We have a new paper out in PLOS this week “Quantifying the Human Impacts on Papua New Guinea Reef Fish Communities across Space and Time” and I’m really excited about it for a number of reasons.
First, the science. This paper started out with an expedition Mark Westneat and I lead to Bootless Bay, Papua New
Guinea while we were at the Field Museum. While I was excited to dive in the heart of the Coral Triangle, I was honestly a little underwhelmed with the diversity when I got there. I think I’d read too many papers and seen too many nature videos and I had gotten my hopes up. When arrived, we found the water silty and the species richness rather low. This got me thinking however about why we found what we did. The most obvious reason was probably about 8km to the North – Port Moresby, the capital of Papua New Guinea, and the largest city in Melanesia(population ~300,000 people). And while I was pretty sure that human population was influencing the community structure of the reef, I wasn’t sure how.
I had two theories; first that people were overfishing the reef – 300k people require a lot of food, and while not everyone in Port Moresby eats fish, enough of them do that it was reasonable for those reefs to be in the crosshairs. Second was environmental degradation. Port Moresby has a long and contested history of colonialism leading to a complex pattern of in-migration and development. The result of which was that there is a large, sprawling city with large amounts of pollution and nutrient loading on the reefs. The question now was how to differentiate between these two causes.
I figured the key to answering this was to look at differential responses among the constituent elements of the community. Essentially I figure overfishing should be more strongly felt in larger fishes than in smaller fishes, as those are the ones people preferentially target. On the other hand, since all fish on the reef live in the same water, poor water quality would impact fishes of all seizes roughly equally. To test these hypotheses we had to get data from reef communities near other human population centers. To do this we scoured the published literature and museum holdings to find four other sites giving us a range of populations from about 16k to 300k. Then we got to work.
Though we had posed it as a question of direct vs. indirect anthropogenic influence, the answer we found though was a little of both. When we ran a regression on the data we found that both slopes were negative, suggesting that the more people there were the less fish we could expect to find. However the slope of the line for fished species was significantly more negative than the slope for the non-fished. Essentially, while both species were doing poorly, fished species were doing exceptionally poorly. We saw a similar pattern when we looked at the beta diversity. Bootless Bay was more different than the less populace populations, but the fished species were even more different than non-fished.
Now the obvious question you may be asking is, how do we know that Bootless Bay just isn’t naturally less diverse?
There are many environmental factors that can influence diversity and with the data in hand we really couldn’t address them. What we needed to do was find a way to go back in time and see what Bootless Bay looked like before Port
Moresby was a large and international city. We don’t have a Tardis (sadly) but we do have museum collections. We found a series of collections in the Museum Victoria made in Bootless Bay in 1881, 130 years before the collections I made for the Field Museum. At that time Port Moresby was a small colonial outpost surrounded by villages of the local Moutan people, with a population of about 2000 people. When we looked at these collections we found that the ratio of fished to non-fished species was significantly larger in the past, and that six species of fish (with an average size of 69cm SL) were present in the 1880s Bootless that are not present in our modern data collection. Lastly, one species Epinephelus longispinis, which we found in the museum collections, is not currently recognized as being found in Papua New Guinea – a newly discovered extirpation. This shows how historical ecology can provide critical context for modern ecological studies, and how working at a problem from multiple angles can provide robust results.
The second reason why I liked this paper was working with my co-authors Katie Amatangelo and Ruth Hufbauer. They are amazing co-authors and I learned a lot from them throughout this process. We all met via twitter and somehow I was able to convince a plant community biologist and an insect evolutionary ecologist to do marine biology with me. I’m lucky they signed on and I’m excited to work with them in the future. Coauthoring papers with your friends can be a great process as long as you stress communication and clear delineation of roles, authorship and responsibilities before hand. This is probably true of all writing partnerships, but I’m happy to say we have produced this paper with our friendships in tact.
The last reason why I like this paper is that we have used it as a chance to bring together a bunch of disparate and hard to find data that I hope will be of use to others working in the region. We published open access so that people in PNG will be able to read the research that took place on their reefs; we published the data freely here and here. If you’re interested in reef community assembly, there’s a lot that can be done with those data and I hope you have as much fun with them as we did. Have at ‘em! Finally, there’s an Easter egg in the paper. I’m glad it made it through review. Because we’re nerdy like that.