BIODIVERSE BORDERLANDS: MINERAL-RICH
HABITATS OF SOUTHERN CALIFORNIA

Researchers from Scripps Institution of Oceanography and the United States Geological Survey (USGS) set out to conduct work in the Southern California Borderland (SCB). The rugged, steep topography and low-oxygen conditions of the SCB are suitable for precipitation and formation of iron-manganese (Fe-Mn) crusts and phosphorite marine mineral deposits, which were the primary target for research during the expedition. Phosphorite on the seafloor has the potential to be a source of phosphorus for agricultural fertilizer, and both Fe-Mn crusts and phosphorites are enriched with rare minerals that are used in electronics, green energy, and other technologies.

As nations prepare to develop and allow extractive practices of deep sea minerals, baseline biological data and a better understanding of life in these regions are needed to further assess life in such mineral-rich environments.

In addition to characterizing biodiversity in the SCB, the team also explored and sampled a historic DDT waste production barrel dumping site. The site is located off the coast of Los Angeles in the San Pedro Basin. The team collected samples around the barrels to begin to better understand how the DDT and DDT derivatives may be affecting the marine environment.

Specific goals of the expedition included sampling water, rocks, fauna and sediments, recovery of colonization experiments, conducting biodiversity video transects, and 3D imaging. The exploration of biodiversity in the SCB should inform spatial planning by state and federal agencies and potentially reveal conservation and blue economy resource trade offs within deep waters. The study of the DDT dump sites may inform regional and federal decision-making regarding contaminant hazard and reveal whether there is a need for further deep sea remediation.

Over the 10-day expedition, 13 dives at nine locations took place, collecting a total of 350 samples of water, rock, sediment, and fauna. Seventy video transects were recorded for biodiversity assessment and select flyovers were executed to collect 3D imagery. Samples of Fe-Mn crusts were collected at offshore sites and phosphorites were collected at more inshore sites, which will allow for the characterization of associated fauna and microbes. The rocks collected will be analyzed for mineral and biogeochemical composition by the USGS. Biological samples will be assessed by researchers at Scripps Institution of Oceanography for faunal and microbial biodiversity and microbes will be assayed for biopharmaceutical potential.

Additionally, some substrate colonization experiments that had been deployed in 2020 at San Juan Seamount and 40-mile Bank were recovered to determine if microbes and other organisms prefer to colonize different substrates when given the choice, and new experiments were deployed in the region. Visits to DDT barrel dumpsites revealed a solid sedimentary feature surrounding some barrels (precipitated or lithified), with a microbial mat halo at the edge. Sponges were one of the few abundant animals in the nearly anoxic DDT barrel setting.