B. Lundberg1 and Y. Lipkin2
Siganus rivulatus, a successful herbivorous immigrant fish from the Red Sea, consumes along the Israeli east Mediterranean coast a wide variety of algae. Only four of them composed about a half of the bulk of its food, and only twelve, about 80% of it. Seasonal changes in quantitative representation of different algae in the food followed several patterns. Most algae were taken throughout the year. Proportions in the food of some algae fluctuated only slightly during the year, proportions of others were very great during short periods and much smaller during the rest af the year. Polysiponia is an example for the former, Ulva and Spatoglossum, for the later. Among the latter, Ulva bursts in the food contents during the end of winter and spring; Spatoglossum, during the late summer.
Nevertheless, food composition in fish captured at inshore sites differed from that of fish captured offshore. This reflects, to a certain extent, the difference in vegetation between these sites, and the fact that the fish tend to graze in a rather limited area at a time.
Small and large fish take different algal food species. Unexpectedly, small fish clearly prefered some large and robust algae, consuming them in much greater proportions than bigger fish. Also unexpectedly, medium size fish showed preferences and avoidances of their own in regard to the consumption of certain algae, and not merely occupied an intermediate position between small and large fish.
Keywords: Siganus rivulatus, fish food, grazing.
In: Environmetal Quality And Ecosystem Stability . Volume V/B.
Editors.: A. Gasith, A. Adin, Y. Steinberger & J. Garty.
ISEEQS Publication. 1992
Y. Lipkin, S. Beer and A. Eshel
Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
Porphyra lineraris, is the uppermost intertidal macroalga on the eastern Mediterranean coast. It is able to regain photosynthetic activity upon reimmersion, even after drying in air to a stable water content of ca. 5% of fully hydrated plants for a period of three weeks. During desiccation experiments the plants continued net emersed photosynthesis at a maximal rate until their relative water content (RWC) dropped to 60%. Net photosynthetic gas exchange of plants with only 10% RWC was still positive. Photosynthetic rates, however, decreased during the drying process more rapidly than did the respiration rates. During rehydration, plants previously kept dry (5% RWC) for short periods (up to 24 h) regained net photosynthetic capability only when their RWC reached about 35%. The longer the thalli were exposed, the longer they had to be reimmersed in order to regain positive net photosynthesis, and the lower were their photosynthetic rates after full rehydration. After three weeks of exposure, the gas exchange systems of Porphyra plants could still recover, but after one month exposure the plants died. This more or less corresponds with the longest exposure encountered in nature, which is the period of two weeks between successive spring tides. It is suggested that the capability of the photosynthetic systems of P. linearis to recover after such long exposures to dry air is most important for its survival at the high intertidal level it occupies on the rocky shore.
Botanica Marina Vol. 36, pp. 517-523, 1993
L. L. Pereg1 , Y. Lipkin1 and N. Sar2
1Department of Botany, Tel Aviv University, Tel Aviv.
2Faculty of Food Engineering and Biotecgnology, Technion - Israel Institute of Technology, Haifa, Israel.
Halophila stipulacea beds in the northern Gulf of Elat (Red Sea) may be subdivided into three different sub-habitats, each harboring a distinct population of diazotrophs. Nitrogen (N2) fixation in the phyllosphere and in the rhizomes/upper-sediment niche was light dependent, suggesting its dependence on photosynthesis. N2 fixation in the phyllosphere was not affected by the addition of either glucose or 3-3,4-dichloro-phenyl-1,1-dimethyl-urea (DCMU), indicating that the diazotrophs involved carried out non-oxygenic photosynthesis. They may, thus, have been photosynthetic bacteria. N2 fixation in the rhizomes/upper-sediment niche, however, was greatly enhanced by the addition of glucose, but was suppressed in the presence of DCMU. This indicates that the diazotrophs involved here probably possess two photosystems (I and II) and may be Cyanobacteria. The anaerobic rhizosphere, in which fixation rates in light were very slow but were greatly enhanced by the addition of glucose, is probably populated by heterotrophic diazotrophs. Plant and sediment samples used in the present study were collected from the Gulf of Elat between 1990 and 1992.
Marine Biology Vol. 119 pp. 327-333, 1994