Interactive effects of physical factors and hydrocarbon exposure on the survival, development rate and growth of the mud crab Rhithropanopeus harrisii and the horseshoe crab Limulus polyphemus

Abstract

Embryos and juveniles of the horseshoe crab, Limulus polyphemus were exposed continuously to 0, 5, 10, 25 and 50% Water-Soluble Fractions (WSF) of no. 2 fuel oil at temperatures of 20°, 25° or 30° C and one salinity, 32 o/oo S. Exposure lasted four months. Cumulative survival was highest at 30° C and decreased with temperature. The eggs and trilobite larvae were the most sensitive stages. Respiration rates were determined for first-tailed stage animals. A multifactorial design of the three rearing temperatures and salinities of 32 o/oo S (rearing salinity), 20 and 10 o/oo S (hypoosmotic shock salinity) were used. Enough animals survived at 0, 5 and 10% WSF for complete factorial replication. The respiration rates of controls (0% WSF) did not change markedly with salinity. Q₁₀'s for acclimated animals were 2.1, but at 10 and 20 o/oo S they were 1.8 and 1.3, respectively, for the temperature interval from 20 to 30° C. The Q₁₀'s for exposed animals given hypoosmotic shock were greater than 2 and mean respiration rates were higher than those for controls. In a second experiment, larval stages of the mud crab, Rhithropanopeus harrisii were exposed continuously from hatching to 0, 5, 10, 15, and 20% WSF of no. 2 fuel oil for 11 months. The zoeal stages were the most sensitive part of the life cycle. Survival, growth and development rates of crab stages were relatively insensitive to continued WSF exposure. At the end of one year, surviving experimentals produced viable eggs. In a third experiment, the zoeal stages of the mud crab, Rhithropanopeus harrisii were exposed separately to phenanthrene or naphthalene in a factorial combination with three temperatures and salinities. Phenanthrene was much more toxic than naphthalene..