Part 1: Local vs global stressors on coral reefs and kelp forests.

Marine ecosystems are vital, providing habitats for diverse wildlife and numerous benefits to human societies, including food, raw materials, climate regulation, and nutrient cycling. 

The ability of these ecosystems to provide such services depends on key species, known as foundation species, which play a crucial role in maintaining community structure.

Foundation species, such as coral reefs and kelp forests, can significantly influence species interactions, environmental conditions, and resource availability. 

They offer a physical framework for other species, supporting ecosystem integrity through their presence. The loss of foundation species can lead to the collapse of entire ecosystems.

Impact of Climate Change on Marine Ecosystems

Climate change is profoundly altering marine ecosystems through greenhouse gas emissions, leading to long-term changes in temperature, sea ice cover, pH levels, and increased extreme weather events. 

These changes affect the physical, chemical, and biological aspects of marine systems, often with negative consequences.

Marine foundation species and the ecosystems they support face threats from both global climate change and local anthropogenic stressors. 

Understanding these threats is essential for ensuring their survival and continued provision of ecosystem services.

Local and Global Stressors on Marine Foundation Species

General Impacts:

Marine foundation species in coastal zones are under threat from climate change and human activities. The loss of these species and their associated ecosystems incurs costs estimated in the trillions of dollars annually.

Warming temperatures and heatwaves are causing species to shift their ranges poleward and vertically, with significant losses in equatorial regions due to thermal stress. 

Rising sea levels, sedimentation, light, and turbidity changes affect species distribution, with those at lower levels being outcompeted for resources.

Storms, increasingly strong and frequent due to climate change, devastate ecosystems like mangroves and coral reefs. 

The combined effects of climate change and non-climate stressors, such as habitat modification and pollution, often result in significant ecosystem changes, including massive losses of seagrass and kelp forests.

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Coral Reefs:

Coral reefs are highly sensitive to local temperature changes. Even a 1°C increase can disrupt the symbiotic relationship between coral and its photosynthetic partners, leading to bleaching and potential death. 

Approximately 50% of coral reefs have been lost globally due to human activities and climate change. A temperature rise of 1.5–2 °C could result in the total loss of coral reefs.

Heatwaves pose the biggest threat to coral reefs, causing mass bleaching events. 

The global coral bleaching event from 2014–2017 was the worst recorded, with extensive losses. 

As heatwaves become more frequent and intense, reef recovery will be severely hindered, leading to shifts in species composition and ecosystem services.

In regions like the Caribbean, other organisms like seaweeds and sponges are replacing corals as habitat providers. 

However, these organisms do not offer the same long-term benefits as corals, particularly in building reef structures.

Coral reefs, covering less than 0.1% of the ocean’s surface, host roughly 25% of all marine species. 

The loss of coral reefs significantly impacts associated communities, reducing fish abundance and altering species composition. Coral mortality can lead to shifts in fish populations and increased herbivorous fish biomass, affecting human communities reliant on coral reefs.

Kelp Forests:

Kelp forests, composed of large brown seaweeds, are among the most productive coastal ecosystems but are highly vulnerable to climate change. Kelps generally have short lifespans, leading to rapid responses to environmental changes.

Kelp forests are found in cool water regions, primarily in temperate Arctic latitudes. Warming temperatures and heatwaves cause forest deaths and reduced growth. 

Overgrazing by species like sea urchins, expanding their ranges due to warmer waters, also causes extensive damage.

Kelp underwater.
Image credit: Unsplash

Kelp forests at cooler leading range edges in the Arctic may expand due to sea ice loss and increased light, potentially increasing their distribution. 

However, increased turbidity from melting ice may limit this expansion. Losses of kelp forests, reported globally, indicate significant declines in areas like Western Australia, Norway, and Japan.

Climate change alters kelp forests’ genetic makeup, reducing their adaptability. In Australia, genetic diversity is declining, favouring warmer water-adapted species. This shift impacts seabed fauna, reducing diversity as warmer-adapted kelp species replace cooler-adapted ones.

Kelp loss can lead to shifts to other ecosystem states, such as turf-dominated reefs or sea urchin barrens, which prevent kelp recovery even if conditions improve. Gradual warming also causes the tropicalization of kelp forests, increasing the presence of coral and brown algae.

Understanding the local and global stressors on marine foundation species is crucial for their conservation.

Addressing the impacts of climate change and anthropogenic activities through effective management and mitigation strategies is essential to preserving these vital ecosystems and their services to human societies.