Marine heat waves occur when the surface temperature of a marine ecosystem is 90% higher than its typical average temperature for more than five days. These spikes in water temperatures result from anthropogenic, or human-induced, climate change, as the warming atmosphere conducts heat into marine ecosystems through a natural process called air-sea heat flux. This sudden infusion of extremely high temperatures in marine environments is quite unusual as water has a high specific heat capacity–indicating that it takes a plethora of energy to change the temperature of the water. In recent years, marine heat waves have had a higher frequency, intensity, and duration.
Marine heat waves adversely affect aquatic ecosystems and often lead to their subsequent collapse. Greater heat wave frequency correlates directly with an increased probability of coral bleaching events. This phenomenon injures the coral, changes their structure, and heightens their mortality rates. Despite the fact that we have seen instances of regrowth–as mentioned in last month's article–the recurrence of coral bleaching events reduces the "likelihood of reef systems recovering" from such environmental stress. Moreover, coastal and deep kelp forests have been collapsing. This has significant repercussions as kelp forests play a vital role in "[providing] habitat and food" for dozens of marine species. Because of the reduction in kelp biomass, many primary consumers who rely on it as a food source are left to starve, which ultimately leads to consequences beyond the base of food webs. In addition, monotonous and degraded turf seascapes" that don't offer as much ecosystem support" for marine life are replacing previously biodiverse and complex kelp forests. Because of the uninhabitable conditions provoked by marine heat waves and the habitat destruction that follows, many species are forced to relocate to completely new ecosystems. In fact, this is exactly what has been happening in the North Atlantic and Northern Pacific oceans this past month.
Citations
“Climate Change Increases Marine Heatwaves Harming Marine Ecosystems”. Science Brief.https://sciencebrief.org/uploads/reviews/ScienceBrief_Review_MARINE_HEATWAVE_Oct2021.pdf
“What Are Marine Heatwaves? Overview, Effects, and Mitigation”. Treehugger.https://www.treehugger.com/what-are-marine-heatwaves-5207909