Physiological acclimatization in high-latitude zooplankton

Area of Science:

• Marine Biology
• Physiological Ecology
• Oceanography

Background:

• Marine heat waves, like "The Blob" in the Northeast Pacific, cause significant ecosystem changes.
• Physiological acclimatization is crucial for organisms adapting to nonoptimal environmental conditions.
• The marine copepod *Neocalanus flemingeri* is a key species in subarctic Pacific ecosystems, known for lipid accumulation during phytoplankton blooms.

Purpose of the Study:

• To investigate the physiological acclimatization of *Neocalanus flemingeri* to marine heat wave conditions.
• To compare gene expression profiles under varying temperature and phytoplankton abundance scenarios.
• To understand the molecular mechanisms underlying adaptation to environmental stress in marine copepods.

Main Methods:

• Gene expression profiling of *Neocalanus flemingeri* collected over three years (2015-2017) in Prince William Sound.
• Analysis of gene expression patterns in relation to high-temperature years and low phytoplankton abundance years.
• Assessment of metabolic gene regulation, protein synthesis, and muscle function indicators.

Main Results:

• Gene expression differences were more pronounced between high and low chlorophyll (food availability) years than between warm and cool years.
• Down-regulation of genes involved in glycolysis and metabolism indicated modulation of metabolic rates due to prolonged low food.
• Up-regulation of muscle function genes and active swimming behavior were observed, with no suppression of protein synthesis.
• Down-regulation of fatty acid metabolism genes suggested reduced lipid accumulation in low food conditions.

Conclusions:

• *Neocalanus flemingeri* exhibits physiological acclimatization primarily driven by food availability rather than temperature alone.
• Metabolic rates are modulated in response to prolonged periods of low phytoplankton abundance.
• Despite metabolic adjustments, copepods maintained active behavior and protein synthesis, but showed reduced lipid accumulation capacity.