Suspended Algal Dynamics Across a Seagrass Meadow Landscape

Seagrasses are important foundation species in coastal ecosystems that facilitate primary
production of themselves and macro-/microalgae and, through their water-baffling physical
structure, encourage the accumulation of algal material in the system. However, the effect that
seagrass meadows have on the vertical distribution of phytoplankton and suspended algal
material and how that distribution changes seasonally and throughout the meadow landscape is
largely unknown. To resolve this gap, I quantified suspended algal material in the water column
across a seagrass meadow landscape in a temperate coastal lagoon. I collected samples stratified
by depth at heights of 1, 5, 15, and 45 cm above the bottom at sites from which I calculated
chlorophyll a and pheophytin concentrations. These sites were host to varying seagrass densities
and differed in their distances from the meadow edge. I found that chlorophyll a concentrations
were significantly higher in the bottom 1 cm of seagrass meadows than at other depths in the
water column or at sites outside of the meadow. There was also a strong seasonal signal, with
these concentrations most pronounced in late summer. This suggests a seasonal control of
suspended algae concentration in the water column not reported in the literature. I found no
significant relationship between chlorophyll a concentrations and seagrass density or distance
from the meadow edge. Concentrations were instead dominated by the influence of habitat
driven by seagrass presence/absence. These findings reveal spatial and temporal variation in
suspended algal concentrations that likely exert controls on the secondary productivity of the
diverse community of suspension feeding animals and adjacent bivalve aquaculture associated
with this foundation species.