THE MYSTERY OF THE DISAPPEARING SEA GRASS AND BRENT GEESE

sea grass

The oak tree can support over 2300 different species of wildlife. This is easily visible and relatively easy to understand. Perhaps less visible and less known around the coast of the UK  are a group of plants known as sea grass (four species around the coasts of the British Isles) that support a similarly large range of species  such as fish, marine mammals, invertebrates and birds. One of these creatures is the dark-bellied brent goose. Here I will look at the decline of the brent goose population  and how it mirrored a global decline in sea grass in the 1920’s and 1930’s. I consider how the two were connected, but are perhaps not the full story. I also consider some of the arguments, speculation and science at the time and subsequently. I will also look at how the brent goose adapted and how this affected man’s activities.

Key to understanding this is how the brent goose used to be observed and described. The brent goose was originally described as a sea goose in the nineteenth century. In 1987 when I was first going wildfowling the brent goose was common on the marsh, often landing within a few yards of me as if it knew it enjoyed protected status. It was even more numerous on the farmers’ fields behind the sea wall[i]. A hundred years earlier in 1887 Sir Ralph Payne-Gallwey[ii]  makes it clear that the brent goose was never known to  rest on dry land, but rather the banks of ooze and mud, or paddling in the sea, or in a sheltered creek after a storm.

In an era where the shooting man was usually the best informed naturalist it was well understood that the presence of brent geese was linked directly to sea grass, “Let anyone so inclines dissect a brent after feeding, and he will find that he is filled with little ribbon-like pockets of sea grass, some nearly a foot long, all neatly folded as they were taken down.”[iii]

Because sea grass was their main food it was understood that the presence of this plant was what kept them, after their migratory arrival, to one part of the coast, whilst in other locations they were seldom seen. The were also observed, more so than any other geese, feeding during the day with the tide determining accessibility to food.

There are no accurate figures of the population of brent geese in 1887, but from anecdotal observation and accounts of the numbers shot it is likely to have been abundant possibly with numbers exceeding the 100,000 that are seen seasonally around the coasts of the British Isles in 2025. Whatever, the population was, it was due to take a major hit.

In the 1920’s there began a major die off of sea grass that spread throughout the Northern Hemisphere. The Netherlands Section of the International Committee For Bird Preservation  described the effect on brent geese in its post-War report of 1948. This recorded the dsappearance of sea grass, most notably Zostera Marina, almost completely from the Wadden area by 1930. In 1936 brent geese were reported to be, “thin and poor-looking, very tame, appearing on inland meadows and near harbour works which they never did before.” By the time Zostera Marina started to regrow in the Wadden area of the Netherlands in 1948 it appears that brent geese numbers were showing a small improvement, although the surviving birds appear to have adapted feeding by eating other common sea weeds from the submarine dykes and dams around the oyster beds, and on saltings as well as coastal grass meadows.

Similar observations of brent goose decline were made by Arnold Bennington at Strangford Lough in Northern Ireland as described in 1958: “One afternoon recently I went down to Strangford with some friends to see the brent geese, those very shy, dark little fowl that breed up in the far North, and winter on our mudflats.  When I was a boy the population of wintering brent must have been in the tens of thousands.

At ebb-tide on the mudflats of the Foyle, Strangford, and to a lesser extent Larne and Belfast Loughs, the feeding flocks of brent geese made a dark mass hundreds of yards long as they fed on the marine grass. This was the favourite food of the geese, and wherever there was a good supply of zostera marina there you would find brent. About 1925, however, a mysterious plant disease  began to cause a serious decrease in the zostera crop, and this in turn affected the geese. At first they went elsewhere, but the disease was nationwide. Indeed it spread quickly over the whole of the Nortrhern Hemisphere, and the goose population everywhere began to decline. I took samples of the diseased vegetation up to the botany department of Queen’s University where it was being studied, but nobody had any remedy.

The numbers of brent continued to fall until about six or seven years ago[iv] they were estimated at only 500 where they had originally been say 60,000 geese. Now faced with extinction the brent was given complete protection in Northern Ireland and in a few years time this began to show results.”[v]

Why was the sea grass dying? It was, at the time not clear cut and the subject was studied in both North America and Europe with much discussion and argument in the period 1925 through to 1950. The loss of sea grass was significant not just ecologically, but had practical consequences for navigation and coastal erosion or even flood protection as described on the South coast of Britain in 1949: “ The effect of the loss of eel grass on the Devon and Cornwall coasts, at Salcombe its roots and rhizones bind and hold sand. The shore line changed and the stones and seaweed replaced the underground marine fauna.”[vi]

On the Sussex coast the loss of sea grass caused the decay of mudbanks near harbours leading to them shifting  to become an uncharted hazard in shallows.

It is possible that the die off had different local causes in the early twentieth century. In 1909 Professor Letts identifies the growth of Belfast and its resultant sewage feeding the growth of alga refered to as “Ulva” displacing the growth of sea grass whereas in the 1850’s Belfast Lough was unaffected by sewage and was rich with zostera marina (sea grass) whilst the ulva sea weed was almost absent until Belfast had a new drainage system in 1889.[vii]

Similar problems were found in the Tees estuary in Northern England where Dr. Ewart  found similar problems alongside the Tees mussel beds being poisoned as copper sulphate was used to control the “ulva”.

Pollution was largely understood by the public by smell, and as long as the drains and rivers through towns did not flood, stink or become putrid there was low public concern for the environment downstream. Science on the other hand was beginning to understand the effects with Zostera Marina being identified as extracting  cobalt, nickle and manganese from the ocean as early as 1873.[viii]

Elsewhere climate was considered a factor, whether through frost killing sea grass directly, affecting seed, or drought reducing flow into the sea from estuaries increasing the coastal salinity. This was observed in the Montrose Basin in 1890  resulting in the die off os several species, most notably commercially being the oyster that, “once abundant in the estuary is alas only represented now by dead shells.”[ix] The vulnerability of sea grass to climate and salinity change in estuaries is well understood and contrary to United Nations current consideration that sea grass is an effective tool against coastal erosion and flooding the US Army Corps of Engineers  Coastal Engineer Research Centre concluded that sea grass was too vulnerable a plant to be relied upon for this purpose.[x]

In 1933 there was a great deal of speculation in England that sea grass die off was the direct result of oil pollution especially in busy water ways. By 1934 Captain Masters claimed publicly that “oil was destroying weed and sea grass” , this was refuted by Lord Ichester who did not believe it was oil. It appears Lord Ichester was relying upon a Ministry of Agriculture statement of September 1933 that stated that, “As the die off of sea grass was first discovered in America they were confident from their findings that the sort of places where it is dying show that oil waste is not responsible.”[xi]  In 1934 Mr T.G. Tuton is quoted as a government official that observed a reduction in the growth of sea grass at Holy Island, however the clear reality is that a British Government, with very poor finances, could afford to put virtually no resources into the die off of sea grass with properly financed studies left for American and Canadian scientists.

The study of the die off of sea grass was effectively led globally by the US Department of Agriculture Bureau of Biological Survey  and the biologist  Clarence Cottam. With resources all along both the West and East coasts of America. This found a common element in that where sea grass occurred Labyrinthula – a single cell organism commonly referred to in the 1930’s a slime mould. Now this was found globally  first in America, then in Europe. The effect was to kill off 90% of sea grass in the Northern hemisphere.

However, to assume that a single cell slime mould organism caused the die off on its own is not in itself necessarily the primary cause. It seems possible that the organism has a symbiotic relationship with sea grass, but it is the activation of the organism that may be key, with increase in temperature and reduction in light exposure being two identified key factors[xii]. Could global fluctuation of sea temperature in such cycles as El Nino be a factor? In addition studies of zostera marina show the seed from the plant seldom germinates outside the temperature range 15-20 Celcius.

More recent DNA science has created speculation that sea grass may be subject to a cyclical die off and rejuvenation that has resulted in it evolving as a faster rate than previously thought. It has been generally accepted for over a hundred years that sea grass originated on land as a flowering plant that adapted to marine conditions. With ice ages and changing sea levels this is understandable. But DNA science has charted that instead of happening over hundreds of thousands of years the evolution of sea grass from land to sea possibly happened as recently as 40,000 years ago, a mere blink of the eye in evolutionary terms.  This means that sea grass planting is possibly not vary productive in the long run as maximizing the area and density of coverage may be at the expense of genetic diversity and variation that will occur naturally from seed.[xiii] This means that most projects now involve seed harvesting and dumping of bags of seeds at appropriate sites. However, it also indicates an element of genetic adaptability and I wonder if the plant will adapt over a relatively short evolutionary period in the future.

The problem we have is that when science and politics overlap and seeks solutions to what appears to be common problems the politicians like to be “seen to do something”. This is an issue with the United Nations as largeness and a global view to a problem, in this case sea grass die off, overtakes the local. This sees the undoubted benefits of sea grass to marine life,  carbon capture and environmental health being used to extol the benefits of various projects. But is being seen to do something greater than the value of the action? This is a key question as politicians of all colours and nations propose grand actions.

Returning to the brent goose, in 2025 it has seen great recovery with about 100,000 birds around the British Isles and a population of around 300,000 globally. Did the decline in sea grass cause the decline of the brent goose? Here is a hazard of assuming cause and effect, or at least a single cause. The brent goose was not the only bird to benefit from sea grass, the duck, wigeon also was a major consumer of its seeds. However, wigeon had, and have a more varied diet. It is also a fact that the brent goose did adapt and adjust to other food sources, most notably meadows and pasture in both England and the Netherlands and then arable crops much to the consternation of European farmers near the North Sea coast. There is another key thing to consider as described by Andrew Saint Joseph in 1990[xiv]. Glasnost had enabled British scientists to visit the breeding regions of brent geese in Siberia to study and understand how the breeding of brent geese fluctuated. It has long been observed since the nineteenth century that brent geese have large fluctuations in breeding success. Some years migratory flocks would arrive in the British Isles with no young birds, and other years nearly half the flocks would be juveniles. From this study it is clear that variable weather conditions each year have an impact. It is also clear that there was a correlation between lemming cycles, that is, when lemmings are plentiful the artic foxes concentrate on eating them, and when they are scarce they eat the young geese and their eggs. Indeed, after laying eggs brent geese moult and experience a period of flightlessness adding to their vulnerability.  However, there was also revealed another factor that had not been fully realized. Near the breeding grounds of the brent geese were the remnants of Stalin’s labour camps of the 1930’s and the flightless and breeding geese would be an easy target for hungry mouths. Indeed, this was considered a factor in wartime as hungry Germans were known to predate breeding wildfowl on various locations along the Norwegian coast and both Germans and Dutch consumed wild geese in the Netherlands during the war. Human deprivation is an enemy to wildlife.

The key to both the decline of brent geese and Zostera sea grass  is not to close minds by looking at one answer. However, it is clear that there is an  association between the die off of sea grass and the presence of the ‘slime mould’ labyrinthula. Similarly it is clear there is an association between the decline of brent geese and the reduction in Zostera sea grass.  But the triggers of the sea grass die off cannot be assumed as one cause, similarly our actions to improve this should be equally open minded and subject to constructive criticism.

[i] The farmer Stuart Hay’s battle with brent geese is mentioned in my book Marsh Fen and Town South Lincolnshire and Beyond page 127  ISBN 9798284394380

[ii] Shooting Moor and Marsh by Sir Ralph Payne-Gallwey

[iii] Page 165 Shooting Moor and Marsh by Sir Ralph Payne-Gallwey

[iv] About 1951

[v] Arnold Benington , The Belfast Newsletter 8^th March 1958

[vi] Weston Morning News 9^th November 1949

[vii] The Northern Whig 31^st July 1909

[viii] The Saturday Review 4^th January 1873

[ix] Montrose Standard 25^th July 1890

[x] Coastal  Engineering Technical Aid No. 82-6 December 1982

[xi] Various sources including West Sussex Gazette 28^th September 1933

[xii] Reference Perspectives on the wasting disease of eelgrass Zostera marina  - University of Georgia  7.12.89 along with other references from 1950 onwards

[xiii] Rombury Tiburon Centre for Environmental Studies Department of Biology San Francisco State University  21.02.2014

[xiv] The Living World broadcast on BBC Radio 4 10^th October 1990