Life in the sand pit

On the surface, the sandy beach stretching like a half moon in front of me, looks lifeless. Only the rhythmic pushing and pulling of the water where land and sea meet, provide a bit of motion. On the wet sand a few feet from me, a single Whitefronted plover pair stare at me curiously and the cool wind brings me the sound of kelp gulls. I am the stranger here in this expansive plain of sand. For most of us this is a place of relaxation. A place to walk, build sand castles, to tan, read a book or fish. It is a place to get warm and dry after an ice cold swim in the ocean. Few of us truly understand what really goes on beneath our feet and the interesting ecological habitat the water beneath us offer thousands of animals.

More or less 70% of South Africa's 3000km long coast line, consists of sandy beaches and dunes - dynamic systems changing continuously due to wind, waves and sea currents.  Sandy beach systems comprise a marine wave-driven ecosystem and a terrestrial wind-driven system that together make up the littoral active system – the area in which sand exchange occurs.

Seasonal climate change play an important role in all this. During stormy weather, renown Cape of Storms weather, the sea erodes large parts of the beaches and fore-dunes and deposits the sand as a sandbar offshore. As soon as calmer conditions return, the gentle waves carry the sand  back to the beaches in an unceasingly process of erosion and accretion.

Wave action is the key factor influencing sandy beaches. Strong, high-energy waves cause beaches with coarse sand, while wave action with low energy will lead to beaches with fine, muddy sediments. The grain size of the sand is important, because it influences the sand's capacity to hold water.  Water drains easier out of coarse sand, while fine sand will be inclined to hold the water - this is paramount to the fossorials (digging or burrowing organisms) during ebb.  Animals living in coarse sand are at risk of dehydrating.  On the other hand course sand is well drained and the water in it never becomes stagnant, since there is plenty of air between the grains and water flushes swiftly through the sand, bringing oxygen to the animals living there.  A huge benefit for the sand-living animals is the possibility to dig deeper to wetter, cooler sand to better their living conditions - something animals living on the rocks or in rocky pools cannot do. These animals can therefor decide on which depth they want to live.

Because of wave action, erosion of the beach and immersion in salty water, the beach is a hostile environment for plants, hence beaches usually appear barren, without plant life.  This is why at the West Coast, you'll only find plants growing on the upper beach boundary next to the fore-dunes.  The hardy pioneer species living here, e.g. Sea pumpkin (Arctotheca populifolia) are able to tolerate strong winds, high salt loads and rapid salt movements.  Because no attached plants grow inter-tidally on sandy beaches, and because even microscopic plants such as diatoms occur only in small numbers, there is no grazing herbivores on sandy beaches.  All the animals must depend on plant material and other food being brought into the shore.  Some is blown in from the land, but most of it is introduced by the sea.  Sometimes large amounts of algae and plants are swept up on the beaches after storms. The debris is a main source of food for scavengers.  This is a very unpredictable food-source though, there can be long periods of starvation between periods of  abundance.  A more reliable source of food is the large amount of small organic particles left on the beach by the surf.  Sometimes, in rough conditions, we'll see these particles left as a thick foam, this is a very significant food-source.

The phytoplankton and tiny particles of detritus in the surf zone provide a source of food for zooplankton and large filter-feeders, such as sand mussels.  Some animals such as plough shells and sand hoppers, burrow beneath the surface and then emerge to feed on stranded carrion at low tide.  Living between the sand grains in moist areas are diatoms, fungi, bacteria, protozoa, worms and crustaceans that make a up a complex inter-tidal  food web. 

This important group of organisms is called meiofauna. Although most of them are smaller than 0,5mm, they come in large groups and cover 20-45% of all living bio-mass of African sand beaches.  Where we cannot see between the sand grains, meiofauna form their own intricate food webs of herbivores, carnivores and scavengers.  An ecosystem as advanced and complex as the Serengeti.  The fight for survival is just as severe! 

Sandy beaches not only play a significant role in filtering and purifyiming of large volumes of water,  but also in the breaking down of large amounts of organic materials and the recycling of nutrients back into the larger system.  The process is so efficient that one flush through the sand is enough to break down about 95% of the organic matter present.

Wow! And we are not even touching on all the different adaptations the sand-living animals made to survive the harsh environment.

One is left speechless in the sight of God's omnipotence and omniscience. As you dig deeper into God's creation, your words dry up...

Surf is moving in and out... The wet sand is shiny and then dry again. I smell the sea. I hear the seabirds. But suddenly I am aware of more than just these basics. God's presence is here! He is still actively busy in his creation...

Only thing left for me to do, is to just kneel, right there in the sand... Lord, how majestic is the work of your hands...