Study authors Olivia Nigro, then a graduate student in the oceanography at UHM and now an assistant professor at HPU, and Grieg Steward, professor in the UHM School of Ocean and Earth Science and Technology (SOEST), first assessed Vibrio in 2006 when Oliver Johnson died from a V. vulnificus infection after having cuts and scrapes exposed to Ala Wai Harbor water.
“His exposure occurred after many days of heavy rainfall, which, given our results, suggests this may have been an exacerbating factor,” said Steward. “At the time, we realized there was almost no data on the ecology of V. vulnificus in the canal, or in Hawai’i generally, and remarkably, very little in tropical waters anywhere.”
After a quick pilot study in 2006 that showed the bacteria are present in high, but not unexpected numbers, the team geared up for a year-long study in 2008-2009 with better methods to understand the variability in abundance over a seasonal cycle.
At higher latitudes, the abundance of V. vulnificus shows a very strong seasonal cycle — nearly disappearing in winter when temperatures are cold. In Hawai’i, temperatures are warm year-round, so freshwater input becomes a more important control.
“V. vulnificus occurs naturally in warm, brackish waters,” said Nigro. “So we expect to find this bacterium anywhere that temperatures are warm and freshwater and seawater mix in about equal proportions. When conditions are right, the Ala Wai Canal can be a great incubator for this bacterium!”