Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Contrasting treatment‐specific survival using double‐robust estimators

The Atlantic cod (Gadus morhua L.) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment. Here we show that, in addition to the effects of overfishing, fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea (bottom-up control). Survival of larval cod is shown to depend on three key biological parameters of their prey: the mean size of prey, seasonal timing and abundance. We suggest a mechanism, involving the match/mismatch hypothesis, by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.

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Plankton effect on cod recruitment in the North Sea.

Climate influences a population through a variety of processes, including reproduction, growth, migration patterns and phenology. Climate may operate either directly through metabolic and reproductive processes or indirectly through prey, predators, and competitors. One mechanism that may be particularly important, and which is the focus of this review, is the role of climate in affecting the reproductive success of a predator through its effect on the relative timing of food requirement and food availability during early life stages. This principle — the match or mismatch of predators' requirement with resource availability — originated in the marine literature, where it ini- tially referred to how growth and survival of fish larvae (predator) depends on this production being synchronous with that of their main food items, i.e. early stage zooplankton (prey). Here we review how the match/mismatch hypothesis (MMH) is used to describe climate effects on ecological patterns and processes in both marine and terrestrial systems. In addition to studying match/mismatch sensu stricto, we expand on it to include effects of overall production level and the spatial aspect. Possible impacts of climate change on match/mismatch are examined in the context of one of the most appar- ent effects of global warming: an advancement of spring phenology. As a consequence of different species reacting dissimilarly, even minor changes in climate may invoke non-linear responses unbal- ancing established patterns of synchrony. All components of a food chain cannot be expected to shift their phenology at the same rate, and thus are unlikely to remain synchronous.

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Climate and the match or mismatch between predator requirements and resource availability

Human beings may affect the welfare of fish through fisheries, aquaculture and a number of other activities. There is no agreement on just how to we igh the concern for welfare of fish against the hum an interests involved, but ethical frameworks exist th at suggest how this might be approached. Different definitions of animal welfare focus on an animal's condition, on its subjective experience o f that condition and/or on whether it can lead a natu ral life. These provide different, legitimate, pers pectives, but the approach taken in this paper is to focus on welfare as the absence of suffering. An unresolved and controversial issue in discussion s about animal welfare is whether non-human animals exposed to adverse experiences such as physical injury or confinement experience what humans would call suffering. The neocortex, which in huma ns is an important part of the neural mechanism tha t generates the subjective experience of suffering, i s lacking in fish and non-mammalian animals, and it has been argued that its absence in fish indicates that fish cannot suffer. However, a strong alternative view is that complex animals with sophisticated behaviour, such as fish, probably have the capacity for suffer ing, though this may be different in degree and kind fro m the human experience of this state. Recent empirical studies support this view and show that painful stimuli are, at least, strongly avers ive to fish. Consequently, injury or experience of othe r harmful conditions is a cause for concern in term s of welfare of individual fish. There is also growing e vidence that fish can experience fear-like states a nd that they avoid situations in which they have experience d adverse conditions.

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Current issues in fish welfare

Foraging, growth and survival of Atlantic cod larvae reared in different light intensities and photoperiods

Neither the scale of adaptive variation nor the genetic basis for differential population responses to the environment is known for broadcast-spawning marine fishes. Using a common-garden experimental protocol, we document how larval growth, survival and their norms of reaction differ genetically among four populations of Atlantic cod (Gadus morhua). These traits, and their plastic responses to food and temperature, differed across spatial scales at which microsatellite DNA failed to detect population structure. Divergent survival reaction norms indicate that warm-water populations are more sensitive to changes in food, whereas cold-water populations are more sensitive to changes in temperature. Our results suggest that neither the direction nor the magnitude of demographic responses to environmental change need be the same among populations. Adaptive phenotypic plasticity, previously undocumented in marine fishes, can significantly influence the probability of recovery and persistence of collapsed populations by affecting their ability to respond to natural and anthropogenic environmental change.

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Genetic variation in life-history reaction norms in a marine fish.

Larviculture of Atlantic cod (Gadus morhua): progress, protocols and problems

Foraging, growth and survival of Atlantic cod larvae reared in different prey concentrations

How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks.

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Velmurugu Puvanendran

Papers

Foraging, growth and survival of Atlantic cod larvae reared in different light intensities and photoperiods

Genetic variation in life-history reaction norms in a marine fish.

Larviculture of Atlantic cod (Gadus morhua): progress, protocols and problems

Foraging, growth and survival of Atlantic cod larvae reared in different prey concentrations

Ocean acidification effects on Atlantic cod larval survival and recruitment to the fished population.