Zoogeography of Tropical Western Atlantic Crinoidea (Echinodermata)

Recent collcctions of crinoids from the intertidal zone to ] ,650 m in the tropical western Atlantic have provided significant range extensions for more than half of the 44 comatulid and stalked species known from the region. Of the 34 comatulid species, over 60% are endemic to the region; of the 10 stalked species, 90% are endemic. At the familial level, this fauna has its strongest affinities with the tropical Indo-Pacific region. Comatulids are most abundant above 300 ill, while stalked species occur primarily between 100 and 700 ill. Species that occur primarily above 600 ill (the deepest penetration of the 10°C isotherm in the region) have depth ranges generally narrower than 200 m. Species that are found below 1,000 m generally have much broader depth ranges. During the 1950's and 1960's, extensive collections of marine life were made in the tropical western Atlantic Ocean by M/V OREGON, operated by the U.S. Fish and Wildlife Service, and R/V ]OHNELLIOTTPILLSBURY and R/V GERDA,in connection with the University of Miami's Deep-Sea Biology Program. These collections have generously broadened our knowledge of the marine biogeography of the region, a knowledge based previously on the expeditions of the 19th and early 20th centuries. The recent widespread use of SCUBA in marine research has opened up previously inaccessible environments and has thus added to the picture. This paper summarizes zoogeographical and bathymetric data on the Crinoidea (Echinodermata) collected by these vessels and by SCUBA and presents revised distributions for many of the 44 species, both comatulid and stalked, currently known from the tropical western Atlantic. In this paper, the tropical western Atlantic region extends from southeastern Florida southward along the Antillean Arc to Trinidad, and along the Brazilian coast as far south as Rio de Janeiro, and includes the Caribbean Sea, southern Gulf of Mexico, and the Bahama Islands. The Caribbean, including the Antillean Arc and the Bahamas, constitutes the richest part of this region in both diversity and abundance of crinoids, and is also the most intensively studied part to date. The Blake Plateau and the coast of the United States from southeastern Florida to Cape Lookout, North Carolina, appear to represent a warm temperate transitional zone. At least regarding crinoids, this zone is more closely related to the tropics than to more northerly waters. With the exception of the more tropical Flower Garden Banks, south of Port Arthur, Texas, the northern Gulf of Mexico also falls into this zone. For the crinoid fauna, however, the precise tropical-temperate boundaries in the Gulf are unknown. The difficulties encountered in erecting marine zoogeographic boundaries are compounded by species, including many crinoids, that are limited to warm water latitudes but that live in deeper, colder waters. The parameters governing the distribution of these deep water, tropical species remain largely undefined. The tropical western Atlantic crinoids first became widely known during the period of intensive oceanographic exploration of the late 1800's. The U.S. Coast Survey pioneered the work in this region during the late 1860's (Pourtales, 1867, 1869), followed by the extensive work of BLAKE