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Knauss Lecture Series

12-1 PM Thursday, November 21, 2013 at NOAA Central Library, 2nd Floor, SSMC3

Trophic structure in the Marginal Ice Zone in the Weddell Sea Antarctic

Erica Ombres, Ph.D., NOAA Ocean Acidification Program

Carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured in twenty species spanning four tropic levels from copepod to predatory fish in the marginal ice zone (MIZ) of the Weddell Sea at the beginning of the austral summer. Samples were taken from under the ice, at the ice edge and in the open ocean. A significant trend in the δ13C values of all species was found with the under-ice δ13C values being more depleted than those in the open ocean. This is most likely due to the reduced atmospheric exchange of CO2, upwelled water with depleted δ13C values, and continuous biological respiration under the ice, all of which contribute to very depleted δ13C values. δ15N values were significantly lower in the open ocean than the other ice conditions due to the increased reliance on primary production. Cluster analysis revealed trophic shifts between the different ice zones. The ice edge zone proved to contain the most species and was the best habitat for most species. The trophic shifts observed within species in the differing ice conditions mimicked the seasonal changes they undergo during the course of the productive season every year.

Incubation temperature effects on hatchling performance in the loggerhead sea turtle (Caretta caretta)

Leah Fisher. NOAA’s Ocean Service: Policy, Planning & Analysis Division

Incubation temperature has significant developmental effects on oviparous animals, including determining sex for several species. It has been observed that incubation temperature also affects traits that can influence survival, a theory that is tested in this study for the Northwest Atlantic loggerhead sea turtle (Caretta caretta). We conducted the first controlled laboratory incubation and experiments to test for an effect of incubation temperature on performance of loggerhead hatchlings. Ninety-nine hatchlings were tested produced from eggs incubated at 11 constant temperatures ranging from ~27ºC to ~33ºC. Following emergence from the eggs, we tested righting response, crawling speed, and conducted a 24-hour long hatchling swim test. Data indicate an effect of incubation temperature on survivorship, righting response time, crawling speed, change in crawl speed, and overall swim activity, with hatchlings incubated at 27ºC showing decreased locomotor abilities. No hatchlings survived in both years when incubated at 32ºC and above. Differences in survivorship of hatchlings incubated at high temperatures are important in light of projected higher sand temperatures due to climate change, and could indicate increased mortality from incubation temperature effects.

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