Freshwater vs. Marine Environments
Aquatic biomes are primarily divided between freshwater (low salinity) and marine saltwater (high salinity) environments, each with distinct characteristics and inhabitants. Temperature largely determines which species can survive in particular habitats, while excess nutrients and pollutants represent major threats.
Freshwater environments include streams and rivers with flowing water. Fast-moving streams create rapids that mix air into water, providing high dissolved oxygen levels. Slower rivers have less mixing, supporting species adapted to lower oxygen conditions. Lakes and ponds contain standing water and are divided into zones: the shallow littoral zone near shores, the limnetic zone where rooted plants can't survive, the deep profundal zone without sunlight, and the muddy benthic zone at the bottom.
Marine environments include salt marshes (one of Earth's most productive biomes), mangrove swamps along coastlines, intertidal zones between high and low tides, and magnificent coral reefs (the most biodiverse marine biome). The open ocean is organized into the photic zone where photosynthesis occurs and the aphotic zone which lacks sufficient light, where chemosynthesis (bacteria using energy from chemical bonds) becomes essential.
Did you know? Coral reefs support incredible biodiversity despite living in nutrient-poor waters. They have a symbiotic relationship with algae that helps them thrive, but this relationship breaks down during coral bleaching caused by environmental stressors.
Both freshwater and marine ecosystems can be classified by their primary productivity levels: oligotrophic (low), mesotrophic (medium), and eutrophic (high). Wetlands, which remain submerged for part of the year, are among the most productive biomes but face destruction from human activities including pollution, trash accumulation, and oil spills.