The role of zoobenthos in energy flow in deep, oligotrophic Lake Thingvallavatn, Iceland

Abstract

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 20-1 14 m. Total mean lakewide production was 78 kJ m -* yr -'.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.

The role of zoobenthos in energy flow in two shallow lakes

“…However, in Mirror Lake the herbivores made up 32% and Strayer & Likens (1986) suggested, that in clear lakes much of zoobenthic production may be supported by benthic algae rather than detritus. In accordance with this Lindegaard (1992b) found 60% of the benthic secondary production was herbivorous invertebrates in Thingvallavatn, which has a photic zone reaching 20-30 m depth. The very high benthic diatom net production (9200 kJ m -2 yr-t) in Myvatn (J6nasson, 1979) may easily explain the total dominance of herbivorous chironomids in this lake.…”

“…Predation by fish in both lakes was only about 5-10% Rasmussen, 1990) resulting in large amounts of biomasses leaving the lakes as adult midges (Lindegaard & Jnasson, 1979;Lindegaard & J6nsson, 1987). The ingestion rates found in Myvatn are almost identical to those found in Thingvallavatn, where on a mean lakewide basis, the non-carnivorous zoobenthos utilized about one third of the available food (Lindegaard, 1992b).…”

“…All rates are given in kJ m -2 yr -.P/B and NPE ratios estimated from related species or taken from literature are marked with "*" (Strayer & Likens, 1986). A similar sparsity of carnivores was found by Lindegaard (1992b) in another Icelandic lake, the 114m deep Lake Thingvallavatn. In spite of the low numbers of invertebrate carnivores in Thingvallavatn predation on the littoral zoobenthos was heavy, due to a large population of arctic charr (Salvelinus alpinus L.).…”

“…Sarvala et al (1981) used a NPE of 0.3 in computation of an energy budget for zoobenthos in the Finnish Lake Paajarvi Strayer & Likens (1986) found a NPE of 0.42 by using a variety of literature sources (compiled by Walter (1976)) to estimate community respiration in Mirror Lake. However, Lindegaard (1992b) found -by using the same equations as for M! ?vatn -a NPE of 0.50 for the zoobenthos community in the Icelandic Lake Thingvallavatn.…”

“…The zoobenthos production estimates of Myvatn and Hjarbaek Fjord do not include the proper micro-and meiofauna elements, as sieves with a mesh size of 150 Mm and 200 um were used and manual sorting done at low power (2.5 x magnification). The same procedure was used by Lindegaard (1992a) in Thingvallavatn, andLindegaard (1992b) suggested that production estimates for 'macrozoobenthos' was raised by 25 % if total zoobenthic fauna were included. This factor was applied to the calculation for both lakes ( Table 5).…”