THE ROLE OF ZOOBENTHOS IN ENERGY-FLOW IN DEEP, OLIGOTROPHIC LAKE THINGVALLAVATN, ICELAND

Macrozoobenthos in Thingvallavatn is dominated by 42 taxa. The vertical distribution delimits 5 communities: (1) the surf zone community from 0-2 m, (2) the upper stony littoral community from 2-6 m, (3) the lower stony littoral community from 6-10 m, (4) the Nitella zone community from 10-20 m, and (5) the profundal zone community from 20-114 m. Total mean lakewide production was 78 kJ m-2 yr-1. Herbivores, detritivores, and carnivores contributed 59%, 38% and 3%, respectively. Respiration and ingestion were estimated according to the literature. Net production efficiency averaged 0.50. Ingestion was dominated by herbivores in the littoral zones (46-81%), while detritivores made up 93% in the profundal zone. Total zoobenthic production averaged 6% of estimated available food with a range from 10-11% in the three upper littoral zones to only 2% in the Nitella zone. The profundal fauna converted 6% of the estimated sedimentation of organic matter to secondary production. On a lakewide basis the zoobenthos utilized one third of the estimated potential food resources. Zoobenthic production made up 32% of total secondary production.