No, you don't need a skimmer. And what's more, research is showing how critical it is to maintain the right microbial balance. It doesn't matter if it's sutainable farming or sustaining our physical and mental health or sustaining a healthy reef ecosystem the right microbial balance is essential. In contrast to maintaining a diverse microbiome skimmers are selectively and arbitrarily removing just a subset of the microbes in aquaria and reducing bacterail counts to numbers far below what is found in nature. To think that skimmers can maintain our ssytems for the decades or centuries they should be able to live while skewing the microbial processes doesn't seem realistic to me. Here's videos of some of my skimmerless systems:
90 Gallon Mixed Reef
500 gallon
Mixed Reef started in 1997, 10-07-19
220 Rimless 450 view
And here's some videos you might find informative:
Forest Rohwer "Coral Reefs in the Microbial Seas"
Changing Seas - Mysterious Microbes
Nitrogen cycling in hte coral holobiont
Richard Ross What's up with phosphate"