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.

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

Ocean acidification: will there be ecosystem effects?

Turfs overgrowing coral

Algal turfs overgrowing corals under acidified conditions at CO2 seeps, which we use at “natural experiments”. Note that the seagrass in the middle of the photo also grow well under these conditions.

It has been a while since my last post, for which I apologise, but I have just emerged from a particularly busy period. I was lucky enough to be invited to an ocean acidification round table at the Peter Wall Institute in Vancouver late last year and we have been madly working on multiple papers since then (and I also had a short break over the Christmas week because of sheer exhaustion!). Why are we working so madly to get the papers written? Because the topic of the meeting is both topical and imminently important: how do we predict the ecosystem-level impacts of ocean acidification, and what can we do about it?

Why is this such an important question? The simple answer is that ocean acidification is a direct consequence of increasing CO2 in the atmosphere. It’s simple, indisputable chemistry. As CO2 dissolves into seawater it forms carbonic acid, finally reducing the amount of carbonate in the water (a good diagram of this reaction can be found here). The early research into this field (only 10 years ago now!) focussed entirely on calcifying species, such as gastropods and corals, because they use this carbonate to form their hard structures (calcium carbonate). What we’ve realised more recently, and a big part of my research program, is tha t the extra Carbon in the system (in the form of CO2) is also a resource for some algae and plants, potentially causing a change in the dominant species in ecosystems (see my photo of a “future” coral reef and kelp forest in this post).

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 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!).

I’m happy to say that we made real progress in trying to understand what the likely ecosystem effects are globally, and more importantly the things that we need to know into the future. I won’t pre-empt our publications, but the synopsis is that ecosystems will change, and for the worse. This has been highlighted before, including for Australia, but for the first time I think we’re starting to get at understanding the ecological mechanisms (which is essential if we are to help the systems resist this change!).

Lead by Prof. Chris Harley, and including an amazing group of contributors, I’d say it was the most successful round-table that I’ve been involved with and we’ll have some good papers coming out soon (I’ll be sure to post about them!). If you’re interested in the topic and want more information, I strongly suggest that you watch this video of the public event we held as part of the week’s activities.

 

Digitial library links for:Falkenberg et al. 2013
Russell et al. 2013

Mediation of global change by local biotic and abiotic interactions

Dr Laura FalkenbergThis post is basically a short synopsis of the work done by one of my (now ex-) Ph.D. students, Dr Laura Falkenberg. Laura’s work has turned much of what we thought we knew about the effect of increased CO2 and nutrients on its head; we found synergies where we didn’t expect them (reviewed in a book chapter) and system resilience and resistance to change beyond what we hoped (via strong competitive interaction and trophic links; published in Oecologia, PLoS One and Marine Ecology Progress Series). Laura has certainly helped us look at things in new ways and given us hope that in marine systems where synergies between stressors exist that management of local conditions could potentially buy us some time in mitigating climate change (e.g. reducing nutrient flows into the marine environment, in Journal of Applied Ecology).

Ph.D. thesis: Mediation of global change by local biotic and abiotic interactions
by Dr Laura Falkenberg.

Throughout my Ph.D., I assessed the conceptual model that while cross-scale abiotic stressors can combine to synergistically favour shifts in marine habitats from kelp forests to mats of turfing algae, management of local conditions can counter this change. My experimental manipulations found broad support for the hypotheses that; 1) cross-scale factors (i.e. local and global) can have interactive effects which increase the probability of expansion of turfs but not kelp and, 2) management of local conditions (e.g. maintaining intact forests, limiting nutrient enrichment) can dampen the effects of global change (e.g. forecasted carbon dioxide). I published the results from my thesis in four papers. In the first, I showed that experimental enrichment of CO2 and nutrients influence the biomass accumulation of turf and kelp differently, with turf responding positively to enrichment of both resources while kelp responded to enrichment of nutrients but not CO2. Given that such direct responses could be mediated by interactions with other taxa, in the second paper I considered a key competitive interaction and revealed that the presence of kelp can inhibit the synergistic positive effect of resource enrichment (i.e. CO2 and nutrients) on their turf competitors. Similarly, in the third paper I highlighted the importance of herbivory by showing that under enriched CO2 conditions rates of this process were increased to counter the expansion of turfs. Finally, in the fourth paper, I considered a scenario in which these biotic controls were absent and identified that where multiple resources had been enriched and prompted a synergistic response (i.e. the expansion of turf where CO2 and nutrients are modified), subsequent reduction of the locally-determined factor alone (i.e. nutrients) substantially slowed further expansion of turf algae, but that the legacy of nutrient enrichment was not entirely eradicated. Together, these results represent progress in ecological tests of hypotheses regarding global climate change as they incorporate comprehensive sets of abiotic and biotic community drivers.

You can access all of Laura’s publications from the University of Adelaide’s digital library, or email her for a copy.

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

Atmospheric CO2 reaches 400 ppm

In May 2013 the National Oceanic and Atmospheric Administration in the USA reported that the atmospheric concentration of CO2 at one of their recording stations topped 400 ppm for the first time. The media surrounding this event seems to have been very much based around the event itself with little comment on what it may mean. I find this moderately disappointing because we can be moderately confident of one thing  – increased CO2 in the atmosphere means that more will dissolve into the ocean, which means an increase in ocean acidification (this is classical chemistry!).

Despite the recent efforts of some of the worlds best scientists, both here in Australia and overseas, we still have an incomplete picture of the likely biological and ecological effects of this ocean acidification. However, we can be fairly certain of two things:

1. Ocean acidification will have negative impacts on organisms which form calcareous structures like the shells of molluscs (see pictures below) and the skeletons of corals; and

2. We are becoming increasingly aware that the increase in CO2 as a resource will cause changes to systems that are dominated by primary producers like seagrass and algae (e.g. kelp), mostly for the worse (for a starting point you could look at my webpage, but contact me for more information if you want!).

Unfortunately, as we enter a time of uncertainty for science funding in Australia, we may not develop a complete understanding of the system-wide effects of ocean acidification until it’s too late.

The growing edge of a juvenile abalone under high atmospheric CO2 (ultra-high magnification). Photo: Owen Burnell

The growing edge of a juvenile abalone under high atmospheric CO2 (ultra-high magnification). Photo: Owen Burnell

The growing edge of a juvenile abalone under normal atmospheric CO2 (ultra-high magnification)

The growing edge of a juvenile abalone under normal atmospheric CO2 (ultra-high magnification)