Mass Die-Off Events in Swarming Hyperiid Amphipods: Potential Drivers

Area of Science:

• Marine Biology
• Oceanography
• Zooplankton Ecology

Background:

• Mass stranding events of marine organisms are common, but less studied in pelagic crustaceans like hyperiid amphipods.
• Hyperiid amphipods are key zooplankton, often associated with gelatinous organisms.

Purpose of the Study:

• Investigate the causes of consecutive mass die-off and stranding events of free-living hyperiids in the Red Sea.
• Determine the contributing factors: semelparous reproduction, thermal stress, or physical oceanographic conditions.
• Contextualize findings with a global review of hyperiid swarming and mortality events.

Main Methods:

• Morphological and molecular analyses to identify hyperiid species.
• Analysis of environmental data, including temperature and wind conditions.
• Global literature and citizen science data review for hyperiid mass events.

Main Results:

• The species involved in Red Sea events was identified as *Anchylomera blossevillei*.
• Semelparity was rejected due to a balanced sex ratio and absence of gravid females.
• Thermal stress and parasitic infections were not indicated as causes.
• Oceanographic data revealed cyclonic eddies under weak wind conditions, potentially facilitating stranding.

Conclusions:

• Physical oceanographic conditions, specifically cyclonic eddies, are the likely cause of *Anchylomera blossevillei* mass strandings in the Red Sea.
• Reproductive strategies and thermal stress were ruled out.
• Further research is needed to understand the ecosystem-wide impacts of such hyperiid stranding events.