A review of rice field ostracods (Crustacea) with a checklist of species

Ostracods are very common in rice fields and they can have a significant influence on the rice field ecosystem. They can reach very high densities, often higher than other meiofauna, and their activities can have both positive and negative effects on rice harvests. They directly affect nutrient recycling through excretion, and indirectly by physically disturbing the soil and releasing minerals, thus improving rice growth. On the other hand, ostracods grazing on nitrogen-fixing cyanobacteria potentially reduce rice yields. Rice is a primary staple food for over half of the world’s population, and therefore ostracods can have a significant impact on human food supply. The origin of the rice field ostracod fauna is poorly known, but many rice field ostracods are considered invasive, especially in southern Europe, and from rice fields they have the potential to spread to surrounding natural habitats. Despite their invasive potential and ecological effects on the rice field ecosystem, very little is known about the diversity, ecology and impacts of rice field ostracods in many rice-producing countries. One hundred and ninety-two named ostracod species/subspecies have been reported from rice fields in 26 countries and states worldwide in the published literature; for over three-quarters of rice-producing countries, no data are readily available, and for most of the countries that have available data, diversity is clearly under-reported. Most species that have been documented from rice fields belong to the Cyprididae (78%), a family that makes up approximately 43% of the 2500+ non-marine ostracod species. A further six families (Candonidae, Darwinulidae, Entocytheridae, Ilyocyprididae, Limnocytheridae and Notodromadidae) form the remainder of rice field ostracods. Twenty-two percent of the species reported from rice fields are sexually reproducing, 18% have mixed reproduction, but are mostly asexual, and for 60% males are unknown, and are probably entirely asexually reproducing species. This review and checklist of rice field ostracods are presented to facilitate further research on this group in rice field habitats, research that is crucial for food security in many regions.