The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations



File 20180725 194140 1cri4pn.jpg?ixlib=rb 1.1
Some fish fared better than others amid the extreme temperatures of the 2016 heatwave.
Rick Stuart-Smith/Reef Life Survey

Rick Stuart-Smith, University of Tasmania; Christopher Brown, Griffith University; Daniela Ceccarelli, James Cook University, and Graham Edgar, University of Tasmania

The 2016 marine heatwave that killed vast amounts of coral on the Great Barrier Reef also caused significant changes to fishes and other animals that live on these reefs.

Coral habitats in the Great Barrier Reef (GBR) and in the Coral Sea support more than 1,000 fish species and a multitude of other animals. Our research, published in Nature today, documents the broader impact across the ecosystem of the widespread coral losses during the 2016 mass coral bleaching event.

While a number of fish species were clearly impacted by the loss of corals, we also found that many fish species responded to the increased temperatures, even on reefs where coral cover remained intact. The fish communities in the GBR’s southern regions became more like those in warmer waters to the north, while some species, including parrotfishes, were negatively affected by the extreme sea temperatures at the northern reefs.




Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef


The loss of coral robs many fish species of their preferred food and shelter. But the warming that kills coral can also independently cause fish to move elsewhere, so as to stay within their preferred temperature range. Rising temperatures can also have different effects on the success, and therefore abundance, of different fish populations.

One way to tease apart these various effects is to look at changes in neighbouring reefs, and across entire regions that have been affected by bleaching, including reefs that have largely escaped coral loss.

We were able to do just this, with the help of highly trained volunteer divers participating in the Reef Life Survey citizen science program. We systematically surveyed 186 reefs across the entire GBR and western Coral Sea, both before and after the 2016 bleaching event. We counted numbers of corals, fishes, and mobile invertebrates such as sea urchins, lobsters and giant clams.

Sea temperatures and coral losses varied greatly between sites, which allowed us to separate the effects of warming from coral loss. In general, coral losses were much more substantial in areas that were most affected by the prolonged warmer waters in the 2016 heatwave. But these effects were highly patchy, with the amount of live hard coral lost differing significantly from reef to reef.

For instance, occasional large losses occurred in the southern GBR, where the marine heatwave was less extreme than at northern reefs. Similarly, some reefs in the north apparently escaped unscathed, despite the fact that many reefs in this region lost most of their live corals.

Sea temperatures the culprit

Our survey results show that coral loss is just one way in which ocean warming can affect fishes and other animals that depend on coral reefs. Within the first year after the bleaching, the coral loss mostly affected fish species that feed directly on corals, such as the butterflyfishes. But we also documented many other changes that we could not clearly link to local coral loss.

Much more widespread than the impacts of the loss of hard corals was a generalised response by the fish to warm sea temperatures. The 2016 heatwave caused a mass reshuffling of fish communities across the GBR and Coral Sea, in ways that reflect the preferences of different species for particular temperatures.

In particular, most reef-dwelling animals on southern (cooler) reefs responded positively to the heatwave. The number of individuals and species on transect counts generally increased across this region.

By contrast, some reefs in the north exceeded 32℃ during the 2016 heatwave – the typical sea temperature on the Equator, the hottest region inhabited by any of the GBR or Coral Sea species.

Some species responded negatively to these excessive temperatures, and the number of observations across surveys in their northernmost populations declined as a consequence.

Parrotfishes were more affected than other groups on northern reefs, regardless of whether their local reefs suffered significant coral loss. This was presumably because the heatwave pushed sea temperatures beyond the level at which their populations perform best.

Nothing to smile about: some parrotfishes don’t do well in extreme heat.
Rick Stuart-Smith/Reef Life Survey

Local populations of parrotfishes will probably bounce back after the return of cooler temperatures. But if similar heatwaves become more frequent in the future, they could cause substantial and lasting declines among members of this ecologically important group in the warmest seas.

Parrotfishes are particularly important to the health of coral reef ecosystems, because their grazing helps to control algae that compete with corals for habitat space.




Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef


A key message from our study is not to overlook the overarching influence of temperature on coral reef ecosystems – and not to focus solely on the corals themselves.

Even if we can save some corals from climate change, such as with more stress-tolerant breeds of coral, we may not be able to stop the impacts of warming seas on fish.

Future ecological outcomes will depend on a complex mix of factors, including fish species’ temperature preferences, their changing habitats, and their predators and competitors. These impacts will not always necessarily be negative for particular species and locations.

The ConversationOne reason for hope is that positive responses of many fish species in cooler tropical regions may continue to support healthy coral reef ecosystems, albeit in a different form to those we know today.

Rick Stuart-Smith, Research Fellow, University of Tasmania; Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University; Daniela Ceccarelli, Adjunct Senior Research, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Graham Edgar, Senior Marine Ecologist, Institute for Marine and Antarctic Studies, University of Tasmania

This article was originally published on The Conversation. Read the original article.

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Australian fished populations drop by a third over ten years, study finds


Graham Edgar, University of Tasmania and Trevor J Ward, University of Technology Sydney

Large fish species are rapidly declining around Australia, according to the first continental diver census of shallow reef fish. Contrary to years of sustainability reports, our study indicates that excessive fishing pressure is contributing to decline of many Australian fish species.

In areas open to fishing, we found that exploited populations fell by an average of 33% between 2005 and 2015. This rate closely matches the 32% downward trend in total Australian fishery catches through the same period.




Read more:
Citizen scientist scuba divers shed light on the impact of warming oceans on marine life


In contrast, in marine parks where fishing is prohibited, the same species increased by an average of 25%. Other species not targeted by fishers showed a small downward trend (11% decline in fished zones; 16% decline in no-take marine reserves), indicating that recent marine heatwaves off southeastern and southwestern Australia have probably adversely affected marine life over a wide area.




Read more:
Marine heatwaves are getting hotter, lasting longer and doing more damage


Citizen science

Our audit of 531 study sites was made possible by combining data from 50-metre long transects repeatedly surveyed by Australian Institute of Marine Science and University of Tasmania research divers, and by highly trained volunteers participating in the citizen science Reef Life Survey program.

After the collapse of some high-profile fisheries in the 1990s, such as gemfish, orange roughy and southern bluefin tuna, federal and state agencies took a more conservative approach to fish capture. Australian fisheries are now regarded as among the most sustainable worldwide.




Read more:
Plenty of fish in the sea? Not necessarily, as history shows


Regardless, the prevalence of downward population trends in our investigation indicates that a reduction in fishing pressure and additional caution is needed. Otherwise, more Australian fisheries may not be economically viable if this trend continues.

Our analysis identified a variety of issues that affect fishery management practices, many of which are also evident overseas, including:

  • little relevant data for decision-making related to ecological issues
  • a lack of no-fishing reference areas to scientifically assess impacts of fishing
  • poorly documented stock assessments with limited public accessibility
  • management decisions made by committees dominated by industry-aligned members
  • short-term catch maximisation prioritised over precaution
  • fishery models that rarely consider species interactions or climate impacts
  • wider effects of fishing on ecosystems and their resilience to multiple pressures are overlooked

No-fishing reserves work

Our study indicates that a highly effective but underused tool in the manager’s toolbox is expanded rollout of no-fishing “marine reserves”. Despite receiving wide public support, most Australian marine reserves are small and located in areas with few fishery resources. They consequently house few mature, egg-producing females and do little to assist in the rebuilding of overfished stocks. Nor are they likely to help much in the recovery of important ecosystem functions, as needed for fished-species populations to rebound after climate shocks and other pressures.

The July rollout of Australian Marine Parks, in particular, represents a lost opportunity that may prove a significant problem for fishers. Although covering 2.76 million square kilometres – the largest marine park in the world – it is of limited conservation value.




Read more:
Australia’s new marine protected areas: why they won’t work


Through three rounds of public submissions, each largely aimed at minimising any remaining overlap with current fishing activities, the final zoning plans affect very few stakeholders. The outcome is neither an efficient nor effective solution to the actual problem of protecting the oceans.

For example, the Temperate East Zone covering waters from the Victorian border to southern Queensland includes no new “no-take” reserves shallower than 1,000m depth, although these waters are where virtually all fishing impacts occur in this region.

The widespread declaration of marine parks that allow current fishing to continue is perhaps useful when harmful fishing practices for ecosystems are excluded. However, our study indicates that this basic assumption does not apply to Australian Marine Parks.




Read more:
More than 1,200 scientists urge rethink on Australia’s marine park plans


The ConversationThe environmental and economic debt for future generations is both huge and unfair.

Graham Edgar, Senior Marine Ecologist, Institute for Marine and Antarctic Studies, University of Tasmania and Trevor J Ward, Adjunct professor, University of Technology Sydney

This article was originally published on The Conversation. Read the original article.

‘Gene drives’ could wipe out whole populations of pests in one fell swoop



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Gene drives aim to deliberately spread bad genes when invasive species such as mice reproduce.
Colin Robert Varndell/shutterstock.com

Thomas Prowse, University of Adelaide; Joshua Ross, University of Adelaide; Paul Thomas, University of Adelaide, and Phill Cassey, University of Adelaide

What if there was a humane, targeted way to wipe out alien pest species such as mice, rats and rabbits, by turning their own genes on themselves so they can no longer reproduce and their population collapses?

Gene drives – a technique that involves deliberately spreading a faulty gene throughout a population – promises to do exactly that.

Conservationists are understandably excited about the possibility of using gene drives to clear islands of invasive species and allow native species to flourish.


Read more: Gene drives may cause a revolution, but safeguards and public engagement are needed.


Hype surrounding the technique continues to build, despite serious biosecurity, regulatory and ethical questions surrounding this emerging technology.

Our study, published today in the journal Proceedings of the Royal Society B, suggests that under certain circumstances, genome editing could work.

The penguins on Antipodes Island currently live alongside a 200,000-strong invasive mouse population.
Wikimedia Commons, CC BY

Good and bad genes

The simplest way to construct a gene drive aimed at suppressing a pest population is to identify a gene that is essential for the pest species’ reproduction or embryonic development. A new DNA sequence – the gene-drive “cassette” – is then inserted into that gene to disrupt its function, creating a faulty version (or “allele”) of that gene.

Typically, faulty alleles would not spread through populations, because the evolutionary fitness of individuals carrying them is reduced, meaning they will be less likely than non-faulty alleles to be passed on to the next generation. But the newly developed CRISPR gene-editing technology can cheat natural selection by creating gene-drive sequences that are much more likely to be passed on to the next generation.


Read more: Now we can edit life itself, we need to ask how we should use such technology.


Here’s how the trick works. The gene-drive cassette contains the genetic information to make two new products: an enzyme that cuts DNA, and a molecule called a guide RNA. These products act together as a tiny pair of molecular scissors that cuts the second (normal) copy of the target gene.

To fix the cut, the cell uses the gene drive sequence as a repair template. This results in a copy of the gene drive (and therefore the faulty gene) on both chromosomes.

This process is called “homing” and, when switched on in the egg- or sperm-producing cells of an animal, it should guarantee that almost all of their offspring inherit the gene-drive sequence.

As the gene-drive sequence spreads, mating between carriers becomes more likely, producing offspring that possess two faulty alleles and are therefore sterile or fail to develop past the embryonic stage.

Will it work?

Initial attempts to develop suppression drives will likely focus on invasive species with rapid life cycles that allow gene drives to spread rapidly. House mice are an obvious candidate because they have lots of offspring, they have been studied in great detail by biologists, and have colonised vast areas of the world, including islands.

In our study we developed a mathematical model to predict whether gene drives can realistically be used to eradicate invasive mice from islands.

Our results show that this strategy can work. We predict that a single introduction of just 100 mice carrying a gene drive could eradicate a population of 50,000 mice within four to five years.

But it will only work if the process of genetic homing – which acts to overcome natural selection – functions as planned.

Evolution fights back

Just as European rabbits in Australia have developed resistance to the viruses introduced to control them, evolution could thwart attempts to use gene drives for biocontrol.

Experiments with non-vertebrate species show that homing can fail in some circumstances. For example, the DNA break can be repaired by an alternative mechanism that stitches the broken DNA sequence back together without copying the gene-drive template. This also destroys the DNA sequence targeted by the guide RNA, producing a “resistance allele” that can never receive the gene drive.

A recent study in mosquitos estimated that resistance alleles were formed in at least 2% of homing attempts. Our simulation experiments for mice confirm this presents a serious problem.

After accounting for low failure rates during homing, the creation and spread of resistance alleles allowed the modelled populations to rebound after an initial decline in abundance. Imperfect homing therefore threatens the ability of gene drives to eradicate or even suppress pest populations.

One potential solution to this problem is to encode multiple guide RNAs within the gene-drive cassette, each targeting a different DNA sequence. This should reduce homing failure rates by allowing “multiple shots on goal”, and avoiding the creation of resistance alleles in more cases.

To wipe out a population of 200,000 mice living on an island, we calculate that the gene-drive sequences would need to contain at least three different guide RNA sequences, to avoid the mice ultimately getting the better of our attempts to eradicate them.

From hype to reality

Are gene drives a hyperdrive to pest control, or just hype? Part of the answer will come from experiments with gene drives on laboratory mice (with appropriate containment). That will help to provide crucial data to inform the debate about their possible deployment.

The ConversationWe also need more sophisticated computer modelling to predict the impacts on non-target populations if introduced gene drives were to spread beyond the populations targeted for management. Using simulation, it will be possible to test the performance and safety of different gene-drive strategies, including strategies that involve multiple drives operating on multiple genes.

Thomas Prowse, Postdoctoral research fellow, School of Mathematical Sciences, University of Adelaide; Joshua Ross, Associate Professor in Applied Mathematics, University of Adelaide; Paul Thomas, , University of Adelaide, and Phill Cassey, Assoc Prof in Invasion Biogeography and Biosecurity, University of Adelaide

This article was originally published on The Conversation. Read the original article.

Tropics: Wildlife Populations Collapsing


The link below is to an article reporting on the crisis for wildlife populations in the tropics where wildlife populations have crashed by 61% in the last 50 years.

For more visit:
http://news.mongabay.com/2012/0515-hance-living-planet-report-tropics.html

Kenya: Poachers Killing Rhinos


The link below is to an article reporting on the death of Rhinos in Lake Nakuru National Park. Rhino populations are dwindling quickly throughout Africa due to poachers seeking their ivory.

For more, visit:
http://www.daijiworld.com/news/news_disp.asp?n_id=134790

Butterflies: Genetically Modified Crops Killing Butterflies


The article below reports on how genetically modified crops are killing off Monarch Butterfly populations. There is also a simple answer to the problem revealed in the article.

For more, visit:
http://grist.org/list/study-gmo-crops-are-killing-butterflies/

Koalas: Trees the Key to Growing Populations


A recent report on Koala populations has concluded that more trees are the key to growing populations and spreading habitats. Hardly sounds surprising does it – the article is linked to below.

For more visit:
http://sydney.edu.au/news/84.html?newsstoryid=6826