Getting to grips with cephalopod diversity

The role of a class of mollusks called cephalopods as indicators of ecosystem biodiversity under an EU directive was a new item on the agenda of a recent group meeting.
Published: 20 June 2014

​The experts making up ICES Working Group on Cephalopod Fisheries and Life History (WGCEPH), put their heads together at the Instituto Português do Mar e da Atmosfera (IMPA) in Lisbon this week, 16-19 June, to report on and discuss various issues related to the sea creatures in question, including their relevance within the Marine Strategy Framework Directive (MSFD).

Cephalopods – squid, octopuses, cuttlefish, and nautiluses​ – are ancient, highly-evolved marine mollusks with diverse life histories and a wide range of habitat preferences. With short life cycles (they die after a single reproductive period) and a high production-to-biomass ratio enabling them to rapidly replace themselves, they have opportunistic features which earn them an important place in the trophic structure of marine ecosystems and as the objects of valuable capture fisheries.

Their marked sensitivity to environmental variation, a trait widely documented, makes the task of forecasting numbers and the subsequent management more complicated. Concerning many aspects of the different species' biology (there are 800 species of cephalopods living today), their receptiveness to such change is manifest in stories like that of the octopus, which struggles to tolerate low salinity and migrates to greater depths when salt content decreases at the ocean's surface.

Indicators for biodiversity

Whilst analyzing the significance of cephalopods under the MSFD, WGCEPH considered various descriptors of Good Environmental Status and the animals' potential to provide indicators for biodiversity – a descriptor which also dictates that a species' abundance and distribution match up to prevailing oceanic conditions. Examples of environmental influences such as that of the octopus must therefore be taken into account.

"Fished cephalopods can contribute to indicators in biodiversity," explained Group Co-Chair Jean-Paul Robin. "The distribution range of the species can be affected by natural and anthropogenic factors. For example, climate-induced variation has meant that the common octopus present in the English Channel until the very cold winter of 1963 has not re-appeared that far North since."

Other points addressed by WGCEPH included the use of cephalopods as indicators for trophic interactions, as in MSFD Descriptor 4, and the possibility that their sensitivity to their surroundings could provide evidence in relation to the alteration of hydrographical conditions, as in Descriptor 7. Indicators for all respective descriptors allow progress towards the landmark EU directive to be measured.

WGCEPH's report is due at the beginning of August.

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​Common cuttlefish (Sepia officinalis); ©​ Paul Parsons

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Getting to grips with cephalopod diversity

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