Mortality of marine invertebrate larvae in mercury, copper, and zinc solutions

Abstract

The times taken to kill 50% of their larvae were determined for some species of bryozoans (Watersipora cucullata (Busk), Bugula neritina L.), tubeworms (Spiuorbis lamellosa Lamarck, Galeolaria caespitosa Lamarck), bivalve molluscs (Mytilus edulis planulatus Lamarck, Crassostrea commercialis Iredale & Roughley), and the brine shrimp (Artemia salina L.). The molar concentrations of mercury (added as mercuric chloride), required to kill 50 % of the larvae of the above species in 2 hr were 5.0 × 10^-7M, 1.0 × 10^-6M, 7.0 × 10^-7M, 6.0 × 10^-6, 6.5 × 10^-5M, 9.0 × 10^-4M, and 9.0 x10^-3M, respectively. The pH of these solutions ranged from 7.8 to 8.2. For Watersipora, Bugula, and Spirorbis, mercury was more toxic than copper and copper was more toxic than zinc when the copper and zinc were added as citrates. The following concentrations of copper produced 50% mortality of the larvae in 2 hr over a pH range of 7.0-8.2: Watersipora 9.0 × 10^-6M , Bugula 6.0 × 10^-5M , Spirorbis 8.0 × 10^-6M, Galeolaria 4.5 × 10^-3M, and Mytilus 3.5 × 10^-4M. Comparable data for zinc over a pH range of 7.6-8.0 were: Watersipora 5.0 × 10^-4M, Bugula 8.0 × 10^-5M, and Spirorbis 7.5 × 10^-5M.

During experiments with bivalve mollusc larvae in concentrated copper solutions (5.0 × 10^-2M) it was noted that the pH was sufficiently acid (3.5) to dissolve the shells away. The effect of low pH as a mortality factor in such solutions was investigated using Artemia larvae. It was found that the death rate of larvae in copper concentrations of 1.0 × 10^-1 to 4.0 × 10^-5M, with a pH of 3.2-4.5 was similar to that of larvae in comparable solutions not containing copper, but with a similar pH range. Therefore, the effect of the lowered pH in concentrated copper solutions needs to be taken into account in assessing mortality rates. Of the larvae tested Artemia appeared to have the greatest potential as a test organism for screening potential antifouling compounds.