CRUSTACEAN PLANKTON - (AN OVERVIEW) - LAKE ERIE - CENTRAL BASIN - AVON POINT

Anyone who has come down to the Lake in the morning over the past ten years or so has probably seen me filling up two buckets of water. The animals pictured here are one of the two large groups of animals that I have been keeping track of (the other group is the rotifers, a phylum just as prevalent as the crustaceans here shown but they are very hard to photograph). The three pictures on this page are all crustaceans known as copepods. The top photo is of the suborder Cyclopoida. This .5 mm. to 2.5 mm. animal is said to be the most numerous crustacean in the Lake. The bottom photo is of the suborder Calanoida. The calanoids are generally between 1 to 3 mm. in length. The middle picture is a side view of a copepod showing the many legs that are invisible from the top few.These animals number in the billions when the Lake is taken at as whole. They are also very beautiful, especially the calanoid copepods.

While they are found in the Lake year round the Calanoid’s population peaks in April thru June decreases in July and August, has a small increase in October and then falls to a low level for the rest of winter.

The Cyclopoid copepods follow a similar pattern, with populations peaking from May to July, decreasing in numbers until Aug. and Sept.

The bottom picture of a nauplius, which is an immature copepod. They range in size from .10-mm. to .5-mm.They are abundant from April to July and also have a slight increase in numbers in Sept. and Oct.

There as been a sharp decline in the number of copepods over the years from 1993 to 1999. Why, I don’t know. 

THE CLADOCERANS 

This is another large group of crustaceans found in the Lake. While there are many species found my work has focus on the two most common Bosmina and Daphnia.

The picture below is of Bosmina longirostris, an animal dear to me because it is the first animal I ever saw under a microscope when I began studying the Lake’s microscopic creatures. It looked to me like a legless elephant and I had no idea such animals existed anywhere let alone in Lake Erie. These small crustaceans are found in great numbers in the waters of Avon Point from May to July and to a lesser extant from Sept. to Nov. In the spring period the number of Bosmina can vary from zero to over 1200 per 12.5 liters. What is really unusual about the animals found in the samples is that in one sample taken on Sunday there may only be several animals in it, on Wednesday there may be 500 to 800 animals (I take samples twice a week, usually on Wednesday and Sunday).

(The lower photo while not showing details of the little cladocerans, does give a sense of place. A three dimensional space of, to her anyways, infinite space.) 

The picture below is of a cladocerana who resembles Bosmina but is of the genus Alona, this animal is rarely found in the near shore area of Avon Point.

Daphnia  And  Diaphanosoma

These are two relatively large Cladocerans crustaceans. The top two photos are of Daphnias which are between 1 and 3 mm. long and the bottom photo is of Diaphanosoma which are between 1.5 and 2 mm. long. These animals are found from May to November usually in relatively small numbers. But there have been occasions when Daphnia has occurred in vast swarms.

This swarming is one of the big mysteries I would like to solve.

A water sample of 5 liters taken away from shore had 674 Daphnia in it. A sample of 12.5 liters taken from the end of the jetty had 22 Daphnia in it. The animals where so thick in the water the water looked liked it had a snowstorm going on. How did these animals find each other? Did they follow a chemical trail? How did they manageto swim against the current? What did they gather for? Mating? Feeding? All questions I can’t answer.