Coastal Ecology

4. Sand Dunes and Sandy Shores

Druridge Bay, Northumberland

Cape Coast, Ghana

Development of sand dunes

• Sand dunes are an example of succession: if one progresses inland from the beach one is, essentially, seeing all the stages through which a community develops.

• Really, the only way to appreciate the extent to which the habitat changes on a small scale with time is to make regular visits at different times of the year.

• Ultimately dependent upon one grass species: Ammophila arenaria (Marram grass).

Marram grass

• Tolerates – and, indeed, thrives – on being buried by sand.

• Sand accumulates in the wind shadow behind plants.

• Because plants take a long time to decay the old parts of plants add a fibrous mass to the sand.

• Xerophytic: fibrous rolled leaves with stomata on inside.

Marram grass (continued)

Leaf of marram grass

Leaf of marram grass (SEM)

Leymus arenarius: Sea Lyme grass

• Larger, broad blue-green leaves.

Early stages of sand dune system (mobile dunes)

• Soil essentially just pure sand: well drained, mobile, lacking in nutrients.

• Very few plant species present: at first, just Marram Grass and then a few tap-rooted species start to appear. For example, Dandelion, Coltsfoot. (Tap roots supposedly seek for the water table, which may be many feet below).

Taraxacum officinale: Dandelion

Tussilago farfara: Coltsfoot

Further development of first dunes

• Arrival of leguminous plants such as Bird’s foot trefoil (Lotus corniculatus) and Rest harrow (Ononis repens).

• These have root nodules which contain bacteria responsible for fixing atmospheric nitrogen (useless) into nitrates (usable by plants).

• Thus, the ‘soil’ is starting to become enriched.

Lotus corniculatus: Bird’s foot trefoil

Bird’s foot trefoil (in fruit)

Ononis repens (Rest harrow)

Continuing development

• Further plant growth stabilises the soil.• Break down of dead plants (and the occasional

buried dead seagull) adds to the nutrients in the soil and improves its water holding capacity.

• Mosses growing across the surface of the sand further stabilise the surface.

• Many new plant species appear causing the vegetation community to become more complex and diverse.

Sand dune mosses

• Tortula ruralis

Sand dune mosses

• Hypnum cupressiforme

Geranium sanguineum: Bloody Cranesbill

Calystegia soldanella: Sea bindweed

Tropical species of bindweed: Ipomoea pes-caprae

Rosa pimpinellifolia: Burnet Rose

Galium verum: Lady’s bedstraw

Dune slacks

• Behind the dune ridges, and representing a later stage in development, the dune slacks are produced when there is a stable cover of vegetation and the soil has water holding capacity (partially as a result of humus and decaying plant remains) and nutrients (from the decay of generations of plants.

• Number of plant species continues to increase.

Salix repens: Creeping willow

Epipactis palustris: Marsh Helleborine

Epipactis dunensis: Dune Helleborine

Corallorhiza trifida: Coralroot Orchid

Dactylorhiza incarnata: Early Marsh Orchid

Dactylorhiza fuchsii: Common Spotted Orchid

Dactylorhiza purpurella: Northern Marsh Orchid

Later stages in development

• The continuing development of the succession depends on soil types (and inland land usage to a certain extent – farmers often encroach onto dunes).

• Acidic soils may develop into dune heath.

• Shrub/tree species cause the development of dune scrub.

Problems with sand dunes

• Very fragile habitat.• Fore-dunes susceptible to winter storms.• Dune system in its entirety is a thin skin of

vegetation – as a result, any damage to the surface exposes the sand underneath and wind very rapidly scours this out so that large areas of uncolonised sand exposed.

• Problems range from rabbits to mountain bikers.

Management techniques

• Variety of strategies are used in the management of sand dunes:

• Manually replant with marram grass.• Cover exposed areas with chicken wire.• Bury old Christmas trees (or, in some

instances, e.g. in Jutland, plant pine trees).

• Discourage damaging behaviour – includes fires, camping, bicycles, etc.

Blyth Beach

Common Jellyfish: Aurelia aurita

Common Jellyfish: Aurelia aurita

Common Jellyfish: Aurelia aurita

Compass Jellyfish: Chrysaora hyoscella

Compass Jellyfish: Chrysaora hyoscella

Blue Jellyfish: Cyanea lamarkii

Blue Jellyfish: Cyanea lamarkii

Sea Potato: Echinocardium cordatum

Ensis minor: Razor Shell

Ensis siliqua: Razor Shell

Ensis siliqua: Razor Shell

Scallop

Scallop for the artistically minded

Sea Mouse: Aphrodite aculeata

Sea Mouse: Aphrodite aculeata

Lugworm: Arenicola marina

Lugworm: Arenicola marina

What you cannot see: Diatoms

…and a couple of things to look out for on tropical beaches