Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Northern Sea Nettle - Chrysaora melanaster
Northern Sea Nettle - Chrysaora melanaster

[Image: Chrysaora_jelly.jpg]

Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Semaeostomeae
Family: Pelagiidae
Genus: Chrysaora
Species: Chrysaora melanaster

The northern sea nettle (Chrysaora melanaster), also called a brown jellyfish, is a species of jellyfish native to the northern Pacific Ocean and adjacent parts of the Arctic Ocean. (It is sometimes referred to as a Pacific sea nettle, but this name is also used for Chrysaora fuscescens; the name Japanese sea nettle was used for this species, but that name now exclusively means Chrysaora pacifica. This jelly's medusa can reach 60 centimeters in length with tentacles growing up to three meters. The number of tentacles is up to 24 (8 per octant). It dwells at depths of up to 100 meters, where it feeds on copepods, larvaceans, small fish, large zooplankton, and other jellies. The sting is mild, although can cause serious skin irritation and burning.

[Image: Chrysaora_melanaster-2-800x600.jpg]

Life Cycle
Larval mature into adult body-form that releases eggs and sperm;Fertilized eggs settle to seafloor to produce a small non-colonial benthic form; Life span in Tokyo Bay is 1 year, how ever it is unknown in Arctic.

Open water of temperate northern Pacific Ocean, Arctic Ocean and especially the Bering Sea. Pollock can be the food of Chrysaora melanaster, it also can be the competitor for potentialy limited prey sources.

Influence from Climate Change 
The biomass of Chrysaora melanaster increased in recent years. Climate change caused a more stable and productive surface layer. The stable water column would also can contribute to the warmer surface later in summer in 1990s, which can cause Chrysaora melanaster growth and survival.

Rare Footage Captures Giant Jellyfish Living Under Arctic Ice

By Megan Gannon, Live Science Contributor | October 25, 2017 06:51am ET

[Image: aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1h...g5Mjg2NTQ=]
Scientists spotted this huge jellyfish (Chrysaora melanaster) dragging a crustacean with one of its tentacles under the sea ice covering the Chukchi Sea off the north coast of Alaska.
Credit: Andrew Juhl and Craig Aumack

Biologists who explore the Alaskan Arctic ecosystem aren't just interested in polar bears. Some are also captivated by the "gelatinous species" hidden below the ice.

Now, scientists have published rare footage of one of the Arctic's largest jellyfish drifting beneath the sea ice near Utqiaġvik, also known as Barrow, off the north coast of Alaska.

Such videos aren't easy to get. From May to June each year between 2011 and 2014, the team of researchers drove onto the frozen Chukchi Sea with snowmobiles, sometimes nearly 2 miles (3 kilometers) from shore, and drilled holes into the thick sea ice. They sent a camera-equipped underwater vehicle into the water to have a look at the seafloor. 

The scientists captured footage of algae, crustaceans and several species of comb jellies (also know as ctenophores) under the ice. But the big surprise was finding adults of a species of jellyfish known as Chrysaora melanaster. The bell of this type of jellyfish can reach 24 inches (60 centimeters) across, with its two dozen or so tentacles extending up to nearly 10 feet (3 meters), according to the Census of Marine Life. The researchers counted 55 of these jellyfish, all of which appeared healthy and in their adult, or medusa, stage. They were often dragging their long tentacles along the seafloor, likely trying to pick up food —with some apparent success. At least one of the jellyfish was seen carrying an isopod, a type of crustacean.

The presence of adult jellyfish during the late spring and early summer suggests these C. melanaster medusas can survive the Arctic winter, according to the research published in the journal Marine Ecology Progress Series on Oct. 23. Like most jellyfish, this species was thought to live for only a few months. And scientists thought the species survived the winter only in the polyp stage of their life cycle. (Bottom-dwelling polyps settle on rocks or other surfaces and produce baby jellyfish in the spring.)

"Life under sea ice is like living in a refrigerator—everything slows down," study co-author Andy Juhl, a marine biologist at Columbia University's Lamont-Doherty Earth Observatory, told his department's blog. Juhl and his colleagues think that thick sea ice in winter helps protect the medusas from rough seas, while the low temperatures help slow their metabolism so they don't need much food to survive.

"We believe that the prevalence of jellyfish and ctenophores living through the winter is greater than generally appreciated," the researchers wrote.

The Arctic has been experiencing record-low levels of sea ice in recent years due to climate change. The authors of the new study noted that jellyfish populations could be more sensitive to these changes than scientists had thought.

"Understanding the implications of changing sea-ice conditions will become increasingly important as coastal Arctic seas become more open to transportation, commercial fishing, oil and gas exploration, and other forms of commercial exploitation," Juhl and his colleagues wrote.

Journal Reference:
Purcell JE, Juhl AR, Mańko MK, Aumack CF (2017) Overwintering of gelatinous zooplankton in the coastal Arctic Ocean. Mar Ecol Prog Ser

Jellyfish and ctenophore blooms are of increasing concern for human enterprise in marine waters, although bloom development remains poorly understood. A key factor in population dynamics of blooms is individual lifespan, which for most gelatinous zooplankton is assumed to be only a few months, often from spring to autumn. Accumulating evidence, however, indicates that some species may overwinter. In this study, we used video photography to quantify medusae and ctenophores beneath land-fast sea ice in the Chukchi Sea near Utqiag˙%%KERN_ERR%%vik (Barrow), Alaska, USA, from May to June, 2011-2014. Our data show large Chrysaora melanaster medusae overwintering near the bottom, which could contribute to multiyear population increases suggested for this species. C. melanaster medusae were observed dragging their tentacles along the bottom, possibly feeding on epibenthic macrofauna. This highlights an underappreciated mechanism for benthic-pelagic coupling by gelatinous zooplankton. Additionally, numerous individuals of 3 ctenophore and 1 hydrozoan species were seen primarily at the sea-ice interface rather than near the bottom. We hypothesize that overwintering of medusae and ctenophores under sea ice is favored by the continued availability of prey, related to high productivity in the coastal Arctic, including production by ice algae. Successful overwintering may also relate to physical sheltering and low water temperatures. Overwintering may be a common life-history trait for gelatinous zooplankton, with important implications for understanding annual and interannual population trends in many environments and has important implications for models including jellyfish and ctenophore populations and ecosystem dynamics. 
[Image: wildcat10-CougarHuntingDeer.jpg]

Forum Jump:

Users browsing this thread: 1 Guest(s)