Jellyfish bloom
Blooms may take place naturally as a result of ocean and wind patterns,[1] ecosystem shifts, and jellyfish behaviors though their occurrence is thought to have increased during the last several decades in near-shore regions and shallow seas around the world.
[6] Jellyfish blooms significantly impact ecological community composition and structure by reducing available prey for higher predators.
[7] Recent blooms have commonly overlapped with multiple industries, reducing fisheries catch,[8] clogging fishing nets and power plant pipes,[9] and overwhelming popular beach destinations leading to closures.
[3][11] Eutrophication,[3] hypoxia,[4] rising global ocean temperatures,[2] coastal development,[5] and overfishing, are suspected to be stimulating the growth of jellyfish populations.
[12][13][11][14] Eutrophication, for example, provides an excess of nutrients, which leads to abnormally large algal blooms that support rapid jellyfish population growth.
[18] Fish eggs and small larvae make ideal prey for carnivorous jellyfish and other predators, as they have low escape ability and are larger in size compared to other zooplankton.
In the case of Chesapeake Bay, sea nettles (Chrysaora quinquecirrha) served as a dominant top-down control within the estuarine ecosystem and were tightly coupled with oyster populations.
Non-zooxanthellate jellyfish excrete ammonium and phosphate necessary for primary production and some estimates suggest in some systems they are the second most important source of these nutrients behind weathering.
[7] Alternatively, non-zooxanthellate jellyfish have low C:N ratios which lowers the bacterial growth efficiency and shifts the community toward a respiration-dominated rather than production-dominated system.
[4][22] Jellyfish blooms are generally short lived, collapsing from food limitations, changes in water temperature or oxygen levels, or completing their life cycle.
[23] The death, sinking, and decomposition of jellyfish is rapid and leads to a mass release of dissolved and particulate, organic and inorganic matter in the water column or seafloor creating a significant source of food for the microbial community.
[22][24] In both scenarios the organic matter from the jellyfish is consumed by the bacterial community who simultaneously reduce available oxygen, at times contributing to hypoxia.
[7][24][25][26] In some cases, the jelly-falls are too large for consumption and organic matter accumulates on the seafloor creating a physical barrier for diffusion mechanisms, reducing oxygen transport into sediments.
The accidental introduction in the Black Sea, via ballast water, of the ctenophore Mnemiopsis leidyi and the resulting destruction in the early 1990s of the entire anchovy fishery sector is well known.
[2] One example is found in the Chesapeake Bay estuary, where evidence suggests the presence of sea nettles (Chrysaora quinquecirpha) has a positive effect on oyster populations.
Power plants in Japan use bubble-curtain devices which produce air bubbles near intake valves which lift the jellyfish, reducing the number that are sucked into the pumps.
[9] In coastal areas where tourism is ubiquitous, jellyfish blooms often present a risk to recreational activities due to beach closures and stinging swimmers.
For example, in the Italian peninsula of Salento, there were 1,733 sting incidents requiring medical attention between 2007 and 2011, costing the health services approximately €400,000.
[11] Stings were more commonly reported when wind conditions were blowing perpendicular to shore, which generally brought jellyfish into closer proximity with tourists.
This disproportionate coverage of bloom events changes public perception about the presence of jellyfish, which could lead to the impacts on tourism.
The soft-bodied anatomy of jellyfish makes fossilization rare, which provides challenges to recreate the historical abundances of blooms.
Most preserved jellyfish bloom fossils are from the Cambrian period likely due to the abundance of marine life and lack of terrestrial scavengers during this time.
This lack of data also inhibits researchers' abilities to distinguish between jellyfish bloom oscillations caused by natural versus anthropogenic impacts.
[16] Other studies refute the idea that global jellyfish populations are increasing at all; they state that these variations are simply part of the larger-scale climatic and ecosystem processes.
[16] There have been calls for future research to focus on the ecology of both the medusae and the polyp life stages to better understand bloom dynamics throughout the organisms' entire lifespans.
