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Friday, December 30, 2016

Sea Creatures Part 2—Intertidal Life

“They’re microhabitats for small marine organisms, mainly invertebrates. This one is Pisaster ochraceous, or more commonly known as a purple sea star. These poor guys were almost entirely wiped out nearly 200 years ago by a disease that caused their arms to basically rot away from them.”
Dylan Baker, Oceania: The Underwater City

This post is a continuation of my three-part special on the sea creatures featured in Oceania: The Underwater City. If you haven’t read the first part, you can read it here.

Intertidal Life

Bat Star
By Jerry Kirkhart from Los Osos, Calif. (Bat Star (Asterina miniata)) [CC BY 2.0 (], via Wikimedia Commons

The bat star (Patiria miniata) is an echinoderm, a type of invertebrate. Their common name derives from the webbing between their arms that make them resemble bats. They can grow to 20cm (8in) in diameter and have five to nine arms. They live from Alaska all the way to Baja California in depths up to 290m (951ft)(1). At low tide, they can be found hiding under rocks, in crevices, or among surfgrass(2). Sporting a wide range of solid and mottled colors that include brown, green, purple, orange, red, and yellow(1), the most common coloration is red-orange or mottled white. Their diet consists of dead animals and plants as well as mollusks. At times several bat stars may consume a decaying animal(2).They feed by engulfing and liquefying their prey through digestive juices which then can be sucked up like a drink. At the end of each arm are sensors sensitive to light that can be used to detect prey(1).

To see a photo of a bat star from the Monterey Bay Aquarium, click here

Starburst Anemone
By Brocken Inaglory - Photograped by Brocken Inaglory in Northern California, GFDL,

The starburst anemone (Anthopleura sola) is an anemone that can grow up to 25cm (10in) in diameter. They range from central California to Mexico. Their habitat is in the intertidal zone where they can be found on rocks, in crevices, or in tidepools(3). The colors of the anemone vary from a green color to a white one. Symbiotic algae contribute to the green color of anemones—the more algae, the greener they are(5). Carnivorous in nature, they eat invertebrates like copepods, isopods, amphipods, and other small animals(4). When buried in sand, this species of anemone can survive for around three months by metabolizing its own body. Unlike its sister species, Anthopleura elegantissima, they are solitary and do not clone themselves(3).

They have special tentacles called acrorhagi that they use to attack encroachers to their territory. The acrorhagi have nematocysts (or stinging cells) on the end of the tentacles that can be used to harm the invader. The stinging cell with come off and continue to sting the enemy repeatedly until one of them concedes defeat(5).

One of my sources for this blog post has some beautiful photographs of this species. Click here if you want to see them. You'll have to scroll halfway down the page before they show up.

Gooseneck Barnacle
By USFWS - Pacific Region (pollicipes_polymerus) [CC BY 2.0 (], via Wikimedia Commons

The gooseneck barnacle (Pollicipes polymerus) is another species with the range from Alaska to Baja California. They grow upward on stalks that can reach 8cm (3in) high and are surrounded by shell plates and scales. Due to their outer protective build, they are well adjusted to fight desiccation. They live in the middle intertidal zone just like the starburst anemone. Aggregating in clusters, often around the California mussel (Mytilus californianus)(6), they grow so densely together that sometimes individuals grow on top of one another(7). They are filter feeders, consuming detritus by opening up their shell to use cirri (like feeding legs) to catch the detritus floating by in the water. Their diet consists of plankton, larvae, amphipods and more. Birds, sea stars, and snails prey upon the gooseneck barnacle(7). Slow growers, they can live for 20 years(6).

California Mussel
By Sharon Mollerus (California Mussels  Uploaded by JoJan) [CC BY 2.0 (], via Wikimedia Commons

The California mussel (Mytilus californianus) is a numerous species all up and down rocky shores of the Pacific coast of America from Alaska to Baja California(8). They have shells with a bluish-purple and black shell tipped with white (if the shell has eroded there) and can seldom be found as deep as 24m(79ft)(9). Inhabiting the high tide zone, they are susceptible to desiccation. They grow in tight clumps and dominate the area in which they choose to settle. Sea star predation helps to keep their numbers in check(10). They grow to 13cm (5in) and dine on detritus and plankton. To feed, they open their shells to stretch out their cilia, which they fan to draw in small particles of food. To keep themselves from being washed away by the incoming tide, the mussels attach themselves to rock (or any sturdy surface) with byssal threads. Byssal threads are a sticky glue-like substance that they secrete and hardens when exposed to sea water. A mussel can move its location by severing old byssal threads and shifting to a new spot. Crabs, lobsters, and sea stars are their predators(8).

Ochre sea star
By Jerry Kirkhart from Los Osos, Calif. [CC BY 2.0 (], via Wikimedia Commons

The ochre sea star (Pisaster ochraceus) is also known as the purple sea star. Even though they are known as the “purple” sea star, they can also be orange, yellow, brown, or have a reddish tint(11). They have 4-7 arms and grow from 25-45cm (4-11in) in length(13). Like many other creatures in this post, they are found from Alaska to Baja California and can live as deep as 90m (295ft). Although they can live up to 20 years in the wild, they are predated upon by sea otters and seagulls and are susceptible to the seastar wasting disease (11)(13). P. ochraceus is considered a keystone species, which means that their presence is crucial to the overall health of the ecosystem(13).

Mussels, barnacles, limpets, snails, and chitons make up their diet. To feed on the shelled organisms, they invert their stomachs and insert them into the shells to feed. They eat so many mussels that they actually limit them from living in lower tide zones(11). Their mouth is located on the bottom (oral) side with their anus on the top (aboral) side. Tube-like feet are used for locomotion. They don’t have muscles, but instead a water-vascular system moves their limbs in a hydraulic pressure system(12). They also have no brain, only a nerve ring that along with radial nerves comprises the nervous system(13).

Plant Life
By Peter D. Tillman (Own work) [GFDL ( or CC BY 3.0 (], via Wikimedia Commons

Surfgrass or (Phyllospadix torreyi) is not a type of algae, but an angiosperm, meaning that they have true roots, leaves, and stems. Each leaf blade is about 2mm (0.07in) wide and can be as long as 3m (10ft). They inhabit the mid to low tidepools from British Columbia down to Baja California. Surfgrass are marine primary producers, making them food for many different species. They also harbor species like the spiny lobster. Not quite a keystone species, they do have many benefits including helping to prevent erosion by stabilizing the ground and improving water clarity. They are vulnerable to desiccation during low tides and also don’t do well with pollution. Coastal development is one of the only threats to this species(14).

You’ve reached the end of the blog post for this week. Stay tuned (or subscribe to the blog) to be notified of next week’s post, which will feature the conclusion of this three-part special—the creatures of the deep-sea.

References and Further Reading

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