on the beach (Nadeau and Berquist 1977). 

 Although the spilled Venezuelan crude oil 

 is considered to have low toxicity, the 

 strong winds and the wave action in shal- 

 low waters combined to produce dissolution 

 and droplet entrainment that yielded an 

 acutely toxic effect. This wave entrain- 

 nent carried oil down into the turtle 

 grass, killing the vegetation. Lacking 

 the stabilizing influence of the seagrass, 

 extensive areas were eroded, some down to 

 the rhizome layer. Some turtle grass 

 rejuvenation was noted in January 1974, 

 and by 1976 renewed seagrass growth and 

 sedinent development were observed. Sur- 

 veys of the epibenthic communities showed 

 a general decline following the spill, but 

 infaunal sample size proved too small 

 (Nadeau and Berquist 1977) to yield defin- 

 itive results. 



In July 1975 a tanker discharged an 

 estimated 1,500 to 3,000 barrels of an 

 emulsion of crude oil and water into the 

 edge of the Florida current about 40 km 

 (25 mi) south-southwest of the Marquesa 

 Keys. The prevailing winds drove the oil 

 inshore along a 50-km (31-ni) section of 

 the Florida Keys from Boca Chica to Little 

 Pine Key. Chan (1977) observed no direct 

 damage to turtle grass, manatee grass or 

 shoal grass. The natural seagrass drift 

 material apparently acts as an absorbent 

 and concentrator of the oil. This mate- 

 rial was deposited in the intertidal zone 

 where the oily deposits persisted at least 

 1 month longer than the normal seagrass 

 beachwrack, and Chan thought that this 

 reduced detrital input into the dependent 

 ecosystems. The amphipods and crabs typi- 

 cal of this zone did not occur in the pol- 

 luted material. The author attributed 

 mass mortalities of the pearl oyster 

 ( Pinctad a radia ta) a grass bed inhabitant, 

 to some soluble fraction of petroleum. 

 The severest impacts were in the adjacent 

 mangrove and marsh communities where 

 plants and animals were extensively dam- 

 aged. Among the effects noted was the 

 increase in temperature above the lethal 

 limit of most intertidal organisms caused 

 by the dark oil coating. 



From various studies it is obvious, 

 then, that even when the seagrasses them- 

 selves apparently suffer little permanent 

 damage, the associated fauna can be quite 



sensitive to both the soluble and insol- 

 uble fractions of petroleum (Figure 25). 



Considering the vast amount of ship 

 traffic that passes through the Florida 

 Straits, it is somewhat surprising that 

 there have not been more reported oil 

 spills. Sampling of beaches throughout 

 the State has shown that a considerable 

 amount of tar washes up on Florida 

 beaches, and that the beaches of the 

 Florida Keys are the most contaminated 

 (Romero et al . 1981). In this study, 26 

 beaches throughout the State were sampled 

 for recently deposited tar. The density 

 of ship traffic and the prevailing south- 

 easterly winds, result in no tar accumula- 

 tion on many beaches on the gulf coast, 

 while the largest amounts are found 

 between Elliot Key and Key West. Of the 

 26 sample stations, 6 were in the Keys be- 

 tween Elliot Key and Key West, and there 

 were 10 on each coast north of this 

 region. The average for the six Keys 

 stations was 17.2 gm tar/m^ of beach 

 sampled, with the station on Sugarloaf Key 

 showing the highest mean annual amount of 

 40.5 gm/m . By comparison, the average 

 annual amount for the 10 east coast 

 beaches north of f^iami was 2.5 gm/m"^, and 

 the average for the west coast beaches 

 north of Cape Sabel was only 0.3 gm/n-. 

 The implication of this study is quite 

 frightening, for as damaging and unsightly 

 as an oil spill can be on a beach, the 

 potential for damage is inestimably higher 

 in a region such as the Florida Keys with 

 its living, biotic interfaces of mangrove, 

 barely subtidal seagrass flats, and shal- 

 low coral reefs. 



8.4 TEMPEPATUPE AND SALINITY 



Tropical estuaries are particularly 

 susceptible to damage by increased temper- 

 atures since most of the community's 

 organisms normally grow close to their 

 upper thermal limits (Mayer 1914, 1918), 

 The Committee on Inshore and Estuarine 

 Pollution (1969) observed that a wide 

 variety of tropical marine organisms could 

 survive temperatures of 28°C (32°F) but 

 began dying at 33° to 34°C (91° to 93°F). 

 In Puerto Rico, Glynn (1968) reported high 

 mortalities of turtle grass and inverte- 

 brates on shallow flats when temperatures 



88 



