Primary production in three subtropical seagrass communities: a comparison of four autotrophic components

A one-year study was conducted in which seagrass communities in Tampa Bay, the
Indian River Lagoon, and the Little Bahama Bank were monitored quarterly for primary production,
standing stock biomass, and nutrient concentrations. Primary production rates were
measured in situ for the following jour community autotrophic components: seagrasses, their
associated epiphytic flora, phytoplankton and microbenthic algae. Photosynthetic rates were
compared both within and between locations to determine the relative significance of the primary
producers, and the contribution by each to areal, i.e., community production (mg C
m⁻³h⁻¹). In general, all species of seagrasses, their associated epiphytic flora and microbenthic
algae produced at similar rates at all locations. The Indian River Lagoon had phytoplankton
primary production rates that were greater than both seagrass and microbenthic algal production
rates. Phytoplankton in Tampa Bay had primary production rates greater than all other community
photosynthetic components, and primary production rates by all photosynthetic components
in the nutrient-deplete Bahama Banks were similar. Therefore, the majority of the community
primary production, i.e., the production base, in Tampa Bay and the Indian River Lagoon is
contributed by phytoplankton. These areas are characterized by anthropogenic perturbations
and associated high nutrient concentrations. Historical data indicate that phytoplankton, turtle
grass and microbenthic algae were, at one time, equally productive in Tampa Bay. Increased
phytoplankton production has reduced the relative importance of seagrasses and microbenthic
algae to community production in this area. It is suggested that the relative contributions by the
components of the photosynthetic community are affected by nutrient availability. Nutrient enrichment
may induce a shift in the production base from benthic plants to phytoplankton. A shift
of this type may be interpreted as an ecological indicator of either eutrophication or environmental
stress in a coastal marine environment.

Florida Atlantic University. Harbor Branch Oceanographic Institute contribution 482

This manuscript is an author version with the final
publication available and may be cited as: Jensen, P. R., & Gibson, R. A. (1986). Primary production in
three subtropical seagrass communities: a comparison of four autotrophic components. Florida
Scientist, 49(3), 129-141.