Oxyrrhis is widely regarded as having global distribution, but there are limited studies of its geographic range. Most published data describe the range of
Oxyrrhis as areas of the Atlantic and Pacific coasts of the USA, the Gulf of Mexico, the Atlantic coasts of Europe, the Mediterranean and Baltic Seas, the Persian Gulf, the Indian Ocean, and the western Pacific. Its presence has been confirmed in the southern hemisphere, such as in or around Australia, South Africa, Brazil, and it is rare or absent in polar seas (northern Norway, Iceland), however there have been small sample sizes in these polar regions.
Oxyrrhis is rare in open water but has been found to inhabit the coastal waters of some remote islands including Hawaii and the Azores. The genus shows both widespread distributions and endemicity through its various clades. It has been discovered that one clade of
O. marina has widespread distribution, covering both coasts of North America and the eastern Mediterranean Sea, while the other clade is only found in the Baltic Sea and Red Sea. In terms of habitat,
Oxyrrhis is common in many intertidal and coastal habitats. There is potential sampling bias when assessing its distribution, as virtually all samples have been from coastal areas, mainly
intertidal pools, rather than the
open ocean.
Oxyrrhis is unlikely to be exclusively intertidal and is probably a small component of coastal and oceanic
plankton communities, while there is anecdotal evidence that it occasionally grows in shallow embayments. Differences in the temperature and salinity ranges of
O. marina and
O. maritima suggest that the two lineages have different ecophysiology.
O. maritima lives in tidal pools with a relatively high salinity and temperature, while
O. marina lives in water columns which have a lower salinity and temperature. The highest temperature for positive growth of
O. marina is likely to be around 32 °C and 32 °C or higher for
O. maritima.
O. marina only grows at a salinity >=4 ppt and the growth rate increases with salinity up to 50 ppt.
O. maritima grows at a salinity of 2 ppt, and growth rate also increases up until 50 ppt.
Oxyrrhis is highly important in marine communities, playing an essential role in pelagic food webs as they both consume
phytoplankton in addition to
ciliates,
bacteria, and the eggs, early nauplii stages, and adults of some metazoans, amongst other prey items. They additionally act as prey for upper trophic levels, which include some metazoans, ciliates and other dinoflagellates. These consumption rates by
Oxyrrhis can exceed 60% of the daily phytoplankton production in many of oceanic and coastal systems. By feeding on and being predated upon by a broad range of organisms,
Oxyrrhis significantly affect food web structure, carbon cycles and energy flows within the marine planktonic community. == Description of the organism ==