by Robert Day
The last 40 years have seen unprecedented growth in Homo sapiens's understanding of biological mechanisms. Molecular biology in particular is quickly advancing to the point where life is not so much a mystery, as a series of patented industrial processes. Unfortunately, the impressiveness of this achievement seems marred by science's failure to stem the effects of our concomitant population explosion. As governments world-wide rushed to jump on the lucrative biotechnology band-wagon, financially supporting the study of biological diversity and environmental protection became about as fashionable as a bubbling treasure chest in a reef tank. In view of this, what new tools can science educators use to foster a greater respect for biological diversity and a better understanding of the interdependence of living things ?
Traditionally, biologists of yester-year would receive their training in ivy-clad, stone buildings with lavish, oak interiors. Every dark corner was filled with ancient, gargoylish specimens. Each bottled beast or squashed stem would be tagged with a hand-written label, penned using that indecipherable, italic script that only senior professors can truly master. The characteristic aroma of moth balls hung heavy in the air. Classes consisted of memorizing the names of dead specimens, some of which bore more resemblance to jars of obscure French hors d'oeuvres than to their formerly animated selves. I suspect that this experience, at both the high-school and college level, may have discouraged many potential conservationists. Let's face it; it's hard to feel much empathy for anything floating in a jar of rancid brown fluid.
Today, driven by harsh economic reality and a better understanding of the biochemical similarities between living things, many universities have consolidated or down-sized traditional departments like "Zoology" and "Botany" to make way for the glistening formica, applied research and material rewards of new molecular labs. Undergraduates interested in biology tend to head towards these labs because they want to be employable, and because most perceive the genetic construction of custom organisms as more glamorous than staring into the sad glass eyes of a stuffed animal in a dusty museum. Ironically, this trend has led to a shortage of classically trained taxonomists at the very time they are most needed by science to catalogue and protect what remains of earth's living diversity before it vanishes forever.
As part of a recent review of the undergraduate curriculum, instructors at The Ohio State University began to look for new ways to teach animal taxonomy. From the outset, we had several goals in mind:
1) Because students respond best to visual aids that slither, wiggle, or bite, we wanted to give them the opportunity to observe and identify live animals, rather than dead ones.
2) We wanted to reduce the wear and tear on our preserved specimens, which are becoming increasingly expensive and hard to replace.
3) We felt that contemporary biological education should promote respect for living things and the value of biological diversity in a dynamic ecosystem.
This seems like a formidable list of demands, but we have found that many of them can be met using a carefully managed set of aquaria and terraria. Our collection includes displays that mimic tropical marine, temperate marine, freshwater, bog, leaf litter, and desert habitats. The displays are not large, nor are they especially technically complex, yet they collectively hold many hundreds of animal and protist species, including representatives from all thirteen of the major phyla we cover in our introductory Zoology class. The displays are able to sustain a high level of diversity at minimal cost, despite the year-round onslaught of sampling and examination by multiple classes of up to forty inquisitive students.
To ensure that the displays are used as a fully integrated part of our classes we assembled a simple video system that has proven invaluable to this type of teaching. A video camera with a 6 - 20 x macro zoom lens is used to introduce students to larger specimens. For smaller beasties, we mount the camera on a standard compound microscope. Images are displayed on a high resolution TV monitor and can be recorded on a VCR. This allows a large group to conveniently observe and discuss the details of a particular critter. Even specimens that are relatively infrequent within their displays can usually be located by a trained instructor, observed by the entire class, then quickly returned to their tank. The VCR allows students to review images later at their own pace. Thanks to the falling price of digital technology and color printers, we also have the capability to computer-capture, manipulate and inexpensively print images of our specimens. Students use this technology as a quick, cheap alternative to photography that complements their own sketches and helps them illustrate special projects effectively. The images of specimens appearing in this article were all recorded using this equipment.
Our displays are unlike those of most aquarium hobbyists because their purpose is quite different. To maintain them as practical, educational models of real world ecosystems we have had to unlearn some of the "golden rules" of aquarium science. Drawing inspiration form the work of Walter Adey at the Smithsonian Institute1 and from the ecological implications of the fledgling science known as "complexity"2 we have tried to set up each display to be as natural, physically diverse, ecologically complex and self sufficient as possible. Our displays rely heavily on the activities of the inhabitants to help self-filter and efficiently distribute energy throughout the system. Some use no electric pumps or filters at all and are almost completely maintenance free.
We generally avoid large, expensive vertebrates and ignore mainstream ideas about which animals are "desirable" or "undesirable". Instead we try to find cheap, (better yet, free) hardy species that can stand frequent removal and examination. We favor anything that will breed explosively, colonize rapidly and find a niche where it can establish an independent, reproducing population. Whenever possible, we try to involve students in the collection of specimens from unthreatened field locations using environmentally friendly techniques. We purchase very few live organisms from pet stores. When we do, we aim for common or captive-bred species. We also accept some unwanted specimens from local hobbyists who might otherwise discard them.
Most of our freshwater specimens are common species collected locally from any old pond, pool or puddle within walking distance. In the summer we employ another high-tech collection method called "leaving the windows open", which allows an amazing variety of flying beasties to invite themselves into our displays. Our marine creatures arrive mainly as juvenile hitch-hikers on algae collected during field trips along the coasts of Massachusetts and Florida. This approach saves money, and shows students that a responsible scientist can strive to study life without perpetually depleting natural populations.
Tiny species are welcome; they breed and mature quickly, help improve student microscopy skills and demonstrate that the greatest diversity is found amongst the small invertebrate phyla. (Did you know 95% of all living things are smaller than a ping-pong ball?)
Drab, cryptic species are also fine; they teach students to be patient, observant and to identify partially visible organisms by looking for key taxonomic features. Bristle worms, spaghetti worms, Aiptasia, isopods, amphipods, synaptid sea-cucumbers and other so-called "undesirable", prolific organisms are welcome in our marine tanks. They demonstrate the biology of their taxa perfectly well and our system contains nothing expensive for them to exclude or consume anyway.
Widespread predation ? That's OK too; we use it to realistically show ecological relationships between organisms. We try to include every element of a natural food chain in our tanks and estimate that most of our specimens catch 30-50 % of their food from the system. This makes our specimens behave more naturally, and their healthy diet seems to prevent illness.
Perpetual succession ? Why fight it ? For the most part we allow our tanks to live out continual ecological changes just as the natural environment does. Ongoing subtle changes in the make-up of our communities mean that students will always have something new to find. It also teaches students about the mechanisms that control diversity and occasionally, about the finality of extinction.
Lush plant and algal growth ? Great ! It increases the number of micro-habitats and contributes to invertebrate and protist diversity. It also helps us to inexpensively feed our grazers and filter-feeders. We add generous doses of commercial or home-made trace elements and believe it or not, we actually add nitrates and phosphates to most of our displays in order to maintain rapid photosynthesis. (I can hear you all cringing !) Interestingly, when we test our tank's nitrate / phosphate levels, they are very low, or totally absent. (Now who's crazy ?) We have found that natural filtration by well-lit plants and algae, and by the inhabitants of a generous layer of natural substrate is so effective that we rarely need to bother with water changes.
To give FAMA readers a better idea of the way our displays work, I will briefly showcase just three of them for you.
Our tropical marine system is the flagship, and most complex of our displays. It consists of three interconnected tanks with a total volume of about 200 gallons. The same water circulates around all three tanks, but by varying conditions in each we've been able to generate ecological partitioning such that the total biological diversity is higher than in a single tank of equivalent volume. For filtration we use a protein skimmer with ozone, a trickle filter and a couple of supplemental under-gravel filters. The tanks are illuminated by a mixture of cool white and actinic fluorescent bulbs, and a single 175 watt metal halide. Every other day we add commercial or home-made algal nutrients to encourage the growth of macro-algae, which thrives throughout the system, giving it a somewhat jungle-like appearance. To prevent macro-algae from eventually over-growing everything we occasionally harvest a few handfuls, puree it into an "algal slurpee" then return it to the tanks. (A gesture our filter feeders always seem to appreciate.) Ecologically speaking, management acts like these simulate natural disturbance events (like storms) and help to maintain long term diversity. The inhabitants include at least ten species of crustaceans and seven species of polychaetes, the largest of which, "George the clam worm" has surprised everyone by growing to a length of more than four feet. The system also boasts reproducing representatives from about ten other phyla. We have a few familiar species of donated marine fish, but we are most fond of our Gambusia, which seem quite happy in salt water and reproduce in large numbers. The Gambusia occupy an important niche in our tank's food chain somewhere between microscopic organisms and larger fish. Since we elect to keep no corals which could be damaged by frequent student sampling, the system resembles the diverse ecology of the Florida Keys' shoreline and quiet residential canals rather than a reef.
Our freshwater bog consists of a 35 gallon tank containing a bed of unwashed gravel and flat rocks from a local stream. The rocks are stacked to create a multi-layered arrangement of terraces and separated pools. We have found this type of sub-division within our displays to be a useful diversity-maintaining device, just as physical separation helps to maintain diversity in nature. The tank is lit by a single shop light containing one 40 watt cool white and one 40 watt actinic bulb. A single concealed power-head draws water from the bottom of the tank and distributes it as a gentle cascade over the terraced rocks. The tank contains a lush growth of many different plants, mosses and algae. There is no other filtration and we perform no water changes. The animal community includes newts, frogs, fiddler crabs, crayfish, multiple species of snails, slugs, annelids, insects and planktonic crustaceans. The only fish in the tank are a couple of pudgy cory cats and countless prolific guppies, probably the descendants of feeders that nobody remembers buying. Those of you turning your noses up at the idea of keeping lowly feeder guppies in an aquarium are over-looking that they demonstrate Osteichthyes anatomy admirably; they survive out of water better than most fish and they fit under a microscope.
Our "leaf litter" tank is somewhat of a misnomer, since technically, it started life as a professor's compost heap, transplanted into a twenty-five gallon tank. We have since added more leaves, logs, plant material harvested from other tanks, even half-eaten sandwiches and banana peels left behind by students. The only maintenance required is an occasional sprinkling of fresh water onto the surface. The water percolates downwards until it settles in a bed of coarse gravel supported by an under-gravel plate. By dropping a small PVC pipe down what would be the lift tube, we are able to siphon off this soluble waste-laden water. This tank is a favorite amongst the students since it's easy to take small samples of material and sift through them under a microscope. The tank is populated by a staggering variety of protists, nematodes, annelids, mollusks, insects, centipedes, millipedes, chelicerates and a pair of rarely seen, burrowing salamanders of the genus Ambystoma.
The type of aquaria we maintain at OSU is certainly not for everyone. Some aquarists may even consider them nightmarishly ugly (all that visually impenetrable plant growth, swarms of small, drab beasties and no rare fish). However, beauty is in the eye of the beholder. Natural aquaria are easy to maintain, relatively cheap to run and spectacularly diverse. They quickly earn your respect and fascination by humbling the taxonomic knowledge of even the most experienced aquarist. If you're a hobbyist with limited resources, fascinated by natural ecological interactions, and if you have access to a small area of unthreatened natural habitat as an initial source of diversity, then the natural aquarium is definitely for you. If you are an educator, I heartily recommend this cost effective, active learning tool that gets the students to class early, keeps them late and introduces them to biological principles in a way that text books and preserved specimens alone simply can't match.
References:
1) Adey, W.H., Loveland, K. (1991) Dynamic Aquaria. Academic Press.
2) Waldrop M.M. (1993) Complexity. Simon and Schuster.
