Assessing Global Kelp Forest Change: From “Little” To “Big” Data

I can feel the energy of the waves gently pushing at my body, the sound of bubbles rising by my ears. I look down at my underwater clipboard and carefully write down “5”; the number of kelp stems, or fronds, that I’ve just counted. I let my tethered pencil go, and it floats up in front of me as a fish swims by. Everything seems to move in slow motion around me. I am relaxed, but focused. I need to finish measuring all the kelp plants along three, 20m transect lines laid out in front of me; an ambitious task for a single, one and a half hour dive.  I’ve had a lot of practice, though, and I know I don’t have a moment to waste, so I push on.

“Does anyone collect data by hand anymore?” one of my EDC colleagues recently asked in a meeting where we were discussing how to engage students in working with professionally-collected data. “I do!” I replied. In a world of “big data” its easy to lose track of the idea that there are still many scientists, in the lab or in the field, who run careful experiments and make detailed observations on relatively small scales.

But among ecologists, in particular, there is increasing recognition that taking a broad global perspective can reveal critical threats to our world’s ecosystems, and motivate political action and public engagement necessary for meaningful change. As a result, there have been many global-scale analyses attempting to identify long-term trends in critical ecosystems or species groups, such as coral reefs, phytoplankton, seagrasses, and fishes. In many cases, these studies have highlighted alarming rates of decline in response to human stressors such as climate change, resource extraction, and pollution.

Kelps are large brown algae that provide food and habitat for many commercially, ecologically, and culturally important species in coastal zones of temperate and polar regions worldwide. Focused regional studies have highlighted kelp declines in many places in response to a variety of stressors, yet we had no comprehensive understanding of how kelp forests globally are responding to human pressures.

So, myself, and 12 other scientists gathered in 2012 at the National Center for Ecological Analysis and Synthesis at the University of California Santa Barbara to bring together our collective knowledge and data to see if we could paint a picture of what is happening in the world’s kelp forests. Over big glasses of wine from the Santa Barbara hills, hovered over our glowing computers in fancy downtown restaurants, we put our heads together to identify the most critical questions to ask about the nature of kelp forest change.

We identified that one of the most important first tasks was to bring together all the data we could find on kelp abundances from around the world, and analyze these data to identify whether or not we see kelp forests declining on a global scale, like many other species.

Easier said than done, we realized. We spent years following these meetings seeking out data sets, cleaning and re-formatting them, and compiling them into one global database. The result? 8,846 individual measurements of kelp abundance from 34 regions around the globe, collected from a time span ranging from 1952 to present. Phew! It’s amazing to realize that each one of those data points was carefully collected and written down by individual SCUBA divers, just like myself. I wonder how many times fish swam by?

So, what did we find when we analyzed these data? It’s complicated. It would be easier to tell you that kelp forests are declining globally, like many other species, but that’s not exactly what we found. Instead, we found there were a lot of differences across regions. We saw kelp declines in 37% of regions, but there was no change in many places, and even increases in some.

When we looked on a global scale, there was a small overall decline. We spent many weeks discussing how to interpret this small global decline – was it cause for concern? Do we think it’s representative of what is happening in most regions? Does it really represent a long-term trend or is it more recent?

Our conclusion ended up being that kelp forests are at threat in some parts of the world, but they are doing relatively well in many places. We don’t interpret our results to indicate that kelp forests are declining globally – but rather, that there are a lot of local factors at play. In places where we see pollution, invasive species, and overfishing, we see declines. But in places where we see good pollution management, the establishment of marine protected areas, and the rehabilitation of important ecosystem-balancing predators, kelp forests are doing relatively well. 

I think our findings are ‘good news’; there is hope for kelp forests. They are highly resilient species – they react quickly to disturbances, but they also recover quickly. If we work hard to minimize local stresses to kelp forests, we may be able to protect them and all the benefits they provide to humans.

Over 8,000 data points is not “big data” in many fields, but in kelp ecology, it’s about as big as it gets. It’s been an interesting process for me to see what insights can be gleaned from combining many individual observations into a large-scale analysis. The interesting part? After all that, one of the main takeaways from our study was that regional experiments and observational studies are the most important way to understand kelp forests and to ensure their health into the future. Insights from “big data” are undeniably invaluable in many fields, including ours, but nothing can replace the careful observations of individual scientists, written by hand in field books and on underwater paper, often with fish swimming by.

The study was published last week in the Proceedings of the National Academy of Sciences of the USA.  The full article can be viewed here.

Kira Krumhansl was lead author of the paper.

Citation: Krumhansl K, Byrnes J, Okamoto D, Rassweiler A, Novak M, Bolton JJ, Cavabaugh KC, Connell SD, Johnson CR, Konar B, Ling SD, Micheli F, Norderhaug K, Perez-Matus A, Sousa-Pinto I, Reed DC, Salomon AK, Shears NT, Wernberg T, Anderson RJ, Barrett NS, Buschmann AH, Carr MH, Caselle JE, Derrien-Courtel S, Edgar GJ, Edwards M, Estes JA, Goodwin C, Kenner MC, Kushner DJ, Moy FE, Nunn J, Steneck RS, Vasquez J, Watson J, Witman J (2016) Global patterns of kelp forest change over the past half-century. Proceedings of the National Academy of Sciences of the USA doi: 10.1073/pnas.1606102113