Ostracod Research at the Lake Biwa Museum, Japan

Robin James Smith


Most free-living ostracods are considered to feed on algae and organic detritus, but some ostracods are omnivores, predators and scavengers. Additionally, some ostracods have commensal relationships with (mostly) other larger crustaceans, such as crayfish, while a small number of ostracods are parasites on sharks, sea urchins, polychaete worms and amphipods.

Whether ostracods are prey or predator of certain groups can be related to population densities. In experiments with fish fry and ostracods, it was noted that the fish eat the ostracods, but if the number of ostracods is large, the tables are turned; the ostracods attack and eat the fish fry, leaving just the vertebrae and scales (Liperovskaya 1948).

In the marine genus Rutiderma males and females have different feeding strategies; females are predators, while males, with more poorly developed maxillae, are probably detritus feeders (Kornicker 1985).

The freshwater ostracod Heterocypris incongruens grazing algae on a fallen leaf.

Organic detritus Organic detritus (i.e. the remains of dead organisms and faecal material) is an important food source for many species (Cannon 1933; Kornicker 1975; Fryer 1997; Strayer 1985; Modig et al. 2000; Smith & Delorme 2010).
AlgaeA wide variety of algae is eaten by ostracods, including diatoms, single-celled algae, colonial algae and filamentous algae. In a study, a large quantity of algae was found in the guts of nine freshwater ostracod species. Marine myodocopids also consume algae (e.g. diatoms) as well as other things (Liperovskaya 1948; Kornicker 1975; Arashkevich 1977; Strayer 1985; Fryer 1997).
BacteriaBacteria is a food source for ostracods, including sulfur-oxidizing bacteria in a cave system (Liperovskaya 1948; Peterson et al. 2013).
Cyanobacteria (blue-green algae)Blue-green algae have been found in ostracod guts, and ostracods have been reported feeding on microbial mats of blue-green algae in hot springs (Liperovskaya 1948; Wickstrom & Castenholz 1985).
FungiThe hyphae of fungi have been found in the guts of the freshwater ostracod Heterocypris incongruens (Liperovskaya 1948).
ProtozoansProtozoans, including radiolarians, feature in the diets of ostracods (Liperovskaya 1948; Arashkevich 1977).
Plants and pollenPlant material, rotten wood and pollen have been found in the guts of ostracods. They also eat fallen leaves (Liperovskaya 1948; Campbell 1995; Fryer 1997).
Rotifers (Rotifera)Experimental evidence indicates that ostracods ingest rotifers (Liperovskaya 1948).
Oligochaetes (Annelida, Oligochaeta)Ostracods can tackle oligochaetes much larger than themselves by attacking in packs (Liperovskaya 1948).
Polychaete worms (Annelida, Polychaeta)The spines and bristles of polychaete worms have been found in the guts of some myodocopid ostracods, and observations of myodocopids attacking live polychaete worms have been reported (Kornicker 1975; Vannier et al. 1998).
Round worms (Nematoda)Nematodes have been recovered from the guts of ostracods (Kornicker 1967; Kornicker 1969; Kornicker 1975).
Arrow worms (Chaetognatha)The remains of arrow worms have been found in ostracod stomachs (Cannon 1940).
Copepods (Crustacea, Copepoda)Copepods are eaten by both marine and freshwater ostracods (Cannon 1933; Kornicker 1967; Kornicker 1969; Kornicker 1975; Kornicker et al. 1976; Arashkevich 1977; De Deckker 1983).
Other ostracods (Crustacea, Ostracoda)Studies have shown that a small part of the diet of the marine giant ostracod Gigantocypris muelleri is made up of other ostracods, and marine planktonic halocyprid ostracods are consumed by Macrocypridina castanea. In non-marine habitats, Australocypris insularis was reported to feed on other smaller ostracod species, while Heterocypris incongruens is known to be cannibalistic (Kornicker 1969; Kornicker et al. 1976; Moguilevsky & Gooday 1977; Campbell 1995; Rossi et al. 2011).
Mysids (Crustacea, Mysida)The remains of a mysid have been reported from the stomach of Macrocypridina castanea (Cannon 1933).
Krill (Crustacea, Euphausiacea)Parts of krill appendages have been found in the stomachs of Macrocypridina castanea (Kornicker et al. 1976).
Water fleas (Crustacea, Caldocera)As well as consuming dead cladocerans, ostracods also predate on live specimens. Observations revealed that ostracods attack the antennae of Daphnia first, immobilising the victim before killing and eating it (Liperovskaya 1948; Fryer 1997).
Non-biting midge larvae (Insecta, Diptera, Chironomidae)Ostracods have been known to eat non-biting midge larvae by attacking in groups (Rossi et al. 2011).
Mosquito larvae (Insecta, Diptera, Culicidae)Mosquito larvae can be attacked and eaten by ostracods (Rossi et al. 2011).
Snails (Mollusca, Gastropoda) The young of freshwater snails are predated on by ostracods, including snails that are a vector of the disease schistosomiasis. A shell of a heteropod (planktonic gastropod) was recovered from the stomach of a marine ostracod (Müller 1890; Sohn & Kornicker 1972).
Amphibian eggs (Amphibia, Anura)Some common species of freshwater ostracods have a taste for both toad and frog eggs (Gray et al. 2011; Ottonello & Romano 2011).
Fish (Osteichthyes)Young fish have been found from the guts of the marine giant planktonic ostracod Gigantocypris mulleri, and freshwater fish fry can also be attacked by ostracods. The marine bioluminescent ostracod Vargula tsujii is reported to feed on the mucus and small pieces of skin of live fish, apparently not causing serious damage, but if the fish is attacked by isopods, Vargula tsujii will enter the fish's wounds to feed on the internal organs (Cannon 1940; Liperovskaya 1948; Stepien & Brusca 1985).
Dead animalsA variety of dead animals, such as fish, squid, annelid worms etc. are scavenged by some species of ostracods (Vannier et al. 1998).

Note that studies of gut contents of ostracods are not able to determine if organisms have been actively predated or scavenged.

Parasitic and commensal ostracods

Sharks and rays (Chondrichthyes)The myodocopid ostracod Sheina orri is a parasite on the gills of the epaulette shark and the bluespotted ribbontail ray, while Vargula parasitica has been found on the gills and in the nasal tubes of hammerhead sharks (Wilson 1913; Bennett et al. 1997).
Fish (Osteichthyes) The marine bioluminescent ostracod Vargula tsujii is a noctunral feeder on the mucus and small pieces of skin of live fish, apparently not causing serious damage. Occasionally, fish will shake off the ostracods or swim away. If the fish is injured, the ostracods may predate the fish (see above table). A handful of Vargula parasitica specimens have been recovered from the gills of two species of fish, the rock hind and the blue runner (Wilson 1913; Stepien & Brusca 1985).
Decapods (Crustacea, Decapoda) The Cytheroidea family Entocytheridae is a large groups of about 220 species, most of which are found clinging to crayfish in an apparent commensal relationship. They are also found on a species of freshwater crab (Hart & Hart 1974).
Amphipods (Crustacea, Amphipoda) Several species of Paradoxostomatidae ostracods of the genus Acetabulastoma are parasites on amphipods. Some Entocytheridae species are commensal on amphipods (Schornikov 1970; Hart & Hart 1974).
Isopods (Crustacea, Isopoda) Groundwater isopods are the hosts of a small number of Entocytheridae species (Hart & Hart 1974).
Sea urchins (Echinodermata, Echinoidea) Sea urchins in the Pacific are the hosts of the genus Echinophilus, a parasitic genus of Paradoxostomatidae. A species of the Pontocypridoidea genus Pontocypria is also found in association with echinoids, although the exact relationship remains unclear (Schornikov 1973; Maddocks 1979; Kretzler 1984).
Starfish (Echinodermata, Asteroidea)Pontocypria helenae can be found clinging to the tube feet of three species of Antarctic starfish, in a probable commensal relationship (Maddocks 1968).
Polychaete worms (Annelida, Polychaeta)Mungava riseri, a marine Candonidae, is found attached to and eating the gills of a polychaete worm (Maddocks 1979).
Sponges (Porifera)A study of a marine sponge collected in Madagascar, revealed a commensal species, Pontocypria humesi, living inside. In Lake Titicaca, Chlamydotheca incisa, normally found in temporary habitats, was found associated with a freshwater sponge (Maddocks 1968; Martens & Harrison 1993).

Often the exact relationship between symbiotic ostracods and their hosts i.e. if they are parasitic or commensal, is not clearly known.

The entocytherid ostracods are mostly found on crayfish, and probably feed on detritus on the body of their hosts, but their ecology is poorly understood.

The red swamp crayfish - a home for entocytherid ostracods.


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