I think the idea behind this is that algae are more space-efficient than trees at producing oxygen and/or capturing CO2. Of course this is also ignoring that the bulk of a tree’s volume is high above the ground, and they also provide other things like shade and shelter for insects etc.
I always sacrifice some small piece of fruit or meat to them when the wasps are getting annoying. 65% of the time, it works everytime and they fuck off with their gift and never come back