CHAPTER 2 



AIJTECOLOGY OF SEAGRASSES 



2,1 GROWTH 



A renarkable sirilarity of vegetative 

 appearance, growth, and morphology exists 

 among the seagrasses (den Hartog 1970; 

 Zienan and Wetzel 1980). Of the local 

 species, turtle grass is the nost abun- 

 dant; its growth and Morphology provide 

 a typical scheme for seagrasses of the 

 area. 



Tonlinson and Vargo (19GG) and Tom- 

 linson (1969a, 1969b, 1972) described in 

 detail the morphology and anatomy of tur- 

 tle grass. The round-tipped, strap-like 

 leaves emanate from vertical short shoots 

 which branch laterally from the horizontal 

 rhizomes at regular intervals. Turtle 

 grass rhizomes are buried in 1 to 25 cm 

 (0,4 to 10 inches) of sediment, although 

 they usually occur 3 to 10 cm (1 to 4 

 inches) below the sediment. In contrast, 

 rhizomes of shoal grass and Halophila are 

 near the surface and often exposed, while 

 manatee grass rhizomes are most typically 

 found at an intermediate depth. Turtle 

 grass roots originate at the rhizomes or 

 less frequently at the short shoots. They 

 are much smaller in cross section than the 

 rhizomes, and their length varies with 

 sediment type, organic matter, and depth 

 to bedrock. 



Cn a turtle grass short shoot, new 

 leaves grow on alternating sides from a 

 central neristem which is enclosed by old 

 leaf sheaths. Short shoots typically 

 carry two to five leaves at a time; in 

 south Florida, Zieman (1975b) found an 

 average of 3.3 leaves per shoot in the 

 less productive inshore areas of Biscayne 

 Bay, and 3.7 leaves per shoot at stations 



in the denser grass beds east of the Flor- 

 ida Keys. Short shoots in areas exposed 

 to heavy v/aves or currents tend to have 

 fewer leaves. 



The growtfi of individual leaves of 

 turtle grass in Biscayne Pay averages 2.5 

 mm/day, increasing with leaf width and 

 robustness. Rates of up to 1 cm/day were 

 observed for a 15- to 20-day period (Zie- 

 man 1975b). Leaf growth decreased exponen- 

 tially with aoe of the leaf (Patrieuin 

 1973; Zieman lfi75b). 



Leaf width increases with short shoot 

 age and thus with distance from the rhi- 

 zome I'leristem, reaching the community max- 

 imum 5 to 7 short shoots back from the 

 growing tip (Figure 5). The short shoot 

 has an average life of 2 years (Patriquin 

 1975) and may reach a length of 10 cn 

 (Tomlinson and Vargo 1966). A nnv short 

 shoot first puts out a few small, tap ""red 

 leaves about 2 cm wide before producing 

 the regular leaves. New leaves are produc- 

 ed throughout the year at an average rate 

 of one new leaf per short shoot every 14 

 to 16 days, and times as short as 10 days 

 have been reported. In south Florida the 

 rate of leaf production depended on temp- 

 erature, with a rate decrease in the cool- 

 er winter months (Zieman 1975b). The rate 

 of leaf production varies less throughout 

 the year in the tropical waters of Barba- 

 dos and Jamaica, according to Patriquin 

 (1973) and Greenway (1974), respectively. 



2,2 REPRODUCTIVE STRATEGIES 



Seagrasses reproduce vegetatively and 

 sexually, but the information on sexual 



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