Purple Sea Star (Pisaster ochraceus)

One thing I absolutely loved to do as a kid was wander around rocky shores, looking for any form of life. I’d lift up whatever rocks I could to search for crabs, I’d run from tidal pool to tidal pool to peer at starfish and sea anemones. I love living in Ontario, but one thing I desperately miss is the ocean. So today I’m going to going to write about a species of sea star, to fully embrace my nostalgic mood.

Probably the most common starfish I encountered as a child were large purple ones. Unsurprisingly, these are known as purple sea stars, but confusingly are also known as ocher sea stars, since not all of them are purple. They can also be orange, yellow, red or brown. That being said, most of these guys are purple, so I’ll refer to them as purple sea stars. They have five legs, each of which can be from 10 to 25 cm long. Purple sea stars are covered in very small spines, which are no bigger than 2 mm in height.

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An example of some colour variants in purple sea stars. Image credit: D. Gordon E. Robertson

Purple sea stars live in the Pacific Ocean, from Alaska to California. Depthwise, they can be found from 90 m to the low-tide zone. They are commonly found along the coast, on mussel beds and rocky shores. Special suckers on their feet allow purple sea stars to cling to rocks with great force, so they can withstand violent waves.

Despite their harmless looks, purple sea stars are quite vicious eaters. They feed mainly on mussels, but will also eat chitons, limpets, snails, barnacles, and sea urchins. They will swallow their prey whole if they can, grabbing their meal with their tubular feet and then everting their stomach onto their prey. The digestive enzymes in the starfish’s stomachs will then liquify the victim, so it can be easily ingested.

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A purple sea star. Image credit: D. Gordon E. Robertson via Wikipedia

Mussels try and defend against starfish by clamping their shells together very tightly, but sea stars are patient hunters. Mussels need to open their shells slightly, both to breathe and to feed. The starfish then use their strong feet to pull the mussel shell further open, and insert part of their stomach into the shell, digesting the poor mussel inside. Purple sea stars have quite large appetites, with one sea star being able to eat eighty Californian mussels a year (a California mussel can reach lengths of 20 cm, so they aren’t small).

Purple sea stars breeding from May to July, with both sexes releasing gametes into the water. If all goes well, sperm and eggs meet in the ocean,  and the fertilized eggs can drift around until they hatch. Sea stars progress through a number of larval stages, and at this stage of their life the little starfish are filter feeders, relying on plankton to sustain them. Purple sea stars live to be at least four years of age, and may live much longer.

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I decided to try something a bit more abstract for this week’s drawing. I had fun with all the shapes!

Purple sea stars aren’t just pretty; they are an extremely important species. Thanks to their diet, purple sea stars help keep mussel populations under control. A loss of only a few purple sea stars leads to a drastic increase in mussel populations. When sea stars are present, the intertidal ecosystem is diverse, instead of becoming dominated by mussels. So next time you see a sea star, remember that they help keep our oceans wonderfully diverse!

Cover image source

Mudskipper (subfamily Oxudercinae)

I can’t believe I haven’t blogged about mudskippers yet. They are such a unique and weird group of fish that they definitely deserve a spot on this blog. After all, any fish that skips around on land without a care in the world is worth writing about.

There are about 41 species of mudskipper, in the subfamily Oxudercinae. They are found in coastal areas of Africa and the Indo-Pacific. Thanks to their ability to do well out of water, mudskippers are able to thrive in changing habitats, such as mangrove forests and intertidal areas. They can be found in freshwater, saltwater, or brackish water, depending on the species.

Mudskippers vary in size from 7 cm to 25 cm, again, depending on the species. As their name suggests, mudskippers are often found in muddy areas. To help camouflage themselves in these habitats, they are often a simple brown colour. Their eyes are located  at the top of their heads, which allows mudskippers to see both above and below water at once. The eyes can move independently of one another, giving the fish a broad field of vision.

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Two mudskippers hanging out, enjoying their time on land. Image credit: Bjorn Christian Torrissen via Wikipedia

As you can imagine, mudskippers have to have a number of adaptations to make their lifestyle viable. One of the most notable of these are mudskippers’ pectoral fins. These fins are long and have a kind of ‘joint’ in them, which allows the fins to act like legs. Very muscular tails also help mudskippers move on land; using their tails to propel themselves, mudskippers can ‘skip’, launching themselves up to 60 cm.

The second set of adaptations mudskippers possess have to do with breathing. Like amphibians, mudskippers can breathe through their skin, as well as through the lining of their mouths. This type of breathing only works when the skin and mouth are wet, which means mudskippers can’t survive in non-humid environments. When mudskippers leave water for land, they fill their gill chambers with water, which gives them an extra source of oxygen while on land.

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A slightly prettier species of mudskipper. It’s still well camouflaged though! Image credit: Bjørn Christian Tørrissen via Wikipedia

Mudskippers dig burrows while they are on land, to keep themselves safe from predators, to thermoregulate, and for reproductive purposes. The burrows are dug so at least part of them is submerged, but often this water has very low oxygen concentrations. Mudskippers work around this by gulping oxygen and releasing it into the burrow.

Male mudskippers display to attract females, using a combination of manly push-ups and acrobatic leaps into the  air. If a female mudskipper is impressed by a male’s antics, she will waltz back to his burrow, and the two will mate. The female then lays her eggs on the roof of the burrow, and leaves. Male mudskippers are responsible for guarding and aerating the eggs.

It never ceases to amaze me how adaptable animals are. Fish that spend a significant portion of their time out of water have got to be some of the coolest animals around. I’m a big fan of them, anyway.

Cover image credit: H. Krisp via Wikipedia

Sally Lightfoot Crab (Grapsus grapsus)

Most of the time when animals have funny names, it’s the common name of the animal that brings us amusement. The scientific names of animals are generally pretty boring and unintelligible. Today’s animal, the sally lightfoot crab, is an exception to this rule. Or so I thought it was. I originally read the animal’s name as “Graspus graspus” which would be a great name for a crab. About halfway through this post, I realized I had misread the name, and it is the far more boring “Grapsus grapsus”. After some quick research, I believe that grapsus comes from the Greek for crab, which means the sally lightfoot crab’s actual name means “crab crab”. So I guess it’s a little funny, but not exactly what I originally wanted.

My rambling aside, let’s talk about the actual animal! Sally lightfoot crabs are found in coastal areas in North and South America, and on islands from the Caribbean to the Galapagos. They like warmer areas, living in tropical and subtropical waters. The crabs will live in any areas with rocky shores, and usually stay at or above the spray line (the area above high tide that is usually not submerged in water).

These crabs are not particularly large, reaching between 5 to 8 cm in shell width. They are quite pretty crabs, being either bright red or yellow with fun black or green markings. Their feet are a nice cheery yellow and their claws are usually red. Young crabs are dark and blend in with the surrounding rocks.

Reproduction in sally lightfoot crabs occurs year round, with egg hatching occurring during full moons. Males compete for females by facing off with other males and doing a little “dance”. The crabs hold hands, then step left and right, presumably sizing each other up. If neither crab backs off, they will start fighting, which involves the crabs trying to break each others claws off. Sounds pretty nasty to me. Once males have won the right to mate, they deposit their sperm into females, who use what they need to fertilize their eggs and store the rest for later use.

Once their eggs are laid, females carry them on their bellies until the little crabs are ready to hatch. When the eggs are ready, female Lightfoot crabs helps them hatch by rubbing the eggs between their bodies and rough surfaces. The larvae hatch into the ocean where they swim out to deeper waters and begin to develop. Once they start looking like a crab, the young lightfoots make their way to the intertidal zone and start their adult lives. While they are still young, juvenile crabs tend to live in groups, while adult crabs are generally solitary.

Some young sally lightfoot crabs hanging out together.  Image source: Wikipedia

Some young sally lightfoot crabs hanging out together.
Image source: Wikipedia

Sally lightfoot crabs eat a wide variety of food, including sponges, molluscs, crustaceans, and small vertebrates. They have very strong feet which allow them to wander along the waterline looking for food without being washed away. These crabs have also been known to eat ticks off of live marine iguanas, helping the big reptiles be rid of parasites.

Although they weren’t named as wonderfully as I thought they were, I’m actually pretty impressed with sally lightfoot crabs. They are a pretty neat species.

Cover image source: Wikipedia