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Squid pro quo

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Vol.4. 14th June 2017

Guest post by Dr Vladimir Lapitkhovsky - CEFAS, UK

 

Dr Vladimir Laptikhovsky (CEFAS, UK) is an expert on cephalopods (squid, octopus, cuttlefish etc). He is on board the RRS Discovery to find out what the birds in the mid-Atlantic and in the focal area south of the Charlie Gibbs Fracture Zone are feeding on, and if squid play an important part in their diet and their reason for journeying out there.

 

Throughout their evolutionary history, both fish and cephalopods were competing in marine habitats for the same food resources. In respect of biodiversity, this race was eventually won by fish that account for eighteen thousand described marine species versus around eight hundred species of all squids, octopods and cuttlefishes combined. However, cephalopods are very abundant in respect of biomass and often play a crucial role in food webs of productive oceanic areas. In recent decades their numbers began to rise worldwide due to better resilience under increasing fishing pressure and climate changes[1].

 

'Albatrosses at sea' by Euan Dunn 

 

Creatures of eternal darkness

Tasty and abundant cephalopods are important source of food for many pelagic seabirds, and their importance is not restricted to a few species normally living within diving depths of petrels, shearwaters and albatrosses. A common belief is that biological matter is “raining” from surface waters (where it is produced) to the oceanic abyss thus providing meagre supply for hungry creatures of eternal darkness. But there is also an oppositely directed flow primarily used by seabirds, and this flow is supported by cephalopods.

 

First, for a few months (regardless of how deep adult squid live) the hatchlings of many species ascend to grow and forage close to the surface, where water is warmer and food is plentiful. On the other hand, after spawning and death, many squid float up to the surface providing an important source of energy for seabirds. For example, deep-sea cephalopods account for ~75% of winter food by weight in wandering albatrosses in the Southern Indian Ocean[2]. These squid reproduce only once in their lifetime and could (at least some of them) surface soon after the egg release, still half-alive, because of the change in buoyancy. Such representatives of the family Onychoteuthidae were even described as a new genus – Chaunoteuthis, so different were they from immature specimens known to science. The albatrosses are also able to hunt in dusk for mesopelagic squids that aggregate in the Antarctic Polar Front area (and likely – in other polar frontal areas), and raise to surface every night. Seabirds catch even species that lacks photophores (light organs) so are not easily seen in darkness[3].

 

'Albatross' by Euan Dunn

Into the abyss

The “Discovery” is heading now to the recently created Charlie-Gibbs Marine Protected Area (MPA), where a total of 53 cephalopods are listed, nearly all of them being deep-sea species. During this expedition, we will try to reveal to what extent the light-less and gloomy oceanic abyss nurture seabirds, which come to forage this remote mid-oceanic corner even from the Southern Hemisphere. We know nothing about their feeding habits in these offshore waters, as scientific efforts in respect to predominating Great and Sooty shearwaters were historically spread across easily accessible inshore shallow areas of Canada and Europe. Hopefully, this survey would provide some key information essential for the understanding of the entire ecosystem of this MPA, including the extent of squid-regulated flow of nutrients from the very bottom of this waste oceanic area to the very top of it. It also might shed some light on stability of its trophic structure facing the occurring climate changes, which are particularly conspicuous in the Arctic and adjacent areas.

 

Follow the RSS Discovery's position on the National Oceanography Centre's 'Vessel Tracker'.


[1] Doubleday et al. 2016 Current Biology 26

[2] Cherel & Weimerskirch, 1999, Mar Ecol Prog Ser,188

[3] Rodhouse & Boyle 2010 ICES J Mar Sci 67