Interactions of Globobulimina Auriculata with Nematodes: Predator Or Prey?

Studies of carnivorous behaviour of benthic foraminifers are rare and mostly focused on laboratory experiments. Controlled experiments have shown that some agglutinated and intertidal species prey on meio- to macrofaunal metazoans. Here we present observations of the behaviour of specimens of the infaunal benthic foraminiferal species, Globobulimina auriculata and G. turgida, made within several hours of collection from ∼117 m depth in the Alsbäck Deep of the Gullmar Fjord, Sweden. We observed live nematodes within the tests of G. auriculata. Video observations recorded over a 17-hour period showed a G. auriculata specimen with a living nematode whose tail appeared to be entangled within the foraminifer's reticulopodial network. The nematode eventually coiled around the foraminifer's aperture and became much less active, though ingestion into the foraminifer's test was not documented. If these observations indicate feeding by G. auriculata, they differ from previous observations of predation by Ammonia tepida, which utilised external reticulopodial activity to extract the soft tissue of its prey. An alternative interpretation of the video observations, consistent with the observations of the live nematodes inside G. auriculata, was that the nematode was attempting to prey upon the foraminifer. The G. turgida specimens, in contrast, relatively quickly surrounded themselves in soft sediment spheres commonly seen in deposit-feeding foraminifers, and were never observed with nematodes within their tests. We speculate that these contrasting feeding strategies might reduce competition and facilitate the coexistence of these two globobuliminid species.