Seasonal plankton succession is in accordance with phycotoxin occurrence in Disko Bay, West Greenland

Abstract

Harmful algal blooms (HABs) are occurring more frequently in the world's oceans, probably as a consequence of climate change. HABs have not been considered a serious concern in the Arctic, even though the Arctic warms faster than any other region. While phycotoxins and toxin-producing phytoplankton have been found in Arctic waters on several occasions, there is a lack of information on seasonal succession of species and whether the occurrence of harmful species correlates with the presence of their respective phycotoxins. Hence, there is no baseline to assess future changes of HABs in this area. Here, we investigated two periods, from winter to spring and from the spring bloom until summer, in Disko Bay, West Greenland and followed the succession of toxins and their producers using metabarcoding, as well as analyses of particulate and dissolved toxins. We observed a typical seasonal succession with a spring bloom dominated by diatoms, followed by dinoflagellates in summer, with the two most important potentially toxic taxa found being Pseudo-nitzschia spp. and Alexandrium ostenfeldii. The Pseudo-nitzschia spp. peak correlated with a clear increase in particulate domoic acid, reaching 0.05 pg/L. Presence of Alexandrium ostenfeldii could be linked to an increase in spirolides, up to 56.4 pg/L in the particulate phase. Generally, the majority of detected dissolved toxins followed the succession pattern of the particulate toxins with a delay in time. Our results further show that Arctic waters are a suitable habitat for various toxin producers and that the strong seasonality of this environment is reflected by changing abundances of different toxins that pose a potential threat to the ecosystem and its beneficiaries.

Transition from a Mixotroph/Heterotroph Protist Community During the Dark Winter to a Photoautotrophic Spring Community in Arctic Surface Waters

“…Diatoms are typical spring bloom organisms and are often the dominant taxa in Arctic spring blooms [22,[35][36][37]. The genera, Thalassiosira spp.…”

“…Phaeocystis spp. have an advantage over diatoms, because they are not dependent on silicate concentrations, which diminish quickly during the spring bloom [37]. Compared to some other Arctic phytoplankton species, Phaeocystis spp.…”

“…Equal volumes (10 L) of water from ve depths (5, 10, 20, 30 and 40 m) were pooled in order to obtain these depth-integrated samples. Data for Chlorophyll a (Chl a), and particulate organic carbon and nitrogen (POC and PON) as biomass and nutrition status proxies were retrieved from supplementary material of Bruhn et al [37]. The following method of size fractionation might have impacted the integrity of more fragile cells, which could have fragmentized under the pressure of the vacuum ltration.…”

“…Overall, this method holds more scienti c value than it has drawbacks, allowing e.g. insights in seasonal colony formation of the haptophyte Phaeocystis pouchetii, and was successfully applied in other eld studies several times [53,8,37]. Therefore, the remaining 47.5 L pooled sample was size fractionated through a series of lters.…”

“…POC and PON as biomass proxies. Data were retrieved from Bruhn et al[37].In total, 4,009 different ASVs were assigned to protists in the metabarcoding analyses. The 300 most abundant protist ASVs accounted for 81 to 98 % of all reads, depending on the sampling date, of which 97 % were present in all three monthly phases.…”