The Ucluelet Aquarium operates on an unfiltered, open system that pumps in water directly from the harbour. Because the water is unfiltered, we have plankton from the harbour water flowing directly into our tanks. This means that we don’t have to feed any of our plankton eaters, but it also means that we are constantly cleaning our tanks of unwanted growth. Our waters are teeming with life, most of which is too small for us to see. Given time, this microscopic plankton might grow into organisms that are more familiar to west coast beachcombers. This concept sparked our idea for the “Empty Tank” whereby we leave a tank empty with only water from our pumps flowing into it, don’t clean it and then see what settles inside. Its’ been just over two months now since we started, and in that time we’ve seen everything from hydroids to fish come through the pipes to make a home in the now “not so empty” tank. Colonizers include: hydroids, bryozoans, barnacles, mussels, tunicates, nudibranchs, a variety of other unidentifiable life forms, and most recently, crab larvae.
The Empty Tank isn’t the only tank that contains creatures sucked in through the pipes. Last week we replaced the sand substrate in our Orange Sea Pen tank and found that about 750 Soft-Shelled clams and Nuttall’s cockles had settled within. These clams would have arrived into the tank via the pipes as larvae, and then grown to about an inch in a three month time span. There were so many clams embedded in the sand that they began to compete with the Orange Sea Pens for space.
In nature, planktonic larvae use a variety of factors to determine which areas are good to settle and grow depending on suitable substrate, food availability, predator abundance etc. Some are more picky then others, but with the variety of habitats in all of our tanks, larvae are bound to find the real-estate they like.