Seasonal changes in the communities of photosynthetic picoeukaryotes in Ofunato Bay as revealed by shotgun metagenomic sequencing

Abstract

Small photosynthetic eukaryotes play important roles in oceanic food webs in coastal regions. We investigated seasonal changes in the communities of photosynthetic picoeukaryotes (PPEs) of the class Mamiellophyceae, including the genera Bathycoccus, Micromonas and Ostreococcus, in Ofunato Bay, which is located in northeastern Japan and faces the Pacific Ocean. The abundances of PPEs were assessed over a period of one year in 2015 at three sampling stations, KSt. 1 (innermost bay area), KSt. 2 (middle bay area) and KSt. 3 (bay entrance area) at depths of 1 m (KSt. 1, KSt. 2 and KSt. 3), 8 m (KSt. 1) or 10 m (KSt. 2 and KSt. 3) by employing MiSeq shotgun metagenomic sequencing. The total abundances of Bathycoccus, Ostreococcus and Micromonas were in the ranges of 42-49%, 35-49% and 13-17%, respectively. Considering all assayed sampling stations and depths, seasonal changes revealed high abundances of PPEs during the winter and summer and low abundances during late winter to early spring and late summer to early autumn. Bathycoccus was most abundant in the winter, and Ostreococcus showed a high abundance during the summer. Another genus, Micromonas, was relatively low in abundance throughout the study period. Taken together with previously suggested blooming periods of phytoplankton, as revealed by chlorophyll a concentrations in Ofunato Bay during spring and autumn, these results for PPEs suggest that greater phytoplankton blooming has a negative influence on the seasonal occurrences of PPEs in the bay.

Metagenome-based diversity analyses suggest a strong locality signal for bacterial communities associated with oyster aquaculture farms in Ofunato Bay

“…Ofunato Bay, winter is usually delayed due to the late arrival of the cold Oyashio Current from the north, and in our study, we found the seawater temperature in March 2015 to be lowest, ranging from 4.6 to 6.4˚C at the three sampling stations (Reza et al, 2018b;Rashid et al, 2018). Thus, May, August, November and March are spring, summer, autumn and winter, respectively, in the bay.…”

Seasonal and annual changes in the microbial communities of Ofunato Bay, Japan, based on metagenomics

“…This reconstruction would have facilitated nutrient flow from the rivers and sewage near Ofunato Bay, which is an enclosed bay and would have retained the nutrients. The other possibility is the presence of nutrient uptake competitors in the bay, such as small eukaryotes, including photosynthetic picoeukaryotes 71 , which would have been trapped on the 5.0 or 0.8-µm filters.…”

Sources of off-flavor in pangasius catfish (Pangasianodon hypophthalmus) ponds

“…The changes in distribution and abundance are thought to be linked to alteration of physico-chemical factors of pond water. 32 Previous studies showed that species of Aphanizomenon, Oscillatoria, and Pseudanabaena from catfish aquaculture ponds produce 2-methylisoborneol. 33 Geosmin and 2-methylisoborneol are also responsible for many of the off-flavor episodes/problems in municipal drinking water systems worldwide.…”