134
and is under the umbones. Margin is smooth. Pallial line is wide. Anterior adductor
scar is very small, posterior is large. External ligament is much concealed, extending more than half-way from the beaks to the highest point of the shell. Sculpture of
fine has concentric lines. Colour is purple, blue, and sometimes brown, occasionally
with prominent dark brown to purple radial markings. Periostracum is almost black,
dark brown, or olive. Interior is pearl-white with a wide border of purple or dark blue.
Mytilus edulis has been harvested for centuries. Blue mussel shells have been
found in kitchen middens dated at 6000 B.C. Until the nineteenth century, blue mussels were harvested from wild beds in most European countries for food, fish bait
and as a fertilizer. Blue mussels are widely distributed in European waters, extending from the White Sea, Russia as far as south as the Atlantic coast of Southern
France. Mytilus edulis has a wide distributional pattern, mainly due to its abilities to
withstand wide fluctuations in salinity, desiccation, temperature, and oxygen tension. Therefore, this species occupies a broad variety of microhabitats, expanding
its zonational range from the high intertidal to subtidal regions and its salinity range
from estuarine areas to fully oceanic seawaters. Highly tolerant of a wide range of
environmental conditions, the blue mussel is euryhaline and occurs in marine as
well as in brackish waters (Baltic) down to 4‰, although it does not thrive in salinities of less than 15‰ and its growth rate is reduced below 18‰. Blue mussels are
also eurythermal, even standing freezing conditions for several months. The species
is well acclimated for a 5–20 °C temperature range, with an upper sustained thermal
tolerance limit of about 29 °C for adults. Its climatic regime varies from mild, subtropical locations to frequently frozen habitats. M. edulis typically occurs in intertidal habitats, although this distribution appears mostly controlled by biological
factors (predation, food competition) rather than by its capacity to survive subtidally, as demonstrated by offshore mussel culture using longlines. When predators
are lacking, M. edulis subtidal aggregations can reach a 1.2 m thickness and individuals attain large sizes in a relatively short period of time. Although blue mussels
can live up to 18–24 years, most cultured mussels are produced in less than 2 years.
In the wild, M. edulis settles in patches of open spaces, quickly building a dense
population referred to as ‘mussel beds’. Although showing a seasonal pattern, the
reproductive cycle of M. edulis can exhibit considerable temporal and spatial variation. Gonads are usually ripe by early spring in European waters; mussels commonly show a significant loss of condition following spawning. Rapid gametogenesis
leads to fully ripe gonads again in summer. Although directly driven by food availability and temperature, reproductive cycles in M. edulis may vary latitudinally,
both in terms of onset and duration. High fecundity and a mobile free-living larval
phase are two characteristics that have contributed to the development of mussel
culture; in fact, the natural abundance of M. edulis larvae has been the key for such
development. Exports mainly comprise processed products, which provide added
value, and may be a major driving factor for M. edulis culture development. Import
prices tend to be lower compared to export prices, reflecting the role of processing
in this market, and facilitating international trades when local production cannot
sustain the demand (FAO 2019a) (Fig. 3.1).
3 Molluscan Shellfish
and is under the umbones. Margin is smooth. Pallial line is wide. Anterior adductor
scar is very small, posterior is large. External ligament is much concealed, extending more than half-way from the beaks to the highest point of the shell. Sculpture of
fine has concentric lines. Colour is purple, blue, and sometimes brown, occasionally
with prominent dark brown to purple radial markings. Periostracum is almost black,
dark brown, or olive. Interior is pearl-white with a wide border of purple or dark blue.
Mytilus edulis has been harvested for centuries. Blue mussel shells have been
found in kitchen middens dated at 6000 B.C. Until the nineteenth century, blue mussels were harvested from wild beds in most European countries for food, fish bait
and as a fertilizer. Blue mussels are widely distributed in European waters, extending from the White Sea, Russia as far as south as the Atlantic coast of Southern
France. Mytilus edulis has a wide distributional pattern, mainly due to its abilities to
withstand wide fluctuations in salinity, desiccation, temperature, and oxygen tension. Therefore, this species occupies a broad variety of microhabitats, expanding
its zonational range from the high intertidal to subtidal regions and its salinity range
from estuarine areas to fully oceanic seawaters. Highly tolerant of a wide range of
environmental conditions, the blue mussel is euryhaline and occurs in marine as
well as in brackish waters (Baltic) down to 4‰, although it does not thrive in salinities of less than 15‰ and its growth rate is reduced below 18‰. Blue mussels are
also eurythermal, even standing freezing conditions for several months. The species
is well acclimated for a 5–20 °C temperature range, with an upper sustained thermal
tolerance limit of about 29 °C for adults. Its climatic regime varies from mild, subtropical locations to frequently frozen habitats. M. edulis typically occurs in intertidal habitats, although this distribution appears mostly controlled by biological
factors (predation, food competition) rather than by its capacity to survive subtidally, as demonstrated by offshore mussel culture using longlines. When predators
are lacking, M. edulis subtidal aggregations can reach a 1.2 m thickness and individuals attain large sizes in a relatively short period of time. Although blue mussels
can live up to 18–24 years, most cultured mussels are produced in less than 2 years.
In the wild, M. edulis settles in patches of open spaces, quickly building a dense
population referred to as ‘mussel beds’. Although showing a seasonal pattern, the
reproductive cycle of M. edulis can exhibit considerable temporal and spatial variation. Gonads are usually ripe by early spring in European waters; mussels commonly show a significant loss of condition following spawning. Rapid gametogenesis
leads to fully ripe gonads again in summer. Although directly driven by food availability and temperature, reproductive cycles in M. edulis may vary latitudinally,
both in terms of onset and duration. High fecundity and a mobile free-living larval
phase are two characteristics that have contributed to the development of mussel
culture; in fact, the natural abundance of M. edulis larvae has been the key for such
development. Exports mainly comprise processed products, which provide added
value, and may be a major driving factor for M. edulis culture development. Import
prices tend to be lower compared to export prices, reflecting the role of processing
in this market, and facilitating international trades when local production cannot
sustain the demand (FAO 2019a) (Fig. 3.1).
3 Molluscan Shellfish