What was done
The authors used "appropriate measures of biodiversity" to test "whether a molluscan death assemblage from a single sand beach on the north Cornish coast is representative of the biodiversity of the regional species pool," after which they "compare[d] the biodiversity of a fossil death assemblage from the same coast, laid down when the climate was similar to that of the present Mediterranean, to assess possible climate change effects."

What was learned
It was determined that the death assemblage of molluscs from the sandy beach at Harlyn Bay, north Cornwall, was "fully representative of the biodiversity of the regional species pool from all habitat types."  A late Pliocene fossil assemblage of molluscs from St. Erth Pits, north Cornwall, was also found to be "not significantly different in biodiversity ... from the present-day regional species pool."

What it means
Noting that the climate of the late Pliocene was similar to that of the present-day Mediterranean, the authors conclude that "predicted changes in climate, by the end of this century, will not affect molluscan biodiversity, although the species composition will undoubtedly change."  With respect to this latter change, they note that if the climate warms by 2°C over the next 50 years, "we can expect future latitudinal shifts in the marine biota of 300-600 km."

In enlarging upon these findings, the authors note that although "there is increasing concern about the effects of global warming on biological diversity," in coastal marine ecosystems "widespread extinctions seem unlikely, but changes in community distributions and compositions will inevitably occur."  These changes, they say, "will track the timing of global warming quite closely because of the high fecundity and dispersal capabilities of most marine organisms."

In summary, coastal marine ecosystems will likely experience latitudinal shifts and species redistributions in response to any additional warming that may occur in the future, but it is unlikely that any extinctions will occur, as the species that comprise these ecosystems can readily relocate themselves and thereby follow latitudinal shifts in water temperature.