T. johnsoni is likely the smallest that occupy the kelp wrack, ranging from 1.0mm to 2.5mm. These flies can be found in large numbers in kelp wrack, particularly at night. The flies serve as a food source for a range of predatory arthropods due to their size. Their larvae are also consumed readily by predators and are responsible for large amounts of kelp removal. T. johnsoni may have a diet of fluids or bacteria from kelp, but no confirmations have been made.