Both direct and indirect effects of human population pressure structure Papua New Guinea coral reef fish comminutes
Understanding the relative contribution of factors influencing the distribution of biodiversity is one of the major goals of ecology. Yet species are heterogeneously distributed and differences in species number among sites does not per se imply anthropogenic perturbations to the system. Rather, differences in species richness could be due to biological, physical or anthropogenic differences.
Here we compare the reef fish fauna of Papua New Guinea across five different localities. These sites include both mainland Papua New Guinea (Madang, Milne Bay, Bootless Bay) and New Ireland (Kimbe Bay, Bismark Sea) and span over an order of magnitude of human population. Using a list of 470 species in 29 families and 120 genera we first determined the degree of similarity among these various sampling locations. Then we tested if any observed differences are due to environmental impacts or fisheries specific differences. We did this by partitioning the fauna into fished and non-fished spices. If the observed differences among populations are similar in fished and non-fished populations then we can infer that those differences are driven by environmental causes, however if we see significant differences among populations that are targeted and those that are not, we can infer that the observed differences in species composition are being driven by fishing. Finally, we also compare the modern Bootless Bay with collections made between 1881-1889.
The reefs of Bootless Bay, which has the highest human population, are less diverse than those of other areas. These low numbers appear across both fished and non-fished sets, suggesting that fisheries pressure alone is not the sole factor driving this reduction in alpha diversity. However, even given that general pattern of lower diversity within Bootless Bay, the fished species are significantly reduced when compared to non-fished, suggesting that proximity to population has a disproportionate impact on large bodied species. The historical data also suggest that Bootless Bay was more diverse at the end of the 19th century with a fished species was 3.4 times more likely than a non-fished species to be present in the historical than modern data sets. Furthermore, seven species were found in the historical data, but not modern data sets, including one that has been extripated from Papua New Guinea. These results show the lower levels of diversity within Bootless Bay in both space and time result from environmental impacts acting influencing all species and fisheries pressure selectively reducing large bodied species.