Survival and recovery of the foraminifer Amphistegina gibbosa and associated diatom endosymbionts following up to 20 months in aphotic conditions

Abstract

Abstract Dormancy in the Foraminifera has been observed widely across the phylum in reaction to a variety of triggers including, in the diatom symbiont-bearing foraminifer Amphistegina gibbosa, extended periods of darkness. Resumption of activity in the host-symbiont holobiont was noted, but not fully documented, in specimens reintroduced to light following up to 12 months in darkness. Here, criteria for documenting recovery included resumption of reticulopodial activity in the host and return of pre-treatment golden-brown color characteristic of an active symbiotic diatom population. Reticulopodial activity resumed in nearly all treatment specimens (>95%) following 12 months in darkness, and in >70% of the specimens when reintroduced to light following 20 months in darkness. Image analysis using the percent of the foraminiferal surface area showing golden-brown color as a proxy for recovery of the endosymbionts showed return of such color within days for shorter treatments (7 and 12 months in darkness), but slower and less complete return in longer treatments (15 and 20 months), indicating increased susceptibility to photic damage of symbionts as the length of dormancy increased.