Dissertation - HQ

Oriented swimming and passive advection 157
and those initial dispersal routes are therefore ignored in the present
temperature situation while they become available after the 2ºC increase.
And some of them are optimal, hence chosen. In those trajectories, the
maximum distance from the release point is greater than along all
others, thereby increasing the mean distance at the population level. In
addition, a closer look at the promontory case for example (Figure 6.20),
shows that, for some trajectories, the maximum distance from the release
point does not change, yet the shapes of optimal trajectories change
within this range. In particular, some larvae spend more time far from
the release site after the 2ºC increase (inset in Figure 6.20). This increases
the mean distance from the release point along such trajectories. Both
effects (increased maximum distance in some trajectories and increased
mean distance in others) contribute to the unexpected result that mean
distance from the release point at population level is larger after a 2ºC
increase in temperature, even though self-recruitment rate is higher.
Constant maximum
but increased mean
Figure 6.20 Comparison between five trajectories of P. amboinensis in the present
situation (top) and after a 2ºC increase in water temperature (bottom), in the
promontory case. In the climate change scenario, larvae spend more time farther
down in the lee of the promontory than in present conditions. One trajectory
is highlighted in the main figure and presented alone in the insert to highlight
this fact more clearly.