Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems

Area of Science:

• Marine Ecology
• Biogeochemistry
• Oceanography

Background:

• Ocean deoxygenation is a growing global concern, driven by climate change and human activities.
• Long-term effects of declining oxygen on benthic communities and sediment biogeochemistry are not fully understood.
• Benthic ecosystems play crucial roles in marine carbon and nutrient cycling.

Purpose of the Study:

• To investigate the impact of deoxygenation on benthic assemblages and biogeochemical functioning.
• To identify critical oxygen thresholds affecting marine ecosystems.
• To understand the feedback between benthic communities and sediment processes under low oxygen conditions.

Main Methods:

• Studied a natural dissolved oxygen gradient in the Estuary and Gulf of St. Lawrence.
• Analyzed macrobenthic community structure and biodiversity.
• Assessed sediment biogeochemistry and bioturbation rates.

Main Results:

• Observed non-linear responses in biodiversity and ecosystem function to decreasing oxygen levels.
• Identified a critical oxygen threshold of approximately 63 μM.
• Documented a drastic reduction in bioturbation below this threshold, leading to altered organic matter metabolism.

Conclusions:

• Bioturbating species play a key role in mitigating biogeochemical consequences of hypoxia.
• Deoxygenation significantly alters benthic community structure and function.
• Findings aid in predicting future changes in benthic ecosystems under ongoing ocean warming and deoxygenation.