Big mouths, glowing spines

Dragging a net through the water, Ricardo Letelier and Angel White come up with bizarre creatures: animals with long antennae and others with a mouth twice the size of their bodies. Plants with spines. Some with tails that propel them like tiny rockets. The scientists’ net is standard equipment in oceanography, but the microbes they catch are anything but ordinary. Gazing at them through a microscope is like visiting a zoo on another planet.

Ocean plankton
Angel White photographed this organism during a recent cruise to study Trichodesmium, a microbe that can thrive on nitrogen from the atmosphere.

The two Oregon State University oceanographers are on the R/V Melville in the South Pacific between Chile and Easter Island. To scientists, the voyage is known by the acronym BiG RAPA, which stands for Biogeochemical Gradients: Role in Arranging Planktonic Assemblages. It is sponsored by the Center for Microbial Oceanography: Research and Education (C-MORE), at the University of Hawai’i at Manoa. Other scientists on-board are from Chile, Hawaii, UC-Santa Cruz, MIT and Woods Hole. C-MORE is a National Science Foundation-funded Science and Technology Center.

Faculty members in OSU’s College of Oceanic and Atmospheric Sciences, Letelier and White are investigating plankton that carry out photosynthesis, and by so doing, give us oxygen to breathe, fish to eat and ocean wonders from colorful squid to the largest mammals on the planet. Trouble is, we don’t really know how this medley of microbes works. Those that photosynthesize — the plants known as phytoplankton — have an appetite for carbon, nitrogen, phosphorus and iron, the building blocks of life. But how much of those nutrients do they need? And what happens to those elements after the plants are eaten or decomposed? How does this community change as temperature and chemistry shift along a gradient from the well-fed, nutrient-rich waters off Chile to the almost desert-like conditions of the open ocean? What will happen as ocean waters absorb increasing amounts of carbon-dioxide and become more acidic?

The answers are critical to our understanding of the oceans, not to mention our future. Microbes account for most of the biomass in the seas, far outstripping fish and marine mammals. Moreover, recent research reports suggest that as the oceans warm, phytoplankton populations will decline. In reviewing more than a century of data, researchers at Dalhousie University in Nova Scotia reported last summer that plankton have been declining about 1 percent per year on a global basis (Boyce, et al, “Global phytoplankton decline over the past century,” Nature, 2010).

Letelier and White are quick to note that at a C-MORE research site north of Hawaii, plankton production has been increasing over the last two decades. Some types, especially those that sip nitrogen from the air, do quite well in waters with additional carbon. Scientists on the BiG RAPA cruise are conducting experiments to see how CO2 concentrations affect phytoplankton behavior. The expedition, which began on Nov. 14 in Chile, is scheduled to conclude on Dec. 14 at Easter Island. See videos from the cruise produced by C-MORE.