<![CDATA[Learning about marine ecosystems is often hampered by students' difficulty in visualizing abstract concepts and a lack of contextual teaching materials relevant to their surroundings. This study aims to develop teaching materials in the form of an encyclopedia of unique biota based on Sabang Island's local potential and to evaluate its validity, practicality, and initial effectiveness in improving students' conceptual understanding. The research used a Research and Development method, applying the 4D model (Define, Design, Develop, and Disseminate). Seven material and media experts comprehensively assessed the product's feasibility and validity, while five education practitioners evaluated its practicality. Additionally, an initial evaluation of the shift in student learning outcomes was conducted using a one-group pretest–posttest design involving 46 high school students in a coastal area socio-ecologically equivalent to Sabang Island. The results showed that experts declared the developed encyclopedia highly valid, giving it a “Very Good” rating across all evaluated aspects (General Appearance, Word Usage & Language, Presentation, and Content Suitability). In terms of practicality, the product was also deemed highly practical for learning, earning a “Very Good” rating in three key aspects (Ease of Use, Usefulness, and Efficiency) and a “Good” rating in the Interest aspect. Furthermore, the analysis of learning outcomes showed an average N-Gain of 0.3844, which falls into the moderate category, indicating a positive trend in student conceptual understanding after product utilization. Based on these findings, the local potential-based encyclopedia "Umbak Gembara" is highly feasible and practical, showing strong initial indications as an independent learning resource that can meaningfully bridge abstract biological concepts with the reality of coastal ecosystems. However, since this initial effectiveness finding relies on a single trial group, future comparative experimental studies are needed. Keywords: encyclopedia, unique biota, local potential, sabang island, conceptual understanding.]]>
