One condition that enhances the potential for upwelling occurs when the surface water temperature, and therefore seawater density at the surface of the ocean, is similar to that of the mid-water. Notice how the cold water carried southward by the California current produces a small change in temperature with water depth on the continental slope near San Francisco as compared to the region off Hawaii. What is expected?In addition to effects of habitat degradation, warmer ocean temperatures will cause distribution shifts in some tropical fishes, increasing the geographic ranges of some species and decreasing the ranges of others, including some commercially important species.
What we are doing about it?Experimental and observational work is underway to investigate the adaptive capacity of tropical fish.
SummaryClimate change is expected to affect populations and communities of tropical marine fishes in many ways, ranging from indirect effects associated with habitat degradation and altered resource availability to direct effects of rapidly changing environmental conditions. 1 ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD, Australia. Alistair Cheal has worked as a reef fish ecologist at the Australian Institute of Marine Science for over a decade.
Dr Mark Meekan is a Principal Research Scientist in the Perth office of the Australian Institute of Marine Science. Associate professor Marcus Sheaves, is a senior lecturer in Marine Biology at James Cook University. Dr Hugh Sweatman is the leader of the AIMS long-term Monitoring Program on the Great Barrier Reef. Australia has over 1.5 million km2 of tropical coastal waters (territorial area within the continental shelf) extending from Queensland and the Great Barrier Reef (GBR) on the east coast, across the Northern Territory and Arafura Sea region, to Western Australia and Ningaloo Reef on the west coast. Although most coastal fishes are closely associated with reefs or other benthic substratum as adults, nearly all species have a lifecycle that includes a pelagic larval stage, which lasts for a period of weeks to months, depending on the species (Leis 1991).
Climate change is expected to affect individuals, populations and communities of coastal and demersal fishes through a range of impacts on the larval, juvenile or adult phases (Munday et al. Predicting the changes that will occur to tropical coastal fishes as a result of climate change is challenging because of complex interactions between the physical environment, physiological and behavioural responses of fishes at different life history stages, energy transfer between trophic levels, and the effect of habitat structure on ecological processes and interactions (Figure 1). Observed Impacts:Coral reefs have been studied more intensively than other tropical marine environments. Loss of live coral cover has the greatest effect on those species of fish that rely on live coral for their diet, habitat or settlement (Wilson et al. Australia’s coral reefs have suffered several significant episodes of coral bleaching since the mid 1990’s. Averaged across all 48 reefs surveyed by the LTMP, there was little change in species richness and diversity of fish communities sampled between 1993-2007 (Delean and De’ath 2008). The structure of fish communities at Scott Reef in Western Australia also changed substantially following the mass coral bleaching in 1998 (Halford and Caley 2009). A range of other impacts on tropical coastal fishes are expected (Table 1) and there are indications that some of these are already occurring. Many tropical marine fishes have large latitudinal ranges that extend across temperature gradients of 3-4oC.
Finally, small increases in SST are expected to increase larval survival of marine species by reducing the duration of the pelagic phase (O’Connor et al.
Increased SST is predicted to have a range of impacts on tropical fish populations and communities (Table 1).
Increased temperature could have either a positive or negative effect on adult performance, depending on the current temperatures experienced by individuals relative to their thermal optimum for physiological activities (Munday et al.
Together these results suggest that reproductive performance of some species will be affected as early as 2030 and many species could be impacted by 2100 (Table 2).
The spawning season is thought to be cued by temperature in many tropical fish species (Hilder and Pankhurst 2003, Pankhurst and Porter 2003).
Early developmental stages of reef fishes are particularly sensitive to temperature changes. The limited evidence available suggests that a 3oC increase in SST would reduce the PLD of larval reef fishes between 12-25% (Munday et al. Species of tropical reef fishes living at the same location on the GBR differ greatly in their sensitivity to temperature increases. Finally, nearshore and estuarine fishes show consistent assemblage composition across large latitudinal gradients, indicating they are adapted to highly variable environments, and so are likely to be less affected by physical changes such as rising SST than fish with more restricted physical tolerances. Changes to major ocean currents, wind-driven surface currents, upwelling and other types of hydrodynamic features could have important effects on the dispersal and survival of tropical fish larvae (Munday et al. It is more certain that there will be greater vertical stratification of the water column, which will tend to reduce nutrient enrichment of surface waters.
Stronger tropical storms will compound reef degradation caused by coral bleaching and ocean acidification and cause increased disturbances in other habitats beside coral reefs.
Acidification of the ocean is expected to significantly affect Australia’s coral reefs, especially after 2030 when aragonite saturation levels are projected to become marginal for coral growth (Guinotte et al. Of greater concern is that CO2 levels projected to occur by 2100 can impair sensory functions and alter a broad suite of behaviours in larval, juvenile and adult fishes. Geographic range shifts towards higher latitudes have been observed in many terrestrial and aquatic species and there is high agreement they will occur in most ecosystems as temperatures increase.
There is reasonable empirical and experimental evidence to support projections about changes in life histories, shifts in the spawning season, reproductive declines, and reduced pelagic durations in coastal fishes with a 2-3oC increase in SST and consensus in these projections is moderate. The confidence levels for other predicted impacts (Table 1) are LOW, both for 2030 and 2100 because there is either limited evidence available to support the projections, limited agreement, or both. Some acclimation and adaptation to increased SST will almost certainly occur among Australia’s tropical marine fishes, however, the extent to which fishes can withstand projected increases in SST will vary among species, depending on their current ranges, temperature tolerances, genetic population structure, and generation times.
Despite the potential for acclimation and adaptation, populations of some species on the GBR appear to be living close to their thermal optimums. Some small-bodied species, such as most gobies, have short generation times that should favour local adaptation over the next 50-100 years.
It has recently been discovered that some reef fishes may have more capacity for thermal acclimation than previously thought.
For commercially and recreationally exploited fishes, human adaptation responses should include incorporating larger “safety margins” into harvest levels to provide some insurance from greater variability in population fluctuations and uncertainty about other climate change impacts. More research is required before we can predict the full ramifications of climate change on tropical coastal fishes and develop better strategies for minimising the impacts (Wilson et al. The AIMS Long Term Monitoring Program (LTMP) has surveyed 47 reefs in the Great Barrier Reef (GBR) annually since 1993. University researchers have monitored fish populations at specific locations in tropical Australia for various periods of time.
Although reef fishes on the GBR are monitored annually by the AIMS LTMP, and to a limited extent by some other programs, there is little monitoring of non-reef and inshore fishes. Greater resolution of spatial and temporal variation of key physical parameters, including sea surface temperature, pH, pCO2, productivity, and surface currents is required. An improved understanding of the capacity for fish populations to adjust to changes in environmental conditions over years to decades is urgently required. Great Barrier Reef Marine Park Authority (2007) Great Barrier Reef coral bleaching surveys 2006 : undertaken as a part of the climate change coral bleaching response plan, March-April 2006.
BEDMAP 2, showing that the bedrock on which the West Antarctic Ice Sheet rests is well below sea level.
The West Antarctic Ice Sheet is currently warming particularly rapidly, and this warming is associated with increased ocean temperatures and changes to atmospheric circulation, which drives increased upwelling of deep, relatively warm oceanic water onto the continental shelf.
Ice shelves around the West Antarctic Ice Sheet are thinning as they are melted from below by upwelling warm ocean currents. Because of these factors, the West Antarctic Ice Sheet could rapidly and catastrophically melt, resulting in as much as 3.3 m of sea level rise within 500 years. Share thisIf you enjoyed this post, please consider subscribing to the RSS feed to have future articles delivered to your feed reader. Hi Joe, haven’t seen much pubished on evidence of seasonal changes in velocity being attributed to increased meltwater supply like in Greenland – maybe a future research avenue?! It appears then that glacier or ice shelf thinning is the key preconditioning factor for collapse, retreat and acceleration, whether you are in Antarctica of Greenland. The reason for writing this and one other post was to point out that moulins were not significant to ice sheet acceleration.
The energy that powers cars will still come from the Earth, but now it will be from a geothermal plant that produces a liquid fuel.
Unlike regular gas, burning methanol doesn’t emit carbon monoxide, soot, or other carcinogens. The volcano-powered plant in Iceland is already running to demo the technology and will grow the project next year. And soon, they hope to prove that their technology can be affordable even in places that don't happen to have volcanoes. We consulted NOAA and Weather West and it looks like El Nino in California should mean higher than average precipitation with near average temperatures. This allows the surface water and mid-water to mix vertically since the pycnocline is not well developed. In the short-term (up to 2030), the projected impact of climate change on Australia’s tropical coastal and demersal fishes is largely tied to the fate of critical benthic habitats, especially for coral reef environments, which are highly vulnerable to elevated temperature, ocean acidification and more intense storms. These waters are inhabited by approximately 2000 species of marine fishes (Allen and Swainston 1988). When sufficiently developed, the larvae settle to the benthos, usually in the same general habitat as juveniles and adults (Booth and Wellington 1998). Over the past few years there has been increased research into the effects that changes to the physical environment have on the ecology and biology of tropical marine fishes. The potential impacts of climate change on populations and communities of tropical coastal fishes will depend on complex interactions between changes in the physical environment (e.g.
Recent episodes of coral bleaching caused by elevated sea temperatures have seriously degraded reefs around the world (Wilkinson 2004). During the 1998 global mass bleaching event sea surface temperatures in the GBR reached the highest ever recorded. Since the mid 1990’s outbreaks of crown-of-thorns starfish and severe storms appear to have caused most of the coral mortality on the GBR and climate-induced coral bleaching has so far contributed relatively little to observed coral loss (Osborne et al. Similarly, there was little change in the averaged abundances of major trophic groups of fishes including herbivores, planktivores, benthic feeders and predators across all reefs (Delean and De’ath 2008). Species richness declined in 4 fish families following the bleaching, but had recovered in 2 of them (surgeonfishes and parrotfishes) within 5 years.
Geographic range shifts are a common response of animals to climate change, with many species expanding to higher latitudes in both terrestrial and aquatic ecosystems as global temperatures increase (Hickling et al. Life history traits of some species covary in a predictable way with these latitudinal and temperature gradients (Choat and Robertson 2002, Robertson et al. Fishes are ectotherms and temperature changes of a few degrees Celsius can influence their physiological condition, developmental rate, growth rate, reproductive performance and behaviour.
Consequently, the effects of increasing temperature on reproductive performance could potentially be ameliorated to some extent by shifts in the seasonal timing of spawning (Munday et al. Small temperature increases may accelerate larval development, increase larval growth rate, and reduce pelagic larval duration (PLD; McCormick and Molony 1995, Wilson and Meekan 2002, Meekan et al.
Range limits may increase or contract depending on current distributions and thermal tolerances (Munday et al. Some species are highly sensitive to a 2-4oC increase in average summer temperature, whereas others appear to be much more tolerant (Nilsson et al. This may reduce the productivity of plankton communities that are an important food source for many tropical marine fishes, or are the food source for invertebrates that the fish prey on. Many coastal environments such as mangroves and seagrass beds, provide juvenile fish with protection or food resources (Sheaves and Molony 2000). Projected impacts of climate change on populations and communities of tropical coastal fishes in Australia and the level of certainty associated with these predictions for 2100.
Observed and projected impacts of climate change on tropical coastal and demersal marine fishes in Australia.
There is good evidence and strong consensus that coral bleaching has affected fish community structure at several locations on the Great Barrier Reef and at Scott Reef in WA. Range shifts have already been observed in Australia’s temperate marine environment and there is some evidence that such shifts may already be underway for tropical species.
For example, a 1.5°C increase in average summer temperatures causes significant declines in growth and reproductive output of the spiny damselfish A.
Habitat degradation will also retard adaptation to other climate change impacts by reducing genetic variability within populations and by reducing genetic connectivity between populations (Munday et al. In some cases, lower harvest rates will need to be revised because of the possibility that habitat loss and reduced productivity at lower trophic levels (i.e prey species) will lead to less productive populations of larger predatory species that are favoured by commercial fisheries (Brander 2007, Graham et al. Much of the available data comes from temperate species and these results might not be directly applicable to tropical marine fishes.
The projections are critical for understanding how population dynamics and connectivity patterns may change over the coming century.


Understanding the habitat requirements of fishes throughout their life will enable more precise predictions to be made about the long term consequences of declining habitat quality.
Moreover, most research on climate impacts for tropical fishes has focussed on small coral reef species and there is an obvious need to consider larger species important to fisheries. A greater understanding of spatial and temporal variation in distributions and abundances is required to assess potential climate change impacts in these environments.
Elevated CO2 levels do not appear to directly affect the growth and survival of small demersal fishes, but larger pelagic species might be more sensitive to future rises in CO2. A team of trained divers surveys fishes by underwater visual census and records corals and other benthic organisms along the same sections of reef at each visit. The LTMP also provides situational awareness on threats, such as coral bleaching and crown of thorns starfish outbreaks. James Cook University has surveyed fish populations on 3 reefs in the Townsville region on a biannual basis since 2002, and Western Australian researchers are also active from Rottnest island north. Joint publication of Australian Institute of Marine Science, Western Australian Museum and Woodside Energy. We need to know the answer to this question if we are to mitigate effectively against sea level rise, particularly when it’s associated with storm surges, hurricanes and extreme weather events, which test our already strained flood defence schemes. Since 1900 AD, a long-term cooling trend that began around 5000 years ago and culminated in the Little Ice Age in the 1750s (with its ice fairs on the frozen River Thames) has been reversed.
The West Antarctic Ice Sheet is drained by fast-flowing, marine-terminating ice streams and it is surrounded by floating ice shelves. Although there may be more snow over the Antarctic Ice Sheet under a warmer climate, this too could lead to changes in glacier dynamics. Modified from the IPCC sea level rise estimates (from Wikimedia Commons) and using estimates from Bamber and Aspinall 2013, assuming a uniform rate of sea level rise. Rates such as these are common in the geological record, but these dynamic behaviours are too difficult for even our most complex computer models to solve. Is it the case in Antarctica – like it is thought to be in Greenland – that faster melt increases moulin formation and hydrological transport to the bed, resulting in slippage of ice into the ocean?
Certainly there’s room for a blog post about different behavious in Greenland & Antarctica!
The mechanisms for ice shelf thinning include basal melting (from warming ocean waters), surface melting, reduction in glacier inflow and rift development. Now, as the power plant runs, Carbon Recycling has started capturing the carbon dioxide emissions and turning it into methanol, a liquid fuel that can either be used to power cars or to make products like plywood and paint. But it’s trickier at places like coal-fired power plants, where emissions are a mix of chemicals that are expensive to separate.
There is good evidence and strong consensus that climate-induced coral bleaching affects the community structure and abundance of reef-associated fishes, especially when it leads to the structural collapse of reef habitat.
Some species, such as some snappers and groupers, settle into shallow inshore and estuarine habitats and migrate to reefs or deeper inter-reefal areas as juveniles or subadults (Sheaves 2005). However, the number of studies remains low and most experimental research has involved small, site-attached coral reef species.
Coral mortality from bleaching has caused significant declines in the diversity and abundances of reef fishes in some places (Jones et al. Approximately 42% of GBR reefs bleached to some extent in 1998, although the 2002 bleaching event was more extensive (Berkelmans et al.
There were, however, large and important changes in fish abundance and community structure at specific reefs where coral cover had declined significantly (Halford et al. In the other 2 families (butteflyfishes and damselfishes ), both species richness and total abundance declined and remained lower than pre-bleaching after 5 years, especially on the reef slope. Consequently, the projected 1-2oC increase in SST by 2030 and 2-3oC increase by 2100 are expected to have significant impacts on coastal marine fishes. At least some tropical coastal fishes appear to be closely adapted to the local thermal environment (Pankhurst and Porter 2003, Nilsson et al. 2008a), however this could lead to a mismatch in the optimal time for reproduction compared with the optimal time for larval survival (Edwards and Richardson 2004).
2003, Green and Fisher 2004, Sponaugle et al 2006), provided temperatures do not exceed thermal optima. Simulations using coupled biological-physical models indicate that this will tend to reduce the spatial scale of pelagic dispersal.
Planktonic food chains will also be less productive at higher temperatures (McKinnon et al. Changes in rainfall and terrestrial runoff are expected to have greatest effects on nearshore and estuarine species. Changes in the extent and proximity of the various habitat types would affect their function as nursery grounds for a range of commercially valuable fish species.. Confidence levels were assigned using the IPCC framework for considering available evidence and expert judgements. Consequently the confidence level is HIGH for this observed impact, although the impacts are currently isolated and not sufficiently widespread to be detected at regional scales (e.g. There is less evidence and less consensus that similar trends will be observed with a 1-2oC increase in SST. 9-10 years in some groupers and snappers), which would greatly reduce the potential for local adaptation, unless there is considerable genetic input from populations that are already adapted to warmer waters (Munday et al. There is now ample evidence that high CO2 levels could be a serious threat to marine fishes because they affect cognitive function and behaviour of marine fish. Fishes from a list of 191 species, representing 10 families, are counted at three sites on each reef. AIMS has been monitoring fish and coral communities on Scott Reef in Western Australia on a semi-regular basis since 1994. Similarly, there is currently insufficient monitoring of fish populations throughout NW Australia. However, uncertainty in the response of polar ice sheets to climate change limits our ability to project sea level rise into the future. Global sea level is now rising at a rate of 3.1 mm per year, which will lead to a total rise of 18-59 cm by 2100 AD. Much of the rock on which the ice sheet rests is below current sea level, and the bedrock slopes downwards towards the centre of the ice sheet. A new paper in the journal Nature Climate Change by Bamber and Aspinall has attempted to untangle this thorny problem. The CO2 emissions from the geothermal plant are easier to capture and use because they're more concentrated. Already, they're producing enough methanol to help offset the fuel emissions of tens of thousands of cars.
In the longer-term (after 2030), sea level rise and altered rainfall patterns are expected to also significantly alter coastal wetlands that are important nursery areas for estuarine and nearshore species. 1997, Choat and Russell 2009), with a smaller number of species inhabiting inter-reefal areas, inshore and estuarine water, or the pelagic zone above the continental shelf.
Changes to sea surface temperature (SST), ocean pH, and circulation patterns are expected to influence a suite of biological and ecological characteristics of marine fishes, including: physiological condition, life history traits, the timing of spawning, reproductive output, larval development, population connectivity and geographic distributions (Table 1).
Changes in fish community structure tended to lag behind changes in the benthic habitat by 12-18 months.
Similar shifts by tropical marine fishes are projected to occur in Australian waters (Munday et al. Reef fish species tend to be shorter lived and reach smaller maximum sizes at higher temperatures (Munday et al. The greatest problems are expected for fish that use photoperiod to cue reproduction, because these species may not shift their spawning cycle as SST increases.
Such changes could improve larval survival and recruitment if larvae can consume sufficient additional food to support the increased energetic demand of developing at a higher temperature. A 20% reduction in PLD for a common reef fish in the Caribbean changed the modal dispersal distance predicted by simulations from ~50km to mostly self-recruitment (10’s km) and also reduced the number of larvae dispersing long distances (Munday et al. Most tropical coastal fishes are geographically widespread, but some species have restricted distributions within Australia’s tropical zone.
One important commercial and recreational species, Lethrinus miniatus (sweetlip or redthroat emperor) has an apparent upper thermal limit of about 28?C and is expected to become significantly less abundant in tropical coastal waters (Munday et al.
These results suggest that range shifts to cooler southern locations will occur rapidly for some species, but more slowly for others species. However, at this time, the projections of how ocean currents will change lack sufficient confidence and resolution at scales relevant to the ecology of marine fishes to allow meaningful predictions to be made about the likely impact on tropical coastal fishes. The ability of fishes to access wetland habitat is influenced by flooding from storms (Sheaves et al.
The direction and magnitude of this impact is likely to vary spatially, determined by the details of specific habitat change, and is likely to depending on the specific requirements of different species. A further concern is that increased levels of dissolved CO2 could affect the physiological performance and behaviour of some marine fishes (Ishimatsu et al. It is uncertain how quickly range shifts will occur for most species, therefore the certainty of this impact for 2030 is only MODERATE. Maintaining and restoring habitat quality for coastal marine fishes should be a major focus for climate change mitigation responses in the coastal environment (Pratchet et al. Limiting fishing pressure on larger mobile species, and species that perform key ecological roles is also important as many of these species are more vulnerable to increased fishing pressure than climate change (Graham et al. However, very little is known about how increased SST and CO2 might interact to affect marine fishes. The potential for adaptation will ultimately determine the consequences of climate change for all ecological communities. In all areas, more robust estimates of annual catch and effort trends for demersal fish species from all sectors (commercial and recreational) are necessary. Effects of climate-induced coral bleaching on coral-reef fishes: ecological and economic consequences. Multiple disturbances and the global degradation of coral reefs: are reef fishes at risk or resilient? Proceedings of the National Academy of Sciences of the United States of America 101: 8251-8253.
Most of this rise is caused by thermal expansion of the ocean and the melting of small ice caps and glaciers. Because of this, the ice sheet is unstable, because as water gets deeper, more icebergs are calved, increasing ice discharge. Rapid removal of bounding ice shelves, such as those around Pine Island Glacier, could therefore result in increased thinning and recession of grounded glaciers, initiating a positive-feedback loop that could be catastrophic. Glaciers will flow faster, discharging more icebergs into the ocean, negating any impact the increased snowfall would have in mitigating sea level rise. They pooled different assessments by numerous experts in order to reach a consensus on likely sea level rise by AD 2100.
On marine terminating outlet glaciers the mechanisms to trigger thinning is surface ablation causing thinning, and potentially basal melting. And the geothermal plant also provides cheap, renewable electricity to power the conversion to methanol. In addition to the effects of habitat degradation, warmer ocean temperatures are projected to cause distributional shifts in some tropical fishes, increasing the geographic ranges of some species and decreasing the ranges of others, including some commercially important species.
Although the confidence in most projections about the impact of climate change on Australia’s tropical coastal fishes remains moderate-low, and unforseen impacts are likely to occur, there have been significant advances in our understanding of some climate change threats (e.g.
2008) especially in locations where the structural complexity of the reef habitat has been significantly reduced (Graham et al.
Declines in population abundance in these species can occur rapidly following coral loss, and are greatest for more specialised species, such as those that live or feed on just 1-2 species of coral (Munday 2004, Pratchett et al. In 2002, approximately 54% of GBR reefs suffered bleaching, with more bleaching on inshore reefs compared with mid-shelf and offshore reefs. Nevertheless, sustained and ongoing climate change will have increasing impacts in coming years, including increases in the intensity and frequency of coral bleaching (Hoegh-Guldberg 1999, Donner et al. Recovery of fish communities was observed as coral cover returned, but was still incomplete after 5 years.
2010), with growth rates and reproductive capacity declining at higher temperatures, even when additional food is available to fuel higher metabolic rates at higher temperatures. However, recruitment may fail at times and places where food is limited because larvae will be more susceptible to starvation at higher temperatures (Munday et al. At least 90 species of fishes from the northern half of the GBR do not currently occur, or are relatively uncommon, in the southern or far-southern regions of the GBR (Munday et al. As a result, local fish communities will change, not just due to the selective effects of habitat loss on different species, but also due to difference in thermal tolerances among species.
At the same time consumers will have increased metabolic demands due to higher metabolic rates at higher temperatures.


Sea level rise will influence connectivity among estuaries, estuarine wetlands and freshwater habitats (Sheaves et al. The confidence level is LOW for observed impacts on geographic ranges, life history traits, and larval recruitment patterns, because there is limited evidence available to date and it is difficult to distinguish climate change effects from natural variation (e.g. Similarly, there is now sufficient empirical and theoretical evidence to support projections about increased variability in recruitment patterns and an overall reduction in productivity by 2100. This indicates that acclimation of some physiological traits to higher temperatures may occur in some species as the climate warms over coming decades. Our rudimentary understanding of the potential for acclimation and adaptation by marine fishes to novel environmental variation is one of the most serious gaps in our knowledge. However, the large polar ice sheets have the potential to contribute to sea level rise above and beyond this modest rate.
Ice streams in West Antarctica are also melted rapidly at their base by those warming ocean waters, leading to melting, recession into deeper water and more melting again.
Increased meltwater from melting ice shelves also produces a layer of cold, fresh water on the ocean’s surface, which easily freezes, increasing winter sea ice extent. Bamber and Aspinall used a mid-range carbon emissions scenario, with an increase of 3.5°C above pre-industrial temperatures.
Life history traits and population dynamics will be affected by warmer temperatures, with potential implications for fisheries yields. Recent surveys indicate further recovery to coral and fish communities at Scott Reef (Anon 2010; Smith pers.
Recruits of tropical species are being recorded in increased abundance in sub-tropical and temperate locations and in some instances these fish, have persisted for several years (Booth et al.
Juveniles are also expected to reach their asymptotic size at a faster rate at higher temperatures. In a long-term study in French Polynesia, larval supply of coral reef fishes declined by >50% below average during the 1997-98 El Nino, when average SST was 3.5°C above the mean, and increased nearly 250% during La Nina years, when temperatures were almost 2°C below the mean (Lo-Yat et al. For example, adults of the spiny damselfish, Acanthochromis polyacanthus, lost weight when reared at 3oC above the average summer temperatures experienced in the wild, regardless of the amount of food they consumed (Munday et al. This suggests that reduced PLDs at higher temperatures could reduce population connectivity. Some species will expand into current-day sub-tropical or temperate locations as temperatures become more favourable at these locations in the future. There is also evidence that populations on the southern GBR have greater capacity to cope with elevated temperatures than populations of the same species on the northern GBR (Gardiner et al. Consequently, there might be a general decline in the productivity of fish assemblages in tropical waters (Brander 2007, Cheung et al. A decrease in the frequency of flooding will lead to less regular connectivity (Sheaves 2005). 2006), changing the ability of fish like barramundi, Lates calcarifer, to access crucial juvenile habitats. Similarly, the aerobic performance of two species of cardinalfishes from Lizard Island (northern GBR) declined by 50% with a 2oC increase in SST above the summer average (Nilsson et al. It should be recognised, however, that the vast majority of tropical marine fishes in Australia are not exploited and the most practical mitigation response for these species (apart from reducing greenhouse gas emissions) is to maintain population resilience by reducing other stresses.
Marshall) Great Barrier Reef Marine Park Authority and Australian Greenhouse Office, Townsville, pp. The West Antarctic Ice Sheet alone could raise global sea levels by 3.3 m if it all melted.
The West Antarctic Ice Sheet may therefore be inherently susceptible to ever faster glacier recession, and could pass tipping points that mean rapid sea level rise irrevocably occurs.
Sea surface temperatures are directly related to snowfall, so cooler sea surface temperatures and more sea ice may actually decrease snowfall over Antarctica. They found that the average rate of sea level rise from just the Greenland and Antarctic ice sheets agreed upon by these experts was 5.4 mm per year by 2100 AD.
Altered oceanic circulation and ocean acidification could also have very significant effects on populations and communities of coastal fishes in the longer term. The amount of suitable habitat for reef fishes declines further if the effects of coral bleaching interact with other disturbances that kill live coral, such as outbreaks of crown of thorns starfish, increasingly severe storms, or terrestrial pollution.
However, the effect of reduced PLD on connectivity was also strongly affected by the dispersion of habitat patches.
Some other southern GBR species, however, are confined to coral reefs and are unlikely to persist in non-reef areas, even if temperature become favourable in these locations. This could impair the viability of wetland habitats in many areas of the dry tropics, and move some wet tropics wetlands towards the intermittent connectivity currently a feature of the dry tropics. Sea level rise is expected to enhance connectivity between habitats that are normally isolated at low tide. 2009d), the latter making larval fish attracted to odours they normally avoid, including smells from predators and unfavourable habitats (Munday et al. It is unlikely that any trends in these variable could be distinguished from natural variation by 2030. Reducing terrestrial runoff, improving water quality, limiting the extent of destructive fishing practices (e.g. Pine Island Glacier, one of the fastest ice streams in the world, is already thinning and receding, making it susceptible to rapid recession in ever deeper water.
Combined with melting glaciers and ice caps and thermal expansion of the ocean, Bamber and Aspinall gave a range of 33-132 cm, with 62 cm the average estimate, for sea level rise by 2100. There are a many critical knowledge gaps in our understanding of the effect of climate change on tropical marine fish, including how predicted effects on individuals and populations will scale-up to influence community structure and function, and the degree to which fish will acclimate or adapt to the expected rapid climate change.
The interacting effects of climate change and other stresses to reef habitats (Pratchett et al. Importantly, many reef fish that specialise on live coral are dependent on coral species that are susceptible to coral bleaching (e.g.
Scott Reef in Western Australia suffered severe bleaching in 1998, with an 80% reduction in coral cover recorded (Smith et al. Changes included increases in abundance of large herbivores and decreases in abundance of both coral-dependent fishes and also some species with no obvious dependence on coral.
Persistence is largely determined by overwintering temperatures, which have been increasing over the past decade (Figueira and Booth 2009). Increased larval supply during La Nina years was correlated with increased ocean productivity (chlorophyll-a). In areas of high reef density, simulations predicted that local connectivity networks would strengthen with decreased PLD because more larvae would be exchanged between nearby reefs. The region around 18oS appears to be an important biogeographic boundary for many fish in the northern GBR (M Emslie pers comm), Consequently, most range extensions are likely to be south of this region.
Consequently, the geographic ranges of these species will contract towards the far southern GBR. Therefore, northern populations are at greatest risk of decline, even if they experience a smaller increase in SST compared with southern populations.
Beyond direct effects on the ability to access wetlands, any reduction in the amount or regularity of rainfall would reduce the viability of wetland pools as fish habitats and nurseries. However, human responses to prevent inundation of urban areas and farmland as sea level rises could also cause compression of coastal habitats, reducing connectivity and the habitable area for some nearshore fish species. 2005).Studies in Australia have found no evidence that elevated CO2 levels have a direct negative effect on the growth, survival or swimming performance of larval or juvenile reef fish (Munday et al. Whether these species will be able to adapt quickly enough to rapidly increasing temperatures will depend on their generation times and genetic connectivity with other populations. Non-reefal environments and commercially important species are especially understudied in relation to climate change impacts.
2011b) have the potential to substantially alter the structure of fish communities in tropical Australia (Wilson 2008a).
The proportion of species that increased or decreased in abundance varied among reefs, but 45 to 71% of fish species decreased in abundance on some reefs. There have also been increasing anecdotal reports of larger tropical species being sighted and caught as far south as Perth in Western Australia in recent years (Wilson pers. This is the first evidence that life history traits of tropical marine fishes may be altering in response to climate change. These results suggest that increased temperatures can have negative effects on affect both the reproductive output by adults and the survival of larvae in the plankton, leading to a reduced supply of larvae to replenish benthic populations. The speed and extent of range expansions will depend on: (1) thermal sensitivity, being faster for more sensitive species (Nilsson et al. For these species, smaller ranges would ultimately increase the risk of extinction from other impacts. Productivity will probably increase at some locations where local changes to current and upwelling improve nutrient supplies to surface waters. Extended drought allows freshwater pools to dry and saline pools to develop extremely hypersaline conditions (Sheaves et al. A more likely scenario for these thermally sensitive species is that northern populations will decline as SST increases, but the species might become more abundant further south (i.e. Key strategies in mitigating effects of climate change on coastal marine fishes are to maintain and restore habitat quality, incorporate climate uncertainty into fisheries management plans, and limit impacts of other human activities likely to reduce the sustainability of fish populations. If coral does not recover in the longer-term (after 5-10 years), impacts can be more substantial with up to 75% of fish species declining in abundance, including many species with no apparent reliance on live coral (Jones et al. A localised severe bleaching event in the southern GBR in 2006 caused 40% coral mortality in the Keppel Islands (Great Barrier Reef Marine Park Authority 2007), but little impact elsewhere. The magnitude of change in species abundances increased linearly with the magnitude of coral decline.
Therefore, projecting the effect of reduced PLD on connectivity patterns is challenging, and the outcome is likely to differ between locations with contiguous tracts of reef, such as barrier reefs or fringing reefs, and locations with a more fragmented distribution of reefs (Munday et al. Similarly the development of otoliths (ear bones made of aragonite) appears to unaffected by CO2 levels likely to be experienced in surface-ocean waters over the next 50-100 years (Munday et al. These behavioural alterations significantly increase mortality of fish in natural reef habitat, with potentially far-reaching implications for population replenishment, community structure and ecosystem function (Munday et al. Whether such impact will be widespread by 2030 depends on the accuracy of predictions about the level of degradation on coral reefs by this date, which are still debated. Although severe bleaching events have occurred on Australia’s coral reefs, there has also been significant post-bleaching recovery (Smith et al. The apparent increase in larger, mobile, tropical species, is associated with a strong La Nina pattern and anomalously high water temperatures (4-5°C above summer averages) extending into higher latitudes (Pearce et al. Pathways for synthesis of reproductive hormones are temperature sensitive in fish (Pankhurst and Munday 2011) and it is possible that reproduction may be severely curtailed by rising water temperature, even in species that exhibit some capacity for acclimation to higher temperatures over a number of generations (Donelson et al.
In either case their function as fish habitats is significantly altered, exacerbating the reduction already occurring through the construction of weirs and pasture ponding (Hyland 2002).
2011a,b) However, nearly all the research to date has concerned small demersal-spawning reef fishes, which might be adapted to variable CO2 levels, especially during early development.
2009a) and (3) ecological interactions with different competitors and predators at more southerly locations. It is possible that pelagic species and broadcast spawners are more susceptible to higher CO2 levels during early development (Munday et al. Skeletons of dead corals ultimately erode and collapse thereby reducing topographic and habitat complexity.
New research has found that these diverse behavioural and sensory effects are caused by interference with neurotransmitter function by changed ion concentrations in the tissues of fish exposed to high CO2, (Nilsson et al. This leads to further changes to the fish community, including reductions in species richness, taxonomic distinctness and abundance (Graham et al.
Finally, Booth and Beretta (2002) observed significant declines in the recruitment of 3 species of damselfishes at One Tree Island immediately following the 1997-1998 bleaching event.
Together these studies indicate that coral bleaching in conjunction with other major agents of disturbance has already had a significant effect on the abundances and community structure of fishes on some reefs on the Great Barrier Reef. They also suggest that significant changes to fish communities will become more widespread if mass coral bleaching occurs more frequently in the future (Table 2). 2012), thus increased CO2 concentrations could be a serious threat to marine fishes in the later part of the century. However, smaller size classes of larger species also decline in some instances, suggesting that the contribution of these species to ecosystem function and fisheries could be undermined in the future (Graham et al.



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