Defining Marine Spatial Units: Realms, Biomes, Ecosystems, Seascapes, Habitats, Biotopes, Communities and Guilds

Abstract

We distinguish between concepts used to classify and map geographic areas, with examples from the marine environment. Biomes are large areas dominated by long-lived plants providing habitat for other species. Ecosystems are areas where biological interactions and energy fluxes are greater within the area than with adjacent ecosystems. Realms are defined by their geographically rare (endemic) species whereas habitats, communities, whereas biotopes are characterized by the most abundant and/or conspicuous species. While ecosystems and biomes contain guilds of species, they are not defined by them, so their species composition varies geographically. Seascapes, like landscapes, are defined by their physical geography (topography, physiography) alone. However, depth zones are distinguished by environmental conditions, notably light, temperature, oxygen, and nutrients. The term regions is applied to areas with varying ad hoc criteria for their delimitation, including geographic, environmental, biological, and management suitability. Alternative terms for, and examples of, these concepts are provided. Classifications can show relationships within concepts (e.g., habitats, realms) but different concepts (e.g., seascapes and habitats) should not be forced into simple hierarchical systems. The spatial relationships of world realms, biomes, and ecosystems are mapped. Authors are encouraged to apply concepts appropriately and minimize jargon so as not to confuse or alienate readers.