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On marine aquaria

Tuesday, July 22nd, 2008

When I was a youth, I had a fresh-water aquarium.  It was a certain amount of trouble, but not too much.  The fish were attractive, and some of them managed to reproduce, which was a pleasant surprise.  The main reason that it was a tolerable hobby for a young person is that there are plenty of fresh-water plants that can grow, and even take root.  This means that the whole issue of the various interlocking cycles of nutrients–but primarily nitrogen–can stay in pretty good balance.  The basic idea is to keep the fish and the plants in balance–and then be sure to take care of routine maintenance.

At that time, I believed that marine aquaria were harder, much harder.  Partly, most marine organisms have a narrower tolerance for changes in the environment; and partly, it’s harder to establish appropriate plant life to deal with the excreted nitrogen.

During my recent travels, I spent some time with friends who have marine aquaria [not just one, but three!].  I spent lots of time watching.  One of my prejudices is that the marine life other than fish doesn’t get around much.  Wrong!  One tank contains the “exiles”–creatures that are not good company.  Besides the catfish, which seem to be able to eat anything smaller than them, there was a sea urchin.  Silly me, I thought that sea urchins sat in one spot.  Not a chance–every time I passed by, Spike [the sea urchin] was in a different spot in the tank–and I suspect that if I had hung out for a while I could actually have seen him moving. 

In talking to the owners, I found that the difficulties of maintaining a marine aquarium are more challenging than I had imagined.  The nitrogen cycle is crucial, of course, but the limited range of tolerance of the life can mean that you can wake up and everything is dead.  Ugh.  One factor can be the complicated way in which the processing changes with the day/night cycle.  In this case, they finally found a way to cycle the water from the tank into another holding area that is full of algae.  There, the light is on at night, when it’s dark in the main tank–so the algae are processing the nitrogen while the fish sleep.  And, ultimately, one way to remove nitrogen from the tank is to scoop up a handful of algae an get rid of it.

On top of the biochemistry, there is also sociology–it turns out that lots of the creatures that one might want to have do not “play well with others”.  In some cases, they take it to the extreme of eating them–that’s why Spike ended up in the exile tank.  In my fresh-water aquarium, I was dealing with only fish and plants–and maybe a snail or two–it was easy enough to get good advice about what fish did well in a “community tank”.   But in a marine tank, we might want a whole variety of phyla–corals, starfish and sea urchins, molluscs, crustaceans–in addition to fish.  And even the fish can be quite aggressive toward one another.  There was a guide to the various creatures that pointed out these problems; oh, and one other–some marine creatures can be fatal to humans. [The guide gives the example of the blue-ringed octopus, for which there is no anti-venin available.  They do say not to try to keep one; but I imagine that there are people crazy enough to think that they can manage it.]

Seeing the care that’s necessary in the microcosm got me thinking again about the extent to which the ocean out there needs me to be more careful–and needs me to encourage my government not to underestimate the ways in which humans can disrupt an ecosystem that we can’t do without.