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controlled by salinity and has been identified to occur in oligohaline to
polyhaline conditions at locations where fresh water inflow is presently
occurring.
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-7
A record of past ecosystem conditions can be reconstructed by analysis of
sediment cores, and several such studies have been conducted in Biscayne
Bay. Stone et. al. (2000) used analysis of sediment cores to reconstruct
changes in conditions in the Featherbed Bank area of Biscayne Bay. Wingard
et al. (2003a, b) have examined cores from Central, South-Central and
Southern Biscayne for stratigraphic evidence of pollen, forams, ostracodes,
mollusks, and combined this information with geochemical data as part of a
paleoecological study of Biscayne Bay. Evidence suggests that over the last
500 years significant changes have occurred, including a general increase in
the salinities in South Central Biscayne Bay, and more stable conditions over
the last 100 years.
Phytoplankton
Phytoplankton are microscopic floating aquatic single-celled plants. They
grow abundantly in oceans around the world and are the foundation of the
oceanic food chain. Small fish, and some species of whales, eat them as food.
Because phytoplankton depend upon certain conditions for growth, they are
a good indicator of change in their environment. Even under ideal
conditions an individual phytoplankton only lives for about a day or two.
The largest phytoplankton include diatoms, coccolithophorids, and
dinoflagellates. The smallest phytoplankton, the ultraphytoplankton (which
includes picophytoplankton), include a single-cell planktonic form of the
blue-green algae known as the cyanobacteria.
A significant amount of present research is being conducted on the
phytoplankton that are associated with ‘red tide’, an increasingly frequent
condition in which specific phytoplankton become so numerous that they
become toxic to other marine life. In Biscayne Bay, the interest in
phytoplankton has primarily been related to the blooms that are associated
with discharges of nutrient-laden run-off from uplands. Although
phytoplankton are vitally important as primary producers, due to a variety of
factors, including their relatively short life cycles, and current-related
transport, most phytoplankton would not serve as good indicators of the
salinity regimes that are desired in the Biscayne Bay MFL project. A potential
exception to this, however, are benthic diatoms, which are described below..
Diatoms
Diatoms are minute unicellular or colonial algae, organisms that are
abundant in fresh water, estuarine and marine aquatic ecosystems from
tropical areas to polar seas. Although sometimes epibenthic or epiphytic,
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-8
most diatoms are planktonic. Benthic diatoms have been used as indicators
of environmental change, and interpretation of data from sediment cores
taken in northeastern Florida Bay have been used to reconstruct changing
historical salinity regimes in that Bay (Huvane & Cooper (2000)). Diatoms are
a constituent of periphyton, and as such, are being used as an indicator of
environmental conditions in Everglades National Park. Wanless (1984)
reported that in Biscayne Bay, living diatoms were generally most numerous
in northern Biscayne Bay and that their abundance decreased toward the
south.
Although phytoplanktonic diatoms are a valuable component at low levels of
the food web, for a variety of reasons, including varying sensitivities to
salinity and other water quality parameters, their typical existence as
plankton, small size, difficulty in sampling and analyzing, diatoms do not
appear to be suitable as indicators of estuarine conditions in Biscayne Bay.
Benthic diatoms, however, have been used to examine trends in salinity
associated with the "white zone" (Ross et al. 2002, Gaiser and Wachnicka
2003) and may be useful for such situations.
Listed Species
Listed species are those individual species of flora and fauna that have been
designated by the state of Florida as ‘endangered’, ‘threatened’ or ‘species of
special concern’ and/or designated by the federal government as ‘endangered’
or ‘threatened. Review of information (FGC, 1997) and other information from
the State of Florida (Chap 68, F.A.C), the U.S. Fish and Wildlife Service (USFWS),
the National Marine Fisheries Service (NMFS) and others, indicate that several
species that are listed at the state and/or federal levels are known to inhabit the
project area (Table 2). Although extremely low numbers and/or their
vulnerability to other non-freshwater flow related conditions render most of
these species inappropriate as indicators of estuarine health, the presence of
some individuals of these species within the project area requires that specific
consideration be given to ensure that reductions in fresh water do not result in
situations that could be viewed as non-compliance with state and/or federal
protected species regulations (e.g., Florida Wildlife Code, Federal Endangered
Species Act, as amended). Narrative descriptions are provided for those species
which could potentially be affected by reductions in freshwater.
Table 2
Marine and Estuarine Species that are State-listed and/or Federally-listed Species
and which are known to occur in Biscayne Bay and/or Adjacent Areas
1
Common Name Scientific Name Designation
FL Federal
Potentially
adversely affected
by reductions in
freshwater?
Comments
Fish
Key Silverside Menidia conchorum T No
Year-round resident in lower Keys, euryhaline
Not known to occur in Biscayne Bay
Mangrove Rivulus Rivulus marmoratus SSC No
Year-round resident, seems to prefer salinities of 20-35 ppt
Distribution largely coincident with Cardisoma guanhumi
Key Blenny Starksia starki SSC No
Not known from Biscayne Bay, but present on Looe Key, Monroe Co. Prefers
coral reef habitat; marine salinities
Smalltooth Sawfish Pristis pectinata E No