Featured Scientist: Michael Landry

As we wrap up this year's survey, the first of two annual research surveys in the Gulf of Mexico for the NOAA RESTORE Act Science Program, we'd like you to get to know the PI from Scripps Institution of Oceanography, Professor Mike Landry! Read on as he describes his research and our cruise goals in his own words!

"I am a biological oceanographer. I have been on many ocean research expeditions over the years (since the 1970s), but never on a cruise in the Gulf of Mexico, never on a NOAA ship and never with fisheries scientists trying to understand a specific fisheries-related problem. So this particular cruise is special and a new learning experience in many respects. At the same time, it is also familiar. What we have investigated on past expeditions is how plankton food webs in different areas of the oceans function under different environmental conditions in order to understand the “rules” of why systems vary and how they respond to change. Our hope in this project is to apply the techniques that we have developed and the results from past experiences to characterize the unique aspects of the Gulf of Mexico habitat that lead to rapid growth and success of larval bluefin tuna (why do momma tunas migrate vast distances to spawn in only few small places in the ocean?) so that fisheries scientists might be better able to predict how they might be affected by future ocean changes.

Above: Groups of water bottles to
be sent to different depths
Below: Our filtration set up -
6 bottles at once!

"In this project, we are taking two approaches to studying food-web relationship and rates. One is experimental, involving direct measurements of community composition, productivity and nutrient uptake by phytoplankton, the microscopic plants of the sea. We also measure the consumption (grazing) of phytoplankton by zooplankton, the slightly larger but still pretty small protozoa and small animals that comprise the first 2-3 steps of the ocean food web. This is the “what is there,” "what are they doing,” and “how fast are they doing it” part of the study. Phytoplankton often go through one or two generations (cell divisions) per day, and they get eaten almost as fast as as they divide, so the tricky part of these experiments is separating the two rates (production growth and grazing loss) that are going on at the same time. We have a technique for this, which involves dilution of the grazing impact (using filtered water, changing the encounter frequency of predators and prey) in some of our experimental bottles. It is also important that we run our experiments under natural conditions of underwater light and temperature, so all of our experimental bottles that contain the plankton that we collected at different depths are put in net bags and attached at same depth to a line underneath a free-floating drifter float that we track by satellite for a day before picking up and exchanging bottles for a new batch of experiments. After a lot of filtering, preservation or freezing, and later analysis in our lab on shore, we should have a pretty good picture of how productivity and nutrients are moving through various routes in the food web to get to the specific zooplankton prey that bluefin tuna larvae like to eat.

Tom (L) and Mike (R) attach bottles to the sediment trap array

Mike (L) and Aki (R) hunt for BFT using microscopes onboard

"In the second approach to this study, we will use the tuna larvae themselves to tell us where they reside in the food web and what is the main source of nutrients (nitrogen) for primary production. This information resides in the nitrogen isotopic composition of the amino acids that make up the proteins of the tuna larva muscle tissue, which varies with the source of nitrogen (N2 gas for nitrogen fixation versus nitrate from deep water upwelling) and the number of predator-prey steps that the nitrogen has taken to get to the larvae, starting from phytoplankton. This sounds complicated, but the isotope analysis is easier to do than all of the experiments that are needed to assemble the food-web picture. One of our goals is to see if results from these two approaches agree, which has never been done before for any system because the isotope approach is so new. If this works out, it would validate using the isotopes in future studies, or also to look at changes in food-web structure and nitrogen sources that may have already occurred with climate change, using the muscle tissues of fish samples that have been taken in the past and preserved in museum collections."