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McIvor et al. (1994) summarize the effects of freshwater flow on mangroves and
note that moderate salinities produce the optimum conditions within the
mangrove community and maximize primary productivity.
Tidal Marshes
Located landward of the mangrove zone are various transitional zones. The
vegetation makeup of these transitional zones depends upon local topography,
historical rates of sea level rise, frequency of fire, surface water flows and surface
and subsurface soil salinities. Historically, there were greater surface and
subsurface freshwater flows near the coast, and thus descriptions of the coastal
vegetation of the Bay describe freshwater marshes composed of herbaceous
vegetation located immediately behind a narrow fringe of mangroves. Ross et al.
(2000) describes changes to this “white zone” in the “Southeast Saline
Everglades” 50 years after the original description by Engler (1952), and
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-2
describes four marsh types starting with the coastal prairie behind a mangrove
fringe, then the Rhizophora scrub, Cladium-Eleocharis-Rhizophora marsh, and finally
the Cladium marsh located farthest from the coast. A total of 29 species of plants
are documented to occur in these zones.
Ross et al. (2002) further documents the characteristics of the “white zone” and
adds details about the microflora, specifically the distribution of 154 diatom
species along a salinity gradient from coast to inland saline marsh.
Grossenbacker (pers. comm.) has indicated that for most of Biscayne Bay proper,
less than 70 acres of true tidal marsh may still exist based upon the “Advanced
Identification of Possible Future Disposal Sites…” (ADID) study conducted in
1994 jointly by the U.S. Environmental Protection Agency, U.S. Army Corps of
Engineers and Dade County (U.S. E.P.A. 1994).
Tidal marshes perform similar functions to mangroves, and often have lower
salinities than mangrove areas, thus overlapping the important oligohaline
habitat type where water flows are sufficient to reduce salinities to 5 psu or less.
In other parts of Florida, the oligohaline salt or tidal marsh is often a critical
nursery habitat for commercially and recreationally important fish and shellfish
including snook (Centropomus undecimalis), tarpon (Megalops atlanticus), redfish
(Scieanops ocellatus), and blue crab. In addition, these habitats support the forage
fish food base (Fundulus spp., Cyprinodon variegatus, Lucania parva, Floridichthys
carpio, Peocilia latipinna) for many other species (Lewis et al. 1985) (Durako et al.
1985). Documentation of this functional role in salt marshes of Biscayne Bay is
only well documented for the forage fish food base (Lorenz 1999, 2000, Lorenz et
al. 2002).
Seagrass Meadows and Macroalgae
Seven species of seagrass occur in the Bay: turtlegrass (Thalassia testudinum),
shoal grass (Halodule wrightii), manatee grass (Syringodium filiforme), paddlegrass
(Halophila decipiens), stargrass (Halophila englemanii), Johnson’s seagrass (Halophila
johnsonii), and wigeon grass (Ruppia maritima).
Macroalgae occur mixed with seagrass meadows, and as dominant macrophytes
where sediment thickness is too shallow to support seagrass (< 15 cm), or water
depths too great to support seagrass which typically require more light (i.e., 25%
of the light striking the water’s surface), or too turbid to transmit the required
levels of light. Generally, macroalgae fall into three categories as to life-form:
epiphytic on other plants, drift and attached. Epiphytic algae on mangrove prop
roots and pneumatophores include Bostrychia montagnei. Drift algae include
Hypnea spp., Laurencia spp. and Gracilaria spp. Attached green algae are very
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-3
common mixed with seagrasses, or as stand-alone communities in hardbottom
areas mixed with sponges and soft corals and include Halimeda spp., Penicillus
spp., and Caulerpa spp.
Seagrass distribution consists of few meadows around the mouth of the Oleta
River, large areas of shoal grass and manatee grass in the northern portion of the
Bay transitioning to predominantly turtlegrass in the southern three sub-regions.
A band of shoal grass occurs along the western shore of the central and southcentral portions of the Bay. Recent work indicates that some wigeon grass occurs
where the lowest salinities occur (D. Mir-Gonzalez, pers. comm.). It appears that
Johnson’s seagrass, a species designated as “threatened” by the federal
government, does not occur south of Virginia Key (NMFS, 2002), but the reasons
for this pattern of spatial distribution are not known.
As noted by Alleman et al. (1995), many species of small shrimp (both caridian
shrimp and juvenile penaeid shrimp), crabs, polycheate worms, clams, snails,
echinoderms and fish (both adult and juvenile) are found in this habitat. The
commercially and recreationally important fish and shellfish species, pink
shrimp (Farfantepenaeus duorarum), stone crabs (Menippe mercenaria), spiny lobster
(Panulirus argus) and spotted seatrout (Cynoscion nebulosus) are important
components of the fauna of seagrass meadows.
Oyster Bars
The American oyster, Crassostrea virginica, is a common component of the
estuarine fauna from the Gulf of St. Lawrence down the Atlantic Coast, into the
Gulf of Mexico and around to the Yucatan peninsula (Galtsoff 1964). The bar or
bioherm formation is typical and provides a physical structure supporting
dozens of resident species including polycheate worms, amphipods, crabs and
small fish (Bahr 1981).
As a habitat component of Biscayne Bay, oysters were historically very common.
Smith (1896) states “…There is a luxuriant growth of oysters in parts of Biscayne
Bay.” Meeder et al. (1997) report that “North Bay supported an active oyster
fishery until the 1920’s when Haulover Cut was constructed and reduced North
Bay renewal time…”
In contrast Alleman et al. (1995) only mention in passing that “Historical
freshwater inflows (both ground and surface water) were large and well
distributed spatially and seasonally, which presumably supported a richer
estuarine fish fauna than we find today…”, and mentions that Smith (1896)
“reported black drum (Pogamias cromis) as common near oyster beds in the bay
and red drum (Sciaenops occelatus) abundant in all seasons. These estuarine fish
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-4
are no longer common in Biscayne Bay…” presumably because of the lack of this
habitat feature (both dynamic and static components, Browder and Moore 1981).
The Unit Management Plan for Oleta River State Park (FDEP, 2002) reports the
existence of a live oyster reef (bioherm) at the mouth of the Oleta River. No
further details are given.
Meeder et al. (1997) characterize three submerged plant communities along five
transects located from Dinner Key to the Mowry Canal and notes that only fossil