The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
waters. Other species that occurred only during the drought are species that are tolerant
of low salinity (Chaetogaster diastrophus, Dero pectinata, Tropisternus blatchleyi,
Thienemanniella sp., and members of the dipteran families Dolichopodidae, Ephydridae
and Stratimyidae). Some of these taxa are common in non-flowing waters and can be
associated with vegetation, such as mats of filamentous algae. Reductions in current
velocities and the proliferation of algal mats in the spring run during the drought may
have been a factor contributing to the presence of these taxa. Factors related to current
velocity and physical habitat may also have been factors in their disappearance with
return of normal flow and reduction of algal mats in the last two collections.
Possibly the most striking finding in the presence/absence data are the large number of
taxa which colonized the spring upon the return to normal flows. A total of thirty-one
taxa were first recorded in the final two collections by the FWC. Eight taxa highlighted in
blue were first recorded in November 2001 after four months or normal flow, while
another twenty-three taxa highlighted in green were first recorded in December 2003
after eighteen months of normal flow. The qualitative sampling effort and methods
employed by FWC were more rigorous than the methods employed during brief
SWFWMD/FDEP survey, so it is possible that some of the taxa recorded in the final two
collections were also present in 1997. However, given the consistency of the FWC
methods, it is more certain that these species were truly absent from the high salinity
collections during the 2000-2001 drought. The total number of taxa recorded in the final
drought collection (July 2001) was 37, compared to 60 taxa recorded on December
2003, demonstrating a strong rebound in species richness with the return to normal
flows from the spring pool.
A number of the taxa that first appeared in the final two collections are commonly
abundant in fresh water, but also are found in low salinity tidal creeks. These taxa
include Hydra sp., Prostoma sp., Apedilium sp., Microvelia sp., Pachydiplax longipennis,
members of the annelid family Naididae and members of the Zygoptera (damselflies)
genera Enallagma and Ischnura. The pelycpod Cyrenoididae floridana is the most
estuarine taxon first collected in the last two samples, as it is common in Tampa Bay,
but almost never found in true fresh water (