at the Lake Biwa Museum, Japan
Robin James Smith
Seas and oceans. Ostracods live in the seas and oceans throughout the world, from the deep through to the shorelines, coral reefs, sea mounts and on many types of sediments, from gravels to mud. They can be found at all latitudes, from the tropics to the polar regions.
Most species are found living on the bottom, but some species are planktonic.
Photo: The English Channel, UK
Marine coastlines. Ostracods are common along coasts, in inter-tidal zones, rock pools and between the sand grains of beaches.
Many species of ostracods are associated with particular types of seaweeds.
Photo: The coast of Brittany, France
Brackish salt marshes and estuaries. Ostracods tend to be low diversity in brackish waters, such as in estuaries and salt marshes, but they can be very abundant.
There are some freshwater and marine species that can tolerate brackish water conditions, but other species are mainly or only found in brackish habitats.
Photo: Salt marshes, British Columbia, Canada
Lakes and ponds. Of the estimated 304 million natural lakes in the world (Downing et al. 2006), the vast majority are home to ostracods.
Photo: Spirit Lake, Haida Gwaii, Canada
Ancient lakes. Although rare globally, ancient lakes are home to 25% of all non-marine ostracod species. Many of these species are endemic (Martens & Savatenalinton 2011).
Photo: The ancient Lake Orhid, Macedonia / Albania
Artificial lakes, ponds and reservoirs. Due to their desiccant resistant eggs, many species of ostracods rapidly colonize artificial water bodies.
Photo: An artificial pond, Kusatsu, Japan
Rivers. In slow flowing rivers and streams ostracods can be abundant on and in the substrate and amongst water weeds.
In faster flowing rivers ostracods tend to live interstitially, i.e. in the spaces and gaps between sediment grains of the river bed and in gravel banks lining the rivers.
Photo: A river, Shiga Prefecture, Japan
Channels, ditches. Artificial channels and ditches are often colonized by ostracods. Even small drainage ditches along the edges of roads can be home to ostracods.
Photo: An artificial channel, Kanazawa, Japan
Rice fields. Rice fields are a major habitat for freshwater ostracods, and often ostracods are the most abundant animal group in such habitats. They can reach very high densities and influence the growth of the rice, both in positive and negative ways.
Many species of ostracods in rice fields, especially in Europe, are probably invasive, accidentally transported on farm machinery and rice plants. From rice fields they are able to colonize surrounding natural habitats (Valls et al. 2014).
Photo: Rice field, Shiga Prefecture, Japan
Wet leaf litter. Some ostracod species can utilize very small drops of water, and films of water in leaf litter and soils.
If moisture levels decrease too much, ostracods can enter a torpid state by tightly closing their carapaces. One species has been reported to survive over a year in soil with 4 to 5% water content this way (Horne 1993).
Photo: Wet leaf litter, Kanazawa, Japan
Springs and seeps. The discharges of small springs and seeps can harbour a diverse ostracod fauna. Some species are strongly related to such habitats, although can occasionally be found in other habitats too.
Photo: A spring, British Columbia, Canada
Caves. Ostracods can be found in cave systems, but diversity and abundance tend to be low. Sometimes typical surface-dwelling species opportunistically colonize caves, but there are a small number of species that are only known from such habitats.
In 2012 an ostracod species was discovered in a cave in South Korea that belonged to a genus thought to be extinct since the Eocene. It appears that this lineage moved from lake environments to caves at some point in the past (Smith et al. 2012).
Photo: A cave, Korea
Groundwater. The often vast and unseen groundwater habitats harbour diverse ostracod faunas. The groundwater fauna is very different to the species living in surface water bodies, with many species and genera only known from these habitats (e.g. Smith 2011). Many groundwater species are endemic to small regions.
Access to groundwater is limited to wells and boreholes, which means that sampling these habitats is restricted. Because of this, groundwater ostracod faunas are still poorly known in most parts of the world.
Photo: A well, Shiga Prefecture, Japan
ReferencesDowning, J. A. et al. 2006. The global abundance and size distribution of lakes, ponds, and impoundments. Limnology and Oceanography, 51, 2388-2397.
Horne, F. R. 1993. Survival strategy to escape desiccation in a freshwater ostracod. Crustaceana, 65, 53-61.
Smith, R. J. 2011. Groundwater, spring and interstitial Ostracoda (Crustacea) from Shiga Prefecture, Japan, including descriptions of three new species and one new genus. Zootaxa, 3140, 15-37.
Smith, R. J., Lee, J., Choi, Y. G., Chang, C. Y. & Colin, J-P. 2012. A Recent species of Frambocythere Colin, 1980 (Ostracoda, Crustacea) from a cave in South Korea; the first extant representative of a genus thought extinct since the Eocene. Journal of Micropalaeontology, 31, 131-138.
Valls L, Rueda J, Mesquita-Joanes F, 2014. Rice fields as facilitators of freshwater invasions in protected wetlands: the case of Ostracoda (Crustacea) in the Albufera Natural Park (E Spain). Zoological Studies, 53, 1-10.