Marine Biology Report: Carcinus maenas Reproduction and Life Cycle

This report provides a comprehensive overview of Carcinus maenas, commonly known as the green shore crab. It details the crab's life cycle, beginning with mating, which typically occurs in the spring after the female molts. The report describes the premating embrace, sperm transfer, and egg-laying process, including the number of eggs carried by the female. It further explores the development of the eggs in deep water, the larval stages (Nauplius, Zoea, and Post-larva), and the crab's vertical migration patterns. The report also examines the crab's habitat, including where the juvenile crabs live, and references supporting studies on the crab's foraging behavior, body size variations, and population dynamics. This report offers valuable insights into the biology and ecology of the Carcinus maenas.

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1MARINE BIOLOGY
Introduction
Carcinus maenas is also known as littoral crab or green shore crab. It is mainly found in North
America and South Africa. Its lifespan is up to 6 years, the female used to live for and 3 years
and the male crab used to live for 5 years (Stevens, Lown and Wood 2014). The process of
mating starts with the melting of the outer shell by the female crab. Mating generally happens in
the spring, which is the breeding season for the green shore crab. At this time the male green
crab starts find the newly shredded crab female crab for mating. They generally attract each
other by using a chemical with fragrance known as pheromones. After the chemical connection
was formed the pair performs the premating embrace, at this time the male crab wrap his claws
around the female. This embrace occurs for many days, after that the female starts the molting
of the outer shell at it can be easy for mating. The male transfer the sperms and the female
stores the sperm in a sac called spermatheca until the female is ready to use it. The shore crabs
are commonly found in the rocky shore. They can be found under the algae and the rocks
during the high tide but rest of the time they can be found on the shores and also in the deep
water.
The female crab lays eggs which I being carried by her under the abdomen in a pouch. At a
time they can carry 100,000 to 2,000,000 eggs. Then these eggs are fertilized by the sperms of
the male which the female crab had stored in a sac. After the fertilization the female crab travels
to the deep water, where the eggs used to develop. The eggs takes around two weeks for the
fully development and to hatch (Lord and Williams 2017).
Once the egg starts developing into the larva; these larva returns to the surface waters for two
weeks. When the larva enters into the final stage of development the young crabs then travel to
the coastal waters. There they starts their molting cycle and live their life as a juvenile crab. The
larva is having three stages Nauplius, Zoea and Post-larva (Kelley et al. 2014). The larva of the
crab undergoes vertical migrations because as per their structure of exoskeleton their
appendages are on their sideways so they cannot move horizontally and they had to move
vertically only. The larva of the crabs is omnivorous; the zoea larva generally eats small
crustaceans, larva and detritus. The settling larvae consisted of stages G through I1. These
stages consist of the metamorphosing period and it shows the behavior that is related to the
transport of the tidal stream. The settling stage is done in the month of February especially in
the deep waters and in the late March in estuaries. The juveniles crabs generally lives in the
sand also they are being found in higher proportion in between the mussels (Chakravarti and
Cotton 2014).

2MARINE BIOLOGY
References
Chakravarti, L.J. and Cotton, P.A., 2014. The effects of a competitor on the foraging behaviour
of the shore crab Carcinus maenas. PloS one, 9(4), p.e93546.
Kelley, A.L., de Rivera, C.E., Grosholz, E.D., Ruiz, G.M., Yamada, S.B. and Gillespie, G., 2015.
Thermogeographic variation in body size of Carcinus maenas, the European green crab. Marine
biology, 162(8), pp.1625-1635.
Lord, J.P. and Williams, L.M., 2017. Increase in density of genetically diverse invasive Asian
shore crab (Hemigrapsus sanguineus) populations in the Gulf of Maine. Biological
Invasions, 19(4), pp.1153-1168.
Stevens, M., Lown, A.E. and Wood, L.E., 2014. Camouflage and individual variation in shore
crabs (Carcinus maenas) from different habitats. PLoS One, 9(12), p.e115586.