Balanidae Genus: Balanus Distribution
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These are very prolific and easily seen on the Balanus balanus shoreline nearby. Class: Maxillopoda Order: Sessilia Family: Balanidae Genus: Balanus Distribution This species Balanus balanus is distributed over the entire Barnacles collectively are northern hemisphere. It occurs in large numbers in the more global in distribution. The northerly seas including the Arctic Ocean. It has been Family Balanidae are the introduced to Argentina where it is displacing other species and stalkless barnacles and the is considered invasive. It is abundant in Nova Scotia coastal Genus Balanus includes the waters including Burntcoat Head. acorn and rock barnacles. Although they have been found at water depths up to 600 m Habitat most barnacles inhabit shallow waters, with 75% of species Barnacles are encrusters, living in water depths of less than 100 m. Balanus balanus is a attaching themselves cold water species found between low water and from 60 to 150 permanently to a hard metres deep. They attach themselves to a variety of substrates substrate. The most including bedrock, boulders, pebbles and shells. They will also common, "acorn barnacles" attach themselves to man made objects such as docks and the grow their shells directly hulls of various sizes of water craft. They seem to favour onto substrates, they do not habitats with strong currents. use stalks. They are sessile (non-motile) suspension feeders, and have two Food nektonic (active swimming) larval stages. Post larval barnacles Most barnacles are filter dwell continuously in their shell. They send out feathery “legs” feeders. They feed by into the water at high tide to catch plankton as it floats by. capture of zooplankton These feathery appendages beat rhythmically to draw plankton using modified thoracic and detritus into the shell for consumption. The “legs” push the limbs. When they feed, plankton down into their opening (mouth). Comb-like structures they open the plates at the near the mouth remove the plankton from the legs before they top of their shells, and stick stick out again for more. The first larval stage feeds on coastal out their feathery, fan plankton. The second does not eat. shaped legs. This species cross-fertilize with adjacent barnacles. Fertilisation Reproduction takes place over the course of a few days in each group of These are hermaphrodites. barnacles. They brood fertilized eggs within their shells. Eggs Each barnacle contains change colour from cream to orange and then to a greyish- both male and female brown as they begin to develop. reproductive organs. Development Nauplii: The number of nauplii produced in a single yearly After about forty days of brood varies with the age and size of the parent. It is estimated a embryonic development, young adult at one year of age may produce 3,000 to 4,000 and a the nauplii (larvae) are two year old measuring on average 20 mm is capable of released into the water. This producing up to 20,000. Larger individuals at 30 mm may is the first freely swimming produce even more. larval stage. They settle into Cypris: This is an active site-selection phase when the cypris are beds of plankton to feed seeking permanent attachment prior to becoming adults. They and further develop, are able to delay metamorphosis until a suitable substrate such as molting several times as a rock or stone is located. When the cypris larvae have selected a they grow. It takes about site and are ready to settle they “glue” their heads to hard one month to develop to surfaces. Once attached, they change into juvenile barnacles, their second larval stage. miniatures of the adults. They become cypris larvae. Young adults: Each builds its own fortress, a cone-shaped This is a non-feeding, limestone shell with a trap door in the ceiling. The newly swimming phase prior to metamorphosed cyprid develops slowly reaching 1 mm diameter becoming an adult. in a few weeks and 7 mm by fall. The growth rate then slows over the winter and the year old barnacle averages 8 mm. Characteristics The adult outer shell is They typically possess six overlapping plates steeply conical and circular and two sets of opercular plates to protect their in shape. The cone base has opening. The cover plates protecting the lid are an irregular edge. The usual shaped like a bird’s beak. When water covers a diameter is two to three cm barnacle, the trap door opens, and the feathery but can grow to five cm. It legs emerge to sweep the water for plankton has prominent longitudinal and detritus. When the tide is out, barnacles ridges and has a greyish- close their trap doors to conserve moisture. white appearance. They spend the rest of their lives in this position—head down and feet up. Adaptations They are well adapted Within the intertidal zone, different species of barnacle live in against water loss. When very tightly constrained locations, allowing the exact height of an intertidal zones become dry assemblage above or below sea level to be precisely determined. they close their trap doors. Clustering is a component of fertilization, allowing for insertion Closure of these plates also of the long, extensible penis from one barnacle into the mantle provides protection from of a nearby mate. They are stationary and predators. Plate thickness it is essential that the barnacles live no builds up with the more than three to five centimetres accumulation of calcite apart to mate. Cement glands within the crystals. antennae produce the strong, brown glue that fastens it to its base. Status/Threats Globally they are under no They are vulnerable to dredging and to particular threat. They are sedimentation reducing suitable substrata very prolific. for settlement by larvae. Sightings in Nova Scotia These occur in many coastal areas and are Easily seen in coastal areas easily seen on the nearby shoreline. including locally. .