CHAPTER 1 



INTRODUCTION 



1.1 SEAGRASS ECOSYSTEMS 



Seagrasses are unique for the marine 

 environment as they are the only land 

 plant that has totally returned to the 

 sea. Salt marsh vegetation and mangroves 

 are partially submerged in salt water, but 

 the seagrasses live fully submerged, 

 carrying out their entire life cycle com- 

 pletely and obligately in sea water (Fig- 

 ure 1). 



Seagrass meadows are highly produc- 

 tive, faunally rich, and ecologically 

 important habitats within south Florida's 

 estuaries and coastal lagoons (Figure 2) 

 as well as throughout the world. The com- 

 plex structure of the meadow represents 

 living space and protection from predation 

 for large populations of invertebrates and 

 fishes. The combination of plentiful shel- 

 ter and food results in seagrass meadows' 

 being perhaps the richest nursery and 

 feeding grounds in south Florida's coastal 

 waters. As such, many commercially and 

 ecologically significant species within 

 mangrove, coral reef, and continental 

 shelf communities are linked with seagrass 

 beds. 



Although the importance of seagrass 

 beds to shallow coastal ecosystems was 

 demonstrated over 60 years ago by the 

 pioneering work of Petersen (1918) in the 

 Baltic Sea, it is only in the past 10 to 

 15 years that seagrasses have become wide- 

 ly recognized as one of the richest of 

 ecosystems, rivaling cultivated tropical 

 agriculture in productivity (Westlake 

 1963; Wood et al . 1969; McRoy and McMillan 

 1977; Zieman and Wetzel 1980). 



Studies in the south Florida region 

 over the past 20 years have demonstrated 

 the importance of the complex coastal 

 estuarine and lagoon habitats to the pro- 

 ductivity of the abundant fisheries and 

 wildlife of the region. Earlier studies 

 describing the link between estuarine sys- 

 tems and life cycles of important species 

 focused on the mangrove regions of the 

 Everglades (W.E. Odum et al . 1982), al- 

 though the seagrass beds of Florida Bay 

 and the Florida Keys have been identified 

 as habitats for commercially valuable spe- 

 cies, as well as for organisms that are 

 important trophic intermediaries. Many 

 species are dependent on the bays, la- 

 goons, and tidal creeks for shelter and 

 food during a critical phase in their life 

 cycle. 



Many organisms that are primarily 

 characterized by their presence and abun- 

 dance over coral reefs, such as the enor- 

 mous and colorful schools of snappers and 

 grunts, are residents of the reef only by 

 day for the shelter its complex structure 

 provides, foraging in adjacent grass beds 

 at night. These seagrass meadows, often 

 located adjacent to the back reef areas of 

 barrier reefs or surrounding patch reefs, 

 provide a rich feeding ground for diurnal 

 reef residents; many of these organisms 

 may feed throughout their life cycle in 

 the grass bed. The juveniles of many 

 Pomadasyid species are resident in the 

 grass beds. As they grow, however, their 

 increasing size will no longer allow them 

 to seek shelter in the grass and they move 

 on to the more complex structure of the 

 reef for better protection (Ogden and 

 Zieman 1977). 



