There’s an invasion plaguing the coastal waters of Southern California. Waves of tiny interlopers spark havoc at fisheries, clog municipal water pipes and frustrate boaters who must dislodge buckets of sea crud. They’ve altered our coastal regions’ ecosystems, endangered native fish and birthed such nasty problems as “swimmer’s itch.” Accelerated in recent decades by international trade, invasive sea creatures have hitchhiked here in and alongside massive cargo vessels from around the globe.