(hir Liviiif; Resources — Caiiskil & Murine Emsystcms 



273 



Seagrass ecosystems are widely recognized 

 as some of the most productive benthic habi- 

 tats in estuarine and nearshore waters of the gulf 

 coast. Seagrass meadows provide food for win- 

 tering waterfowl and important spawning and 

 foraging habitat for several species of commer- 

 cially iinportant finfish and shellfish. Physical 

 structure provided by seagrasses affords juve- 

 niles refuge from predation and allows for 

 attachment of epiphytes and benthic organisms. 

 Seagrass communities also support several 

 endangered and threatened species, including 

 some sea turtles and manatees. Changes in sea- 

 grass distribution can reflect the health of a 

 water body, and losses of seagrasses may signal 

 water-quality problems in coastal waters. 

 Losses of seagrasses in the northern Gulf of 

 Mexico over the last five decades have been 

 extensive — from 20% to 100% for most estuar- 

 ies, with only a few areas experiencing increas- 

 es in seagrasses. 



Although often considered continuous 

 around the entire periphery of the gulf, sea- 

 grasses exist only in isolated patches and nar- 

 row bands from Mobile Bay. Alabama, to 

 Aransas Bay. Texas (Figure). This pattern of 

 occurrence results from a combination of low 

 salinities, high turbidity, and high wave energy 

 in shallow waters. Seagrasses are more exten- 

 sively developed from Mobile Bay to Florida 

 Bay (Figure). Although freshwater submerged 

 aquatic vegetation also occurs throughout gulf 

 coast estuaries and river deltas, its distribution 

 is not considered in this article. 



Seagrass habitats in the Gulf of Mexico have 

 declined dramatically during the past 50 years, 

 mostly because of coastal population growth 

 and accompanying municipal, industrial, and 

 agricultural development. Although proximate 

 causes of local declines can sometimes be iden- 

 tified, most habitat loss has resulted from wide- 

 spread deterioration of water quality (Neckles 

 1993). 



The total seagrass coverage in the shallow, 

 clear waters in protected estuaries and 

 nearshore waters of the Gulf of Mexico coastal 

 states is estimated to be 1.02 million ha (2.52 

 million acres: Duke and Kruczynski 1992). 

 About 693,000 ha (1.71 million acres) of sea- 

 grasses occur in waters of the Florida Big Bend 

 and Florida Bay (Figure). The remaining 

 324,000 ha (800,000 acres) are within gulf estu- 

 aries, with about 95% in the estuarine areas of 

 Florida and Texas. Florida Bay seagrass mead- 

 ows occupy about 550,000 lia ( 1 .36 million 

 acres), while the seagrass meadows of the 

 Florida Big Bend area cover about 300,000 ha 

 (740,000 acres; Zieman and Zieman 1989). 



Six species of seagrasses occur in the Gulf 

 of Mexico: turtle grass (Thalassici testudinum). 



shoal grass (Halodide wrighiii). manatee grass 

 {Syriugodiiim fdifoniie). star grass (Halophda 

 cni>elmaimi). Halophila decipiens, and widgeon 

 grass (Ruppici imiiitima). The latter has a distri- 

 bution in water with lower salinity, but is com- 

 monly reported in association with the seagrass- 

 es throughout the gulf coast. 



Case Histories 



Sarasota Bay 



Between 1948 and 1974, South Sarasota and 

 Roberts bays lost 193 ha (477 acres) or 25%: 

 Dryman, Blackburn, Dona, and Roberts (a dif- 

 ferent Roberts Bay) bays lost 31 ha (77 acres) or 

 29%: and Lemon Bay lost 55 ha (136 acres) or 

 21% of seagrasses (Evans and Brungardt 1978). 

 Losses have been attributed mainly to dredge- 

 and-fill activities and decline in water quality 

 (Wolfe and Drew 1990). Improved water quali- 

 ty in Little Sarasota Bay caused seagrasses to 

 increase between 1948 and 1974 by 14 ha (34 

 acres) or 9%. 



Tampa Bay 



In Tampa Bay (Figure), turtle grass and 

 shoalgrass are dominant, and widgeon grass, 

 manatee grass, and star grass are also found. A 

 historical estimate places 30,970 ha (76,527 

 acres) occurring within the shallow- water mar- 

 gins of Tampa Bay before human influence (ca. 

 1876: Lewis et al. 1985). Based on 1981 esti- 

 mates of seagrass coverage, a reduction of 81 % 

 of seagrasses has occurred in Tampa Bay: 5,750 

 ha (14,208 acres) were present in 1981. The 

 most striking decrease occuned between 1940 

 and 1963, when about 50% of the grass beds 

 were lost (Lewis et al. 1985). During this peri- 

 od, Hillsborough Bay alone lost 94%- of its 

 grass beds. Old Tampa Bay lost 45%, and 

 Tampa Bay proper lost 35%. These losses have 

 been attributed primarily to direct dredging of 

 grassbeds and major shoreline modifications 

 through filling and siltation (Wolfe and Drew 



Seagrass 

 Distribution in 

 the Northern 

 Gulf of 

 Mexico 



by 

 Lawrence R. Handley 



National Biological Service 



Figure. Study sites along the Gulf of Mexico region. 



