Plants
Coastal habitats are believed by many to be the nearest to a natural habitat that we have left in the British Isles. This is largely because the activities of man which have for centuries modified the habitat further inland through agriculture and forestry have not had a similar impact on our coastal areas. Grazing of salt marshes and dune systems does take place but has limited effect on the species composition of these areas - the forces of nature (tidal influxes) tend to have a greater control than man induced management. However reclamation through the construction of sea walls and development can totally modify the coastal habitat.
There is a close relationship between the plants and animals in any habitat, but the mud flats of an estuary are probably one of the richest we have in terms of food resource. Living in the mud there are a whole range of small animals providing food for birds and fish living in the estuaries and themselves feeding on the fragments of decaying vegetation and lower plants. The plants also provide a good source for the birds, fish and insects present - they occupy a vital part in the food chain.
Within the harbour several different associations of plants exist. Moving from the lowest levels below low water mark the seaweeds, eel grass (Zostera) and algae are found. Beyond the low water mark a succession of vegetation can be found through to the development of salt marsh to the sea wall. The tidal area of the harbour provides a habitat in which only a fairly restricted range of plants is able to survive. The plants have special features, which enable them to grow in salt water and enable them to withstand periods of submersion and exposure. For some distance beyond the high tide mark certain of these specialities persist enabling the plants to withstand the salt carried by onshore winds. Differences in the deposited materials within the harbour also allow for variations in plant associations and, in addition to the main salt marsh, both sand dune and shingle communities are found.
Listed and described below is a small selection from each of the major vegetation zones within the harbour.
Over and above the plants which occur "naturally" in the harbour two plants which have had quite a dramatic effect on the nature of the harbour are non native or introductions.
Rice Grass (Spartina sp.) / Japanese Seaweed (Sargassum muticum) / Seaweeds / Flowering Plants / Marsh Samphire or Glasswort / Salt Marsh Grass / Sea Pursiane / Sea Lavender / Sea Aster / Sea Beet / Sea Couch / Wild Carrot / Sea Bindweed / Yellow Horned Poppy
Rice grass Spartina sp.)
Originally recorded from Southampton Water 100 years ago is believed to have originated from America. It has spread along the South Coast colonising the soft mud flats of the estuaries. At its peak in Chichester Harbour about 20 years ago it grew to between l' and 2' high and was very luxuriant. In comparison it now appears very stunted and the mud flats which it once stabilised are now breaking up and reforming at a lower level to become once again covered with algae and seaweed. It is not absolutely certain why this is happening but it seems most likely that the plant having built up the mud flats, has now made the habitat unsuitable for itself and is in decline.
Japanese seaweed (Sargassum muticum)
Another introduction, thought to have been brought here by ships and shellfish. It is highly invasive and has spread to both sides of the English Channel and to the Pacific coastline of North America. It tends to be found in channel beds attached to small pebbles, but frequently is floating free and presents a hazard to powered boats. Various control methods have been tried from mechanical to hand clearance, but as yet they have been unsuccessful.
If we look now at the 'natural' succession starting below and just at low water mark:
Seaweeds
In the form of green, brown and red algae are all present
in Chichester Harbour and recorded species number in the order
of 60 different varieties. The most noticeable are perhaps
the green or brown algae of which Enteromorpha and Ulva of
the green ones are dominant. Enteromorpha has a tubular construction
whereas Ulva (Sea Lettuce) is flat in form. Both plants are
important in the food chain. Ulva being a favoured food of
the small snail Hydrobia which in turn provides food for Shelduck,
Enteromorpha being eaten by the Brent Geese.
Of the brown algae the Fucus are most noticeable with their
flat brown fronds often with occasional air bladders. (Fucus
contrasts with Japanese seaweed in being much more robust
with wider thicker fronds and fewer air bladders). If not
floating free Fucus is attached by a 'hold-fast' to a small
pebble or rock.
Flowering plants
The first of the flowering plants to occur in the tidal area is Zostera or Eel grass. It represents the only flowering plant which grows totally submerged by the sea. The plants possess roots and have long narrow grass-like leaves. The flowers are inconspicuous with no petals, the male and female parts being also reduced. Eel grass provides an important constituent of the diet for Brent Geese. Following a disease which caused the decline of Zostera in the 1930's, it was not present in the harbour to any large extent again until the late 1970's.
Higher up the succession where areas of mud are above the water for longer periods of time colonisation by salt marsh plants occurs.
Marsh Samphire or Glasswort (Salicornia)
Is one of the first to appear above the low water mark. It is very fleshy, the stem of the plant retaining water to enable it to live within the tidal area. There are several varieties, some of which turn bright red as the season advances, although they are generally green. The inconspicuous flowers appear in late summer. In some areas the plants were harvested and burnt to produce soda ash for glass making or cooked and eaten.
Salt marsh grass (Puccinellia)
A true grass and one of the next plants to appear in the salt marsh. It is very stiff and with a slightly grey appearance, tightly compacted and grows to about 15cm.
Sea pursiane (Halimione portulacoides)
A more shrubby plant which dominates the high salt marsh around the harbour. Its characteristic grey-green leaves with small scales help reduce moisture loss in dry weather. The flowers are inconspicuous appearing as golden yellow in late summer.
Sea lavender (Limonium)
Is a more attractive plant of the salt marsh, although not especially common in Chichester harbour. The leaves form a rosette at the base of the plant and the flowering stem produces blue-mauve flowers in July and August. The seed heads remain through the winter, the seeds providing food for the seed-eating finches during the winter.
Sea aster (Aster tripolium)
A late flowering plant of the salt marsh producing daisy-like flowers with blue-ray petals with a yellow centre attractive to butterflies. The leaves are thick and fleshy.
From the salt marsh the transition is often abruptly altered
by the presence of a sea wall - a man-made sea defence created
to prevent flooding by salt water of the often-reclaimed land
beyond.
Of the plants to be found on the sea wall the three most common
are Sea beet, Sea couch grass and Wild carrot.
Sea beet (Beta vulgaris)
A sprawling plant, again with thick fleshy leaves and an often red striped stem. As might be expected the leaves of the plant can be eaten after cooking if picked early in the season. The plant produces rather insignificant flowers from July to September. This family of plants is the origin of many of our domestic vegetables.
Sea couch (Agropyron pungens)
A true grass with very stiff parallel- veined leaves with a rather blue-green colour. The inflorescence (flower head) of the grass is called a spike made up of small spikelets which are found in two alternate ranks each side of the stem.
Wild carrot (Daucus carrota)
Flowering between June and August the wild carrot flower is often pink in its early stages, starting off with a flat flower head developing into a more rounded cushion-like shape. The flower head is made up of many individual flowers in a structure called an 'umbel'. Very often the central flower is dark red and resembles a fly sitting on the cushion of flowers - this helps attract other insects, which aids pollination.
Behind the sea wall there is often a ditch - this is frequently
where some of the material which has been used to build the
sea wall has been taken from. It also serves as an important
drainage feature. It often lies at or below sea level and
whilst water drains from the ditches at low water there is
occasionally back-flow at high water. The water in these ditches
is often brackish - a mixture of salt and fresh water.
One plant, which thrives in such conditions, is Sea Club Rush
(Scirpus maritimus). The plant is in fact a member of the
sedge family with triangular shaped stems. It can grow to
about 1m high and in late summer bears heads of brown flower
spikes.
Where fresh water flows into the estuary such as at Fishbourne,
and is not channelled through a pipe under the sea wall, the
natural succession from salt marsh to fresh water marsh takes
place. Here, the high salt marsh dominated by salt marsh grass
and sea purslane takes us into reed beds of Phragmites australis
- these reeds survive because the fresh water flowing in dilutes
the saltwater to a level that they can tolerate. The reed
beds themselves are a very valuable habitat, and support several
breeding birds including Reed warbler and Reed bunting. The
seed heads provide food, and duck find shelter in amongst
the reed stems.
In addition to the main salt marsh habitat there are two
other habitats characteristic of the harbour - sand dunes
and shingle.
The main area of sand dunes is at East Head - one of only
two sites in West Sussex, the other being at Climping dunes
near Littlehampton. The dunes are made up of deposits of wind-blown
sand. They tend to be unstable and it is only the binding
effects of vegetation that can give them strength - but they
are still vulnerable to erosion, especially through the effects
of winter storms and the effects of trampling.
A limited number of plants can survive in these conditions
- perhaps the most important because of its binding effect
on the sand is Marram Grass (Ammophila arenaria). Its leaves
help to trap sand and its roots and shoots have the capacity
of growing through increasing deposits of sand - the old roots
helping to bind the sand. Like Couch grass its inflorescence
is made up of a series of spikelets - which are of a white
fluffy appearance. Once stabilised other plants can grow on
the dunes.
Sea Bindweed (Calystegia soldanella)
As the name suggests is another plant that helps stabilise
the dunes. Related to the garden bindweed it has a similar
habit of sprawling over the ground and rooting deeply. It
is an uncommon plant as its habitat is so restricted. It has
an attractive pink trumpet-shaped flower from June to September,
with white stripes that help to lead insects to the centre
of the flower.
Shingle occurs in small patches around the harbour edge -
this time it is material carried and deposited by the sea.
Shingle spits are also quite unstable and very few plants
are able to survive until the shingle is stabilised by a few
pioneer plants like Sea beet and Couch grass.
Yellow horned poppy (Glaucium flavum)
Is one of the most attractive plants that does grow on the shingle. The large yellow flowers appear throughout the summer but they wither soon after opening. The leaves of the plant are formed in a rosette and are frosted with silvery hairs - a protection against the scorching effect of salt laden winds and sun on the exposed shingle. The name derives from the seedpod which is long, narrow and curved. The plant has deep roots, which are able to penetrate the shingle to find moisture deep down in the shingle bank.
The visitor will notice the wind sculptured shapes of the trees and shrubs which surround the harbour - the effects of salt laden winds carry as far as the Downs when the young growth of trees can be scorched by the winds in spring.
The old oaks are a particular feature of the harbour and where they come down to the harbour edge uninterrupted by a sea wall we have an example of a situation which would have existed 4000 years ago, when after the last ice age natural colonisation of the British Isles took place leading to the development of a more or less totally wooded landscape leading down to the coastal area - today one does not have to walk far from the coast to see how changed that landscape has become.
The near to natural state of much of the harbour, the variety of species which the habitat supports and its significance in the county, British Isles and Internationally for certain plants and birds make it worthy of designation as a site of Special Scientific Interest - please respect this importance - admire the plants, but do not pick them, leave them for others to enjoy, and observe the birds - watch them from a distance and try not to disturb them.
This article is from a Fact Sheet written by Ann Griffiths.
