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salinities. Adult tarpon snook and fat snook might be as they are dependent on fresh water
connected to the ocean.
Mote Marine Laboratory
Interviewee: Ernie Estevez, Senior Scientist. Interviewer: R. Lewis. Interview date:
September 29, 2003.
Dr. Estevez has published several seminal pieces on the process of establishing
MFLs, including a major summary paper in the same issue of Estuaries referenced by others.
As with several other interviewees, he is not very familiar with Biscayne Bay, although he
remembered the issue of groundwater flows and springs in the bay had been discussed in the
past. He suggested that it might be helpful to obtain and review a paper about a circular
spring in Biscayne Bay, around which circular zonation of seagrasses of various species was
reported.
To save time, since it was a phone interview, I indicated that I was very familiar with
his work (he and I co-authored the estuarine profile for Tampa Bay in 1987 for the U.S. Fish
and Wildlife Service), and his recent publications on MFLs, and asked him if there was
anything new to add subsequent to the publication of those papers. He indicated that his
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recent field work in several riverine estuaries in Charlotte Harbor and Tampa Bay had raised
interest in oysters as VECs. During discussion concerning the potential use of VECs based
on salinity, he noted that one needs to be careful about other factors that can influence the
distribution and abundance of VECs besides salinity alone. He described his findings that
oysters, if present, are often found in a bimodal distribution of small forms with the larger
oysters found in the optimum salinity zone. Upstream of that zone, oysters are stressed or
killed by freshwater, and downstream of that zone, oysters are frequently diseased, or have
heavy predation, and are also very small compared to those in the optimum zone.
M.A. Roessler & Associates, Inc.
Interviewee: Martin A. Roessler. Interviewer: G. Braun. Interview date: October 20, 2003.
Mr. Roessler has been conducting research in Biscayne Bay for many decades in a
variety of capacities, including as a researcher at RSMAS and as a consultant for BNP. We
discussed the status of our search for suitable indicator organisms of ecosystem health and/or
significant harm, and the potential benefits and drawbacks of several species, as follows. He
does think that pink shrimp may be suitable indicators, as even though they are replenished
on an annual basis from an external population (i.e. Tortugas); there may be a size class
whose absence could be an indicator of significant harm. He suspects that there may be
salinity-specific issues regarding the life cycles and/or presence of juvenile blue crabs, and
thinks that the population of spotted seatrout is too low to be a good indicator, at least for the
lower bay. He concurs that mullet may be a potential indicator, but that the relative absence
of this species in the southern bay may be due to a variety of factors far outside the scope of
salinity regimes.
He suggests that we investigate the salinity requirements for sustainable populations
of land crabs (Cardisoma guanhumi) as successful reproduction in this species may be tied to
lower-than-marine salinity regimes. He also suggests that there may be some species of
barnacles that would be of assistance, although he could not identify any individual species.
Regarding potential use of seagrasses as indicators, he suggests that changing
sediment conditions could be equally as important as salinity in determining their spatial
distribution and health.
FINDINGS
1. Regarding the establishment of MFLs, it appears that Biscayne Bay (BB) should be
separated into six sub-regions, based on varying levels of exchange between freshwater
and marine conditions. Varying salinity regimes and the presence/absence and
abundance of varying flora and/or fauna will likely result in different indicators being
established for each sub-region.
2. The majority of the research and scientific data available for Biscayne Bay are focused
on southern portions of the Bay, particularly those waters within Biscayne National Park
(BNP). With an apparent lack of information on northern areas of BB, the team refocused on searching for, obtaining and reviewing additional information about this
portion of the study area (e.g., Management Plan for Oleta River State Park and the
current draft of the Management Plan for Biscayne Bay Aquatic Preserve). Because
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detailed information regarding the presence, absence and/or abundance of freshwaterdependant species in this area of the Bay remains in short supply, it is possible that Task
5 will include suggestions that additional information is needed in this area.
3. For the Central Bay (most of BNP), many of the interviewees indicated that the species
that would be the best indicators of healthy estuarine conditions are currently no longer
present or are present in such limited numbers or distribution that they would not serve as
good indicators. In large part, the absence of these species seems to be the result of past
modifications of the delivery of freshwater into the Bay, including highly variable
fluctuations in freshwater flow and development, including canal construction and
construction of features that have re-directed surface and/or subsurface flow. These
interviewees suggested that even the existing minimum flows are sub-optimal, and that,
because the ecosystem is currently in a state of significant harm, the MFL process should
identify target estuarine systems, such as Historic Creek and Black Point (completed
preliminary restoration design projects by SFWMD), which should be developed as “full
range” estuarine systems with the target of reestablishing a continuum of freshwater
marsh, brackish marsh, mangrove, and inshore estuarine (mesohaline) conditions along a
gradient from upland to bay. The interviewers suggested that these projects should be
monitored in advance of construction (5 years minimum) for baseline conditions
(physical and biological), restored, monitored and water flows adjusted through adaptive
management to achieve the full range of salinities targeted as performance standards.
4. For the South Bay, there are expansive wetlands (white zone and mangrove fringe) that
lend themselves to monitoring of the VEC’s of numbers of feeding Roseate spoonbills
and survival of juvenile American crocodiles. The optimum salinity regime necessary for
both of these species appears to be similar. Further review of information available for
these species may reveal the exact target range, but this range has not yet been identified.
5. For central and southern areas of the Bay, several of the experts identified that, in their
opinion, maintaining minimum flows is currently thought to be less of a problem than the
large pulse discharges of freshwater that cause wide and rapid swings in salinity (i.e. 25
ppt in 24 hours or less). They indicated that, although it may be outside the specific
scope of the MFL process, there needs to be consideration given to the fact that the
existing floral and faunal assemblages near canal discharges are largely restricted to those
organisms that can survive these un-natural changes in salinity, and that ideally, salinity
changes should be moderated to reduce the wide swings to something less than 6 ppt per
24 hours period, and some range “not to exceed” to reduce the stresses to fish and
wildlife using both areas. When asked, the BNP staff agreed that this approach may
result in a conversion of turtle grass meadows to shoal grass or mixed shoal grass and
widgeon grass meadows, and that was an acceptable change.
6. For the Central Bay, no further reduction in freshwater inputs should be allowed due to
reservations of water currently available due to the potential for this portion of BB to
become over time a hypersaline lagoon, similar to documented problems in Florida Bay
and portions of northern Cuba.
7. In addition to the previously identified potential indicator species listed by Alleman
(2003) (i.e., pink shrimp, blue crab, American oyster, stone crab, American crocodile,