Literal biodiversity reservoirs, coral reefs and associated ecosystems are in grave danger from natural and human-made disturbances. The latest World Resources Institute assessment is alarming with 75% of coral reefs reported as endangered worldwide, a figure that may reach 100% by 2050. The numbers are concerning, particularly as coral reefs provide sustenance and economic benefits for many developing countries and fish biodiversity on coral reefs partly determines the biomass available for human consumption.
A Multi-Facetted Biodiversity
While phylogenetic diversity in communities is acknowledged for its vital heritage value, illustrating, as it does, a "part" of the tree of life, ecosystem functional diversity has long been overlooked in impact studies. An ecosystem's richness is also measured both in taxonomic biodiversity terms (number of different species) as well as by the number of lineages or functions performed by many ecosystem goods and services.*
There have not as yet been any studies into the impact of human activity on coral fish community taxonomic, functional and phylogenetic taxonomic diversity loss.
Functional and Phylogenetic Diversity Loss Revealed
After sampling 1553 fish communities through underwater surveys in 17 Pacific countries, researchers assessed the taxonomic, functional and phylogenetic diversity levels of a group of species fished along a human density gradient ranging from 1.3 to 1705 persons per sq. km of reef.
The social and environmental data were collected under the PROCFish and CoFish projects co-ordinated by the Secretariat of the Pacific Community and funded by the European Union.
The results showed a sharp drop in functional and phylogenetic diversity levels, particularly above 20 people per sq. km of reef, while species richness was barely affected along the gradient.
When human population density reached 1700 persons per sq. km of reef, the impact on functional and phylogenetic diversity levels (-46 % and -36 %, respectively) was greater than on species richness (-12 %).
A Tree of Life that Needs Protecting
The research shows that species numbers are a poor indicator of anthropogenic pressure, while two other biodiversity components are far more heavily affected by human density. These components make up the tree of life, i.e. the diversity of biological traits and phylogenetic lineages that are essential for coral systems to function.
The researchers emphasised how important it was to conserve all the components of biodiversity. They also recommended using trait and lineage diversity as reliable and sensitive indicators of damage to species communities.
*Some reef fish species play key roles in ecosystem functions: regulating competition between algae and coral colonies; and creating areas that are conducive to recruiting coral larvae by bio-erosion, etc.
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