Losing Nemo: The Ticking Clock on Marine Defaunation

By Rachel Stoddard, Biology, 2017

It is no secret to mankind that humans negatively impact many animals and species. Our history has been fraught with instances of human-caused extinctions, with some studies putting the first extinction as early as 132,000 years ago. However, the focus in these conversations has always been centered on terrestrial fauna. The vastness of the ocean and the relatively low direct contact with humans established the belief that human activity had little to no impact on the oceans. In the past few decades, however, more and more evidence has piled up showing that humans are in fact disturbing marine ecosystems.

This past January, leading marine scientists from several institutions, including University of California Santa Barbara, Rutgers University, and University of Washington, collaborated on a comprehensive review of current marine defaunation. Their research found that in the past 514 years, there have been only 15 marine animal extinctions, in comparison to the 514 terrestrial animal extinctions. While this may initially appear encouraging, their deeper analysis of marine populations and ecosystems showed cause for deep concern about the fate of the ocean.

The ocean has less endemism than terrestrial environments — meaning that it is more rare to find marine species with only one small, specific habitat. While lower rates of endemism may contribute to the lower rates of species-wide extinction in the oceans, further analysis showed that local extinction was very common in marine fauna, with up to 90 percent of pelagic fish, those that humans are most likely to come across, experiencing range contractions. Analyses also showed that ecological extinction and commercial extinction was also on the horizon for many marine species if human activity continues in the same direction. To make matters worse, habitat loss in the ocean is steadily increasing from the overabundance of nutrients in the water — also known as eutrophication — primarily from agricultural run-off, seabed mining, port traffic and many other factors that are contracting the area of the ocean that can be safely occupied by marine life.

As of right now, marine animals are facing extinction rates comparable to terrestrial defaunation rates pre-industrial revolution, which is considered by many to be the starting point of significant human-caused environmental change. Scientists now fear that history is on the brink of repeating itself in the marine sphere. Even worse, marine habitats provide especially difficult challenges for conservationists as they are harder to access and protect. The mobility of marine animals also makes marine management a more complex task.

Despite the clear pattern of marine defaunation, the authors of the study found many reasons to be hopeful. Marine animals are still far better off than those on land, and there is still a chance to avoid the total decimation that is currently being experienced in terrestrial fauna. Conscientiousness in the next few decades in our marine management could mean the difference between marine animals thriving or facing mass extinction.

The Royal Society of Publishing (2014). DOI: 10.1098/rspb.2013.3254.

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