Investigating the effectiveness of geochemical proxies of hypoxia exposure in otoliths of Atlantic croaker and closing thoughts on the REUAugust 5th, 2013 Posted in Uncategorized | No Comments »
Hello everyone, my name is Branden Kohler. This summer I have been investigating the effectiveness of geochemical proxies of hypoxia exposure in otoliths of Atlantic croaker with my mentors: Dr. Ben Walther and John Mohan. Hypoxia, or low dissolved oxygen content can have a significant negative impact on growth and reproductive health of fishes. Determining an accurate proxy for hypoxia exposure that reflects lifelong individual exposure histories would allow for more accurate assessments about the impact of hypoxic events. Fish otoliths, or ear stones, grow in ring-like patterns throughout the fish’s life and certain ions present in the water column have been shown to be incorporated into the rings of the otolith. Redox-sensitive elements such as manganese (Mn) incorporated into otoliths could therefore be valuable proxies for hypoxia exposure. The purpose of this research is to determine if Mn found in the otoliths of Atlantic croaker (Micropogonias undulatus) indicates hypoxia exposure in the northern Gulf of Mexico. Fish (N=120) were collected from sites during research cruises in October 2011 (flood year) and August 2012 (drought year), to determine if there would be a difference in otolith Mn between a large hypoxic zone caused by flooding and a small hypoxic zone caused by drought. The otoliths were sectioned to expose the core and analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) in order to determine the concentrations of elements along a life history profile for each fish. Unexpectedly, there was no significant difference in average, maximum or total Mn:Ca in otoliths according to year of collection. There was significant variation by region, with sites in the eastern Gulf of Mexico, which were putatively normoxic control sites, showing significantly higher ratios of Mn:Ca than the central or western regions where hypoxic zones typically occur. This geographical pattern could reflect differences in the sediment composition between the eastern and central/western regions. The effectiveness of manganese as an accurate proxy of hypoxia exposure in fish does show promise in certain regions, but more research is needed to validate it’s possible utility in other locations.
My time spent here in Port Aransas has been truly amazing. There definitely have been many great times and fun exploits with great people. While I’m leaving on Friday to return to Pennsylvania in order to finish off the summer and my education back at Kutztown, I will treasure all of the memories and great friends I have made here and would be thrilled to come back again.
Hello my name is Emily Pinckney and this summer I studied the effects of crude oil on coastal diatom health with the help of my mentor, Dr. Deana Erdner. The effects of oil on marine ecosystems have become a subject of intense study since the Deepwater Horizon oil spill in 2010. One area that has historically not received much attention is the effect of oil on phytoplankton. Because phytoplankton are major primary producers, forming the base of aquatic food webs, negative impacts from oil exposure can have knock-on effects throughout the ecosystem. Similar studies in the past have been performed to observe the interaction between oil and phytoplankton, and whether oil leads to cell death. My experiment is different because I examined both sublethal stress and death in phytoplankton exposed to both oil and dispersant at realistic concentrations.
I tested two species of coastal diatoms, Pseudosolenia and Thalassiosira. After exposure to different concentrations of oil plus dispersant, I measured total cell numbers, the proportion of dead cells, and the proportion of cells that showed signs of oxidative stress. The cultures were tracked for 4 days. The two species showed different responses to the oil and dispersant mixture. Thalassiosira did not show oxidative stress and the mixture of crude oil and dispersant neither hurt nor helped the cells. However, Pseudosolenia showed an increase in oxidative stress, a short spike in cell death, and a stimulation of growth at the higher oil concentrations. These results increase our knowledge of the impact of oil use and the importance of phytoplankton to our world. Future studies might focus on verifying these results, and looking more into the role of dispersant in cell health.
I’ve really enjoyed my time here in Port Aransas and all the adventures I experienced this summer. Even though I have to leave Texas behind, I’m taking with me amazing memories and some life-long friendships.
By Madison Moon and Branden Kohler
We had the opportunity to interview Dr. Bryan A. Black following his presentation on coupled marine-terrestrial ecosystems. Dr. Black got his B.S at Westminster College and his M.S and Ph.D at Pennsylvania State University. The original focus of his work was forest ecology and dendrochronology but after a post-doctoral experience he decided to take a chance and begin to study the otoliths of rock fish. He began to apply his experience in dendrochronology to otolith analysis. Initially he believed it was only a temporary position, however he became very interested in the research and decided to pursue it as a permanent career. Dr. Black uses synchronous growth patterns that can be found in trees as well as in the otoliths of fish to draw comparisons about past climate and forest disturbances as well as potentially model future environmental conditions. This research began in Oregon but nine months ago he joined UTMSI as an assistant professor. As well as being a professor, he continues to travel the world to collect samples and offer seminars to educate other scientists about his research techniques. In the future he plans to expand his research to include applying his techniques to other ecosystems and species.