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crab, Menippe mercenaria and horseshoe crab, Limulus polyphemus) ) that
are present in Biscayne Bay and which are potential indicators of desirable
estuarine salinities. Information regarding the life cycles and salinity
preferences for each of these species is provided below.
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-37
Blue Crab
The blue crab is a fairly abundant marine crustacean that inhabits coastal
waters from Massachusetts Bay southward to the eastern coast of South
America (Hill et. al. 1989.). They are the major commercial crab fishery in
the U.S., representing approximately 50% of the total weight of all species
of crabs harvested (Thompson 1984, NMFS 1986). A considerable amount
of work regarding the life cycle and other aspects of blue crab biology has
been conducted, with much of it centered on the economically important
population that exists in Chesapeake Bay.
The blue crab appears to use areas of varying salinities at various times of
their life cycle. Mating occurs primarily in relatively low-salinity waters
in the upper areas of estuaries and lower portions of rivers (Pyle and
Cronin, 1950; Darnell 1959; Williams 1965; Tagatz 1968). After mating,
females migrate to high-salinity waters in lower estuaries sounds, and
nearshore spawning areas (Churchill 1919; Darnell 1959; Fischler and
Walberg 1962). Hill et. al. (1989) indicate that blue crab zoeae hatch in
Chesapeake Bay Chincoteague Bay, Delaware Bay, and other estuaries,
and then drift out to sea, where they fed and grow, after which they
migrate vertically in the water column to reach flood and ebb tides which
then transport them back into the bay area.
The blue crab is a major entity in estuarine food webs, both by consuming
a variety of other plants and animals, and by serving as prey for a variety
of commercially and/or recreationally important species of fish, birds and
other animals.
Various studies reported by Hill et. al. (1989) have documented that the
blue crab exists in waters of highly variable salinities, ranging from 0-34
ppt; that salinities of 22-28 ppt are needed for normal hatching of eggs and
for normal development of zoeae; and that “specific salinity levels are not
critical for post-larval crabs”. Laboratory studies reported by Guerin et.
al. (1997) corroborate these data, which led to a conclusion that: “Salinity
had no effect of growth rates of C. sapidus by any measure or weight or
carapace width”.
Stone crab
The stone crab is a fairly abundant marine crustacean that inhabits coastal
waters from approximately Cape Lookout, North Carolina southward
throughout the Gulf of Mexico to the Yucatan, Mexico, the Bahamas, Cuba
and Jamaica. (Lindberg 1984). It is a major commercial crab fishery in
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-38
Florida (Lindberg 1984). As a result of this economic value, a considerable
amount of work regarding the life cycle and other aspects of stone crab
biology.
The stone crab appears to use areas of fairly constant, nearly marine
salinities throughout their life cycle. Mating and spawning has been
documented to occur year-round in Biscayne Bay (Lindberg 1984), with
spawning peaking during August and September. Development of the
planktonic larvae to first crab stage usually takes 27-30 days, and larvae
pass through five zoeal stages. Although field studies documenting larval
growth may be lacking, culture-reared specimens were documented to
have optimal growth rates and best survival at a temperature of 300C and
“salinities in the range of 30 to 35 ppt” (Lindberg 1984).
The stone crab is a significant entity in both marine and estuarine food
webs, both by using their powerful claws to catch and consume a variety
of animals, and by serving as prey for a variety of fish, cephalopods, sea
turtles and predatory gastropods.
Various studies reported by Lindberg (1984)) have documented that the
stone crab is generally considered to be a euryhaline species. Ambient
salinities at stone crab study sites have been documented to range from
16.3-32 ppt near Cedar Key (Bender 1971) and 29-38 ppt in Biscayne Bay
(Cheung 1969).
Horseshoe crabs
The horseshoe crab is a fairly abundant marine arthropod that inhabits
estuarine and marine waters from mid-coast Maine southward to the Gulf
of Mexico. Horseshoe crab eggs have fairly recently been identified as a
major food source for migrating shorebirds, and various research is
currently being conducted to learn more about the habits and habitats of
this unusual benthic creature. In Florida, the FWC’s Florida Marine
Research Institute is currently conducting a survey to obtain records and
ultimately develop a database of horseshoe crab mating/spawning areas.
A query of their database revealed several reportings from Biscayne Bay,
but the Bay does not appear to be a major stronghold for this species.
Horseshoe crabs typically inhabit estuaries and coastal areas where they
spend nearly all of their lives under water. Adults emerge to lay eggs on
sandy beaches, after which larvae eventually become planktonic. Mating
and spawning has been documented to occur year-round in Florida, with
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-39
spawning peaks apparently being coincident with tidal and/or climatic
conditions that resulted in atypically high water levels (Ehrlinger 2002).
Various studies reported by Ehrlinger (2002) have documented that
horseshoe crabs are very tolerant of widely variable salinities. Embryos
have been shown to develop at salinities up to 40 ppt, and optimal salinity
ranges are generally accepted to be 20-30 ppt, and laboratory tests have
revealed that both embryos and larvae successfully developed, hatched
and molted at salinities as high as 60 ppt (Ehrlinger (2002)).
Fish
Alleman et al. (1995) notes that 512 fish species have been reported from
Biscayne Bay. Commercial fisheries catches, both by weight and value, were
however dominated by bait shrimp (juvenile to adult F. duoaram) based upon
data reported in 1984. Gray snapper (Lutjanus griseus), white mullet (Mugil
curema), pilchard (scaled sardine), white grunt (Haemulon plumieri) and spotted
seatrout were the five most abundant finfish harvested by recreational
fisherman.
Creel survey data for Biscayne National Park (BNP) for the years 1976 to 1998