Shionodiscus gaarderaesp. nov. (Thalassiosirales, Thalassiosiraceae), a bloom-producing diatom from the southwestern Atlantic Ocean, and emendation ofShionodiscus bioculatusvar.bioculatus

Abstract

The recently established diatom genus Shionodiscus is characterized as possessing a labiate process on the valve face and strutted processes with long internal and reduced, or no, external extensions. Many Thalassiosira species with these features were transferred to this new genus, as well as some with short internal, strutted process extensions. Examination of samples from the Argentine continental shelf and slope waters, and from the Beagle Channel, revealed the presence of a small centric diatom that formed an extensive bloom in slope waters during spring 2005 and 2006. Analysis by light and electron microscopy revealed high similarity to specimens previously referred as Thalassiosira bioculata var. raripora. This name was never effectively published; nevertheless, the name has been adopted and observations referring to it have been reported on several occasions. Here we trace the usage of the (nomenclaturally invalid) name Thalassiosira bioculata var. raripora in the literature, and formally describe the species as Shionodiscus gaarderae, based on our observations and comparison with previous reports. A morphological comparison of this and similar taxa is also provided. In addition, we offer an emended description of S. bioculatus var. bioculatus from Ostenfeld material sampled from the 'Färöer Island Naströ Fjord Plankton (16.9.1902)', held in the Hustedt collection. Finally, we propose the transfer of Thalassiosira rosulata to Shionodiscus.

Response of a natural Antarctic phytoplankton assemblage to changes in temperature and salinity

“…However, the valve morphology of the specimens observed in our study does not coincide with any of these species, but corresponds to S. gaarderae described by Ferrario et al (2018). This small species is known to occur in the Norwegian and North Seas, with peak abundance (5 × 10 5 cells l −1 ) during spring in sea water temperature ~ 9 °C, and also in sub-Antarctic waters from the Argentine Sea (Ferrario et al, 2018). In the latter, extensive blooms of S. gaarderae (up to 4.5 × 10 6 cells l −1 ) were recorded during spring in shelf-break waters from 39°S to 48°S at temperatures ranging from 5 to 9 °C (Ferrario et al, 2018).…”

“…expecta, S. perpusilla, S. oestrupii, S. frenguelli, S. frenguelliopsis, S. poroseriata, S. ritscheri, and S. trifulta (Scott and Marchant, 2005, all of them previously described as Thalassiosira species). However, the valve morphology of the specimens observed in our study does not coincide with any of these species, but corresponds to S. gaarderae described by Ferrario et al (2018). This small species is known to occur in the Norwegian and North Seas, with peak abundance (5 × 10 5 cells l −1 ) during spring in sea water temperature ~ 9 °C, and also in sub-Antarctic waters from the Argentine Sea (Ferrario et al, 2018).…”

“…This small species is known to occur in the Norwegian and North Seas, with peak abundance (5 × 10 5 cells l −1 ) during spring in sea water temperature ~ 9 °C, and also in sub-Antarctic waters from the Argentine Sea (Ferrario et al, 2018). In the latter, extensive blooms of S. gaarderae (up to 4.5 × 10 6 cells l −1 ) were recorded during spring in shelf-break waters from 39°S to 48°S at temperatures ranging from 5 to 9 °C (Ferrario et al, 2018). In our experiments, S. gaarderae continued to grow in high-temperature treatments until day 5, when NO 3 concentrations were on average 0.2 μM (Fig.…”

Long‐term studies on West Antarctic Peninsula phytoplankton blooms suggest range shifts between temperate and polar species

“…In contrast, high regional Chl‐ a concentrations were observed along the southern part of the King George Island during February 2012 and 2018. This finding suggests a potential regional event, which aligns with previous observations documenting the presence of S. gaarderae in open water areas (Ferrario et al., 2018). Therefore, it is possible that the observed blooms may have been advected from outside of the cove.…”

Microbial plankton configuration in the epipelagic realm from the Beagle Channel to the Burdwood Bank, a Marine Protected Area in Sub-Antarctic waters

“…Shionodiscus gaarderae (Fig 11) suggests a fast population response to triggering factors such as nutrient pulses and stratified conditions. This species has been recently identified and described by Ferrario et al [82] from specimens collected along the Argentine Sea, where its population was responsible of large blooms in slope waters during springs [82]. In fact, at the particular station 17, the branch of the ACC that surrounds the bank clockwise, creates a small eddy (see Figs 5D and 6B in [54]) before ongoing northwards…”