Thermal Tolerance of Siphonaria normalis Embryos on Oʻahu, Hawaiʻi
Date
2021
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Abstract
As average global temperatures continue to rise leading to hotter conditions, there
is a need to understand the impact of heat stress on the vulnerable life stages of marine
organisms. Thermal tolerance studies assessing the impact of elevated temperatures on
ecologically important intertidal organisms are necessary to predict future species
distributions. This study focuses on an abundant but rarely studied intertidal species on
the island of Oʻahu, the false limpet Siphonaria normalis, by examining the thermal
tolerance of the embryos. S. normalis embryos develop intertidally in benthic egg masses,
in the same environment as the adults. Embryos are often more vulnerable to thermal
stress than adults. Egg masses that were 1-2 days old were exposed to a range of elevated
temperatures between 35 °C and 50 °C in an incubator for 2 hours. These ranges of
temperature and time of exposure have been observed in field settings. Treated egg
masses were subsequently maintained at a constant temperature of 24 °C until embryos
matured to an encapsulated crawling stage, in which they metamorphose into a juvenile.
Video data, taken every 2-3 days to follow the development of the mass, were evaluated
for percent survival and deformities in growth. Results showed that embryonic survival
was significantly lower following the treatment of 45 °C and 50 °C than of lower
temperatures. We observed that after thermal treatments, most embryos continued to
develop for some time before dying. We therefore explored the relationship between
temperature and the stage that embryos developed into before they died. These data
suggest that the survivorship of Siphonaria normalis embryos on the island of Oʻahu
experience higher instances of mortality at elevated temperatures. This study has broader
implications for the survivorship of S. normalis in a changing climate.
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climate change, marine ecosystem, rising sea temperature
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42 pages
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Johnson, Michaela
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