A recent study by Dr Bryony Caswell, from the University of Liverpool’s School of Environmental Sciences, in collaboration with Dr Angela Coe, from the Open University, has found similarities in the declining size of ocean clams to those of clams that lived some 183 million years ago.

The beginning of the Jurassic period  was a time which, like today, underwent similar levels of climate change and yorkshire_coast_walk_seasimilarly decreasing levels of oxygen in the oceans.

The study took place in Whitby, on the Yorkshire Coast and over 36,000 clams were examined. It was found that the size of the 183 million year old clams shrank in line with the diminishing levels of oxygen in the waters.

Decreasing levels of oxygen in the water effects the chemistry of the ocean, this in turn then controls the levels of algae present, and consequently changes the whole food chain and biodiversity in the seas.  Areas of ocean with low levels of oxygen are deemed to be ‘dead zones’ and currently 7% of the world’s waters are classified as such. This figure has increased rapidly over the last 50 years, with high pollution levels and rapid climate change taking the blame.

During the period of the Jurassic studied by the researchers, many species became extinct, and some flourished. The Pseudomytiloides dubius clam, alive during this period, was one such lucky flourisher- being small in size, reaching sexual maturity rapidly and reproducing on a large scale- it had the traits necessary to see out such climatic turbulence. As similar pattern can be observed in areas of ocean with low levels of oxygen in the modern day coot clam.

The implications of this study are severe. Currently 14% of the animal protein in the human diet comes from the sea. With other recent studies of oxygen levels in the oceans projecting a decrease of 25% in the mean size of individual animals by 2050, this does not bode well for an ever increasing global population.

Dr Caswell comments on the study: “By examining changes in the oceans that happened millions of years ago we are able to piece together more of the picture of what is likely to happen in our own time as a result of declining oxygen levels.”

“Unfortunately, our research has shown that if ocean oxygen levels continue to decline, within the next few decades to centuries, it is likely that marine molluscs and possibly other seafloor animals will be smaller and there will be fewer species.  This reduction in body-size and biodiversity has profound implications for the animals in our seas and the people who rely on them for food.”

The full published report can be found in December’s Geology.