The effects of long-term, low-level thermal additions on the marine epibenthic community were investigated in a laboratory flow-through system maintained at temperature differentials of 0C (an unheated control), 2C, 4C, and 6C above the ambient temperature. The communities were allowed to develop on unglazed ceramic tile plates over a three-year period and were sampled nondestructively at monthly intervals for percent cover by individual species. Recruitment also was assessed at monthly intervals. Within the laboratory system, increasing temperatures had a pronounced effect upon recruitment of individual species and on some attributes of the permanent community, namely number of species and diversity.