Jassa falcata

Researched By	Jacqueline Hill	Data Supplied By	MarLIN
Refereed by	Prof. P. Geoff Moore
Taxonomy
Scientific name	Jassa falcata	Common name	An amphipod
MCS Code	S569	Recent Synonyms	None
Phylum	Crustacea	Subphylum
Superclass		Class	Eumalacostraca
Subclass	Peracarida	Order	Amphipoda
Suborder	Gammaridea	Family	Ischyroceridae
Genus	Jassa	Species	falcata
Subspecies
Additional Information	Jassa falcata shows marked variation in shape and relative proportions of the taxonomically useful characteristics vary with growth stage. Therefore, the taxonomy of Jassa falcata has proved to be problematic. The species Jassa marmorata and Jassa herdmani are easily confused with Jassa falcata so that some of the literature on Jassa falcata may refer to these species or a mixture of Jassa species (Conlan, 1990).
Taxonomy References	Howson & Picton, 1997, Hayward & Ryland, 1995b, Fish & Fish, 1996, Lincoln, 1979, Conlan, 1990
General Biology
Growth form	Articulate	Feeding method	Predator, Active suspension feeder
Mobility/Movement	Swimmer, Crawler, See additional information, Temporary attachment	Environmental position	Epibenthic, Epiphytic
Typical food types	Unselective suspension feeder of detritus and small organisms.	Habit	Tubiculous
Bioturbator		Flexibility	High (>45 degrees)
Fragility	Intermediate	Size	Small(1-2cm)
Height	Insufficient information	Growth Rate	0.07 mm/day
Adult dispersal potential	10-100m	Dependency	Independent
Sociability	Gregarious
Toxic/Poisonous?	No
Additional Information	Jassa falcata builds tubes, from debris, among algae and hydroids, and on solid surfaces and structures. Males and females live in separate tubes constructed of pieces of debris cemented together, the tubes often forming dense mats. This species is essentially a benthic tube dwelling amphipod although intermittent swimming and crawling is common. Jassa falcata is generally a suspension feeder, however, large specimens have also been seen to capture and feed upon other smaller amphipods and ostracods to supplement their diet. Growth rate is given as maximum growth rate observed in laboratory investigations at varying temperatures. Maximum growth took place at 20 °C (Nair & Anger, 1979).
Biology References	Hayward & Ryland, 1995b, Fish & Fish, 1996, Baardseth, 1970, Nair & Anger, 1979, Conlan, 1990
Distribution and Habitat
Distribution in Britain & Ireland	Found on all British coasts. Reported from several sites around the coast of Ireland.
Global distribution	Cosmopolitan in temperate and warm-temperate waters; widespread and frequently recorded in Atlantic, Pacific and Indian Oceans, both north and south of the equator. Reported from most coastal regions of North East Atlantic, and often locally abundant.
Biogeographic range	Not researched	Depth range	Lower eulittoral to 5 m
Migratory	Non-migratory / Resident
Distribution Additional Information	This species is an important fouling organism. The animals construct tubes from pieces of debris and sediment cemented together, often forming dense mats, particularly in warm water discharge pipes from power stations (Fish & Fish, 1996). Reported to depths of 5m in Japan (Kamenskaya, 1977). Jassa falcata is often found inhabiting Laminaria holdfasts and so may be found at the greater depths inhabited by some kelps. Jassa falcata appears to be out-competed by Parajassa pelagica or unable to survive in very strong wave action at shallow depths (K. Hiscock personal communication).
Substratum preferences	Other species (see additional information), Algae, Artificial (e.g. metal/wood/concrete), Bedrock	Physiographic preferences	Open coast, Strait / sound, Enclosed coast / Embayment
Biological zone	Lower Eulittoral, Sublittoral Fringe, Upper Infralittoral	Wave exposure	Very Exposed, Exposed, Moderately Exposed, Sheltered
Tidal stream strength/Water flow	Strong (3-6 kn), Moderately Strong (1-3 kn)	Salinity	Full (30-40 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)	V
Distribution References	Hayward & Ryland, 1995b, Lincoln, 1979, Picton & Costello, 1998, Costello et al., 1989
Reproduction/Life History
Reproductive type	Gonochoristic	Developmental mechanism	Direct Development
Reproductive Season	All year	Reproductive Location	Insufficient information
Reproductive frequency	Annual protracted	Regeneration potential	No
Life span	<1 year	Age at reproductive maturity	<1 year
Generation time	<1 year	Fecundity	Insufficient information
Egg/propagule size	Insufficient information	Fertilization type	External
Larvae/Juveniles Larval/Juvenile dispersal potential Insufficient information Larval settlement period Not relevant Duration of larval stage Not relevant
Additional Information	Reproduction, and therefore production of gametes, occurs throughout the year although some seasonal peaks of reproduction have been observed. In Helgoland waters, for example, two peaks were observed, the main one in summer and another smaller peak in winter (Nair & Anger, 1980). The mating system is polygynous. Several broods of offspring are produced, each potentially fertilised by a different male. Males are believed to seek out mature females attracted by female pheromones. There is no sperm storage, and fertilisation is external. There is no larval stage. Embryos are brooded in a marsupium, beneath the thorax, formed by the oostegites (a series of flattened plates projecting from basal segments). Embryos are released as subjuveniles with incompletely developed eighth thoracopods and certain differences in body proportions and pigmentation. In laboratory investigations, life span, time to maturity and fecundity were strongly influenced by temperature (Nair & Anger, 1979). At 20 °C the time to reach maturity is 2 months, about half the value observed at 10 °C. Field investigations in Helgoland observed age at maturity to be 6 months for new generations produced in low winter temperatures of 7-8 °C (Nair & Anger, 1980). Growth rate also increases with increasing temperature but life span is shorter and individuals are smaller at higher temperatures (Nair & Anger, 1979).
Reproduction References	Barnes, 1980, Nair & Anger, 1979, Nair & Anger, 1980