Dominance of photo over chromatic acclimation strategies by habitat-forming mesophotic red algae

Chromatic acclimation shapes phytoplankton biogeography

Marine photoautotrophs have evolved to exploit the ocean's variable light conditions, with chromatic acclimators being able to adjust their pigment content to better match the ambient light color. The impact of chromatic acclimation on phytoplankton distribution and competition is not well understood despite its global importance. This study explores chromatic acclimation's role in shaping the biogeography of Synechococcus, a widespread cyanobacterium. We integrated three pigment types into a global ecosystem model: a green-light specialist, a blue-light specialist, and a chromatic acclimator. Laboratory studies defined each type's specific absorption properties. Our results indicate that chromatic acclimation offers an evolutionary advantage by enabling Synechococcus to adapt to varying light environments. This ability to mimic blue- and green-light specialists and enhance absorption at intermediate states, particularly in areas with high seasonal light variations, increases Synechococcus distribution and biomass. Thus, chromatic acclimation affects ecosystem functioning and biogeochemical processes in the ocean.

Function and stability of mesophotic coral reefs

The function and stability of mesophotic coral ecosystems (MCEs) have been extensively studied in recent years. These deep reefs are characterized by local physical processes, particularly the steep gradient in irradiance with increasing depth, and their impact on trophic resources. Mesophotic reefs exhibit distinct zonation patterns that segregate shallow reef biodiversity from ecologically unique deeper communities of endemic species. While mesophotic reefs are hypothesized as relatively stable refuges from anthropogenic stressors and a potential seed bank for degraded shallow reefs, these are site-specific features, if they occur at all. Mesophotic reefs are now known to be susceptible to many of the same stressors that are degrading shallow reefs, suggesting that they require their own specific conservation and management strategies.