The implications of climate change on land can be easily seen, as an increase in storms, drought and other extreme weather patterns are becoming increasingly common. However, many changes are also found within the world’s oceans in the form of marine heatwaves.
Unusually warm oceans can have widespread impacts on marine ecosystems. Extremes in weather are often natural, caused by cyclical changes such as El Nino or La Nina, yet anthropogenic climate change is making these events more intense. The Ridiculously Resilient Ridge, a static high pressure region in the atmosphere established itself off the Pacific coast of North America in 2014, causing a lower than average amount of heatloss from the ocean to the atmosphere. This ridge also deflected winter storms, changing the expected weather for the time of year. This, coupled with a change in surface waters of the Pacific Decadal Oscillation (PDO), the warming phase linked with El Nino, caused an increase in water temperature of 2.5 degrees Celsius, in an area termed ‘The Blob’. The outcomes of this warming had numerous social, environmental and economic impacts.
Warmer waters are typically less nutrient rich due to the lack of upwelling from nutrient dense cold waters. Due to this, there is typically a reduction in phytoplankton productivity. These means that zooplankton and higher levels of the food chain would also be impacted. Commercially important species such as crab and salmon may experience declines which would have a negative impact on fisheries in the effected areas.
It is not only these issues that have impacted fisheries but also the occurrence of harmful algal blooms (HABs). Fish, birds, sea lions and other marine species have been poisoned by domoic acid which is associated with the algae. Salmon fisheries around Monteray Bay in California faced closure due to the level of toxicity becoming too high. Domoic acid toxicity can be very harmful to both marine organisms and humans, and can sometimes cause death.
Warmer water can also often change the distribution of species, as when the blob was taking place, anchovy and sardine populations relocated northwards in search of cold water copepods to feed on. This caused thousands of sea lions and their pups to starve, causing the Marine Mammal Centre to experience a record breaking year, treating over 1000 starving sea lions, as well as 220 with domoic acid toxicity. This shift also caused warm water species such as thresher sharks, sunfish and tuna to be found outside of their usual habitats. These changes may have disastrous implications for the food web across the pacific, as there would be changes in production, competition and predator-prey relationships.
It is not only sea lions that have been impacted by lack of food, but sea birds too. Cassins Auklets have been washing up dead in huge numbers due to the loss of food source. Other species, such as 22 differing kinds of sea star have been impacted by warming temperatures too. The temperature increase has been directly correlated with the occurrence of starfish wasting disease, which causes lesions on their bodies, which eventually become big enough for their internal anatomy to come out.
Changes in species abundance, as well as the introduction of new species may change the biology and biodiversity of the ecosystem, leading to widespread tropic changes that may be detrimental to the ecological balance.
Another aspect that hiders biodiversity is coral bleaching. In 2014, Hawaii experienced a mass bleaching event, which was put down to the blob. When put under stress, such as rising temperatures, corals release their zooxanthellae, which is responsible for providing them with energy through photosynthesis. By expelling it, their endosymbiosis is ended. This causes limited growth until new zooxanthellae is picked up, and if it does not, the coral cannot recover and dies. This has a knock on effect for all of the species relying on the reef system for food and shelter.
This warming is just one of many that have been are are currently happening globally. It is essential, therefore, that we all take action against climate change in order to stop the frequency and severity of these events to increase.