Keystone Species in Our Aquariums by Aquariumpros.com staff

Keystone Species in Our Aquariums

by Aquariumpros.com staff
Reprinted with permission
http://www.aquariumpros.com/company
Aquarticles

Introduction:
The purpose of this article is to provide a brief lesson in a topic in the science of ecology, in order to illustrate one aspect of how our hobby may have a negative influence on the environment. This may make some readers uncomfortable, and so it should. However, there are recent studies which indicate that current practices in the collection of marine fish for the aquarium trade, may be one factor contributing to the gradual destruction of coral reefs around the world.

To some, denial comes easy, making understanding harder to attain. As our business name suggests, we are "Aquarium Professionals," and the aquarium industry is how we make a living. As such, it would be irresponsible of us to deny any negative aspect of our industry, real or imagined. Issues like this require closer self-examination, introspect and understanding in order to find the truth. Only by doing so, can we hope to preserve the industry from which we derive our income. To ignore such issues, or pretending they don't exist, will eventually lead to the creation of regulations and laws which may severely limit the living resources we love and enjoy in our aquariums. Most of the people who lobby for and create these laws, may not share our love of this hobby. They may also lack our unique understanding of the how our hobby makes important contributions to society and to science.

Definitions:
Without getting into a complete discourse on biotope or habitat ecology, which is beyond the scope of this article, we will discuss one principle of ecology for the purposes of illustrating the cause and effect of changes to species population, particularly as it relates to the aquarium trade: This is the principle of a "keystone species."

While the precise definition of keystone species is a matter of controversy amongst ecologists, we feel that these debates over definitions are not as important as simply accepting the fact that there are species whose very existence influences and even controls the existence of more than one other species. Some ecologists believe that only predators are keystone species.

We disagree, and accept the definition given by Power, et al. 1996, who state that a "broader definition of a keystone species" is: " . . . those species whose existence have an effect on an ecosystem that is large, and disproportionately large, relative to its population within that ecosystem (in contrast to "dominant species", which are large populations of species in a given ecosystem)." A simpler definition might be: Species populations which play crucial roles in an ecosystem community, and whose removal would have a profound effect on the composition, structure and functioning of that community.

Importance:
We should point out that by these definitions, keystone species do not have to be animals. They may be plants, algae, or even bacteria. Keystone animal species do not have to be predators, or even very large. By the above definition, they need only be an important habitat modifier, such as a pollinator, or seed disperser. One classic example are sea otters which eat sea urchins which eat kelp which forms a habitat for thousands of species. Another would be beavers, which through their engineering activity with trees, modify habitats by creating new ponds, that in turn, serve as habitats for many other organisms.

The important question for aquarium keepers to ask is: Is the collection of tropical fish affecting the environment by lowering populations of keystone species? Many environmentalists and ecologists say yes. There are many who believe that the collection of fish for the aquarium trade should be well-regulated in the countries where they're collected.

Keystone Fish Species:
Many fish species have been classified as keystone species in smaller bodies of freshwater, such as lakes, ponds and streams, as well as inland seas, and even in rivers. That is because these bodies of water are more enclosed and relatively small when compared to the oceans, making them easier to study.

One of the problems of identifying keystone fish species in the ocean is that we still know relatively very little about the inter-species relationships of many fish in specific marine habitats. Because of the sheer volume and physical space involved, it is sometimes even difficult to define specific habitats. These relationships and classifications have often been more clearly defined, only after the depletion or disappearance of fish species. Identification of keystone fish species is also often determined through an observation of dramatic rises or falls in populations of plankton and other invertebrates that represent the food of these fish.

This is particularly true of some food fish in studies of commercial fishing management. For example, the depletion of certain food species such as some flatfish and haddock may very well have caused an over-population of their prey, particular sea star species such as the Crown of Thorns, that in turn are now decimating shellfish such as scallops, and many reefs.

In the tropical fish world, one example of a keystone species would be Parrotfish, which consume hard and stony corals. These fish are equipped with a beak-like mouth, used to scrape and chew corals, polyps, hard shell and all! They digest the algae and polyps in the corals and eliminate the calcium shells of corals as waste in the form of loose sand. The removal of some outer coral material allows for new growth and increased diversity in coral reefs, while the coral sand that Parrotfish eliminate as waste, forms a loose calcareous substrate on the ocean floor that creates new habitats for many other organisms. Parrotfish by the way, should not be kept in home aquariums, as they rarely live in captivity due to their specialized dietary requirements.

Conclusion:
We are in no way saying that any fish which might be a keystone species should not be kept in aquariums. We are saying that while we hobbyists enjoy our aquariums, we also have a responsibility to ensure the preservation of fish in the wild, and their natural environment. This is true not only because we want these beautiful animals to be available for aquariums in the future, but also to ensure the habitats from which they come are not damaged by their collection.

While there is not yet definitive proof that the collection of marine fish for aquariums is a contributing factor to the gradual disappearance of our coral reefs, there is certainly historical precedence proving that the over-harvesting, or irresponsible destruction of, any living resource, can cause major environmental damage, or the extinction of other species. If the aquarium trade is a factor that damages the environment, it is up to us to learn all we can, and regulate ourselves, before others step in and over-regulate US!