Zonation of plants in a fresh-water tidal environment
A. Ingólfsson, B. Johannsson and H. Kristinsson

A fresh-water pond with tidal fluctuations (mean amplitude at spring tides: 1.66 m) in southwestern Iceland was studied. A total of 71 species of plants, chiefly cryptogams, were identified from two transects traversing the intertidal. Zonation of species was obvious. There were a few dominant species, sometimes with sharply coinciding boundaries, and a larger number of less conspicuous species. Species richness of cryptogams increased landwards from a low near the level of mean low water of neaps to reach a maximum slightly below the level of highest annual floods. Only one truly aquatic species was identified from the transects, other species noted being more easily classified as terrestrial. The pattern seen in the pond is compared to that found on a marine tidal shore, where most of the plant species are of aquatic (marine) origin, and species richness shows a low in the upper part of the intertidal. The reason for these differences is probably mainly two-fold. Firstly, the aquatic species of the marine shore have evolved adaptations to a periodically dry environment that fresh-water aquatics have not had a chance to do. Secondly, the terrestrial species do not face the osmotic problems on a fresh-water shore that they encounter on a marine shore. Upper and lower limits of species around the pond are most likely set mainly by physical factors, in contrast to what occurs on the seashore, where biotic factors are of critical importance.

Keywords: zonation, fresh-water, intertidal.
Contents of this volume Sci. Mar. 53(2-3) : 343-347 Back PDF
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