For the final episode in my series on Beach Eggs, we’ll look at some quite unusual ones. First, a couple of echinoderms and sea anemones, and finally my favorite… a marine worm! How does life begin for an echinoderm, a spiny sea critter like a sea star, aka starfish? The top photo shows a “broadcast spawner,” in this case a Striped Sun Star (Solaster stimpsoni) releasing reproductive cells from its arms one June morning. I was not on a beach, but cleaning tanks at the Port Townsend Marine Science Center (PTMSC). All of the volunteers noticed that this gorgeous Striped Sun Star had suddenly begun doing what most sea star species do— broadcast spawn. The females release eggs and the males release sperm at just about the same time. Fertilized eggs divide and the embryos join the rest of the floating plankton in the sea. (Please note: you may need to scroll up and down, even refresh the web page, to view these photos.)
Six-armed Star (genus Leptasterias)
The Six-armed Star is an exception. Unlike most sea stars, it’s not a broadcast spawner. This is a very common sea star on our local beaches, but it’s usually overlooked since it’s so small, usually less than 2” across, and is perfectly camouflaged clinging to grayish boulders in the shade. One spring morning about ten years ago, we PTMSC volunteers were in awe of this mother Six-armed Star protecting her dozens of asterisk-sized babies on the side of an aquarium. I’ve only seen this twice.
Wikipedia quotes from a doctoral dissertation: “Once in contact with the sperm, the female then takes the eggs with her tube feet and forms a brood pouch by arching her arms to provide a protective space to place her eggs… Leptasterias do not go through a larval stage. Instead, the embryos develop and leave the mother after the first three pairs of tube feet have appeared.” I recently read in The New York Times about a biologist at the Smithsonian, Dr. Christopher Mah, who identified a new Antarctic sea star species. He explained that it’s unlike most broadcast spawning sea stars, “which reproduce by shooting their eggs and sperm into the water and leave their young to fend for themselves. But the habit of holding onto offspring — brooding — has evolved multiple times and is especially common in Antarctic waters.” It also happens here in the Salish Sea!
The Purple Sea Urchin (Strongylocentrotus purpuratus) is a very spiny echinoderm that is a broadcast spawner. Since the cloud of microscopic sperm is white, apparently he is a male sea urchin, as the females’ eggs are pale yellow. I’ve never found a Purple Sea Urchin in Port Townsend, but they are ubiquitous at Salt Creek County Park in Clallam County, where I photographed this one. For a fun, short video of the anatomy and life cycle of the Purple Sea Urchin, here’s Scientific American’s “Weirder Than Science Fiction:” https://blogs.scientificamerican.com/observations/weirder-than-science-fiction-how-sea-urchins-reproduce/
Painted Anemone (Urticina grebelnyi)
Here’s my last photo that was not taken on a beach, as this would be extremely rare to observe from a beach. Also in a tank at the PTMSC, this Painted Anemone (Urticina grebelnyi) was broadcast spawning on a March morning, the tiny cells floating past its pastel pink tentacles. Most sea star and anemone species are broadcast spawners, and once egg meets sperm, the little ones must attempt to survive on their own in a sea that’s filled with predators. The Painted Anemone is often mottled red and green, so it is also known as the Christmas Anemone. In case you have an out-of-date field guide, note its correct scientific name is Urticina grebelnyi.
Proliferating Anemone (Epiactis prolifera)
Just like our local Six-armed Star, this Proliferating Anemone (Epiactis prolifera) is not a broadcast spawner. Here you don’t see eggs, but about a dozen tiny, round baby anemones sticking to the safety of their parent’s side. This anemone was protecting its offspring right here in the Salish Sea, by a beach along Indian Island. Not only does the Proliferating Anemone reproduce in an unusual manner, its entire life cycle is unusual. I haven’t found a video to share, but every individual starts out as a female, and later develops testes and becomes a hermaphrodite. In Part 1 of this series, you can see the eggs of some nudibranchs, and a note that most nudibranchs are also hermaphrodites.
Banner Sea-nymph (Nereis vexillosa)
I think the most amazing huge spawning event is that of the marine worm, the Banner Sea-nymph (Nereis vexillosa), also called the Pile Worm. The Banner Sea-nymph, with iridescent pastel colors, is quite beautiful, and large— up to eleven inches long. Spawning occurs at a precise moment— near midnight, at high tide, with a new moon, and after what Andy Lamb calls a “nuptial dance” with a male. Then this polychaete (“many bristles”) marine worm releases her eggs along with part of her own body and a substance that agglutinates in the seawater. In his classic reference book, Marine Life of the Pacific Northwest, Andy Lamb writes, “The doomed female and the fertilized egg mass then sink to the bottom, where the gelatinous unit gradually swells to the size of a chicken egg.” Is this not a unique life cycle?
Banner Sea-nymph (Nereis vexillosa) eggs
Tides can wash these egg masses to shore, and I found thousands of them spread out by Pt. Hudson after the new moon in March. They looked like, hmmm, maybe flattened sausage patties. I wrote to Leslie Harris, Polychaete Collection Manager at the Natural History Museum of Los Angeles County, because she has identified many marine worms for me on iNaturalist. I asked her why I couldn’t find any Banner Sea-nymphs themselves on the beach among so many eggs, and why Port Townsend’s omnivorous gulls and crows weren’t eating these eggs. She explained that this worm has a life span of about two years, then they spawn, and die. She said the dead worms themselves would be a feast for birds, crabs, fish, etc., but there’s “probably some sort of nasty chemical in the mucus or the eggs which deters predation.” I’ve already marked my calendar for the new moon on March 30, 2025, and plan to walk along that same beach during the low tide.