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The urban shelling experience: wrack up a new method – if you get my drift |
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By Bill Frank and Harry Lee |
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Over the past year, using satellite imagery, aerial photography, and topographic maps, the senior author has been surveying the presence of the freshwater Florida Apple Snail [Pomacea paludosa (Say, 1829)] in Duval County. This study, focused on the south side of the county, involves identifying likely snail population areas using the map and photography aids and then conducting an on-site investigation. Previously published material had indicated that “…the species is not able to survive the lower winter temperatures that occur along the northern tier of Florida counties and northward” – a conclusion that was easily proven incorrect. Most of the locations visited during the study were either small lakes (borrow pits/retention ponds) or simply drainage ditches running through residential areas. For the most part, the latter are usually quite shallow and during dry weather have a minimal amount of water. However, following heavy rains, the run-off from the surrounding developed areas can easily raise the water level up to six feet and quickly turn an ankle deep ditch into a raging river. Because of this sudden influx of water, many of the terrestrial mollusks, as well as their empty shells, from the surrounding area are washed into the ditch and ultimately end up in large conglomerations of vegetation at the high water mark (also referred to by some as the high water wrack line; see Freshwater Shell Collecting In Alabama and the Nov.-Dec., 1996 Shell-O-Gram) along with the aquatic species that reside in the ditch itself. One example of this is Bennett Branch on Bowden Road in southern Jacksonville – the topic of this report. |
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Palmetto Vertigo (2 mm.) |
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The sample was oven-dried, kneaded, and sifted. The process allowed culling of a few dozen larger (over four mm) shells and produced a little over a pint of coffee-ground-like material in two grades of minimal dimension, 2-4 mm and less than 2 mm, in about equal volumes. These sub-samples samples were searched using a grid under the stereo microscope at 10 to 20X. Shells were culled, sorted, and identified using the usual methods. The results were rather
productive for a single station - 37 spp., and all but one from the
drift sample. The presence of a both land (26) and freshwater (11)
species contributed to the diversity: |
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| Also see: Pomacea paludosa (Say, 1829) Florida Applesnail | |
| Bennett Branch, Bowden Road, Southeastern Duval County, Florida | |
Bennett Branch, a tributary of Pottsburg Creek (and thence the St.
Johns River), was first visited on 10/20/2005 and a live Pomacea
paludosa was immediately discovered immediately adjacent to
Bowden Road. This was somewhat amazing considering how small the
creek was and its obvious poor water quality. A later article in the
Florida Times-Union confirmed the water quality observation
with a report of a fecal coliform reading of 3,000 (a reading of
over 800 is considered a health risk). A large amount of high water
wrack was also present in the same area which was visually replete
with both terrestrial and aquatic species. The junior author was
told of the profuse wrack and asked whether he would like a gallon
of the material for microscopic examination. Upon his approval, a
return visit to Bennett Branch was made on 11/1/2005 and the sample
was obtained.