Significance of salinity and silicon levels for growth of a formerly estuarine eelgrass (Zostera marina) population (Lake Grevelingen, The Netherlands) |
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Authors: | P Kamermans M A Hemminga D J de Jong |
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Institution: | (1) Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, P.O. Box 140, 4400 AC Yerseke, The Netherlands, NL;(2) National Institute for Coastal and Marine Management, P.O. Box 8039, 4330 EA Middelburg, The Netherlands, NL |
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Abstract: | Since the early 1980s, the eelgrass, Zostera marina L., population in the saline Lake Gevelingen, The Netherlands, is rapidly declining. An earlier study, in which long-term
data on eelgrass coverage in this former estuary were correlated with several environmental variables, showed only one significant
correlation: coverage was positively related to water column silicon levels. In addition, a negative correlation with salinity
was observed, but this was not significant. In the present study, the effect of silicon and the effect of salinity on the
development of Z. marina were investigated experimentally. Enhancement of dissolved silicon concentrations in the water did not stimulate Z. marina above-ground production or an increase in final above- and below-ground biomass. The highly significant correlation between
eelgrass coverage and water column silicon levels, thus, remains to be explained. The results of the growth experiments did,
however, demonstrate a clear effect of salinity on Z. marina growth. Plants cultured at 22 psu showed a higher production of shoots and leaves, resulting in more above-ground biomass,
than plants grown at 32 psu. In addition, below-ground biomass was also higher at 22 psu. Measurements of chlorophyll a fluorescence, performed with a PAM-fluorometer, indicated a reduction of photosynthesis in the high-salinity treatments.
Thus, low salinity stimulates development of Z. marina from Lake Grevelingen. Eelgrass from such a historically estuarine area may be more sensitive to high salinities than other,
more marine populations. Recovery of the autochthonous eelgrass population is expected to be favoured when the estuarine conditions
of the seagrass area are re-established, or when restoration programmes are carried out with allochthonous ecotypes that are
less sensitive to high salinities.
Received: 23 June 1998 / Accepted: 19 November 1998 |
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