Climate change and the aquatic continuum: A cyanobacterial comeback story

Abstract

Billions of years ago, the Earth's waters were dominated by cyanobacteria. These microbes amassed to such formidable numbers, they ushered in a new era—starting with the Great Oxidation Event—fuelled by oxygenic photosynthesis. Throughout the following eon, cyanobacteria ceded portions of their global aerobic power to new photoautotrophs with the rise of eukaryotes (i.e. algae and higher plants), which co‐existed with cyanobacteria in aquatic ecosystems. Yet while cyanobacteria's ecological success story is one of the most notorious within our planet's biogeochemical history, scientists to this day still seek to unlock the secrets of their triumph. Now, the Anthropocene has ushered in a new era fuelled by excessive nutrient inputs and greenhouse gas emissions, which are again reshaping the Earth's biomes. In response, we are experiencing an increase in global cyanobacterial bloom distribution, duration, and frequency, leading to unbalanced, and in many instances degraded, ecosystems. A critical component of the cyanobacterial resurgence is the freshwater‐marine continuum: which serves to transport blooms, and the toxins they produce, on the premise that “water flows downhill”. Here, we identify drivers contributing to the cyanobacterial comeback and discuss future implications in the context of environmental and human health along the aquatic continuum. This Minireview addresses the overlooked problem of the freshwater to marine continuum and the effects of nutrients and toxic cyanobacterial blooms moving along these waters. Marine and freshwater research have historically been conducted in isolation and independently of one another. Yet, this approach fails to account for the interchangeable transit of nutrients and biology through and between these freshwater and marine systems, a phenomenon that is becoming a major problem around the globe. This Minireview highlights what we know and the challenges that lie ahead.

Metabarcoding vs Microscopy: Comparison of Methods To Monitor Phytoplankton Communities

“…It is promising that we observed comparable results with metabarcoding and carbon biomass, but the usability of the distribution pattern of phytoplankton groups may be discussed. In low-salinity areas, like in the northern Baltic Sea and lakes, nutrient load, eutrophication, and climate change often lead to select cyanobacteria. − In the Baltic Sea, the cyanobacteria maximum occurs in summer, indicating a positive response to temperature . Therefore, the proportion of cyanobacteria in the total phytoplankton community could be an indicator of eutrophication and climate impact.…”

Characterizing the Impact of Cyanobacterial Blooms on the Photoreactivity of Surface Waters from New York Lakes: A Combined Statewide Survey and Laboratory Investigation

“…Φ app,RI for bloom exudates accounted for 60 ± 6% to 66 ± 4% of those for the supernatants and showed positive correlations with %Chl-a cyano (Spearman's ρ = 0.678−0.909; p = 0.0001− 0.0185; Figure S21), reaffirming the association between enhanced photoreactivity and cyanobacterial abundance for whole water samples from bloom-impacted CSLAP lakes. Compared to Otisco Lake water, S19) and * k t t , HDO, DOM 3 HDO (8.8−9.9 × 10 8 M −1 s −1 with a median of 9.2 × 10 8 M −1 s −1 ; Table S28) for bloom supernatants were 41 ± 6% to 50 ± 15% higher and covaried with %Chl-a cyano (Spearman's ρ = 0.622−0.832; p = 0.0013−0.0347; Figure S22), suggesting that changes in cyanobacterial abundance also altered 3 ) a m o n g bloom supernatants were accompanied by shifts in the relative contribution from high-energy and low-energy 3 (ranging from 1.9 ± 0.2 to 2.3 ± 0.1; Figure 3a) far exceeded that of Otisco Lake water and fell on the higher end of those reported for extracellular substances produced by cyanobacteria and heterotrophic bacteria (i.e., 1.4−2.4) 26,88 as well as wastewater effluent organic matter (i.e., 1.2−2.3). 53 (ranging from 2.8 ± 0.2 to 3.4 ± 0.2; Figure 3b) was significantly higher than that of Otisco Lake water but overlapped with those measured for Pony Lake fulvic acid (i.e., 2.7) 53 and solid-phase extracted cyanobacterial EOM (i.e., 4.0).…”

Allelopathic Potential of the Cyanotoxins Microcystin-LR and Cylindrospermopsin on Green Algae

“…This is mainly due to a group of secondary metabolites known as cyanotoxins. The cytotoxic effects of these compounds have been well studied in animals and humans [ 3 , 4 ], but there are many questions regarding their effects on the coexisting phytoplankton communities [ 5 , 6 , 7 , 8 , 9 ]. There is still no consensus on the ecological role of the cyanobacterial toxins [ 6 , 10 , 11 , 12 ].…”