Points and Lines - Understanding the health of coral reefs

How many points does it take to make a line? If you ask a mathematician, they'd say two, at the very least. Practically however, we are sometimes asked to draw lines with only a single point. Here in the Phoenix Islands, we are trying to assign a trajectory to these reefs to determine whether they are recovering or declining. In other words, we are trying to draw a line, and the big question is which way the line is pointing--up or down?


Coral near Nikumaroro Island from the current expedition (Photo: Jim Stringer)

There are many scientists on this expedition, all assessing PIPA points in various ways--Tuwake is assessing fish diversity, Larry, Greg and Kate are examining planktonic blue water species, and everyone is contributing their thoughts and observations. Greg is the expedition leader and works on all aspects including the deeper parts with the ROV.

Some of us on the science team (David) have many points from the Phoenix Islands, and based on these points, David has qualitatively drawn a line in his head, and is quantitatively drawing a line from his carefully-collected data points. Others of us (Stuart) have only one point from the Phoenix Islands, but Stuart has other points from remote Pacific atolls (mainly the Northern and Southern Line Islands) that he's using to draw his line. Les works on a global network of reef systems with a focus on Brazil, Belize, the Eastern Pacific and Fiji, and he's using these data (along with his lifetime of reef experience) to qualitatively draw a line as he experiences the myriad reef habitats on the Phoenix Islands.

As for me, I'm trying to draw a line with (essentially) only a single point. This is my first time to the Phoenix Islands, and my first real experience on tropical Pacific atolls. I've had plenty of reef experience in the Caribbean, but the reefs have been very different (barrier reefs or patch reefs), and relatively close to human civilization. Still, I have the literature to draw from, so I guess I have multiple (but different) points as well.


Schooling fish near Nikumaroro Island during the current expedition (Photo: Jim Stringer)

So, with all of these different sets of points and different perspectives, what does our collective line look like? Generally (and it's too soon to tell definitively), I think we all agree that the Phoenix Islands are showing some promising signs of recovery and re-growth. We have been observing lots of coral recruits and juvenile corals, and an extremely healthy fish population. Effectively, the fish are doing a thorough job of keeping the substrate closely cropped, and so we see a reef primed for recovery.

There is a lot of available substrate, lots of crustose coralline algae, and, except for some species, there are enough remaining corals to re-seed the population. Thus, I'd say our lines are all pointed upwards, but given each of our different line-drawing strategies, our lines may have different slopes. Part of the excitement and challenge of this trip is to debate and discuss the points on our lines, and to try to reconcile all of our qualitative observations with the quantitative data that we are gathering on every dive to agree on a line that we think tells the story of the Phoenix Islands at this current point in time.

However, beyond the scope of this trip, coral reef scientists are busy gathering data to plot lines to chart the progress or decline of reefs everywhere. Our scientific discipline is full of lines: this reef looks better, this reef looks worse, this reef has more coral, this one less. there is no shortage of lines, moving in all directions. This can be a bit confusing to interpret, especially when trying to implement policy based on the direction and slope of these lines. In the end, it seems that these lines all call for more reef management, more human action to stop overfishing, more creation marine reserves and to temper the effects (and stop!) climate change. Despite all of these data, however, the message hasn't quite yet been embraced globally.


Near McKean Island during the current expedition (Photo: Jim Stringer)

Though these reefs are remote, they have been undeniably impacted by global change (noted in previous posts here, here, here and by David here). Yet, there are still many places in the world that do not protect their oceans. Ocean stewardship is still a relatively new concept with some. There has been important, recent advancement, though. After all, I'm writing this post from the world's largest marine reserve*. Many other reserves are in various stages of completion, and, with hard work, it is still possible to achieve our goal of healthy reefs worldwide. But, we're not there yet. Despite all of these compelling lines, we're still left with the majority of reefs struggling for their very existence.

And so, I leave you with this. We're busy trying to gather data points in order to generate a line. But how many lines does it take to make the point?

-Randi

*At the time this was written in 2009, PIPA was the largest MPA in the world. It remains one of the world's largest.