Nutrient Limitation in Phytoplankton

Methods

Summary

Before my team and I boarded the research vessel, we cleaned 36x 1 liter bottles to reduce trace metal contamination. We rinsed each bottle once with Milli-Q water, filled the bottles with less than 1% Citranox soap to sit for about one week, rinsed the bottles with Milli-Q water 4-5 times, filled the bottles with 5% Hydrochloric Acid to sit for about two weeks, and then rinsed each bottle with less than 1% Hydrochloric Acid with a pH of 2. Bottles were double bagged with plastic zip lock bags to maintain cleanness. Before the experiment was conducted, bottles were labeled and rinsed with local seawater before being filled up with local surface seawater using the FISH water pump. Once the bottles were filled, iron, zinc, cobalt, iron and cobalt, and iron and zinc were added respectively to each bottle for two experiments. The last two experiments utilized vitamin B-12 as a replacement for cobalt treatments. Bottles were placed into either an outdoor incubation that is a square container with circulating seawater or an indoor incubation that is a greenhouse tent with grow lights inside. To measure growth rate, about 200 milliliter of water was filtered using a vacuum pump on glass fiber filters every 3rd and 5th day. The glass fiber filters were placed in glass tubes and soaked in 6 milliliters of 100% acetone overnight in a -4 degree Celsius freezer. During the next day, filters were removed from the glass tubes and chlorophyll was measured using a Turner Designs 10-AU Fluorometer.

Challenges

Challenges experienced within this project include risk of contamination from seawater. Since we are using low amounts of nutrients, contamination risk from other nutrients is high especially during the use of an outdoor incubator that recirculates local seawater. 

Pre Analysis Plan

My current hypothesis include that phytoplankton species experience cobalt limitation in the Costa Rica Thermal Dome and iron limitation near the Equator in the Pacific Ocean. Iron limitation in phytoplankton near the Equator may be indicative of observed ammonia accumulation in the same area.