This post completes the blog for the 2010 Line Islands Expedition. We invite you to dip into the 45 earlier posts available in the blog archive. There you can follow the Fish, Benthic, and Microbe Teams as they visit the coral reefs at six of the Northern Line Islands, collecting data, samples, and adventures at each.
by Stuart Sandin, head researcher on the Fish Team
After spending the past four weeks surveying six of the Line Islands, our research teams have all made it home safely. Beyond personal health and safety, I am happy to report that we have successfully transported all of our data and samples back to our home institutions. And as a final bonus for our team members from the US, we returned in time to join family and friends for Thanksgiving. All in all, I would call this a successful trip.
Following our first visit to the Line Islands in 2005, our group spent countless hours trying to make sense of our observations. We had found that on intact coral reefs, the biomass of predatory fish can exceed that of their prey. How can a coral reef exist with so many predatory fish harassing their smaller compatriots? We had found that healthier coral reefs have much less seaweed but no increase in the biomass of the fish and other herbivores. Why does the same biomass of algae-eating herbivores control the seaweed effectively on intact reefs, but not on more impacted ecosystems? We had found that microbial concentrations were closely related to the abundance of seaweed on the reef. Are microbes thriving in the water chemistry created by the seaweed, or is the microbial ecology controlled by the geography and oceanography of the island? In this season of thanks and retrospection, my thoughts have returned to these questions, seeking to now incorporate our recent observations into our ecological understanding of coral reefs.
On Kingman and Fanning, we visited shipwrecks to investigate further the effects that a localized perturbation can have on a coral reef. The shipwrecks released something into the water (most likely iron) that led to the rapid decay of the reef habitat even, surprisingly, on a protected reef like Kingman. Corals are replaced by an overgrowth of fleshy algae looking like a fuzzy red turf sprawling across the reef bottom. These reefs, though, are far from dead, as the algal turf appears to make for a terrific habitat for the herbivorous fishes. Schools of convict surgeonfish haunt these coral wastelands, along with countless other fish eating the rapidly growing algae. Benthic and microbial surveys, however, show that the corals are far from healthy (read as ‘dead’) and the microbes are growing prodigiously in these areas. Fish, it turns out, are not sufficient to keep the reef alive in the face of a major physical and chemical insult like a shipwreck.
On this expedition, we had the opportunity to dive more locations on Christmas Island, the largest of the Line Islands, including some of the more remote sites far from the main population. Compared to the degraded sites surveyed there on previous expeditions, these reefs were surprising—filled with large fish, healthy corals, and stunningly clear water. As we moved closer to the main town of London and fishing pressure increased, the reef scene shifted to smaller fish. Even closer to town, the reefs themselves seemed to be decomposing, with corals becoming rare and large, and fleshy algae infesting the reef surface. The dual insults of fishing and pollution (there was an apparent plume of sewage in our study sites nearest to town) led to the effective demise of the coral reef. Somewhere between the remote and the disturbed sites there seemed to be a balance of human use with sustained reef growth.
Perhaps the most memorable event was finally getting to visit Jarvis Island. For me and some others onboard this completed our tour of all eleven Line Islands, and a stunning finale it was. The steep slopes of the leeward side were home to amazing coral terraces. Clouds of colorful planktivorous fish (those colorful little fish that pluck microscopic animals out of the water column) filled every scene. The serenity was suspended intermittently by the strikes of small groupers or snappers, or by the erratic swim-by of excited reef sharks. A nagging concern filled my head as I swam around Jarvis: the water was very cold. Water pushed up from the deep bathed these reefs, greatly altering the chemistry and temperatures of these ecosystems. Classic theory would say that this nutrient-rich water, combined with the annual temperature fluctuations (as our colleagues had informed us), would make for poor conditions for reef growth. How Nature has a way of defying expectations–the most oceanographically intense reef hosted the most prodigious growth of corals and fishes.
None of these observations would make sense if I were to remain entrenched solely in my focal area of fish ecology. The fish may profit from the rapidly growing seaweed near the shipwreck sites, but they can do nothing to control the excessive growth of the microbes. Fishing on Christmas Island may alter the animals swimming in the water column, but multiple insults can lead to much more rapid and catastrophic changes to coral reefs. And the swarms of fish on Jarvis alone cannot paint a full picture of how coral reef ecosystems respond to oceanographic conditions and variability.
I end this expedition as I began, with a wholehearted appreciation for the three dimensions of coral reefs: the fish, the benthic organisms, and the microbes. We measure the health of reefs using these three dimensions in our coral health index, the CHI. Our three teams also study reefs from these three perspectives, the insights from one fueling observations by another. Ahead of us now lie months and years of post-processing and analysis as we extract all that we can from the data, samples, and observations gleaned during this expedition. But at this point, I pause and give thanks for the teamwork, camaraderie, and scientific contributions of our expedition trinity: the Fish, Benthic, and Microbe Teams.