Ocean ecosystems could take millennia to recover from climate change

The ecosystems of the world’s Ocean’s are in trouble. Recent reports have documented the impacts overfishing, the decline of apex predators and the buildup of plastic as well as other pollution. Ocean ecosystems are also being threatened by climate change and, according to a new study, it may take thousands of years for marine life to recover.

The study, led by Sarah Moffitt, a scientist from UC Davis Bodega Marine Laboratory and Coastal and Marine Sciences Institute, appears online in the Early Edition of the journal Proceedings of the National Academy of Sciences (PNAS).

It is the first to fully record the disturbance and recovery of a sea floor ecosystem following rapid climate change and the results show that sea floor recovery is measured in thousand year scales and not 100 year scales.

Moffitt and her colleagues used a sediment core gathered off the coast of Santa Barbara, California to analyze the impact of the last significant period of deglaciation.

That period, like this one, featured an abrupt warming of the climate, expansion of low oxygen zones in the oceans and melting polar ice caps.

In total, Moffitt looked at fossils from more than 5,400 invertebrates that lived bowed 3,400 and 16,100 years ago.

“After the initial sampling at sea, I took the entire core, which was about 30 feet long. I cut it up like a cake, and I sampled the whole thing. Because of that, I had the whole record,” said Moffitt in a statement.

Previous studies, showing more rapid recovery of ocean ecosystems, focused primarily on foraminifera, single celled organisms, rather than multicellular life.

Moffitt, whose background is in marine ecology, found abundant and diverse ecosystems at the start of the deglaciation period. The following warming and loss of oxygen however was accompanied by a rapid decline in those ecosystems to the point where the fossils nearly disappeared entirely for a time. The study concluded that a decrease in oxygen levels of between 0.5 and 1.5 mL/L could result in a major restructuring of seafloor communities.

“These past events show us how sensitive ecosystems are to changes in Earth’s climate — it commits us to thousands of years of recovery. It shows us what we’re doing now is a long-term shift — there’s not a recovery we have to look forward to in my lifetime or my grandchildren’s lifetime. It’s a gritty reality we need to face as scientists and people who care about the natural world and who make decisions about the natural world,” said Moffitt.

The dangers noted by Moffitt will no doubt be compounded by other stresses being placed on ocean ecosystems.

A study released in February showed that, in 2010, more than eight million tons of plastic trash found its way into the world’s oceans, with much of it ending up in the sea floor communities that Moffitt was studying. Eight million tons of plastic is the equivalent of five grocery bags of plastic trash for every foot of coastline in the world.

Another study, released in 2006, showed that the oceans may be devoid of seafood by 2048 due to overfishing and many of the ocean’s top predators, such as sharks, appear to be leading the decline.

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