|Abstract or Summary
- Effects of light intensity, exposure to desiccation, reduced
salinity, and thermal elevation on the functional and structural characteristics
of marine benthic diatom communities were investigated
in a laboratory model ecosystem and a respirometer chamber.
Measurements of biomass (dry weight and ash-free dry weight)
and chlorophyll a were made for each of the communities. Population
studies were performed to determine community structure. Finally,
photosynthetic rates of the communities at selected light intensities
were determined in the respirometer for communities developed in
experiments designed to test the effects of exposure to desiccation
and variations in light intensity.
Biomass accumulated most rapidly on substrates subjected to
high light intensities, without exposure to desiccation. Under intertidal
conditions, biomass accumulation was progressively greater
with less exposure to desiccation. Organic material (ash-free dry
weight) was greater on substrates from summer than winter experiments.
Both reduced salinity and thermal elevation interacted with
light to stimulate algal production, and mats of Melosira nummuloides
developed rapidly and floated to the surface.
Communities acclimated to different light intensities and periods
of desiccation responded differently to various light intensities in the
respirometer chamber. Substrates receiving little atmospheric exposure
developed thicker layers of biomass permitting significantly
higher rates of photosynthesis as light intensity increased. Generally,
substrates developed at low light intensities attained a maximum
photosynthetic rate at the lower light intensities in the respirometer,
presumably because of an acclimation phenomenon.
Community structure, as computed by the Shannon-Weaver information
function, showed increasing diversity with increasing atmospheric
exposure. During the summer experiment this was caused by
an increase in the number of species, but in the winter experiment
this was caused by a greater evenness of distribution of the species
within the community. In the experiments designed to determine the
effects of light intensity, diversity decreased with increasing light
intensity during the summer, but the opposite pattern was observed
in the winter. In both experiments the number of species decreased
with progressively higher light intensities; evenness of species numbers in the summer decreased with increasing light intensity,
but increased with increasing light intensity in the winter. Communities
developed under conditions of reduced salinity or increased
temperature showed decreasing diversity with increasing light intensity.
This was due both to fewer species and an unevenness of species
Results of these experiments demonstrate the potential of the
laboratory model ecosystem as a tool for the investigation of simplified
communities. It may be used to gain information that can supplement
and help understand concurrent field observations.