Bioassays to determine acute toxicity of petroleum to a species should be con- 

 ducted with the most sensitive stage in the life cycle of that species. Allen (1971) 

 tested the effects of WSF from 16 crude and fuel oils on the development of sea 

 urchin eggs. Little or no effect was seen on fertilization; however, 1 1 oils affected 

 cleavage at concentrations of 6 percent WSF or higher. Nicol et al. (1977) reported 

 that similar concentration of WSF (6 percent) from a No. 2 fuel oil also affected 

 cleavage of eggs and larval development in sand dollars. Larvae and juvenile forms 

 have often been found more vulnerable to oil than are adults (Table 2). Wells and 

 Kat7 suggested that the greater sensitivity of crustacean larvae was linked to molting 

 (Wells. 1972). Subsequent work by Mecklenburg et al. (1977) indicated molting 

 shrimp larvae were about five times more sensitive than nonmolting larvae. Recent 

 studies report, however, that early life stages are not the most sensitive for some 

 species of shrimp (Neff et al., 1976) and polychaete (Rossi and Anderson, 1976). 



Numerous studies have reported sublethal effects of petroleum on marine orga- 

 nisms. A sublethal effect is any abnormal response observed during exposure of an 

 organism to nonlethal concentrations of toxicant. Sublethal studies are valuable in 

 the assessment of the potential for damage at oil concentrations that are more prob- 

 able in the environment than LCs<> values. Metabolic rate measurements such as 

 respiration rates generally show an increase in metabolism owing to stress at low oil 

 concentrations (Hargrave and Newcombe, 1973). Respiration rates continue to 

 increase with increased oil concentrations until near-lethal concentrations result in 

 reduced rates. Bradycardia (slowing of the heart) was measured in sea catfish by 

 Wang and Nicol at 0.01 ppm (less than 10 percent of the LCs ( >) of a No. 2 fuel oil 

 (Nicol and Wang. 1977). Feeding responses deteriorated at about 0.038 ppm (27 per- 

 cent of the LC«i). Atema and Stein ( 1974) reported feeding behavior of the lobster 

 was affected by relatively low concentrations of crude oil. Recently, modifications to 

 the feeding behavior of marine copepods have been reported at concentrations of 

 0.25 ppm of fuel oil accommodated in seawater (Berman and Heinle, 1980). Total 

 suppression of feeding or suppression of feeding on small particles between 7 and 1 5 

 /jm in diameter was observed. Feeding on particles larger than 15 jim was increased 

 in some cases. 



Chemotaxis of a snail (Jacobson and Boylan. 1973) and phototaxis of barnacle 

 larvae (Donahue et al., 1977) were altered by WSF from fuel oils. 



Many of the biological effects attributed to stress from sublethal concentrations of 

 pollutants should be reflected in growth rate. The growth rate of an organism is an 

 ecologically significant parameter that can easily be measured in the laboratory. 

 Reduced growth rate of the polychaete worm Neanthes arenaceodentata has been 

 reported by Anderson in 3 percent WSF of a No. 2 fuel oil (Anderson, 1977). The 

 concentration of total hydrocarbons was 180 ppb; total naphthalene concentration 

 was 60 ppb. Neff et al. (1976) exposed larvae of the mud crab Rhithropanopeus 

 harrisii to WSF of No. 2 fuel oil for 6 months. Survival of larvae in the lowest two 

 concentrations (0.16, 0.31 ppm total hydrocarbons) was similar to controls (~ 90 

 percent). Survival in 0.63, 0.94, and 1.26 ppm concentrations were 76, 30, and 6 

 percent, respectively. After 6 months, the mean size of crabs in the control group was 

 larger than that of the 0. 16, 0.31, and 0.63 ppm groups but smaller than that of the 

 0.94 and 1.26 ppm groups. Larvae of the mud crab Eurypanopeus depressus (Smith) 

 were exposed to 4.3 and 8.7 ppm concentrations of WSF of Kuwait crude and devel- 

 opment followed through crab stage five (Cucci and Epifanio, 1979). Increased 

 mortality and duration of intermolt periods were observed in larv ae exposed contin- 

 uously from hatching. Larvae not exposed to WSF before zoea stage three showed 

 slower growth than controls but no higher mortality. An extra morphologically 

 abnormal megalopa stage was observed for some exposed individuals. The percent- 

 age of animals that exhibited the extra abnormal stage increased in the higher con- 

 centration of WSF. Decreased growth of larvae of the amphipod Gammarus 

 oceanicus during a 60-day exposure to WSF from a Venezuelan crude was reported 

 by Linden (1976). 



105 



