The zoobenthic community of shallow salt pans in Austria - preliminary results on phenology and the impact of salinity on benthic invertebrates

A three-year project on the benthic community of salt pans (shallow saline lakes) in the Seewinkel area of Eastern Austria has been carried out since 1996. Most of the salt pans investigated are very shallow (mean depth mostl y < 0.5 m), highly alkaline and inorganically turbid. Salinity ranged from 1.6 to 4.5 g l(-1) in 1996 and 1997, but reached its highest values (> 50 g l(-1)) during the dry summer of 1998. A comparison of the benthic communit y in 20 salt pans at two sampling dates in 1997 revealed a negative relatio nship between salinity and species richness of Oligochaeta and benthic Crus tacea. However, the decline of diversity was observed at salinity values mu ch lower that those reported in the literature for most benthic invertebrat es. It is thus doubtful whether or not salinity has in fact directly affect ed the benthic community in the salt pans of Seewinkel. Rather, it is sugge sted that biotic interactions controlled by changes in the hydrochemical si tuation are responsible for the reduction in diversity of the benthic commu nity. Actual experiments or more detailed data on changes over a full gradi ent of salinity will be necessary to attribute changes in the species compo sition of benthic invertebrates to any environmental impact with certainty. The phenology of benthic invertebrates in Unterstinker, a sub- to hyposali ne (0.5-20 g l(-1)) salt pan studied in greater detail, was distinctly infl uenced by the development of submerged macrophytes. Abundances of chironomi ds and crustaceans, the two dominant major benthic groups, were high only i n June and July, when Charophyceae had stabilized the lake bottom and preve nted further erosion of fine sediments. Substrate characteristics and the a bundance of macrophytes appeared to determine the seasonal development of t he benthic community as long as the ion concentration remains low (< 3 g l( -1)).