A balance in the various ecosystems around the world is what is vital for a sustainable and healthy planet
Sandy beaches may at first seem barren and devoid of life but that’s because most life elements are hiding beneath the sand only becoming active at high tide or at night.
Characterised by instability, sandy beaches are constantly changing as sand is continually lifted and shifted by the action of waves and wind. Flora and fauna have had to adapt to this incessant instability and constant change in order to survive. Most seaweed cannot grow in beachy areas as there is nothing to attachment themselves to. However, beyond the beach, in the dunes, a vast number of plants thrive. Animal life on the sandy shore is limited to birds and extremely small species such as worms and crustaceans, which live in the spaces between the sand grains. Somer bigger species such as plough snails and crabs burrow and into the sand following the rhythms of the rising and falling tide. The food web is very much dependent upon plankton, seaweed and other edible food items which are deposited on the beach by wave action.
White steenbras (Lithognathus lithognathus), three spot swimming crabs (Portunus sanguinolentus), cuttlefish, lesser guitarfish (Acroteriobatus annulatus) and eagle rays (Pteromylaeus bovinus) cruise over the sand feeding on plough snails (Bullia digitalis), sand mussels (Donax serra) and sand prawns (Callichirus kraussi)
A variety of bird species such as there White-fronted plover (Charadrius marginatus), Damara tern (Sternula balaenarum), Kelp gull (Larus dominicanus) probe the exposed beach for crustaceans, bivalves, molluscs and other animal and planet matter.
Rocky shores are characterised by the life that lives in the intertidal zone – the area between the high tide and low tide water mark. Exposure to surf and sun differs considerably, relative to the rise and fall of the tide. Marine flora and fauna which occupy the rocky shores need to be extremely hardy and easily adaptable in order to survive.
Plants and animals need to deal with very strong wave action, avoid predation and adapt to changing currents. Filter feeding organisms such as black mussels (Choromytilus meridionalis), oysters (Striostrea margaritacea) and barnacles thrive during high tide as the wave action brings nutrient rich water.
Adaptations are vital for the survival of plants and animals which find themselves exposed and in direct sunlight during low tide. Certain seaweeds such as sea lettuce (Ulva lactuca) can tolerate very harsh conditions by surrounding themselves with a mucous layer. Crabs (Cancer productus), snails (Bullia digitalis) and bivalves (Perna perna) have thick shells which help to slow evaporation.
Mangroves (Rhizophora mangle) are clusters of small, shrub-like trees which are found in tropical to subtropical tidal areas. Mangroves dangle their roots in saline or brackish water and are able to withstand high salinity levels
Forests of these plants provide a safe shelter for a variety of marine life and are important nursery areas for young marine animals. These ecosystems are generally found in warmer areas between the latitudes of 32 degrees north and 38 degrees south.
Some mangrove residents include: Mangrove kingfisher (Todiramphus chloris), Giant mud crab (Scylla serrata), Mangrove red snapper (Lutjanus argentimaculatus), and in the more tropical regions dolphins, manatees and turtles.
Estuaries are dynamic systems or bodies of water found where a river meets the sea. They are home to unique plant and animal communities which have adapted to the constantly changing salinity levels.
Estuaries provide calm nursery grounds for many fish species such as dusky kob (Argyrosomus japonicus), leervis (Lichia amia) and support a large number of wading birds; pied advocate (Recurvirostra avosetta) and the lesser flamingo (Phoeniconaias minor). Estuaries are delicate, vital and one of the most productive ecosystems in the world. They provide a source of food, shelter, migration stopovers and a breeding ground for a variety of species.
Bacteria, microscopic diatoms, small bivalves, sand prawns and burrowing worms thrive in estuaries – feeding on detritus (decaying plant matter).
In tropical regions, estuaries are often lined with mangrove swamps, creating an entirely different ecosystem within itself.
Kelp forests are one of the most productive ecosystems on Earth, supporting high levels of diversity and primary production. They occur sub-tidally off the south- west coast of Southern Africa in cold, nutrient rich water.
The most dominant feature of kelp forests is of course, kelp (Ecklonia maxima) (Laminaria pallida). Despite kelp looking very much like land plants, they are in actual fact giant brown algae (Phaeophyceae). Kelp form underwater forests by attaching themselves to a rocky seabed and create intricate ecosystems which provide an important, complex, three-dimensional habitat for marine life. They also help to break the force of wave action.
They provide shelter and a food source for a diverse range of animals – Cape urchin (Parechinus angulosus), abalone (Haliotis midae), hottentot (Pachymetopon blochii), galjoen (Dichistius capensis), spotted gully shark (Triakis megalopterus) and west coast rock lobster (Jasus lalandii), just to name a few. Kelp is also a nutrient rich food source for sandy shore scavengers who feed off broken pieces of kelp deposited on the beach during high tide.
Coral reefs are found in tropical regions which have ocean temperatures warmer than 26 degrees Celsius. The coral reefs of South Africa are found along the east coast. In such environments, the diversity of life is high whilst nutrient levels are low creating a very competitive living space for most species. Corals are colonial anemone-like animals which cluster to develop extensive reefs by slowly depositing skeletons made of calcium carbonate.
The living corals capture food particles by using their tentacles. They also house microscopic algae in their cell walls which make use of the corals waste products to photosynthesise, ultimately providing the coral with food. Healthy coral reef ecosystems provide a shelter for many species which have developed symbiotic relationships to help ensure their survival in such a predatory environment. An example of an effective symbiosis is the clown fish (Amphiprion allardi) and sea anemone (Heteractis aurora) who offer each other protection from predators in the potentially dangerous reefs.
Who calls coral reefs home?
Invertebrates such as species of coral, sponges, crabs, shrimp, lobsters, anemones, worms, bryozoans, sea stars, urchins, nudibranchs, octopuses, squid, and snails all call coral reefs home.
The resident vertebrates may include a wide variety of fish, sea turtles and marine mammals such as seals and dolphins
The word “pelagic” is derived from Ancient Greek and means “open sea”. The pelagic zone is the upper layers of the open ocean waters.
The open ocean consists of an infinite amount of plankton which spend their lifespan in a drifting state. Plankton which is derived from the word “planktos”, meaning wandering, refers to the organisms which form the very basis of the food web.
Phytoplankton is a microscopic plant-like organism and form the basis of the food web in this ecosystem. Phytoplankton provides a source of food for zooplankton (microscopic animals) and other larger animals which feed on the zooplankton.
Life in the pelagic zone consists of significantly different forms. Planktonic species have adapted to floating, drifting and minimal swimming whilst some of the fastest predatory fish such as sail fish (Istiophorus) and short-fin mako sharks (Isurus oxyrinchus) are also found here. Areas where productivity of phytoplankton is high, large shoals of fish such as sardines (Sardinops sagax), snoek (Thyrsites atun) and yellow tail (Seriola lalandi lalandi) will occur.. Predatory marine animals feed in this high ecological zone as there is an abundance of food. Many zooplankton species move to the surface at night and sink during the day, often followed by fish and squid.