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reduces turbidity and erosion.
The federal recovery team identified five criteria on which to consider
designation of critical habitat: 1) populations that have been documented to
persist for 10 or more years; 2) persistent flowering populations; 3) the
northern and southern limits of the species range; 4) unique genetic diversity;
and 5) a documented high abundance compared to other areas in the species’
range. Based on these criteria, ten areas, ranging in size from approximately
2 acres to 18, 757 acres have been designated as critical habitat for Johnson’s
seagrass. The largest of these, and the only one to occur within the MFL
project area is the Biscayne Bay area, which accounts for 83% of the
designated critical habitat for this species (Figure 8).
The recovery plan identifies a number of actions that are to be taken place in
order to meet the recovery goal of delisting the species after assuring its
persistence throughout its range. Although implementation of many of the
identified actions will have no effect on MFL rule development, specific
activities that are worth monitoring include:
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-32
Action #2: Initiate a range-wide monitoring program. Monitoring is to be
performed to detect any changes in the southern distributional limits or range
extensions, and specifically; “An important goal of the initial mapping would
be to identify if any major distributional gaps presently exist in the southern
part of the range.” (NMFS2002).
Action #3: Refine habitat requirements. Data are to be collected regarding
various water quality parameters, including temperature, salinity, light
intensity… to increase understanding of the conditions in which Johnson’s
seagrass survives.
Action #5: Determine and implement habitat management needs and
techniques. The recovery team intends to work with FDEP and WMDs to
develop water quality based targets for use in protecting seagrass
populations. WMDs will develop Pollutant Load Reduction Goals (PLRGs)
for SWIM waters. FDEP will use these PLRGs to determine Total Maximum
Daily Loads (TMDLs) for waters that are on the State’s list of impaired
waters.
Oysters
This summary of American oyster biology related to salinity is formatted after
that of Meeder et al. (2001) with additional review information from Galtsoff
(1964), Castagna and Chanley (1973), Lough (1975) Bahr (1981) and Burrell
(1986).
While live oysters have been collected across their range at temporary salinities
ranging from 0 psu to 40 psu, the various life stages of the oyster each has
different optimum requirements: Egg and sperm production does not occur
below salinities of 7.5 psu, maximum survival of 2 day old larvae occurs at
salinities of 19-30 psu, and 10 day larvae at 8-30.5 psu. Temperature is another
important parameter and certain optimums are reported for various populations.
Larval development is optimum at 25-29 psu, and spat grow best at 15-26 psu.
Best adult growth is in the same range, 14-30 psu. Moderate salinities of less
than 15 psu for a significant period in the year may be beneficial through
exclusion of less euryhaline predators and reduction in common disease
organisms (Burrell 1986).
Oysters can close their shells and survive on stored reserves and apparently
carry out anaerobic respiration to avoid death when external conditions are
lethal, such as long periods of 0 psu salinities. Periods of closure can range up to
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-33
10 days. In his review of requirements for establishment and persistence of
oysters as oyster bars, Meeder et al. (2001) notes that salinity and “steady food
bearing water currents are essential.” Oysters are very specific suspension
feeders, filtering seawater for phytoplankton. Evidence shows they can be very
specific for certain phytoplankton groups or even species.
Oyster larvae settle from a planktonic life form onto many surfaces. Galtsoff
(1964) describes these as “…rocks, gravel, cement, wood, shells of other
mollusks, stems and leaves of marsh grass…tin cans, rubber boots,… tires, glass,
tar paper…plastic…There is no evidence that the larvae are selective in finding a
suitable place to set, provided the surface is not covered with slimy film, detritus
or soft mud.” The latter two are however common features in certain areas along
the west side of Biscayne Bay where historical oyster bar deposits are found.
Meeder et al. (2001) concluded that "a range of salinities of 5-20 psu…may be
optimal for C. virginica in South Florida” and proposed a target salinity range for
a tidal creek restoration project of 5-15 psu in the wet season and 10-19 psu in the
dry season. The existing salinities in the area have a mean of 15 psu in the wet
season and 25 psu in the dry season.
For this restoration project specific construction activities and freshwater flows
were recommended along with the addition of several barge loads of shell to
provide a base for a new oyster reef to overcome the problem of needing suitable
settling substrate for oyster larvae (Meeder et al 2001, 2002).
Crustaceans
Crustaceans, which include lobsters, shrimp, crabs and barnacles are mostly
aquatic arthropods that are categorized in the class Crustacea. Numerous
species of crustaceans inhabit Biscayne Bay. Most are marine organisms that
prefer typical marine salinities of + 35 ppt, and are species whose presence,
absence and/or abundance would not serve as good indicators of adverse
impacts associated with reductions of inflow of fresh water. Many individual
species tolerate wide variations in salinity. Several species, however which are
present in Biscayne Bay for all or portions of their life cycles could potentially
serve as indicators of desired salinity regimes. These include shrimp and crabs
(Order Decapoda), as described hereafter. In addition to having life cycles that
include estuarine waters (see Appendix C), several of these species (i.e., pink
shrimp, blue crab and stone crab) are recognized as being “of major importance
to commercial, sport or bait fisheries” (Idyll, 1966).
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-34
Shrimp
Shrimp found in Florida’s coastal areas include members of the Penaeidae,
which include pink shrimp (Farfantepenaeus duorarum), and brown shrimp
(Farfantepenaeus aztecus) and members of the Palaemonidae, which include
grass shrimp (Palaemonetes pugio). Of the several kinds of shrimp that are
documented to occur in Biscayne Bay, pink shrimp are the most abundant
(Cantillo, et. al., 2000). Grass shrimp, which are known to inhabit
Biscayne Bay are well documented to be able to withstand wide ranges of