Aquariums as Ballast Holds

Humans and their seafaring activities have literally turned the composition of marine fauna in many areas of the world on its head.

There are a fascinating couple of chapters in Alan Burdick’s book Out of Eden: An Odyssey of Ecological Invasion (Farrar, Straus and Giroux, New York, 2005), where Burdick spends time hanging out with marine biologists, particularly James Carlton, as they study the marine invertebrate fauna of San Francisco Bay.

Carlton is a world-renowned specialist in marine ecological invasions. In a 1995 field report he coauthored (Carlton and Cohen), 212 exotic species were found in San Francisco Bay. As quoted in Out of Eden, Carlton says, “Anywhere in the marine environment, we may seriously underestimate the number of invasions because we simply don’t know about all the tiny stuff: the worms, the protozoans, the filamentous algae, the diatoms and dinoflagellates – there are literally hundreds of species. We say there are 212 introduced species in San Francisco Bay. There could be 400 or 500.”

How did all of these marine invertebrates come to reside in San Francisco Bay? Especially given that the majority of marine invertebrates are too frail to handle moving from coastal zones to open ocean zones of higher salinities. Likewise, many invertebrate species have very short life cycles, not nearly long enough to drift across wide expanses of ocean.

The answer is that humans and their seafaring activities have literally turned the composition of marine fauna in many areas of the world on its head. Carlton has been able to prove that much of the nonnative fauna found in the world’s estuarine areas is the result of ballast water dumping by large private and commercial ships.

Ships have entered San Francisco Bay through the Golden Gate since before the Gold Rush days of the 1850s. Early wooden-hull sailing ships brought plenty of invertebrate hitchhikers that either bored into or glued onto the outside of these ships’ hulls. Modern ships travel much faster and many organisms are swept clean of ocean-going ships before they ever reach their destinations. Modern shipping has also seen the widespread usage of anti-fouling paints that act as pesticides against undesirable marine hitchhikers.

The bigger problem is ballast. In the days of sailing ships, empty cargo holds were filled with dry ballast – rocks, sand, etc. – so that ships didn’t ride high as they traversed the open ocean. But with the advent of large, modern steel-hulled container ships, dry ballast became impractical and was replaced by quicker, easier and less expensive seawater ballast. Modern container ships pump thousands of gallons of ballast water from their harbors of origin and then flush this same ballast water into destination harbors and bays (legislation is starting to require ballast exchanges out at sea, as well as sanitization of ballast water). Obviously, more than seawater is sucked up into the ballast holds of these colossal ships (some modern oil tankers are five football fields long).The incredible speed of modern shipping combined with the lower salinities of the ballast water they transport allows adult and larval forms of many organisms to make trans-oceanic voyages that would otherwise be impossible on their own steam.

In 1989 Carlton secured a couple of containers of ballast water from a Japanese container ship off the coast of Oregon. He took it back to his laboratory and found 50 different species of marine organisms – not a one native to Oregon coastal waters. Carlton found nonnative crabs, shrimp, barnacles, mussels, clams, diatoms and dinoflagellates. And while Carlton undoubtedly safely disposed of his two buckets, the same cannot be said for the Japanese container ship or all of the subsequent container ships to arrive in Oregon since 1989.

Burdick writes in Out of Eden, “Scientists have concluded that ballast water release has been a vector of marine organism invasions since at least 1910, when the Chinese mitten crab suddenly appeared in Germany. Carlton believes that the rate of ballast-water introductions has increased in the past two decades, mainly due to the rate of global trade doubling every seven years for the past several decades; some 80 percent of which is conducted by ship. On any given day, 35,000 commercial and private ships are in motion, carrying – and dumping – billions of gallons of ballast water.”

Implications for the Hobby
So what does the ballast water of commercial shipping concerns have to do with your 55-gallon saltwater setup or your 30-gallon freshwater planted tank? Well, when you think about it, our aquariums are really just ballast holds in miniature.

We may start with aged tap water and add marine salt (if we are setting up a saltwater setup), but then we add all kinds of other things, such as Florida or Fiji live rock (it’s called live rock because its swarming with all kinds of minute critters, including some hitchhikers like mantis shrimp that can decimate the “native” fauna in our tanks); fishes, corals and other invertebrates, often from completely different parts of the globe; we add marine algae; nuisance algae often finds its way into our systems; we add all kinds of live foods, such as rotifers, brine shrimp nauplii, zooplankton, phytoplankton, copepods, etc.; we incorporate aquatic plants from all over into the décor of our freshwater planted tanks and aquatic snail eggs often come attached with some of these plants.

The problem, just like when a large ship jettisons its seawater ballast, comes when we need to do water changes. Do we simply pour the buckets of fouled tank water into the gutters outside our homes that drain directly to the ocean or a local inland waterway, or do we properly dispose of aged tank water and old live rock, for that matter, correctly? Our old tank water can be poured on a rock garden and then percolate down through the soil with little consequences to the environment. Soil is an amazing cleaning agent and breaks down a lot of stuff.

Most of what we keep wouldn’t be able to survive in North American fresh or marine waters, but it only takes one “super invasive” to give the hobby a black eye, with the negative PR and pending legislation that would inevitably follow should the hobby be found liable.

Most invasive aquatic organisms either do not survive, or they initially proliferate, are checked and fill a niche, eventually settling into a new marine fauna mosaic. Some such as the zebra mussel (freshwater species that can tolerate brackish or estuarine conditions) find a new environment with even better conditions (no zebra mussel predators) than from where they came from, and these “super invasives” quickly overwhelm their “adopted” homes, with dire consequences for native fishes, invertebrates and even humans (decimated fisheries, for example).

The zebra mussel (Dreissena polymorpha) first showed up in one of the Great Lakes in 1985 or 1986, the result of a ballast water dump by a ship originating from either Europe or the Black Sea. In the 20 plus years since the zebra mussel first entered North American waters, it has expanded its range to almost one third of the country. Zebra mussels pack themselves so densely on every available surface that they leave no place for native freshwater mussels to reside. The will even cover the tops of native clams so densely that the clams can’t open their shells to feed or breed; they can’t even move about due to the weight of zebra mussels on them.

Ballast water dumps have introduced species of dinoflagellates into areas where they weren’t formerly found. Carlton believes that some of these invasive dinoflagellate species may be responsible for the red tides that began occurring with frightening frequency in the 1970s.

As far as the hobby is concerned, it has been mentioned as a possible vector for the Caulerpa outbreak in California, for northern snakehead (Channa argus) releases in the Mid-Atlantic states, for Pterois volitans appearing off the southeastern coast of the United States and for many others. Never release anything into our native waters. It is better to humanely freeze anything you can no longer keep. And dispose of all those “tiny things” in your dirty tank water by draining the old tank water onto a rock garden or patch of naked earth, but never directly into a storm drain.

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