A vibrant, bioluminescent underwater world teeming with diverse microalgae species.

Hidden Wonders: Unveiling the Secrets of Microalgae in Our Ecosystems

Theo Raines in Climate & Environment August 2025 • 4 min read.

"Tiny but mighty, microalgae play a crucial role in aquatic environments. Explore their diversity, ecological functions, and why they matter to our planet's health."

Microalgae are the foundation of many aquatic ecosystems, particularly in shallow lakes. Unlike larger aquatic plants, microalgae can quickly shift their dominance based on water conditions. These tiny organisms, both in the water column and on the sediment, are essential for linking inorganic compounds to the food web, providing vital nutrients to higher trophic levels.

In shallow estuaries, a fascinating phenomenon often occurs: high benthic microalgal biomass exists alongside low primary production and phytoplankton biomass, while pelagic areas boast high rates of primary production. This contrast highlights the complex interactions within these ecosystems, influenced by factors like light availability, grazing pressure from zooplankton, and the settling of phytoplankton cells onto the sediment.

The opening and closing phases of estuaries significantly impact microalgae populations. For example, during closed phases, diatoms may dominate phytoplankton communities, while open phases see an increase in dinoflagellates and cryptophytes. Nutrient availability and light penetration play critical roles in these shifts, underscoring the dynamic nature of these environments.

Diversity and Ecological Significance of Microalgae

A vibrant, bioluminescent underwater world teeming with diverse microalgae species.

The diversity of microalgae in ecosystems like Lake St. Lucia is remarkable, reflecting the variety of habitats and environmental changes. While long-term quantitative studies are limited, the existing research reveals a complex community structure, especially among cyanobacteria and diatoms. These microorganisms form prominent benthic mats, particularly under hypersaline conditions, showcasing their resilience to extreme environments.

Cyanobacteria, or blue-green algae, are key players in these mats, thriving in high temperatures, intense sunlight, and hypersalinity. Species like Leptolyngbya, Anabaenopsis arnoldii, and Lyngbya can withstand salinity levels up to 100. These mats create unique micro-environments, often trapping oxygen and supporting a diverse eukaryotic community. In extreme conditions, Leptolyngbya may dominate, reducing the diversity of other organisms.

Possible factors affecting the spatial and temporal distribution of microalgae:

Light Availability
Nutrient Levels
Salinity Fluctuations
Grazing Pressure

Diatoms also contribute significantly to microalgal diversity, with numerous species identified in various habitats within Lake St. Lucia. Studies have revealed that benthic, epiphytic, and planktonic diatoms respond differently to environmental conditions. Salinity appears to be a primary driver of diatom population structure. Different communities thrive in different areas based on their salinity tolerance, from the marine-influenced mouth and Narrows to the brackish lakes area.

Why Microalgae Matter

Understanding microalgae is crucial for maintaining healthy aquatic ecosystems. These tiny organisms play a significant role in primary production, nutrient cycling, and supporting complex food webs. By studying their diversity, ecological functions, and responses to environmental changes, we can better manage and conserve these vital components of our planet's ecosystems. Continuous monitoring and research are essential to uncovering further secrets of microalgae and harnessing their potential benefits.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1017/cbo9781139095723.012, Alternate LINK

Title: Microalgae

Journal: Ecology and Conservation of Estuarine Ecosystems

Publisher: Cambridge University Press

Authors: Renzo Perissinotto, Guy C. Bate, David G. Muir

Published: 2013-05-16

Everything You Need To Know

What role do microalgae play in aquatic ecosystems, especially in places like shallow lakes?

Microalgae serve as the cornerstone of many aquatic food webs, especially in shallow lakes. They facilitate the crucial link between inorganic compounds and the food web by converting inorganic substances into organic material through photosynthesis, which is then consumed by zooplankton and other organisms. This process provides essential nutrients to higher trophic levels, sustaining the entire ecosystem.

Why do we observe such contrasting levels of primary production and phytoplankton biomass between benthic and pelagic zones in shallow estuaries?

In shallow estuaries, high benthic microalgal biomass can coexist with low primary production and phytoplankton biomass. This occurs because benthic microalgae are heavily influenced by factors such as light availability at the sediment surface, nutrient resuspension from the sediment, and grazing pressure from benthic invertebrates. The pelagic zones, on the other hand, often experience high rates of primary production due to better light penetration and nutrient availability in the water column.

How do the opening and closing phases of estuaries affect the composition of microalgae populations, particularly the shift between diatoms, dinoflagellates, and cryptophytes?

During closed phases of estuaries, diatoms often dominate phytoplankton communities due to their ability to thrive in nutrient-rich conditions with reduced water flow. When the estuary opens, there is an increase in dinoflagellates and cryptophytes. These shifts are due to changes in salinity, nutrient availability, and light penetration, which favor different species at different times.

How do cyanobacteria, like Leptolyngbya, create unique micro-environments in hypersaline conditions, and what are the implications for biodiversity?

Cyanobacteria, such as Leptolyngbya, Anabaenopsis arnoldii, and Lyngbya, form prominent benthic mats in hypersaline conditions. These mats create unique micro-environments by trapping oxygen and supporting a diverse eukaryotic community. Leptolyngbya can dominate in extreme conditions with salinity levels up to 100, potentially reducing the diversity of other organisms. These mats are crucial for primary production and nutrient cycling in extreme environments.

Why is it important to study and understand microalgae, and what potential benefits can be derived from this knowledge?

Understanding the diversity, ecological functions, and responses to environmental changes of microalgae is essential for effectively managing and conserving aquatic ecosystems. By continuously monitoring and researching microalgae, we can uncover their potential benefits, such as their role in carbon sequestration, biofuel production, and wastewater treatment, further enhancing the health and sustainability of our planet.