Severe climatic events affect all species, but there is little quantitative knowledge of how sympatric species react to such situations. We compared the reproductive seasonality of sea turtles that nest sympatrically with their vulnerability to tropical cyclones (in this study, "tropical cyclone" refers to tropical storms and hurricanes), which are increasing in severity due to changes in global climate. Storm surges significantly decreased reproductive output by lowering the number of nests that hatched and the number of hatchlings that emerged from nests, but the severity of this effect varied by species. Leatherback turtles (Dermochelys coriacea) began nesting earliest and most offspring hatched before the tropical cyclone season arrived, resulting in little negative effect. Loggerhead turtles (Caretta caretta) nested intermediately, and only nests laid late in the season were inundated with seawater during storm surges. Green turtles (Chelonia mydas) nested last, and their entire nesting season occurred during the tropical cyclone season; this resulted in a majority (79%) of green turtle nests incubating in September, when tropical cyclones are most likely to occur. Since this timing overlaps considerably with the tropical cyclone season, the developing eggs and nests are extremely vulnerable to storm surges. Increases in the severity of tropical cyclones may cause green turtle nesting success to worsen in the future. However, published literature suggests that loggerhead turtles are nesting earlier in the season and shortening their nesting seasons in response to increasing sea surface temperatures caused by global climate change. This may cause loggerhead reproductive success to improve in the future because more nests will hatch before the onset of tropical cyclones. Our data clearly indicate that sympatric species using the same resources are affected differently by tropical cyclones due to slight variations in the seasonal timing of nesting, a key life history process.

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Reproduction is a key life-history process often constrained by abiotic conditions, which affect resource availability and influence reproductive output, including the number of females in a population that reproduce within a given year. We investigated whether population-level fluctuations in reproductive effort (i.e., the number of nesting females) result in fluctuations in the number of offspring produced under environmentally stochastic conditions. Here we show that timing and frequency of tropical storms constrain reproductive success in green sea turtles ( Chelonia mydas (L., 1758)); in years when storms arrive early or when multiple storms occur most green sea turtle nests are inundated by seawater and fail to hatch. Although equal proportions of the nests were destroyed by tropical storms in peak and non-peak nesting years, significantly more hatchlings emerged from nests during peak nesting years. Thus, the cyclic patterns of green sea turtle reproduction result in cyclic patterns of hatchling emergence under high levels of nest failure owing to seawater inundation. Ultimately, green sea turtle reproductive success is constrained by the timing of tropical storms in relation to the nesting season. Continuing increases in the severity of tropical storms from changing global climates could contribute to a higher proportion of nesting seasons with low reproductive success, such that population growth rates are slowed, which may have long-term negative effects on the ability of this species to recover to historical levels.