biological patterns are correlated with seasonal changes in environmental parameters. 
All measured abiotic patterns fluctuated over the course of a year; however, only a 
few exhibited seasonal patterns. Water temperature had an obvious seasonal pattern of 
considerable amplitude. A maximum temperature of 36°C was recorded in summer and 
a minimum of 12°C in winter. Nitrite and nitrate had no apparent seasonal pattern. 
However, orthophosphate levels were greatest in spring and summer and ammonia 
concentrations were generally greatest in the summer and fall. These patterns could be 
due to terrestrial runoff from heavy summer rains and fall turnover in the canal. Mid¬ 
day irradiance at the study site did not exhibit much seasonality. Macrophyte 
associations in three habitats - bay flat, canal ledge, and canal slope - were 
investigated. Dominant species on the bay flat were Batophora oerstedi and 
Acetabularia crenulata. In the canal, the dominants were Batophora and Laurencia spp. 
{L. poitei and L.obtusa). In all habitats, seasonality occurred at the community and 
population levels. The macroalgal associations can be subdivided into winter and 
summer communities, with significant seasonal differences in at least two of the 
following community characteristics: species richness, species diversity, total 
vegetational abundance, and the abundances of species. The seasonal pattern differed 
with habitat; species diversity increased on the bay flat, decreased on the canal slope, 
and remained the same on the canal ledge from summer to winter. The different 
patterns are in part due to differences in species composition and relative abundance 
among habitats. Community seasonality was due primarily to fluctuations in the 
abundances of species present in both periods rather than changes in species 
composition. Ten species varied seasonally in population abundance. These include the 
dominants of each habitat except the canal slope. Batophora abundance was highest in 
the summer and fall. Schizothrix sp. also was more abundant in summer. The other 
species, Acetabularia, Laurencia spp, Chondria tenissuma, Heterosiphonia sp., 
Polysiphonia sp., Jania rubens, and Griffithsia tenius were more abundant in winter. 
These results support the hypothesis of the presence of winter- and summer- 
optimum plants in the Florida Keys. Batophora was reproductive throughout the year; 
however, the reproductive activity varied seasonally. Reproduction was greatest in 
fall (mid-October to mid-December). The fall reproductive pulse may be triggered 
mainly by the abrupt drop in water temperature with the passage of the first fall cold 
front, or occasionally a late summer hurricane. Net photosynthesis and respiration 
varied seasonally but with different patterns. Net photosynthesis was highest in 
summer and lowest in winter. It was positively correlated with temperature, but not 
correlated with any other parameter. Respiration was greatest in fall when 
reproductive activity was maximal. Respiration was not correlated with any 
environmental parameter. Whereas seasonality in net photosynthesis is influenced by an 
environmental factor, temperature, seasonal variation in respiration appears to be the 
result of a biological phenomena, reproductive activity, and not directly influenced by 
abiotic factors within the ranges observed here. The P/R ratio was always greater 
than one, thus Batophora metabolism was not energy limited. Batophora's apparent 
capacity for year-round growth and reproduction could explain its ability to rapidly 
colonize and dominate newly exposed substrate. I believe temperature is the major 
abiotic causal factor in the seasonality observed in this study. Seasonal patterns in 
Batophora photosynthesis, reproduction, and abundance, and the abundances of other 
species closely follow that of temperature. Photoperiod, irradiance, and wave action, 
which could explain why Batophora abundance on the canal slope did not vary 
seasonally, probably play a secondary role to temperature. 
1981 
Powell, G. V. N. (1983) Food availability and reproduction by great white herons, Ardea 
herodias : a food addition study. Colonial Waterbirds . 6:139-47. 
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