of Rhipocephalus , Udotea , and Acetabularia 

 produced at least as much mud as Penicil- 

 lus in the same locations. 



In the Bight of Abaco, Neumann and 

 Land (1975) calculated that the growth of 

 Penicillus . Rhipocephalus , and Hal imeda 

 produced 1.5 to 3 times the amount of mud 

 and Hal imeda sand now in the basin and 

 that in a typical Bahamian Bank lagoon, 

 calcareous green algae alone produced more 

 sediment than could be accommodated. Bach 

 (1979) measured the rates of organic and 

 inorganic production of calcareous siphon- 

 ates in Card Sound, Florida, using several 

 techniques. Organic production was low in 

 this lagoon, ranging from 8.6 to 38.4 g 

 ash free dry weight /m-^/yr, and 4.2 to 

 16.8 g CaCOj/m^/yr for all the species 

 combined. 



In addition to the calcareous algae, 

 several algae are present in grass beds as 

 large clumps of detached drift algae; the 

 most abundant belongs to the genus Lauren- 

 cia . The areal production of these algae 

 is low compared with the seagrasses. Jos- 

 selyn (1975) estimated the production of 

 Laurencia in Card Sound to average about 

 8.1 g dry weight /m-^/yr which was less 

 than 1% of the 1,100 g/m-^/yr estimated by 

 Thorhaug et al . (1973) for turtle grass 

 from the same area. 



The least studied components of the 

 algal flora are the benthic nicroalgae. 

 In studies of benthic production through- 

 out the Caribbean, Bunt et al . (1972) cal- 

 culated the production in Caribbean sedi- 

 ments to average 8.1 mg C/m-/hr (range = 

 2.5 to 13.8 mg) using I'+C uptake. By com- 

 parison, sediments from the Florida Keys 

 yielded 0.3 to 7.4 mg C/m-/hr fixation. 

 These values were equivalent to the pro- 

 duction in the water column. Ferguson 

 et al . (1980) briefly reviewed inicroalgal 

 production values and indicated that light 

 and thermal inhibition can occur, particu- 

 larly in summer. 



Epiph y tic Algae 



One of the main functions for which 

 seagrasses have been recognized has been 

 the ability to provide a substrate for the 

 attachment of epiphytic organisms. Al- 

 though unifying patterns arc beginning to 



emerge, the study of epiphytes has suf- 

 fered from what Harlin (1980) described as 

 the "bits and pieces" approach. 



An annotated list of 113 species of 

 algae found epiphytic on turtle grass in 

 south Florida was compiled by Hunm"(1964). 

 Of these only a few were specific to sea- 

 grasses; most were also found on other 

 plants or solid substrate. Later, Ballan- 

 tine and Humm (1975) reported 66 species 

 of benthic algae which were epiphytic on 

 the seagrasses of the west coast of Flor- 

 ida. Rhodophyta comprised 45% of the 

 total, Phaeophytas were only 12%, and 

 Chlorophytas and Cyanophvtas each repre- 

 sented 21% of the species. Harlin (19P0) 

 compiled from 27 published works a species 

 list of the microalgae, macroalgae, and 

 animals that have been recorded as epiphy- 

 tic on seagrasses. The algal lists are 

 comprehensive, but none of the reports 

 surveyed by Humm list the epiphytic inver- 

 tebrates from south Florida. 



Harlin (1975) listed the factors 

 influencing distribution and abundance of 

 epiphytes as: 



(1) Physical substrate 



(2) Access to photic zone 



(3) A free ride through 

 waters 



(4) Nutrient exchange with 



(5) Organic carbon source 



moving 

 host 



The availability of a relatively stable 

 (albeit somewhat swaying) substrate seems 

 to be the most fundamental role played by 

 the seagrasses. The majority of the epi- 

 phytic species is sessile and needs a sur- 

 face for attachment. The turnover of the 

 epiphytic community is relatively rapid 

 since the lifetime of a single leaf is 

 limited. A typical turtle arass leaf has a 

 lifetime of 30 to 60 days' (Zieman 1975b). 

 After a leaf emerges there is a period be- 

 fore epiphytic organisms appear. This may 

 be due to the relatively smooth surface or 

 the production of some antibiotic compound 

 by the leaf. On tropical seagrasses the 

 heaviest coatings of epiphytes only occur 

 after the leaf has been colonized by the 

 coralline red algae, Fosl iella or Melobe- 

 sia . The coralline skeleton of these algae 

 may form a protective barrier as well as a 

 suitably roughened and adherent surface 

 for epiphytes (Figure 15). 



44 



