EFFECTS OF AN OIL AND GAS-PRODUCTION EFFLUENT ON THE COLONIZATION POTENTIAL OF GIANT-KELP (MACROCYSTIS-PYRIFERA) ZOOSPORES

Point sources of pollution (e.g. industrial and municipal outfalls) ma y produce ecological impacts at distant locations if pollutants affect dispersive propagules. We used laboratory experiments to determine ho w water-column exposure to produced water (= the aqueous fraction of o il and gas production that is typically discharged into coastal waters ) influences the colonization potential of giant kelp (Macrocystis pyr ifera) zoospores on the bottom. Zoospores were maintained in suspensio n at relatively low densities in 18-liter containers and exposed to on e of five concentrations of produced water for varying amounts of time . Zoospore swimming generally decreased with increasing produced-water concentration and exposure duration; however, the specific pattern of decrease differed between experimental trials done on different dates . The effect of exposure duration on the ability of swimming zoospores to attach to plastic dishes placed on the bottom varied with produced -water concentration. Zoospores placed in produced-water concentration s of 1 and 10% showed a steady decline in their ability to attach with increased exposure; lower concentrations of produced water had no suc h effects. The percentage of zoospores that germinated after attachmen t varied tremendously with exposure duration and date of experimental trial. Zoospores that settled during the first 12 h after release had very poor rates of germination, indicative of a short precompetent per iod. Surprisingly, exposure of suspended zoospores to high concentrati ons of produced water during the first 12 h reduced this precompetent period and greatly improved germination success on the bottom. The mag nitude of this enhancement, however, varied among dates. The results s uggest that adverse effects of discharging produced water on planktoni c zoospores of giant kelp would most likely be limited to the immediat e vicinity of the outfall.