Why Are Some Seamounts Biological Hotspots?
NOAAAn anemone on relatively young lava flows at Volcano W.
Two oceanographic features—underwater mountains and boundaries between water masses—might provide a nexus for biological diversity, according to a new study supported by the Lenfest Ocean Program.
Even some non-scientists have suspected that marine life would be attracted to underwater mountains, also known as seamounts. In the Chronicles of Narnia, C.S. Lewis imagined an underwater civilization where such places were the most hospitable parts of the ocean. “The sea-people… return home to the heights for rest and peace, courtesy and council, the sports, the dances and the songs,” Lewis wrote in The Voyage of the Dawn Treader.
Biologists have found that this fanciful story holds some truth: some seamounts attract a wide array of species. However, they have not been able to explain why this is not true of all seamounts, at least in the Pacific Ocean. The answer could be useful in conserving life in the ocean, in particular for deciding whether to limit fishing at or near certain seamounts. A September 2015 paper led by Telmo Morato at the University of the Azores sets out a research agenda to explain this phenomenon and gives the beginnings of an answer
Their answer so far has to do with oceanic fronts, which are basically the watery version of atmospheric fronts: boundaries between water masses that differ in temperature or density. Oceanic fronts are often associated with enhanced biological productivity and diversity. Focusing on tuna, the study compared 1,649 seamounts in the Pacific, some of which are aggregating sites for tuna and some of which are not. Then they asked whether oceanic fronts could explain the difference: using satellite maps of sea surface temperature to detect fronts, the researchers assigned a front frequency to each of the seamounts.
They found that seamounts with a high front frequency were more likely to aggregate tuna than seamounts with an average front frequency. But this relationship was not simple. Seamounts that were near a front more than 44 percent of the time were significantly more likely be aggregation sites for tuna than those with lower frontal frequencies. But once front frequency fell below 44 percent, it appeared to have no effect on aggregation.
This finding is preliminary, since many other factors might drive biological activity at seamounts. The paper suggests additional research to address these possible factors. This proposed research agenda will now be reviewed by the Secretariat of the Pacific Community, an international organization that provides information to help member countries manage their aquatic resources, including tuna fisheries.
About the Study
Morato, T., P.I. Miller, D.C. Dunn, S.J. Nicol, J. Bowcott, and P.N. Halpin. 2015. “A perspective on the importance of oceanic fronts in promoting aggregation of visitors to seamounts.” Fish and Fisheries, DOI: 10.1111/faf.12126
