What at first appears to be a blanket of fine snow on the sea bed is actually a patch of bleached coral off the northern shore of Papua New Guinea. As sea temperatures rise, this scene is becoming more and more common in coral reefs around the globe. Rising temperatures make corals expel their zooxanthellae (algae with which corals have a symbiotic relationship), leading to starvation.

This is particularly bad news because once a reef dies, it turns to rubble, making it impossible for new coral to grow on top of it. This essentially turns what was once a flourishing biodiversity mini-hotspot into a sort of ecological deadzone.

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Unlike most hydrozoans, species in the order Narcomedusae do not ordinarily have a polyp stage. Pictured is Aegina citrea.

Photo credit: Tracy Clark

Stalked jellyfish species, Lucernaria quadricornis

Photo © Kåre Telnes

Unlike their free-swimming cousins, stalked jellyfish spend their lives in one place, attached to seaweed or sea grasses. Despite being usually anchored to one place, these animals can still bend and move around to help them catch prey. The species shown is Haliclystus octoradiatus.

Photo © RLLord

The kaleidoscope stalked jellyfish (Haliclystus auricula), like all stalked jellyfish, spends its life attached to marine vegetation.

Photo © Marco Faasse

The helmet jelly (Periphylla periphylla) is one of the most common deep sea jellyfish in the world and is found in every ocean except for the Arctic. Living between 1000 and 7000 meters depth, it moves up to shallower waters at night because light is toxic to the species. To avoid predation, the helmet jelly can use bioluminescence as a means of distracting predators.

Photos © Kåre Telnes

A red medusa (Atolla gigantea) found by NOAA’s ocean exploration crew.

Stalked jellyfish species, Sasakiella cruciformis

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Jellyfish species, Chrysaora helvola

(Photo source)

Mediterranean jellyfish, Cotylorhiza tuberculata

(Photo by dgheban on deviantART)