Shallow coastal lagoons are subject to
anthropogenic nutrient enrichment and
disturbances that result in loss of seagrass
ecosystems. These losses have generated a
desire by coastal managers for tools to
monitor existing seagrass meadows, and to
restore those that have been lost. The
following Chapters in this dissertation
address aspects of these issues. Chapter 1
documents a nearly 16 month study of Zostera
marina seasonal and year-to-year leaf and
rhizome morphology and growth in Ninigret
Pond, R.I. Individual shoots produced
approximately 0.11 leaves per day from March
to December. Shoot surface area and the
length of the longest leaf on a shoot were
significantly different between summers. The
estimates of the plastochrone interval
obtained using rhizome and leaf tagging were
closely correlated making rhizome tagging an
option for assessing shoot dynamics.
Chapter 2 is a collation of data from two
mesocosm experiments in which the
concentration of nutrients in plant tissue are
correlated to N and P loading rates. The
ranges in tissue nutrient concentration are
then used to construct a preliminary first order
index of nutrient loading rates. This endeavor
was moderately successful for N but not for P.
Chapter 3 is an investigation, using
mesocosms, of the single and interactive
effects of nutrient loading and summer water
temperature on phytoplankton, drift
macroalgae, and eelgrass. Phytoplankton
and macroalgae responded to nutrient
enrichment in early and late summer,
respectively. Significant declines in eelgrass
can be expected under conditions of nutrient
enrichment coupled with higher summer
water temperatures. Chapter 4 is a study of
the amount of light required for Z. marina
seedlings that have the potential to be used
as a restoration tool. Seedlings were
subjected to three light levels over their first
summer. Decreasing the light available to
eelgrass seedlings decreased lateral shoot
formation and biomass and increased the
length and width of leaves. Reducing light to
10% of incident compromised survival, shoot
growth, size and biomass.