What’s in a little noise?

Different sources of noise in the marine environment. Image source: http://www.marineinsight.com/marine/environment/effects-of-noise-pollution-from-ships-on-marine-life/

Everyone has seen some sort of human impact in the ocean, from plastic washed up on the beach, to a plankton bloom driven by nutrient pollution, possibly even something as confronting as a fish kill (or even dolphins!). But what about the things you can’t see, say some noise?

Marine noise pollution has again become topical in South Australia, with the announcement that seismic surveys in the waters south and west of Kangaroo Island will begin in 2015. But this raises the question, what do we know about the effects of seismic surveys? The answer is…. not much. There is obviously immense community concern, and I was lucky enough to talk about it on ABC radio today.

For those of you who don’t know, the most common method of seismic surveys in marine waters is to use an array of air guns that are towed below the surface (at say, 8 m depth) behind a ship, firing in a sequence at intervals from seconds to minutes. The sound that is reflected back is then analysed to tell you what is on and under the sea floor, important information if you’re looking to extract resources. These surveys can span hundreds of square kilometres and run for months.

There is some literature on the effect of these surveys, but woefully little, and none in this region. The little information that we do have suggests that the effects will be variable, depending on taxa. Whales and dolphins seem to alter the way they communicate and potentially migration routes or residency patterns, at least in the short term, which is concerning because of the seasonal Blue Whale and Southern Right Whale populations in this region. Fish may become stressed and migrate away from the testing area, which includes important fisheries for species such as the Southern Bluefin Tuna. In contrast, it seems that at least some invertebrates may not be affected. I would reiterate, however, that the evidence in either direction is extremely sparse, which concerns me because this region (South Australia) is a global hotspot for species diversity and endemism.

This is where the discussion collides with another topical issue in Australia – how much information do we need to properly assess applications to develop marine resources, and which activities should we allow in our marine (and terrestrial) environments in the name of “progress”? Although some development and an increase in productivity is good, there is more and more support from the scientific community to make sure we don’t damage our environment beyond repair. I won’t go into detail on this, however, as others have written about this topic in much more depth. But, I note that other countries are taking the issue of marine noise seriously, and discussing it, so why aren’t we?

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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!

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

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.

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