Abstract
The two-toned pygmy squid ( Idiosepius pygmaeus, Streenstrup,
1881) is a small, tropical cephalopod that inhabits seagrass meadows and
is known to attach to blades of seagrass using a specialised adhesive
organ. A global decline in seagrass habitat due to anthropogenic
disturbances may threaten the species that rely on seagrass meadows for
shelter, foraging and other crucial activities. It is unclear if
I. pygmaeus can utilise alternative habitats in the absence of
seagrass. Here, we test the effect of habitat type, material and
composition type, and the presence of conspecifics on the settlement
preferences of I. pygmaeus. Individuals each underwent three
separate experiments: 1) testing the preference between their known
habitat, Zostera muelleri subsp. Capricorni and potential
substitute, Sargassum, 2) testing the preference to attach to a
natural or artificial structure of similar shape and size, and 3)
testing the preference of identical habitats, one with a conspecific
adhered to and one without. We found that I. pygmaeus did not
have a strong preference for either Zostera or Sargassum.
However, a strong preference was found for attachment to the natural
structure over the artificial one. There was also strong evidence for
the use of conspecific cues in habitat choice, with 75% of individuals
selecting the habitat that contained a conspecific. As habitat loss is
the leading cause of species extinction, the knowledge of habitat
preferences for I. pygmaeus is vital in order to assess their
risk of population decline. The findings of this study suggest that
I. pygmaeus could utilise an alternative habitat in the presence
of seagrass meadow reduction, which is under threat from human activity.