Marine Ecology Research

Stanford & NOAA | 2011-2014

During my time at Stanford, I researched many topics in marine ecology, including: diet and tumors in Hawaiian green sea turtles; ocean acidification and coral-algal phase shifts on the Great Barrier Reef; and oceanography and marine physiology of squid in the Central Tropical Pacific Ocean. 

Diet and Tumors in Hawaiian Green Sea Turtles

NOAA Pacific Islands Fisheries Science Center

Honolulu, HI // 2012-2013

Fibropapillomatosis (FP) is a widespread and often fatal disease for green turtles (Chelonia mydas) and has known links to herpesviruses. Prior research has found that elevated nitrogen in the nearshore marine ecosystem in Hawaii is being taken up and stored by invasive macroalgae as arginine. Because arginine is crucial to herpes growth, the turtles who eat this algae are at risk of developing FP outbreaks, but no one has ever tested this mechanism in the turtle tissues themselves.

During an internship with NOAA in Honolulu, I collected and prepared tissue samples from shells of deceased sea turtle shells. The individual pieces of the turtle shell grow like fingernails and are called scutes. To better understand the role of diet in promoting FP outbreaks, we ran stable isotope analysis (SIA) on scute tissues to ascertain dietary differences, comparing tumored and disease-free turtles. We also compared the results to SIA values of known food sources.

 

The data that we collected from the work I did showed results consistent thus far with the mechanism for dietary promotion of FP (elevated  δ15N levels and lower δ13C in FP turtles than the rest of the Hawaiian population). I presented a poster on the preliminary results at the International Sea Turtle Society 33rd Annual Symposium in February 2013. The research continued after my internship and the results are now published.

Ocean Acidification and Coral-Algal Phase Shifts

Stanford & University of Queensland

Heron Island, Australia // 2011

Studies have shown that ocean acidification due to increasing levels
of atmospheric CO2 has adverse effects on many marine organisms and complex implications for coral community structure and resilience. Past studies have predicted that declining seawater pH could increase the competitive advantage of macroalgae over corals, facilitating coral-algal phase shifts.

 

At Heron Island, on the Great Barrier Reef, I investigated if the palatability of algae would change with decreasing pH in order to better understand the role of herbivores in controlling algal growth and maintaining healthy, coral dominated systems as well as reversal of these phase shifts.

 

I subjected three species of algae – Halimeda sp., Sargassum sp., and Padina sp. – to differing levels of pH that represented current and future ocean acidification scenarios in experimental aquaria for one week. I then tethered them on a reef flat for a three day consumption trial to test for differences in herbivore consumption.

 

There was a significant effect of algal species and pH on the loss of algal biomass. Grazing on Halimeda and Sargassum amongst pH treatments was negligible, but Padina was grazed significantly more at the lowest pH than for the ambient or mid pH treatment. This could be explained by differential effects of pH on the structural and chemical defenses employed by the algae to avoid predation, but further research is needed to confirm this hypothesis.

 

Although not definitive, if ocean acidification compromises the structural defenses of calcareous algae with low chemical defenses (such as is the case with Padina), previously unpalatable algae may become available for consumption by generalist herbivores, enhancing the ability of herbivores to control algal growth. 

Oceanography and Marine Physiology of Purpleback Flying Squid

Stanford: Hopkins Marine Station and Stanford@Sea

Between Hawaii and the Line Islands // 2013-2014

Sthenoteuthis oualaniensis, the purpleback flying squid, is an abundant, widely distributed, and ecologically important squid. On a round-trip oceanic transect through from Honolulu, HI to Palmyra Atoll, Kiribati, I researched size variation in the normal form of S. oualaniensis with respect to latitude and depth of the oxygen limited zone (OLZ).

 

I found that squid were larger further North of the equator, but that size was better explained by depth of the OLZ, with a shallower OLZ corresponding with larger squid. This finding has implications for understanding the environmental factors that may precipitate speciation in squid. It is also important to understand how marine species more generally are affected by shoaling OLZ/OMZs, as they are expected to expand horizontally and vertically with climate change over the coming decades.

After returning to Stanford, I used satellite remote sensing to examine if sea surface temperature (SST) and chlorophyll a concentration were related to size-at-maturity of S. oualaniensis, as the squids’ metabolism and growth are closely related to temperature and food availability. I found that chlorophyll a concentration poorly explained the variation in size-at-maturity, but seasonal SST had an almost perfect positive linear relationship.

 

I concluded that while OMZ depth and SST might contribute synergistically to squid size-at-maturity, further physical oceanography research is necessary to completely understand which (if either) is more significant. This research is important as SST is expected to increase and OMZs are expected to expand in range and intensity due to global climate change.