Mortality and productivity of eelgrass Zostera marina under conditions of experimental burial with two sediment types

Abstract

Mortality and productivity of Zostera marina L. were assessed to examine the effects of experimental burial using 2 types of sediment: (1) sand (6 and 0.2% silt-clay and organic matter content, respectively); and (2) silt (27 and 3.3% silt-clay and organic matter content, respectively). Z. marina was buried to 0, 25, 50, 75 and 100% of its average aboveground height (16 cm) in an existing eelgrass bed using 2 types of sediment characterized as either silty or sandy. Increasing percentages of plant burial significantly increased mortality and decreased productivity. Survival and productivity of eelgrass were substantially reduced when only 25% of the plant height was buried. Plants buried 75% or more of their height were characterized by survival and productivity measures of 0. No statistically significant differences in plant mortality or productivity were found between the 2 sediment types in this experiment. Changes in morphology of the plants were detected in measures of leaf length and surface area in a short duration (12 d) trial of the experiment, apparently in response to senescence, but etiolation was not observed. Results of this experiment indicate Z. marina can only tolerate rapid sedimentation events that cover less than half of its photosynthetic surfaces. Furthermore, the lowest levels of burial treatments (25% of plant height) resulted in mortality greater than 50%, indicating that even this small level of rapid sedimentation is significantly detrimental to Z. marina.