The Ecology of the Seagrasses of South Florida - USGS National ...

Mangroves and coral reefs are rarely, When assessing the role of seagrassif
ever, in close proximity because of es, sediment stabilization is also of key
their divergent physio-chemical require- importance. A1 though the seagrasses themments,
but seagrasses freely intermingle
with both communities. Seagrasses also
selves are only one, or at most three species,
in a system that comprises hundreds
form extensive submarine meadows that fre- or thousands of associated plant and aniquently
bridge the distances between reefs mal species, their presence is critical
and mangroves. Seagrass beds of the larger because much, if not all, of the community
mangrove-1 ined hays of the Everglades and exists as a result of the seagrasses. In
Ten Thousand Island region, while being a their absence most of the regions that
small proportion of the total bottom cov- they inhabit would be a seascape of unerage
of these bays, are the primary zones stable shifting sand and mud. Production
where important juvenile organisms,
as shrimp, are found.
such and sediment stabil ization would then be
due to a few species of rhizophytic oreen
a1 gae.
There are two major internal pathways
along which the energy from seagrasses is
made available to the community in which
they exist: direct herbivory and detri tal
1.2 CLIMATIC ENVIRONMENT
food webs. In many areas a significant South Florida has a mild, semitropiamount
of material is exported to adjacent cal maritime cl imate featuring a small
communities. daily range of temperatures. The average
Direct grazing of seagrasses is conprecipitation,
air temperature, surface
water temperature, and surface water safined
to a small number of species, al- linity, for Key Mest are given in Table 1.
though in certain areas, these species may Water temperature and salinity vary seahe
quite abundant. Primary herbivores of sonal ly and are affected by individual
seagrasses in south Florida are sea tur- storms and seasonal events. Winds affecttles,
parrotfish, surgeonfish, sea ur- ing the area are primarily mild southeast
chins, and possibly pinfish. In south to easterly winds bringing moist tropical
Florida the amount of direct grazing
varies greatly, as many of these herbiair.
Occasional major storms, usually
hurricanes, affect the region on an avervores
are at or near the northern 1 imit of age of every 7 years, producing high winds
their distribution. The greatest quandry and great quantities of rain that lower
concerns the amount of seagrass consumed the salinity of shallow waters. During
Iay the sea turtles, Today turtles are
scarce and consume a quantitatively insigthe
winter, cold fronts often push through
the area causing rapid drops in temperanificant
amount of seagrass. However, in ture and high winds that typically last 4
pre-Columbian times the population was to 5 days (Warzeski 1977, in Flulter 1977).
vast, being 100 to 1,000 times - if not In general, sumner high temperatures are
greater - than the existing population. no higher than elsewhere in the State, hut
winter 1 ow temperatures are more moderate
Some grazers, such as the queen (Figure 3).
primarily scrape the epiphytic algae on Water temperatures are 1 east affected
the leaf surface. Parrotfish preferen- on the outer reef tract where surface waconch,
appear to graze the leaves, but
tially graze the epiphytised tips of sea- ters are consistently mixed with those
grass leaves, consuming the old portion of
the leaf plus the encrusting epiphytes.
from the Florida Current. By contrast the
inner regions of Florida Bay are shallow
and circulation is restricted. Thus water
The rletri tus food web has classical 12 te~pwatures here change rrzpldly wi tk sudbeen
considered the main path by which the den air temperature variations and rain.
energy of seayrasses makes its way through
the food web. Although recent studies
Water temperatures in Pi ne Channel dropped
from 2Qo to 12OC (68' to 54OF) in 1 day
have painted to increased importance of
grazing in some areas (Ogden and Zienan
the passage of a major winter
::Azin?Zieman, personal observation).
1977), this genera? ization contl'nucs to be These stows cause rapid increases in sussupported.
pended sediments because of wind-i nduced
4