5.1 ASSOC lAFEP ALOAE 



Major sources of priinary production 

 for coastal and estuarine areas are the 

 Fol lowing: 



(1) Macrophytes (seagrasses, nan- 

 groves, macroalgae, and marsh 

 grasses) 



(2) Bonthic inicroalgae (benthic and 

 epiphytic diatons, dinoflagcl- 

 lates, filanentous green and 

 bluegreen algae) 



(3) Phytoplankton 



Although in deep, turbid northern 

 estuaries, such as the Chesapeake or Dela- 

 ware Bays, phytoplankton may be the doni- 

 nant producer, in most areas that have 

 been investigated the macrophytes are the 

 most important primary producers, often by 

 an overwhelming margin. 



Productivities of phytoplankton, 

 marsh grasses, and seagrasses in a North 

 Carolina estuary were compared by Williams 

 (1973); areal production values were 53, 

 249, and 678 g/m"/yr, respectively. Hhen 

 the total area of the estuarine sound sys- 

 tem available to phytoplankton and sea- 

 grass was considered, the seagrass produc- 

 tion for the entire estuary was still 

 about 2.5 times the annual contribution of 

 the phytoplankton. In the clearer waters 

 of the Florida estuaries and coastal zone, 

 the difference is considerably greater. 

 In Boca Ciega Bay, Taylor and Salonan 

 (1968) estimated that total production, 

 which was primarily macrophytes, was six 

 times the annual phytoplankton production. 

 Thayer and Ustach (1981) have estimated 

 macrophytes to account for about 75% of 

 the plant production in the estuarine- 

 coastal area of the northern Gulf of 

 Mexico. 



Benthic Algae 



Algal communities on hard substrates 

 can consist of hundreds of species from 

 all of the major macroalgal phyla. The 

 areas inhabited by seagrasses do not offer 

 an optimal habitat for most algae, which 

 require hard substrate for attachment of 



their holdfast. Primary substrate for 

 algae will include (1) the sediments, (2) 

 the seagrasses themselves, and (3) occa- 

 sional rocks or outcrops. In addition 

 many macroalgae in south Florida form 

 large unattached masses on the sea bottom, 

 collectively known as drift algae. 



Although much of south Florida offers 

 sufficient hard substrate for algal at- 

 tachment, notably the reef tracts and the 

 shallow zones bordering many of the keys, 

 the dominant substrate type is not solid. 

 In many areas mangrove prop roots, oyster 

 bases, and scattered rocks or shells and 

 to manmade structures such as bridge sup- 

 ports and canal walls offer the primary 

 algal substrates. 



The only algae able to consistently 

 use sediments as substrate are (1) the 

 mat-forming algae and (2) members of the 

 order Siphonales (Chlorophyta) which 

 possess creeping rhizoids that provide an 

 anchor in sediments (Humm 1973). Ainong 

 the most important genera are Hal imeda , 

 Penicillus , Caulerp a, Rhipocephalus , and 

 Udotea (Tigure 14). These algae are 

 important as primary producers of organic 

 carbon; of even greater importance, all 

 but Caulerpa produce calcium carbonate for 

 their skeleton which, upon death, becomes 

 incorporated in the sediments. 



These algae have limited sediment 

 stabilizing properties, the main utility 

 of their rhizoidal holdfasts being to 

 maintain then in place. Because they do 

 not have a large investiture of structure 

 in the sediments, they can more rapidly 

 accommodate changes in shifting sediments, 

 while still maintaining some current 

 buffering capacity. In this capacity 

 they form a prior successional stage for 

 seagrasses (Williams 1981). 



Production of lime mud by these algae 

 can be enormous. Hal imeda tends to break 

 up into characteristic sand-sized plates, 

 while Penicil lus produces fine-grained 

 (less than 15i_, ) araoonitic mud. Stockman 

 et al. (1967) estimated that at the 

 present rate of production, Penicillus 

 alone could account for all of the fine 

 mud behind the Florida reef tract and 

 one-third of the fine mud in northeastern 

 Florida Bay. In addition, the combination 



42 



