''Amphibalanus improvisus'', the bay barnacle, European acorn barnacle, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

acorn barnacle Acorn barnacle and acorn shell are Common name, vernacular names for certain types of stalkless barnacles, generally excluding goose barnacles, stalked or gooseneck barnacles. As adults they are typically cone-shaped, symmetrical, and attached to r ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Balanidae The Balanidae comprise a family of barnacles of the order Balanomorpha. As a result of research published in 2021 by Chan et al., the members of the family Archaeobalanidae were merged with this family. Genera These genera belong to the family B ...

Description

''Amphibalanus improvisus'' has a smooth white or pale grey conical calcareous shell composed of six fused plates. There is an oval or rhombic opening at the top which is blocked by two hinged plates. Adults usually grow to about in diameter and in width though they are sometimes larger than this and can grow taller when densely packed. The base is characteristically grooved radially. This species can be confused with the striped barnacle (''

Amphibalanus amphitrite ''Amphibalanus amphitrite'' is a species of acorn barnacle in the Balanidae family. Its common names include the striped barnacle, the purple acorn barnacle and Amphitrite's rock barnacle. It is found in warm and temperate waters worldwide. Desc ...

'') and in European waters with the northern rock barnacle (''

Semibalanus balanoides ''Semibalanus balanoides'' (common barnacle, common rock barnacle, northern rock barnacle) is a common and widespread boreo-arctic species of acorn barnacle. It is common on rocks and other substrates in the intertidal zone of north-western Euro ...

'') or the rock barnacle (''

Balanus crenatus ''Balanus crenatus'' is a species of acorn barnacle in the Balanidae family. It is found in the North Pacific and the North Atlantic Ocean. Description The shell of ''B. crenatus'' is made of six calcareous plates and grows up to across. The up ...

'').

Distribution

''Amphibalanus improvisus'' has a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

and is found in temperate and tropical parts of the Atlantic Ocean, the Arctic Ocean, the Baltic Sea the North Sea, the Mediterranean Sea and the Black Sea. It is not known where the species natural range lies but it may have originated in North America. It has colonised many parts of the world's oceans including the Indo-Pacific and Australasia as a

biofouling Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...

agent on the hulls of

ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...

s. It was one of the first recorded introductions to the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

, having been found in

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

and

Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...

in 1844, the

Elbe The Elbe (; cs, Labe ; nds, Ilv or ''Elv''; Upper and dsb, Łobjo) is one of the major rivers of Central Europe. It rises in the Giant Mountains of the northern Czech Republic before traversing much of Bohemia (western half of the Czech Repu ...

estuary in 1854 and

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...

in the 1880s.

Habitat

''Amphibalanus improvisus'' is found, sometimes in vast numbers, down to a depth of about on rocks, man made structures, buoys, ships' hulls, the shells of crabs and molluscs, and certain seaweeds. It has been known to block the water intake pipes of factories and power stations. It is tolerant of both high and low salinity levels and is often found in estuaries and low salinity bays. As an invasive species it competes with native organisms and it is an unwanted coloniser of the shells of cultivated oysters and mussels and aquaculture cages.

Biology

''Amphibalanus improvisus'' is a

filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

. It extends its six pairs of modified legs called cirri to catch

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and other organic material floating past. It is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

and sperm is passed into the cavity of a neighbouring barnacle through a long penis. The eggs are fertilised and brooded in the cavity and hatch into nauplius larvae which drift with the currents. After six naupliar stages occupying two to five weeks, these become cyprid larvae and find a suitable surface on which to settle. Here they cement themselves to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

and undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

into juveniles. There may be several broods in the year but usually just two in the cooler waters of the Baltic and only one in low salinity environments.

References

External links

''Balanus improvisus''
European Network on Invasive Species * {{Taxonbar, from=Q2378433 Barnacles Crustaceans described in 1854 Taxa named by Charles Darwin