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the seagrass is within the polyhaline zone. Assuming that the ideal environment
for a given species, or the maximum zone of production (or growth, survival,
food web production for that species) is this type of habitat, the freshwater flows
shown are optimum for creating habitat for that species. Conversely, if
freshwater inputs are reduced the overlaps change, and less polyhaline seagrass
meadow is available. Thus depending on what the Valued Ecosystem
Component (VEC) may be for a given area, freshwater inputs can be designed (if
they can be controlled) to optimize habitat for that VEC.
This concept of static and dynamic habitats can be used in a number of ways to
evaluate the necessary freshwater needs of an estuary. As discussed below, these
can include, Valued Ecosystem Components, as discussed in the previous Section
BFA
Figure 15
Stationary and dynamic habitat components,
from Browder and Moore (1981).
BFA
Figure 16
Graphic representation of the range of salinity zones overlaid on a typical tidal creek
system entering a higher ocean habitat (modified from Mitsch and Jorgensen 2004).
Tidal Flows
Freshwater Inflows
BFA
Figure 17
Graphic representation of salinity zones around a
submerged artesian well in a marine environment.
Freshwater Source
Oligohaline
Mesohaline
Polyhaline
Euhaline
BFA
Figure 18
Graphic showing the location of a seagrass bed in the estuary.
Seagrass Meadow
BFA
Figure 19
Graphic showing static habitat (seagrass meadow) with dynamic habitat (freshwater
inflow) overlay and resulting seagrass/salinity zones under normal flow conditions.
Seagrass in the
Euhaline Zone Seagrass in the
Polyhaline Zone
Seagrass in the
Mesohaline Zone
Normal Flows
Potential Alternative Approaches for MFL Development for Biscayne Bay
Freshwater Flow and Ecological Relationships in Biscayne Bay 5-7
4, indicator species, presence/absence/vitality of preferred habitats, ecological
preservation, pre-development scenarios, requirements for preferred fish
communities, community indices, food web support and soil characteristics.
Jackson et al. (2000) outlines a process to evaluate ecological indicators
specifically of interest to the Office of Research and Development of the
U.S.E.P.A. The outline lists 15 guidelines for indicator evaluation to structure
presentation of alternatives for evaluation but does not describe a selection
process. Some of the guidelines are however relevant to the process of Biscayne
Bay MFL ecological indicator identification. These include relevance to identified
assessment questions and ecological functions within the specific ecosystem
under evaluation; logistics requirements and ultimately the costs for
implementation; discriminatory ability among sites along a known gradient;
ability to provide information to support a management decision or to quantify
the success of past and future decisions.
Two presentations at the Estuarine Indicators Workshop (29-31 OCT 2003,
Sanibel Island, Florida) were applicable to the question of how to evaluate
various ecological indicators for final selection for the Biscayne Bay MFL.
The presentation by Bill Dunson (Dunson 2003) on choosing fish “bio-indicators”
listed five characteristics of an ideal estuarine indicator:
1. Mix of taxonomic groups
2. Mix of tropic groups
3. Sensitivity to the abiotic parameter(s) of interest
4. Important to stakeholders
5. Existence of robust prior database on the bio-indicator(s)
Similarly, Louis Toth (Toth 2003) explained the process of prioritizing 140
potential indicators of success in the restoration of the Kissimmee River. Seven
characteristics were evaluated:
1. Sensitivity to project effects
2. Reliability of response
3. Rapidity of response (for early warning and mid-course corrections)
4. Ease/economy of monitoring
5. Feedback to management (adaptive management)
6. Relevance to endpoint (sociopolitical evaluation and data availability)
7. Importance of endpoint (subjective evaluation of public opinion)
Potential Alternative Approaches for MFL Development for Biscayne Bay
Freshwater Flow and Ecological Relationships in Biscayne Bay 5-8
A scale of 1-5, with 1 being the highest rating (thus the lowest total value of a
given rating meant the highest priority) was used. A combination of the Dunson
and Toth methods were used in the analyses presented here.
Alternative approaches considered for the Biscayne Bay MFL development
included:
· Valued ecosystem components
· Indicator species
· Presence/Absence/Vitality of Populations of Indicator Species
· Pre-development scenarios
· Ecological preservation at existing conditions
· Requirements for preferred fish communities
· Community index
· Food web support
· Soils
These nine approaches were then individually evaluated for each sub-region of
the Bay for strengths, weaknesses, opportunities, threats, cost effective
performance standards and speed of information return to managers for
adaptive management decisions.