Boiling Cold Water at Jarvis Island

By Jennifer Smith, head researcher on the Benthic Team

Anthais swarm over a coral-covered landscape at Jarvis Island. Photograph by Jen Smith.

Before dawn yesterday we crossed the equator, arriving soon thereafter at Jarvis Island. This small, US-owned island, part of the new Pacific Remote Islands Marine National Monument, is about as far away from sizable human populations as one can get. Upon awakening, the first thing I noticed was that the water around the ship was boiling. There were some ridiculously strong currents with eddies swirling among whitecaps, but that was not the only source of the churning. The surface as far as I could see was alive with dolphins gracefully coming up for a breath of air. Clearly these waters must be productive. Sitting nearly on the equator, Jarvis lies in the flow of a number of strong currents that drive cold nutrient-rich water up from the depths, nutrients that feed the thriving food web we encounter on our first dive.

We roll off our Zodiacs and into the water—brrrrr! Wow! Yes, the upwelling of cold water is immediately obvious, nearly 2 °C colder than the last island. But the sensation of cold is rapidly overwhelmed by excitement as we are greeted by a number of curious and fairly large gray reef sharks, black jacks, groupers, snappers, and representatives of a number of other fish species. The landscape is impressive—a gradually sloping reef to about 30 ft, then a sheer vertical drop to the depths. Hovering at the edge here is like watching Blue Planet live and in 3D. The bottom of the reef is covered in delicate rosettes of Montipora, a purplish-orange plate coral that resembles huge roses when viewed from above.

Based upon our impressions from the first dive, we all believe that Jarvis represents an important site for our research. Building on the data from our previous expedition to only four of the Line Islands, it was difficult to unequivocally separate the impacts of natural oceanographic factors from those due to nearby human populations. We needed a “control” island, one with a naturally high input of nutrients (nitrogen and phosphorous), one that demonstrates that high nutrient levels alone do not lead to the algal bloom or phase shift that is so often seen near highly populated areas. Jarvis is such a site. Here, in the absence of humans, the reef is able to incorporate and use these extra nutrients to support a fish community that has more biomass than has been found on just about any other reef on the planet. Jarvis is one thriving reef.