August 10, 2021 | Margaret Helder

Glass Sponges: Lessons from the Deep

How can a “simple” or “primitive” sponge
surprise engineers with its optimal physics?

 

by Margaret Helder, PhD

It is not every day that one discovers living organisms which were formerly known only as fossils. One such remarkable story took place off the northwest coast of British Columbia (Canada) where some glass sponge reefs were first detected. Canadian scientists mapping the seafloor near Vancouver Island came across some signals suggesting that there were huge, mysterious mounds on the sediments below them. That was 1987. Upon further investigation, the scientists discovered that the mounds were, in fact, reefs made up of glass sponges. The reefs, in 200 meters of water, covered about 1000 square kilometers of sea floor and rose as high as a seven-story building. The really remarkable thing, however, is that these glass sponge reefs had formerly been known only as fossil deposits such as enormous cliffs stretching on land from Portugal to Romania. According to standard geological dating, these reefs are found in rock strata identified as Triassic to Eocene.1 No such reefs were known in the sea today. But here they were, reefs made up of some living creatures and some skeletons of once living specimens.

A spectacular group of Venus flower basket (Euplectella aspergillum) glass sponges with a squat lobster in the middle. Credit: NOAA Okeanos Explorer Program, Gulf of Mexico 2012 Expedition. Public domain.

About sponges

Not only are these reefs remarkable for their living fossil status, but the glass sponges themselves are an astonishing group of organisms, many of which are still extant. They are exclusively marine, solitary creatures living mostly in deep cool oceans. Apparently, a lot more them are known from the fossil record, but today there are still about 500 species or about 7% of the former total diversity of this group.2

The lowest lying reliable sponge remains are silicious spicules from a basal Cambrian formation in Iran.3 These earliest convincing fossil sponge remains appear near the Precambrian-Cambrian boundary, more or less at the onset of the Cambrian explosion.4 As these artifacts are found so far down in the rock record, and are by far the least complicated of animals, scientists consider them to be the most primitive. It really is quite amazing that we are at all interested in the glass sponges. This group, which we might expect to be uninteresting by virtue of their very uncomplicated body plan, is instead beautiful and so spectacularly sophisticated that modern engineers study sponge features in order to improve their own designs.

Curiosities

Basic sponge anatomy.

The sponges (phylum Porifera) are considered to be the most primitive (least complicated) of all animal designs, and the glass sponges (class Hexactinellida) are considered to be the simplest, most primitive design of the sponges. Certainly, all sponges lack features that most animal designs exhibit such as a nervous system (for external perception and internal coordination), a digestive system (for food intake and waste output), and a circulatory system (for gas and nutrient exchange.) What characterizes all sponges is pores through one or two layers of cells into a central common area. Water carrying food particles and oxygen enters this area and leaves, often through a larger opening. These organisms may exhibit several types of cells, but no special tissues or organs. These creatures scarcely sound like promising candidates for such adjectives as beautiful and sophisticated.

Sponges do, however, exhibit supporting material to give their bodies shape. While the other two classes develop skeletons made of calcium salts or hardened proteins, the Hexactinellida exhibit glass spicules which exhibit six-rayed symmetry. These spicules are synthesized by the cell matter. They are then fused together to form the supporting skeleton. Most of these skeletons, ranging from 10 – 30 cm (4-12 inches) tall, are strikingly beautiful. The sponge body often resembles a hollow cucumber or deep cup with a sieve-like covering over a large outflow feature.

Most sponges exhibit two layers of cells with a gelatinous-like layer between them. This interior material contains other types of cells and the skeleton. The glass sponges however are different. They exhibit only a cobweb-like net of cellular material suspended between the silica scaffolding of the skeleton. The living material is called a syncytium because it has only one large external cell membrane with lots of nuclei inside the soupy cell material or cytoplasm.5 There are rivers within the cytoplasm which carry nuclei and other cell organelles around the whole body. Lining the central cavity are smaller chambers with flagella extending from the plasma membrane. The flagella expedite the passage of water to interior surface areas where food particles (bacteria) are engulfed. That more or less covers the body plan of glass sponges. What more can there be to learn from them?

The arrangement of skeletal parts and the whole animal architecture turn out to be engineering marvels. The design choices which the sponges make turn out also to be optimal for many modern engineering assignments.

Learning from the best

Some of the earliest interest in the glass sponge skeleton was in fiber optic capabilities of glass fiber tufts in a species called Venus’ Flower Basket (Euplectella aspergillum).6 These tufts , about 5-18 cm (2-7 inches) long and the approximate thickness of human hair, extend outward from the base of the animal. The longest such spicules, as much as 30 cm (12 inches) are found in the Hyalonema sieboldi glass sponge. Like the entire glass skeleton, these spicules are synthesized by the living tissue. Nobody knows exactly what use the sponge individual has for these long strands, but they exhibit some amazing properties. Where the sponges live, no sunlight penetrates, but there may be other organisms with bioluminescent capacities. Thus, there is the possibility for some sources of light. At any rate only visible white light passes through these biological fibers.7 What we do know is that these sponge fibers are able to function as optical glass fibers with features which are even better than our commercial fiber-optic systems.8

Venus Flower Basket, Credit: Kesari Lab/Brown University

All sponge skeletal elements are formed using the enzymes silicatein and silicase. The discovery of those enzymes holds promise for new commercial manufacturing techniques. For the first time, strategies may be possible to allow for the production of inorganic structures by organic molecules.9 This could be significant for commercial processes. Since the glass sponge models are formed at ambient temperatures, they have the capacity to incorporate extra impurities which improve the signal. Also, because they contain layers of proteinaceous material, they resist cracking.10

The most prominent component of the glass sponge body design is of course the glass skeleton. Since the architecture of the Venus’ Flower Basket (E. aspergillum) is unusual, an American team has experimentally evaluated the tolerance of this design for critical loading and stress. Such studies have revealed “unexpectedly – that the skeletal system of E. aspergillum is very close to this design optimum.”11 Apparently, as far as architects and designers are concerned,

Grid-like open-cell lattices, such as those found in the skeletal system of E. aspergillum, are commonly employed in engineering contexts owing to their reduced weight, high energy absorption and ability to control the propagation of thermal and acoustic waves.12

Closeup of the top of a Venus flower basket sponge (NOAA Library)

To find out why the sponge skeleton has such interesting properties, the Fernandes team set up four different grid designs. Option D was a 2-dimensional square divided into quarters. Option C added cross bracing to each quarter so that each square was divided into four equal triangles. Option B added the cross bracing to only two squares (numbers one and four) of the design, while the other two squares were open. Option A, the most elaborate design, mimics the Venus Flower Basket design. It had double strands of cross bracing in squares one and four, while the others were open. When these designs were tested for load-bearing capacity, design A (like the Venus’ Flower Basket) displayed the best resistance to buckling stress. Having demonstrated the superior resilience of design A, the scientists wondered if they could improve on this glass sponge design. They conducted seven separate optimization experiments. Their studies demonstrated that “the sponge-inspired design provides a superior mechanism for withstanding loads.” 13

As a result of their studies the scientific team concluded that

The results presented here therefore demonstrate that, by intelligently allocating material within a square lattice, it is possible to produce structure with optimal buckling resistance.14

This, of course, is precisely what the sponge with no brain is unable to do, but which an intelligent designer knows how to achieve.

Habitat challenges

It is obvious that the glass sponges live in a habitat which involves special challenges. They mostly grow as solitary individuals or small clumps at depths of 1500-3000 feet (450-900 m). The body is anchored to soft sediments on the sea floor, not the best substrate for maintaining one’s position. The problem is compounded by the average water currents in the first 30 cm or 12 inches above the sea bed. Here the currents move at 0 – 11 cm per second or about 6 m to 20 feet per minute.15 How do these animals survive in this habitat? A team of Italian and American scientists researching this topic declared that the sponges display “exceptional structural properties” which enable them to thrive.  In fact, their study reveals “mechanisms of extraordinary adaptation to live in the abyss.”16 They were able to make these statements because they had carried out experiments on this capability.

Venus Flower Basket on the Davidson Seamount at a depth of 2572 meters. Credit: NOAA/Monterey Bay Aquarium Research Institute. Public domain.

The major problem with glass sponge habitat is the chaotic water currents which threaten to collapse their delicate bodies or wash them away. The scientists therefore compared the sponge body architecture with other similar designs. They compared a solid cylinder, a solid cylinder with spiral ridges on the surface, a hollow cylindrical lattice, and a hollow cylindrical lattice with spiral ridges on the exterior (which resembles the actual sponge body). They subjected each design to the same kind of water currents and evaluated water flow around the structure, behind and inside it (if it was hollow).  The cylindrical lattice exerted a marked stabilizing effect on water currents downstream. Thus, they reported of the sponge-like model:

One of the implications of the presence of this nearly quiescent region downstream of the porous model is a reduced hydrodynamic load. In turn, this will mitigate the bending stress experienced by the skeletal system, thereby further contributing to its exceptional mechanical stability. 17

In the sponge-like model, additionally, the outside ridges drastically contribute to slower and more gentle vortices inside the body, which would enable the animal to better capture rare bacterial cells for food. Overall, the research team declared that

Our computational results reveal a rich multifaceted role of the skeletal motifs for E. aspergillum on the flow physics within and beyond its body cavity.18

All the skillful design choices displayed by this glass sponge, therefore, have important things to teach our best designers of skyscrapers, bridges, ships, planes and anything that must respond safely to forces imposed by the flow of air or water.19

How did a lonely sponge learn all this?

A little reflection shows that the sponges are ill-equipped to develop such finesse on their own. Chance processes like natural selection show zero potential for supplying the information needed for such a profound connection between structure and function. These organisms are not primitive. And their fossil location at the bottom of Cambrian rocks does not record early evolution but rather that they were among the first creatures engulfed by sediments from the global flood. The glass sponges may be uncomplicated in outer body form, but they are the best possible designs for their lifestyle. They represent a beautiful expression of the creation.

References

1. Evolution-based dates of 220 to 40 millions of years (my) respectively.

2. Martin Dohrmann et al. Phylogeny and Evolution of Glass Sponges (Porifera, Hexactinellida). Syst. Biol. 57 (3): pp. 388-405. See p. 388.

3. Jonathan B. Antcliffe, Richard H. T. Callow, Martin D. Brasier. 2014. Giving the early fossil record of sponges a squeeze. Biological Reviews 89 (4): 972-1004. See p. 972.

4. The sudden appearance of many animal body plans is called the Cambrian explosion. It is dated at about 535 my according to evolutionary reckoning.

5. Cells in most organisms have one nucleus and a plasma membrane enclosing the nucleus and small amount of surrounding cytoplasm.

6. The common name has been adopted in honor of the fact that a mated pair of shrimp are often permanently trapped within these sponge bodies. The Japanese venerate such artifacts as symbols of constant marital bliss.

7. Werner E. G. Muller et al. Novel photoreception system in sponges?: Unique transmission properties of the stalk spicules from the hexactinellid Hyalonema sieboldi.  Biosensors and Bioelectronics. 21 (7):1149-1155. See p. 1149.

8. Vikram C. Sundar et al. Fibre-optical features of a glass sponge. Nature 424 p.899.

9. E. G. Muller et al. 2007. The unique skeleton of silicious sponges (Porifera: Hexactinellida and Desmospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review. Biogeosciences 4 pp. 219-232. See p. 219.

10. Sundar et al. 899.

11. Matheus C. Fernandes et al. Mechanically robust lattices inspired by deep-sea glass sponges. Nature Materials 20 pp. 237-241. See p. 237.

12. Fernandes et al. 237.

13. Fernandes et al.   240 .

14. Fernandes et al.   240 .

15. Giacomo Falcucci et al. Extreme flow simulations reveal skeletal adaptations of deep-sea sponges. Nature 595 (7868) pp. 537-541. See p. 537.

16. Falcucci et al. 537.

17. Falcucci et al. 539.

18. Falcucci et al. 541.

19. Tor Vergata. 2021. Glass sponges reveal important properties for the design of ships, skyscrapers and planes of the future. Phys.Org July 21 pp. 3.


Margaret Helder completed her education with a Ph.D. in Botany from Western University in London, Ontario (Canada). She was hired as Assistant Professor in Biosciences at Brock University in St. Catharines, Ontario. Coming to Alberta in 1977, Dr Helder was an expert witness for the State of Arkansas, December 1981, during the creation/evolution ‘balanced treatment’ trial. She served as member of the editorial board of Occasional Papers of the Baraminology Study Group in 2001. She also lectured once or twice a year (upon invitation) in scheduled classes at University of Alberta (St. Joseph’s College) from 1998-2012. Her technical publications include articles in the Canadian Journal of Botany, chapter 19 in Recent Advances in Aquatic Mycology (E. B. Gareth Jones. Editor. 1976), and most recently she authored No Christian Silence on Science (2016) which promotes critical evaluation of scientific claims. She is married to John Helder and they have six adult children.

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