Cell Size reduction and restoration of seasonally dominant diatoms in Lake Biwa

概要

Phytoplankton is the base of aquatic food webs and is significant for climate
regulation and biogeochemical cycling. They are the primary producers in aquatic
ecosystems, which contributes to nearly 50 % of global net primary production. Diatoms
(Bacillariophyta) are the most diverse and ecologically essential phytoplankton groups.
Since diatoms are ubiquitously distributed in lakes, their abundance and composition
rapidly respond to subtle environmental changes. They have been used as one of the most
valuable organisms in biomonitoring studies. Diatoms reproduce sexually or asexually to
carry forward their generations. Cell size restitution in diatoms is thus an essential factor,
and sexual reproduction is the primary way of restoring the cell size of the population.
That is why studying cell size restitution and sexual reproduction is essential to
understanding their morphological evolution. Even though sexual reproduction in
diatoms is worth exploring, it is an understudied aspect of diatom life cycle dynamics.
Studying the life cycle stages of the diatoms concerning various environmental
parameters is thus necessary.
Materials and Methods
Firstly, five-year monthly samples were collected, and the cell size and density of
F. crotonensis were estimated in the north basin of Lake Biwa. Vertical temperature
profiles were measured with a CTD profiler, and the total nitrogen, phosphorus, and
silicate concentration data were obtained from the literature. The relationships between
the cell size of F. crotonensis and some environmental factors and between the cell
density of the diatom and the factors were examined. Secondly, sampling was conducted
to study the cell size changes of the seasonally dominant diatoms Aulacoseira granulata,
Aulacoseira ambigua f. japonica, Fragilaria crotonensis, and Praestephanos suzukii.
Both biotic and Abiotic samples were collected from the north basin of Lake Biwa. A
total of 24 bi-monthly water samples were collected from June 2020 to June 2021 from
the epilimnion (euphotic zone, 5m) and the hypolimnion (50 m). ...