Bythotrephes longimanus

Bythotrephes longimanus
The spiny water flea (below), and the fishhook waterflea (above)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Branchiopoda
Order:	Cladocera
Family:	Cercopagididae
Genus:	Bythotrephes
Species:	B. longimanus
Binomial name
Bythotrephes longimanus (Leydig, 1860)
Synonyms
Bythotrephes cederstroemi

Bythotrephes longimanus (also Bythotrephes cederstroemi), or the spiny water flea, is a planktonic crustacean less than 15 millimetres (0.6 in) long. It is native to fresh waters of Northern Europe and Asia, but has been accidentally introduced and widely distributed in the Great Lakes area of North America since the 1980s. Bythotrephes is typified by a long abdominal spine with several barbs which protect it from predators.

Description and taxonomy

Bythotrephes longimanus is a cladoceran crustacean (water flea) recognizable with its straight tail spine averaging about 70% of its length. Adult individuals have three to four barbs on the spine while juveniles have only one pair. The animal has one large eye that is usually black or red. It also possesses a pair of swimming antennae and four pairs of legs, of which the first pair is used to catch prey. Mandibles are used for consumption of prey.

The spiny water flea is similar to another introduced cladoceran of the same family, the fishhook waterflea Cercopagis pengoi, which however has a more slender spine featuring a prominent loop-like hook at its end (see figure). There is also variation in the shape of the more robust spine of Bythotrephes itself. Specimens arising from sexually produced eggs have a completely straight and relatively shorter spine. In parthenogenetically produced animals the spine features a kink in the middle (figure). Previously, the kinked-spined animals were thought to be a separate species Bythotrephes cederstroemi.

Diet

The spiny water flea preys on smaller planktonic organisms. Its diet consists mostly of zooplankton including "Daphnia" and smaller crustaceans. Bythotrephes can consume 10–20 prey organisms a day. It may also eat other small organisms it comes across.

Reproduction

The spiny water flea can reproduce quickly with upwards of ten offspring every two weeks. Since the crustacean is only active from late spring to fall, eggs may lie dormant for the winter and hatch when the body of water has warmed up. The eggs are resilient to weather conditions allowing the eggs to survive extremely cold conditions. Though the majority of the water flea's population is female, it is capable of asexual reproduction as well as sexual reproduction.

Geographical range

The spiny water flea is native to northern Europe and Asia, and some parts of central Europe. However the water flea has spread in recent years to many areas throughout Europe including some ports and inland lakes outside its natural range.

In 1984 the crustacean was found in Lake Huron and soon spread to the other Great Lakes and some inland lakes within the Midwest, including over 60 inland lakes in Ontario. It is thought to have been introduced by untreated ballast water from international ships. Concern has increased to the impact of this invasive species in the Great lakes region and other areas it might have been accidentally introduced. The spiny water flea, eggs and larvae may be caught up in fishing line, downriggers, fishing nets, and other fishing equipment which has caused the spread of the water flea to inland lakes and rivers.

Impact in introduced areas

Bythotrephes competes with several fish including panfish and perch for prey. These smaller fish are not able to feed on the spiny water flea itself because of the barbs the flea possesses. The spiny water flea's diet consists mostly of Daphnia zooplankton, leading to competition with small and baby fish, and also with native water flea species. Daphnia zooplankton populations have declined in recent years though there is no conclusive evidence as to the cause.

The spiny water flea, is causing serious concerns in the lakes of Canada. The problem is that it feeds on zooplankton and can actually eliminate zooplankton species. As zooplankton is the backbone of aquatic food chains, this tiny crustacean presents a serious risk to the ecosystem. The eggs survive even after being dried out or eaten by fish.

External links

• http://www.seagrant.umn.edu/exotics/spiny.html
• Invading Species.com [1]
• GLANSIS Species FactSheet
• Species Profile- Spiny Water Flea (Bythotrephes longimanus), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Spiny Water Flea.