Any map of San Diego contains a space that is almost unknowable to us. For most San Diego residents, any comfortable familiarity with our local landscape cuts off directly at the coastline.
This reality was highlighted for me with the discovery that just 20 miles west of Del Mar and 3,400 feet below the ocean surface, part of our local environment includes a methane seep and an extraordinary community of organisms that live there. The seep was found during the San Diego Coastal Expedition (SDCoastEx), a multidisciplinary research cruise aboard Scripps Institution of Oceanography, UC San Diego research vessel Melville. I was lucky enough to be a part of this cruise, where I along with eleven other Scripps graduate students had the chance to study the oceanic landscape off of San Diego.
SDCoastEx was a student-led cruise. Students conceived the science projects completed aboard the ship, wrote the research proposal to fund the trip, and led the science while on board the trip. The chief scientist was also a student, Scripps’ Christina Frieder, who was responsible for coordinating the different research teams and scheduling the 24-hour ship operations, in addition to sampling for her own research. Among U.S. oceanography programs, opportunities to plan, fund, and execute oceanographic expeditions are unique to Scripps Oceanography students. It is thanks to the UC Ship Funds program that we were able to experience this.
In addition to the spectacular methane seep discovery, during this cruise we gathered water and sediment samples that will help us to characterize a region just off the coast of San Diego known as an Oxygen Minimum Zone (OMZ), a region of the ocean where oxygen levels are at their lowest. Chemists aboard SDCoastEx collected oxygen, pH, and various nutrient measurements that will be used to map the San Diego OMZ, the most detailed survey of this region to date. These data will be used in studies of the current state of the San Diego coast. It will also be a way to determine to what extent the region is changing. There is some evidence that the San Diego OMZ is moving into shallower waters, and the best way to see if this is happening is to make detailed surveys like the one completed on this cruise.
The extent of the San Diego OMZ could have impacts on the ability of animals that require oxygen for survival to live in these regions. During SDCoastEx, we collected sediment samples throughout the OMZ and carefully searched for small invertebrates. We used trawls to collect larger animals from the seafloor. By mapping where animals were found along with chemical data collected from each site, we may now have some ability to predict the effects of changes to the OMZ on the organisms that live there.
My own research during SDCoastEx focused on bacteria living in the OMZ sediments. Some types of bacteria are not dependent on oxygen for survival but instead breathe alternatives to oxygen that are found in the water column and in sediments. I am currently using the sediment core samples that we collected on the cruise to search for a group of very unique bacteria called actinomycetes, which grow in filaments in the sediments and produce diverse complex small molecules with pharmaceutical value.
In fact, they may even use some of the small molecules that they produce to help them live in oxygen-limited environments. The samples I collected will allow me to determine where they are producing these small molecules, and if they can live in parts of the sediment with low oxygen. So far, very little is known about how these organisms live in sediments so it is very exciting to be able to collect samples from a region that is now fairly well characterized, thanks to all of the data collected on the trip.
During this cruise, we were able to successfully capture what the OMZ looks like, but just for a moment in time. Just like on land, the underwater environment experiences seasons, and in the winter the oxygen levels should be higher in the region we sampled. We will be going back to the same sites in December to compare the chemistry, animals, and bacteria of the OMZ to what we found in July. We’ll also get a chance to check out the seep in more detail. All of the students that have been working on the SDCoastEx cruises are enthusiastic about their own and each other’s research, and I am very excited for another chance to work with this group to explore San Diego’s most mysterious landscape.
– Kelley Gallagher is a third-year student with microbial ecologist Paul Jensen.