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.


Photo courtesy of the NOAA photo library ( 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.

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

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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Ocean Acidification science: insightful and essential

Turfs overgrowing coralThe concentration of carbon dioxide in the atmosphere is rapidly increasing as we burn fossil fuels. Nobody doubts this. One of the emerging global consequences of this activity is Ocean Acidification (OA); approximately 30% of the CO2 that we emit into the atmosphere is dissolved into the oceans, forming carbonic acid and reducing the pH of the seawater. This is basic chemistry and can already be measured in many marine waters of the world.

The biological and ecological consequences of OA are, however, more complex to understand. Therefore, over the past two decades there has been a dramatic increase in the number of scientific studies investigating the effects of OA. Last week, a review of over 465 of these studies, written by Christopher Cornwall and Catriona Hurd, was published in the ICES Journal of Marine Science. They assessed a number of different scientific methods for rigour and concluded that overall OA science is well designed and executed, and provides useful insights into a complex problem.

There has been some good coverage of Cornwall and Hurd’s paper (e.g. in the journal Nature). Unfortunately, some media outlets misrepresent the findings of the paper. This is of great concern, as the inaccurate and sloppy journalism threatens an essential branch of marine science. I asked Cornwall to write something for this post:

Recently the Daily Mail reported that climate scientists are doom-mongering because their work is flawed. This report is misleading and only serves to introduce misinformation into the public arena.

The Daily Mail quotes an article in Nature by Cressey (2015) that highlights research by Cornwall and Hurd (2015).  Science is always evolving, and its aim is to improve both methods and theory in any given field, to be better equipped to answer the most complex of questions.   Cornwall and Hurd was merely a call for improvement in only one aspect of research amongst a multitude of methods.  The report in the Daily Mail misrepresents our findings.  There is overwhelming evidence that the effects of ocean acidification will impact our oceans through reductions in the growth and calcification rates of calcified organisms (e.g. shellfish, corals, etc., that make calcium carbonate ‘skeletons’), and an alteration of the behaviour of other marine invertebrates and fish.  This fact is unequivocal.  Rather than being “flawed”, the majority of ocean acidification studies have been carried out carefully, using a multitude of methods, and most provide extremely useful and insightful data on this complex problem.

Certainly, the consequences of OA are complex and modified by interactions with other stressors (e.g. nutrient pollution, global warming) and biotic interactions such as herbivory, competition and habitat complexity. This does not mean that the OA science to date is flawed, it simply means that we have more research to do to understand the future impacts. We need to understand all of the effects of OA, from the physiology of single organisms, through population dynamics and up to ecosystem-level interactions. This pattern of discovery is across all of science. For example, Einstein’s theory of relativity is complex. Physicists are making great discoveries but still have research to do. Ocean Acidification is no different.

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!

Relevant experimental scales for Ocean Acidification

Degraded reef where kelp have been replaced by algal turfs

Degraded reef where kelp have been replaced by algal turfs

In a few of my posts have discussed the potential effects of ocean acidification (OA), caused by the dissolution of CO2 into seawater, on marine ecosystems. What I haven’t really discussed yet is how we make these predictions, because quite frankly attempting to predict the effects of OA is a difficult prospect. There are a couple of different ways that you can make such predictions, but for me one of the most obvious and effective ways is to identify the key species’ in a particular marine ecosystem and then experimentally expose them to elevated CO2 based on the various emissions scenarios. On the surface that sounds simple…… but it turns out to be quite hard. The most simple way to do it is to bring organisms back into the lab and do the experiments there. True, it’s easier to manipulate the CO2 by bubbling mixed air with elevated concentrations of CO2 under lab conditions, but invariably you end up with a situation where you’re looking at the physiological responses of organisms. This is a very valid thing to do, but you can also be in for some surprises when you try to scale up to identify ecological effects. For example, based on

laboratory based experiments we have predicted that algal turfs will replace kelp forests and corals under

Healthy forest of the kelp Ecklonia radiata

Healthy forest of the kelp Ecklonia radiata

future OA conditions (picture to the right; link to the kelp study) because these algal turfs use the extra CO2 as a resource and grow faster. This conclusion, based on physiological changes, was and still is quite valid. HOWEVER, when we scaled up our experiments to mesocosms (literally “medium” experimental environment or ecosystem) and included the kelp we discovered that the kelp were able to resist a lot of this effect by suppressing the growth of the turfs. But, realising that this mesocosm study was also limited because it only occurred over one generation of kelp, and you may need to study multiple generations because the adults may not be the “weak point”, we took this work up to the next scale, field experiments at naturally occurring CO2 vents – currently our best “ecosystem” approach to understanding OA.

But we were interested in not only the larger, system response, but also how well our other experiments may predict ecosystem outcomes. We tested this thought by combining laboratory and field CO2 experiments (which is difficult but possible) and data from ‘natural’ volcanic CO2 vents. Interestingly, and to our great

Coral reefs are structurally complex and "cemented" together by Crustose Coralline Algae.

Coral reefs are structurally complex and “cemented” together by Crustose Coralline Algae.

relief, we found that algal mats showed the same direction of response to elevated CO2 (i.e. they grew more) across all scales of experiments but that the strength of response was modified by the ecosystem complexity. Basically, the things that either eat or suppress the growth of algal turfs slow the rate at which they will come to dominate the systems. BUT, we did find that these turfs have enhanced productivity and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions.; that is, our original predictions from the laboratory experiments that these weedy turfs could come to replace kelps and corals seems to hold up, it’s just that the rate of change will be a bit slower.


Digital library links for:
Lab based kelp study (Russell et al. 2009)
Kelp resisting turfs (Falkenberg et al. 2012)
Need to study multiple life stages (Russell et al. 2012)
Field manipulations of CO2 (Kline et al. 2012)
Ecological outcomes across different experimental scales (Connell et al. 2013)

Don’t forget to remember the past

I have recently returned from the 10th International Temperate Reefs Symposium in Perth. It was great to spend a week talking good science

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

Seagrass may increase their productivity in the future as they use CO2 for photosynthesis.
Photo: Owen Burnell

with a vibrant group of great scientists. There was an array of talks from classical marine ecology (which is great to see!) to novel modelling approaches and plenty of discussion of human impacts in marine systems. In the rare moments of quiet since my return I’ve been thinking about the main message that I took away from the meeting, and it’s this: anthropogenic climate change may be new to the planet, but we were studying the effects of human activities on ecosystems for several decades before we even realised that climate change was happening. So why is it that we seem to have abandoned ecology in our race to understand climate change?

While I was writing my talk for the conference I realised that, in general, research into the effects of climate change in marine ecosystems has been hampered by not looking at the literature on other human impacts. For example, there is a rich and abundant literature on how excess nutrient loads degrade ecosystems and change their structure and function. Yet, it is only recently that we have realised that CO2 is a “nutrient” or resource in marine systems. This seems logical; after all, plants use inorganic carbon for photosynthesis.  However, the story isn’t that simple, with different algae and seagrasses using different forms of carbon for photosynthesis. Even more confusing is that it looks like the “weedy” species will benefit by switching to the most abundant source of carbon and start to dominate ecosystems (see some of my papers and Harley et al. for the ecosystem effects and Raven & Hurd for the physiological aspects)! But I digress….

The point is that for some reason we don’t seem to draw on this older literature for the general principles of what we may expect to see as CO2 concentrations increase in the oceans. We’re starting to catch up, but the lost time is frustrating – let’s not make the mistakes of past generations but rather learn by them.

Digital library links for: Connell & Russell 2010