On the Relationship between a Novel Prorocentrum sp. and Colonial Phaeocystis antarctica under Iron and Vitamin B12 Limitation: Ecological Implications for Antarctic Waters

Francesco Bolinesi,Maria Carmen Valoroso,Angelina Cordone,Emanuela Serino,Maria Saggiomo,Serena Aceto,Olga Mangoni

doi:10.3390/app10196965

Francesco Bolinesi, Maria Carmen Valoroso + Show 5 more

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https://doi.org/10.3390/app10196965

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Abstract

We collected live mixed natural samples from the northeastern Ross Sea during the austral summer of 2017 and isolated a novel Prorocentrum sp. (Dinophyceae) associated with mucilaginous Phaeocystis antarctica (Coccolithophyceae) colonies. The haptophyte P. antarctica is a key species of the phytoplankton community in the Ross Sea, where blooms are subjected to iron limitation and/or co-limitation with other micronutrients (e.g., vitamin B12) during the summer. We first performed preliminary genetic analyses to determine the specific identity of the novel Prorocentrum sp., which indicated that it represented a previously undescribed species. The formal description of this new species is in process. To further assess its relationship with P. antarctica, we obtained their monospecific and mixed cultures and evaluated their responses to different irradiance levels and iron and vitamin B12 limitation. Our results indicated differential susceptibility of the two species to iron limitation and differential photosynthetic plasticity under high irradiance. Iron limitation reduced colony formation in P. antarctica and decreased the chlorophyll-a content in Prorocentrum sp., whereas B12 limitation did not affect growth or photosynthetic efficiency in either species. In addition, P. antarctica could photosynthesize efficiently under different irradiance levels, due to its ability to modulate the light adsorption cross-section of PSII, whereas Prorocentrum sp. exhibited lower photosynthetic plasticity and an inability to modulate both the maximum photochemical efficiency and effective adsorption cross-section of PSII under high irradiance. The trophic interaction between Prorocentrum sp. and P. antarctica could present ecological implications for the food webs and biogeochemical cycles of the Antarctic ecosystem. Considering the predicted climate-driven shifts in global ocean surface light regimes and changes in iron or vitamin B12 transfer, which are most likely to impact changes in the phytoplankton community structure, our results present implications for carbon export to deeper waters, ecological functioning, and associated biogeochemical changes in the future.

Highlights

The Ross Sea is regarded to be the most productive area of the Southern Ocean, playing a key role in the transfer of atmospheric carbon to the ocean’s interior and in global climate regulation [1,2].The high productivity of this region is linked essentially to its phytoplankton community, which is dominated primarily by various diatoms (Bacillariophyceae) and the coccolithophyte Phaeocystis antarctica
30 mL of sea water was withdrawn from the Niskin bottles, prefiltered through a 300 μm mesh (Nitexs, Wildlife Supply Company, Buffalo, NY, USA) to remove most metazoan plankton, and inoculated in 60 mL flasks filled with sterilized Ross Sea water enriched with 20% light 1 (L1) medium
Antarctic new species of Prorocentrum sp. and Phaeocystis antarctica ironand andrelationships vitamin B12 limitation, and waters, the main objective of this work was to describe the under responses between a new the consequent ecological for Antarctic

Summary

Introduction

The high productivity of this region is linked essentially to its phytoplankton community, which is dominated primarily by various diatoms (Bacillariophyceae) and the coccolithophyte Phaeocystis antarctica. These two functional groups exhibit different temporal and spatial patterns, with P. antarctica dominating the early seasonal blooms in the polynyas [2,3,4,5], accounting for more than 60% of the primary productivity in the southern Ross Sea [6], whereas diatoms dominate the coastal waters and the shallow upper mixed layer during the summer. In the case of other less abundant groups, an increase in dinoflagellates, silicoflagellates, and heterotrophic protists has been reported in the phytoplankton communities later in the growing season [23,24,25,26]

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