Annual variations in density, morphology, pigment levels, carbohydrate levels and photosynthetic characteristics of Zostera marina L. (eelgrass) from a coastal lagoon and from an unprotected area in the open coast were compared to understand the environmental regulation of this species growing near the southern limit of its distribution in the eastern Pacific. From January to April of 1997, light attenuation coefficients at the lagoon and the open coast increased six-fold as a result of sediment resuspension caused by storms in the area. During the storms, in situ irradiance was reduced two-fold at the lagoon. Irradiance values at the open coast, however, were reduced to nearly zero for >3 weeks, promoting the disappearance of the open coast population. At the open coast, eelgrass shoots died after sugar and starch content in the leaves decreased by approximately 85% after 3 weeks of light limitation. The re-appearance of eelgrass seedlings at the open coast coincided with the end of the winter storms in the area and decreasing water column turbidity. Maximum photosynthesis values of eelgrass from the open coast were two-fold greater than those from lagoon plants, except during March-June when seeds germinated at the open coast. Similarly, survival and leaf carbohydrate content of eelgrass from both sites decreased by >90% when incubated for 3 weeks in darkness. Collectively, these results indicate that the disappearance of eelgrass at the open coast is regulated by irradiance and not by an endogenous cycle. Although eelgrass can succeed in the open coast given sufficient light during the year, the accumulation and mobilization of carbon reserves appear to play a key role in the dynamics of eelgrass survival in temporally variable environments. (C) 2002 Elsevier Science B.V All rights reserved.
