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Rockfish show lost diversity

Pete Wilton

A new way of measuring biodiversity, developed at Oxford University, has shown how genetic diversity, as well as population numbers, can plummet due to human activity.

The lost biodiversity is epitomised by a study of the plight of rockfish: ancient species once well-known to California's coast-dwellers.

Mike Bonsall of Oxford's Department of Zoology, along with colleague Sandrine Pavoine, was part of the team reporting their research in a recent issue of Ecology Letters. I asked Mike about rockfish, their decline, and how the new approach might help conservationists:

OxSciBlog: What's been the impact of fishing on rockfish populations?
Mike Bonsall: Awful. First it has to be realised that rockfish are extremely long-lived vertebrates. Some species live for up to 50 years and others have been recorded to live for over 200 years. As the technological ability to harvest fish from the ocean has increased we have overexploited (and collapsed) many stocks.

Rockfish are no exception: by 2003, some species were down to less than 5 per cent of their 1970 levels - so, over 40 years, (and given these harvested species live for more than this time period) we have selectively removed the reproductive cohort and the stocks have no opportunity to recover.

OSB: How has fishing affected the genetic diversity of rockfish?
MB: Sustained fishing affects not only biomass (population size) but also genetic diversity. We have shown that the declining numbers with a rockfish hotspot (off the west coast of California) is accompanied by changes in the phylogenetic (evolutionary) structure of the species assemblage.

For instance, evolutionary-old (basal) species had higher contributions to the diversity and large-bodied species were shown to decline (affecting genetic diversity).

OSB: What advantages does you approach have over other ways of measuring biodiversity?
MB: Our approach allows us to see if changes between communities (either in time or across space) correspond to changes in the different evolutionary lineages (and species that evolve from each lineage). We can weight species differently (depending on their rarity) and allow different classical indices for biodiversity to be used in our ecological-evolutionary analyses. In sum,  our methodology has broad applications that can be used to integrate geographical space, current history (ecological time) and evolutionary history in measuring biodiversity.

OSB: How might your approach be applied to the study of other at-risk species/ecosystems?
MB: It could be applied widely, to many species: We are currently using it to explore how butterfly diversity alters on chalk grasslands and how plant communities are structured in Algerian marshes. However, there is a debate in ecology about whether communities are structured randomly (neutral) or by the evolution of niches. Our approach will allow us to explore a range of different communities where evolutionary histories are well-known to understand the relative contribution of neutral versus niche mechanisms.