Higher temperatures can facilitate pathogen virulence, survival, and transmission rates 9, while lower productivity can depress host population parameters and individual body condition, thus compromising fish immune response 21, 22. In the Galapagos Islands, El Niño periods are characterized by increased SST and decreased marine biomass production 19, 20. Most disease outbreaks reported from wild fish populations involve multiple pathogens and are associated with concomitant environmental stress 15, 16, 17, 18. Less is known regarding the etiology and implications of disease in wild finfish populations 15, or how these will be affected by climate change 16. Considerable focus has also been given to human health concerns such as increased incidence of harmful algal blooms with warming ocean temperatures 14. Global warming has accelerated the reporting of disease in wild marine populations by pushing organisms such as corals past their thermal tolerance limits, resulting in coral bleaching and increased susceptibility to associated pathogens 12, 13. Diseases of marine organisms have been extensively studied in high-value organisms such as oysters 10, and are particularly prevalent in aquaculture conditions 11, where high densities and stagnant water tend to favor outbreaks and where it is easier to detect, track, and manage disease. The three most extreme El Niño events on record all occurred in the past four decades and have been progressively stronger 7, suggesting that the frequency and magnitude of major ENSO events will increase with global warming 5, 6.Įxtreme events such as El Niño pose one of the largest global threats to ocean ecosystem health 2, and there is growing concern regarding how climate change will foster the spread of disease 8, 9.
The combination of enhanced radiative forcing and altered circulation can also exacerbate natural phenomena such as the El Niño-Southern Oscillation (ENSO), increasing the frequency of extreme climate events 5, 6. In marine ecosystems, increased greenhouse gases are altering both ocean chemistry and circulation 2, 3, which can cause abrupt and persistent changes in local sea surface temperature (SST) and productivity 4. We hypothesize that this outbreak was precipitated by the persistent warm temperatures and lack of planktonic productivity that characterize extreme El Niño events, which are predicted to increase in frequency with global warming.Īs one of the most pervasive anthropogenic impacts on the planet, climate change affects a myriad of physical processes that govern the conditions for life 1. In January 2016, disease prevalence reached 51.1% in the ring-tailed damselfish Stegastes beebei (n = 570) and 18.7% in the king angelfish Holacanthus passer (n = 318), corresponding to 78% and 86% decreases in their populations relative to a 4.5-year baseline, respectively. Disease prevalence rates were linearly correlated with density in three fish species. A bacterial culture isolated from skin lesions of two of the affected fish species was identified by sequencing of the 16S rRNA gene as a Rahnella spp. Disease signs included scale loss and hemorrhagic ulcerated patches of skin, fin deterioration, lethargy, and erratic behavior.
This coincided with a novel ulcerative skin disease affecting 18 teleost species from 13 different families. The 2015–16 El Niño generated a +2.5 ☌ sea surface temperature anomaly in the Galapagos Islands lasting six months. Here we describe an unprecedented multi-species outbreak of wild fish disease driven by a climate perturbation.
Climate change increases local climatic variation and unpredictability, which can alter ecological interactions and trigger wildlife disease outbreaks.
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