A Method of Sampling the Littoral Macrofauna and Its Application

The purpose of this work is to describe and test a method of separating the benthic macrofauna from the phytomacrofauna in the littoral zone of a lake. These two groups of animals can be distinguished quantitatively by removing the plants from a square frame about 90 cm high and sampling the benthos in the same area with an Ekman dredge. A more complete sample of the littoral fauna can be obtained in this way. Also, it is possible to study the relative contribution of the plants and the bottom to the total fauna and the factors affecting the quantity and distribution of various organisms. An illustration of the use of the sampler for these purposes is presented. Benthos refers to the animals which live on the bottom. Phytomacrofauna defines the animals which live in association with the plants. It is necessary to make this distinction because the term benthos has been used rather loosely in reference to the littoral zone. All of the animals which are collected by a dredge have usually been referred to as benthos even though the plants and the mud are obviously different habitats. Phytomacrofauna is composed of the animals which cling to the stems and leaves, the forms which swim among the plants like the Hydracarina and Amphipoda, and the species which mine the various parts of the plants. The latter group have not been considered here because special sampling and handling techniques are required in order to study them. Fishes have been ruled out arbitrarily. The requirements for taking separate samples of the benthos and phytomacrofauna at the same time and place are: (1) the plants must be removed first, and (2) the bottom should be undisturbed. Three methods have been described for the collection of plants. Ball (1948) used a which grabbed plants as it was drawn through the water, and McGaha (1952) mentions a similar method. Rosine (1951) waded among submerged plants, broke the stems by hand, and gently eased them into a fine-meshed dipnet. Andrews and Hasler (1943) designed a canvas bag which could be lowered over the plants. A zippered side enabled the operator to reach in and detach the plants from the bottom. The bag was closed and lifted from the water with the plants inside. The plants are torn out by the roots during the operation of the plant hook and the canvas bag, and neither method would provide an undisturbed sample of the bottom. The dipnet method of Rosine is not adapated for quantitative collection in a circumscribed area and probably does not sample the animals swimming among the plants completely. Several types of dredges have been used to sample the littoral fauna. A hoe dredge was designed by Scott, Hile, and Spieth (1928, 1938) for their work in Wawasee and Tippecanoe lakes, Indiana, and a somewhat similar apparatus was used by Rawson (1930) in Lake Simcoe, Ontario. A dredge of the Ekman or Petersen design has been used extensively in recent years. Ball (1948, 1949) and Eggleton (1952) employed both types in their work on Michigan lakes. Wohlschlag (1950) and Deevey (1941) mounted an Ekman dredge on a pole or rod. None of the dredges separates the benthos and phytomacrofauna. In addition, the roots of plants may prevent the dredge from penetrating far into the mud. The polemounted Ekman and the Petersen dredge overcome this difficulty. However, the plants dangle from the jaws when either type of dredge is used, and the animals which cling to the plants are partially lost as the dredge is hauled to the surface. Also, the plants usually prevent a tight closure of the jaws as Rawson (1930) mentioned.