The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
Appendix B are color coded to denote combinations of dates when various taxa were
recorded. Twelve taxa shown in orange were recorded by SWFWMD/DEP in 1997 but
not recorded again in subsequent collections. Notable in this group are three species of
freshwater snails (Gastropoda – Amnicola dalli johnsonii, Planobella scalaris, and Elimia
floridensis). A bivalve mollusk found in 1997 that is more euryhaline (Modiolus modiolus
squamosus) was also not recorded in subsequent collections from the spring run.
All collections by the FWC beginning in 2000 have found dense populations of the
exotic snail Tarebia granifera. Tarebia is native to southeast Asia and was introduced
to Florida in the 1930s via the aquarium industry. It can thrive in both fresh and brackish
waters, and is abundant in some streams and springs in Florida. In many cases it can
outcompete native snail species and achieve high densities. FDEP and SWFWMD staff
do not recall observing an overabundant snail in the spring run during 1997, and it is
believed the reported absence of this snail in 1997 was not the result of a
misidentification. It is not certain when Tarebia colonized Sulphur Springs Run, but it
appeared to thrive in the high salinity conditions observed during the 2000 drought. The
disappearance of freshwater snails recorded in 1997 could have resulted from the high
salinity that occurred during the 2000 drought. However, the proliferation of Tarebia
may have contributed to their disappearance, and the inability of these species and the
euryhaline Modiolus modiolus squamosus to recolonize the spring with the return of
prolonged normal flows in 2002 and 2003.
Other species that were limited to the 1997 sample included an oligochaete (Dero
obtusa), an amphipod (Gammarus tigrinus), a cumacean (Alymyracuma sp), a mysid
(Taphromysis bomanii), and a tanaid (Tanais sp.). These are euryhaline species that
are common in tidal creeks. Three insects that were restricted to the 1997 collection
(Endotribelos hesperium, Polypedilium scalaenum, and Engalla civille) are common in
fresh water, but are also tolerant of low salinity.
The ten taxa shown in yellow showed an interesting pattern; in that they were present in
1997, absent during the high salinity collections of May 2000 and July 2001, and
reoccurred in the last two samples that corresponded to the return of normal flows.
These species are also common in fresh and low salinity waters. Given the level of
effort by the FWC, this observed pattern of disappearance and reoccurrence in the
spring run is probably real and not a sampling artifact. Furthermore, it is likely that the
high salinity values that occurred during the drought and the return to low salinity values
in the final two samples, were a factor in this pattern. It is unclear why some species
have been able to recolonize the spring while other taxa have not.
Sixteen taxa highlighted in red first appeared in the high salinity samples of May 2000
and July 2001, but were not recorded in the final two collections. Two polychaetes in
this group (Neanthes succinea and Stenoneries martini) are common in west-central
Florida estuaries, and salinity increases during the drought probably played a role in
their occurrence in the spring run. This contrasts with the polychaete Laeonereis culveri,
which was present in 1997. Laeonereis is also euryhaline, but often found in low salinity
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