Macroalgae (seaweeds) produce unique bioactive metabolites that have enabled their survival for millions of years, offering significant potential for human benefits. In the Israeli Mediterranean Sea, no comprehensive systematic surveys of seaweeds have been published since the 1990s, and their chemical composition remains largely unexplored. This study presents an extensive survey of intertidal seaweed communities along the shallow Israeli coastline, documenting their spatial, temporal, and biochemical diversity. Of the 320 specimens collected, 55 seaweed species were identified: 29 red (Rhodophyta), 14 brown (Phaeophyceae), and 12 green (Chlorophyta). A significant shift in species abundance was documented, with a single dominant annual bloom occurring during spring, unlike previously reported biannual blooms. Chemical analysis of the dominant species revealed significant seasonal variations in compound levels, with higher protein content in winter and increased antioxidant capacity during spring. Phenolic and natural sunscreen compounds (mycosporine-like amino acids, MAAs) showed no general seasonal trend. These findings highlight the optimal environmental conditions for seaweed growth and underscore their potential for aquaculture and biotechnology. We hypothesize that the ecologically unique conditions of the Israeli Mediterranean Sea may foster resilient seaweed species enriched with distinctive chemical properties, suitable for nutritional, health, pharmaceutical, and nutraceutical applications, particularly as climate-adaptive bioresources.