Voyage of discovery – on the choppy waters of the Gulf of the Farallones
By Ryan Hartnett | August 4, 2015
Coauthored by Claire Peaslee
People interested in ocean life often talk about “the marine food web,” but how does this ecosystem actually work? How does something as big as a humpback whale get energy that arrives in the ecosystem as sunlight?
It’s only natural that large and dramatic creatures like whales and sharks get our attention. But they can only exist thanks to very tiny and abundant life forms, mostly unseen by humans. These plant and animal plankton are a major focus of studies now under way in ocean waters just offshore of the San Francisco area. Scientists are detailing this region’s exceptional biodiversity – not only fishes, seabirds, and marine mammals but small shrimp-like krill, microscopic plants, and even the nutrients required for productivity.
Investigating the ocean ecosystem takes skill and determination: it’s not as simple as walking into a marsh or meadow to sample the water and plants. For a glimpse into how it’s done – and some of the challenges involved – here is a report from a recent research cruise.
In June of this year, to augment my graduate studies in marine biology, I joined a crew of 7 other scientists for several days aboard a 67-foot NOAA research vessel, the R/V Fulmar. I helped gather data for Applied California Current Ecosystem Studies (ACCESS), a partnership between Cordell Bank and Greater Farallones National Marine Sanctuaries and Point Blue Conservation Science.
I took on the duties of a back-deck hand, helping to process samples of animal plankton, called zooplankton. We lower a large hoop net 50 meters down to collect these small drifting creatures. Analyzing the samples lets us understand the changing composition of the plankton community near the sea surface.
My job was to sample the very small zooplankton, which we pull up using a 333-micron net (1 micron is a millionth of a meter). With a smaller hoop net with an even smaller mesh, I also took samples of phytoplankton – plant plankton. These were for the California Department of Health to learn about the microscopic plants in the water – especially relevant now because of a harmful algal bloom up and down the West Coast.
I also collected sea water samples for later analysis in our phytoplankton ecology lab at Romberg Tiburon Center, where I’m doing research for my master’s thesis. I’m measuring nutrients composed of nitrogen and phosphorous, and how they change in the ocean – the basis for long-term trends among marine animals.
The weather offshore was generally windy – typical for June. On day 1, on our way to the Farallon Islands we saw quite a few humpback whales and also some of the first blue whales I’ve seen. Activity was low on our return trip, but very near the mainland we saw a humpback spout. Minutes passed, then lo and behold – the whale breached right in front of us! Our photographer was ready and captured an awesome sequence (example below).
On each transect line that we travel, observers on the top deck record the marine mammals and seabirds seen. At the same time, we work on the back deck to find out how much krill are present in the water. We use a large sampling device called a Tucker Trawl to gather samples from three different depths, up to 200 meters. On the June 2015 cruise, the krill we saw were mainly young (juvenile) and small. In more productive conditions we would expect to see more adult krill in the zooplankton.
What we did see in our back-deck samples were a lot of small, soft-bodied invertebrates – not jellies but free-floating tunicates (little known to land dwellers). Because they filter-feed for plant plankton, they compete with krill for food. Even so, the top-deck observers reported seeing a fair number of marine mammals.
On day 2 we headed for Cordell Bank (about 25 miles SW of Bodega Bay), in high swells and gusting winds! From the far end of our transect line, we worked our way back toward shore and were able to sample at two stations. Then conditions got worse, forcing us to head in to port.
Unfortunately, the rest of our multi-day cruise was postponed due to strong weather. Even so, there was plenty for me to look forward to on the mainland – including the Cordell Bank and Greater Farallones National Marine Sanctuary expansion celebration!
My academic work is closely connected with ACCESS. With my San Francisco State University advisors, Drs. Karina Nielsen and Frances Wilkerson, and with Dr. Jaime Jahncke at Point Blue, I’m studying how physical ocean dynamics alter the nutrient supply in this marine ecosystem, with rippling effects on the living community as a whole. One result will be a baseline for future comparisons, helping people understand and manage ocean resources in a changing world.
Footnote: Ryan soon was aboard the Fulmar again, on an ACCESS cruise in July. In favorable ocean conditions, researchers found abundant krill, huge numbers of humpback whales, and much more! See the stories, photos and videos from the July cruise, and read a blog by NOAA teacher-at-sea Mike Wing.