to document changes in vegetation. The stations differ in both mean salinity and salinity 
variation. Mean surface salinities at the outermost stations ranged from 31 %o 
(western transect) to 23 °/oo (eastern). At the uppermost stations, mean surface 
salinities were: 15 %o (western), 10 (central) and 11 (eastern). Temporal variation 
in salinity was highest at the upstream stations and lowest at the outer stations, 
except in the central transect, where all stations were variable. Upper stations ranged 
from near fresh to over 30 %o during the past year. The western outermost station 
was the least variable, ranging from 28 to 34 %o. Vegetation in the entire area was 
sparse (0 to 600 g dry mass nr 2 ), perhaps owing in part to fluctuation in salinity. 
Least variable stations had the greatest biomass. The outermost stations were 
dominated by turtlegrass ( Thalassia testudinum) or the calcareous alga Penicillus. 
Dominants change to widgeongrass ( Ruppia maritima) and the algae Chara and Batophora 
at the upstream stations. Shoalgrass (Halodule wrightii) was common at intermediate 
stations. Vegetation at upstream stations was dynamic. In March 1986, the upstream 
stations of the central transect were covered with dense stands of Ruppia, Chara and 
Batophora. Salinity was 13 %o, suitable for the growth of these plants. By May, 
however salinity rose to 26 %o and the vegetation had disappeared. Despite the return 
of lower salinities, vegetation at these stations remained sparse. Vegetation at the 
other upstream stations was sparse throughout the study period. The potential for 
dense stands of submerged vegetation is perhaps present at some or all of these 
upstream stations, but the frequency and magnitude of fluctuations in salinity may 
prevent stand development. 
1987 0 
Dawes, C. J. (1987) The dynamic seagrasses of the Gulf of Mexico and Florida coasts. Fla. 
Mar. Res. PubL 42:25-38. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] Of the seven species of 
seagrasses that occur in Florida and the Gulf of Mexico, three species form the 
dominant biomass in open shallow water (0.5 - 5 m): Thalassia testudinum (turtle 
grass), Syringodium filiforme (manatee grass), and Halodule wrightii (shoal grass). 
Although a much smaller plant by comparison, Halophila decipiens forms large meadows 
in deep waters (5 - 100 m). Halophila johnsonii and H. englemannii occur mixed in 
shallow-water seagrass communities. Ruppia maritima forms dense stands at the 
mouths of rivers where salinities rarely exceed 10 %o, on tidal flats where it is 
exposed to desiccation, and in subtidal areas of higher salinity. One hundred and 
thirteen algal epiphytes have been identified in seagrass blades around Florida. Up to 
120 macroalgal species have been identified in seagrass communities. Proximate 
constituent and kilocalorie levels have been used to demonstrate that the rhizome of the 
larger seagrass species is a storage organ with soluble carbohydrate changing 
seasonally. Cellulose fiber levels in the blades of the three larger seagrasses are 
similar to those of true terrestrial grasses, being highest in the blades of H. wrightii, 
and correlating with water movement. The biomass of six seagrass communities on 
Florida's west coast averaged 385 g dry wt nrf 2 , and energy levels averaged 981 kcal 
m' 2 . Caloric values are highest in seagrass communities during the summer, and range 
from a 15-month winter low of 344 to a summer-fall high of 1837 kcal nrr 2 , of which 
drift and attached seaweeds account for 75%. The lack of information regarding 
epiphyte biomass, energetics, and productivity, as well as the need to model a T. 
testudinum seagrass community, and the need for more growth and energetics 
information on the below-ground component of seagrass communities are pointed out. 
1987 0 
Fry, B., S. A. Macko, and J. C. Zieman (1987) Review of stable isotopic investigations of 
food webs in seagrass meadows. Fla. Mar. Res. PubL 42:189-209. 
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