Coastal Ecosystems: Characteristics, Resources, Impacts, and Hazards
Coastal Ecosystems
Coastal ecosystems share abiotic elements of both terrestrial and marine ecosystems, resulting in a complex and unique environment. Three key coastal ecosystems stand out:
Mangroves
Mangrove forests are characteristic of inter-tropical coastal areas influenced by tides and sheltered from the open ocean, such as estuaries, bays, and lagoons. They thrive in shallow waters with silt and clay sediments. Mangroves play a crucial role in coastal protection against wind and wave erosion, in addition to regulating the water balance between the sea and freshwater sources.
Seagrasses
Seagrasses appear in the subtidal zones of coastal areas with soft, predominantly sandy bottoms. They are higher plants with leaves, flowers, and fruits that cover the seabed. Seagrasses are essential for marine ecosystems because they:
- Stabilize marine sediment with their rhizomes.
- Provide shelter, resting areas, feeding grounds, and reproduction sites for many species.
- Export production to nearby ecosystems.
- Increase the usable surface for epiphytic organisms.
Coral Reefs
Coral reefs are solid structures found in the coastal seabed of the intertropical zone. They primarily consist of accumulations of hard corals that require temperatures between 19-27°C, thus appearing only in low latitudes. While most coral structures do not photosynthesize, they are associated with calcareous algae and microscopic dinoflagellates in a symbiotic relationship. Therefore, these ecosystems are found in the photic zone, never deeper than 50 meters. The limestone reef is of organic origin, deposited by corals over thousands of years. The importance of reefs lies in three key areas:
- Biodiversity: Reefs provide shelter for numerous species.
- Coastal Protection: Reefs act as a natural barrier, protecting the coast against erosion and waves.
- Human Actions: Coral reefs are a unique resource that should be preserved and used wisely.
Coastal Resources
Fisheries Resources
Coastal areas support two types of fishing: inshore fishing and shellfish harvesting. Aquaculture is also a booming resource.
- Inshore Fishing: This type of fishing takes place near the coast using small boats with crews of no more than 10. They typically do not spend more than a day at sea and unload their daily catch at auction.
- Shellfish Harvesting: This specific fishing method involves collecting live bivalve molluscs buried in the intertidal zone. Shellfish can be wild or cultivated. Depending on the season, gear, and target species, harvesting can be done on foot at low tide or by boat at high tide.
- Aquaculture: This involves farming commercially important fish species, particularly finfish, crustaceans, and molluscs. The goal is to reproduce and improve the environmental conditions experienced by these species to ensure their development. Aquaculture has seen tremendous progress in recent years, currently producing about 50% of the seafood consumed worldwide. Two types of aquaculture can be distinguished:
- Freshwater Aquaculture: Commonly utilizes farms and cages suspended in rivers or lakes.
- Marine Aquaculture: Can be developed in fish farms, with good results for species like turbot, flounder, eel, and sea bass. Shellfish are also grown in closed systems.
Mineral Resources
- Sea Salt: Halite (NaCl) has been used since ancient times and remains an industrially important mineral. It is extracted through evaporation in salt pans.
- Fertilizers: Phosphorite and apatite are marine sedimentary rocks used to obtain phosphates for agricultural fertilizers.
- Building Materials: Sand and gravel are extracted from the seabed.
Energy Resources
- Fossil Fuels (Oil and Natural Gas): The majority of the planet’s oil and gas resources are located under the continental shelf, i.e., along the coasts.
- Tidal Energy: A renewable energy source that utilizes the tidal cycle to generate electricity in plants that store water during high tide and release it during low tide.
Water Desalination
Desalination offers a significant opportunity to provide water for irrigation and human consumption in areas with water scarcity.
Shipping
Despite being slow, shipping remains relevant due to its low cost and ability to transport large quantities of goods.
Leisure Activities
Leisure is one of the primary resources provided by the sea, mainly through tourism.
Impacts on Coastal Areas
Shoreline Pollution
- Urban Wastewater: Generated from domestic activities and services in coastal towns. This wastewater has a high organic matter content and contributes to thermal pollution. If the population is connected to a sewage system with a treatment plant, the wastewater is treated and returned to the environment with lower contamination levels.
- Industrial and Agricultural Wastewater: Industrial wastewater is characterized by a wide variety of pollutants. Depending on the industry, metals, chemicals, and other harmful substances can be found.
- Oil Spills: Can be accidental (e.g., boating accidents) but more frequently result from illegal tank cleaning at sea, leading to oil slicks and tar on the coasts.
- Waste: The sea has traditionally been used as a dumping ground. All kinds of waste have been deposited in the oceans, from plastics and fishing gear that become death traps for marine organisms to drums of nuclear waste.
Impacts on Coastal Dynamics
- Changes in Littoral Drift: Numerous public works, particularly the construction of dams, ports, and jetties, alter the natural movement of sediment along the coast.
- Changes in Sedimentation: Human activities can cause an increase or decrease in sedimentation rates through changes in river basins that discharge into coastal areas.
Impacts on Landscape
Uncontrolled urban development in coastal tourist areas significantly impacts the landscape. The construction of access roads, buildings (especially high-rises), promenades, and entertainment facilities disrupts the natural landscape, transforming what was once a natural coastal environment into an urban or rural sprawl.
Overfishing
One of the major human impacts on the biosphere occurs on commercially exploited marine species. Biological rest periods have proven useful for regenerating fish stocks, but they are either insufficient, not properly applied, or both.
Hazards in Coastal Areas
Several hazards are prevalent in coastal areas:
Waves
Waves are formed by direct wind (forced waves) and propagate through wave motion, continuing beyond the wind’s influence (free waves). Forced waves can reach heights of 15 meters, have a long lifespan, and travel vast distances before breaking on the shore and receding. As waves approach beaches, they can be diverted parallel to the coastline, creating longshore currents that significantly impact sediment transport. Storm waves, particularly in the North Sea and the East Coast of the USA, can cause extensive coastal devastation. Waves contribute to coastal erosion and pose risks to human life and property.
Tsunamis
Tsunamis are giant waves, reaching up to 40 meters high, caused by underwater earthquakes or landslides, volcanic collapses, or the collapse of icebergs in coastal areas. They are also known as rogue waves, and their effects on the coast are devastating. Seismic tsunamis typically occur in shallow bays, and an abnormal withdrawal of water from the coast minutes before the wave’s arrival is a characteristic warning sign. Tsunamis can penetrate up to 300 meters inland, destroying everything in their path and causing numerous deaths and economic losses.
Tides
Tides are the daily rise and fall of sea level, primarily caused by the gravitational pull of the Sun and the Moon due to their proximity to Earth. Tides can generate significant horizontal displacement of water particles, creating tidal currents that cause flood (inflow during rising tide) and ebb (outflow during falling tide). These currents can sometimes be very strong (4 m/s during flood), posing risks to navigation. Tides are predictable, and empirical tables specify the times and days of different tidal movements, allowing for preventive measures.
Dunes
Dunes pose a risk due to their displacement by wind. They can encroach on productive land, obstruct communication routes, infrastructure, and human settlements, and contribute to erosion. Protection mechanisms against dune movement involve planning and hindering their progress through barriers or cuttings, and especially stabilizing the dunes with vegetation.