What lies beneath (part 2) – The Cyclopoid Copepods

The exploration of aquatic microinvertebrates continues this quarter with the cyclopoid copepods. Briefly, the aquatic microinvertebrates are those animals without a back bone and smaller than 2mm. They are also called the aquatic microfauna.

You may recall from part 1 that aquatic microinvertebrates are largely made up of four groups of microbugs: copepods, rotifers, ostrocods and cladocerans. Cyclopoids are part of the former group, fast-moving ‘microbugs’ distinguished by the shape and segmentation of their antennae. 

There are 27 Genera found within Australian inland surface waters and approximately 150 different species, each with their own ecology and environmental preferences. How many of those species are present in the Hobsons Bay wetlands at any one time, as well as how many individuals of each species, depends on a number of factors including the temperature and pH of the water, the abundance of food, and the level of chemical inflows, freshwater and rainfall.

To imagine them, think of a takeaway soy sauce container but with two rounded egg sacs at one end. At the front are the two conspicuous antennae.

At around one millimetre in length, these micro-invertebrates may look inoffensive but their appearance belies an insatiable appetite. Some species are known for attacking almost anything that swims past. 

Sometimes a lone cyclopoid comes across fish larvae just hatched from eggs.  These fish larvae (often called fry), still have the yolk sac attached to them and are relatively immobile (refer to the picture below). The cyclopoid begins to attack the larva and pretty soon, it is joined by another cyclopoid and then another. Even though the cyclopoid is around one tenth the size of the fish larva, they are not deterred from their mission. One by one, more cyclopoids join in and the onslaught can last for over an hour. In one study nearly 90% of fish larvae present were removed by cyclopoid predation.

Photo Robert Berdan www.scienceandart.org

It is their appetite and meal choice which makes a number of species useful for humans. Species such as Mesocyclops aspericornis and Macrocyclops albidus are known to prey on mosquito larvae and have therefore been cultivated in some countries as an effective means for reducing disease-bearing mosquito populations. 

This is one of the benefits we’ve enjoyed from learning more about this hidden world. Cyclopoids are extremely important in freshwater ecology. With other groups of these tiny animals, they help to drive the ecology of wetlands, ponds, dams, billabongs, reservoirs and lakes.

If you have any questions or you’re interested in finding out more, please contact Rob Walsh at rwalsh@australianwaterlife.com.au