Effect of Climate Change on Turtle Breeding

Many studies are now focused on how climate change is going to impact organisms with temperature-dependent sex determination (TSD). TSD is where during embryonic development ambient temperature determines the sex of the offspring, in most reptiles high temperatures induce a high female percentage. Climate change is an extreme threat for these organisms as global warming produces an extreme sex ratio that could possibly lead to extinction. Marine turtles are one of those such species, increases in temperature cause a skewed ratio of more females than males. Wright et al. (2012) examined the effect of climate change on marine turtles by testing to see if skewed offspring sex ratios persist into adulthood and whether variation in male mating success impacts the population’s genetic variance. They tested their hypothesis by doing genetic tests in conjunction with a tracker turtle to observe the migration route. The author’s found that despite a 95% female sex ratio there were at least 1.4 reproductive males per breeding female, suggesting that the interval between male reproducing periods is quite short. The scientists suggest this shows that male mating patterns have the potential to buffer the disruptive effects of climate change but that the growing temperatures still might increase sex ratios to the point that genetic diversity becomes so limited that populations could become endangered. –Connor O’Boyle

            Wright, L., Stokes, K., Fuller, W., Godley, B., McGowan, A., Snape, R., Tregenzal, T., Broderick, A., 2012. Turtle mating patterns buffer against disruptive effects of climate change. Proc. R. Soc. B., doi:10.1098/rspb.2011.2285.

Understanding how climate change might impact organisms with TSD is a crucial part in conservation of those organisms. Usually TSD is experienced during embryonic development; even small temperature changes can have a profound effect on offspring sex ratios. Because most organisms with TSD already have skewed offspring ratios, studying the mechanisms and implications of temperature-dependent sex determination was mostly academic. Ever since scientists recognized steady increases in global temperatures, studies on TSD and the impact of rising temperatures on these organisms has become more conservation based. Most species of marine turtles have TSD, with females being reproduced at a much higher rate at high temperatures. The 50% sex ratio temperature for green turtles is 29°C; however this species lives in areas above that temperature so a female-skewed ratio is common. This is true for green turtles, which are the species the authors looked at. Due to the lack of information regarding adult sex ratios in marine turtles and mating behavior in male turtles the authors set out to find out more and figure out what could possibly protect the turtles from climate change effects.
            Wright et al. conducted their study in a wild population of green turtles at Alagadi beach, northern Cyprus, during the breading season of 2008. They obtained tissue samples from twenty nesting females with known identity and twenty-three offspring from one or more clutches (A clutch is basically a dog litter but for turtles) per female. The dataset was made up of 809 offspring from 37 clutches. The sex of the offspring was estimated based on incubation time. The scientists genotyped the individuals whose tissue samples they obtained, then used these samples to determine population allele frequency to see if they deviated from Hardy-Weinberg equilibrium (HWE). Also using the genotyped samples, they ran a paternity analysis using parentage inference software. The authors placed a transmitter to a male turtle from the same study site and the male was tracked via satellite for 81 days.
            The authors found that the offspring tested were 95% female and a minimum of twenty-eight unique males sired offspring from twenty nesting females, showing that there was a higher sex ratio of breeders than expected at 1.4 males to each female. The runs identified twenty family clusters with a single mother and all her offspring with one or multiple fathers. The results also indicated that no male produced offspring using multiple mothers.  The loci the authors tested were within HWE and the probability of multiple paternities, assuming two fathers had skewed paternal contributions, was 0.876. The turtle with the transmitter travelled close to multiple nesting beaches in Cyprus and Turkey then traveled to North Africa. The route is consistent with a mate searching behavior as the breeding sites within 20 km of the route account for 58% of green turtle nesting areas in the Mediterranean.
            The findings that more males contributed to reproduction than females were surprising due to the female dominant hatchling ratio seen at the studied rookery. The author’s results suggest that males have more frequent breeding periods than females, resulting in sex ratios of adults on breeding grounds that are much less female dominant. This more frequent breeding period for males also helps explain why the skewed ratio for turtles is able to persist. The frequent breeding period for males however will not keep the turtles safe from a low population variance. Wright et al. propose an alternative explanation for the breeding behavior, males breeding at the study site might have originated from other locations that produce a more even offspring ratio, sometimes region courtship allows a male to migrate and have multiple breeding females along the migration path. This is supported by the results from the tracker. The turtle’s journey suggests the male stops to mate at multiple breed grounds. Wright et al. highlight the role of mating behavior in maintaining relatively equal operational sex ratios with their study. The breeding behavior in green turtles warrants more analysis as it might be a crucial part of the population variance. Understanding mating patterns might help researchers preserve genetic variance that might be a crucial part of marine turtle’s ability to cope with climate change.        

Models for the Impact of Climate Change on Marine Ecosystems

Using models to predict future changes in ecosystems has become a key tool in tracing the impacts of climate change. These models are more difficult to make in marine ecosystems because of the number of variables. Researchers in Australia are trying to create new models, which is perfect because of the marine biodiversity and amount of data available. Fulton (2011) examined the effect of climate change on three different areas, SE and NW Australian coastline, and the Great Barrier Reef (GBR).  She used a combination of models and model parameters to simulate the changing distribution of species within these areas, and was able to model the entire ecosystem as a whole. One of her main findings was that there were common winners and losers among the SE and NW Australian zones but different from the GBR. The results showed how there are no clean rules on how climate change will affect marine ecosystems. These models however can help humans manage resources better as climate change makes species more vulnerable. The data suggest that in Australia, the climate change scenarios seem to benefit primary producers and basic ocean ecosystem components, which could cause major ecological restructuring.  This result led Fulton to conclude that current fishery management will have to change. She suggests a dynamic strategy of using closed off areas to check the balance of currently fished areas. –Connor O’Boyle

Fulton, E., 2011. Interesting times: winners, losers, and system shifts under climate change around Australia. ICES Journal of Marine Science 68, 1329—1342.

      Fulton used a complex model, the end-to-end (or whole-of-system) model to simulate climate change/human pollution’s impact on marine ecosystems. She looked at the marine ecosystems around Australia, specifically the NW and SE Australian coastal areas and the GBR. These models attempt to integrate abiotic, biotic and anthropogenic factors which will allow further investigation of how climate change will impact Australian ecosystems. For the SE Australia model she used the Atlantis computer system. Atlantis was originally developed for the evaluation of SE Australian federal fisheries; the model however is useful for climate related questions due to its ability to integrate large amounts of variables.  Fitting these variables with the appropriate data would be challenging but in the case of Australia there are 20—90 years of catch history for most species plus other model specific data.
The NW Australian area was modeled using the InVitro model system. This was done by combining two models, the InVitro-NWS and the InVitro—Ningaloo, both developed for evaluating multiple management strategies in NW Australia. Just like Atlantis, the different factors changing the ecosystem, such as human pollutants, differing weather patterns, and even the effects of human tourism are represented by equations or cellular automata. The GBR region was modeled using the Ecoscape system. This model has 32 groups; pelagic and benthic primary producers (surface level to sea floor), as well many benthic invertebrates. The model includes 23 fish groups as well as groups of concern including sea turtles and certain migratory sea birds.  In order to compare the areas, Ecospace models were run for both the NW and SE Australian areas. For every model, the water column properties were simulated using an ocean forecast model developed by Commonwealth Scientific and Industrial Research Organization (CSIRO). This was also used to represent storms, and sea-level rise. NPZD models were used in conjunction with the CSIRO models in the Ecospace framework to more accurately model water mechanics. All models were run from 2010-2060, only changes in relative biomass of primary producers, detritus, plankton, pelagic fish, benthic invertebrates, demersal fish, and top predators were reported.
            The models indicated that there will be a 5—22% biomass increase in plankton in NW and SE Australia. A 20—105% increase in other pelagic invertebrates is indicated as well as 21—881% increase for fish biomass. Demersal fish will experience an 8—35% decline in the GBR. Top predators and benthic invertebrates responded differently in every model, there is turnover in the types of benthic invertebrates that dominate, moving to those that can cope with the changes in temperature, sources of production, detrital loads, and ocean acidification. Squid and sharks initially increased but decreased after 2040 due to poor environmental conditions. In comparing the different simulations, if factors affecting ecosystems are considered in isolation then results were within 10—15% of the values reached during regular simulations. If factors such as acidification are taken into account in conjunction with other variables the values run 40% lower, thus showing the dramatic effect of certain driving mechanisms, particularly increased in atmospheric CO­ independent of warming.

            Fulton suggests that the current models show that in the targeted Australian regions there was an increase in primary producers and pelagic ecosystems components. Each system will have its own set of winners and losers, but the ecosystem will remain in balance as new species fill the gaps. The NW and SE Australian regions increased in overall biomass and the GBR declined in overall biomass. She suggests that Australian fisheries need to switch to management practices that use a dynamic model. Using reference areas, the active fishing areas could be compared to fish free zones, judging the potential of new ecosystem structures. Fulton warns that these models must be taken as theoretical. The parameters of the models limit their range. So no matter how complex the models, they must always be partnered with quantitative experiments in the field. 

Artic Ecosystems Response to Climate Change

Sea ice conditions are an important factor in the health of many arctic mammals use the sea ice to breed and to carry out many social behaviors.  The harp seal is one of those species, using the sea ice as a substrate for pupping and nursing its young.  Johnston et al. (2012) examined the impact of decreased sea ice on harp seal mortality. The scientists used Northern Atlantic Oscillation (NAO) data to represent climate change; NAO is the dominant pattern in climate variability in the North Atlantic. The breeding regions that Johnston et al. used were located in the Northeastern US, the Gulf of St. Lawrence, and the White Sea near Norway.  Using the NAO data, sea ice measurements, and recorded mortality rates of deal harp seal pups, the authors established a relationship between decreased sea ice ice/poor NAO conditions and increased mortality in young harp seals. They also established a link between NAO conditions and sea ice cover. Johnston et al. suggest that the harp seal is stable at the moment, but could be harmed by the cumulative effect of human influences and rapid climate change. –Connor O’Boyle
            Johnston, D., Bowers, M., Friedlaender, A., Lavigne, D., 2012. The effects of climate change on harp seals (Pagophilus groenlandicus). PLoS One 7, e29158.

Johnston et al.studied the effect of climate change on harp seals in three ways.  They examined the differing sea ice levels in the Gulf of St. Lawrence with neonatal mortality rates in harp seals in the Northeastern US. The authors linked NAO conditions to differing sea-ice levels and did a retrospective cross-correlation analysis of NAO conditions and sea ice in two breeding regions of harp seals. Lastly they showed the relationship between NAO conditions and sea ice by doing linear multiple regression models that accounted for short-term variation in ice driven by the NAO.  In order to link reductions in sea ice cover and seal mortality the scientists used mortality data for dead harp seals and compared that with sea ice cover data from the Gulf of St. Lawrence during the same time period. For the retrospective analysis of NAO conditions and sea ice the authors looked at two breeding regions of harp seals, the Gulf of St. Lawrence and White Sea region. The authors compared these two areas within a retrospective assessment of published harp seal neonatal mortality data. They conducted a wider investigation using two addition breeding regions from Newfoundland and the Greenland Sea. This second investigation was used to assess longer-term trends in sea ice cover across the entire North Atlantic.  Johnston et al. used sea ice data obtained from the National Sea Ice Data Centre and NAO data from the National Center for Atmospheric Research.
            The results showed that sea ice and seal mortality were significantly correlated.  Lighter ice conditions were linked with increased numbers of stranded dead seals. The regression model between NAO data and seal mortality showed a similar relationship. Breeding regions in the White Sea and the Gulf of St. Lawrence showed significant differences in sea ice cover and NAO data. In the White Sea heavier ice coverage was seen during negative NAO periods and lighter ice coverage was seen during positive NAO periods. The western North Atlantic ice conditions were opposite with heavier ice coverage during positive NAO periods and lighter ice coverage during negative NAO periods. The results from their mixed effects models revealed a statistically significant annual decline of sea ice cover in all four breeding regions, regardless of variation in NAO conditions.
            The negative relationship between sea ice coverage and seal mortality rates shows how climate change is having an impact on seal populations. The scientist’s regression revealed that an increase in first year mortality occurred in years with lighter sea ice coverage and lower NAO index values. This also shows how the NAO determines sea ice dynamics in harp seal breeding regions. The retrospective analysis of NAO conditions revealed that the NAO was consistently negative in light ice conditions in the Northwest Atlantic, and in years with less ice coverage the harp seal populations decreased significantly. The Northeast Atlantic breeding regions are out of phase with the NAO and the NAO was positive in times of decreased sea ice, years with decreased seal populations correlated to positive NAO indices and lower sea ice levels. The fluctuations of harp seal populations over time corresponds to increases and decreases in sea ice as well as the NAO indices, showing how climate change directly impacts sea ice levels, which then disrupt harp seal reproduction. The authors found that the ice cover in the breeding habitats for harp seals has been declining since 1979, and along with this the harp seal’s yearly mortality rate has gone up since 1979. Johnston et al. conclude their paper by stating that harp seals could be a vulnerable species in the future. The authors state that the harp seals are well suited to deal with natural shifts in climate however the cumulative effects of human influences such as hunting and global warming could put them at a higher risk. Other artic seal species could be at risk as well sharing many of the characteristics and breeding regions of the harp seal.       

Antarctic marine ecosystems response to Climate change

The western peninsula of Antarctica is home to one of the most diverse and abundant aquatic ecosystems. This area is also one of the most susceptible to climate change with 5-6 °C increases in mean winter air temperature and subsequent decreases in sea-ice. Trivelpiece et al. (2011) looked at two penguin species, Adélie and chinstrap penguins, and their unusually linked trends in population trajectory. The authors studied these two penguin species on the Western Antarctic Peninsula (WAP) in order to link decreasing biomasses in Antarctica Krill to the declining penguin populations. An interesting aspect of the decline of these two species is that Adélie penguins favor pack-ice in the winter and the chinstrap penguins favor ice-free water during winter, but both species are experiencing population declines. The scientists found that the decline of both can be explained by decreasing krill biomass owing to climate change and increased krill predation from humans and whales. Trivelpiece et al. suggest that the Krill harvesting be monitored more closely and that the chinstrap penguin be monitored by the International Union for the Conservation of Nature as a vulnerable species. –Connor O’Boyle
            Trivelpiece. W., Hinke, J., Miller, A., Reiss, C., Trivelpiece, S., Watters, G.,2011. Variability in krill biomass links harvesting and climate change to penguin population changes in Antarctica. Proceeding of the National Academy of Science of the United States of America 108, 7625—7628.

            The sea-ice in Antarctica plays a crucial role in the marine ecosystem, regulating diet and creating habitat for many organisms. As sea-ice has been declining the populations of Adélie and chinstrap penguins have declined more than 50%. The authors analyzed the previous thirty years of studies and found that before 1987 the size of these populations, due to their different preference in winter feeding, were negatively correlated. However, since 1987, both species have declined together. These contrasting patterns can be explained by recruitment trends. In the earlier period with the negative correlation, the winters with increased sea-ice had increased numbers of juvenile Adélie penguins returning to breed. Whereas winters with decreased ice had increased numbers of juvenile chinstrap penguins returning.  In the most current period, both species have experienced large declines in juvenile survival and there is no longer a large flux between populations. The authors note similar population declines throughout the Scotia Sea so their WAP data are not anomalies.
            Antarctic krill are the dominant prey of an almost every top predator in the Antarctic marine environment. It has been estimated that 150 million tons of krill were available to support top predators such as penguins. The penguin populations of many species increased dramatically during the years in which human hunting dramatically decreased whale populations around the world. The authors found, by analyzing the Adélie penguin diet using fossil eggshell material in extinct colonies, that an abrupt shift happened in the last 200 years from a mainly fish diet to a mainly krill diet. This could be a good thing for the Adélie penguins but the scientists say it is not certain whether these penguins could switch back to their previous diet. Currently both the Adélie and chinstrap penguins are heavily dependent on krill; even though the krill biomass has significantly been reduced both species rely almost solely on it. The reproductive success of krill has been linked to sea-ice extent, and the decrease in ice accumulation related to global warming correlated with a large decline in krill in Antarctica. In addition krill fishery has increased from 50,804 tons in 2002—2003 to 202,346 tons in 2009—2010. Because to new products are being made from krill, including Omega-3 pills, the krill fishery is poised to expand, further stressing penguin populations.
            The authors conclude with a warning that with increased fishing and warmer Antarctic winters, krill populations will continue to decline and with them the Adélie and chinstrap penguin populations. Trivelpiece et al. suggest thatchinstrap penguins could be the more vulnerable of the two due to their restricted range and historic dependency on krill.  

Coral Range expansions due to Climate Change

Coral are some of the most important aquatic organisms on planet earth. Not only are coral species primary producers but they create habitats and are the basis of some of the largest aquatic ecosystems. Yamano et al. (2011) studied coral species off the coast of Japan and found large-scale evidence of the poleward range expansion of modern corals. Using data collected from the temperate waters around Japan, they found northern range shifts and no southern expansion on ranges. Their findings suggest that tropical coral and their associated organisms will undergo rapid fundamental modifications with continued sea temperature increases. They warn that these modifications could damage native temperate coral species because of higher growth rates that tropical coral species exhibit.  In addition to out-competing temperate corals tropical coral species could provoke the migration of tropical organisms that live around or on the tropical coral species. –Connor O’Boyle
Yamano, H., Sugihara, K., Nomura, K., 2011. Rapid poleward range expansion of tropical reef corals in response to rising sea surface temperatures. Geophysical Research Letters 38, L04601.

Long-term, large-scale observations were required for finding the effects of climate change on coral distribution ranges.  Yamano et al. accomplished this by choosing the coastal areas around Japan where there are sub-tropical and temperate coral species with 80 years of national records. The records have detailed measurements of coral species and ranges including the regions sea-surface temperatures. The authors selected coral species from eight temperate region’s of Japan along a latitudinal gradient,  distinguishing four distinct periods of coral exploration that were to be used for the study. The first period was in the 1930s, the second was in the 1960/70s, the third was 1980/90s, and the fourth period was in the 1990s to the present. Yamano et al. conducted surveys in the latest period, observing coral occurrence and identifying coral taxa. The eight study regions were located in areas that showed significant sea-surface temperature rises in winter and were in marine protected areas, to lessen anthropogenic impacts. The coral species that were compared were selected on three criteria: species had to occur in the area of interest, be distributed at depths of ten meters, and had to have distinct growth forms that could be identified without collecting them, because a lot of the old data were qualitative. Nine species were selected for data collection and their expansion rate was calculated by occurrence records based on the four periods. The authors used the year that new colonies of coral were found to keep calculations consistent.
            The results showed that four of the nine species exhibited poleward expansion since the first time period. The other five species remained stable during the four time periods. Out of the species that exhibited northward range expansion, the authors singled out two tropical Indo-Pacific reef species, Acropora hyacinthus and Acropora muricata, to indicate the expansion of tropical species into temperate regions. All of the expanded species are labeled either “Near threatened” or “Vulnerable” by the International Union for Conservation of Nature (IUCN), showing the need for these species to migrate to more tolerant temperatures. The coral species that showed expansion also exhibited successful spawning, indicating that these species have the potential to repopulate. Temperate areas may serve as refuges for many tropical corals in a time when tropical oceans and seas are becoming dangerously warm. However these expansions could have large effects on temperate ecosystems, due to a heightened growth rate exhibited by tropical corals. Tropical coral species could fit into niches that were previously inhabited by a temperate coral species and out-compete them, disrupting an entire ecosystem. The tropical organisms that thrive on particular species of coral could start migrating northward and compete with local temperate organisms. An example of such a problem would be northern migration of certain toxic microalgae that live around tropical coral. The authors suggest that more interest should be paid to this aspect of our ocean’s corals and that the migration of tropical corals is a mostly unexplored domain in climate change models. 

Coral Reef Ecosystem’s Response to Climate Change and Over-Fishing

The coral reefs in our ocean have some of the largest and most dynamic ecosystems on the planet. Predicting how these ecosystems respond to climate change and over-fishing could let scientists inform and influence policy makers to make the right decisions regarding our oceans. Graham et al. (2011) examined coral reef fish and developed a model to predict their extinction vulnerability due to climate change. They used both climate change variables and variables that integrated over-fishing in their model. The authors found that while most reef fish are not at extreme risk of extinction from climate change, when pressures from climate change and over-fishing are both applied to the coral ecosystem, the entire fish community is extremely vulnerable. These fish are a key part of the thriving coral ecosystems and transport nutrients through it. A promising discovery of this paper was that over-fishing seems to have a larger impact on these species than does climate change, making commitment to fishery programs a foreseeable solution.—Connor O’Boyle

Graham, N.,Chabanet, P., Evans, R., Jenning, S., Letourneur, Y., MacNeil, M., McClanahan, T., Ohman, M., Polunin, N., Wilson, S., 2011. Extinction vulnerability of coral reef fishes. Ecology Letters 14, 341—348.

Graham et al. developed a two variable approach to coral reef fish extinction vulnerability. This system set climate vulnerability against extinction risk, with each fish species being evaluated for four climate change variables. These four variables were diet specialization, habitat specialization, recruitment specialization for live coral, and body size. Diet specialization evaluates a species dependency on a coral diet. Habitat specialization influences the amount of population decline when there is a coral loss. Recruitment specialization expresses a species’ dependency on coral during settlement and early life. The inclusion of body size as one of the variables represents a trend that small-bodied fish are often closely associated with the reef structure/matrix and therefore are more prone to predation if there is coral loss. The four variables were quantified for 134 species of coral reef fish, including juvenile and adult stages, by expert knowledge/FishBase.

The extinction risk index was based on four indicators of extinction risk, geographical range size, occupancy, numerical rarity, and depth range. The species’ geographical ranges were calculated using polygons over coastal waters/reefs where the species were present. Occupancy measured the number of fish occupying a single area based on 66 surveys of coral reef locations across the Indian Ocean. Numerical rarity was calculated from fish density data from a 1990s dataset for geographical locations. Depth ranges represent the higher risk of shallow coral habitats to climate change and over fishing. The authors obtained data for depth ranges by using FishBase and current literature. The four risk variables were combined with the four climate variables and weighted by a panel of experts; the authors called this the “expert ranked weighting scheme” or Analytic Hierarchy process (AHP). The AHP weighted the variables against each other, making a matrix, and applied to the scaled data for each variable. These weights were then used to calculate the final indices for every species.

The four main groups of coral reef fish the authors were studying were surgeonfishes, parrotfishes, butterflyfishes, and wrasses. All four groups had sufficient data and varied significantly in the assessed variables. The authors assessed how well their model worked by using it with the data collected from the inner Seychelles islands (a mass coral bleaching event). They calculated the percent change in abundance for the species present between 1994 and 2005, the coral bleaching event happened in 2008. The model fit was assessed using Baynesian goodness-of-fit, where deviations showed either good or bad model fitness. In addition to testing the model the scientists assessed the combined effects of climate change and over-fishing using a fuzzy logic expert system (which is a collection of functions and rules that are used to reason about data).

Graham et al. found that obligate corallivores (butterflyfish and other fish that need live coral polyps to feed) were the most impacted by the climate changes followed by facultative corallivores (more lenient in terms of diet than obligate corallivores) and micro-invertivores (fish that eat the invertebrates living in the coral). Fifty-six out of the 134 species investigated showed a high vulnerability to climate change. When used for the coral bleaching event in the Seychelles islands, the model produced a negative relationship that had a well-fit correlation. The authors found a negative and convex relationship in species vulnerabilities to both over-fishing and climate change. This means that species are either highly susceptible to over-fishing or climate change, rarely both.

Overall the authors found that certain functional groups of reef fish were more vulnerable to climate change. However, no single functional group was more prone to global extinction. Obligate corallivores were the most vulnerable, however most obligate corallivores have broad dispersal so if local extinctions take place the overall species will most likely survive by spreading into new habitats. This suggests that adjacent reefs may support recovery from climate change alterations. The fish that were least vulnerable to climate change, the roving grazers and scraper/excavators, were the most vulnerable to over-fishing. The species most vulnerable in the authors’ model was the tubelip wrasse, L.unilineatus. The recovery of these species will depend on their specific habitat regeneration and connectivity to unaffected populations. Thirty seven percent of the 56 highly vulnerable species had multiple attributes that made them susceptible, showing that species face multiple facets of climate change threats. Every fish species was sensitive either to over-fishing or to climate change. This means that in a world where both over-fishing and climate change are in progress, current communities of fish could be under severe risk. Because we have more control over fishing than climate change the authors propose stricter limitations on coral reef fishing in the short term and continued pressure to alter our global climate impact in the long term.

Western Australian fish populations Response to Climate Change

Population distribution changes for Australian fish could provide scientists with a useful tool in predicting the effects of climate change.  Bond et al. (2011) examined 43 species of Australian freshwater fish and quantified their results into species distribution models (SDMs).  The SDMs provided a useful approach for examining predicted range shifts and provided a clear way of describing the types of environment in which these species of fish will be encountered. When SDMs were combined with future climate scenarios the models predicted future population and range shifts that in some cases described total population loss. In conclusion the author’s remark on their ability to predict current and future distributions using statistical models but that the models are just a step and future efforts in mechanistic modeling and in climate scenarios will be needed to further understand the effects of climate change on fish species.
Bond, N., Thomson, J., Reich, P., Stein, J., 2011. Using species distribution models to infer potential climate change-induced range shifts of freshwater fish in south-eastern Australia. Marine and Freshwater Research 62, 1043—1061.    

            Bond et al. used fish distribution data from survey records drawn from the Victorian Department of Sustainability and Environment’s Aquatic Fauna Database (AFD). In gathering these data they excluded sites below large impoundments because of markedly atypical behavior created by those sites.  They gathered their environmental data from a digital elevation model (DEM), which characterized stream networks all across Victoria. To enhance model sensitivity they restricted the environment data to areas that fish had been officially surveyed and recorded. For the data characterizing river flows, they used gauge data from 120 unregulated sites around Victoria that had significant records to quantify water flow patterns. Although high flow events couldn’t be modeled, they predicted that this would be offset in their model by the large effect that low flow events have on fish distribution. Their climate scenarios came from changes in temperature, precipitation, and evapotranspiration (the water put back into the atmosphere by plant respiration and evaporation). These scenarios corresponded to low, median, and high estimates for 2030, and were run in tandem with hydrologic model data. The statistic modeling was based on a system of boosted regression trees, a form of model averaging; model fit was based on residual error (R2).
            Their results showed only five of their water flow models (hydrologic models) could be confidently predicted, with high water flow characteristics showing very poor residual error (R2<0.4). The SDMs for the current fish populations were extremely accurate, with only two species with inaccurate predictions. They ran the climate scenario prediction for domestic and exotic fish species and found the results differed, but overall the species showed strong and consistent range patterning.
Their overall goal of making SDM’s to describe historical distributions of the 43 specifies of fish was accomplished successfully. The climate scenarios that were found could provide a useful approach to examine future range shifts. BRTs (Boosted Regression Trees) successfully carried out the model’s predictions and their capacity to fit non-linear response functions helped describe species response to environmental changes. Bond et al.analysis suggests that the non-linear associations of water flow/climate variables is common, thus why the BRTs are such an extremely useful modeling tool.
SDMs showed the combined impacts of altered temperature and water flow patterns rising from climate change in south-eastern Australia caused distribution and population changes in freshwater fish.   One of the main findings was that the fish shifted up along an elevation gradient, and also south in direction in response to the climate change scenarios. Although the results are just models the authors suggested they represent an important step in finding the long-term understanding of finding climate change impacts and their response strategies.   

Marine Ecosystem’s Response to Climate Change

The impact of climate change on marine ecosystems is still poorly understood. The distribution of marine populations in response to climate change could be a key clue to the future of marine ecosystems in our changing world. Sorte et al. (2011) studied the population-level variation of temperature tolerance in several populations of marine invertebrates. There were three separate case studies, all designed to better understand the lethality of rising water temperature. The authors identified the western Atlantic as a target zone for populations right at the edge of their temperature tolerance. They found both mussel and subtidal epibenthic (organisms living on the sea bed) species showed the highest susceptibility to temperature change. By compiling experimental data with current thermotolerance data and climate predictions the authors concluded that most populations of the intertidal Littorina snail were able to overcome geographic differences in temperature tolerance via acclamation. The authors concluded that particular species’ life history strategy and dispersal ability may determine their temperature adaptation abilities more than their overall geographical location.—Connor O’Boyle

Sorte, C., Jones, S., Miller, L., 2011. Geographic variation in temperature tolerance as an indicator of potential population responses to climate change. Journal of Experimental Marine Biology and Ecology 400, 209-217.

The relationship between ocean temperature changes and marine ecosystems is an important and relevant issue in the current changing climate. Sorte et al. studied multiple marine species and their physical and biological patterns to address how tolerances vary geographically and whether certain species have better ability to acclimate. They hoped to provide a starting point on which broader questions on the future of marine ecosystems could be based.

In their study they did three main experiments, the first was a trans-continental comparison using species that were geographically isolated, to test the impact of geographic location on a species survival. They collected four epibenthic species that grow on both the East and West coast of the United States and looked at their responses to their geographical independent temperature fluctuations. In their second experiment the authors compared mussel populations from France and the USA, in their abilities to cope with lab controlled marine temperature changes. The third experiment tested the long-term temperature acclimatization of Littorine snails from the same region of the western Atlantic.

The results of these experiments showed that the East Coast populations of epibenthic species were living closer to their tolerance levels than the West Coast ones, and that the higher temperature fluctuations on the East Coast of the United States create a greater risk for these species going forward. The authors concluded that if acclimatization is similar within species, individuals on the East Coast could experience dramatic population declines because of the current proximity of water temperatures to lethal levels. The authors found the mussels from France had a higher temperature tolerance than the US population, but both decreased in tolerance after multiple temperature exposures. These findings led the authors to believe that finding temperature history of a population’s habitat is essential in predicting the survivability of that population. The findings of the last experiment showed that temperature tolerance increased with lab acclamation but the response in geographic temperature tolerance differed between the species of snail. They concluded that in populations with low tolerance, survivability would depend on dispersal distance and the specific environmental behaviors (such as using tall eel grass to buffer temperature change).

The authors concluded that additional studies need to be made to analyze coping behaviors for species experiencing wide temperature changes in order to accurately predict population change. They found that in tunicates and bryozoans the temperature tolerance was related to habitat temperatures. The differences in tidal habitat zone could play a large part in a species’ ability to adapt and the authors established that populations with limited dispersal distances could be negatively impacted because of their inability to find suitable water conditions to recolonize. The organisms living in the western Atlantic could experience more drastic population change due to the heightened water temperature levels with species living in water very close to their lethal temperature.