Sleep walking copepods? Calanus diapausing in hypoxic waters adjust their vertical position during winter

Area of Science:

• Marine biology
• Zooplankton ecology
• Oceanography

Background:

• Hypoxia, or low oxygen levels, is increasing in oceans globally.
• Zooplankton, like Calanus helgolandicus copepods, are crucial to marine food webs.
• Understanding how zooplankton cope with hypoxia is vital for predicting ecosystem changes.

Purpose of the Study:

• To investigate the overwintering strategies of Calanus helgolandicus in hypoxic conditions.
• To determine the minimum oxygen tolerance and behavioral responses of these copepods.
• To assess the impact of hypoxia on their survival and energy reserves.

Main Methods:

• Continuous acoustic monitoring of Calanus helgolandicus populations.
• Measurement of dissolved oxygen levels in Oslofjorden, Norway.
• Analysis of copepod vertical distribution and mortality rates.

Main Results:

• Calanus helgolandicus demonstrated a minimum oxygen tolerance of 0.2-0.3 mL O2 L-1 at 8°C.
• Copepods vertically migrated to shallower waters as hypoxia progressed upwards.
• Low mortality was observed in early winter due to predator exclusion, but increased as oxygen levels declined.

Conclusions:

• Calanus helgolandicus possesses sufficient energy reserves for long-term overwintering in hypoxic environments.
• Seasonal migration patterns and vertical distribution are key survival strategies.
• Ocean deoxygenation due to climate change may significantly impact copepod populations and marine ecosystems.