Aquatic ecology and Biodiversity

Unit 12- Aquatic biodiversity and conservation

12.1.5. Threats to aquatic biodiversity
Anthropogenic activities are causing species to disappear at an alarming rate. It has been estimated that between 1975 and 2015, species extinction will occur at a rate of 1 to 11 percent per decade. Aquatic species are at a higher risk of extinction than mammals and birds. Freshwater and marine ecosystems face similar threats. Runoff from agricultural and urban areas, the invasion of exotic species, and the creation of dams and water diversion have been identified as the greatest challenges to freshwater environments. Overfishing is the greatest threat to marine environments thus, the need for sustainable fisheries has been identified by the Environmental Defense Fund as the key priority in preserving marine biodiversity. Other threats to aquatic biodiversity include urban development and resource-based industries such as mining and forestry that destroy or reduce natural habitats. In addition, air and water pollution, sedimentation and erosion, and climate change also pose threats to aquatic biodiversity.
Invasion of exotic species
Biodiversity loss in many aquatic ecosystems is due to the introduction of exotic species. An exotic species is a non-native plant or animal deliberately or accidentally introduced into a new habitat. Such species include plants, fishes, algae, molluscs, crustaceans, bacteria, and viruses. Species that are able to grow, reproduce and survive outside of the habitats where they evolved are also referred to as alien, introduced, invasive, non-native, or non-indigenous species.
Exotic species are introduced into marine areas by means of transplanting or commercial shipping. It has been reported that ship ballast water is responsible for the transport of approximately 3,000 species worldwide each day. Exotic species can have many negative impacts on the environment, the economy and human health. When species are introduced into an area, they may cause increased predation and competition, disease, habitat destruction, genetic stock alterations and even extinction.
Habitat loss and degradation
Marine ecosystems are experiencing high rates of habitat loss and degradation. Shoreline stabilization, development of large ports, mangrove deforestation, coral and sand mining and the existence of densely populated coastal cities all contributed to this loss. The introduction of structures such as fishing harbours, jetties and other structures has interrupted important longshore current movements. As a result, beach fronts and marsh communities are becoming eroded and experiencing increased sand loss.
Construction of dams
Construction of dams across the rivers leads to the destruction of feeding and breeding grounds of many freshwater fishes and also the migratory fishes to a greater extent. Excess release of water from the reservoir and diversion of river water for agricultural and industrial purposes may also results in the destruction or degradation of freshwater fish habitats. Thus, destruction of natural habitats leads to the loss of biodiversity in that region.
Human bias
Losses to aquatic biodiversity are also linked to pests or threats towards species that are either unobserved or whose existence and importance to aquatic ecosystems are unknown. Often times "pest" or "threat" species such as sharks have been hunted to near extinction upsetting the natural balance of their associated ecosystem. Purposeful usage of dynamiting and fish poisons may also cause severe fish biodiversity loss.
Overexploitation of species
Overexploitation of species affects the loss of genetic diversity and species abundance of both individual and /or groups of interacting species. Modifications of gear and vessel efficiency have caused a significant decrease in fish populations. In particular, increasing human populations have placed increasing demands on the sea food. Incidental by-catch from fisheries operations also contribute to the decline in aquatic biodiversity. By-catch is the accidental capture of non-commercial or restricted commercial fishing species, which takes place during fishery operations. By-catch can include marine mammals, sea turtles, seabirds, and sharks. For example, sharks are a by-catch product in tuna and swordfish fisheries operations. Most of the time the entire shark is discarded at sea after the removal of their fins, since shark fins in demand as they are considered a delicacy in Asian culture.
Freshwater populations have also been affected by overfishing. Over harvesting can greatly affect the biodiversity of many important aquatic ecosystems and local industry and the economy.
Aquaculture
Aquaculture production has increased greatly in partial response to the decline in fisheries. Certain types of aquaculture can also contribute to the degradation of natural environments in many parts of the world. For example, it can contribute to the accidental release of non-native species, habitat conversion, pollution, as well as actual elimination of more fish than is being produced. For example, in the salmon farming industry, fish faeces and uneaten fish feed can also contribute to pollution. In order to control fish disease during the process of aquaculture, the use of antibiotics in fish feeds has increased. Antibiotics may leave residual traces in uneaten feed and fish faces trapped in sediments and potentially leading to toxic conditions for species. Antibiotic use in aquaculture also leads to the development of bacteria, which is antibiotic-resistant.
Pollution
Oceans have historically been the dumping grounds for the wastes from society. Pollution has been considerably damaging to aquatic ecosystems and may consists of agricultural, urban and industrial wastes containing contaminants such as sewage, fertilizer, and heavy metals, pesticides and other harmful substances that have proven to be very damaging to the loss aquatic habitats and species.
Sedimentation
Land management practices including urbanization, farming, forestry practices and industrialization have all contributed to the increased flow of sediments, in turn impacting aquatic resources. As a result of these activities, sediment runoff into rivers, lakes, streams, and estuaries has increased and is adversely affecting the biodiversity of these areas in a number of ways. Physical structure of the habitats changed due to increased sediment load, introduction of pollutants through sediment run off, creating respiratory and feeding problems by sediment settling over the bottom living organisms, especially coral reefs and covering of spawning habitats by the sediment settlement.
Climate change
Global climate change poses serious threats such as sea level rise, increase of sea surface temperature, ocean acidification, etc. to many aquatic ecosystems. In the last century, increased global temperature has caused sea levels to rise approximately 15 - 20 cm (6 - 8 inches) worldwide, and is expected to continue to rise at an average rate of 1 – 2 mm/year. At this rate, low lying areas and coastal aquatic ecosystems such as estuaries, marshes, and mangrove forests are being threatened. Higher salinities caused by increased evaporation, greater levels of tidal inundation, increased occurrences of flooding, and increased shoreline erosion are significantly altering the composition of these ecosystems, affecting both the plants and animals living in these habitats. Increase in sea surface temperature due to global warming is also reported to affect the coral reef ecosystem to a greater extent by bleaching and mortality of corals. Similarly, due to the high accumulation of carbon dioxide in the sea leads to the ocean acidification which is a major setback for many of the animals to build their exoskeleton, particularly, phytoplankton of cocolithophores, corals and molluscs. Thus, the species diversity and productivity of the marine ecosystems are greatly affected. If suitable measures are not taken to help prevent further global warming, aquatic biodiversity could be greatly affected. This climate change will not only alter the species composition of the various aquatic systems but also causes extinction of species in aquatic systems.