Use of shelter by the small Patagonian octopus Octopus tehuelchus: availability, selection and effects on fecundity

Shelters on the sandy bottom area of the Northwest San Matias Gulf (Argentina) consist mostly of shells of invertebrates.Small octopuses Octopus tehuelchus d'orbigny use the shells of gastropods Zidona dufresnei, Odontocymbiola subnodosa and Buccinanops gradatum, barnacles Balanus sp. and clams Pitar rostratus and Amiantis purpurata.Intermediate-size octopuses use mainly oyster shells Ostrea puelchana.Large octopuses used a variety of shelters made up by parts of shells or other sources.Shells of 0. puelchana were the most important shelter for brooding females.Most eggs (ca 90 %) were placed on the concave valve.When clams were used as the brooding shelter, however, eggs were evenly distributed between the 2 valves.The quality of shelter affects reproductive output, particularly that of larger females.