The persistence of most coastal marine species depends on larvae finding suitable adult habitat at the end of an offshore dispersive stage that can last weeks or months. We tested the effects that ocean acidification from elevated levels of atmospheric carbon dioxide (CO2) could have on the ability of larvae to detect olfactory cues from adult habitats. Larval clownfish reared in control seawater (pH 8.15) discriminated between a range of cues that could help them locate reef habitat and suitable settlement sites. This discriminatory ability was disrupted when larvae were reared in conditions simulating CO2-induced ocean acidification. Larvae became strongly attracted to olfactory stimuli they normally avoided when reared at levels of ocean pH that could occur ca. 2100 (pH 7.8) and they no longer responded to any olfactory cues when reared at pH levels (pH 7.6) that might be attained later next century on a business-as-usual carbon-dioxide emissions trajectory. If acidification continues unabated, the impairment of sensory ability will reduce population sustainability of many marine species, with potentially profound consequences for marine diversity.climate change ͉ larval sensory mechanisms ͉ population connectivity ͉ population replenishment O cean acidification caused by the uptake of additional carbon dioxide (CO 2 ) at the ocean surface is now recognized as a serious threat to marine ecosystems (1-4). At least 30% of the anthropogenic CO 2 released into the atmosphere in the past 200 years has been absorbed by the oceans, causing ocean pH to decline at a rate Ϸ100 times faster than at any time in the past 650,000 years (1, 4). Global ocean pH is estimated to have dropped by 0.1 units since preindustrial times and is projected to fall another 0.3-0.4 units by 2100 because of existing and future CO 2 emissions (1, 5-6). Considerable research effort has focused on predicting the impact that reduced carbonate-ion saturation states that accompany ocean acidification will have on calcifying marine organisms, particularly corals and other invertebrates that precipitate aragonite skeletons (2-3, 6). However, the effects that ocean acidification will have on other marine organisms, including fishes, remain almost completely unknown, especially for conditions of atmospheric carbon dioxide and seawater pH that could occur in the near future (4, 7-9).The persistence of most coastal marine species depends on the ability of larvae to locate suitable settlement habitat at the end of a pelagic stage that can last weeks or months. Accumulating evidence for reef fishes suggests that both reef sounds (10) and olfactory cues (11-13) are used by larvae to locate reefs. The olfactory organs of many reef fishes are well-developed by the end of the larval phase (14-15), and it has recently been shown that larvae of some species can discriminate the smell of water from their natal reef compared with water from other reefs (13), which provides a mechanism to explain high levels of selfrecruitment in some reef fish populations (16)(...

Phenotypic plasticity, both within and across generations, is an important mechanism that organisms use to cope with rapid climate change. While an increasing number of studies show that plasticity across generations (transgenerational plasticity or TGP) may occur, we have limited understanding of key aspects of TGP, such as the environmental conditions that may promote it, its relationship to withingeneration plasticity (WGP) and its role in evolutionary potential. In this review, we consider how the detection of TGP in climate change experiments is affected by the predictability of environmental variation, as well as the timing and magnitude of environmental change cues applied. We also discuss the need to design experiments that are able to distinguish TGP from selection and TGP from WGP in multigenerational experiments. We conclude by suggesting future research directions that build on the knowledge to date and admit the limitations that exist, which will depend on the way environmental change is simulated and the type of experimental design used. Such an approach will open up this burgeoning area of research to a wider variety of organisms and allow better predictive capacity of the role of TGP in the response of organisms to future climate change.

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How populations and species respond to modified environmental conditions is critical to their persistence both now and into the future, particularly given the increasing pace of environmental change. The process of adaptation to novel environmental conditions can occur via two mechanisms: (1) the expression of phenotypic plasticity (the ability of one genotype to express varying phenotypes when exposed to different environmental conditions), and (2) evolution via selection for particular phenotypes, resulting in the modification of genetic variation in the population. Plasticity, because it acts at the level of the individual, is often hailed as a rapid-response mechanism that will enable organisms to adapt and survive in our rapidly changing world. But plasticity can also retard adaptation by shifting the distribution of phenotypes in the population, shielding it from natural selection. In addition to which, not all plastic responses are adaptive—now well-documented in cases of ecological traps. In this theme issue, we aim to present a considered view of plasticity and the role it could play in facilitating or hindering adaption to environmental change. This introduction provides a re-examination of our current understanding of the role of phenotypic plasticity in adaptation and sets the theme issue's contributions in their broader context. Four key themes emerge: the need to measure plasticity across both space and time; the importance of the past in predicting the future; the importance of the link between plasticity and sexual selection; and the need to understand more about the nature of selection on plasticity itself. We conclude by advocating the need for cross-disciplinary collaborations to settle the question of whether plasticity will promote or retard species' rates of adaptation to ever-more stressful environmental conditions. This article is part of the theme issue ‘The role of plasticity in phenotypic adaptation to rapid environmental change’.

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Climate change is predicted to increase ocean temperatures and alter plankton communities that are food for many marine fishes. To examine the effects of increased sea surface temperature and fluctuating food levels on reef-fish reproduction, breeding pairs of the coral reef damselfish Acanthochromis polyacanthus were maintained for a full summer breeding season in an orthogonal experiment comprising 3 temperature and 2 food levels. Water temperatures were the current-day average summer temperature for the collection location (28.5°C) and temperatures predicted to become close to the average for this region over the next 50 to 100 yr (30.0 and 31.5°C). Pairs were fed either a high or low quantity diet based on average and minimum feeding rates in the wild. Both water temperature and food supply affected reproductive output. Fewer pairs bred at elevated water temperatures and no pairs reproduced at either of the higher temperatures on the lower quantity diet. Furthermore, eggs produced were smaller at 30.0 and 31.5°C compared to those at 28.5°C. Histological analysis of the gonads and steroid hormone measurement did not reveal any apparent differences in patterns of oogenesis among treatments. However, spermatogenesis was reduced at high temperatures despite some increases in plasma androgen levels. Reduced breeding rate at warmer temperatures combined with reduced sperm production indicates the potential for significant declines in A. polyacanthus populations as the ocean warms.

Determining the capacity of organisms to acclimate and adapt to increased temperatures is key to understand how populations and communities will respond to global warming. Although there is evidence that elevated water temperature affects metabolism, growth and condition of tropical marine fish, it is unknown whether they have the potential to acclimate, given adequate time. We reared the tropical reef fish Acanthochromis polyacanthus through its entire life cycle at present day and elevated ( 1 1.5 and 1 3.0 1C) water temperatures to test its ability to thermally acclimate to ocean temperatures predicted to occur over the next 50-100 years. Fish reared at 3.0 1C greater than the present day average reduced their resting oxygen consumption (RMR) during summer compared with fish reared at present day temperatures and tested at the elevated temperature. The reduction in RMR of up to 69 mg O 2 kg À1 h À1 in acclimated fish could represent a significant benefit to daily energy expenditure. In contrast, there was no acclimation to summer temperatures exhibited by fish reared at 1.5 1C above present day temperatures. Fish acclimated to 1 3.0 1C were smaller and in poorer condition than fish reared at present day temperatures, suggesting that even with acclimation there will be significant consequences for future populations of tropical fishes caused by global warming.