The Big Life In Between Grains

Photo from Entouriste

Let's imagine ourselves walking along the shore, adoring this stretch of white sand.

What do you see? Apparently, it's too tricky to tell. 

Only if we find ourselves curious and play with the sand for a bit we'll be able to spot some critters. There could be hermit crabs trotting along, worms making tunnels, and seaweeds washing ashore. Or there could be a seabird waiting for its meal. 

But for the most part, life on the shore seems quiet and empty.

Now, if we change the scenery and make a visit to a busy thriving forest, how would our "lifeless" beach compare?

As anyone who's been in a forest, it's easy to tell the animals are there. We can tell there are cicadas, birds, earthworms, a variety of plants, and fascinating insects we don't know about. We know it's alive from the cacophony of sounds and colors.

In fact, Professor E.O. Wilson remarks that, when we put a cap on all the living terrestrial groups, only seven different phyla exist in the woods [1].

But when we drench our feet in sand and foam, it's a different story...

“The surf may at first seem lifeless, composed of water and soil and washed clean. The opposite is true … among the grains of sand in the surf zone, you will in time find twice the number of phyla." -E.O. Wilson

The beach, in fact, holds 14 different phyla against the seven in the forests. Professor Wilson talks about diversity here, not population in numbers [1].

Who knew that the sand alone hosts an impressive universe of little, wriggling creatures down our feet? 

The Interstitial Breathes

These invisible organisms breathing in between grains are called meiofauna (smaller than 1 mm but larger than about 45 microns), and they comprise as Wilson calls the "little-known planet." 

Purely meiofaunal organisms alone make up five out of the 34 recognized phyla in the animal kingdom. They are literally a thriving empire of organisms—one footprint of moist sand carries as big as 50,000 to 100,000 individuals [2].

These meiofauna—gastrotrichs, kinorhynchs, gnathostomulids, loriciferans,  nematodes, priapulids,  rotifers, tardigrades—are easy to overlook but they're actually there, clinging for life, clad with smart adaptations suitable for a life in the interstitial.

They're small but they boast complex physiology comparable to the relatively huge macrofauna. They have also developed an array of adaptations to their ever-shifting habitats: Tardigrades (water bears) have claws and suction in their toes to grip on grains; kinorhynchs use their spine-bearing mouth to hook into sand or mud; free-living nematodes possess slender bodies, easing in between grains and use thread-like setae to hold on to their substrate; gastrotrichs are known to hang too tight to their substrate with a strong adhesive.

Check out this creative and interactive infographic (Hakai Magazine) of some meiofauna and the challenges they face in their big world [3].

Photo of a gastrotrich (David Scharf/Corbis, Hakai Magazine)

The Beach We Came to Know

Meiofauna bridge important links in benthic food webs. Aside from serving as important food to many organisms, they are key decomposers which feed and break down detritus, thus keeping microbial communities active and enhancing nutrient recycling. Through bioturbation and burrow construction (plus their sheer number) they render stability to our benthic ecosystems and shape them as we have them today [5].

Ultimately, these make them the very life of the beach: without meiofauna, our beach is but a mire of untouched, organic debris [2].

A clear grasp of their number and diversity, though, remains to be seen. Wilson says we haven't even come close to documenting all of them; there's just a lot to learn and new worlds to discover [1]. And new ways of seeing things, too. 

The next time we go the beach and grab a fistful of sand, we know we're not alone—a multitude of organisms keep us company, living their big lives in between grains. 

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If you have more information on meiofauna and other non-fish organisms, we'll be happy to have you as one of SeaLifeBase collaborators. Let us know by sending us an email or visiting our FaceBook page.

[1] Krulwich, R. (2016, March 3). An empty beach isn't empty at all. National Geographic. Retrieved from http://bit.ly/1Umi4SB

[2] Mason, A. (2016, March 21). The micro monsters beneath your beach blanket. Hakai Magazine. Retrieved from http://bit.ly/2vi5aPL

[3] Mason, A., Garrison, M. & Kingdon, A. (2017, April 28). Life interstitial. Hakai Magazine. http://bit.ly/2w5DLxW

[4] Gerlach, S. A. (1978). Food-chain relationships in subtidal silty sand marine sediments and the role of meiofauna in stimulating bacterial productivity. Oecologia, 33(1), 55-69.

[5] Schratzberger, M. & Ingels, J. Meiofauna matters: the roles of meiofauna in benthic ecosystems. Retrieved from https://bit.ly/2KP4hCz