In early July 2000, Miyakejima Island's 7,000-year-old volcano roared back to life. Continual eruptions led to the entire population being evacuated over the next two months as emissions of very fine, extremely heavy ash were replaced by lethal gases gushing daily from a new 400-meter-deep crater. What we islanders had expected to be a "normal" Miyake eruption has turned out, instead, to be the most severe volcanic activity there in 2,500 years.
Prior to these latest eruptions, Miyakejima's unique wildlife was well-known and of global significance. Obviously, scientific research was essential from the beginning to determine what effects this historic event was having on such precious flora and fauna.
Now, two years later, Miyake islanders are still refugees, unable to return in the forseeable future. And although copious funding has become available for infrastructure reconstruction, biological investigations have been almost nonexistent.
It was therefore with immense interest that -- in my capacity as the environmental consultant to the government of Miyakejima -- I recently boarded a small fishing boat at Shikinejima Island to investigate the extent of volcanic damage to the island's submarine habitats.
Surveys that I led there in the 1970s, at Ofunato Bay, near the port of Igaya on the island's northwest coast, had resulted in the collection of specimens of 91 species of stony corals, 80 of which were reef-building forms -- bringing world attention to the island as one of the world's richest sites for high-latitude corals.
In addition, our team collected about 155 species of mainly tropical marine algae brought along from equatorial regions by the warm Kuroshio Current (aka, the Japan or Black Current). As I had also used the bay as my main site for studies on reef-fish ecology, I had considerable data for the purpose of post-volcano comparisons -- including numerous one-hour fish-counts prior to the latest eruption, which yielded an average of around 80 species.
Five river courses enter Ofunato Bay, and though they are usually dry, after storms and typhoons they empty torrents of water into the bay. During the numerous severe storms that hit the island in the two years after the eruption, these rivers became purveyors of tons of volcanic mud, boulders, trees and other debris. This made me wonder what remained of that once globally important underwater habitat.
As with Ofunato Bay, I had also collected detailed data from Gakkoshita, a favorite divers' site near the former village of Ako (before it was destroyed by an eruption in 1983), and from Toga Bay, beneath beautiful Toga Shrine on the southwest coast of the island. At both these sites, too, pre-eruption one-hour fish-counts had logged around 80 species.
My first dive in this month's survey was a 75-minute inspection of Toga Bay. There, the corals and other marine life had been deteriorating gradually since the mid-1970s, when construction of a paved road to the bay had led to massive freshwater runoff and siltation after heavy rains. This was followed by an influx of coral polyp-destroying crown-of-thorns starfish in 1979 and 1980, and my discovery -- for the first time in the world -- of massive coral destruction by swarms of the tiny snail Drupella fragrum which, like the starfish, prey on coral polyps.
After the destruction of Ako, a new settlement was built on the northern side of the bay. What had formerly been mainly forest was replaced by buildings, paved roads and agricultural fields. A concrete culvert directed all rain runoff -- as well as soapy dishwater, hot bathwater, chemical fertilizers and insecticides -- directly into the bay. Marine algae increased, as corals gradually died.
During the continuing eruptions since 2000, though, only minimal volcanic ash and no serious mudflows have entered Toga Bay. Hence, I wondered, what, if any, effects from the volcano would I find?
The 27-degree waters of the Kuroshio Current were crystal-clear, with 30-meter visibility. Immediately, as I dropped to a depth of 12 meters, I was amazed at the gorgeous scene in front of me. The wide expanse of Acropora corals that covered much of the shallow waters in the bay showed absolutely no sign of their pre-eruption algal competition, and were in the best condition I had seen them in since the mid-1970s! Reef fishes of immense variety were abundant, and a small school of large barracuda approached me with curiosity. Shortly after, I was circled by a school of large amberjacks and rainbow runners.
Altogether, I recorded 72 species of reef fishes -- no significant change from my pre-eruption count of around 80 -- including eight adult pairs of anemonefish (Amphiprion clarkii) , 42 subadults and a clutch of eggs -- results also comparable to my data from the 1970s and '80s. Huge typhoon waves rearing up to 12 meters high, and the flow of the Kuroshio Current and other tidal currents had cleansed the bay of volcanic ash. As well, with no human pollution for merely two years, the bay's fauna was in the best condition I had recorded in more than 25 years!
I was delighted . . . but then, my enthusiasm was soon dampened as I surveyed Ofunato Bay. Although this had once been the most biologically diverse location on the island, thanks to the flow of currents and its sheltered, northwesterly position, most of its coral cover had already been destroyed by harbor construction in the 1990s.
Of what little remained, I found, more than 90 percent had been destroyed by volcanic mudflows and landslides from surrounding cliffs. I could only find five coral species at the same site where more than 80 were collected in the 1970s. I found only a single striped cowfish (Lactoria fornasini) swimming through silty, low-visibility waters at the site where I formerly collected data on seven harems, numbering 37 fish. Not just that, but my entire '70s and '80s study population at nine anemonefish sites had been destroyed. A new sea anemone site disclosed a single large adult female anemonefish and a very small but apparently sexually functional male.
To make matters even worse, construction of a large pier was in progress, denying me access to my former angelfish study site. I am certain that this is seriously damaging the habitat by altering the flow of tidal currents that play a major role in the spawning success of angelfish and many other reef fishes.
In short, the rich biodiveristy of Ofunato Bay -- where I logged only six fish species this time, representing a staggering 94 percent plunge from my pre-eruption counts -- had been all but totally destroyed by a combination of human and volcanic activity.
My third and final dive site was at Gakkoshita, once a gorgeous coral site above a 30-meter drop-off. Here, the ill effects of the volcano were clear to see. Although volcanic ash had been minimal there during the eruption, a dry river bed at the north edge of the former, pre-1983-eruption community of Ako had brought tons of volcanic mud into the bay during heavy rains. Many corals were dead and those silt-weakened ones still living were being engulfed and slowly killed by a very fine, red algae.
On a happier note, the fish fauna at Gakkoshita was faring better than the corals. In addition to an eyeball-to-eyeball encounter with an enormous grouper, I recorded nine harems of Japanese angelfish (Centropyge interrupta), totalling around 35 individuals -- about equal to pre-eruption data for the same site. In terms of diversity, though, my count of 37 species there was only half the pre-eruption number.
In conclusion, my surveys of the three most biologically diverse shallow-water sites at Miyakejima Island clearly show that the current eruptions have resulted in serious damage to marine life. It is therefore urgent that suitably funded efforts are made in the near future to conserve what remains of the island's world-class underwater treasures, and to ensure that conservation of nature is a key consideration in any future development programs.
