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  Habitats - Sand Dunes    

Sand dunes
The information presented here has been written by Ted Brambleby, Adventure Education,
Marine Environments Field Study and Resource Centre, Hastings Point Beach, NSW

Beach Life Zones

The Beach Link

Biologists often divide sandy beaches in to 3 biological zones. Stretching our analogy of skin and dunes a bit further let's look a bit closer at the very outer layer, a vast flexible sheet of dead cells, a layer on which bacteria flourishes, mites munch and warm springs poor out their evaporative fluids to keep internal engines cool. Here there is a balanced ecology continuos interplay between the living and the dead, a margin from which the life beneath can breath and itself experience a dynamic and sustainable sanctuary. The beach is a margin of sand in a dynamic ebb and flow in resonance with tides winds currents waves and time and merging with the integrity of the dune ecology it both forms feeds and protects.
from "The Blue Layer"

Our northern NSW Beaches are chiefly by definition dissipative. Off shore shallow sandbanks release the initial energy from ocean swells as they break and send secondary waves with low residual energy gently up and down the beach. The dissipative beaches are wide, gently sloping, slow draining and quite firm underfoot because the fine sand particles fit close together. These beaches support a relatively high variety of burrowing organisms. Because of it's shallow gradient these beaches also act as traps for another group of organisms,

The Blue and White Armada that drifts across our ocean in huge surface floating clouds, feeding on each other and the vast array of oceanic plankton they pass across on their journey. There is a remarkable story related to this strange community. This is told in another Habitat of the month. Look for 'The Blue Layer' coming soon!




Ghost Crab

Sandpiper searching for food

Food Webs on Coastal Beaches

The Producers which fuel Beach food weds include Phytoplankton, microscopic benthic algae and large detached plants such as Kelp, Sargassum seaweed, Sea grasses and Mangrove seeds. Rip currents provide cells of recirculating seawater therefore nutrients. These favour proliferation of diatoms amongst the sand grains. A phytoplankton Chaetoceros armatum that blooms in the ocean under certain conditions becomes deposited on the beach as a familiar green scum.

Diatoms betweens sand grains provide the chief food for bi valves and other filter feeders. Surf and off shore Phytoplankton produce organic matter by photosynthesis. When they wash ashore and are buries in the surface layers of sand these cells are consumes by copepods, nematodes, flatworms and other sand grain fauna. The cells are also broken down by bacteria and Protozoans, which in turn are eaten by sand microbes including water bears and small nematodes.

The fine organic particles released by dead plant and animal cells called detritus are retained near the surface on our wide dissipative beaches. This serves to enrich and widen the food web. The most important of food on many beaches are the stranded clumps of seaweed and sea grasses that get washed ashore. They are rapidly attacked by amphipods after nightfall and are the major food source for the larvae of kelp flies. Amphipods can be seen jumping around clumps of seaweed at night. Scavengers such as Isopods and Ghost Crabs quickly zone in on animals such as dead fish. Sea Jellies, Blue bottles, Blue suns, By the wind sailors, Sea lizards and Purple bubble snails.

Fine organic matter released and trapped by surface sand grains are sieved and filter by the sand bubbler crab whose bubble like castings can be seen characteristically on the low tide strand particularly in the early morning. Both amphipods and isopods become in turn food for beach foraging shore birds such as sandpipers and oyster catchers.

Pipis however can be negatively effected by accumulation of stranded Sea Weed. It prevents their food hopping tide chasing migration as well as their burrowing and feeding patterns. Seaweed that accumulates in the surf zone can be a rich source for amphipods, which in turn attract small predatory fish, which feed on them and inturn shelter amongst the seaweed to escape predatory sea birds.

The beach food web establishes a regime of circulating organic matter, nitrates, phosphates, minerals and through continuous decomposition by bacteria the generation of carbon dioxide. This provides a ready made source of plant food to help jump start the plant pioneers (Spinifex) into initiating the establishment of dunes, the outer skin that protects the inner integrity of all our coastal environments.

Next -   Skin Care Stategies or Dune Management 

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Find out about:

The beauty of sand dunes, more than just skin deep, but that is where it all starts
Function of dunes
Humble beginnings - The infant dune and its journey
Sand is made from 2 sources
Key members of nature's green dune squad and their significance
Beach Life Zones
Food Webs on Coastal Beaches
Skin Care Stategies or Dune Management


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