Pétur M. Jónasson, Kirsten Hamburger, Claus Lindegaard, Ebbe Lastein and Peter C. Dall†:

Respiratory adaptation of zoobenthos to access to oxygen and habitat structure in dimictic eutrophic lakes affecting vertical distribution. Scientia Danica, Series B, Biologica, Vol. 5. 38 pp. Illustrated DKK 100,- ISSN 1904-5484. ISBN 978-87-7304-390-5.

The vertical distribution of zoobenthos in eutrophic lakes is a classic and important theme in European limnology. Previous research has focused on feeding types, food resources and to some extend available oxygen as well as quantities of zoobenthos in relation to food production. This ecosystem paper synthesises recent and unpublished data of respiration measurements of zoobenthos and its adaptation to the vertical gradient of oxygen in Lake Esrom, Denmark, a classic eutrophic lake in general representing the glaciated eutrophic lakes of Northern Europe south of the Baltic Sea. The lake has been investigated at all ecological levels, but especially the understanding of ecological behaviour of zoobenthos with its 300 benthic species has improved. Depths zones of occurrence and peak density for each species are characteristic as well as its respiration model in relation to oxygen saturation of its habitat. The size of respiration has been related to diurnal and annual variation in oxygen of the habitat. Respiration measurements, from oxygen saturation to the critical point of respiration where it takes a sudden drop is characteristic for most of the 22 relevant species investigated in relation to oxygen saturation at the lake habitat and explains the type of living and surviving.

In relation to habitat two features of the respiratory pattern are important:

1) the critical point, and

2) the initial decrease of the respiration from saturation to the critical point.

To facilitate comparison between the species the relative respiration rates measured in the interval from saturation to the critical point are shown as function of the oxygen saturation and linked to the depth zone for the occurrence of the species at their peak density. According to respiratory pattern each species is characterised as either regulator, moderate regulator or conformer, judged from the percentage respiration at 25 % oxygen saturation. A synthesis of available data shows clearly that in the surf-zone of the shallow littoral and the macrophyte zone the zoobenthos is able to adapt to and resist diurnal oxygen variation either as conformers or moderate regulators. However, in the sublittoral shell-zone only a few moderate regulators are able to exist and in the profundal only regulators which contain haemoglobin or are able to exist on glycogen respiration during long-term anoxia survive.

Key-words: Zoobenthos respiration, oxygen saturation, oxygen uptake, critical point, conformers, moderate regulators, regulators, survival in anoxia, glycogen, haemoglobin.