The Essex Coast

Background

Essex has one of the longest coastlines of any county in England, being over 350 miles along, and has many different types of marine habitat along it's length. Much of the coastline is undeveloped but most of it has artificial sea defences that prevent it from being a truly natural habitat. 

Some efforts have been made in recent years to experiment with what is termed as managed retreat as sections of sea wall are removed and the incoming tide allowed to flow up to it’s natural level.  These efforts have been made in part as an attempt to increase the amount of one type of coastal habitat that has suffered greatly from the introduction of sea walls which is salt marsh.  Managed retreat is also seen as a cheaper alternative to constant sea defence improvements and maintenance which is an ever increasing drain on resources particularly when the age of many of the defences is considered. Another factor that makes managed retreat more attractive is the  constantly rising sea levels that they are having to cope with, in part due to global warming but also due to the realignment of the UK part of the continental crust after the end of the last ice age known as isostatic rebound. 

The Essex coast is highly utilised by both commercial and pleasure boating groups ranging from the oyster fisheries around Mersea Island to the large port at Harwich on the commercial side and from sea kayaking and dinghy sailing to power boating and motor cruising on the pleasure side.

Geology

The geology of the Essex coast is an unfortunate one.  Made up of soft sedimentary rock laid down over the ages at the bottom of seas of varying depth it is naturally prone to erosion.  The best example of this is the Naze cliffs at Walton-on-the-Naze where a top layer of permeable Red Crag lies on top of the impermeable layer of London Clay.  Rain water percolates down through the Red Crag until it reaches the London Clay and can no longer take the easy route downwards.  The water then flows along the top of the London Clay causing an instability that is attacked by wind, weather and waves until a portion of the Red Crag slips off the  London Clay and is washed away.  The rate of erosion in this area is about 1m per year and explains why there are second world war coastal defence emplacements on the beach instead of on top of the cliff.  The constant erosion of these sedimentary cliffs also provides a constant supply of marine fossils.

Habitats

                Salt Marsh

                Found at the upper tidal levels of most marine and estuarine mudflats is an area of salt-tolerant grasses and other herbaceous plants known as salt marsh.  Salt marsh is found in sheltered areas of accretion and usually where tidal amplitude is pronounced.  This makes estuaries an ideal location for salt marshes as there is generally a high sediment load being carried by the mature river which due to the slow flow of the water and the flocculation due to meeting salt water is readily dumped around the mouth.              

                Salt marsh begins to form when pioneer plants begin to grow on a slope of coastal mud bank that has accreted to a minimum level of MHWN.  The surface of the mud will already have been moderately stabilised by the presence of a diatom film and the roots of these halophylic plants help to bind the mud even further. The presence of the plant above ground has the effect of slowing the water flow around them leading to increased rates of accretion.

                It is unusual for a complete covering of these pioneers and so as the water flows more slowly where the plants grow increased accretion occurs and where there is only bare mud the faster flowing water begins to form small channels between the clumps of plant growth which eventually become creeks which help the tide to inundate the salt marsh and also to uncover it more quickly when the tide recedes.

                Estuaries

This type of habitat is the most variable of the habitat types found around the Essex coast and hence can be quite a challenging place to live.  For example, at any one spot in an estuary the salinity can change from fresh to completely marine and be at any point in between on every ebb and flow of the tide.  This can cause great stress for aquatic organisms and as a result of this combined with other factors such as the increasing time of exposure to the air the further up an estuary an organism is found, many marine organisms will not be found in estuaries and the further up an estuary samples are taken the fewer species are to be found. 

This is not to say that estuaries are not full of life but rather the species found there tend to be more specialised.

                Sandy Beaches

                Shores comprising of coarse sediments such as sand and shingle are known as high energy environments as they are dominated by wave action.  Due to the constant pounding of the waves in these areas any form of sedentary organism e.g. plants or fixed animals, are usually excluded.  Beach profile can vary from gently sloping in areas of high wave action and steeply sloping in areas of low wave action.  Beaches can be of one profile on one visit and then can be completely different on another.  This is a great demonstration of the instability of the sediment on this type of shore which has no natural cohesiveness.  Littoral and sublittoral areas can be stabilised by the actions of an organism but this would be only in a very localised way and not a permanent feature.  Larger areas can be stabilised by the roots of some halophylic plants, but this would only happen in areas of sand that had been thrown above MHWS and so were already out of the influence of tidal action, to form a dune.

                Sandy shores support many types of species but not a very large biomass due to the instability of the sediment.  This often leads casual observers to consider these areas lifeless whereas in reality life is there but needs to be sought out.  Many organisms come in with the tide such as fish and crabs whilst others use a form of surfing using the waves to travel up and down the beach then swiftly burrow to feed then surf on again.  As these actions all happen beneath the water it is not easily viewed.

                Mudflats

                Mudflats are differentiated from sandy beaches by the predominant particle size of the sediment.  Basically muddy shores have an average particle size of 63mm or less whereas sandy shores have an average particle size above this.  This may at first glance appear arbitrary but is based on the properties of particles above and below this size.  Particles below 63mm tend not to be single grains such as those found on sandy beaches but a conglomeration of tiny particles.  Very small particles have a tiny surface charge that in fresh water keeps them apart by mutual repulsion but in saline conditions this charge is reduced and the particles begin to be attracted to each other and combine to form secondary particles or flocs.  It is this flocculation and the resultant stability of sediment beds made from them that make mudflats an ideal habitat for burrowing organisms and very high biomasses occur.

                The most obvious indication of the amount of biomass present in mudflats is the vast number of wading birds that feed on them.  Essex is home to some vast colonies of migratory birds during the winter months that take advantage of both our milder weather and the vast quantities of food available.

                Saline Lagoons

                Lagoons are bodies of saline water that are partially separated from the sea and that retain water at low tide.  The level of salinity can vary greatly from brackish to hypersaline. 

                Artificial Structures

                There are many and varied artificial structures along the coast of Essex from Piers to Pill Boxes, but they all provide, in some way, an extra habitat dimension that isn’t naturally found in these parts.  That dimension is rock hard stability.  From the concrete structure to the granite boulder these features all bring with them the characteristics of a rocky shore habitat into an area of otherwise soft geology.

                Rocky shores often offer the best opportunities to view marine life as many of the organisms found here are sedentary and easily accessible pools can provide hours of interest for viewers of all ages.

Pressures

                Enhanced Global Warming

                Pretty much getting the blame for everything these days, the enhanced greenhouse effect is possibly adding to the earth's natural greenhouse effect without which the earth would be no more than a frozen ice world.  There are many and varied reports of what this is doing to our coast but the main ideas are that the sea is becoming warmer, the sea level is rising and that certain aspects of seawater chemistry are changing.  All of these factors can affect marine organisms in various ways. 

Rising sea levels from ice sheet melt and isostatic rebound are a problem for two main reasons, if the sea level rises too fast then organisms will find it difficult to keep pace by relocating further up the beach; the introduction of sea walls around the coast means that instead of the rising water being able to convert low lying areas into new intertidal habitats the habitats that are there get squeezed between the new sea level and the wall until the high tide reaches the wall and important habitats disappear.

Rising sea temperatures have lead to a variety of documented changes in recent times.

                Isostatic Rebound

                When the ice sheets covered Scotland and much of northern England the weight of the ice pushed that part of the crust down into the Earth's crust.  Even now, thousands of years after the ice retreated, Scotland is slowing springing up from it's depressed position but, like a see-saw, this means that the South is being pushed back down to where it's natural level lies.  This movement accounts for about 1.5mm of sea level rise around the Essex coastline every year and with some ancient beaches in Scotland now to be found at 30m above sea level, this movement over long time periods cannot be easily ignored. 

                Marine Pollution

                There are many types of pollution that have a detrimental effect on the marine environment and those organisms living in it.  The subject is a vast one and as such only a limited review will be made here.  One of the most prevalent pollutants is nitrogenous runoff from arable farmland.  Much of the fertiliser that is applied to the field by farmers is dissolved by rainfall or irrigation then percolates through the soil until it reaches the natural low point of the local area which invariably is the local stream or river.  This then runs downhill to the eventual estuary adding it's load to the coastal waters.  Many of the rivers in Essex are hypernutrified due to this and hence the coastal waters also have an elevated level of nitrogen and phosphates.

                Marine Litter

                Litter is unfortunately an ever present threat to marine life and with the increase in the use of plastics, this litter remains in the environment for a very long time.