Extreme Temperatures Reduce Copepod Performance and Change the Relative Abundance of Internal Microbiota

Area of Science:

• Marine Biology
• Microbial Ecology
• Climate Change Science

Background:

• Copepods are abundant marine invertebrates and crucial food sources.
• Copepods are sensitive to rising ocean temperatures.
• The influence of internal microbiomes on copepod thermal tolerance is poorly understood.

Purpose of the Study:

• To investigate how elevated temperatures affect the life history traits of the tropical copepod *Acartia* sp.
• To analyze changes in the copepod's internal microbiome composition under thermal stress.
• To link microbiome shifts to copepod performance under warming conditions.

Main Methods:

• Assessed survival, development, and reproduction of *Acartia* sp. at 26°C, 30°C, and 34°C.
• Analyzed internal microbiomes using high-throughput 16S rRNA gene sequencing.
• Quantified operational taxonomic units (OTUs) and microbial community composition.

Main Results:

• Copepod performance peaked at 30°C, with reduced growth, survival, and reproduction at 34°C.
• Warming did not alter OTU richness or biodiversity indices.
• Significant shifts in the relative abundance of Proteobacteria, Actinobacteria, and Bacteroidota were observed, with thermophilic bacteria increasing at extreme temperatures.

Conclusions:

• Elevated temperatures significantly alter the internal microbiome of *Acartia* sp.
• Changes in specific bacterial phyla, such as Proteobacteria and Bacteroidota, may explain reduced copepod performance under thermal stress.
• Understanding these microbial dynamics is essential for predicting the impact of climate change on marine invertebrates.