SPATIAL HETEROGENEITY OF MACROPHYTES IN LAKE GALLOCANTA (ARAGON, NE SPAIN)

The spatial distribution of macrophytes (Ruppia drepanensis Tineo and Lamprothamnium papulosum (Wallr.) J. Gr. was studied along transects p erpendicular to the shoreline in Lake Gallocanta (Aragon, NE Spain) in 1988 and 1990. In the shallow zone, a gradient from the shoreline to offshore waters was clear: Small R. drepanensis plants were the only c olonizers of nearshore waters affected by wave action and desiccation. R. drepanensis and L. papulosum coexisted at intermediate depths in t he shallow zone. L. papulosum reached higher biomasses than R. drepane nsis in the deepest parts of the shallow zone. In the deepest zone of the lake, stands of the two species did not overlap. Individual plants of R. drepanensis occured patchily within a sparse prairie of L. papu losum. This spatial pattern was observed at different lake levels, sug gesting that macrophytes are adapted to fluctuations of environmental conditions. In very shallow water the macrophytes decay as indicated b y negative net production and low chlorophyll a/chlorophyll b and plan t K+ concentration/water K concentration ratios.