Abundances of Micrometazoans in Three Sandy Beaches in the Island Area of Western Lake Erie

During August 1978 the interstitial micrometazoa of 3 beaches on Kelley's, Pelee and South Bass Islands in the western basin of Lake Erie were sampled. Representatives of the following taxa were found: Acarina, Cladocera, Copepoda, Ostracoda, Gastrotricha, Oligochaeta, Rotifera, Tardigrada and Turbellaria. The South Bass Island beach had the greatest mean density of micrometazoans (46.5/cm), followed by the Pelee Island (14.2/cm) and Kelley's Island (5.2/cm) beaches. The South Bass community was numerically dominated by turbellarians, the Pelee community by rotifers and the Kelley's community by rotifers and gastrotrichs. The mean density of total fauna decreased with depth in the sand (70% in the top 1 cm) except at subsites in the wave-influenced zone at the water's edge where 60% of the fauna were found in the 2—3 cm depth fraction. The densities of most taxa were significantly affected by an interaction between position on the beach and depth in the sand. Densities of the 4 most abundant rotifer genera (Trichocerca, Lecane, Wierzjskiella and Cepbalodella) varied among beaches and as a function of position and depth. The gastrotrich genera Chaetonotus, Ichthydium and Lepidodermella exhibited strong differences in their distributional patterns, with only one genus abundant at any beach, position or depth. The tardigrades Hypsibius augusti and Hypsibius saltursus were found in low densities (combined mean of 0.5/cm) below the waterline only on Pelee Island. OHIO J. SCI. 82(5): 246, 1982 INTRODUCTION beaches. A typical 10 cm of surface sand Pennak (1940) described a diverse t a k e n 1 5 ° c m shoreward from the water's community of micrometazoans living e d S e o n t h o f b e a c h 5 s contained 10,000 among the sand grains of several Wisconsin protozoans, 400 rotifers, 40 copepods, 20 tardigrades and lesser numbers of other 'Manuscript received 20 January 1981 and in remicrometazoans such as gastrotrichs, olivised form 28 July 1981 (#81—3). gochaetes and turbellarians. Although OhioJ. Sci. MICROMETAZOA OF SANDY BEACHES 247 similar communities in marine habitats have received considerable attention since Pennak's study (Svedmark 1964, Fenchel 1978), the micrometazoa of sandy freshwater habitats have been largely ignored in North America, and no published accounts are available for Lake Erie. A lack of suitable keys, scattered literature, and various sampling and extraction difficulties may account for this lack of information. The objectives of this study were to identify the taxa of micrometazoa present in selected Lake Erie beaches and to estimate their relative abundances with respect to depth in the sand and position on the beach. METHODS AND MATERIALS The 3 study sites were located on beaches on Kelley's Island, Pelee Island and South Bass Island in the western basin of Lake Erie. The small beach on S. Bass Island faces northeast and lies in a protected cove near the town of Put-in-Bay, Ohio. The beach on Kelley's Island is large (200 m long) and open to the north; the study site was located at the far eastern end of the beach in order to avoid areas used extensively for recreation. The Pelee Island beach is on the eastern side of the island, well exposed to wave action. This beach had the steepest grade of the three. All beaches were sampled within a 3-wk period in August 1978. Each beach site was divided into 3 subsites based on distance from the water's edge. One subsite was located at the water's edge (0 m position), a second subsite was located 1 m shoreward (+ 1 m position), and a third subsite was located 1 m lakeward (— 1 m position) (fig. 1). At each position 3 cores were obtained for faunistic analysis by inserting a 20-cm plastic syringe with the tip cut off into the sand to a depth of 3 cm. Upon removal, the cores were extruded by pressing on the plunger, and sliced off at 1 cm intervals. Each depth fraction (0—1, 1—2 and 2—3 cm) was then placed into a numbered 75-ml glass jar. The fauna were extracted from each depth fraction by serial decantation with 1% MgCl2 and preserved by adding sufficient 100% formalin with rose bengal to bring the concentration of formalin in the supernatant to 10%. (Rose bengal stains the fauna bright red for ease of recognition.) Multiple, whole Sedgwick-Rafter cell counts conducted under a stereomicroscope at 50X were used to enumerate the fauna. Cells were filled by decanting the excess fluid from each jar, swirling the remaining contents, and transferring 1-ml aliquots to the cells via a large bore pipette. Six aliquots per jar were counted. This procedure avoids sieving losses and approaches 100% efficiency in sands with + 1 •