Thursday, April 2, 2015

Ocean Acidification on the South Coast: Nature at Bat

March 23, 2015, ran in early April, 2015

Understanding ocean acidification is not simple, because the process of acidification is not simple. Neither is the rest of nature simple. Nature is more complex that we can imagine. We can over-harvest, mine, bomb, poison, pave and otherwise mess up this great world, do our very best to destroy the ecology that supports our lives, and yet, nature bats last.

There’s some predictability: If we pump greenhouse-warming gases into the atmosphere, the atmosphere will warm up. We are doing this. It is warming. Those gases are absorbed by water all over the world, because the balance of gases in the atmosphere is reflected by the balance of absorbed gases in the water. It’s a slow process, because there is a lot of water, which can hold a lot of carbonic acid and heat. That slow time lag between absorption and response has tricked many into thinking that what we do doesn’t matter to the global ecology.

Then there are down-welling and up-welling areas. There are areas of the oceans where cold salty water accumulates and drops down into the depths. Called ‘down-welling’ areas, these occur in the north Pacific, north Atlantic, south Indian Ocean and around Antarctica. Bottom flowing currents move the cold, salty water across the seafloor towards continents, where this water rises to the surface, called ‘upwellings’. There are upwelling areas all around the world. Some run all the time, others only with winds from certain directions. In the Pacific Northwest, upwelling usually occurs when winds are from the northwest in sunny, dry weather.

Upwelling in action:  Fog forms over cold water, comes ashore over the beaches, and dissipates over warmer land. On the horizon, blue water indicates the water there is warmer, not upwelled. This aerial is looking north over Ft Stevens across the Columbia Entrance to Cape Disappointment.  Photo by Kathleen Sayce
A summer day with active upwelling here on the South Coast is foggy with northwest winds. It’s sunny inland, it might even be sunny on Willapa Bay, but on the ocean beach it’s foggy. The fog is created when cold, old, very salty ocean water comes to the surface and cools the air. Onshore winds push the cold air onshore one, two, five, ten or twenty miles.

In the water, something more complex is going on when the acidic upwelled water reaches the surface. This water is typically thirty to fifty years old, and can be much older. It’s very salty. It’s high in some nutrients, and low in oxygen. As upwelled water rises to the surface, nutrients are taken up by phytoplankton that live only as deep as sunlight can penetrate into the water––usually less than fifty feet. Phytoplankton grow quickly in summer, tiny single-celled plants that can divide several times a day under good conditions. Those old nutrients are food for the phytoplankton.

Zooplankton can’t keep pace with the growth of plants. Not all phytoplankton cells are eaten, and when the excess cells die, they fall to the seafloor and decompose. This strips oxygen from the water column and seafloor, killing those animals that need oxygen to survive. Their bodies also decompose. More oxygen is tied up in each new wave of decomposition, forming a dead zone of low to no oxygen that expands as summer progresses.

A large dead zones appears each summer along the Pacific Northwest Coast; this year it persisted through winter. It typically extends from south Vancouver Island to northern California. Affected animals include crab, clams, fish, zooplankton, and more. Some fungi and bacteria thrive in low oxygen conditions, and they flourish in this dead zone, growing into huge carpets of mixed species––all thriving on no oxygen and high nutrients.

The second complexity is that this water is more acidic than it was a few hundred or even a few thousand years ago. Remember, what goes into the atmosphere is absorbed into water. With increasing amounts of carbon dioxide in the atmosphere, then in the water there is more and more carbonic acid, increasing the acidity of seawater.

The third complexity is that this cold, old upwelled water is low in calcium, and the local rivers are also low in calcium. For mollusks, calcium is essential to form shells. It also goes into solution (dissolves) easily in more acidic water, and as we have learned in the past ten years, more acidic water is not good for oysters and other bivalve larvae.

There’s always a weak point, a stage in a life cycle when each organism is most vulnerable to what appear to be tiny insignificant changes. For shellfish, this is as larvae, as they undertake the change from the free-swimming form to the shelled form, prior to settling down to become adults. At this stage, oysters and other bivalves grow their proto-shells. But in more and more acidic water, larvae can’t maintain shells, because the calcium dissolves out as fast as shell forms. The larvae linger for days to weeks, trying to make the change. Eventually they die.

But wait, you say, isn’t there deep, cold, low acid water off Hawaii? Hasn’t at least one oyster grower got a hatchery there, safe from the upwelled water? Yes. But oysters are not dominant species of food webs in the oceans of the world. Coccolithophores are a key animal, tiny calcium-shelled zooplankton that eat phytoplankton, and in turn are eaten by larger zooplankton and fish, which are eaten by larger fish, and on up the food web. Take coccolithophores out, and oceanic food webs aren’t just on a diet, they collapse. Fish populations go down; larger fish, birds and mammals that live on them are impacted too. Fishing fleets. Tribes. Food processors. Sport fishers. Oceanside restaurants selling fish and chips. Anyone who eats, catches, processes, and sells saltwater fish is affected.

So there you have it, a quick look at the complexity of ocean water chemistry, and the complexity of the ocean food web, and a hint at the coming changes in ocean ecology. There’s nature, standing near the plate, swinging the bat to warm up. She’s thinking about what she’ll do this time. She might bunt, and take out some nearshore ecosystems in a few key areas. Leave some other spots alone. Or swing for the fence, and crash major cocolith’ populations, along with sardines, anchovy and herring. If that happens, tuna, salmon, and other major fish populations go too, as these fishes are their key food sources. We simply don’t know what nature’s going to do in response to our plays, this time, or next time. We will have all the innings we can manage to stay in the game, but nature bats last. 

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