How do we Know What’s in the Ocean?

I recently came across a neat new study that took advantage of 39-year long records of fish assemblages from power plant cooling intake systems on the California coast. It was fun (with the blurry glasses of hindsight) to remember my time collecting similar data from a different power plant, located in San Diego Bay. That plant was shut down, and then imploded quite spectacularly in 2010, and was cooled a little differently from those in the study above, simply sucking in bay water for cooling, and straining out larger marine life with rotating metal screens.

To estimate the impact of these kinds of seawater cooling systems on marine life, we would take shifts over 24 hours (I usually got the middle-of-the-night shift, for some reason), and every few hours would catch everything on the screens in buckets. Then, we would sort through this material, identifying, measuring, and weighing every animal in the buckets. I learned quite a lot about the animals that live in San Diego Bay - I never knew, for instance, that seahorses live there - and had some interesting encounters trying to measure live stingrays without being stung, or counting and measuring hundreds of dead anchovies that were full of wiggling worms (gag). So I was excited to see that these kinds of records have been put to use in clever scientific ways (like the study above), other than simply assessing whether the plants should continue to operate.

The ocean is often more difficult to study than the land - a big reason is that it's hard to see what's in there. Humans don't survive well underwater, so we have to come up with all sorts of contraptions to get a peek underneath the surface: SCUBA, submersibles, and ROVs (remotely operated vehicles), for example. Even then, we sometimes can't see very far (if the water is murky or we go below the sliver of surface water where sunlight penetrates), so we have to rely on methods other than visual surveys to find out what lives in the ocean.

A seemingly simple method is just to toss out various kinds of nets off of a ship, drag them through the water at different depths (or across the bottom, a very destructive practice), and see what gets trapped. But, the ocean is large, and nets can't (and hopefully won't) catch everything. Actually cataloguing every marine animal in the ocean is a monumental effort, and the Census of Marine Life made a huge stab at this with several targeted field projects.

But using other sources of data, like the power plant records, we can also learn a lot about what lives in the ocean and how this might be changing over time. For instance, fishermen throw quite a few nets and hooks into the ocean, so interacting with these groups and using catch records can be one way to obtain scientific data with less sampling effort. Other clever methods include using historical trophy fish photographs to see how catches have changed in size and type over time, excavating pits below living reefs and identifying the remains of marine organisms buried in the sand, or digging through old trash piles (middens) from early societies to see what they were eating.

What other sources of data can you think of to find out what lives (or used to live) in the ocean?

References

Cramer, K.L., et al. Anthropogenic mortality on coral reefs in Caribbean Panama predates coral disease and bleaching. Ecology letters 15: 561-567 (2012).

Erlandson, J.M. et al. Human impacts on ancient shellfish: a 10,000 year record from San Miguel Island, California. Journal of Archeological Science 35: 2144-2152 (2008).

McClenahan, L. Documenting loss of large trophy fish from the Florida Keys with historical photographs. Conservation Biology 23: 636-643 (2009).

Miller, E.F, McGowan, J.A. Faunal shift in southern California's coastal fishes: A new assemblage and trophic structure takes hold. Estuarine, Coastal and Shelf Science 127: 29-36 (2013).

Ticheler, H.J., Kolding, J., Chanda, B. Participation of local fishermen in scientific fisheries data collection: a case study from the Bangweulu Swamps, Zambia. Fisheries Management and Ecology 5(1): 81-92 (2002).

All photos from Author's collection