Updated: 31 jan. 2021

When species co-occur in a certain habitat and use similar food resources, competition can take place. In this context, we refer to the concept of ‘ecological niche’, i.e. the multidimensional space defined by what organisms feed on and the habitat they occupy. The degree of niche similarity can help understanding the potential for competition among organisms, especially when resources are scarce. Cephalopods (e.g. squids and octopus) are overall understudied, despite their important role both as prey and predators in marine food webs. Under pressing climate and environmental changes, which are intensified in Arctic regions, it is important to better understand the role of cephalopods in the food web.

A team of researchers, including the Portuguese Dr. Filipe Ceia and Dr. José Xavier, recently published a study in Nature analyzing the potential for competition among the three Arctic bobtail squids Rossia palpebrosa, R. magaptera and R. moelleri. The species were collected in the Kara Sea, Barents Sea and Greenland from 2003-2019, depending on the region. Researchers used the food web markers carbon (δ13C) and nitrogen (δ15N) stable isotopes to infer diet and niche ecology. Levels of these isotopes can be measured in animal tissue and indicate the feeding sources (δ13C; e.g. feeding on bottom vs feeding on the water column) and trophic position (δ15N; role in the food web, e.g. primary, secondary consumer).

The three species co-occur, have similar body size and feed near the bottom of the ocean, mostly on crustaceans, marine worms and fish. So how do they partition their habitat to avoid competition? Here is how:

a) R. moelleri inhabit the water column more often;

b) R. megaptera and R. moelleri migrate, while R. palpebrosa may be more sedentary;

c) R. megaptera and R. moelleri show more distinct differences in body size between males and females, and females tend to occupy a larger ecological niche than males (i.e. females are less picky with their food);

d) Diets of R. megaptera and R. moelleri change less regionally compared to R. palpebrosa;

e) R. megaptera and R. palpebrosa eat more crustaceans, while R. moelleri eats more fish;

f) The diet of R. palpebrosa and R. moelleri becomes more specialized (a.k.a. pickier with their food) as they grow up, while the diet of R. megaptera becomes less specialized;

g) R. palpebrosa and R. moelleri use similar ways to reduce competition within each species, different from R. megaptera, that is the first two species favor smaller individuals and the niches of different size classes largely overlap, while R. megaptera favors larger individuals.

Given that none of these traits was shared among the three species, all traits together form a pattern in which each species ends up with a unique strategy of resource and habitat use.

And what about the impacts of climate change in these species? R. palpebrosa and R. moelleri will likely not be affected since the first has a more flexible niche and thermal tolerance and is currently the most widespread of the three species in the Arctic, and the second is an Arctic-adapted species. For R. magaptera, since this species inhabits warmer waters, climate change will likely create better conditions for niche expansion in the Barents Sea and strengthen their advantage in West Greenland.

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Source: Golikov A V, Ceia FR, Sabirov RM, Batalin GA, Blicher ME, Gareev BI, Gudmundsson G, Jørgensen LL, Mingazov GZ, Zakharov D V, et al. 2020. Diet and life history reduce interspecific and intraspecific competition among three sympatric Arctic cephalopods. Sci Rep. 10:21506. doi: 10.1038/s41598-020-78645-z.

Author: Sara Pedro