Clean Up Crew

Natural coral reefs are oligotrophic (i.e. nutrient-poor) environments. What’s more, they tend to harbor an unusually high density of very hungry animals. Given their extremely low levels of algal productivity, and their minimal quantities of organic sediments, one could easily describe these environments as pristine.

Aquariums? Pristine? By and large, not so much. Especially when they contain more than one or two fish. Poopy sludge all over! And algae over the sand, over the rock, over the tank panels… Is that what you imagined when you built your saltwater aquarium system? Very likely not! Most probably, you envisioned something naturally clean like the reef itself.

To have such a system, free of fouling algae and detritus, one must include all members of the natural reef community. This certainly includes certain herbivores (especially algae-grazers) and detritivores. These animals should be well-represented in any aquarium big or small. While they are not always very colorful or exciting, they serve a vital purpose--cleaning. Thus, collectively, they are referred to as the clean-up crew.

These assemblages typically include “cleaner’’ animals such as snails (Nassarius, Trochus, Astrea, etc.), sea urchins or decapod crustaceans such as small, reef-safe shrimps or crabs. While dominated by invertebrates, there are a few small fish species that fit the bill. Indeed, to achieve maximum cleaning efficiency, the more the diverse the crew, the better!

This crew is truly a team. The most carefully selected clean-up crews do not exhibit undue or excessive competition. Firstly, one should be careful not to get too many individuals of the same species. It may be tempting to do just that when frustrated with, say, huge films of prolific green algae. But issues might show up down the road through overstocking or starvation that occurs after the food source has been depleted. For example, snails might starve to death; worse, deaths of these little gastropods often go unnoticed, leading to decomposition, nutrient spikes and increased levels of organic waste.

Secondly, and perhaps even more importantly, for excessive competition and maximum efficiency, the team should exhibit strong niche partitioning. In other words, make sure that each type of animal has its own resources and is specialized in exploiting them. For example, pincushion urchins and Nassarius snails both eat algae; however, while the urchin consumes it more quickly, the snail can alternately use detritus as a resource. Though Nassarius snails consume detritus more efficiently than copepods, copepods nevertheless are much smaller and so gain access to tiny pools of sludge (e.g. between little fissures in the rock) that are unreachable by the snail.

In this article you will learn how particulate organic matter and algae accumulate in aquaria as well as which types of clean-up crew animals most effectively eliminate which types of these waste accumulations.