Tales from Oceanic I slands: The Biogeography of I nsular Marine Gastropods from off Brazil by José H. Leal A newly created volcanic island is devoid of life, until it is colonized by organisms from other, geologically older areas. The classical theory of island biogeography discusses how physical factors, such as the surface area of an island, its age, and its distance from the mainland interact to determine how quickly such an island will be colonized and how many species are likely to live there. Other factors besides physical ones are important too. Each particular species has a certain mixture of capabilities and limitations that define its ability to disperse and colonize an island. The study of the processes that make it possible for these shallow water benthic (bottom-living) creatures to cross stretches of deep water and colonize a geologically young oceanic island is a paramount aspect of marine biogeography. Most true oceanic islands have originated from volcanic activity in the deep ocean floor. As a result of plate tectonics and sea-floor spreading through geological time, weaker regions of the oceanic crust have been punctured sporadically by hot magma from below. Big piles of solidified lava and debris produced in these areas during periods of intensified volcanic activity create true oceanic islands and submerged seamounts. Such islands occur off the coast of Brazil: in the western extremity of the Romanche Trench off northeastern Brazil are the Fernando de Noronha Archipelago and Atol das Rocas; more to the south, in the eastern end of the Vitoria-Trindade Seamount Chain (also known as Martin Vaz Fracture Zone), are the islands of Trindade and Martin Vaz Archipelago. Created since the birth of the Atlantic some 100 million years ago, these islands have formed chains perpendicular to the South American coast. In the case of this particular ocean, the islands and seamounts situated closer to the continent are usually older than those found in the open ocean, a consequence of the local direction of sea-floor spreading. My dissertation project at the Rosenstiel School of Marine and Atmospheric Science/University of Miami consists of a biogeographical study of the prosobranchs (hard shelled, benthic, or bottom-dwelling, gastropods) from these islands in the southwestern Atlantic Ocean. The main goals of my research are to survey the prosobranchs found in these islands and to attempt to determine why they are there, i.e., how the faunal composition of each island can be determined by the interaction between the physical factors of the island and the capabilities and limitations of the each species present there. More than 320 species of mollusks live in these islands, over a third the number of species Professor Rios examined in 1985 for the entire Brazilian coast. The mollusks included in my study come from samples I collected, by SCUBA in the shallows and dredging in the depths, as well as from E.C. Rios' collection in the Museu Oceanografico do Rio Grande, Brazil, and from other museum collections worldwide.