Shift in algal blooms from micro‐ to macroalgae around China with increasing eutrophication and climate change

Abstract

Blooms of microalgal red tides and macroalgae (e.g., green and golden tides caused by Ulva and Sargassum) have caused widespread problems around China in recent years, but there is uncertainty around what triggers these blooms and how they interact. Here, we use 30 years of monitoring data to help answer these questions, focusing on the four main species of microalgae Prorocentrum donghaiense, Karenia mikimotoi, Noctiluca scintillans, and Skeletonema costatum) associated with red tides in the region. The frequency of red tides increased from 1991 to 2003 and then decreased until 2020, with S. costatum red tides exhibiting the highest rate of decrease. Green tides started to occur around China in 1999 and the frequency of green tides has since been on the increase. Golden tides were first reported to occur around China in 2012. The frequency of macroalgal blooms has a negative linear relationship with the frequency and coverage of red tides around China, and a positive correlation with total nitrogen and phosphorus loads as well as with atmospheric CO2 and sea surface temperature (SST). Increased outbreaks of macroalgal blooms are very likely due to worsening levels of eutrophication, combined with rising CO2 and SST, which contribute to the reduced frequency of red tides. The increasing grazing rate of microzooplankton also results in the decline in areas affected by red tides. This study shows a clear shift of algal blooms from microalgae to macroalgae around China over the past 30 years driven by the combination of eutrophication, climate change, and grazing stress, indicating a fundamental change in coastal systems in the region.

Spatiotemporal Expansion of Algal Blooms in Coastal China Seas

“…These regional differences, while noteworthy, do not distort the representation of year-to-year variability and human-related impacts that we have tried to emphasize. A recent paper by Feng et al 4 shows that blooms have shifted from microalgae to macroalgae in the last three decades. The decrease in the frequency of microalgal blooms and the increase in intensity and affected area shown in our study suggest an increase in the duration of single bloom and a spreading of the locations of blooms around the Chinese coast.…”

“…Algal blooms are a growing concern in aquatic environments and are characterized by the excessive proliferation of phytoplankton species that might have detrimental effects on tourism, human health, and the surrounding ecosystems. − The algal blooms caused by certain species can release toxins that persist in the water or enter the food chain and can lead to an increase in fish mortality rate, the closure of fisheries and aquaculture operations, and severe consequences for the well-being of coastal communities. − Furthermore, the decomposition of some dense nontoxic algal blooms can deplete oxygen in bottom waters and create anoxic “dead zones” that cause widespread mortality in fish and invertebrates, which can potentially restructure entire ecosystems …”

The Prevalence of Marine Lipophilic Phycotoxins Causes Potential Risks in a Tropical Small Island Developing State

“…Small island developing states (SIDS) were officially acknowledged as a distinct group at the United Nations Conference on Environment and Development in June 1992, owing to their small size, geographical isolation, limited resources, and susceptibility to various environmental and economic risks. , SIDS are widely recognized as being highly vulnerable to the impacts of climate change, which adversely affect food security, employment, and income. An adverse consequence of climate change is the increasing frequency of harmful algal blooms (HABs). − The toxigenic microalgae can produce marine lipophilic phycotoxins (MLPs), which can accumulate in a wide range of marine organisms such as shellfish (crustaceans, clams, mussels, scallops, and mollusks, etc. ), coral reef fish (moray eel, grouper, snapper, etc.…”

Nitrogen availability regulates the effects of a simulated marine heatwave on carbon sequestration and phycosphere bacteria of a marine crop

“…Nitrogen limitation can stunt algal growth and nitrogen enrichment is known to reduce the negative impacts of high temperatures on growth and photosynthesis in the giant kelp Macrocystis pyrifera (Fernandez et al 2020). However, excess nitrogen can cause problematic seaweed blooms (Schmidt et al 2012;Feng et al 2023).…”