Will shrinking body size and increasing species diversity of crustaceans
follow the Warming of the Arctic litoral ?
Over thirty species of littoral marine Gammaridea occur along the coasts
of the North Atlantic. From one to several species can coexist in a
single region. There is an evident, inverse relationship between egg
incubation time and temperature (from 14 to > 120 days) and
consequent trends in the size of the animals on reaching maturity (from
5 mm in warmer waters to 30 mm in the coldest ones) and in lifespan
(from < 6 months to > 5 years). Littoral
gammarids are a good example of the shrinking size effect of increasing
temperatures and size-related species diversity. In large species the
annual cohorts of the population (3 to 5 annual size groups)
functionally replace the adults of smaller species. The ongoing warming
of the European Arctic seas may extend the distribution limits of boreal
species so that more Gammarus species may appear on northern coasts
hitherto occupied by just one or at most two species.