Robert W. Pennak

Toward a classification of lotic habitats

SummaryA world-wide system for classifying brooks, streams, and small rivers is proposed, using the following criteria: width, flow, current speed, substrate, summer temperatures, winter temperatures, turbidity, total dissolved organic matter, total dissolved inorganic matter, water hardness, dissolved oxygen, rooted aquatic plants, streamside vegetation. Some of these criteria have much greater biological implications than others. It is contended that widely separated lotic habitats that are similar in the above features have biotas consisting of ecologically similar and parallel clusters of species. There are, nevertheless, many kinds of “atypical” polluted and unpolluted lotic habitats that cannot be classified with respect to these criteria.

Biology of Rotifers

Parallelism in the evolution of rotifers is revealed in the repeated appearance, reduction, consolidation or enlargement of common structures as well as by left-right handedness. A possible phylogenetic scheme of rotifer evolution is given. Parallelism is usually understood as similar evolutionary patterns in genetically unrelated organisms (Schmalhausen 1964). It can be revealed in evolution of very different morpho-functional formations. Although rotifers are a relatively small group (about 2000 species) they show a remarkable diversity of morphologial, morphofunctional and ecological characters, which complicates their taxonomic arrangement and their systematics. However, with a detailed study of the group, one can identify in rotifers relatively few fundamental structures (Dogiel 1938). The number of instances in which parallelism manifests itself is great. This paper deals with a few, principally external, characters that current taxonomists study due to extensive previous description of similar characters at the anatomic and ultrastructural levels (Beauchamp 1909; Remane 1929-33; CU:ment 1980). Parallelism in the evolution of rotifers is revealed by: I) the repeated occurrence of unitypical structures; 2) the repeated reduction of unitypical structures leading either to a complete disappearance of a character (complete reduction) or to asymmetry (partial reduction); 3) the repeated appearance (oligomerization; Dogiel 1954) of identical structures; 4) a repeated increase of the number of structures (polymerization; Dogiel 1954) though it is not typical of rotifers; 5) a similarity in form attained by Hydrobiologia 104, 3-7 (1983). @ Dr W. Junk Publishers, The Hague. alternative paths treated partly as a manifestation of right-left handedness (enantiomorphism or chiralism) i.e. left-right biological isomery (Kasinov 1973). Similarity in unrelated characters of external morphology of rotifers used by taxonomists occurs more frequently at specific and generic levels. This can be traced in characters such as body and appendage shape, sculpturing of the body surface, shape and length of head appendages (palps, auricles), dorsal and lateral antennae, structure of the foot and its separate features (toes, claws, foot glands, peduncles, etc.). Several examples are given below. The body in most rotifers is flattened dorso-ventrally, but in the genera Colurella, Trichocerca, Gastropus and Ploesoma (each belonging to a different family) it is compressed laterally. Long lorica spines are observed on the dorsal plates in the genera Squatinella and Notholca (S. longispinata, S. leydigii, S. variegata, N. cornuta), and the lateral plate in Notholca and Lecane (N. triarthroides, L. monostyla). Lateral long auricles of the corona are developed in seven genera, belonging to three different families. Among these similar structures we can mention the rostrum of the head which is typical of many species of the genera Notommata, Proales, Bryceella, Rhinoglena and also of the

In situ measurements of net primary production in a Colorado mountain stream

Six stations were established on a Colorado mountain stream, and net primary productivity was measured in situ during all seasons. For 24-hour periods the dissolved oxygen and temperature of the water were electronically monitored over an undisturbed 1 x 1 m section of rubble bottom enclosed by a large plastic dome tightly fitted to the substrate. A submerged pump maintained a current within the dome, and the whole apparatus was submerged below the stream level. The bottom community net metabolism varied between heterotrophy and autotrophy with no correlations with altitude, season, light, water chemistry, and temperature. Readings were all very low and ranged from -27.38 to 35.59 grams of carbon fixed per square meter per year. There were no correlations between biomass of the bottom fauna and net community productivity.

Distribution and ecology of amphipoda (crustacea) in Colorado

Hyalella azteca is common and distributed in a wide variety of standing waters and springs of plains and mountains between 1050 and 3400 m in Colorado. Gammarus lacustris is uncommon and generally restricted to mountain ponds and lakes between 2500 and 3400 m where water temperatures do not exceed 20 C. Hyalella was found at 148 stations and Gammarus at 29 stations. Both species are characteristic of littoral areas containing rooted macrophytes and coarse bottom debris; such waters are anaerobic or frozen to the bottom in winter. No significant habitat differences were found with respect to pH, water color, total dissolved solids and minimal dissolved oxygen concentrations. Hyalella occurred over a greater range of water hardness, but in laboratory aquaria both species had similar survivorship curves in hard waters. The thermal death point for Gammarus was 26-28 C; for Hyalella it was 35-37 C. Crangonyx gracilis and Hyalella azteca inermis were each collected at single localities in Colorado.