Temperature reduces fish dispersal as larvae grow faster to their settlement size

1. As species struggle to cope with rising ocean temperatures, temperate
marine assemblages are facing major reorganisation. Many benthic species
have a brief but critical period dispersing through the plankton, when
they are particularly susceptible to variations in temperature. Impacts of
rising temperatures can thus ripple through the population with
community-wide consequences. However, responses are highly
species-specific, making it difficult to discern assemblage-wide patterns
in the life histories of different fish species. 2. Here we evaluate the
responses to temperature in the early life histories of several fish
species using otolith reconstructive techniques. We also assess the
consequences of future warming scenarios to this assemblage. 3. We sampled
recent settlers of 9 common species across a temperature gradient in the
Mediterranean Sea and obtained environmental data for each individual.
Using otolith microstructure we measured early life traits including
pelagic larval duration (PLD), growth rate, settlement size, hatching and
settlement dates. We used a GLM framework to examine how environmental
variables influenced early life history parameters. 4. We show that
increasing temperature results in considerable reduction in the dispersal
potential of temperate fish. We find a nearly universal, assemblage-wide
decline in pelagic larval duration (PLD) of between 10-25%. This was
because, with increasing temperature, larvae grew quicker to their
settlement size. Settlement size itself was less affected by temperature
and appears to be an ontogenetically fixed process. 5. Given current
estimates of ocean warming, there could be an assemblage-wide reduction in
larval dispersal of up to 50 km across the Mediterranean, reducing
connectivity and potentially isolating populations as waters warm.
06-Jan-2021