Climate change and the collapse of fisheries

This is the thiFishing down foodwebsrd article in the series that I’m writing for a Chinese magazine targeting wildlife conservation. As you may guess, they started with Panda conservation, so the magazine is called Giant Panda, but they are running a series on exploitation of natural resources. So far I have covered overfishing, trawling and longline fishing. In this current article we discuss the interaction between fishing and climate change. I say we, because this article was led by Charlee Corra, a postgraduate student of mine. Charlee really deserves the credit for this one!

The first article in this series discussed the effects of overfishing and how it causes degradation to the environment. However, changes to the environment also affect fisheries and their sustainability. In any ecosystem, the survival of a species is dependent on its ability to grow to maturity and reproduce, which is in turn dependent on many factors such as environmental conditions that support healthy physiological functioning. Temperature, salinity, and water quality are all examples of integral abiotic factors that can have the power to support life or pose a serious threat. Global climate change is rapidly altering these environmental conditions, and thus altering marine communities in a way that scientists, fishermen, fisheries managers, and policy makers must understand in order to predict future stocks and improve sustainable practices

How the environment affects plants and animals
Physiology:  Marine organisms differ widely in their tolerance of environmental conditions. Some animals can survive better under stress than others. These differences in biological responses determine where an organism can live. For example, in the intertidal zone temperature sets the upper limits of species distributions such that barnacles, mussels or oysters with a greater heat tolerance live higher on the shore than those with a lower tolerance. While almost every organism has the ability to withstand heat stress to varying degrees, most organisms are also adapted to the temperatures in their particular habitat. Thus, many species, and even populations, have different thermal limits beyond which survival is brought into question. As an extreme example, imagine that you grew up in the polar regions and summer for you only gets as hot as, say, 10°C and you were put in the desert in summer – you would be above your thermal tolerance and likely would die.

The water chemistry of our oceans also heavily affects physiological functions. Calcifying organisms, such as corals, oysters, mussels, and some crustaceans, rely on specific levels of CO2 (usually low) and several other chemical compounds (usually high) in order to induce the chemical reaction that allows them to make their skeletons and shells. Changes to the water’s chemistry can compromise the structural integrity of these essential parts. Of particular concern is that constant and increasing CO2 emissions are causing more CO2 to dissolve into the ocean, causing Ocean Acidification (OA). OA is already making it difficult for shelled organisms to make their shells in some parts of the ocean! You can do a small experiment to demonstrate this effect: put a small seashell or piece of egg shell into a glass of an acidic liquid like Cola or vinegar and watch it slowly dissolve (this can take a day or two).

Climate change and long-term climate shifts: Climate fluctuates and changes naturally across many different time scales from seasonal to multi-decadal and millennial. However, in the last two centuries industrial activity has begun to influence these cycles, mostly because of emissions of greenhouse gases such as CO2 into the atmosphere. Of particular concern is that in addition to causing OA this CO2 also causes the earth’s atmosphere to warm, in turn warming the ocean. Unless something is done to change this trajectory, CO2 levels will continue to rise, negative effects on the environment will become stronger, and the impacts on marine habitats and communities will become more visible.

Shifts in distribution of plants and animals: As environmental conditions change, and especially as oceans warm up, many species are predicted to move poleward to higher latitudes to live in more optimal conditions. These range shifts are not always consistent or predictable among organisms or across regions due to complex ecological interactions with other physical and biological factors such as currents and larval dispersal, competitors and predators. Importantly, as the distributions of different species change, the balance of ecosystems is upset and their function is degraded.

Just as with other species, climate change will invariably impact fish populations and dynamics. For example, fish populations may either get smaller where they currently are or move to a new area. Adjusting fishing practices and quotas to these changes is essential for the future of sustainable fisheries.

Trawler

Photo courtesy of the NOAA photo library (www.photolib.noaa.gov) Photographer: Robert K. Brigham

Effects of climate change on fisheries
Range shifts represent a huge threat to the productivity and success of fisheries, especially when they occur to economically and socially important species. In addition to losing an important species as its range shifts poleward, fisheries may be further affected by the opening of a gap in the ecosystem that can become occupied by a new species. This ultimately changes the structure and function of the ecosystem, potentially reducing the productivity of not only that single fishery but also the ecosystem overall.

In addition to range shifts, decreases in abundance of fish may also occur simultaneously. For example, warming has already caused decreases in populations of Norwegian Cod, leading to a less sustainable fishery. In such cases, the fishermen must either change to another fishery or risk damage to the fishery, degradation of the ecosystem and going out of business.

Together, the combination of range shifts and declining abundance has the potential to be devastating to fisheries if vulnerable fish stocks are fished at the same intensity.  Particularly sensitive fish stocks could easily collapse under these combined pressures. Considering that over 80% of the world’s fisheries are either already fully fished or over-exploited, collapses will become more likely under future conditions. However, armed with more accurate knowledge of how fished populations will be impacted, fishing regulations could be fine-tuned to protect the viability of fished species and avoid such a bleak future.

Predicting future stocks
Knowing that these issues exist, a lot of research is currently being done to predict the trajectory of future fish stocks and assist in managing fisheries in a more sustainable way. Because we are trying to predict what will happen in the future, one of the common techniques is to use computer-generated models which use complex calculations based on as many environmental and biological variables as possible to predict the effects of climate change on fish populations. These models take into account the physiological effects of climate change (mentioned above) on the targeted species to predict parameters such as growth, survival, and reproductive output to determine the future supply of adults. Then, in combination with experiments to test the outputs of these models, managers and policy makers decide how many and what type of fish can be caught annually to avoid depleting populations but also to maximize profits and food security. Importantly, these models can, if used properly, help managers prepare for the future of fisheries and to hopefully avoid more fisheries collapsing. However, it is extremely important to remember that predictions are not certainties and models, while very powerful tools, are far from perfect. There will always be variability across regions and habitats due to the interaction of many different factors and projections might represent some outcomes but not all.

It is important to remember that we can formulate all the regulations that want, but unless we are also simultaneously making an effort to decrease or mitigate the impacts of a changing climate on the ocean and its ecosystems, fisheries will continue to decline. The ocean is an important source of food for humans. In many countries seafood is a way of life. Many smaller communities rely exclusively on fish and other marine organisms for protein.  Therefore, it is important for everyone to understand how climate change will impact on the ability of marine organisms to survive because our fate is inextricably intertwined with that of the marine environment.

Scariest part of climate change isn’t what we know, but what we don’t

A good colleague of mine at The University of Adelaide, Corey Bradshaw, recently posted a blog on what we don’t know about climate change….. and the answer is scary. It is such a poignant article that I thought I would share it again here.

ConservationBytes.com

image-20150731-18728-1ntffbr © Nick Kim

My good friend and tropical conservation rockstar, Bill Laurancejust emailed me and asked if I could repost his recent The Conversationarticle here on ConservationBytes.com.

He said:

It’s going completely viral (26,000 reads so far) in just three days. It’s been republished in The Ecologist, I Fucking Love Science, and several other big media outlets.

Several non-scientists have said it really helped them to understand what’s known versus unknown in climate-change research—which was helpful because they feel pummelled by all the research and draconian stuff that gets reported and have problems parsing out what’s likely versus speculative.

With an introduction like that, you’ll just have to read it!

“It’s tough to make predictions, especially about the future”: so goes a Danish proverb attributed variously to baseball coach Yogi Berra and physicist Niels Bohr. Yet some things are so important — such as…

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When global warming and shifting-baselines syndrome collide

We are having a strange summer in South Australia. First it was mild, then it was late, now it’s hot. So, the weather is a hot topic (pardon the pun) in every conversation. Invariably, conversation then leads onto climate and global warming. And that’s where things get interesting because, as I’ve discussed before, humans and all other organisms experience weather, not climate. In one such conversation with a friend I brought up an excellent article published recently in The Conversation. The article outlines a scary truth; by the end of February 2015 the global temperature has been above the long-term average for 30 years (see the second figure from NOAA, below). My friend said to me, in a very tongue-in-cheek way, “well, I’m 30-ish, which means that they ARE average temperatures to me!”

And that is part of the problem with climate change. It is now easy to demonstrate that temperatures are warming. In Australia, we’re starting to get used to hot summers and bush fires. Even amongst normal inter-annual variation, it’s certainly not difficult to see where the temperature trend is going from the temperature records:

This pattern is repeated globally:

But why can’t we seem to accept the data to all agree that the earth is warming and that we’re the cause?

The problem is three-fold. First, there is the shifting-baselines syndrome. Basically, the idea behind this syndrome is that what you experience in your lifetime is “normal” to you. As with my friend, if you’re only 30 years old (or younger!) then these current temperatures are “normal”. But that doesn’t mean that they ARE normal; the data clearly show that we’re warming outside pre-industrial climatic patterns.

Second, and related to the first, is that we only experience weather. If it rains, we get wet. If it’s winter, we put on a jacket. If it’s summer, we go swimming. We don’t experience “averages.” Some colleagues and I recently published a paper explaining the different effects of climate and weather, noting that without understanding these differences we will not be able to predict what will happen to our marine ecosystems. Yet, policy-makers generally conflate climate with weather, and so we continue to hold to bad policy.

The third, and possibly worst reason, is that in an attempt to “sell the story” the global media still pretends to provide a balanced report. What this means for them is that one person who speaks out against the science underpinning our understanding of climate change gets equal voice to the thousands of scientists who recognise the rigor of this science. That is not only unbalanced, but simply confuses the public into thinking that there is some debate. There is not. To paraphrase the start of the Conversation article, let’s call it, the climate has changed and we’re the cause.

Can nature compensate for human impacts?

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 seeps, which we use at "natural experiments". You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 - 10 plants per metre!).

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 vents, which we use at “natural experiments” to try and understand the effects of carbon emissions on our oceans. You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 – 10 plants per metre!). This is a system that has been pushed past its ability to resist or compensate for human activities.

One thing that humans are really good at is having an impact on the environment through their activities. The problem is that we generally don’t realise that we’re having an impact until something changes in a drastic way. We talk about things called phase-shifts, where the environment changes from one “phase” to another. Good (and unfortunately common) examples are the loss of kelp forests for bare reef, seagrass meadows for bare sand, or coral reefs for algal habitats. In all of these cases, the environment has been degraded to the point where it no longer functions as it should, meaning that biodiversity and productivity are massively reduced.

There are two questions to ask here, (1) why don’t we see these phase-shifts coming, and (2) does nature have any resistance to them? A new paper by one of my PhD students, Giulia Ghedini, shows that nature may actually try to resist human-caused stressors (such as increased nutrient pollution, ocean acidification, warming) by increasing the strength of compensation. In this case, Giulia found that the compounding effects of multiple disturbances increasingly promoted the expansion of weedy algal turfs (which replace kelp forests), but that this response was countered by a proportional increase in grazing of those same turfs by gastropods. This is a natural compensatory mechanism, but it has limits.

What does this mean for our understanding of phase-shifts? First, it means that nature is stronger at resisting than we realised. BUT, because it is extremely difficult to either see or quantify this resistance we generally don’t realise it is happening…. until it stops. Then, once we push the systems past their ability to compensate for the increased pressure we place on them we see a sudden shift. It’s like watching a duck on a river – it may look extremely calm on the surface, seemingly stationary, but underneath it is paddling extremely hard. At some point the current strengthens too much and it can’t paddle harder and so, seemingly suddenly, the duck begins to float down the river.

Unfortunately, when put together, this means that more systems may be more stressed than we realise, and the only way to stop detrimental phase-shifts is to take the conservative approach and start to reduce our impacts on these systems. For example, we know that nutrient pollution, carbon emissions, overfishing and many other activities have damaged marine ecosystems, why not begin to reduce our impacts before we add more systems to the list of those we didn’t realise were at breaking point?

Declining productivity

We’ve all heard about productivity, but I suspect that the only context most people have heard the term used in is about the productivity of the workplace, or perhaps the economy.

Phytoplankton may be tiny but they are the base for much of what we see and use in the ocean!

Phytoplankton may be tiny but they are the base for much of what we see and use in the ocean!

Economists and governments are certainly concerned with productivity. But, we should all be concerned with productivity – of the oceans.
As we burn more fossil fuels and pump carbon dioxide into the atmosphere we are making astonishing changes to the global climate systems. Not the least of these is the addition of billions of tons of CO2 to the surface waters of the ocean. What does this mean for productivity of the oceans? A cursory analysis would lead you to believe that because many photosynthetic plants and algae can use in photosynthesis that productivity would increase. As the oceans produce about 50% of the oxygen we breathe and provide us with a substantial amount of food and other resources you may think that this would be a good thing. Unfortunately, the evidence is stacking up that productivity won’t increase, and in fact it is likely to decrease.
I have previously posted on work by my research group where we experimentally project that ecosystem productivity in temperate waters is likely to decrease because of an indirect effect whereby highly productive kelp forests will be replaced by lower productivity systems dominated by algal mats. Of potentially greater concern, however, is the emerging data from open-ocean pelagic systems. Recent work by Professor Kunshan Gao from the State Key Laboratory of Marine Environmental Science, Xiamen University, has demonstrated that the projected concentrations of CO2 in our oceans by 2050 (assuming we don’t suddenly decide to stop burning carbon!) will actually cause a decrease in the productivity of phytoplankton. And, the situation was even worse when the phytoplankton were exposed to increased light intensity, which will happen as the upper ocean that they live in shoals towards the surface. This result was initially surprising given that both light and CO2 are required for photosynthesis. In combination and high enough concentrations, however, they inhibit photosynthesis, leading to a decline in productivity.

What does all this mean? The changes that are happening in the ocean because of changes to our climatic systems, including (but not limited to) increased availability of CO2, ocean acidification and warming are going to be with for a very long time. The resources that we currently expect from the oceans will change, many declining. How do we stop this? By being a little smart – let’s stop burning carbon for fuel!

Eutrophication offsets sea urchin grazing on seagrass caused by warming and OA

Amblypneustes pallidus in a Posodonia seagrass meadow. Photo: Owen Burnell

Amblypneustes pallidus in a Posodonia seagrass meadow.
Photo: Owen Burnell

The title to this blog seems a bit counterintuitive, almost like eutrophication is a good thing. Don’t believe that for a second! In a recently published paper, Owen Burnell of the University of Adelaide presents some interesting data on the interactions between eutrophication (an all too common local stressor), ocean acidification and warming (both increasingly alarming stressors of global origin). As I keep discovering, interactions between these stressors never seem to turn out the way we expect:

The accumulation of atmospheric [CO2] continues to warm and acidify oceans concomitant with local disturbances, such as eutrophication. These changes can modify plant– herbivore grazing interactions by affecting the physiology of grazers and by altering the nutritional value of plants. However, such environmental changes are often studied in isolation, providing little understanding of their combined effects. We tested how ocean warming and acidification affect the per capita grazing by the sea urchin Amblypneustes pallidus on the seagrass Amphibolis antarctica and how such effects may differ between ambient and eutrophic nutrient conditions. Consistent with metabolic theory, grazing increased with warming, but in contrast to our expectations, acidification also increased grazing. While nutrient enrichment reduced grazing, it did not fully counterbalance the increase associated with warming and acidification. Collectively, these results suggest that ocean warming and acidification may combine to strengthen top-down pressure by herbivores. Localised nutrient enrichment could ameliorate some of the increased per capita grazing effect caused by warming and acidification, provided other common negative effects of eutrophication on seagrass, including overgrowth by epiphytes and herbivore aggregation, are not overwhelming. There is value in assessing how global and local environmental change will combine, often in non-intuitive ways, to modify biological interactions that shape habitats.

Digital library

Disrupting synergies – making things not so bad.

Healthy forest of the kelp Ecklonia radiataI’ve posted on synergies between environmental stressors (what most people think of as pollution) before. Basically, a synergy is when the impact of the two stressors, say increased CO2 nd nutrients, is greater than the sum of their individual impacts. Once you recognise that synergies can occur, and are often much worse than we predict, the next question is can we do anything to stop them? The short answer is in most cases yes.

The way that synergies work means that, theoretically, if you remove one of the stressors then the “extra” impact should also be removed. In essence, if a synergy is 1 + 1 = 5, then removing 1 means that 1 + 0 = 1. When you’re talking about impacts to ecosystems that are essential to our GDP and way of life (not to mention that they have intrinsic value anyway) that is a really big consideration.

One of my Ph.D. students has just published a rather elegant study demonstrating it is possible to disrupt a synergy between CO2 and nutrients that has the potential to cause the loss of our kelp forest ecosystems. Basically, where CO2 and nutrients cause the synergistic growth of “weedy” species of algae you can remove the nutrients and remove the synergy. There is, however, a caveat. If you wait to remove the nutrients from the system then a large part of the impact will remain – things won’t go back to normal.

The thing that I like most about this outcome is that it provides useful information to the people who manage our coastal waters. If you are concerned that increasing concentrations of CO2 will have a negative impact in areas around major population centres then recycling and redirecting treated waste water away from the ocean, such as into industry or agriculture, can increase the resilience of marine systems. But, timing matters. Sooner is better.

Common synergies

Image

Algal turfs (brown fuzzy stuff) are overgrowing the hard corals at high CO2 concentrations near volcanic vents – a good “natural” experiment. Note also that the seagrass (green, long leaves) are also doing well – a subject for another post.

We frequently hear about “climate change” in the media these days. How could you avoid it? If you do a search of the scientific literature there are thousands of publications a year on the topic. When thinking about the worlds oceans, the most common things that we hear about are ocean warming or ocean acidification (aka. the “evil twin” of warming). Do you notice somthing about this statement? We hear about warming OR acidification. But is this a realistic scenario?

We as scientists commonly break things down into their components and try to understand them one at a time. This is understandable, because the best way to comprehend the functioning of amazingly complex systems is to break them down their component parts and then put them back together again. In this case, however, we are just starting to understand that by breaking things down to individual conditions, either temperature or acidification, we may be missing the most important part of the study. My research group started to realise this in 2009 when we discovered that, when increased in combination, carbon dioxide and nutrients had a massive effect on the growth of “weedy” species of algae which can help to maintain the loss of kelp forests (download the paper here). In hindsight, this result should not be so surprising – both carbon and nitrogen are resources which the algae use to grow. Isn’t hindsight a wonderful thing?

What was surprising is that when carbon dioxide was elevated in the absence of nutrients these algae didn’t respond by grow faster. In fact, they didn’t respond at all to the increased availability of carbon. This means that CO2 and nutrients cause a synergistic response in these algae – where the response to the combined conditions is greater than the sum of responses to the individual conditions (see here for a good review on the topic).

What now worries us is that increasing availability of carbon in the oceans will happen with ocean warming – these are not either/or conditions. Indeed, the first warning shots were fired when we discovered that these same “weedy” turf algae showed the same synergistic growth in response to combined CO2 and warming (see our results published here). We can do something about nutrient pollution (something I will post on in the near future), but CO2 and warming are inherently linked. I think it is time to not talk about warming or acidification but rather to discuss them in tandem.

Report card on Australia’s oceans

I love being a scientist. It can be the most self-indulgent of careers and I feel lucky to live in a society that allows me the freedom to pursue ideas and information. I have the opportunity to explore ideas about how humans interact with our oceans, how we do bad things to them, and most importantly to me, try to figure out how to help them recover. The first step is gathering this information so that people can access it.

While scientists often disagree on things (a very important part of the job), getting a group of scientists together on a problem can truly help to pull together a massive amount of information very rapidly. In this spirit, the “Marine Climate Change Impacts and Adaptation Report Card (Australia)” was released last week. I am lucky enough to have been involved with two of the chapters, observed impacts of Ocean Acidification and observed impacts on marine Macroalgae. Unfortunately, I’d have to say that things aren’t looking good. We are only at the leading edge of some of the changes we are going to see over the next 100 years and some of the observed changes are already bad.

An example that most people wouldn’t know about (because you can’t see it from the surface) is the shift in the distribution of some algae. Algae, aren’t they just the “seaweeds” that we see washed up on the beach? Well, yes, but before they get to the beach they are the foundation of many food webs of the ocean; if they are lost then so are the ecosystems that they support. I must be honest here, when we started this project I didn’t actually expect to find anything to have happened yet, but it has. We have documented substantial southward shifts of entire assemblages of these algae on both the east and west coasts of Australia.Why? The waters of both coasts have warmed rapidly over the past 50 years. In fact, the Leeuwin Current was so strong this year with warming and El Nino that it pushed well into South Australia (see here for a Sea Surface Temperature image from IMOS). Not unheard of, but becoming stronger and more common.

Are we in danger of losing our iconic kelp forests? If so, what will happen to the ecosystems that they support (including 100’s of millions of dollars worth of fisheries)? Only time will tell, but I sincerely hope we can figure out a way to help them…..

The present…..

 

 

 

 

 

 

 

 

 

The future?

Super trawler, Super bad?

Over the past week there has been a lot of media attention thrown at the imminent arrival of a super trawler in Australian waters. It seems that there is strong objection from a lot of the population but objections are far from unanimous. So, what are the issues surrounding super trawlers? Well, it depends on your point of view:
1. Bycatch.

Bycatch, or non-target species caught in the nets, is an issue with trawlers – all trawlers. The size of the nets on super trawlers will mean that there is a large amount of bycatch (e.g. dolphins, turtles, sea birds) regardless of devices designed to limit bycatch being placed in the nets. This is sad and wasteful, but an issue with all trawling activities.

As an aside, I personally don’t believe that the use of the term “gently” with reference to these excluder devices
(“excluder device inside the net guides the animals gently up to an escape hatch on the top panel on the net” – see the article on ABC news for the full quote)

2. Jobs.

If I were the owner of a smaller trawler, I wouldn’t like to be sharing my fishery with this boat. Hundreds of fishermen around the world have been put out of business by big boats and collapsing fisheries……

3. Overfishing.

This is an interesting one. TECHNICALLY, if an effective quota system is in place on this fishery then the addition of this super trawler will not increase the likelihood of over fishing. However, I think this is the main issue in the debate. If you look at global fisheries, the vast majority are either fully or over exploited already. A lot are in an unarrested free-fall. Why? Because we’ve become way too good at catching fish. Our current level of technology means that if we don’t have accurate assessments of fish stocks, and believe me this is a supremely difficult task (so all credit to the people who have to figure it out), then we have the industrial power to over fish a stock before we even know it’s happening. In my mind, this is the real issue with such large boats.

But, this also brings me back to one of the issues I have with the way that society currently looks at problems. If you break something, or there is too little of what you want, don’t change what you’re doing just engineer a better way. With fishing that means bigger, more efficient boats. With climate change, it means geoengineering or carbon mitigation. But, why capture carbon dioxide through a chemical reaction and inject it deep into the ocean rather than switching to non-carbon based sources of fuel? At best you’re buying time to make appropriate changes, at worst you’re creating a false sense of security that will lead to disaster.

Are we risking the same choice with the super trawler?