Approximately 200 radiolarian species have been collected and identified from the water column and Holocene sediments of the Gulf of Mexico and adjacent seas using Nansen closing nets, DUCA high-speed plankton nets, water bottles, bottom grabs, and gravity and box cores. None of the identified species are endemic to the Gulf of Mexico. Most species appear to be endemic to or indicative of tropical surface water, subtropical underwater, North Atlantic central water, subantarctic intermediate water, and North Atlantic deep water. These water masses enter the Gulf of Mexico through the Yucatan Channel.

Living radiolarian diversities (number of species present) and densities (number of individuals/cu m of water filtered) are generally low in waters over the continental shelves in the Gulf of Mexico. Diversities and densities are highest in the surface waters of the open gulf, peak at about 100 m, and decrease to minimum values with increasing water depth.

Radiolarians are low in diversity and density in most shelf, slope, and basin-floor Holocene sediments. The fossil record for radiolarians in gulf sediments is characterized by sparse occurrences in surficial Holocene sediments, absence from subsurface Holocene to mid-Miocene sediments, and moderate occurrences in many mid-Miocene and older sediments.

Conditions of hypersalinity and/or anoxia appear to enhance radiolarian preservation in fossil sediments in the Gulf of Mexico. Previously unsampled subsurface Holocene to mid-Miocene sediments deposited under these conditions should be useful in future studies of radiolarian biostratigraphy and paleo-oceanography in the gulf.

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