We have damaged our oceans so comprehensively that most of us would struggle to wrap our heads around it. Big, heavy trawls have clear-felled three-dimensional habitats that took thousands of years to build, leaving only rubble. These were the nurseries for next year’s fish. Mechanized trawling has enabled us to take vast quantities of fish, not only for our plates, but also for fish oil, farm fertilizer, aquaculture feed, and many other uses. And we have indeed taken vast quantities… in many cases, now as we look back, too many for the ocean to replenish. The United Nations has declared that 77% of fish stocks for which we have data are fully exploited or overexploited.
Warming water might seem like a nice thing for those of us who enjoy the ocean, but for fish and other species that need oxygen, it’s a death sentence. Warmer water holds less oxygen than cooler water. Even one little degree can add up when each breath becomes just a little bit harder and takes just a little bit more energy. So as heavy breathers like fish and crustaceans struggle, low breathers like jellyfish have the advantage.
So too, pesticides, herbicides, biocides, DDTs, PCBs, dioxins, gender benders, heavy metals, and thousands of other chemicals are discharged by factories and hospitals and you and me, making their way into the oceans… and god only knows what effect these have on different species. Plastics blow and flow their way into the ocean – where they never break down, they simply break apart into smaller and smaller pieces – and they have become essentially a sixth food group for just about any animal looking for easy prey. Plastic acts like a toxic bullet, with the surface concentrating toxins up to one million times that of the surrounding seawater, and even in the stomach, it never breaks down, it merely prevents hunger signals and the animal dies of starvation with a gut full of plastic.
And day after day after day of urban discharge – for decades – has turned coastal waters into dead zones, where a cycle of too many nutrients leads to too many phytoplankton, which leads to too many zooplankton, and all of these things dying uneaten leads to not enough oxygen, and the only winners, it seems, are jellyfish and toxic algal blooms.
And if all that’s not enough, the oceans are becoming corrosive by absorbing the staggering amounts of carbon dioxide that we discharge into the atmosphere. We are only just beginning to understand the full impact of this reduction in pH. Creatures with shells and skeletons find it harder to make new shell and repair damaged parts, while simultaneously their existing shell disintegrates away in a process similar to osteoporosis. And metabolic processes that rely on pH cues, like spawning and growth, get discombobulated with even very slight changes.
These three trophy photos taken in the Florida Keys, USA, in the 1950s (top), 1970s (bottom left), and 1990s (bottom right) tell the story of the impact of fishing on local ecosystems. Not only has the size of the fish taken become smaller over time, but the whole community has shifted from large resident fish to smaller transitory fish. (images from the collection of the Monroe County Library)
We are all aware of these stressors, some more so and others less so. But while we tend to see them individually, in truth they act on ecosystems all at the same time and often synergistically, such that the whole is often greater than the sum of the parts. And as these stressors cause disruption to normal ecosystem function, ecosystems reshuffle. There are winners and losers.
In part 1 of The Rise of Slime: Jellyfish Behaving Badly, we explored the observation that jellyfish blooms appear to be on the increase, and that this is not in our best interest. The ocean is our life support system. We get our food and our oxygen here, it buffers the effects of climate change, and it supports our commercial and industrial activities and inspires our artistic endeavors.
In some cases we’ve been looking the other way as our ecosystems falter, but more often than not, we simply look on in astonishment. Our notion of the ocean as vast and its bounty unlimited is grandfathered in from an age long ago, long before mechanized trawling and dead zones and plastics. Our ability to strip the oceans has outpaced our ability to comprehend its impact.
When I say “impact” most of us still think of this as impact on the ocean. We still don’t instinctively “get” that this means “impact on us”.
Check out the third installment of Lisa-ann Gershwin’s series Rise of Slime next week!
Lisa-ann Gershwin is the Director of the Australian Marine Stinger Advisory Services, and is now with CSIRO Marine and Atmospheric Research in Australia. Her most recent book is Stung! On Jellyfish Blooms and the Future of the Ocean published by the University of Chicago Press.
The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.