Ramesh Gulati: a personal approach,based on his retirement lecture

Historical and modern migrations and dispersal of most marine organisms (intertidal, benthic, meiofaunal, planktonic, nektonic, or neustonic) are classically interpreted in terms of their natural dispersal potential. Exceptions are introduced species, largely recognized since the 19th century, known to have been transported by human activities. However, humans were transporting species along coastlines and across oceans for millennia and centuries prior to the advent of the first biological surveys. Thus, the presumptive natural distributions of many species may be questioned. Reviewed here are some basic concepts about invasions of non-native species. Human activities move species isolated in time and space from other oceans or continents, and thus human-mediated transport does not simply speed up natural dispersal processes. Both past and modern-day invasions are often overlooked, leading to an underestimation of the scale of invasion diversity and impact. Because vectors, donor regions, and recipient regions change over time, invasions will continue along long-standing but un-managed corridors. The impact of most invasions has never been studied and, therefore, it is not possible to conclude that most invasions have no impact, nor is it generally possible to say that invasions have become `integrated' into a community or ecosystem in ecological time. Finally, invasions in the ocean are not limited to harbours and ports, but are found in a wide variety of marine habitats, ranging from the open ocean continental shelf to exposed rocky shores. The existence of human-mediated vectors has created extraordinary challenges to our understanding and interpretation of the ecology, biogeography, evolutionary biology, and conservation biology of marine communities.