8.5 



AVERAGE LEAF WIDTH 



7.5 



LEAF 



RHIZOME MERISTEM 



BRANCH OR 

 SHORT SHOOT 



RHIZOME 



DISTANCE BETWEEN BRANCHES 



Figure 5. Diagram of a typical Thalassia 

 width on the older, vertical short shoots. 



reproduction of the south Florida sea- 

 grasses is sketchy at best. The greatest 

 amount of information exists for turtle 

 grass, because of the extensive beds and 

 because the fruit and seeds are relatively 

 large and easily identified for seagrass- 

 es. In south Florida buds develop in Jan- 

 uary (Moffler et al . 1981); flowers, from 

 mid-April until August or September (Or- 

 purt and Boral 1964; Grey and Moffler 

 1978). In a study of plant parameters in 

 permanently marked quadrats, Zieman noted 

 that at Biscayne Bay stations flowers ap- 

 peared during the third week in May and 

 fruits appeared from 2 to 4 weeks later. 

 The fruits persisted until the third week 

 of July, when they detached and floated 

 away. 



2.3 TEMPERATURE 



One of the first mental images to 

 be conjured up when considering the trop- 

 ics is that of warm, clear, calm water, 

 abounding with fish and corals. This image 



shoot. Note increasing blade length and 



is only partially correct. Tropical 

 oceanic water in the Caribbean is typi- 

 cally 26° to 30°C (79° to 86°F), and feels 

 cooler than one would at first suspect. 

 In the past, lack of familiarity with 

 tropical organisms led many otherwise cap- 

 able scientists to view the tropics and 

 subtropics as simply warmer versions of 

 the temperate zone. Compared with their 

 temperate counterparts, tropical organisms 

 do not have greatly enhanced thermal tol- 

 erances; the upper thermal limit of tropi- 

 cal organisms is generally no greater than 

 that of organisms from warm temperate re- 

 gions (Zieman 1975a). In tropical waters, 

 the range of temperature tolerance is low, 

 often only half that of organisms from 

 equivalent temperate waters (Moore 1963a), 

 This is reflected in the seasonal r9nge of 

 the surrounding waters. At 40° north lat- 

 itude, the seasonal temperature range of 

 oceanic surface water is approximately 

 10°C (50°F), while at 20° north, the range 

 is only 3°C, reaching a low of only 1°C 

 (33.8°F) at about 5° north. However, be- 

 cause of the extensive winter cooling and 



12 



