GRADIENT OF HUMAN IMPACT
Anthropogenic influence on the marine environment was studied in Kingman, Palmyra, Fanning and Christmas islands. These islands exhibit a gradient of human population. Kingman island has no people, Palmyra has 15 people, Fanning has 1000 people and Christmas has 10,000 people. Reef fish biomass density was also analysed by atolls and consumer classes. Inverted trophic pyramids were observed for fish populations. That is, tertiary consumers like sharks make up most of the biomass on Kingman, while no sharks were observed on Christmas. This change is due to overfishing. The switch in macroorganismal trophic pyramids was paralleled by a ten-fold increase in microbial numbers on Christmas. Metagenomic samples were taken from reef crevices and surfaces from the four islands and 100-0.45 p.m microbial and viral fraction were analysed by 454 pyrosequencing. The number of potential pathogens dramatically increased with human population. Comparison of phage hosts between Christmas and Kingman Islands showed that more viruses infecting pathogens also increased with people. Over the same gradient, coral cover decreased and prevalence of coral disease increased with humans. Based on these results, Rowher and colleagues propose that the decrease in big fish leads to an increase in algal abundance. More algae means more food for the bacteria, including the pathogens. These pathogens overgrow the coral and kill them.. Additional sequencing of microbial and viral communities will help increase our understanding of coral reef decline.
Editorial comment: This is just an extract from the discussion. The discussion may well prove useful to the International Census of Marine Microbes (providing a census of marine life). More detail is available on website: http://www.icomm.mbl.edu