Caring for the Coasts

Coastal habitats at the land–sea interface span from hard substratum, rocky intertidal environments to sediment-covered estuaries, salt marshes, eelgrass beds, mangals (mangrove habitats), and sandflats and mudflats (Figure 1). Sedimented intertidal and subtidal nearshore habitats occur globally; sandflats and mudflats occur from the equator to the poles, in contrast to temperate latitude salt marshes and tropical mangroves. Seagrasses occur globally except at the poles. The accessibility of these habitats has enabled studies that generated important ecological paradigms, but the extremely harsh conditions of some of these environments limits transferability of knowledge to other habitats. Many species cannot tolerate energy from waves, potential aerial exposure, and fluctuating temperatures and salinities, resulting in low species diversity, but the availability of abundant sunlight, nutrients from land, and substrata all help support high abundances of tolerant species. Indeed, these habitats provide critical support for abundant juveniles of many commercial species, among others. The structural complexity afforded by seagrass beds, salt marshes, and mangals also pre-empts coastal erosion.1 Sandflats and mudflats are generally the least productive sedimented habitats. Nonetheless, their invertebrate fauna such as mud shrimp (amphipods) support migratory seabirds and other transient species. The plants that dominate eelgrass, salt marshes, and mangals produce organic matter and biogenic habitat that support high abundances of other species that utilize the plant detritus, associated grazers, and structural complexity to avoid predators. Microbial breakdown of organic material can exhaust oxygen, resulting in hypoxia (low oxygen) near the seafloor or just below the sediment surface, reducing species richness.