What are thin layers?

In undisturbed seas without turbolation bays and fjords and so on, we tend to have nutrient, bactirial layers, phytoplanktopn layers that can be very thin because of densit. They attract other organisms. Forms layers. Down left – upper mixed layer we have phytoplancton and the zooplankton follows. The laer mooves slowly downwards. Antoher layer below the pycnocline – another stage or population. There are both physical and behaviral processes operating around thin layers