Factors influencing successful settlement and metamorphosis of the common spider crab Maja brachydactyla Balss, 1922 (Brachyura: Majidae): Impacts of larval density, adult exudates and different substrates.

Abstract The common spider crab Maja brachydactyla is an important wild marine resource in many countries in the NE Atlantic region that also has potential in aquaculture. The larval cycle has been replicated successfully in captivity, with highest mortality evident during larval settlement and metamorphosis to first juvenile stage. As an approximation to understanding natural settlement requirements of this species, we examined the need for individual culture to produce first juveniles in the hatchery. In addition, we assessed whether presence of adult exudates and/or a number of different settlement substrates (natural and artificial) influenced larval settlement and metamorphosis under laboratory conditions. Our data demonstrate that M. brachydactyla megalopae reared in communal culture showed similar survival and shorter developmental duration into juvenile crab when compared to individual culture. Presence of adult exudates did not influence the larval survival or development duration to metamorphosis. Survival was not different between control conditions (absence of substrate), artificial substrata (100 to 1000 μm nylon mesh) or natural substrates except for "mud" substrate where no larvae survived to first juvenile stage in this treatment. Duration of the megalopa stage was also not influenced by type of substrate added (natural or artificial) or to a control (no substrate). Results in the present study indicate that M. brachydactyla culture will not require provision of special requirements since communal larval rearing is an efficient and low cost viable strategy and specific exudates or substrates are not required to produce juveniles. Highlights • The production of Maja brachydactyla juveniles is possible employing low cost technologies. • The juvenile production can be realized under mass culture conditions. • The mass production of juveniles is available without special requirements, i.e. adult odours or substrates. [ABSTRACT FROM AUTHOR]