Aequorea victoria is a jellyfish in Puget Sound,Washington State, from which the luminescent protein aequorin and the fluorescent molecule GFP have been extracted, purified, and eventually cloned. These two products have proven useful and popular in various kinds of biomedical research in the 1990s and 2000s and their value is likely to increase in coming years; GFP is particularly easy to use and has wide-ranging value as a fluorescent marker-protein. Along with use of these products, comes a certain popular press explaining their source, with various factoids usually included about the jellyfish. Many inaccuracies have emerged from this press, and it might be difficult for someone to get the story right by reading what has been published. Because I study medusae, including Aequorea victoria in Friday Harbor, Washington, the source of most harvested specimens, I feel that I have become an unwilling but central player in this unintentional and seemingly never-ending misinformation campaign. Nearly every time that my photographs have been used by someone other than myself, the explanation of the photograph is somehow wrong.
Natural history of Aequorea victoria and related species
Tiny jellyfish, including Aequorea, are asexually budded off their hydroid colonies in early spring in the Puget Sound / Strait of Georgia region of Washington State and British Columbia. Like other hydromedusae, Aequorea medusae initially grow quite rapidly, putting most of their energy into somatic growth, resulting in increasing size. For Aequorea victoria, the rate of growth in size diminishes after they reach several cm in diameter, and most energy is then put into gamete production. Like other hydromedusae, Aequorea then free-spawn either eggs or sperm (each jellyfish is one sex or the other) into the sea daily, where the eggs are fertilized, develop into a swimming planula larva, and eventually settle and grow into a new hydroid colony. The hydroid of Aequorea has barely been studied and in fact has rarely been collected in the field - we know virtually nothing about its ecology other than the fact that it lives attached to the bottom or to hard substrates such as shells on or near the bottom. It is fairly easy to grow in culture in the laboratory.
Adult Aequorea victoria medusae in Puget Sound reach about 5 to 10 cm in diameter. They feed primarily on soft-bodied prey including other jellyfishes, ctenophores, and appendicularians. Most probably live 6 months or less in the field. The entire population of Aequorea medusae disappears (dies) by mid-autumn every year. Polyp colonies persist on the bottom and produce a new generation of medusae each spring, using specific, but undetermined, environmental cues for the fairly precise timing of this annual event.
Aequorea medusae used to be enormously abundant during the summer in Friday Harbor, Washington, during at least the 1960s through the 1980s. Hundreds of thousands of medusae were harvested during that period by scientists interested in their luminescent properties. Aequorea medusae have become relatively scarce in the 1990s and 2000s and we do not know why - this change does not seem to be due to overcollection. In fact, numbers of all 75 or so species of hydromedusae are substantially down in the region now (thus exonerating the biologists who collected large numbers of only one of two of the species), but the decrease in Aequorea is especially noticeable since they are relatively large and used to be so plentiful, dominating the summer surface plankton. Knowledge about the ecology of the benthic polyps now seems even more important for understanding the present trend. I have witnessed an enormous change from the late 1970s to the present, particularly in numbers of Aequorea, and have a 30-year data set, yet to be fully analyzed, that shows these vast jellyfish declines in Friday Harbor.
Aequorea medusae are found from the Bering Sea to southern California in the northeast Pacific (I do not know the distribution in the northwest Pacific; similar medusae also occur in the North Atlantic). Several names have been applied to the northeast Pacific jellyfish, of which Aequorea victoria is only one, and perhaps not even the "best" one. Other names used in the literature for these animals include Aequorea aequorea, Aequorea forskalea and Aequorea coerulescens. Some specimens in Alaska get much larger, commonly to 20 cm diameter. It is not known if they are the same as or a different species than the more southerly populations. Sorting out the names and life cycles of these temperate Aequorea species has not been an easy task, or it would have been done long ago - cloning the protein aequorin from the jellyfish was perhaps a much more straightforward proposition at the time it was accomplished. A genetic study of the differentAequoreas may now yield the associations without the arduous life cycle work; collections over the entire geographic range would still be useful.
Aequorea bioluminescence
Aequorea medusae bioluminesce only around the margin; such luminescence does not show in the above images - Dr. Osamu Shimomura's image of Aequorea bioluminescence - that green ring is IT, all the rest of the jellyfish is "unlit." Dr. Shimomura is the scientist who began studying bioluminescence of Aequorea in 1961 at the Friday Harbor Laboratories, ultimately leading to the use of two bioluminescent proteins from this jellyfish in all sorts of biological research . Bioluminescence ofAequorea, as in most species of jellyfish, does not look like a soft overall glow, but occurs only at the rim of the bell (the localization of bioluminescence in jellyfish appears to be genus- or species-specific), and would appear as a string of nearly-microscopic fusiform green lights, given the right viewing conditions.
The luminescent light produced by Aequorea is actually bluish in color, attributable to a molecule known as aquerin, but in a living jellyfish it is emitted via a coupled molecule known as GFP, which causes the emitted light to appear green to us. Read about the history of GFP for an in-depth introduction by Nikon to fluorescent proteins including specific information about these jellyfish proteins.
It is not well understood how and why jellyfish use their bioluminescent capabilities, or what biological function this serves. Jellyfish do not flash at each other in the dark, nor do they glow continuously. Whereas scientists who study jellyfish bioluminescence can easily stimulate medusae and thereby see their bioluminescent response, this is rarely seen in undisturbed animals. I have spent many hours in the dark watching medusae contained in a 2 m tall by 1 meter wide cylindrical aquarium and remember only one occasion when I saw what seemed to be "auto-bioluminescence," that is, light emission that was not stimulated by a human. It is possible that the medusa in this case (Mitrocoma cellularia, not even Aequorea victoria) had hit something, perhaps another medusa or the wall of the aquarium, but I could not discern the precise cause of this rare display.
If you live near or visit Puget Sound, the Strait of Georgia, Southeast Alaska, or even Prince William Sound, you may see Aequorea medusae at the surface of the sea in the summer. If you pick up one of these medusae at night (they do not sting) and shake it gently in your hand in the dark, you will see the marginal ring of green bioluminescence. The glow of light lasts a few seconds. Some luminescent particles may stick to your hand after you put the animal back in the water.
Choice and use of species name for Aequorea
This is a big problem and has led to the use of at least three different species names (Aequorea aequorea, A. forskalea, and A. victoria) in the modern literature for what is very likely all the same animal in the NE Pacific (I am not even discussing whether the Pacific and Atlantic material is the same right now). A fourth name, Aequorea coerulescens, is being used in Japan, but not on the American side of the North Pacific. In fact, even more names were available, but have not been used in the scientific literature by experimentalists, so will not be included in the present discussion.Aequorea aequorea (Forskal, 1775) was originally applied to specimens in the Mediterranean and then in the North Atlantic. These were also at times called A. forskalea, but Henry Bigelow, in 1913 stated about Aequorea aequorea "This species has universally been called forskalea, following Peron and Lesueur (1809), but this name was expressly given by them to the Medusa aequorea of Forskal (1775), and all modern authors are agreed that the animal in question is the same that Forskal described" - this statement means that Bigelow felt that A. aequorea is the correct scientific name for everything also called A. forskalea in the literature. F. S. Russell, another highly reputable jellyfish systematist, in 1953 chose to accept only A. forskalea as the name for all of these medusae, stating that the species name aequorea was preoccupied by an unidentifiable species.
Bigelow, already familiar with the North Atlantic fauna, in 1913 carefully compared Aequorea specimens in Alaska with those in Friday Harbor, and arrived at using two variety names in order to differentiate the very large Alaskan Aequorea aequorea var. albida from the smaller Alaskan and Friday Harbor specimens Aequorea aequorea var. aequorea. (Russell did not look at Pacific material.) No one since Bigelow's time has published a comparison of Alaskan and Washington Aequorea. My own incomplete study indicates that medusae being called Aequorea coerulescens (Brandt, 1838) in Japan look like those designated A. aequorea var. albida by Bigelow. The type locality for Aequorea coerulescens is the open Pacific, about half-way between California and Hawaii. I have collected these plate-sized Aequoreas on rare occasions in the open ocean off central California and in Friday Harbor. In Alaska, small specimens of Aequorea, which are the size of Friday Harbor A. aequorea var. aequorea (Bigelow's distinction) all havethat morphological look, making it very uncertain if the big ones are another species or their morphology changes (gaining LOTS of radial canals) with size.
Arai and Brinckmann-Voss in 1980 reexamined Aequorea from southern British Columbia, comparing it with specimens and drawings of European material. They found several characters which they felt were unique to the NE Pacific material and which warranted assigning it the name Aequorea victoria(Murbach & Shearer, 1902), although they chose not to acknowledge the older name Aequorea flava(A. Agassiz, 1865), for medusae described and illustrated from the Gulf of Georgia, which must be the same as those commonly collected in nearby Friday Harbor. Aequorea coerulescens is the other possibly good older name, having been applied to specimens from San Diego and Unalaska Island in the Aleutians, as well as Japan.
It is particularly difficult to assign species names to Aequorea based on morphological characters, which are quite plastic in this group. Species are distinguished morphologically by a combination of the numbers of tentacles, radial canals and marginal statocysts, but at least tentacles and radial canals, and probably statocysts, are added as the medusa grows. A molecular project aimed at discovering relationships between the common temperate Aequoreas in the North Atlantic and North Pacific would seem both timely and important at this point. Dr. Mike Dawson, now of the University of California at Merced, has begun a project comparing genetic material in Aequorea medusae collected from around the world. He should eventually be able to shed some light on the systematics of these medusae. (Dr. Dawson is doing a similar project on the (unrelated) moon jellies in the genus Aurelia.) When the species are finally sorted out, nomenclatural rules determine that the names given to each animal will be the oldest (first) name applied to each species.
In summary, for those of you reading the scientific literature, there is one common Aequorea in Washington and southern British Columbia waters, no matter what species names have been applied to it in the literature. This "Friday Harbor Aequorea" may or may not turn out to be the same species as is found in New England and Europe, or further south into California. The much larger, dinner-plate sized Aequorea common in Alaska and Japan (and on rare occasions seen in Friday Harbor) may or may not be the same species, but until recently this glorious animal had not been used by experimentalists; it has only recently appeared in the aequorin/GFP literature, as A. coerulescens (sometimes misspelled).
