Littoral zone
The nearshore zone of oceans, lakes, and rivers.
The littoral zone, also called the nearshore, is the area of an ocean, sea, lake, or river lying close to the shore. It creates extensive, productive habitats at land-water edges. In coastal ecology, this zone spans the foreshore between high and low water marks, but geographically it includes all neritic waters over continental shelves.
Quick Facts
- Continental shelves area
- about 7% of the surface area of the oceans
- Productivity comparison
- can reach levels comparable to tropical rainforests
Facts from the source article.
Definitions and characteristics
The littoral zone has no single definition; what is regarded as its full extent and how it is divided into subregions varies in different contexts. For lakes, it is the nearshore habitat where photosynthetically active radiation penetrates to the bottom in sufficient quantities to support photosynthesis. Along marine coastlines, it can extend to the edge of the continental shelf, where water is shallow enough to allow photosynthesis. The use of the term varies from one part of the world to another and between disciplines; for example, military commanders and marine biologists define it differently. The US Navy, US Army Corps of Engineers, US Environmental Protection Agency, and UK Ministry of Defence each have their own definitions with legal or operational implications. The adjacency of water gives distinctive characteristics to littoral regions, including erosive landforms such as sand dunes and estuaries, and the natural movement of the littoral along the coast is called littoral drift. Biologically, the ready availability of water enables a greater variety of plant and animal life, particularly extensive wetlands, and the additional local humidity due to evaporation usually creates a microclimate supporting unique organisms. The word littoral derives from the Latin noun litus, litoris, meaning "shore"; the doubled t is a late-medieval innovation, and the spelling litoral is sometimes seen.
In oceanography and marine biology
In oceanography and marine biology, the littoral zone is extended roughly to the edge of the continental shelf. Starting from the shoreline, it begins at the spray region just above the high tide mark, moves to the intertidal region between high and low water marks, and then out to the edge of the continental shelf. These three subregions are called the supralittoral zone, the eulittoral zone, and the sublittoral zone. The supralittoral zone, also called the splash, spray or supratidal zone, is above the spring high tide line and is regularly splashed but not submerged by ocean water; seawater penetrates these areas only during storms with high tides. Organisms there must cope with exposure to fresh water from rain, cold, heat, dryness, and predation by land animals and seabirds; patches of dark lichens can appear as crusts on rocks, and some periwinkles, Neritidae, and detritus-feeding Isopods commonly inhabit the lower supralittoral. The eulittoral zone, also called the midlittoral or mediolittoral zone, is the intertidal zone or foreshore, extending from the spring high tide line to the spring low tide line, alternately exposed and submerged once or twice daily. Organisms there must withstand varying temperature, light, and salinity, yet productivity is high; wave action and turbulence shape cliffs, gaps, and caves, offering habitats for sedentary organisms. Protected rocky shorelines usually show a narrow, almost homogenous eulittoral strip marked by barnacles, while exposed sites show a wider extension divided into further zones. The sublittoral zone starts immediately below the eulittoral zone, is permanently covered with seawater, and is approximately equivalent to the neritic zone. In physical oceanography, it refers to coastal regions with significant tidal flows and energy dissipation, typically extending to the edge of the continental shelf at depths around 200 meters.
In freshwater ecosystems
In a freshwater lake, the littoral zone is the shallow area near the shore where enough sunlight reaches the bottom for plants to grow. While this is the ecological definition, some agencies, like the Minnesota Department of Natural Resources, use a simpler rule and call any part of a lake less than 15 feet deep the littoral zone. These fixed-depth definitions are less accurate for ecology but are easier to use when making depth maps or when light data is missing. Despite being just the edge of lakes, the littoral zone covers about 78% of the world’s total lake area. This zone can be a narrow strip or a wide, marshy wetland. Plants here are arranged by how deep they can grow, forming four typical bands from the shore outward: wooded wetland, wet meadow, marsh, and aquatic vegetation. The size of each band depends on the shoreline shape and how water levels have changed over time. Wet meadows, in particular, get larger when water levels naturally rise and fall. Many lake and river animals rely on these wetlands because rooted plants offer both shelter and food, making a large, healthy littoral zone a sign of a thriving water body. The plants in this zone are called macrophytes, and they come in four types: those that stick up above the water, those with leaves floating on the surface, those that drift freely, and those that grow completely underwater. Where these plants grow marks the edge of the littoral zone, though some spots stay bare if the bottom is too rocky, the water too dark, or the waves too strong. These macrophytes make the littoral zone one of the most productive habitats on Earth, and they help regulate the global climate by storing carbon.
Habitats in littoral zones
The shallow waters along the edges of lakes and ponds, known as the littoral zone, are a hub of activity. Many animals, from mammals and waterfowl to insects and reptiles, rely on both this aquatic area and the surrounding land for food and shelter. Even creatures we typically think of as open-water dwellers often depend heavily on resources found here. Compared to the deeper, muddy bottom, the littoral zone has more oxygen, a more complex structure, and a greater variety of food, which supports a huge number of insects and creates intricate food webs. Looking at fourteen of the world's largest lakes, these bodies hold a significant share of global freshwater life: 15% of all freshwater fish species, 9% of non-insect invertebrates, and 2% of aquatic insects. Remarkably, over 93% of these species live in the narrow strip of the littoral zone, and 72% are found nowhere else, even though this habitat makes up only a tiny portion of the lake's total area. Because this zone is popular for recreation and industry, it suffers heavily from human impacts like nutrient pollution, invasive species, acidification, climate change, and water level shifts. Despite being more damaged than deeper waters, the littoral zone receives less scientific attention. Protecting the biodiversity of large lakes will require a better understanding of this critical area and focused efforts to reduce human harm along the shoreline.
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