A BIOLOGICAL SURVEY OF BALLAST WATER IN CONTAINER SHIPS ENTERING HONG-KONG

The role of ballast water in the introduction of exotic species has re cently received extensive attention. The aim of this study is to asses s the importance of ballast water discharge as a vector for the introd uction of exotic species into Hong Kong waters. Twelve ballast water s amples were collected from 5 container ships entering Hong Kong betwee n June 1994 and October 1995. The ballast water originated from ports on both sides of the Pacific Ocean. At least 81 species from 8 animal phyla and 5 protist phyla were found. Most of the major marine taxonom ic groups were represented and many planktonic larval stages were incl uded. Species richness in the ballast tanks decreased with the age of ballast water. Copepoda was the most diverse and abundant taxonomic gr oup. The density of calanoid and cyclopoid copepods decreased with the age of ballast water, but that of harpacticoid copepods did not chang e significantly with time. Bivalve, crustacean, polychaete and ascidia n larvae from ballast water samples were observed to settle in laborat ory culture tanks. The mussel Mytilopsis sallei which was introduced t o I-long Kong in 1980, was one of the bivalves that settled readily. R esults of this study indicate that ballast water can be a major source for the introduction of exotic species to Hong Kong waters. Regulator y guidelines on the discharge of ballast water should be established.