Spatial patterns and population dynamics of plant-associated microcrustacea (Cladocera) in an English shallow lake (Little Mere, Cheshire)

Abstract

Little Mere (Cheshire) is a small (2.7 ha) and shallow (average depth 0.7 m) fertile lake in Cheshire, UK. Nymphaeids cover almost 40 % of its entire surface during the growing season (April to October) and practically all the rest is covered by a mixed community of submerged plants. The lake was intensively sampled for plant-associated Cladocera and zooplankters from April 1998-April 2000. Samples were collected at five sites across the lake, three of them located within lily beds, the other two over submerged plant beds of mixed composition. Specific sampling techniques were developed for floating lily leaves, petioles, submerged plants and water. Significant horizontal differences were identified for most cladoceran species, both open-water and plant-associated, for chydorid periphyton scrapers and for filter-feeders. Daphnia hyalina (L.) and Ceriodaphnia sp were significantly more abundant in lily beds than in more open water in both growing seasons, suggesting lily beds are an effective refuge against fish predation. Size-structure and egg-ratio data support this contention. Egg-ratio models were examined for Daphnia hyalina and Simocephalus vetulus (O.F. Muller), a plant-associated cladoceran. The fertility of S. vetulus in lily beds was generally high throughout growing seasons. The construction of egg-ratio models for this species was hampered by their generally very patchy distributions.