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VALUED ECOSYSTEM COMPONENTS
SFWMD (2002d) defines valued ecosystem components (VEC's) as “…a species,
community, or set of environmental conditions and associated biological
communities that is considered to be critical for maintaining the integrity…” of a
given estuarine ecosystem.
VEC's represent the full suite of plant and animal communities, individual
species, substrate characteristics (hardbottom, softbottom), and water quality
conditions (salinity zones, dissolved oxygen zones, etc.) that when taken together
or individually are valued for aesthetics, commercial or recreational fisheries
values, or heritage values. Once these are listed as they are in Section 6 above, the
question is which of these, or components of each, may have higher or lower
"values", and which are indeed sensitive to freshwater inputs to the estuary.
Mangroves for example are VEC's for all the estuaries in the southern half of
Florida, but are relatively insensitive to salinity changes over a very wide range
since they are facultative halophytes not obligate halophytes. That is they can
grow in totally fresh water, or survive in interstitial salinities as high as 55 psu
for red mangroves and 90 psu for black mangroves. The American oyster, on the
other hand is an obligate marine organism, but cannot persist in any numbers to
Potential Alternative Approaches for MFL Development for Biscayne Bay
Freshwater Flow and Ecological Relationships in Biscayne Bay 5-9
form an oyster bar unless very specific salinity and bottom characteristics are
present.
INDICATOR SPECIES
SFWMD (2002d) defines an indicator species as one where a change in
abundance, distribution or condition can be related to flow or salinity. Criteria
for selection may include commercial, recreational or aesthetic value, ecological
importance, and whether it is a listed species or an endemic species.
Starting with the full suite of VEC's for Biscayne Bay, Table 4 was prepared and
lists potential indicator species for minimum flows and levels, based upon their
occurrence in Biscayne Bay, life history, review general estuarine literature and
specific literature on Biscayne Bay, interviews and personal communications.
Sources of information include Serafy et al (1997) who collected 95 taxa of fish
from the Bay, Serafy et al (2003) who extended this work to mangrove fringed
shorelines in the central, south-central and southern portions of the Bay, and
Alleman (personal communication) who has prepared a draft table of species
salinity relationships in the Bay that lists twelve species of fish, three
invertebrates, wading birds as a group, and two species of seagrasses. Ault et al.
(2001) reported via visual census or creel survey data, and collected a total of 325
species of fish and macroinvertebrates from 77 families within Biscayne National
Park. Thorhaug et al (2001) lists two marine mammals, eight marine or estuarine
reptiles, thirteen coastal birds, two fish, twenty-nine corals and ten marine plants
as listed marine or estuarine species of concern in the Bay. Diatoms appear to be
a sensitive indicator of both existing salinities and historic salinities (Ross et al.,
2002, Gaiser and Wachnicka 2003) and are included as a group. Alleman et al.
(1995) specifically cite the diamondback terrapin (Malaclemys terrapin), the
mangrove water snake (Nerodia fasciata compressicauda), and the American
crocodile (Crocodylus acutus) as important potential indicator species for
freshwater inputs to the Bay.
From the information provided in this table it is apparent that not all the species
considered occur throughout the entire Bay. For a species to be considered for
use as an indicator species for a particular portion of the Bay, it must occur there,
or have occurred there in the recent past and have some reasonable chance of
returning in sufficient numbers to persist there if it is to be considered. Thus the
American crocodile can be considered for portions of the Bay, but not all, since it
is not reported for all parts of the Bay and is not likely to occur in some parts of
the Bay except very rarely.
Table 4
Potential indicator species for freshwater minimum flows and levels
establishment in Biscayne Bay.
5-10
Potential Indicator Sub-region
Scientific Name Common Name Snake Cr &
Oleta R.
North Miami
River
Central South
Central
S
PLANTS (Microphytes – diatoms) ***
SSS
PLANTS (Macrophytes)
Avicennia germinans Black mangrove * S ** S * S * S
Cladium jamaicense Sawgrass * S
Conocarpus erecta Buttonwood *
Distichilis spicata Saltgrass *
Eleocharis cellulosa Spikerush * SS
Halophila decipiens Paddle grass *
Halophila englemanii Stargrass
Halophila johnsonii Johnson's
seagrass
* * *
Halodule wrightii Shoal grass * * * * *
Juncus roemerianus Black needlerush *
Laguncularia racemosa White mangrove * ** * *
Rhizophora mangle Red mangrove * S ** S * S ** S
Ruppia maritima Wigeon grass * * *SSS
Spartina spartinae Cordgrass
Syringodium filiforme Manatee grass * * * * * *
Thalassia testudinum Turtle grass * * ** **
ANIMALS
Invertebrates
Callinectes sapidus Blue crab
Crassostrea virginica American oyster * *
Farfantepenaeus duorarum Pink shrimp ***SSS ***SSS
Limulus polyphemus Horseshoe crab
Menippe mercenaria Stone crab
Mixed spp of benthic
macroinvertebrates,
(epifauna & infauna)
* * * ** *