Dominance of the spineless

 kw: book reviews, nonfiction, science, oceanography, biology, invertebrates, medicine

Behold a gallery of sponge animals. They headline The Ocean's Menagerie: How Earth's Strangest Creatures Reshape the Rules of Life by Drew Harvell.

Considering the matter for a moment, I concluded that the word "reshape" in the title ought to be "reveal." I suppose the publisher thought the title as it is makes better clickbait.

The thousands (almost 10,000 so far) species of sponge comprise the phylum Porifera. Their shapes and sizes are so variable, that pores are the only consistent feature. Brainless, apparently without nervous systems, they are remarkably successful predators. Most consume plankton (little floating things), but some grow over and consume coral animals, and some have inner chambers with other critters such as shrimp living inside. The shrimp gets a safe home, and the sponge eats the leftovers the shrimp drops. Being stationary, sponges need good defenses against predation and against diseases caused by bacteria, fungi and viruses. Dr. Harvell tells us that they have the most multifarious immune system of all animals. Her particular interest is figuring out how their various chemical defenses work, and which ones might lead to medical advances for humans. She writes, "…I call the capability to produce potent biologically active chemicals a sponge superpower." Sponge research is likely to lead to either better antibiotics, or to new alternatives to antibiotics, for example.

This image shows several corals along with a variety of sea anemones, which are related to corals. Both are members of the phylum Cnidaria, which also includes jellyfish (called "jellies" by scientists because they most definitely aren't fish). The phylum contains more than 11,000 species. Though they are  brainless, they have simple nervous systems that coordinate their movements.

The basic body plan is a radially-symmetric, columnar tube with only one opening (a combined mouth-anus) surrounded by stinging tentacles. Sea anemones are larger and solitary, while corals are colonial and build skeletons; the stony corals build mineral skeletons that form the backbones of reefs.

Stony corals are the subject of the second chapter (of 8). They are considered a "canary in the coal mine" related to ocean acidification. Later in the book we find that the pH of the ocean is presently very near 8.0; elsewhere I read values ranging to 8.05. A century ago ocean pH was about 8.15

Sidebar on pH: It is a logarithm, the negative logarithm of hydrogen ion concentration in water. Pure, distilled water has pH of 7, which means that the concentration is 10^-7, or one ten-millionth, or one hydrogen ion per ten million molecules of water (pH=7 is called "Neutral"). Thus a pH of 8 means one hundred-millionth. Putting these on a linear scale, adjusted with 1 meaning one per billion (pH=9) and 10 meaning pH=8, pH=8.05 converts to 8.9 and pH=8.15 converts to 7.08. Dividing the linear values, 8.15/7.08 = 1.15, which means that "acidity" is 15% greater at pH=8.05. Both these values are slightly alkaline, one more than the other.

What does 15% extra acidity mean to a coral (or any other ocean creature that uses calcite for its skeleton or shell)? Acid dissolves calcite, which doesn't dissolve when pH is 7 or larger. Acids have lower pH. For example, the pH of orange juice is about 4, and lemon juice pH is less than 3 (sour! You can taste pH). In sum, getting calcite to precipitate out of sea water is easier, and takes less chemical energy, when the water is a little alkaline. It takes a coral more energy to form its calcite skeleton at pH=8.05, compared to 8.15. Do note that fears of "shells dissolving" in the oceans any time in the near future are groundless. However, corals and shelled animals are having a little harder time forming their skeletons and shells.

On to Chapter 3, about sea fans and other gorgonians. These are also in the phylum Cnidaria, and are often called "soft corals" because they don't form rocky skeletons, using chiton or similar biopolymers instead. The word "gorgonian" refers to the Gorgon of mythology, who had snakes instead of hair on her head. An early biologist thought that these animals looked a little like that.

Collecting part of one of these is easier than collecting a stony coral: you don't need a hammer and chisel! And collecting is what the author did, of many of these creatures. Soft corals have immune defenses nearly as potent and various as sponges do, plus stinging cells like other cnidarians. Usually, the stinging cells, or nematocysts, not only immobilize prey, they also fend off most predators. Most. That word introduces the fourth chapter.

The term "sea slug" is rather ugly, because most of us know slugs in the garden as voracious pests, with slippery grayish bodies that offend most folks. I like the term "Nudibranch" better; it means "naked gills". As this illustration shows, these oceangoing mollusks are often beautiful. Being mollusks, they are members of the second largest phylum, Mollusca, with at least 100,000 species, and perhaps a million or more—we know so little about the ocean… Mollusks have a pass-through body, with both mouth and anus, plus a brain and nervous system. 

Nudibranchs' bright colors warn of a darker side to them. Many are venomous, but not in the way a snake or spider is. Many nudibranchs eat corals and other cnidarians, and they have an astounding biochemical trick: they can capture the nematocysts of their prey without setting them off and incorporate them into their own frilly tissues. Brushing up against one is like encountering a jellyfish and can sometimes be life-threatening.

The giant clam, subject of Chapter 5, is a quite different kind of mollusk, with a different superpower. They channel light and even shift its color, to "feed" symbiotic algae that provide much of the clam's nourishment.

The bright colors of their mantles are a combination of filtered light and fluorescence. Ultraviolet and violet-blue light in particular are useless for inducing photosynthesis. Fluorescent chemicals convert some of these "blue and ultra-blue" colors to colors the algae can use. In addition, the algae are arranged in small physical structures that stack them in ways that increase their overall efficiency. We have a lot to learn from clams! On a side note, we learn that these big clams cannot close their shell all the way. Old rumors about divers being trapped by giant clams are bunk.

One more group of mollusks fills Chapter 6. The skin of an octopus is possibly the most complex organ in the animal kingdom. This image shows an octopus most of the way through a rapid transition into looking like a lumpy rock. A careful look will reveal an eye, and further down, a few of the suckers that haven't yet been tucked under.

Octopuses, cuttlefish, and squids can change color, not just wholesale, but in patterns. The first two can also raise lumps, bumps and spikes in their skin to produce all kinds of shapes. A moment before this photo was taken, the octopus had smooth orange-red skin. It changed so fast that it seemed to vanish before the diver's eyes. Single frames from the video showed that the entire transformation took about a quarter second (7 or 8 frames in a 30-fps video). Great numbers of tiny muscles surround chromatocytes (color organs the size of a poppy seed) and sections of skin (to shift from flat to bumpy or spiky), under direct nerve control. Perhaps that is why an octopus or cuttlefish has nine brains. Lots of logistics going on!

Back to Cnidaria for Chapter 7: Jellies and their light shows. I have only seen these animals at the surface. On a couple of occasions my friends and I pulled dozens of 2-foot-wide jellies out of the surf at Huntington Beach in California, to make swimming safer. If you dive at night, you are more likely to see the light show. Not only jellies, but many other soft-bodies sea critters make their own light, or have captured special bacteria that do it for them. This amazing medusa has several colors of bioluminescence. It was photographed by its own light.

How poor is our land-borne experience! We have only fireflies and glowworms (certain female fireflies) and a number of other beetles to light up an evening, and a few species of glowing mushrooms. In the ocean, 90% of species produce light. Naturally, scientists are scurrying to learn their secrets. One is very useful already: green fluorescent protein (GFP), derived from a jelly. DNA to produce it is easy to splice into various parts of other animals' genomes, producing mice that glow green, or small fish with certain organs that glow with varying brightness as metabolism waxes and wanes.

Another phylum shows up in the last chapter, Echinodermata, the "spiny skins". Sea stars (colloquially, starfish) are not quite radially symmetric, as the Cnidaria are. There is a respiratory port off-center on top, making them bilaterally symmetrical, just barely.

This gallery shows 13 species of sea star, and three related echinoderms. The phylum contains more than 7,500 species so far known, while we have fossils of 13,000 extinct species. All are predatory.

This chapter focuses first on an experiment in removing sea stars from a section of seacoast. The area became overrun by mussels, which grew to the size of footballs. Where sea stars were present, there were still lots of mussels, but also areas where many other animals could settle, which greatly increased biodiversity.

More recently, there was a "starfish pandemic", and nearly all the common ochre stars along the west coast of the US and into Canada died, plus just as many "sun stars", a deep-water species with 24 arms. Over time, natural selection did its work and the numbers of ochre stars began to recover, but not, at the date of writing, the sun stars. The author and others are doing captive breeding to develop a resistant variety of sun star, in hopes of repopulating the deep coastal plain. Why, you might ask? Sun stars prey on sea urchins. If unchecked, sea urchins eat all the kelp. Kelp forests protect many species of fish and other pelagic (midwater) animals, including commercial species. Sun stars in deeper water and ochre stars in tidal areas are keystone predators: their presence controls the biodiversity of entire areas.

Throughout the book the author complains of the effects of climatic warming and ocean acidification that are based on increasing carbon dioxide in the atmosphere. In the ocean areas she frequents, the effects are visible. She calls it a Gut Punch. Her Epilogue is a long plea for more rational approaches to management of the ocean. While I agree with her on one level, I find it sad that we, as a species, find the need to "manage" 3/4 of the planet's surface. What we really need is to manage ourselves, but the lesson of the Bible, along with most other religious texts, is that humans excel at mismanagement, and any god you may imagine has a hard time keeping us in check. 

For context: The God of the Bible spent two millennia dealing with one family, the descendants of Abraham, to finally rid them of their tendency toward idolatry. He has spent the two millennia since then dealing with the spiritual descendants of Abraham, that is, the Christians, and has yet to rid them (us) of their (our) tendency to divide (there are more than 40,000 "denominations"), primarily over opinions, which are our modern idols. Mismanagement of the human soul is the source of mismanagement of planet Earth. This is why we need a Savior.