Status of Critical Habitats and Invasive Species

Critical habitats that have been impacted by anthropogenic pressures in Chesapeake Bay (CB) and the northern Adriatic Sea (NAS) include seagrass beds and tidal marshes (both systems), oyster reefs (CB), coral reefs (NAS), beaches (CB), and coastal lagoons (NAS), all of which support important ecological services. Major anthropogenic pressures include excess nutrient loading (eutrophication), coastal development, climate change (sea‐level rise and increases in water temperature), invasive species, and overfishing. Acidification (driven by both climate change and eutrophication) likely impacts calcareous organisms more in CB than in the NAS. While the rapid loss of oyster bars during the 20th century was primarily due to overfishing and disease, loss of oxygenated habitat also contributed. These pressures are likely to persist, and may become greater in the future, yet there are signs of recovery. The CB seagrass beds began a comeback in the mid‐1980s after decades of decline from eutrophication, mainly driven by anthropogenic nitrogen reductions. In the NAS, eutrophication in lagoons led to episodic bottom‐water anoxia and a shift from benthic to pelagic primary production. Eutrophication and overgrazing by sea urchins contributed to the decline of the NAS brown algal forests. Following nutrient reductions over the past two decades, there has been a slight recovery of canopy‐forming algae along the Croatian Istrian peninsula and the Slovenian coastline.