Sydney Institute of Marine Science

Mosman, Australia

Sydney Institute of Marine Science

Mosman, Australia
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Dafforn K.A.,University of New South Wales | Dafforn K.A.,Sydney Institute of Marine Science
Management of Biological Invasions | Year: 2017

Habitat modification and the introduction and establishment of non-indigenous species (NIS) are two of the greatest threats to global biodiversity. Human modifications of marine habitats include the introduction of boating infrastructure, coastal defences and offshore energy installations that are occurring at an increasing rate. These artificial structures are now widely recognised as providing opportunities for the establishment and dispersal of non-indigenous fouling species in new regions. This is driving increased interest into how structures might be designed and built to limit their suitability for invasive species. At the same time the potential for artificial habitats to provide habitat to native and threatened species means that the control of NIS on these structures should not just rely on antifouling. Green or eco-engineering aims to incorporate ecological theory and principles into the design of engineered structures. When combined with other management strategies that aim to increase the resistance of recipient environments there is the potential to enhance practical barriers against invaders in an increasingly developed ocean. Here I explore examples of NIS facilitation by artificial structures and the ecological theories that could be used to reduce opportunities for NIS establishment and spread. Examples include (1) manipulating the physical and chemical properties of structures to enhance native recruitment over NIS, (2) enhancing resource use of structures by native species through “pre-seeding”, (3) providing opportunities for native grazers and predators to easily access structures, and (4) considering the timing of construction/maintenance/decommissioning for artificial structures such that resources are not made available when propagule pressure is also high. These examples are not exhaustive, but rather provide a discussion point for managers of biological invasions to generate further research and application over larger spatial scales. © 2017 The Author(s). Journal compilation & REABIC.


News Article | November 15, 2016
Site: www.csmonitor.com

While increasing at some sites, kelp, a useful indicator of an ecosystem's health, is undergoing a worldwide decline. A school of sardines swims through a kelp forest at the Channel Islands National Marine Sanctuary off California's coast. Since the area was declared a marine sanctuary five years ago, scientists have observed more lobsters, fewer urchins, and healthier kelp forests. Kelp, with its incredible ability to overcome biological stressors and grow back quickly, is an important indicator of how healthy the ocean is. As such, two studies published recently in the Proceedings of the National Academy of Sciences, attempted first to quantify the health of kelp forests around the globe, and then to determine what can cause this resilient species to enter a large-scale decline and how that impacts the ecosystem as a whole. “When kelps show dramatic changes, increases or decreases, that indicates that there has been a real change in the ecosystem,” Jarrett Byrnes, co-author of the first study and an assistant professor of biology at University of Massachusetts, Boston, tells The Christian Science Monitor. “Kelps are very resilient, they respond very quickly after environmental predation. Anything that can drive a long-term change in a kelp population has got to be pretty big.” Kira Krumhansl, a postdoctoral fellow at Simon Fraser University in British Colombia who led the first study, looked at the whether kelp populations were more impacted by local stressors, such as poor water quality and overfishing, or global stressors, such as ocean temperature warming cause by human activity. By analyzing kelp abundance at more than 1,000 sites across the globe, Dr. Krumhansl and her team determined that 38 percent of the world’s kelp forests have declined over the past 50 years, while 25 percent have increased. The lack of a global trend in the health of kelp forests suggests that it is the regional differences that drive the success of failure of a kelp population more than the global factors. “Climate change is impacting kelp forests, but what really drives variation across regions is what is occurring at a local scale,” Krumhansl tells the Monitor. “Kelps’ ability to persist through sources of stress is attributed to their capacity to grow quickly and recover quickly, but this also indicates that where we do see decline in kelp we are really tipping the level of stress over a critical threshold beyond which these species can recover.” Picking up on that line of reasoning, the second study looked into a kelp population in Australia that may have tipped over that threshold because of an invasion of tropical herbivorous fish into the New South Wales Sea that have been eating the kelp. Using video footage from 12 kelp forest sites between 2002 and 2011, the research team from University of New South Wales in Australia (UNSW) observed that while only 10 percent of kelp showed bite marks from fish in 2002, six years later 70 percent of kelp had been chewed. The dramatic kelp deforestation coincided with an 0.6 degree Celsius temperature rise in the New South Wales Sea, which ushered in a 20 percent increase in various species of tropical fish in the ecosystem – in a phenomenon called tropicalization. “We call it a homogenization of community,” Adriana Vergés, a researcher in the School of Biological, Earth and Environmental Sciences at UNSW, told The Guardian. “It’s a bit like globalization – everything starts to become the same everywhere.” By eating the kelp, these non-native tropical fish disrupt the ecosystem. Peter Steinberg, the director of the Sydney Institute of Marine Science who contributed to the UNSW study, told The Guardian the damage that the fish – and by association the temperature change – caused to this kelp forest ecosystem was concerning because it showed that tropicalization could be triggered by a smaller increase in ocean temperature than expected. While kelp have proven they can survive in warmer waters, although they thrive at cooler temperatures, those warmer waters bring with them other environmental changes that can prove to be too much for the kelp. Therefore the temperature range that will initiate a massive kelp decline increase, which is bad new for the species and processes that in turn depend on kelp. “Kelp forests are important ecosystems because they support diverse communities of organisms in coastal zones, including many fishery species, and they provide a mechanism of carbon storage in coastal zones, they shelter shorelines from incoming wave actions,” Krumhansl told the Monitor. “They prove a number of benefits to humans, they are really critical for our livelihood and survival.”


News Article | November 15, 2016
Site: www.csmonitor.com

While increasing at some sites, kelp, a useful indicator of an ecosystem's health, is undergoing a worldwide decline. A school of sardines swims through a kelp forest at the Channel Islands National Marine Sanctuary off California's coast. Since the area was declared a marine sanctuary five years ago, scientists have observed more lobsters, fewer urchins, and healthier kelp forests. Kelp, with its incredible ability to overcome biological stressors and grow back quickly, is an important indicator of how healthy the ocean is. As such, two studies published recently in the Proceedings of the National Academy of Sciences, attempted first to quantify the health of kelp forests around the globe, and then to determine what can cause this resilient species to enter a large-scale decline and how that impacts the ecosystem as a whole. “When kelps show dramatic changes, increases or decreases, that indicates that there has been a real change in the ecosystem,” Jarrett Byrnes, co-author of the first study and an assistant professor of biology at University of Massachusetts, Boston, tells The Christian Science Monitor. “Kelps are very resilient, they respond very quickly after environmental predation. Anything that can drive a long-term change in a kelp population has got to be pretty big.” Kira Krumhansl, a postdoctoral fellow at Simon Fraser University in British Colombia who led the first study, looked at the whether kelp populations were more impacted by local stressors, such as poor water quality and overfishing, or global stressors, such as ocean temperature warming cause by human activity. By analyzing kelp abundance at more than 1,000 sites across the globe, Dr. Krumhansl and her team determined that 38 percent of the world’s kelp forests have declined over the past 50 years, while 25 percent have increased. The lack of a global trend in the health of kelp forests suggests that it is the regional differences that drive the success of failure of a kelp population more than the global factors. “Climate change is impacting kelp forests, but what really drives variation across regions is what is occurring at a local scale,” Krumhansl tells the Monitor. “Kelps’ ability to persist through sources of stress is attributed to their capacity to grow quickly and recover quickly, but this also indicates that where we do see decline in kelp we are really tipping the level of stress over a critical threshold beyond which these species can recover.” Picking up on that line of reasoning, the second study looked into a kelp population in Australia that may have tipped over that threshold because of an invasion of tropical herbivorous fish into the New South Wales Sea that have been eating the kelp. Using video footage from 12 kelp forest sites between 2002 and 2011, the research team from University of New South Wales in Australia (UNSW) observed that while only 10 percent of kelp showed bite marks from fish in 2002, six years later 70 percent of kelp had been chewed. The dramatic kelp deforestation coincided with an 0.6 degree Celsius temperature rise in the New South Wales Sea, which ushered in a 20 percent increase in various species of tropical fish in the ecosystem – in a phenomenon called tropicalization. “We call it a homogenization of community,” Adriana Vergés, a researcher in the School of Biological, Earth and Environmental Sciences at UNSW, told The Guardian. “It’s a bit like globalization – everything starts to become the same everywhere.” By eating the kelp, these non-native tropical fish disrupt the ecosystem. Peter Steinberg, the director of the Sydney Institute of Marine Science who contributed to the UNSW study, told The Guardian the damage that the fish – and by association the temperature change – caused to this kelp forest ecosystem was concerning because it showed that tropicalization could be triggered by a smaller increase in ocean temperature than expected. While kelp have proven they can survive in warmer waters, although they thrive at cooler temperatures, those warmer waters bring with them other environmental changes that can prove to be too much for the kelp. Therefore the temperature range that will initiate a massive kelp decline increase, which is bad new for the species and processes that in turn depend on kelp. “Kelp forests are important ecosystems because they support diverse communities of organisms in coastal zones, including many fishery species, and they provide a mechanism of carbon storage in coastal zones, they shelter shorelines from incoming wave actions,” Krumhansl told the Monitor. “They prove a number of benefits to humans, they are really critical for our livelihood and survival.”


News Article | November 10, 2016
Site: www.sciencedaily.com

An analysis of the health of highly impacted coral reefs off Singapore during a 27-year long period has shown they are more resilient to the impacts of human activity and warming than expected. A UNSW-led international team found that shallower reefs rebounded rapidly from a major bleaching episode in 1998, despite experiencing such high levels of sedimentation that underwater visibility was typically less than 2 metres. "It is remarkable that diverse shallow coral communities can persist in such adverse conditions," says study first author Dr James Guest, formerly of UNSW and now at the Hawai'i Institute of Marine Biology. "Undoubtedly, Singapore's reefs have suffered as a result of human activities, but the recovery of corals at shallow sites is really surprising given how impacted this environment is. It really shows how tough corals can be." Study senior author UNSW Professor Peter Steinberg adds: "This is by no means a cause for complacency regarding the state of our reefs, but rather highlights that if we can reduce local stressors, reefs are more likely to be able to rebound from the effects of global stressors such as climate change." The study by the team, which includes researchers from UNSW and the Sydney Institute of Marine Science, the National University of Singapore, Nanyang Technological University, and Singapore's National Parks Board, is published in the journal Scientific Reports. In the past 200 years, Singapore has been transformed from a forest-covered island with about 150 people to a highly urbanised city-state of more than 5.4 million. Extensive coastal construction, dredge spillage and land reclamation have resulted in high sedimentation rates, turbidity and pollution, putting immense pressure on the surrounding coral reefs. Between 1986 and 2012, coral communities at 15 sites south of the main island were regularly surveyed, and the results have been analysed for the new study. Coral cover during this 27-year period declined at all sites -- by about 12 per cent at the shallower depths of 3-4 metres and by about 30 per cent at the deeper depths of 6-7 metres. There was a particularly large decline in the first decade due in part, the authors suggest, to unmitigated dumping of dredge spoils in the late 1980s. In 1998, a major bleaching event occurred as the result of high water temperatures associated with an El Nino. However, corals at shallower reef sites were remarkably resilient to this event, showing signs of recovery within a decade. By 2008 coral cover had increased to about 1993 levels. Corals at deeper sites were less resilient, with coral cover at these sites continuing to decline. However, none of the sites were overtaken by large fleshy seaweeds, as has been seen on impacted reefs elsewhere in the world. The lack of recovery at deeper sites may be due to low light levels or a lack of unsuitable substratum for new corals to settle and survive. The researchers suspect the resilience at shallow sites is due to an abundance of coral species which have fast regrowth rates and can tolerate environmental stresses such as high levels of suspended sediments. It is also possible the turbidity of the water could offer some protection by reducing the light and the impact of heat stress, as well as slowing down the growth of fleshy seaweeds. Reefs in Singapore appear to have undergone substantial bleaching again this year, which is likely to test whether the resilience to bleaching observed in previous decades is still present on these reefs.


News Article | November 8, 2016
Site: www.eurekalert.org

An analysis of the health of highly impacted coral reefs off Singapore during a 27-year long period has shown they are more resilient to the impacts of human activity and warming than expected. A UNSW-led international team found that shallower reefs rebounded rapidly from a major bleaching episode in 1998, despite experiencing such high levels of sedimentation that underwater visibility was typically less than 2 metres. "It is remarkable that diverse shallow coral communities can persist in such adverse conditions," says study first author Dr James Guest, formerly of UNSW and now at the Hawai'i Institute of Marine Biology. "Undoubtedly, Singapore's reefs have suffered as a result of human activities, but the recovery of corals at shallow sites is really surprising given how impacted this environment is. It really shows how tough corals can be." Study senior author UNSW Professor Peter Steinberg adds: "This is by no means a cause for complacency regarding the state of our reefs, but rather highlights that if we can reduce local stressors, reefs are more likely to be able to rebound from the effects of global stressors such as climate change." The study by the team, which includes researchers from UNSW and the Sydney Institute of Marine Science, the National University of Singapore, Nanyang Technological University, and Singapore's National Parks Board, is published in the journal Scientific Reports. In the past 200 years, Singapore has been transformed from a forest-covered island with about 150 people to a highly urbanised city-state of more than 5.4 million. Extensive coastal construction, dredge spillage and land reclamation have resulted in high sedimentation rates, turbidity and pollution, putting immense pressure on the surrounding coral reefs. Between 1986 and 2012, coral communities at 15 sites south of the main island were regularly surveyed, and the results have been analysed for the new study. Coral cover during this 27-year period declined at all sites - by about 12 per cent at the shallower depths of 3-4 metres and by about 30 per cent at the deeper depths of 6-7 metres. There was a particularly large decline in the first decade due in part, the authors suggest, to unmitigated dumping of dredge spoils in the late 1980s. In 1998, a major bleaching event occurred as the result of high water temperatures associated with an El Nino. However, corals at shallower reef sites were remarkably resilient to this event, showing signs of recovery within a decade. By 2008 coral cover had increased to about 1993 levels. Corals at deeper sites were less resilient, with coral cover at these sites continuing to decline. However, none of the sites were overtaken by large fleshy seaweeds, as has been seen on impacted reefs elsewhere in the world. The lack of recovery at deeper sites may be due to low light levels or a lack of unsuitable substratum for new corals to settle and survive. The researchers suspect the resilience at shallow sites is due to an abundance of coral species which have fast regrowth rates and can tolerate environmental stresses such as high levels of suspended sediments. It is also possible the turbidity of the water could offer some protection by reducing the light and the impact of heat stress, as well as slowing down the growth of fleshy seaweeds. Reefs in Singapore appear to have undergone substantial bleaching again this year, which is likely to test whether the resilience to bleaching observed in previous decades is still present on these reefs.


News Article | November 16, 2016
Site: www.sciencedaily.com

Seaweed-eating fish are becoming increasingly voracious as the ocean warms due to climate change and are responsible for the recent destruction of kelp forests off the NSW north coast near Coffs Harbour, research shows. The study includes an analysis of underwater video covering a 10 year period between 2002 and 2012 during which the water warmed by 0.6 degrees. "Kelp forests provide vital habitat for hundreds of marine species, including fish, lobster and abalone" says study first author Dr Adriana Vergés of UNSW and the Sydney Institute of Marine Science. "As a result of climate change, warm-water fish species are shifting their range and invading temperate areas. Our results show that over-grazing by these fish can have a profound impact, leading to kelp deforestation and barren reefs. "This is the first study demonstrating that the effects of warming in kelp forests are two-fold: higher temperatures not only have a direct impact on seaweeds, they also have an indirect impact by increasing the appetite of fish consumers, which can devour these seaweeds to the point of completely denuding the ocean floor. "Increases in the number of plant-eating fish because of warming poses a significant threat to kelp-dependent ecosystems both in Australia and around the globe," she says. The study is published in the journal Proceedings of the National Academy of Sciences. The team recorded underwater video around August-time each year at 12 sites along a 25 kilometre stretch of coast adjacent to the Solitary Island Marine Park off northern NSW. During this period, kelp disappeared completely from all study sites where it was initially present. At the same time the proportion of tropical and sub-tropical seaweed-eating fish swimming in these areas more than tripled. Grazing also intensified, with the proportion of kelp with obvious feeding marks on it increasing by a factor of seven during the decade. "We also carried out an experiment where we transplanted kelp onto the sea floor. We found that two warm-water species -- rabbitfish and drummer fish -- were the most voracious, eating fronds within hours at an average rate of 300 bites per hour" says Dr Vergés. "The number of fish that consumed the smaller algae growing on rock surfaces also increased, and they cleared the algae faster when there was no kelp present. This suggests the fish may help prevent kelp regrowing as well, by removing the tiny new plants." In Australia, kelp forests support a range of commercial fisheries, tourism ventures, and recreation activities worth more than $10 billion per year. "The decline of kelp in temperate areas could have major economic and management impacts," says Dr Vergés. The video footage used in the study from 2002 onwards was originally collected for a very different research project -- to measure fish populations inside and outside sanctuary zones in a marine park. But the team realised it could also be used to determine whether kelp was present in the background or not. This unplanned use of an historic dataset is a good example of the value of collecting long-term data in the field, especially if it includes video or photos for permanent records.


News Article | November 14, 2016
Site: phys.org

The study includes an analysis of underwater video covering a 10 year period between 2002 and 2012 during which the water warmed by 0.6 degrees. "Kelp forests provide vital habitat for hundreds of marine species, including fish, lobster and abalone" says study first author Dr Adriana Vergés of UNSW and the Sydney Institute of Marine Science. "As a result of climate change, warm-water fish species are shifting their range and invading temperate areas. Our results show that over-grazing by these fish can have a profound impact, leading to kelp deforestation and barren reefs. "This is the first study demonstrating that the effects of warming in kelp forests are two-fold: higher temperatures not only have a direct impact on seaweeds, they also have an indirect impact by increasing the appetite of fish consumers, which can devour these seaweeds to the point of completely denuding the ocean floor. "Increases in the number of plant-eating fish because of warming poses a significant threat to kelp-dependent ecosystems both in Australia and around the globe," she says. The study is published in the journal Proceedings of the National Academy of Sciences. The team recorded underwater video around August-time each year at 12 sites along a 25 kilometre stretch of coast adjacent to the Solitary Island Marine Park off northern NSW. During this period, kelp disappeared completely from all study sites where it was initially present. At the same time the proportion of tropical and sub-tropical seaweed-eating fish swimming in these areas more than tripled. Grazing also intensified, with the proportion of kelp with obvious feeding marks on it increasing by a factor of seven during the decade. "We also carried out an experiment where we transplanted kelp onto the sea floor. We found that two warm-water species - rabbitfish and drummer fish - were the most voracious, eating fronds within hours at an average rate of 300 bites per hour" says Dr Vergés. "The number of fish that consumed the smaller algae growing on rock surfaces also increased, and they cleared the algae faster when there was no kelp present. This suggests the fish may help prevent kelp regrowing as well, by removing the tiny new plants." In Australia, kelp forests support a range of commercial fisheries, tourism ventures, and recreation activities worth more than $10 billion per year. "The decline of kelp in temperate areas could have major economic and management impacts," says Dr Vergés. The video footage used in the study from 2002 onwards was originally collected for a very different research project - to measure fish populations inside and outside sanctuary zones in a marine park. But the team realised it could also be used to determine whether kelp was present in the background or not. This unplanned use of an historic dataset is a good example of the value of collecting long-term data in the field, especially if it includes video or photos for permanent records. Explore further: A marine heatwave has wiped out a swathe of WA's undersea kelp forest More information: Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1610725113


News Article | December 15, 2016
Site: phys.org

The study includes an analysis of underwater video, covering a 10-year period between 2002 and 2012, during which the water warmed by 0.6 degrees. "Kelp forests provide vital habitat for hundreds of marine species, including fish, lobster and abalone," says study first author Dr Adriana Vergés of UNSW and the Sydney Institute of Marine Science. "As a result of climate change, warm-water fish species are shifting their range and invading temperate areas. Our results show that over-grazing by these fish can have a profound impact, leading to kelp deforestation and barren reefs. "This is the first study demonstrating that the effects of warming in kelp forests are two-fold: higher temperatures not only have a direct impact on seaweeds, they also have an indirect impact by increasing the appetite of fish consumers, which can devour these seaweeds to the point of completely denuding the ocean floor. "Increases in the number of plant-eating fish because of warming poses a significant threat to kelp-dependent ecosystems both in Australia and around the globe," she says. The study has been published in the journal Proceedings of the National Academy of Sciences. The team recorded underwater video around August each year at 12 sites along a 25km stretch of coast adjacent to the Solitary Island Marine Park off northern NSW. During this period, kelp disappeared completely from all study sites where it was initially present. At the same time the proportion of tropical and subtropical seaweed-eating fish swimming in these areas more than tripled. Grazing also intensified, with the proportion of kelp with obvious feeding marks on it increasing by a factor of seven during the decade. "We also carried out an experiment where we transplanted kelp onto the sea floor.We found that two warm-water species – rabbitfish and drummer fish – were the most voracious, eating fronds within hours at an average rate of 300 bites per hour," says Dr Vergés. In Australia, kelp forests support a range of commercial fisheries, tourism ventures and recreation activities worth more than $10 billion per year. "The decline of kelp in temperate areas could have major economic and management impacts," says Dr Vergés. The video footage used in the study from 2002 onwards was originally collected for a very different research project – to measure fish populations inside and outside sanctuary zones in a marine park. But the team realised it could also be used to determine whether kelp was present in the background or not. Explore further: Underwater video reveals culprits behind disappearance of NSW kelp forests More information: Adriana Vergés et al. Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp, Proceedings of the National Academy of Sciences (2016). DOI: 10.1073/pnas.1610725113


News Article | November 14, 2016
Site: www.eurekalert.org

Seaweed-eating fish are becoming increasingly voracious as the ocean warms due to climate change and are responsible for the recent destruction of kelp forests off the NSW north coast near Coffs Harbour, research shows. The study includes an analysis of underwater video covering a 10 year period between 2002 and 2012 during which the water warmed by 0.6 degrees. "Kelp forests provide vital habitat for hundreds of marine species, including fish, lobster and abalone" says study first author Dr Adriana Vergés of UNSW and the Sydney Institute of Marine Science. "As a result of climate change, warm-water fish species are shifting their range and invading temperate areas. Our results show that over-grazing by these fish can have a profound impact, leading to kelp deforestation and barren reefs. "This is the first study demonstrating that the effects of warming in kelp forests are two-fold: higher temperatures not only have a direct impact on seaweeds, they also have an indirect impact by increasing the appetite of fish consumers, which can devour these seaweeds to the point of completely denuding the ocean floor. "Increases in the number of plant-eating fish because of warming poses a significant threat to kelp-dependent ecosystems both in Australia and around the globe," she says. The study is published in the journal Proceedings of the National Academy of Sciences. The team recorded underwater video around August-time each year at 12 sites along a 25 kilometre stretch of coast adjacent to the Solitary Island Marine Park off northern NSW. During this period, kelp disappeared completely from all study sites where it was initially present. At the same time the proportion of tropical and sub-tropical seaweed-eating fish swimming in these areas more than tripled. Grazing also intensified, with the proportion of kelp with obvious feeding marks on it increasing by a factor of seven during the decade. "We also carried out an experiment where we transplanted kelp onto the sea floor. We found that two warm-water species - rabbitfish and drummer fish - were the most voracious, eating fronds within hours at an average rate of 300 bites per hour" says Dr Vergés. "The number of fish that consumed the smaller algae growing on rock surfaces also increased, and they cleared the algae faster when there was no kelp present. This suggests the fish may help prevent kelp regrowing as well, by removing the tiny new plants." In Australia, kelp forests support a range of commercial fisheries, tourism ventures, and recreation activities worth more than $10 billion per year. "The decline of kelp in temperate areas could have major economic and management impacts," says Dr Vergés. The video footage used in the study from 2002 onwards was originally collected for a very different research project - to measure fish populations inside and outside sanctuary zones in a marine park. But the team realised it could also be used to determine whether kelp was present in the background or not. This unplanned use of an historic dataset is a good example of the value of collecting long-term data in the field, especially if it includes video or photos for permanent records. The team behind the study includes Professor Peter Steinberg, director of the Sydney Institute of Marine Science (SIMS), Dr Ezequiel Marzinelli and Dr Alexandra Campbell, also from UNSW and SIMS, Dr Christopher Doropoulos from CSIRO, and other researchers from the University of Queensland, the University of Sydney, the NSW Department of Primary Industries, James Cook University, Centre for Advanced Studies in Blanes Spain, and Nanyang Technical University in Singapore.


News Article | November 14, 2016
Site: www.theguardian.com

Herbivorous tropical fish have destroyed kelp forests in northern New South Wales, showing that even small increases in ocean temperature can lead to kelp deforestation, an Australian study has found. The University of NSW study, published in the Proceedings of the National Academy of Sciences on Tuesday, found that the disappearance of kelp from waters near Coffs Harbour coincided with a threefold increase in the number of tropical fish in the region. The deforestation coincided with an 0.6 degree temperature rise. While that was not enough to directly impact the kelp, lead author Dr Adriana Vergés said it had the “truly catastrophic” effect of attracting hungry fish. The study examined video footage of 12 sites between 2002 and 2011. In 2002, six of the sites contained kelp. By 2010, all the kelp was gone. The proportion of kelp showing signs of bite marks increased from less than 10% in 2002 to more than 70% in 2008, before there was no kelp to measure. At the same time the proportion of tropical fish in the ecosystem increased from less than 10% to more than 30%. Most prolific were surgeonfish, which increased from 9% of the local fish population in 2002 to 33% at the end of the study period in 2011. Once the kelp had been removed, the ecosystem changed “quite dramatically” to become more tropical, in a trend Vergés said could potentially be seen globally. “We call it a homogenisation of community,” she said. “It’s a bit like globalisation – everything starts to become the same everywhere.” Researchers used video originally filmed to catalogue fish populations to track the decline of the kelp forests and also conducted experiments in kelp-free areas to see what fish would appear to snack on a spring of transplanted kelp. In one of the videos, a school of rabbitfish crowded around a scrap of kelp briefly lifts to let a shark glide past, before descending again. In another a lamington urchin, a creature that looks like a bald tennis ball that has been cut in half and covered in white spikes, can be seen motoring towards the kelp from some distance away before crawling on to the frond. Urchins are traditional kelp grazers but this species is tropical. Vergés said the decision to examine the impact of fish stemmed from a similar study into mass kelp death off the Western Australian coast, where a 100km stretch of kelp forests died in a marine heatwave in 2011. That study found the kelp was prevented from regenerating by rabbitfish and parrotfish, which ate any regrowth. The director of the Sydney Institute of Marine Science, Prof Peter Steinberg, who contributed to the UNSW study, said the findings increased the range of temperatures that could be considered to have a catastrophic impact because the tropical fish were triggered by a much smaller increase in temperature. “It may be in Western Australia the heatwave simply beat the fish to it,” he said.

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