The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
Crustaceans also increased greatly between the two periods. Amphipods and isopods
were virtually absent in the 2000 collection, but averaged 12,014 and 3,430 number/m 2
in the combined habitats for 2003. The abundance of aquatic insects also increased
substantially between the two periods.
The data from the December 2003 collection also indicated further shifts in the species
composition of the macroinvertebrate community and changes in the abundance of a
number of taxa. The numbers of Tarebia per square meter were greater in combined
habitats in 2003 (17,884) than in the 2001 (8,766), but still less than half the value
recorded during the 2000 drought conditions. December 2003 represented the longest
period of normal flow among these three sampling dates, demonstrating that Tarebia
can proliferate under a wide range of salinity in the spring run.
A number of taxa had much greater abundances reported for the bare sand habitat in
2003 compared to 2001, including the Dero digita complex, Grandidierella bonnieroides,
Munna reyonoldsi, and a number of insects in the Orders Hemiptera and Diptera. Total
numbers of the amphipods and isopods increased greatly on bare sand between the
two periods. Some taxa, however, were more abundant in the filamentous algae
habitat during 2001, including total Oligochaeta (including members of the family
Naididae) and total numbers of gastropods and amphipods. The reductions in
gastropods in filamentous algae between 2001 and 2003 was largely due to reduced
numbers of Tarebia and Pyrogophus platyrachis; the latter being a euryhaline species
that is widespread in fresh and low salinity waters. By contrast, total isopods
(dominated by Munna reynoldsi) increased greatly in the filamentous algae habitat as
well as on bare sand.
The mean value for total number of organisms combined habitats was greatest for 2003
(104,009 per sq. meter). Mean density values were similar between 2000 and the 2001
collections, but this was largely due to very high numbers of Tarebia in 2000. The
abundance of many other important taxa increased substantially between these periods,
and continued to increase by 2003. These changes are reflected in improved evenness
and diversity index values calculated for the invertebrate community. The mean
evenness values per sample in the combined habitats increased from 0.31 in 2000 to
0.59 in 2001, and remained at 0.59 in 2003. Mean diversity per sample progressively
increased from 0.84, to 2.12, to 2.47 for the three dates between 2000 and 2003.
Taxonomic richness in the combined quantitative samples increased markedly from 20
taxa in 2000 to 42 in 2001, then increased slightly to 45 in 2003.
The changes in the invertebrate community that accompanied a return to normal flows
in 2001 and 2003 can be considered desirable. The qualitative sampling from five dates
showed distinct changes in the species richness of the spring run with changes in flows.
The quantitative samples showed that the diversity and eveness of the invertebrate
community also improved, reflecting substantial increases in many taxa and less
dominance by the exotic snail Tarebia granifera. Importantly, many of the taxa that
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