The anemonefish, now often known as ‘Nemo’, exhibits higher stress and lower reproductive output when its home anemone becomes bleached in warming oceans, finds a study published in Nature Communications this week.

Bleaching occurs when hot water or other stressors cause certain marine animals to lose their green-pigmented symbionts (zooxanthellae), without which they cannot survive. Bleaching is now a well-known phenomenon in corals, but sea anemones can also bleach during heat waves.

When an anomalously warm summer season and El Nino event were forecast for the Great Barrier Reef in 2016, Suzanne Mills, Ricardo Beldade and colleagues capitalized on the opportunity to measure anemonefish stress and reproduction before, during, and after their host anemone underwent bleaching. The authors also identified anemonefish couples that fortuitously resided in anemones that endured the heat without bleaching, providing a natural control group. The results show that fish from bleached anemones exhibit higher stress hormone levels and lower reproductive hormone levels after the onset of bleaching and in comparison to fish from unbleached anemones. Anemonefish couples from bleached anemones spawned less frequently and produced fewer viable young, highlighting the potential for multi-generation effects.

This study underscores the numerous cascading effects of warming oceans on the residents of coral reefs.