ORDER
Calanoida
FAMILY
Acartiidae
TAXONOMY
Acartia clausi Giesbrecht, 1889, Mediterranean Sea.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
Body length 0.045–0.048 in (1.15–1.22 mm) for female and 0.039–0.042 in (1–1.07 mm) for male. Body gymnoplean, with somewhat slender prosome and short, slender urosome of three segments. Antennules long, indistinctly 18-segmented in female; male antennule geniculate on right side only. Antenna with four-segmented exopod and with 6 to 8 supernumerary setae on allobasal segment. Maxillipeds reduced distally. Swimming legs 1–4 all biramous, with three-segmented exopods and two-segmented endopods; fifth legs reduced in female, uniramous ending in tapering spinous process. Male fifth legs asymmetrical, specialized for grasping female and transferring spermatophore during mating.
DISTRIBUTION
Cosmopolitan in temperate and subtropical waters. (Specific distribution map not available.)
HABITAT
Found in near surface depths 0–164 ft (0–50 m), in shallow coastal waters and embayments; rarely in open oceanic waters.
BEHAVIOR
Typically 4–5 generations per year, but up to seven generations reported. Lifecycle consists of six naupliar stages, followed by five copepodid larval stages before final molt into adult. Exhibits daily vertical migration, but only over short vertical range. Feeds near surface waters at night, returning to deeper water during daytime.
FEEDING ECOLOGY AND DIET
A small particle feeder that feeds in near-surface coastal waters; generates water currents by the slow swimming movements of antennae and first legs and captures food particles in laminar flow fields; first legs are involved instead of maxillipeds. Mostly herbivorous; diet includes wide range of minute unicellular phytoplankton such as diatoms, coccolithophores, and dinoflagellates, and ciliate protists. Selective in choice of food particle type.
REPRODUCTIVE BIOLOGY
Mating takes place in water column. Mating behavior is not known, but probably involves male detection of pheromone trail laid down by female. Male grasps female using left fifth leg, and transfers single spermatophore with tip of right leg. Spermatophore discharges into seminal receptacle in female genital region. Sperm stored in seminal receptacle; stored sperm from single mating is probably sufficient for lifetime egg production by female; remating is rare. Female can produce numerous batches of eggs, broadcast into water column at night. Two types of eggs produced, subitaneous eggs, which hatch after about one day, and resting eggs, which have a spiny external coat and sink to lie on sediment. Resting eggs typically act as overwintering stage, hatching in spring.
CONSERVATION STATUS
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
Plays vital role in economy of coastal seas; forms middle link in food chain leading from phytoplankton up to commercially important fish species in estuarine fish spawning grounds and in coastal waters.
