Abstract: The near shore environments of the western Antarctic Peninsula (WAP) harbor extremely high densities of mesograzers (small invertebrate predators approximately 1-25 mm in length) such as benthic amphipods, as well as rich assemblages of macroalgae, endophytes, and macroinvertebrates. Unlike temperate and tropical shallow marine environments, where fish and sea urchins are key grazers structuring the community, mesograzers appear to be much more important in the WAP. Accordingly, the proposed research has two main objectives: (1) To further investigate the interactions between the ecologically dominant large macrophytes, filamentous epi/endophytes, and mesograzers and (2) To determine the nature of interactions between mesograzers and sessile invertebrates. Specifically, the research will examine the following hypotheses: 1: The effects of endophytes on macrophytes are often negative, and consequently macrophytes defend against endophytic infection. 2: Mesoherbivores prevent filamentous algal species, common in the intertidal, from dominating subtidal assemblages. 3: Mesograzer predation pressure on sessile benthic macroinvertebrates, primarily sponges and tunicates, is greatest in shallow habitats dominated by macrophytes, and this impacts depth distributions of macroinvertebrate species. 4: Benthic macroinvertebrates may defend against mesograzers with secondary metabolites which effect molting and/or deter feeding. Broader impacts include involvement of undergraduates, including minorities, in research; training of graduate students, and continuation of the highly successful UAB IN ANTARCTICA interactive web program (two time recipient of awards of excellence from the US Council for Advancement and Support of Education). The researchers also will share their scientific endeavors with teachers, K-12 students, and other members of the community at large while in residence in Antarctica. In addition, the investigators will request the participation of a PolarTREC teacher.