Category Archives: Marine Invertebrates

Sea Star Wasting Syndrome

Sea Star Wasting Syndrome

I mentioned last week in my post about sea stars that beaches on Kodiak teem with an abundant variety of brightly colored sea stars. Sadly, though, sea stars are not as abundant here as they were a few years ago. I took a walk on the beach yesterday and was alarmed by how few sea stars I saw. Those I did see looked healthy, but the vast majority were wiped out by a deadly virus.

 In June 2013, sea stars along the Pacific coast of the United States began dying in large numbers. Die-offs of sea stars have occurred before in the 1970s, 80s, and 90s but never of this magnitude. Within just three years, millions of sea stars from California to Alaska died from a disease called sea star wasting syndrome (SSWS). Sea stars with SSWS develop white lesions in the ectoderm quickly followed by decay of tissue surrounding the lesions which leads to fragmentation of the body and death. Biologists estimated 95% of some sea star populations were decimated by SSWS. While most species of sea stars were affected by SSWS, ochre stars (Pisaster ochraceus) and sunflower stars (Pycnopodia helianthoides) were especially hard hit.

 The syndrome was first noticed in ochre stars in June 2013 along the coast of Washington state. In August 2013, divers reported a massive die-off of sunflower stars just north of Vancouver, British Columbia. In October and November 2013, large numbers of dead sea stars were noted in Monterrey, California, and by mid-December, SSWS had reached southern California. In the summer of 2014, the disease had spread to Mexico and parts of Oregon. SSWS was first reported in Alaska in Kachemak Bay in 2014, but it wasn’t until 2015 and 2016 that sea stars began dying in large numbers in Alaska.

 Biologists are certain sea stars are dying from a virus, but when they isolated the virus, they realized this virus was present in preserved museum samples taken from as far back in the 1940s. They believe some other factor such as increased water temperature or a change in pH is stressing seas stars and allowing an otherwise dormant virus to rage through their populations. Researchers noted an increase in ocean water temperature preceded the outbreak of SSWS, and in areas where the water temperature rose the most, the disease was more widespread. To test the theory that increased water temperature played a big role in the breakout of the disease, scientists placed sea stars in aquarium tanks ranging in temperature from 54 degrees to 66 degrees Fahrenheit. The results were clear, the hotter the tank, the more quickly the sea stars succumbed to wasting.

The drastic reduction in sea star populations is evident on Kodiak Island, and biologists worry how the loss of sea stars will affect the intertidal community. Sea stars are considered a keystone species, important to maintaining diversity in the marine environment. Sea stars eat mussels and sea urchins whose numbers could now explode and decrease biodiversity in intertidal and subtidal communities.

 Scientists consider the recent outbreak of SSWS the single largest, most geographically widespread disease ever recorded, and as ocean temperatures keep rising, they fear the outbreak of the disease will continue.

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Sea Stars of Alaska

Photo by Mary Schwarzhans

Visitors to our lodge are often surprised by the large number of brightly colored sea stars inhabiting the low-tide zone on Kodiak Island. Sea stars are prolific throughout the Pacific Northwest and are critical to the health of intertidal and subtidal communities. Scientists have identified more than 120 species of sea stars in Alaska, including the sunflower sea star, one of the largest sea stars in the world.

Sunflower Sea Star

Sea stars are often called starfish, but since they aren’t fish, biologists prefer the name sea star. Sea stars belong to the phylum Echinodermata. Other echinoderms include sea cucumbers, sea urchins, sand dollars, and brittle stars. Echinoderms usually have pentamerous radial symmetry, meaning the body can be divided into five parts around a central axis. This five-parted symmetry is easy to see in a sea star with five arms, but it is also apparent if you look at the bottom of a sand dollar or the pen of a sea urchin. Some sea stars have more than five arms. A sunflower sea star has twenty arms, but the animal is still divided into five equal parts around the central disk.

Sea Stars are flattened in appearance and may range in size from 1 inch (2.54 cm) to over a yard (1 meter) in width. A sea star has an internal skeleton which is somewhat flexible. The skeleton consists of small calcareous plates bound together with connective tissue. Sea stars may look rigid and sedentary, but the connective tissue between the plates allows them to bend to attack prey, flee predators, and right themselves when they are turned upside down.

Photo by Mary Schwarzhans

A sea star’s anus is in the center of the top side, or the aboral surface of the animal. A circular madreporite is located just off center on the aboral surface, and this madreporite is a critical part of the circulation system of the sea star. Instead of a circulatory system, a sea star has a water vascular system, and the madreporite acts as a trap door through which water can move in and out in a controlled manner. The mouth of a sea star is located in the center of its underneath or oral surface. Open furrows containing tube feet extend from the mouth along the length of each leg.

Sea stars do not have eyes, but they have eyespots that can detect light at the tip of each arm. Interestingly, scientific studies have shown some species of sea stars move toward light while others move away from the light. Neurosensory cells which are sensitive to both touch and chemical tastes cover the surface of a sea star and are particularly dense in the suckers of the tube feet. Many species of sea stars are covered by clusters of tiny, calcareous pincers. These tiny pincers deter predators and keep the surface of the sea star free of parasites and debris. Also on the surface, thin-walled gills protrude between the calcareous plates and serve to exchange respiratory gases and excrete liquid wastes.

Oral Surface

The internal anatomy of a sea star includes the water vascular system, digestive tract, reproductive organs, and nervous system. The water vascular system uses muscles and hydraulics to power a sea star’s tube feet. The tube feet not only allow a sea star to move but are used to grasp prey, and the combined force of numerous tube feet is strong enough to pry apart a clam shell. Most seas stars move very slowly, and their pace is measured in inches per hour, but giant sunflower sea stars can travel at a speed of two feet per minute.

The mouth of a sea star opens into two stomachs connected to paired, lobed organs called pyloric caeca. The pyloric caeca extend into each arm and aid in the digestion of food. Sea stars are either male or female, and their reproductive organs, or gonads, lie between the pyloric caeca in each arm. In the spring, sea stars broadcast either eggs or sperm through pores in their arms into the water where chance fertilization occurs. Sea stars have no brain or central nervous system, but they have a nerve ring in the central disk connected to radial nerves running the length of each arm. The radial nerves are connected to a diffuse network of nerve cells scattered throughout the skin. Sea stars have the ability to regenerate lost arms.

Sea stars utilize a range of habitats and may be found from the shoreline to depths greater than 13,450 ft. (4,100 m). Sea stars consume a wide variety of prey, including sponges, snails, clams, mussels, sea cucumbers, barnacles, anemones, scallops, fishes, and even other sea stars. Some species of sea stars feed on plankton, while other species prefer dead organisms. Sea stars have few predators and are believed to have a lifespan of only a few years.

Next week, I will post about sea star wasting syndrome, a devastating disease that has killed millions of sea stars in the last few years from California to Alaska.

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Moon Jelly

You probably have seen moon jellies at an aquarium. They are the small, round, nearly- transparent jellies most of us picture when we think of jellyfish. The common name moon jelly refers to all species in the genus Aurelia. Species in this genus are so similar to each other they can only be differentiated by DNA analysis. Scientists do not know how many species belong to the genus Aurelia because more are being discovered all the time.

Moon jellies are found worldwide but are most prevalent in the Atlantic, Pacific, and Indian Oceans. They tolerate a wide range of temperatures and salinities and may even inhabit brackish water. In brackish water, the bell of a moon jelly is much flatter due to the decreased salinity. Moon jellies usually stay near the surface and are capable of moving upward on their own but are dependent on wind, tides, and currents for horizontal movement. Currents sometimes bring together thousands of moon jellies in a small area, and these groupings are called a bloom, a swarm, or a smack.

A moon jelly is typically 4 to 5 inches (10 to 15 cm) in diameter. It has a shallow bell that is colorless, except for the horseshoe-shaped gonads that may be tinted violet, pink or yellow. Since the gonads are near the bottom of the stomach, they often take on the color of the prey the jelly has just eaten. The margin of a moon jelly is divided into eight lobes that are fringed by numerous, thin tentacles. Each lobe is divided by a shallow cleft housing a sensory organ that aids the jelly in maintaining its equilibrium. The radial canals of the digestive system are clearly visible and repeatedly branch as they move toward the margin of the jelly. The oral lobes or arms are short and thick.

Moon jellies are carnivorous and feed mainly on zooplankton. They are eaten by lion’s mane jellies, sea urchins, crab, some sea anemones, sea turtles, and shorebirds. Like other jellies, moon jellies have tentacles with stinging nematocysts, but their stings are relatively harmless to humans.

Moon jellies have a lifecycle similar to other jellies. In the medusa or free-floating phase, the male releases a strand of sperm which the female takes through her mouth, fertilizing her eggs. The fertilized eggs develop into larvae in pockets in the oral arms that surround the mouth. The female then releases the larvae, and they settle and develop into polyps. A moon jelly may remain in the polyp stage of its lifecycle for 25 years until conditions are right for the polyp to reproduce asexually by budding. The buds float free and develop into medusae. In the wild, moon jellies only survive about 6-months in the medusa stage, but they may live up to a year as medusae in an aquarium.

Moon jellies are the most commonly kept species in both public and private aquariums. Their wide tolerance of both salinity and temperature make them a good choice as an aquarium species.



Lion’s Mane Jellyfish

The lion’s mane jelly (Cyanea capillata) is the largest known species of jelly. The largest specimen ever recorded was longer than a blue whale; it had a bell diameter of 7 ft. 6 in. (2.3 meters) and tentacles that were 121.4 ft. (37 meters) long. Lion’s mane jellies near Kodiak Island are not nearly that large; a large specimen here would have a bell diameter of 20 inches (50.8 centimeters) and tentacles 29.5 ft. (9 meters) long. Lion’s mane jellies are gorgeous animals that range from red-brown to yellow to white in color. Larger individuals are often red to dark purple while smaller jellies are a lighter orange or tan.

The lion’s mane jelly has a bell that is flattened and thick in the center and thin at the margins. The margin of a lion’s mane jelly is divided into eight, deep lobes, and each lobe is divided by a shallow cleft. A sensory organ called a rhopalium is located in each cleft, and these organs aid the jelly in determining its orientation. Although a jelly does not have a brain, it does have a central nervous system that receives input from sensory organs. Large, sticky tentacles emanate from the margin of the jelly. These tentacles are grouped into eight clusters with each cluster containing over 100 tentacles. Colorful oral arms that are much shorter than the tentacles extend from the center of the bell.

A lion’s mane jelly uses its long tentacles to capture and pull in prey to its mouth in the center of the bell. As with other jellies, the tentacles contain stinging nematocysts. When the tentacles touch a human’s skin, they cause temporary pain, itching, and localized redness. The pain is more intense if these nematocysts get into a cut or sore, or if the contact is around the eyes and nose. I frequently touch the tentacles when cleaning a fouled fish hook, and the tingling, burning sensation usually lasts only a few minutes. The pain is more severe if a person comes into contact with a large number of tentacles, but the stings are not fatal to humans who are in good health.

Lion’s mane jellies eat zooplankton, small fish, and moon jellies. They are preyed upon by anemones, some crab, shrimp, and nudibranchs. Leatherback sea turtles feed almost exclusively on lion’s mane jellies in the summer around Eastern Canada.

Some fish species, such as juvenile Pollack, and some amphipod species are immune to the sting of the lion’s mane jelly and form a symbiotic relationship with the jelly by swimming in the protection of its tentacles.

Our summer guests are often surprised to see an abundance of jellies in the frigid waters of the North Pacific, but lion’s mane jellies are a cold-water species that cannot tolerate warmer water.

Lion’s mane jellies inhabit the open ocean and stay near the surface, usually no more than 65 ft. (20 meters) deep. They can move forward with slow, weak pulses, but they are mostly dependent on wind and currents to move great distances.

Lion’s mane jellies have a one-year life span. The female jelly in the medusa stage carries its fertilized eggs in its tentacles until they grow into larvae. She then deposits the larvae on a hard surface, such as a rock, where they grow into polyps. The polyps reproduce asexually, creating a stack of individuals called ephyrae. Each individual ephyra then buds and breaks away from the stack, developing into the medusa stage.

I never grow tired of watching a beautiful lion’s mane jelly pulsing near the ocean’s surface, often with one or two small fish swimming in its tentacles. This gorgeous creature with its complicated lifecycle is one of nature’s most amazing creations.

My post next week will be about the moon jelly, the most common jelly seen near Kodiak Island. While not as showy as a lion’s mane jelly, it is a fascinating animal that often forms blooms of thousands of individuals.

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There is nothing simple about jellyfish, except the creatures themselves. From their taxonomy to their lifecycles, jellyfish are complicated. When I am out on the boat with our summer guests, I answer many questions about jellyfish, and since I am never 100% certain of my answers, I decided to tackle jellyfish for a blog post. Once and for all, I planned to conquer these gelatinous creatures. The more I read, though, the more confused I became. There are many species of jellyfish, so, of course, lifecycles vary between species and may also vary depending on water temperature and nutrient availability. In this post, I will try to keep things as simple as possible and will describe a generalized jellyfish lifecycle. Keep in mind, though, when it comes to jellyfish lifecycles, there are many exceptions and exceptions to those exceptions.

Our guests ask us: How long can a jellyfish live? What do jellyfish eat? What eats a jellyfish? Why do jellyfish form large groups? How do jellyfish reproduce? Will these jellyfish sting me? Are these jellyfish dangerous?

First of all, most biologists now refer to jellyfish as jellies, because they aren’t fish. This week I will cover basic facts about jellies and tell you about some of the poisonous species. Over the next two weeks, I will discuss two of the most prevalent jelly species in the North Pacific near Kodiak Island.

Let me begin by attempting to explain one of the most complex lifecycles in the animal kingdom. Most species of jellies reproduce by a combination of sexual and asexual reproduction, and their lifecycles include several stages. The jellies you see floating in the ocean are in the adult or medusa stage of their lifecycle. Adults are usually either male or female (not even this is a given with jellies, though), and they release eggs and sperm at incredible rates. When an egg and sperm unite, a larva is produced. Each larva attaches to a hard surface, such as a rock on the ocean bottom. At this point in the lifecycle, the organism is called a polyp.

Polyps have only rarely been seen in the wild, but biologists believe polyps may blanket large expanses of the ocean bottom in some areas. Scientists also think that a jelly may remain in the polyp stage of its lifecycle from days to years or even decades until temperature and food availability are favorable for it to survive as an adult. When conditions are favorable, a polyp elongates and reproduces asexually by budding. These buds develop into young jellies that grow into adults, completing the life cycle. A single polyp may produce a large number of jellies, and a large field of polyps can produce tens of thousands of jellies at a time.

The medusa phase of the jelly may last from a few hours to several months, depending on the species. Most jellies live 2 to 6 months in the medusa stage. The medusa stage is usually the end of a jelly’s lifecycle, but one unusual species, Turritopsis dohrnii, has the ability under certain conditions, to transform from the medusa stage back to the polyp stage, making this species theoretically immortal.


Because polyps bud when conditions are favorable, a large number of medusae may be formed at one time in a particular area. Waves and tidal currents often congregate the medusae in groups of thousands. These groups are called a bloom, a swarm, or a smack. We often see blooms of moon jellies, and when viewed from the deck of our boat, they make a large, white patch in the water that can be seen from quite a distance. When we get closer, we can make out individual medusae in the bloom.

Jellies range in size from a few millimeters in bell height and diameter to nearly two meters in bell height and diameter. The lion’s mane jellyfish (Cyanea capillata) is considered one of the longest animals in the world; its fine, thread-like tentacles may extend to 120 ft. (36.5 meters) in length, although most are much smaller than that.

Medusae are carnivorous and eat plankton, crustaceans, fish eggs, small fish, and other jellies. They use the venom-filled nematocysts on their tentacles to sting and stun their prey, and then they trap the prey in their mucous. Jellies ingest their food and eliminate their waste through the same hole in the center of the bell. Some fish and invertebrate species are immune to the stings of certain jellies and may form symbiotic relationships with them.

One of the questions we are most often asked is what eats a jellyfish? Other jellies are some of the most common predators, but jellies are also food for sea anemones, tuna, shark, swordfish, sea turtles, shore birds, and possibly even salmon. Nevertheless, jellies are not eaten in large numbers, and since many jelly populations have expanded in recent decades, biologists worry that jellies are becoming more dominant in some ecosystems, replacing fish that once thrived in these areas. Jellies can live in areas with low-oxygen levels. In water that has been polluted by agricultural runoff, nutrient levels are high, but oxygen levels are low. These conditions favor jellies over fish that cannot tolerate such low levels of oxygen.

The nematocysts or stinging cells of most jellies are so small they can’t penetrate human skin. Others may cause a slight sting or irritation, but the sting of a few jellies can cause severe pain and in some cases, even death.


The sea wasp box jelly, found in Australia, is considered the deadliest jelly in the world. Since 1954, 5,568 people have died from the sting of this jelly. A sea wasp has 15 tentacles, extending up to ten feet in length. On each tentacle, there are approximately half a million microscopic darts, and each dart is full of venom. One of these darts holds enough venom to kill 60 people. The venom acts very quickly and may cause cardiac arrest in a few minutes. In addition to the venom, the pain of the sting is so intense; it can lead to shock. Some other species of box jellies are also poisonous. One member of the box jelly family, the Irukandji jelly is only 0.2 inches in length, and is nearly transparent, making it almost invisible. Its toxin is 100 times more deadly than that of a cobra’s. The Portuguese Man o’ War is not a jelly but is an organism called a bluebottle. Its sting leaves a welt like a whip mark and may remain painful for days. The venom can cause fever, shock, and may lead to cardiac or pulmonary arrest.

Most jelly stings cause only mild pain similar to a bee sting, so what is the treatment for a jelly sting? Barrier clothing, even something as thin as pantyhose can protect a swimmer or diver. If stung, use a credit card to scrape the affected area to remove remaining nematocysts. A 10% solution of aqueous acetic acid or vinegar may be used to soothe the skin. You can also wash the affected skin with salt water, but do not wash the skin with fresh water, alcohol, ammonia, or urine. These solutions may cause the nematocysts to release more venom.

Over the next two weeks, I’ll write about the two species of jellies we most often see around Kodiak Island. I also want to invite any of my readers who haven’t already done so, to sign up for my monthly Mystery Newsletter. Each month I write about a true crime in Alaska.