The Blue mussel – irreplaceable filter-feeder and geneticist’s favourite | Kamila Sfugier | EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA 1/2015 3 The Blue mussel Biological and ecological characteristics between 0 ppm and 31 ppm. Their growth rate, how- ever, significantly decreases in salinity below 12.8 ppm. – irreplaceable filter-feeder The Mytilus edulis spp. complex includes the three This bivalve attains an average length of 3 to 5 cm, but in and geneticist’s favourite taxa: Mytilus edulis, Linnaeus, 1758; Mytilus gallopro- deeper water forms larger shells of about 9 cm. vincialis, Lamarck, 1819; Mytilus trossulus, Gould, 1850. The outer part of the blue mussel shell is often dark Kamila Sfugier All these species are widely distributed and hybridise blue, blackish or brown. The inner part is silvery and within areas where their habitats overlap (McDonald et slightly pearly. Blue mussels grow a shell consisting of al., 1991). two valves that are opened by two dorsal muscles and coherence with the Curriculum – see. p. 10 Size, shape and colour Scientific classification closed by sphincters (Jura, 2004). Summary: of blue mussels depend Blue mussels are gonochoric, but it is only possible Mussels from Mytilus spp. complex are important in on their habitat. Growth Kingdom: Animalia to identify their gender during the breeding season. In aquatic ecosystems as well as their worldwide economic rate is influenced largely Phylum: Mollusca the Atlantic Ocean breeding takes place from mid-May importance. Annual world production of marine mussels by water temperature, sa- Class: Bivalvia to the end of September. Duration is dependent on nu- for consumption is around one million tons and in Eu- linity, quality and avail- Subclass: Pteriomorphia merous factors, such as food, water temperature and SCIENCE rope exceeds 600.000 tons. These bivalves contain nutri- ability of food. The ideal Order: Mytiloida physical processes in the water column. In stagnant wa- tious proteins, carbohydrates, mineral salts and a small temperature for growth Family: Mytilidae ter it is also possible to find hermaphroditic blue mus- amount of fat, but apart from cooks they fascinate sci- varies between 10 and sels (Saavedra, 1997). entists. The sensitivity of mussels to environmental pol- Subfamily: Mytilinae 200C, while temperatures The breeding strategy of blue mussels is a combina- lution allows their exploitation as bioindicators. Addi- Genus: Mytilus above 270C are consid- tion of three features, i.e., relative fecundity (Bayne et tionally their inheritance of mitochondrial DNA is quite Species: extraordinary. This article aims to present the blue mussel ered lethal. Blue mus- Mytilus edulis (Linnaeus, 1758) al., 1983; Sprung, 1983), comparatively high mortality in the light of its ecology and genetics. sels have a cosmopolitan Mytilus trossulus (Gould, 1850) of larvae (Yap, 1977) and plankton dispersal (Crisp, distribution, inhabiting Mytilus galloprovincialis 1975). Gametes are discharged once or several times SCHOOL Key words: blue mussel, doubly uniparental inheritance, hy- (Lamarck, 1819) bridisation, masculinization water bodies of salinity directly into the water, where fertilisation occurs. In- received: 16.01.2015; accepted: 12.02.2015; published: 27.03.2015 mgr Kamila Sfugier: Institute of Oceanology of the Polish Academy of Sciences, Genetics and Marine Biotechnology Department, [email protected] IN SHORT The Author – Kamila Sfugier – is a participant of the project „Stypendia dla doktorantów województwa podlaskiego”, co-financed within the Operational Programme Human Capital, measure 8.2 Transfer of knowledge, sub-measure 8.2.2 Regional Innovation Strategies, from the European Social Fund, state budget and Podlaskie Voivodship budget. Figure 1. Shape of the shell: Mytilus galloprovincialis, Lamarck, 1819; Mytilus trossulus, Gould, 1850; Mytilus edulis, Linnaeus, 1758 Source: http://naturalhistory.museumwales.ac.uk/britishbivalves EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA | ebis.ibe.edu.pl | [email protected] | © for the article by the Authors 2015 © for the edition by Instytut Badań Edukacyjnych 2015 The Blue mussel – irreplaceable filter-feeder and geneticist’s favourite | Kamila Sfugier | EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA 1/2015 4 Fig. 2. Blue mussel anatomy Due to the low salinity of the Baltic Sea, blue mus- Source: http://www.design-site.net sels have developed a dwarf form (up to 5 cm long), but they constitute about 75% of the epifauna (Jura, 2004). The total population of blue mussels inhabiting the Bal- tic proper to a maximum depth of 25 m (with shell) is estimated at 8 million tons dry weight (Kautsky, 1991). Aquaculture and use in food industry In many countries blue mussels are harvested for consumption. In Poland, however, blue mussels are not commercial owing to their small size. The first men- tion of human blue mussel cultivation in Europe is de- scribed on wooden stakes in 1235 AD, in France. From SCIENCE that time, blue mussel breeding started in Europe over the full area of their distribution. Subsequently breed- dividual development stages of Mytilus have been de- The bivalve lives in shoals in coastal zones. The belt ing techniques emerged in the late 19th century when scribed by Field (1922) and Bayne (1976) and have been of blue mussels starts at a depth of several-metres and aquaculture began to be regarded as a cheap protein divided into three separate phases (Sprung, 1984). The spreads to a depth of 30 m. Blue mussels are highly im- source. Blue mussels then became a very popular dish first larval stage ofMytilus a trochophore is formed – portant filter feeders. They transform the sea water sus- in Western Europe. characterized by the presence of cilia. A larva reaches pension into high-quality proteins which can be used Aquaculture is always in phytoplankton rich zones. a length of up to 120 µm and has a D-shaped shell. Dur- by animals and humans. Individual shoals filter hun- There are several methods used depending on type of SCHOOL ing the growth phase the larva feeds and increases in dreds of cubic metres of water daily. Within an area of size. It loses its D-shape with a velum in its prostomium, 160 km2 near Asko (Sweden) in the northern part of the functioning as a swim organ. In the setting phase, the Baltic proper, all bivalves are capable of filtering the to- planktonic larva is distinguished by the germ of the tal water mass in two and a half months. Shoals of blue foot, head, mantle and mantle cavity. In the pediveliger mussels also provide a good food source for flounder, stage it has a shell, 360 µm in length. Throughout the cod, ray and sturgeon. In the upper water zone, blue various larval stages, the veliger struggles to settle on mussels are eaten mainly by common eiders which can IN SHORT a firm foundation in order to transform into the ulti- dive to a depth of 10 m. The blue mussel’s main preda- mate juvenile form (Flyachinskaya and Kulakowski, tors in Kattegat, the Asterias rubens starfish and Carci- 1991; Sprung, 1984). nus meanas littoral crab, were not able to adapt to the Larvae, capable of floating in the water column, may low salinity of the Baltic. This explains why the blue travel with ocean currents and long distance passive mussel has found such favourable conditions to develop migration is also possible in ballast water (Carlton and in the Baltic Sea, despite its weakened shell structure Fig. 3. Mussel on a rocky shore Geller, 1993). Adult forms may travel attached to hard in lower salinity waters (Reimer and Harms-Ringdahl, Source: http://en.academic.ru/pictures/enwiki/66/Blue_mus- surfaces, like the hulls of ships. 2001). sel_Mytilus_edulis.jpg EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA | ebis.ibe.edu.pl | [email protected] | © for the article by the Authors 2015 © for the edition by Instytut Badań Edukacyjnych 2015 The Blue mussel – irreplaceable filter-feeder and geneticist’s favourite | Kamila Sfugier | EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA 1/2015 5 coast. In Holland, the young are spread over boards in The blue mussel as an indicator species shallow gulfs or sheltered areas where they are attached to the sea floor. They are harvested by dredging with Bio-indication uses life forms as indicators for envi- special nets. In France, cultivation is on rows of wooden ronmental pollution. In general, it is used as a way to as- stakes positioned within the tidal zone. In Spain, blue sess environmental degradation or observe changes in mussels are bred on lines. The Spanish Atlantic coast the biocoenosis or ecosystem. Animals and plants can is favourable for blue mussel growth because of high act as indicator species if they exhibit a narrow band tides which ensure regular exchange of water. Blue of tolerance to a specific factor (stenobiont species). mussels reach commercial sizes after 7-8 months, while Bioindicators are chosen for their particular sensitiv- in other regions (e.g., England) such sizes might be ity to substances of interest. Their reaction functions as reached after 4-5 years. In some places blue mussels are the alarm to warn about contamination. Behavioural farmed just like oysters – in bags on platforms mount- changes in bioindicators indicate stress from disad- ed within a tidal flat or fixed directly to the bottom vantageous or detrimental external factors. To classify species as bioindicators, they must meet several criteria. (Breber and Sirocco, 1998; Bishop, 2001; Bürgin et al., SCIENCE 2001). Primarily, a bioindicator cannot have inherent prob- Bivalves contain high-quality proteins which pro- lems with identification and at the same time it must vide essential building blocks for nutrition. They are be accurately identified, morphologically, anatomically also a perfect source of calcium, fluorine as well as sele- and physiologically. Bioindicators are characteristi- nium that can protect against cancer. They also contain cally species which respond to specific changes in the B and D vitamins which are important for healthy skin, environment in a manner, appropriate to the degree of the central nervous system and structural and function- contamination.