User:LisaTruong3/Biodiversity loss draft

Overfishing
Human demands and consumption have resulted in overfishing, which leads to a loss in biodiversity with reduction to fish species richness and abundances. Reduction in global fish populations were first noticed during the 1990s. Currently, many commercial fishes have been overharvested; approximately 27% of exploited fish stocks in the United States are classified overfished. In Tasmania, it was observed that over 50% of major fisheries species, such as the eastern gemfish, southern rock lobster, southern bulkefin tuna, jack mackerel, and trumpeter, have declined over the past 75 years due to overfishing. Globally, fish abundances have reduced by 38% since 1970.

Fishery methods, such as bottom trawling, have resulted in habitat destruction, resulting spatial diversity and regional species richness to decline. Some studies, including the 2019 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services report, found that overfishing is the main driver of mass species extinction in the oceans.

Marine species richness loss
Marine biodiversity encompasses any living organism which resides in the ocean, and describes various complex relationships within marine ecosystems. On a local and regional scale, marine communities are better understood compared to marine ecosystems on a global scale. In 2018, it was estimated that approximately 240,000 marine species have been documented. Based on this prediction, the discovery of total marine species ranges between 11% to 78% due to uncertainties regarding global marine biodiversity. However, the number of described marine species remains low compared to terrestrial species due to various factors, which includes the assignment of different names for the same species, and insufficient taxa classification. It is likely that many undocumented species has already disappeared. Because not all marine species have been described, it is difficult to provide an accurate estimate of global extinction in marine ecosystems. As a result, abundances of marine species remain uncertain, with estimates ranging between 178,000 to 10 million oceanic species.

With anthropogenic pressure, this results in human activities having the strongest influences on marine biodiversity, with main drivers of global extinction being habitat loss, pollution, invasive species, and overexploitation. Greater pressure is placed on marine ecosystems with human settlements near coastal areas. Other indirect factors that have resulted in marine species to decline include climate change and change to oceanic biochemistry.

Overexploitation has resulted in the extinction of over 20 described marine species, which includes seabirds, marine mammals, algae, and fishes. Examples of extinct marine species include the Steller’s sea cow (Hydrodamalis gigas) and the Caribbean monk seal (Monachus tropicalis). However, not all extinctions are because of humans. For example, in 1930, the eelgrass limpet (Lottia alveus) became extinct once the Zostera marina seagrass population declined upon exposure to a disease. The Lottia alveus were greatly impacted as the Zostera marina were their sole habitats.