Transitions during cephalopod life history: the role of habitat, environment, functional morphology and behaviour.

Cephalopod life cycles generally share a set of stages that take place in different habitats and are adapted to specific, though variable, environmental conditions. Throughout the lifespan, individuals undertake a series of brief transitions from one stage to the next. Four transitions were identified: fertilisation of eggs to their release from the female (1), from eggs to paralarvae (2), from paralarvae to subadults (3) and from subadults to adults (4). An analysis of each transition identified that the changes can be radical (i.e. involving a range of morphological, physiological and behavioural phenomena and shifts in habitats) and critical (i.e. depending on environmental conditions essential for cohort survival). This analysis underlines that transitions from eggs to paralarvae (2) and from paralarvae to subadults (3) present major risk of mortality, while changes in the other transitions can have evolutionary significance. This synthesis suggests that more accurate evaluation of the sensitivity of cephalopod populations to environmental variation could be achieved by taking into account the ontogeny of the organisms. The comparison of most described species advocates for studies linking development and ecology in this particular group.

A review of the factors influencing spawning, early life stage survival and recruitment variability in the common cuttlefish (Sepia officinalis).

Global landings of cephalopods (cuttlefish, squid and octopus) have increased dramatically over the past 50 years and now constitute almost 5% of the total world's fisheries production. At a time when landings of many traditional fin-fish stocks are continuing to experience a global decline as a result of over-exploitation, it is expected that fishing pressure on cephalopod stocks will continue to rise as the fishing industry switch their focus onto these non-quota species. However, long-term trends indicate that landings may have begun to plateau or even decrease. In European waters, cuttlefish are among the most important commercial cephalopod resource and are currently the highest yielding cephalopod group harvested in the north-east Atlantic, with the English Channel supporting the main fishery for this species. Recruitment variability in this short-lived species drives large fluctuations in landings. In order to provide sustainable management for Sepia officinalis populations, it is essential that we first have a thorough understanding of the ecology and life history of this species, in particular, the factors affecting spawning, early life stage (ELS) survival and recruitment variability. This review explores how and why such variability exists, starting with the impact of maternal effects (e.g. navigation, migration and egg laying), moving onto the direct impact of environmental variation on embryonic and ELSs and culminating on the impacts that these variations (maternal and environmental) have at a population level on annual recruitment success. Understanding these factors is critical to the effective management of expanding fisheries for this species.