The down-pointing arrows on the left side of the figure represent the effects of sea otters on the species that are on lower trophic levels. These arrows indicate that sea otters are having a positive effect on these species, meaning they are helping to control or regulate their populations.

The reason why these arrows look different from the arrows on the right side of the figure is that the arrows on the right side represent a system where there are few sea otters. In this case, the down-pointing arrows indicate that the lack of sea otters is having a negative effect on the species that are on lower trophic levels. This means that without sea otters to control them, these species may be able to grow and thrive more easily, potentially leading to overpopulation.

In contrast, the presence of sea otters in the system on the left side of the figure allows them to control these species, keeping their populations in check.