These look like big, orange versions of the yellow nudibranchs known as "sea lemons". We call them sea oranges. I am not good at nudibranch identification but I will guess that it is one of the Dendrodorids. We found it on the urchin barrens, on the west side of Refugio Beach. It was about the size of a golf ball.
It's interesting how everything under water gets named after something above water. We have sea lemons, sea apples, seaweed, sea urchins, and now sea oranges and sea hedgehogs.
Herman Melville wrote in Moby Dick, in the wonderful chapter "Brit":
For though some old naturalists have maintained that all creatures of
the land are of their kind in the sea; and though taking a broad
general view of the thing, this may very well be; yet coming to
specialties, where, for example, does the ocean furnish any fish that
in disposition answers to the sagacious kindness of the dog? The accursed shark alone can in any generic respect be said to bear comparative analogy to him.
The labrador retriever of the sea is definitely the sheephead (which have nothing to do with sheep's heads, so far as I can tell). Sharks seem more like cats: maybe bobcats or cougars. Hermann should have learned to scuba dive.
This beautiful scene from a kelp forest by Jennifer LeMay assisted by Jessie Altstatt was the featured painting at the i Maddonari street-painting festival. That big canvas really gives scope for showing the ocean!
Sea hares are giant, slow-moving, sea-dwelling slugs. They like to inhale lots of seawater to puff themselves up. To deter predators, they release clouds of foul black ink when they feel threatened. They mate in big disorganized clusters and then lay strings of eggs like mad: at times their eggs are all over the place underwater. This one was about 6 inches long, although I've seen much larger. Actually, they sound a lot like the underwater equivalents of rabbits.
Sea apples are short, round sea cucumbers. The frilly stuff is the tongue -- err, feeding apparatus, which they extrude to gather food and then periodically swallow so as to clean off the edibles. I usually think of sea apples as not-particularly-exciting wallpaper on the bottom. They seem to have more interesting structure and color, when seen from close up.
A biologist tells me that this is an isopod, of the genus Idotea. You can see it crawling down the base of the sea apple above.
The invertebrates in this colony look like a field of cyclamen; or more accurately, like a colony of tiny horseshoe worms. The heads are about the size of a pencil eraser. They have very graceful, regular frills: feeding apparatus? I saw these at Goldfish Bowl on Anacapa, although I've also seen identical colonies at Refugio Beach off the mainland.
Recreational fishing in the channel islands has resulted in tiny, undeveloped male sheephead and a lack of big females. Sheephead are naturally territorial; and unlike humans, they all start life as females. The largest fish in a territory becomes male, and enjoys the favors of the resident females. Sheephead have strong jaws and teeth, and are among the few fish that eat urchins, controlling their populations. When a diver enters the territory they swim up to investigate, usually passing a few times. They remind me of labrador retrievers: big, friendly, and not incredibly bright. Spearing a sheephead is as easy as spearing your neighbor's retriever; but it's legal, and a way to gratify our delight in destruction.
Because urchins eat kelp, sheephead are guardians of the kelp, and of
the ecosystem it supports: rockfish, perch, octopi, bryozoans, and so
on. Without sheephead and lobsters, urchins take over. The result is a desert full of starving urchins: the urchin barrens.
So many sheephead have been speared that the male in a territory is often hilariously tiny. His harem consists of even tinier females; small fish don't lay too many eggs, so sheephead are becoming scarce. The big ones in particular are gone. On my first visit to Catalina I remember two divers arguing on the boat back how big the sheephead used to be: "A big as me!" "Heck no, I remember ones as big as volkswagens."
There's no commercial fishing for sheephead, so this destruction was wrought entirely by recreational fishermen: including divers.
This article from the SB Independent describes sciences studies that document the destruction of sheephead:
Juvenile kelp rockfish at Del Mar Cove, Santa Cruz Island. This fish is less than 2 inches long. The skull seems to show through its thin, semitransparent skin, and the fish has a rapt, engaged expression.
On Sunday, 10 May, the visibility was about 20 ft, and the ocean was a chilly 50F off Anacapa. After 30 min at 50 ft, where my 6 mm wetsuit was compressed to 3 mm thickness, my face was stinging and my hands were clumsy. The same high winds that fed the Jesusita Fire have turned the ocean over, bringing cold water laden with nutrients from the deeper ocean up to diveable depths. And the same cool fog that damped the fires made for cool conditions above water and less light below. Nevertheless the dive boats were full, and stacked up next to one another in the Marine Reserve off Anacapa. As we prepared for our 4th dive of the day from the Peace, divers began to drop off the Spectre. The few relaxing atop the Spectre's deckhouse had probably gotten enough May diving for one day.
Before being fitted as a dive boat, the Spectre was an oil platform crew boat, called (I believe) the John Brown. It's been through a number of refits since then, most lately to get less-polluting, more efficient engines.