Temperature influences selective mortality during the early life stages of a coral reef fish

For organisms with complex life cycles, processes occurring at the interface between life stages can disproportionately impact survival and population dynamics. Temperature is an important factor influencing growth in poikilotherms, and growth-related processes are frequently correlated with survival. We examined the influence of water temperature on growth-related early life history traits (ELHTs) and differential mortality during the transition from larval to early juvenile stage in sixteen monthly cohorts of bicolor damselfish Stegastes partitus, sampled on reefs of the upper Florida Keys, USA over 6 years. Otolith analysis of settlers and juveniles coupled with environmental data revealed that mean near-reef water temperature explained a significant proportion of variation in pelagic larval duration (PLD), early larval growth, size-at-settlement, and growth during early juvenile life. Among all cohorts, surviving juveniles were consistently larger at settlement, but grew more slowly during the first 6 d post-settlement. For the other ELHTs, selective mortality varied seasonally: during winter and spring months, survivors exhibited faster larval growth and shorter PLDs, whereas during warmer summer months, selection on PLD reversed and selection on larval growth became non-linear. Our results demonstrate that temperature not only shapes growth-related traits, but can also influence the direction and intensity of selective mortality.     

Nutritional cellular biomarkers in early life stages of fish

Histological (tissular and cellular) indices have a tradition of determining the nutritional condition of fish both in the laboratory and in the wild. The assessment of condition by means of microscopical methods is probably the mos accurate indicator of nutritional status during the early life stages of fish. This success is partly attributable large amount of information that can be derived from their study and because they are thought to be the only true starvation indices. The technique usually consists of the examination of cells and organs and the establishment of a grading system based on the presence/absence of standardised biomarkers. Each organ is examined, and the cellular aspect or tissular cohesion is evaluated qualitatively and even quantitatively in order to obtain a measure of the general condition of a larva. The literature indicates that there are certain tissular and cellular responses to food availability and quality, particularly in the digestive and muscular tissues, which are common to most teleost fish larvae. These responses, which are independent of water temperature, can be used for assessing fish larvae nutritional condition. In this regard, the microscopical organization of the liver hepatocytes, the intestinal mucosa, the exocrine pancreas and the muscular fibers, which are generally used as target tissues and organs to assess the nutritional condition of fish larvae, is deeply reviewed. The advantages and disadvantages of the use of different cellular biomarkers of effect are discussed considering different conditions.     

Freshwater acidification: effects on the early life stages of fish

Summary Over the last 20–30 years there has been a very extensive international research effort into freshwater acidification and the decline or loss of soft-water fisheries. The research includes many laboratory studies on physiology and survival of fish under the conditions caused by acidification. The causes of acidification have become increasingly well understood and accepted. In many countries, industrial and environmental management strategies are being implemented with the eventual aim of halting or reversing acidification in vulnerable areas. Attention has shifted away from research into the effects of acidification on fish, and the number of new papers on this subject is declining. Now appears a good time to review this research.As is often the case in research of this kind, it is difficult to compare work from different laboratories. Especially in earlier work, experimental conditions may not be fully relevant to the field (e.g. in the choice of ambient calcium concentration), experimental media may be inadequately specified (e.g. trace metal concentrations) and analytical techniques may be open to question (e.g. pH measurement). This may explain, in part, why agreement is lacking on many aspects of the physiological effects on the early life stages of fish, as well as the adult stages to some extent. If research is to continue in this field, then adoption of standard soft, acid water media would be of significant benefit. Nethertheless, some very general conclusions on fish early life stages can be reached.There is some evidence of impaired gametogenesis and spawning, but in this area there is still a need for systematic research. After fertilization, the chorionic membranes afford protection from the effects of low pH and especially the accompanying toxic trace metals, notably aluminium. Indeed, dissolved aluminium can ameliorate acid toxicity at this stage in development, possibly by helping to decrease membrane permeability and reduce H⁺ uptake. The main hazard seems to be impaired development (perhaps related to a decline in pH of the perivitelline fluid), often leading to a lack of ability to escape from the chorionic membranes on hatching.After hatching, vulnerability increases. Dissolved aluminium, and other trace metals associated with acidification, become more important. Some studies indicate continuing protection from low pH afforded by low concentrations of aluminium. The causes of death can still only be inferred: much attention has concentrated on mineral uptake and balance, and there is anecdotal evidence of respiratory impairment, although not as unequivocal as it is for postlarval fish. Comparison with the physiological effects on postlarval fish is not necessarily helpful. There seems to be at least one important difference. Unlike postlarvel fish, larvae do not find aluminium at around pH 5.5 (when respiratory effects are probably most important) the most hazardous combination; rather, the greatest danger to larvae seems to be when very low pH (<5.0) and trace metals (including aluminium) combine in some kind of joint toxic effect.There is a great increase in vulnerability once dependence on the yolk has come to an end. This period coincides with the movement from the incubation site in the substratum into the open water, where the relevant water chemistry is likely to fluctuate between greater extremes. However, it is earlier, during autumn rainstorms and spring snowmelt, that pH and concentrations of protective calcium ions usually reach their lowest and metals like aluminium their highest values. In waters where acidification is most likely to occur, the early life stages of many freshwater fish species will be close to their survival threshold and only a slight decline in water quality might result in the loss of a complete year class, which would affect recruitment and eventual population status.With gradual acceptance of the causes and effects of freshwater acidification, the research effort in relation to fish is declining or shifting towards attempts to re-establish fisheries in vulnerable areas. As outlined above, only very general conclusions can be reached on individual life stages, and the relative susceptibilities compared. However, in many respects the sequence of events in the loss of fisheries is not fully understood, and information is lacking on how events at significant stages of the life cycle affect subsequent survival, development and recruitment. Plenty of work is still required.     

Comparative organ differentiation during early life stages of marine fish

The basic developmental mechanisms of teleosts are similar, but there are differences with respect to the timing of developmental events. These events are controlled by genetic and environmental factors. Direct comparisons of organogenesis are complicated due to large variations in egg sizes and incubation temperatures between species. But in general, cultivated small marine pelagic fish larvae originating from rather small eggs (like gadoids, flatfishes, sparids) hatch with a relatively large yolk sac, a larval finfold and subdermal space and under-developed organs. Developmental status at hatch differs between species and the duration of the yolk sac period varies. Main organs and organ systems become functional by first feeding and differentiate during the larval stage and metamorphosis. Species developing directly via large yolk-rich eggs and a long incubation period have a juvenile like morphology and organ functionality at first feeding, sometimes immediately after hatch (like wolffishes). Histomorphological and cell- or organ functional studies of developing embryos and larvae of cultivated species constitute basic information for understanding species-specific events, of utmost importance for improving production protocols. Information is still lacking on early functionality of endocrine and immunocompetent tissues and organs, areas that deserve future focus.     

Inducibility of life history changes by fish kairomone in various developmental stages of Daphnia

Life history changes in Daphnia galeata as a response to part-timeexposure to fish-exuded chemical (FEC) were studied in laboratoryexperiments. Exposure to FEC during one of the juvenile instarsdid not induce significant changes in life history parametersin D.galeata primiparae. Exposure in the first two instars injuvenile development induced earlier maturation, smaller primiparaeand the production of smaller eggs. Exposure in the third andfourth juvenile instars resulted in smaller primiparae withsmaller eggs. The adult daphnids, when exposed to FEC, reducedsomatic growth and produced more and smaller offspring. Resultsof other experiments presented here indicate that the perceptionof fish chemical signal by daphnids is not mediated by the ingestionof a chemically modified diet.     

The early life history stages of riverine fish: ecophysiological and environmental bottlenecks

Fish are good indicators of the environmental health of rivers and their catchments as well as important conservation targets. Bioindication has to be based on an understanding of the requirement of characteristic species with regard to: (a). The match/mismatch between reproductive strategies and environmental conditions. (b). The niche dimensions of critical stages vis-a-vis the key conditions. (c). The availability of microhabitats along the ontogenetic niche profiles, i.e. the connectivity from spawning substrates to early life history microhabitats. The main conditions for the embryonic period are temperature and oxygen supply which are responsible for embryonic mortality, the duration of the period, and size and condition of newly-hatched larvae. For the exogenously feeding larvae the functional of food acquisition, growth and bioenergetics to temperature, food availability and current velocity is decisive. Studies concentrated on Chondrostoma nasus, a target species for monitoring and conservation in large European river systems. Results obtained in experimental studies are compared with those from field studies in order to evaluate the match/mismatch between performances and microhabitat choice and population dynamics in the field. Discrepancies between requirements and field conditions in regulated rivers underline the significance of inshore zones as microhabitats (expressed in the 'Inshore Retention Concept') and the requirement for ecophysiological studies on target species for river restoration and conservation.     

Using physiology and behaviour to understand the responses of fish early life stages to toxicants

The use of early life stages of fishes (embryos and larvae) in toxicity testing has been in existence for a long time, generally utilizing endpoints such as morphological defects and mortality. Behavioural endpoints, however, may represent a more insightful evaluation of the ecological effects of toxicants. Indeed, recent years have seen a considerable increase in the use of behavioural measurements in early life stages reflecting a substantial rise in zebrafish Danio rerio early life‐stage toxicity testing and the development of automated behavioural monitoring systems. Current behavioural endpoints identified for early life stages in response to toxicant exposure include spontaneous activity, predator avoidance, capture of live food, shoaling ability and interaction with other individuals. Less frequently used endpoints include measurement of anxiogenic behaviours and cognitive ability, both of which are suggested here as future indicators of toxicant disruption. For many simple behavioural endpoints, there is still a need to link behavioural effects with ecological relevance; currently, only a limited number of studies have addressed this issue. Understanding the physiological mechanisms that underlie toxicant effects on behaviour so early in life has received far less attention, perhaps because physiological measurements can be difficult to carry out on individuals of this size. The most commonly established physiological links with behavioural disruption in early life stages are similar to those seen in juveniles and adults including sensory deprivation (olfaction, lateral line and vision), altered neurogenesis and neurotransmitter concentrations. This review highlights the importance of understanding the integrated behavioural and physiological response of early life stages to toxicants and identifies knowledge gaps which present exciting areas for future research.     

Effects of ocean acidification on the early life history of a tropical marine fish

Little is known about how fishes and other non-calcifying marine organisms will respond to the increased levels of dissolved CO₂ and reduced sea water pH that are predicted to occur over the coming century. We reared eggs and larvae of the orange clownfish, Amphiprion percula, in sea water simulating a range of ocean acidification scenarios for the next 50–100 years (current day, 550, 750 and 1030 ppm atmospheric CO₂). CO₂ acidification had no detectable effect on embryonic duration, egg survival and size at hatching. In contrast, CO₂ acidification tended to increase the growth rate of larvae. By the time of settlement (11 days post-hatching), larvae from some parental pairs were 15 to 18 per cent longer and 47 to 52 per cent heavier in acidified water compared with controls. Larvae from other parents were unaffected by CO₂ acidification. Elevated CO₂ and reduced pH had no effect on the maximum swimming speed of settlement-stage larvae. There was, however, a weak positive relationship between length and swimming speed. Large size is usually considered to be advantageous for larvae and newly settled juveniles. Consequently, these results suggest that levels of ocean acidification likely to be experienced in the near future might not, in isolation, significantly disadvantage the growth and performance of larvae from benthic-spawning marine fishes.     

Effects of cadmium chloride on the development of rainbow trout Oncorhynchus mykiss early life stages

The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l⁻¹) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l⁻¹ Cd), however, delayed hatching was seen in the 2·50 μg l⁻¹ Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l⁻¹ Cd were 13·9 ± 0·8% shorter in total length ( L _T) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l⁻¹ Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l⁻¹ range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish.     

Recruitment and mortality of early post-settlement stages of benthic algae

Four transitional life history stages are generally recognized for benthic marine algae. On the basis of differences in size, we propose two more: young germlings and young juveniles. Three of these (spores or zygotes, young germlings, and germlings) are considered early post-settlement (EPS) stages. Many of the available data on recruitment and mortality were not collected with EPS stages specifically in mind, and considerable extrapolation and inference are required to interpret effects on early phases. Data on EPS stages, and grazing in particular, are based on the disappearance of early stages (laboratory or field experiments, including outplantings), on indirect information on mortality from manipulations of grazers or juvenile stages, and combinations of observation and manipulation. We also provide original data on the effects of water motion and canopy sweeping on zygote mortality.

The most notable finding is the variability in, and multiplicity of, factors preventing successful recruitment of early life stages. Six intrinsic and about 17 extrinsic factors and/or processes were reported to affect recruitment and mortality. Grazing, canopy, and turf effects appear to be most important, but less well studied factors such as desiccation and water motion may be as important for early stages. Our review indicates that recruitment is highly variable, even episodic, and that mortality at this period is high. Combined, these elements suggest that chance events during EPS stages may play a large role in survival, and perhaps the evolution of benthic algae.     

Grazing by a small fish affects the early stages of a post-settlement stony coral

Short-term experiments were used to isolate the detrimental effects of grazer disturbance on young corals, and determine the stage of development at which recruits are no longer susceptible to this disturbance. Artificial substrata containing an algal matrix and coral recruits of different life stages were exposed to grazing by epilithic algal matrix (EAM) feeding combtoothed blennies, Salarias fasciatus. Single polyp recruits were vulnerable to grazer disturbance, while multi-polyp recruits (ca. 6–8 polyps) survived with evidence of minor damage in the form of tissue and polyp loss. The result indicates that blennies, although small and possessing weak dentition, can negatively influence the survival of young coral recruits. The protruding structure of micro-nubbins, representing juvenile corals were not damaged, suggesting that coral achieving that size and form can escape such damage. Communicated by Ecology Editor Prof. Peter Mumby     

Preparation of chromosomes from early stages of fish for cytogenetic analysis

Techniques previously used to prepare tissues of adult fish for cytogenic analysis were modified in order to obtain large numbers of well-spread metaphases from eggs and larvae. This method was applied successfully in genotoxicity studies of early life stages of Cyprinodon variegatus and Morone saxatilis .     

Effects of the duration of cold stratification on early life stages of the Mediterranean alpine plant Silene ciliata

Cold stratification provided by snow cover is essential to break seed dormancy in many alpine plant species. The forecast reduction in snow precipitation and snow cover duration in most temperate mountains as a result of global warming could threaten alpine plant populations, especially those at the edge of their species distribution, by altering the dynamics of early life stages. We simulated some effects of a reduction in the snow cover period by manipulating the duration of cold stratification in seeds of Silene ciliata, a Mediterranean alpine specialist. Seeds from three populations distributed along an altitudinal gradient were exposed to different periods of cold stratification (2, 4 and 6 months) in the laboratory and then moved to common garden conditions in a greenhouse. The duration of the cold stratification treatment and population origin significantly affected seed emergence percentage, emergence rate and seedling size, but not the number of seedling leaves. The 6‐month and 4‐month cold stratification treatments produced higher emergence percentages and faster emergence rates than seeds without cold stratification treatment. No significant cold stratification duration x seed population origin interactions were found, thus differential sensitivity to cold stratification along elevation is not supported.     

Low oxygen tolerance of different life stages of temperate freshwater fish species

Data on low dissolved oxygen (DO₂) tolerance of freshwater fish species of north‐western Europe were used to create species sensitivity distributions (SSD). Lowest observed effect concentrations (LOEC) and 100% lethal concentrations (LC₁₀₀) data were collected from the scientific literature. Comparisons were made among life stages as well as between native and exotic species. In addition, lethal DO₂ concentrations were compared to oxygen concentrations corresponding to maximum tolerable water temperatures of the same species. Fish eggs and embryos were the least tolerant. Juveniles had a significantly lower mean LOEC than adults, but there was no difference in mean LC₁₀₀ between the two groups. The difference in lethal oxygen concentrations between adults and juveniles was largest for three salmonids, although it remains uncertain if this was a result of smoltification. There were no significant differences between native and exotic species; however, data on exotics are limited. DO₂ concentrations converted from maximum tolerable water temperatures were 3·9 times higher than the measured lethal DO₂ concentrations, which may reflect changes in respiration rates (Q₁₀) and may also relate to the simplicity of the model used.     

Thermal modulation of anthropogenic estrogen exposure on a freshwater fish at two life stages

Human-mediated environmental change can induce changes in the expression of complex behaviors within individuals and alter the outcomes of interactions between individuals. Although the independent effects of numerous stressors on aquatic biota are well documented (e.g., exposure to environmental contaminants), fewer studies have examined how natural variation in the ambient environment modulates these effects. In this study, we exposed reproductively mature and larval fathead minnows (Pimephales promelas) to three environmentally relevant concentrations (14, 22, and 65 ng/L) of a common environmental estrogen, estrone (E1), at four water temperatures (15, 18, 21, and 24 °C) reflecting natural spring and summer variation. We then conducted a series of behavioral experiments to assess the independent and interactive effects of temperature and estrogen exposure on intra- and interspecific interactions in three contexts with important fitness consequences; reproduction, foraging, and predator evasion. Our data demonstrated significant independent effects of temperature and/or estrogen exposure on the physiology, survival, and behavior of larval and adult fish. We also found evidence suggesting that thermal regime can modulate the effects of exposure on larval survival and predator-prey interactions, even within a relatively narrow range of seasonally fluctuating temperatures. These findings improve our understanding of the outcomes of interactions between anthropogenic stressors and natural abiotic environmental factors, and suggest that such interactions can have ecological and evolutionary implications for freshwater populations and communities.     

Maternal warming affects early life stages of an invasive thistle

Maternal environment can influence plant offspring performance. Understanding maternal environmental effects will help to bridge a key gap in the knowledge of plant life cycles, and provide important insights for species’ responses under climate change. Here we show that maternal warming significantly affected the early life stages of an invasive thistle, Carduus nutans. Seeds produced by plants grown in warmed conditions had higher germination percentages and shorter mean germination times than those produced by plants under ambient conditions; this difference was most evident at suboptimal germination temperatures. Subsequent seedling emergence was also faster with maternal warming, with no cost to seedling emergence percentage and seedling growth. Our results suggest that maternal warming may accelerate the life cycle of this species via enhanced early life‐history stages. These maternal effects on offspring performance, together with the positive responses of the maternal generation, may exacerbate invasions of this species under climate change.