Archive for October, 2012

Tatoosh and Ocean Acidification

Wednesday, October 31st, 2012

Long-term studies are rare – the costs in time, effort, enthusiasm, persistence and funding are all formidable. But they are as valuable as they are rare.

One such study, stretching back five decades, is the research on the intertidal community of Tatoosh island, off the northwestern-most point of Washington State, at the mouth of the Strait of Juan de Fuca. Like other long-term studies it has depended on the initial and long-term research of a particular scientist and then his graduate students, and then theirs. In this case Robert Paine started the work, Timothy Wootton and Catherine Pfister are among his graduates students, and their graduate students continue to work with them on the island.

Tatoosh Island from the air – an old lighthouse, some steep cliffs, a few trees, and an extensive and accessible intertidal studied intensely since the 1960s (pbase.com)

The research on Tatoosh has given us insights into how predation and competition structure a community of species, including the concept of keystone species. Recently it has also provided critical evidence of current ocean acidification and correlated changes in the intertidal community.

Because the community has been so well studied for so long, changes in distribution, occurrence and sizes of individuals within populations are possible to recognize when they occur. For more than a decade now Pfister and Wootton have also measured ocean pH levels in great detail. What they are seeing is very troubling.

The intertidal of Tatoosh Island. Cape Flaherty on the Washington mainland is in the background (esa.org)

Concerning ocean pH, they have found that there is considerable diurnal and seasonal variation, a result of variation in sunlight (photosynthesis), darkness (respiration), temperature, phytoplankton abundance, and upwelling of the coastal waters, all of which modify CO2 levels, and hence pH, of the water. This in itself is really interesting, for the extent of the variation is certainly unexpected.

But they also have found a declining trend in ocean pH levels over the eight years of the initial study – 2000-2007. Allowing for the various sources of CO2 variation, and applying some sophisticated statistical tests, they have concluded that the decline in pH is correlated only with increased levels of atmospheric CO2.

In fact, pH dropped 0.045 units over the 8 years, 2.5 times faster than simulation models had predicted. Not good news, but good data, and the first of its kind outside of the tropics.

Species with calcareous shells or skeletons are particularly vulnerable to erosion as ocean pH drops. Over the same time period, several well-studied intertidal species with calcareous shells or skeletons – two species of mussels, and goose barnacles – declined in abundance and mean size, while non-calcareous algae increased in abundance.

Blue mussels Mytilus californianus have declined in abundance and size in the past decade, correlated with the decline in ocean pH (eeb.ucsc.edu)

Why the drop in pH is so great remains unexplained, but further research has addressed the question of whether such a drop in pH is just natural variation, or whether it is new. Mussel shells can last a long time after the animal inside dies, and their age can be determined. They also carry in them a record of the pH of the water they formed in. They provide an extraordinary record to compare with the present changes, dating back not just to the 1960s but as much as 1340 years ago to the middens left by the Makah who fished from the island in summer.

Shells of the intertidal shield limpet, Lottia pelta, though more difficult to analyse, confirm what the mussel shells have shown (wsu.edu)

And the conclusions? For the past decade the ocean waters around Tatoosh are acidifying at a rate faster than predicted. Nothing like this has occurred in the past 1300 years. We clearly don’t know enough yet about the causes, but the only strong correlation is with increased atmospheric CO2.

With the long-term studies of Tatoosh, we have a chance to detect such changes in water chemistry and community structure, and predict their occurrence elsewhere. That’s good science.

Meanwhile, we are warned once again. The emerging new world is going to look a lot different.

Populations of sea birds – murres and gulls – nesting on the cliffs of Tatoosh have also declined by 50% over the past decade (nytimes.com)

Measuring Ocean Health

Tuesday, October 16th, 2012

On a scale of one to 100, the health of the oceans has been given a 60.

We now have an index of ocean health for coastal waters – both global and national. Published in Nature in August, and the result of a huge amount of analysis by a large number of people, it has received a lot of generally favorable press attention. It is intended to be a measure of sustainability, representing benefits that a healthy ocean can provide to people.

The global index of 60 is the area-weighted average score of 10 goals. A comparable graph has been constructed for each of the 171 countries and associated territories that have any coastline at all (oceanhealthindex.org).

The website associated with the Index is excellent. It lets you explore the scores of each country goal by goal, with some detail on what the scores mean actually mean. It’s worth a visit just to see the graphics. If you want to see all the goals for all the countries on a single table, then you’ll need to go to the supplementary material published with the Nature article.

The index for countries ranges from 36 (Sierra Leone) to 73 (Germany and the Seychelles). For the US it is 63, for Canada 70.

The Seychelles, with the highest index (driversforce.ca)

At first blush, this all seems to make some sort of intuitive sense.

But what does it really mean? Unless we have confidence in the choice of goals and the methods of measuring them, the value of the Index may be very limited.

There are some goals (Natural Products, Carbon Storage and Coastal Protection, for example) that look particularly useful – they are based on reliable data and not too many assumptions, and result in a decent spread in scores.

But in contrast, there are two examples (the Mariculture half of the Food Provision goal, and Tourism) where 90% of the world get scores far too close to zero, while a very few countries get around 100. Both goals are important to include, but they clearly need better ways to measure them. Including them at this stage undermines the validity of the Index.

The scores for Fisheries (the other part of the Food Provision goal) are worrisome for a different reason, for they can be difficult to interpret. Generally the scores are all quite low, which seems reasonable. But here a low score can mean either that overfishing has been extensive, or instead that fish are not being harvested up to sustainable limits.

Both the authors and the reviewers agree that this is a first cut that will be improved as more data are gathered. However, if the scores for a few of the goals are unreliable or ambiguous, then the Index is unreliable. And certainly reducing it all to a single number for the world, or even per country, becomes increasingly meaningless.

But I think there is a greater problem with the Index, one that is fixable.

How can we try to compare Barbados with Japan, or the Seychelles with Germany? We can’t, and we shouldn’t. Yet, if you look at the global distribution of index scores, some obvious patterns pop out. For instance, the countries with the lowest index scores are clustered along west Africa. (Map from oceanhealthindex.org)

If you then look at a global map of the 64 Large Marine Ecosystems that have been identified, covering all of the world’s coasts, those countries all share a single Large marine Ecosystem: the Guinea Current, LME #28. That does make sense – it ties the countries and their coastal problems together in a meaningful way.

The Large Marine Ecosystem: The Guinea Current (lme.noaa.gov)

So why not use the index to assess and compare LME’s instead of countries? We would then, for instance, be able to compare the Caribbean LME with the Mediterranean or any other LME, and not have to break it into many small island pieces, or alternatively have to compare it with the entire coastline of Canada or Russia. Comparisons become far more defensible.

This would encourage countries that share an LME to work together to make it more sustainable. In fact, most have agreed for years that the LME approach is the best way to go. The Index could and should provide strong evidence to support this.

So let’s get this right. The Index has great potential, but not in its current form. Its value is in its details, and in its use in guiding us on how to improve the health of LMEs, not in ranking and scoring individual countries.

The current global score of 60 tells us nothing.