Different Places, Different Theories

The Hanse Explorer has left Kingman and traveled south to a populated island belonging to the Republic of Kiribati, Fanning Island (Tabuaeran). Like Palmyra, Fanning’s topography was dramatically altered, in this case by the British in 1888 who blasted a channel to provide easier access to the lagoon. By 1987 the population had grown to only 450, making this 33 km2 island an attractive destination for the government-promoted relocation of people from the more crowded islands in Kiribati. Current population is about 2500, and growing. The deterioration of the reefs here shows what even that modest number of people can do in a couple of decades.

by Stuart Sandin, head researcher on the Fish Team

Chlororus frontalis

Parrotfish hiding under corals at Palmyra. Photograph by Stuart Sandin.

What I enjoy the most about visiting different coral reefs is the fun of considering the different ecology governing each system. On the steep reefs of Curaçao, I pondered the importance of depth in structuring reef communities, with deeper areas getting less sunlight but more nutrients. In the protected reefs of Caribbean Panama, I considered the importance of water movement (or lack thereof) in determining what species arrive to a reef and how those species may change evolutionarily. And on the heavy reefs of Kingman, I think about what it means to be big.

There are really a lot of big animals on Kingman. When we jump into the water, a few grey reef sharks are right there to greet us in the water column. When we reach the bottom, there are aggregations of red snappers, each measuring about a foot or two long. Gliding along the reef slope are manta rays. Scattered across the bottom are table corals that are two diver lengths in width.

I understand why big animals go away when there is more of a human presence on a coral reef. We have fishing gear targeted to catch larger fish. Anchors dropped on reefs tend to break corals into smaller pieces. In general, it takes time to make large animals, and the human propensity to increase the rate of death for many animals inherently leads to a disproportionate number of smaller, i.e., younger, animals. But there is another important question that we have to answer: why should we care if big animals go away? Are larger animals somehow more valuable in terms of ecology or economics? This is why we just visited Palmyra and Kingman, and why we are comparing these islands to others that have fewer large animals.

Diver and grouper, face to face. Palmyra Atoll. Photograph by Stuart Sandin.

So what do we know about large animals. Large animals tend to reproduce more than their smaller counterparts. Some people in fisheries refer to the important BOFF, the Big Old Fat Females. These are the older fish that have large bodies and that are able to produce orders of magnitude more eggs (and thus more babies) than their smaller younger counterparts. This is why in some places we have maximum size limits when fishing some species, to protect the BOFFs. Another factor is that large animals can often travel larger distances (except for corals, mind you!). Therefore, larger animals can find the best environment in which to live, thus capitalizing on the variability in living conditions across the reef. Larger animals are also more energetically efficient. Because of various laws of size scaling, it takes less food per gram to keep a larger animal alive compared to a smaller one.

Looking around at Kingman, we see that there are more benefits to large size. Living in a world dominated by predators, large size gives animals a better chance to survive predation. I pity the small and the young on Kingman…they are best termed ‘bait’ on these reefs. But enough of these little animals survive to make a much smaller number of larger animals, and these large animals make lots of babies, and so the circle is completed. But this is the ecology of size. Aside from a few management protocols like the maximum size limits for some fish, we don’t typically manage marine environments to protect large size. Our job during this cruise is to consider what happens if we don’t manage for size. Yes, it is nice to dive with big animals, but what do the large animals do to help people stay alive and healthy in tropical coastal regions? Maybe we should start thinking about size a bit more. Fortunately we have the protected islands of the remote Pacific to serve as a laboratory for exploring this question.