mitchilli) eggs were stocked at densities from 0.5 to 32.0 l^-1 and larvae were fed on wild plankton (copepod nauplii) in concentrations that ranged from 50 to 5000 prey l^-1. Lined sole (Achirus lineatus) eggs were stocked at 0.5 to 16.0 l^-1 and larvae were fed wild plankton at concentrations from 50 to 1000 prey l^-1. Some larvae of each species survived at all stock and food levels to the transformation stage at 16 days after hatching. Survival rates for both species exceeded 40% when food concentration was 1000 l^-1 or higher. Growth and dry weight yields also increased significantly at the higher food concentrations. Effects of initial stocking density were not well defined, but both survival and growth decreased at the highest stocking rates. Standardized culture of bay anchovy and lined sole larvae can be based on a food concentration of 1000 copepod nauplii l^-1 to routinely produce healthy larvae.     

Interspecific comparisons of growth and diet among late larvae of three co-occurring clupeoid species in the Kii Channel,Japan

Growth and diet were compared among larvae of Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus and Pacific round herring Etrumeus teres. Compositions of prey items of the three species in the same month showed greater similarity than for the same species in different months. Prey size as well as prey taxa of the three species overlapped considerably with one another. Therefore, interspecific prey competition is likely in the case of limited food availability. The most abundant species tended to change from anchovy to round herring in early winter, from round herring to sardine in late winter and from sardine to anchovy in early spring, indicating a temporal segregation in use of the nursery grounds. Similar seasonal changes in growth rates were observed for the three species. Although interspecific prey competition is likely, the temporal segregation and similar temporal changes in growth rates could favor their coexistence.     

Nitrogen balance in marine fish larvae: influence of developmental stage and prey density

The utilization and fate of nitrogen in larvae of plaice (Pleuronectes platessa), blenny (Blennius pavo) and herring (Clupea harengus), from the stage of first-feeding to metamorphosis, was examined under laboratory conditions. Rates of ammonia excretion, primary amine defaecation, and growth in terms of protein-nitrogen were monitored throughout larval life. Data were used to calculate daily ration, the coefficient of nitrogen utilization (absorption efficiency), and gross and net growth efficiencies. The developmental pattern of nitrogen balance was similar for plaice and blenny larvae. These species showed increasing growth efficiency (k₁: 55 to 80%) with decreasing weight-specific waste nitrogen losses with age. Absorption efficiencies. were high (83 to 98%) in plaice and blenny larvae, and tended to increase with development in the former species. Ration relative to body weight decreased with growth in both species. Herring larval development, although at a slower rate than blenny and plaice, appeared normal up to 33 d, after which high mortality occurred. Absorption efficiency in this species tended to decline (83 to 43%) with age, until metabolic costs exceeded the absorbed ration and growth ceased. Artemia sp. nauplii proved a suitable food source for the rearing of plaice and blenny larvae, but this diet may have long-term toxicity or deficiency effects on herring. Availability and density of food affected nitrogen balance in the larvae of all three species. Feeding stimulated the output of wastes in excretion and defaecation by a factor of up to ten times the 12-h non-feeding basal rates. Waste nitrogen output reached a peak some 2 to 3 h after commencement of feeding and returned slowly to the baseline in 5 to 10 h after cessation of feeding. There was an asymptotic increase in ration, ammonia output and growth of larvae as prey density increased. Ration saturated at a higher prey density (>4 prey ml^-1) than either growth or excretion rate (1 prey ml^-1). Thus the efficiency with which food is absorbed and utilized for growth must eventually decline in response to high prey density. The idea that larval fish are adapted to maximize ingestion and growth rate, rather than optimize growth efficiency and thus to respond to prey occurring in either low density or in occasional patches, is supported by these results.     

Swimming behavior of juvenile anchovies (<Emphasis Type="Italic">Anchoa</Emphasis> spp.) in an episodically hypoxic estuary: implications for individual energetics and trophic dynamics

Diel swimming behaviors of juvenile anchovies (Anchoa spp.) were observed using stationary hydroacoustics and synoptic physicochemical and zooplankton profiles during four unique water quality scenarios in the Neuse River Estuary, NC, USA. Vertical distribution of fish was restricted to waters with DO greater than 2.5 mg O₂ l⁻¹, except when greater than 70% of the water column was hypoxic and a subset of fish were occupying water with 1 mg O₂ l⁻¹. We made the prediction that an individual fish would select a swim speed that would maximize net energy gain given the abundance and availability of prey in the normoxic waters. During the day, fish adopted swim speeds between 7 and 8.8 bl s⁻¹ that were near the theoretical optimum speeds between 7.0 and 8.0 bl s⁻¹. An exception was found during severe hypoxia, when fish were swimming at 60% above the optimum speed (observed speed = 10.6 bl s⁻¹, expected = 6.4 bl s⁻¹). The anchovy is a visual planktivore; therefore, we expected a diel activity pattern characteristic of a diurnal species, with quiescence at night to minimize energetic costs. Under stratified and hypoxic conditions with high fish density coupled with limited prey availability, anchovies sustained high swimming speeds at night. The sustained nighttime activity resulted in estimated daily energy expenditure over 20% greater than fish that adopted a diurnal activity pattern. We provide evidence that the sustained nighttime activity patterns are a result of foraging at night due to a lower ration achieved during the day. During severe hypoxic events, we also observed individual fish making brief forays into the hypoxic hypolimnion. These bottom waters generally contained higher prey (copepod) concentrations than the surface waters. The bay anchovy, a facultative particle forager, adopts a range of behaviors to compensate for the effects of increased conspecific density and reduced prey availability in the presence of stratification-induced hypoxia.     

Feeding rates and prey selectivity of planktonic decapod larvae in the Western English Channel

Meroplankton are seasonally important contributors to the zooplankton, particularly at inshore sites, yet their feeding ecology is poorly known relative to holoplankton. While several studies have measured feeding in decapod larvae, few studies have examined the feeding rates of decapod larvae on natural prey assemblages throughout the reproductive season. We conducted 8 feeding experiments with Necora puber, Liocarcinus spp. and Upogebia spp. zoea larvae collected from the L4 monitoring site off Plymouth (50°15.00′N, 4°13.02′W) during spring–summer 2009 and 2010. This period spanned moderate-to-high food availability (0.5–1.6 µg chl-a L^?1), but a great range in food composition with small cells <20 µm dominating in 2010. Daily rations averaged 17, 60 and 22 % of body C for the 3 respective decapod species. Clearance rates differed according to prey type, and all 3 decapod genera showed evidence of selection of dinoflagellates. Importantly, small cells including nano- and pico-plankton were ingested, this being demonstrated independently by flow cytometric analysis of the feeding experiments and molecular analysis. PCR-based analysis of the haptophyte portion of the diet revealed ingestion of Isochrysis galbana by decapod larvae in the bottle incubations and Isochrysis galbana and Phaeocystis globosa by decapod larvae collected directly from the field. This study has shown that pico- and nano-sized plankton form an important supplement to the diverse and variable diet of decapod larvae.     

Physiological energetics of the intertidal sea anemone Anthopleura elegantissima

Energy budgets were calculated for individuals of the sea anemone Anthopleura elegantissima (Brandt), collected in 1981 and 1982 from Bodega Harbor, California, USA. Rates of ammonium excretion were measured in high-and low-intertidal, symbiotic and aposymbiotic sea anemones within 24 h of collection. Among symbiotic and aposymbiotic individuals, no differences in excretion rate were found on the basis of intertidal height. However, rates of ammonium excretion in aposymbiotic anemones (2.14 mol NH ₊ ⁴ g^-1 h^-1) were significantly higher than in symbiotic ones (0.288 mol NH ₊ ⁴ g^-1 h^-1). Rates of excretion were used with estimated rates of oxygen uptake to calculate nitrogen quotients (NQ). NQ and RQ values from the literature were used to calculate an oxyenthalpic equivalent [501 kJ (mol O₂)^-1 for R+U], and mass proportions of protein (54%), carbohydrate (44%) and lipid (2%) catabolized during routine metabolism in this species 24 h after feeding. Integrated energy budgets of these experimental anemones were calculated from data on ingestion, absorption and growth, and estimates of translocated energy from the symbiotic algae. Contribution of zooxanthellae to animal respiration based on translocation=90% and RQ=0.97 are 41 and 79% in high-and low-intertidal anemones, respectively. Calculated scope for growth is greater than directly measured growth in both high-and low-intertidal individuals. The deficit, estimated as 30% of assimilated energy in high-intertidal anemones, is attributed to unmeasured costs (specific dynamic effect) or production (mucus). Low-intertidal anemones lost mass during the experiment, implying that the magnitude of the deficit was greater in these anemones than in upper intertidal individuals. Anemones from both shore levels lost zooxanthellae during the experiment, which contributed to energy loss since the contribution of the zooxanthellae is greater in low-intertidal anemones. Scope for growth is preserved in high-intertidal anemones (29% of assimilated energy) because metabolic demands are lower due to aerial exposure, and prey capture rate is higher compared to lowshore anemones. Although possibly underestimated, lower scope for growth in low-shore anemones may result from continuous feeding and digestion processes that are less efficient than those of periodically feeding high-intertidal anemones.     

Croissance de la larve de l'oursin Paracentrotus lividus

Paracentrotus lividus (Lamarck) larvae were reared to metamorphosis. The larvae were fed on the haptophycean Hymenomonas elongata Droop (Braarud) at three concentrations: 9 to 14×10⁵, 24 to 37×10⁵, 43 to 61×10⁵ μm³ cells ml^-1 d^-1. Optimum growth took place at a density of 24 to 37×10⁵ μm³ algal cells. Growth of the plutei was estimated in terms of weight increases in protein, carbohydrate and lipid; growth equations are given. The relationship between growth and the food ingested was calculated for the different larval stages. Earlier field data for the bay of Villefranche have shown the mean biovolume of nanoflagellates to be 0.65×10⁵ μm³ ml^-1; at such in situ food concentrations, P. lividus larvae would metamorphose only after one month of planktotrophic life. Chemoreception by larvae could lead to prey selection, thereby altering the amounts of protein, carbohydrate and lipid ingested, and hence the duration of larval life.     

Foraging behaviour of larval cod (Gadus morhua) influenced by prey density and hunger

Fish larvae meet diverse environmental conditions at sea, and larval growth and chance of survival depend on a flexible response to environmental variability. The present study focuses on the flexibility of the foraging behaviour of larval cod in a series of laboratory experiments on larval search activity, prey selectivity, and hunger in a variable prey environment. Gadus morhua eggs were collected in March 1992 and 1993 from the Kattegat area, Denmark, fertilised and incubated in the laboratory. After hatching, the larvae were transferred to rearing tanks of 172 litres. The behaviour of larvae (6 to 7 mm long) was observed visually, and prey attacks, swimming activity and gut contents were registered across a range of 1 to 120 copepod nauplii l^-1. When prey density decreased, larvae increased their swimming activity, increased their responsiveness to prey (distance of reaction) and decreased their prey size selectivity. Behavioural response was to a large degree determined by the level of hunger, represented by the number of newly ingested prey in the gut. The findings show that cod larvae have a flexible response to changes in feeding conditions and imply that larvae can grow and survive even in the lower range of (mean) prey densities measured at sea.     

Geographical variations in the trophic ecology of Japanese anchovy, Engraulis japonicus, inferred from carbon and nitrogen stable isotope ratios

Carbon and nitrogen stable isotope ratios of Japanese anchovy (Engraulis japonicus) and their stomach contents were examined and compared among various regions around Japan. Geographical variations in the isotope ratios were found between inshore and Pacific offshore regions. While most of the anchovy samples had isotope ratios around −17.6‰ for δ¹³C and 10.0‰ for δ¹⁵N as median values, higher (more enriched) isotope values were found in the anchovy sampled from inshore regions. On the contrary, lower (more depleted) values were found mostly in the anchovy from the Pacific offshore region including the Kuroshio Extension and Kuroshio-Oyashio transition zones. Higher carbon isotope ratios in the inshore regions may reflect a carbon source from benthic primary producers in addition to phytoplankton possibly through the consumption of the larvae of benthic organisms such as bivalves or decapods, which were found in the stomach contents of the inshore anchovy. Variations in the nitrogen isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level of food webs. Stable isotope ratios are potentially a useful tool for understanding the stock/population structure and migration of anchovy. The present findings indicate the potential importance of the “inshore–offshore” variations in the biology of Japanese anchovy populations in the northwestern Pacific waters.     

Energy storage and dynamics in bay anchovy Anchoa mitchilli

The energy of the body components and the energy costs of spawning and overwintering in the bay anchovy Anchoa mitchilli, the most abundant fish in Chesapeake Bay, were studied to determine seasonal variability during the different stages of its life cycle. Bimonthly samples were collected by trawl from April 1990 through October 1991. Fish condition and body energy levels fluctuated seasonally, and were related to anchovy size. Energy equivalents (cal g^-1 dry wt) was highest in December, before the overwintering period. The somatic weight component increased by 32 to 33% and total body weight by 26% during the spawning season, indicating that feeding not only met energy requirements of daily spawning but also provided surplus energy for growth. The overwintering loss of energy was 33 to 35% of total body calories, and was primarily derived from deposit fat in somatic and visceral tissues.     

Prey selection by resident common bottlenose dolphins (tursiops truncatus) in Sarasota Bay, Florida

Prey selection was investigated in wild, resident common bottlenose dolphins, Tursiops truncatus, during the summer months in Sarasota Bay, Florida, USA. Stomach content analyses of 15 dolphins with extensive sighting histories and well-documented distributions were used to determine prey use. Prey availability was assessed by purse seine surveys. We compared the relative abundances of prey available to estimates of prey use at closely matching spatial and temporal scales. G-tests determined that dolphins in this study significantly selected for prey at the species, family, and soniferous/non-soniferous prey levels (G _adj  = 753.98–1,775.93, df = 1–21, p ≤ 0.01). While comprising only 6.3% of the total available prey, soniferous fishes accounted for 51.9% of the total prey consumed. Manly’s standardized forage ratios and 95% Bonferroni confidence intervals determined significant positive selection for soniferous prey and against non-soniferous prey (β^S = 0.9461 vs. β^NS = 0.0539). Dolphins selected against Gerridae, Clupeidae, and Sparidae (β ≤ 0.0014), as well as against all the species within those families (β ≤ 0.0190). It is likely that passive listening for soniferous prey provides an ecological or energetic advantage to cetaceans utilizing this specific foraging technique.     

Assimilation of dissolved glucose from sea water by the sea bass Dicentrarchus labrax and the sea bream Sparus aurata

Larvae of sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) were transferred to normal or glucose-enriched sea water immediately after mouth opening to assess their ability to absorb and assimilate glucose at the beginning of the larval period. Assimilation was monitored by histological and cytochemical analysis of the liver. The results showed that (1) the larvae of both species regularly ingested water, (2) glucose absorption resulted in glycogen accumulation in the hepatocytes (this was more marked in sea bass than in sea bream), and (3) glucose delayed the pathological effects of fasting. Consideration of metabolic derivatives indicates that hepatic glycogen probably arises from neoglucogenesis.     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Energetics of early development for the sea urchinsStrongylocentrotus purpuratus andLytechinus pictus and the crustaceanArtemia sp.

Embryos and larvae of two species of sea urchin,Strongylocentrotus purpuratus andLytechinus pictus, and larvae of the brine shrimpArtemia sp. (San Francisco brand) were cultured to investigate the contribution of dissolved organic material in seawater to the energetics of early development. When embroys ofS. purpuratus were reared in artificial seawater, a net loss in dry organic mass was observed. In contrast, when sibling embryos were reared to Day 2 under identical conditions in natural seawater, there was either a net increase in dry organic mass or no change. A net decrease in mass was observed in only one of five cultures reared in filtered natural seawater. Energy budgets for each species were determined by giving energy equivalents to the changes in carbohydrate, lipid and protein, and to the rate of oxygen consumption for each day of development. In the case ofS. purpuratus, the use of endogenous reserves accounted for either 0 or 38% of the metabolic demand for two independent cultures reared from Days 0 to 2. For larvae ofL. pictus, reared to 8 d, only 66% of the metabolic demand could be accounted for by the use of endogenous reserves. Sea urchins are capable of transporting dissolved organic material from seawater. Calculations revealed that the energy deficit during the early development of sea urchins (S. purpuratus) could be accounted for by the uptake of dissolved organic matter from seawater. However, for a species that cannot use this resource (Artemia sp.), the metabolic needs during development are supplied through the use of endogenous reserves.     

RNA:DNA ratios and growth of herring (Clupea harengus) larvae reared in mesocosms

Autumn-spawned North Sea herring larvae (Clupea harengus L.) were released in two outdoor mesocosms of 2500 m³ (A) and 4000 m³ (B). The mesocosms were monitored for temperature, salinity, oxygen, chlorophyll a, zooplankton and herring larvae abundance. The density of suitable prey for first feeding larvae (mainly copepod nauplii) was initially low in Mesocosm A (<0.11^-1) compared to in Mesocosm B (>11^-1). Half-way through the experiment the situation was reversed, with higher densities of prey in Mesocosm A (>31^-1) as compared to Mesocosm B (～11^-1). The average temperature declined steadily in both mesocosms from 18°C at release to 11–12°C by the end of the experiment 60 d later. The RNA:DNA values of individual herring larvae were related to protein growth rates and temperature adjusted according to Buckley (1984). A corresponding DNA growth index (Gdi) was given as: Gdi=0.68 TEMP+3.05 RNA:DNA-9.92. The RNA:DNA based growth indices were significantly correlated with other somatic growth estimates. The average estimated protein growth rate in the two mesocosms followed the same temporal pattern as the somatic growth rate, but with a lag of 2 d or more. Residual analysis of the regression of ln RNA versus ln DNA also showed the same temporal pattern as the RNA:DNA ratios, but the shift in condition as estimated by this method occurred more in synchrony with the other somatic growth measures. Larvae in Mesocosm A had RNA:DNA values similar to the starvation control kept in the laboratory the first days after release, confirming that larvae in Mesocosm A initially were in poor nutritional condition. On the other hand, the majority of the herring from Mesocosm B were characterised as starving or in poor nutritional condition towards the end of the experiment. The assessment of growth and nutritional condition were in accordance with independent survival estimates which suggested that the majority of the total mortality occurred during the first 15 d in Mesocosm A and there-after in Mesocosm B.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population‐density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January–September (sardine) and June–November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

Effects of elevated pCO2 and the effect of parent acclimation on development in the tropical Pacific sea urchin Echinometra mathaei

Effects of acclimation to projected near-future ocean acidification (OA) conditions on physiology, reproduction and development were investigated in the tropical sea urchin Echinometra mathaei. Following 6 weeks in control or one of the three elevated pCO₂ (pH_NIST 7.5–8.1; pCO₂ ~485–1,770 μatm) conditions, adult urchins exhibited a slight decline of growth in low pH treatments and moderately reduced respiration at intermediate levels. At 7 weeks, gametes from adults were used to produce larvae that were reared in their respective parental treatments. To assess whether larvae from acclimated parents are more resilient to elevated pCO₂ than those not acclimated, larvae from control animals were also reared in the elevated pCO₂ treatments. There was no difference in female ‘spawnability’ and oocyte size between treatments, but male spawning ability was reduced in increased pCO₂ conditions. In elevated pCO₂ treatments, the percentage of normal larvae and larval size decreased in the progeny of control- and elevated pCO₂-acclimated parents, and arm asymmetry increased. Thus, acclimation of the parents did not make the progeny more resilient or sensitive to OA effects. Negative effects of increased pCO₂ on reproduction and development may impact on recruitment and population maintenance of this species.     

Free amino acid and protein contents of start-feeding larvae of turbot (Scophthalmus maximus) at three temperatures

The contents of free amino acids (FAA) and total protein, together with growth and gut-content, of turbot (Scophthalmus maximus L.) larvae reared at 14, 18 and 22 °C were studied from first-feeding to approximately 140 effective day-degrees post hatch (D_eff ^∘). Artemia franciscana nauplii and two species of rotifers were used as prey. Protein content accounted for about 42 and 26% of dry body mass in the A. franciscana nauplii and the rotifers, respectively. The FAA pool constituted 5.6 and 4.8% of the total amino acids in the same animals. The dry body mass of turbot larvae was exponentially related to D_eff ^∘. Protein and FAA contents were linearly related to dry body mass, and were independent of rearing temperature between 14 and 18 °C. At the end of the experiment, however, turbot larvae at 22 °C had lower gut content values, retarded growth rates, and decreased FAA contents and concentrations. Thus, at this high temperature, turbot larvae seem unable to catch and ingest sufficient prey, or to sustain an amino acid assimilation rate from the intestine sufficient to meet metabolic demands. Received: 2 January 1997 / Accepted: 25 September 1998     

Weak defence in a tritrophic system: olfactory response to salicylaldehyde reflects prey specialization of potter wasps

Predatory arthropods are attracted to infochemicals emitted by their herbivore prey or by the prey’s host plants. We studied such a tritrophic system measuring the olfactory responses of three potter wasp species (Symmorphus murarius, Symmorphus gracilis, Discoelius zonalis, Hymenoptera: Eumeninae) to salicylaldehyde, sequestered as a defence compound by Chrysomela leaf beetle larvae when feeding on Salicaceae, and volatile organic compounds (VOCs) emitted by aspen (Populus tremula, Salicaceae). In electroantennographic recordings (EAG), the highly specialized S. murarius that almost exclusively feeds on larvae of Salicaceae-feeding Chrysomela species was more sensitive to salicylaldehyde than the less specialized S. gracilis, feeding on such Chrysomela species but also weevil larvae. In contrast the related D. zonalis, foraging for microlepidoptera caterpillars on various host plants, did not respond at all. Furthermore, the three wasp species responded differently to aspen VOCs in GC–MS/EAD measurements. These results indicate that the sense of smell of predatory potter wasps differs for prey and plant volatiles among related wasp species according to their degree of host specialization. The considerable differences in salicylaldehyde perception suggest that its originally defensive function has backfired as it is used by specialist potter wasps for prey location. This is an important clue on adaptive mechanisms of the highest trophic level of the well-studied evolutionary arms race among Chrysomela leaf beetles, their host plants and their enemies.