''Balanus balanus'' 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 ...

of acorn

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

in the

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 ...

family. It is native to the colder seas of the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

Description

Unlike most

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s, barnacles are unable to move from place to place. Cement glands near the base of the antennae fix them to the rock. The

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

of this species is conical with a circular base which has an irregular edge and a diameter of up to three centimetres. The surface is ridged and white or pale brown. The cover plates protecting the opening are shaped like the beak of a bird.

Ecology

This species is found at depths of up to and grows on

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

, boulders, pebbles and shells. It seems to favour habitats with strong currents and when overcrowding occurs, adopts different shapes to fit the space available. It is often found growing alongside another 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 ...

''. Other species often found in its vicinity include '' Tubularia larynx'', ''

Obelia geniculata ''Obelia geniculata'' is a species of cnidarian belonging to the family Campanulariidae. The species has cosmopolitan distribution. Population genetics Estimates of divergence times and distinctive haplotypes provide evidence of glacial re ...

'', ''

Pomatoceros triqueter ''Pomatoceros triqueter'' is a species of tube-building annelid worm in the class Polychaeta. It is common on the north eastern coasts of the Atlantic Ocean and in the Mediterranean Sea. Polychaetes, or marine bristle worms, have elongated bod ...

'', ''

Pecten maximus ''Pecten maximus'', common names the great scallop, king scallop, St James shell or escallop, is a northeast Atlantic species of scallop, an edible saltwater clam, a marine bivalve mollusc in the family Pectinidae. This is the type species of th ...

'', ''

Hydroides norvegica ''Hydroides norvegica'' is a species of tube-forming annelid worm in the family Serpulidae. It is found on submerged rocks, shells, piles and boats in many coastal areas around the world. It is the type species of the genus '' Hydroides''. Poly ...

'', '' Chlamys opercularis'' and '' Sertularia'' species.

Coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of re ...

was often present as were the

whelk Whelk (also known as scungilli) is a common name applied to various kinds of sea snail. Although a number of whelks are relatively large and are in the family Buccinidae (the true whelks), the word ''whelk'' is also applied to some other marine ...

, the European edible sea urchin (''Echinus esculentus''), the

great spider crab The great spider crab, ''Hyas araneus'', is a species of crab found in northeast Atlantic waters and the North Sea, usually below the tidal zone. In 1986, two specimens were captured at the South Shetland Islands off the Antarctic Peninsula ...

(''Hyas araneus'') and the shore crab (''

Carcinus maenas ''Carcinus maenas'' is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name eur ...

''). The main

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

is the juvenile

common starfish The common starfish, common sea star or sugar starfish (''Asterias rubens'') is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 c ...

(''Asterias rubens''). Medium sized barnacles seem to be at greatest risk. Small specimens are ignored while large specimens seem able to withstand attack.

Distribution

''Balanus balanus'' is found in the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...

and the more northerly seas of the northern hemisphere. It has been introduced to Argentina where it is displacing other species and is considered invasive.

Biology

Larvae settle out of the

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

in about April and attach themselves to objects on the sea floor. The newly

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...

cyprid A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...

develops slowly reaching diameter in a few weeks and by September. The growth rate then slows over the winter so that the year old barnacle averages . Thereafter it grows at a year and the largest specimens, across are probably four to six years old. Under experimental conditions of total submersion growth is faster and more nearly resemble growth rates of ''

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 ...

'' and ''

''. This may be because these barnacles, being always under water, have a greater continuity of food supply. There is a wide variation in rate of growth and the factors affecting it include currents and nutrient content. A scarcity of

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s in mid-summer may slow growth at this time. ''B. balanus'' is a cross-fertilising

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 the single brood of

nauplii Nauplius, Nauplia or Nauplios , may refer to : Greece-related * Nauplius (mythology), in Greek mythology, the son of Poseidon and Amymone, the father of Palamedes, and also the name of an Argonaut * Nauplia Nafplio ( ell, Ναύπλιο) is a ...

is produced in the middle of winter. In mature individuals (barnacles at least ten millimetres in diameter) the white vesiculae seminales are very much enlarged at this time and filled with

spermatozoa A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...

, occupying much of the body cavity and the

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...

is also greatly enlarged. At the same time, a creamy mass of

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

are present in the ovarian tubules. Fertilisation takes place over the course of a few days in each group of barnacles and the fertilised eggs change to an orange colour and then to a greyish-brown as the nauplii develop. New ovaries begin to form soon after fertilisation, and the testes re-develop during the summer with the size of the penis being reduced. After about forty days of embryonic development, the nauplii are liberated into the water. Many first year specimens are not fully mature in their first winter but those that are liberate 3,000 to 4,000 nauplii. Second year individuals at an average size of twenty millimetres will produce about 20,000 nauplii, whilst larger individuals of thirty millimetres may produce over 100,000. The nauplii feed,

moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

five times and swim with their antennae. It takes about one month for them to develop into the cyprid larvae, the non-feeding stage before adulthood.

References

{{Taxonbar, from=Q3808835 Barnacles Crustaceans described in 1758 Taxa named by Carl Linnaeus