Abstract
Long held notions of the universally asocial octopus are being challenged due to the identification of high-density and interacting octopus populations in Australia, Indonesia, Japan and the deep sea. This study experimentally assessed the social tolerance and presence of potential prey items of Caribbean reef octopus, Octopus briareus, in a tropical marine lake (25°21′40″N, 76°30′40″W) on the island of Eleuthera, The Bahamas, by deploying artificial dens in multi-den groups or ‘units’ in the months of May and June 2019. Fifteen octopus were observed occupying dens (n = 100), resulting in 13 den units being occupied (n = 40). Two examples of adjacent occupation within a single den unit were identified but with zero examples of cohabitation/den sharing. Ecological models showed den and den unit occupation was predicted to increase with depth and differ between sites. Octopus also displayed no preference for isolated or communal units but preferred isolated dens over dens adjacent to others. Additionally, 47 % of occupied dens contained bivalve or crustacean items with no epifauna on their interior surface. The lack of epifauna suggests that these items have been recently ‘cleaned’ by occupying octopus and so represent likely prey. This study presents evidence of possible antisocial den use by O. briareus, a modification of the default ‘asocial’ ignoring of conspecifics typically attributed to octopus. This is likely in response to the high population density and may imply behavioural plasticity, making this system appropriate for further scrutiny as a research location on the influence of large, insular environments on marine species.
Highlights
The social behaviour of animals regularly receives interest in the academic literature, exploring taxa across the animal kingdom (Economakis and Lobel 1998; Ritz et al 2011) and the degree of interaction they have with conspecifics
The ecological predictors initially explored as plausibly influencing occupation included site, month, depth, benthic Simpson’s diversity, Mytilopsis sp. cover, P. radiata cover, calcareous rubble (CR) cover, sediment cover, den unit number, and distance to nearest public access point
This result is unexpected, as the sub-population is thought to be of high density (Aronson 1986) and other work has suggested that increasing population density has the potential to decrease aggression/ increase social tolerance in fish (Ruzzante and Doyle 1993; Syarifuddin and Kramer 1996) and farm animals (Estévez et al 2003; Estévez et al 2007)
Summary
The social behaviour of animals regularly receives interest in the academic literature, exploring taxa across the animal kingdom (Economakis and Lobel 1998; Ritz et al 2011) and the degree of interaction they have with conspecifics. Most motile marine animals interact with other members of Reviewers: D. Marine Biology (2021) 168:61 social behaviour between conspecifics the norm in many species. The collective classification of taxa as nonsocial is, unrealistic and there is a need to explore fringe populations in-situ to assess the varying degrees of interaction between animals before generalised comments can be made about the level of ‘sociality’ that a taxon expresses
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