ANIMAL LIFE IN Pl lE MAIlSII DITCIIES OF THE THAMES ESTUARY. 801

37. Animal Life in the M : d i Ditches of the Tliainus Estuary. By F. J. LAMBEIVY *.

( Witli oue Map.)

jlteceived March 11,1930 : &ad April 15, 930.1

CONTENTS. page I. Introduction ........................ ,*:. .............................. 801

801 803 804 806

VI. Summary ........................................................... 808

11. Topography of the Area investigated ...........................

IV. Animal Life in the Marsh Ditches .............................. V. Notes on the Leigh Ditches .......................................

111. The Origin and Evolution of the Harsh Ditohes ............

I. INTRODUCTION. Tile iiiriin object of this paper is to give i~ description of tlie animal life in the

inrirsli tlitclies of the 'I'hrmes Estuary, and of tlie adverse circumstaiices in wliicli mimy irieinbers of the faune tiiid themselves. Where necessary, notes on the plm ts of tliiu iirea are introduced in order to make as complete au ecological picture as possible. The data liere supplied hm--e been obtained as the result of persorial observation and experience covering a period of 10 years (1920-1929).

The peculiar, and in many ways, highly exacting conditions of life found in estuaries have been already noticed in works of ecology and distribution (of. Robson, "The Animal Life of Estuaries," Journ. Quukett Micr. Club, (2) xv. p. 161,1925). Owiiig to the circumstnnces in which the author has been compelled to work he has l i d little opportunity of studying the litemture on marsh faunas in other areas. H e is, therefore, not aware t o what extent fluctuations in environmental conditions sirnilar to those described in this paper may have been observed else- where ; but it seems that the exceptional local conditions and the special history of the formatiou of the Tliames marshes are sufficiently interesting for publication without discussion on their general ecological importance.

The thanks of the writer are due to Dr. Calman, F.R.S., and Messrs. Gcpp and Monro, of the British Museum (Natural History), for their kind identification of Rriimals rmd plants from the ditches, iilso to Mr. Percy Thonipson and Miss Greaves, of the Essex Museum, Stratford, for similar assistance and advice.

Especial tlianks are due to Mr. Robson, of the British Museum(Natura1 History), not only for the identificittion of material submitted to him, but for his advice, kindly criticism, and personal assistance in the preparation of the paper, which, indeed, without his encouragement would probably never have been written,

11. TO1'OQBAPHY OF THE AREA 1NVESl'IOATED.

The iiiea which is cliscussed in this paper includes the S.E. coast of Esscx from Foiilness 1sl:tiitl UII the east to Betifleet on the west. It does not include Canvey [slatid. The first, seen betyeen Follliless and Slioebury (about 12 miles), apparently originated from the conjoined

* C o m i u d o e t d by a. C. ROBBOX, MA, F.Z.S.

III this area two stretches of marsh are found.

802 MR. F. J. LAMBERT : ANIMAL LIFE IN

deltas of the Roach, Crouch, and Thames rivers. At present this area consists of numerous islands all protected by dykes and separated by passages or creeks linking up the river3 named. Of the creeks, Havengore is now the only one open whioh gives access to the Thames. The others, Shelford Creek and New England Creek, have been dammed by order of the War Office. The former is a paradise for those interested in marine faunas in a transitional stage.

The mainland itself lies to the west of these islands and marshes, the north side of the marsh-area being bounded by the River Crouch. It is uncertain what land movements are taking place, but north of the Crouch, in the Dengie hundred, it is thought that subsidence is in progrese. Certainly the sites of the villas of the Roman city of Oithona are only visible at low tides. Westwards from Shoebury, the soil of whioh is sand and shingle with a foreshore of arenaceous mud, the land

The mainland part of this marsh extends from Wakering to Wallasey.

L I

Marsh areas, Leigh to Benfleet and Wakering to Foulness #.

rises into fairly high uplands (London clay, sometimes topped at places with gravels and sands) faced with reclaimed and unclaimed marsh. Farther to the west a t Southcliurch and Southend the marsh has been built over and modified by urban development.

Beyond Southend one enters the second area of niarsh at the foot of the higher uplands from Leigh to Pitsea (and indeed to Mucking), a very large area. For the purposes of this paper the area is limited by B line drawn north through Benfleet.

The raised permanent way with its projecting banks, separates the ditches which meander through the marsh into brackish ditches on its south side and freshwater ditches on the north side.

At Leigh the railway to London cuts across the marsh.

* New England Island lies between Havengore Island and Foulness Island. Shelford Creek separates it from Foulness Island and New England Creek (now enclosed) isolates it from Havengore Island. Priapralus can be found in Shelford Creek.

A concrete road now links up all three islands with the mainland.

THE MARSH DITCHEB OF THE THAMES ESTUARY. a03

111. THE ORIGIN AND EVOLUTION OF THE MARSH DITCHES. I n the

course of a long period of time, varying in duration according to the volume of flood-waters and the openness to the sea, the littoral becomes banked with mud * tr<Lversed with swins, gullies, and runnels, and rises little by little. Zostera gives way to Ei%teronhorphffi, and Enteronzorpha to the plants of the low marjh, particularly to Obione, Salicomia, tlie Sen Aster, Sen Lzvender, and the grasses (Spartino etc.) of the saltings. These plants hold the silt which becomes consolidated into mud and boiind with roots which eventually become peat. As the vegetation holds, the gullies, with the drainage of the marsh, cut deeper until what was once the level bed of a wide shore, or of a deep stream, becomes a series of islands daily growing higher out of the water and separated (except a t low tide) by miniature lakes and rivers. When the expanse of mgrsh is sufficiently large to cause covetous eyes to be cast upon it, it is taken in hand and a wall of its own soil raised round it higher than the water a t high spring tides and set well back from its outer edge. On each side of the wall is a broad and sometimes deep ditch, the bed of which is always very soft, being formed of the underlying clay which has never dried, and into i t on the inside run the old swins, gullies, and runnels which used to run to the sea and now only take off the rain-water from the land.

For some years aftor the reclamation but little change takes place owing to the sodden condition of the ground ?. On the drier parts the Sea Lavender, ObioPM, and the marsh grasses flourish. I n tlie old gullies (now ditches), Sdicorniu and Yea Aster with Ulua and Enteronzorpha still survive, together with crabs, prawns, gobies, Nereis, Littorina, Paludestrina, Alderia, and Limupontia, and other marine forms, trapped during the process of " inning."

As the land dries, sheep and cattle are sent out. The Sea Lavender is devoured and Obione, dwarfed by drought, is either eaten or stamped out. The ditches become sterilized by alternate floods from rainsand salt water from the sluices in the sea wall ; the old flora and fauna die out and are replaced by seasonal ones able to exist just for as long as their appropriate conditions persist in the ditches.

Wading birds like the Heron introduee new seeds and eggs, the wind-borne flora now finds a congenial soil, the reed appears and eventually fills the ditches, and the sloe (more often than not sterile) borders them. The grass grows out into them, and the bottoms rise with decaying vegetation until, after the passing of. years, the shallower ruiiriels are filled up and are only made visible by the drainage water covering the outline of their old course in the winters $.

The marsh becomes the farm ; the land is put under the plough and sown with grass arid corn, and, beeause the land must be well drained, straight ditches are cut at right angles to the main ditch by the dyke wall. So '' the marsh " finally p%sses, though the sea sometimes recovers its domain, as at New England, a t Maldon, and a t Canvey. Also important changes take place in the relation of levels between the new land inside the wall and the old marsh outside.

Inside the walls the land is cropped incessantly, and so its level never rises, but rather tends to sink by dryness and compression of the peat underneath. Outside, the river and its tides daily bring to tlie river-bed and its marshes their load of silt ; and so with time both the bed and the low marsh tend to rise, and eventually the bed of the river is in height many feet above the level of the

* In most estuaries the tide ebbs inshore first, sometimes three-quarters of an hour before it does in the river fairway : this causes an eddy which deposits silts.

f A s at Creeksea, Wallasey Island (Essex), also the banks of Benfleet Creek, outside the wall. 2 Leigh and Hadleigh marshes would appear from old engravings dated 1832 t o be nearly 100

year8 old, but the old creek leading to Hadleigh Castle becomes visible once again after heavy rains in the winter.

7'he origin of most of the marshes of the Thames Estuary is the same.

But changes are at hand.

And this is not all.

P~oc . ZOOL. S0~.-1930, NO. LII, 52

804 MR. F. J. LAMBCBT: ANIMAL LIFE IN

reclaimed lancl, as a t Leigh, Haverigore, sad New England, and the water from tile sluices draining the land has to pass away through channels many feet deep in the inore Fecerit alluvium oiitside. These sluices are generally iron pipes capped ~ l l c l hinged at the end so thnt at a sufficient depth, if working properly, pressuie closes the cap and prevents ingress of the river or sea to the land, whilst not obstructing the drainage water escaping a t low tide, and i t is through these ch:lnnels and pipes that most of the marine animals in the ditches have to come.

IT. ANIMAL LIFE IN THE DITCHES. It will be obvious that an important part will be played in the animal life of

the ditches by the varying salinity of their waters”. This will be determined by tile salinity of the tidal waters outsidvand tho extent to which they have access to the ditches, by rainfall on the land, the strength of the wind, the amount of sunshine causing evaporation, and the time of the year, for all the water has to

through the ditches, and, with a series of high tides and the high river-bed, it may not be able to escape easily ; whilst a t the same time the same winds which c:Luse the pent up waters may bring heavy rains which flood the land. With changes of such violence it is theoletically probable that a fauna able to endure them must be few in species and sometimes sparse in members. This is actually what I have found.

Conversely, a t times when the external pressure on dykes liven by contraction- fissures causes the walls to give way and the sea breaks in, ponds and ditches of rlormally fresh nater are for n longer or shorter period markedly saline. Nevertheless, the water draining into such ponds and ditches from the land Sooner or later reasserts itself, and the salt water is gradually diluted, and but few marine animals, SO far as I have seen, succeed in maintaining themselves in their new habitat of pure sweet water. The animals which do so are PaJemonEtes vcdrians, Neomysis, the 3-spine Stickleback, and the Eel. I know of no others, brlt it is possible that other forms do survive in some of the ponds and ditches.

A single example will illustrate the association and habitat under discussion. A t Kearsey’s Marsh, Bentleet, on the land side of the railway and towards Leigh, is a sqnare pond connected with a ditch, once part of a brickfield. It contains pure water -f drunk by horses and cattle. Here occur three of the fQrmS just meiitioned, survivors of inundations in 1902 and 1907 from the Ray. The chief water- plant is Potnwiogeton pectinatus. Enteromorpha greatly changed is also present, ~ ’ a ~ ~ m o n ~ t e s varians is there in thousands, half a mile from the sea-water. It is glass-like in appearance and only visible from above by the black mud in the stomachs (apparently the only food). Neomysis is not SO plentiful. Eels, however, were knbwn to be present.

the nature of the mud a t the bottom of the ditches. Having once been tidal banks, all the marshes will contain shells of varions species and, therefore, lime. The soil of Canvey Island is full of cockle shells. A t Leigh few cockles are found, but M ~ ~ , &yobiculuria, and Tellina occur, all having hard shells which resist &corn. position. At New England and Havengore, oysters and Crepidula seem to be present in good numbers and in a very decayed condition. Besides this there is decayed d&ris from the vegetation,and, in Some Soils such as that of the Leigh ditches and Shelford creek, very much iron. which is probably being fixed by the action of bacteria. This is most pronounced where the bed is very soft from the presence of silt and the decay of the local vegetation. It seems largely absent in ditches periodically cleansed (by digging) by the farmer at Leigh and by the war Department along the roadside towards Havengcure Bridge, a t Wakering, where

* The variation is very great in the Thames Estuary, viz. 1.028 in a normally dry 8e8son to an low as 1.010 off the ‘ I Mouse ” lightship on one occasion. t See note in Essex Naturalist,’ xix. pt. V. p. 338,

They breed abundantly. No other inhabitants were observed.

A factor which I think influences the flora, and through the flora the fauna,

THE MARSH DITUHES O F THE TEAM88 ESTUARY. 805

the ditch-beds appear greenish yellow in colour, as against the reddish brown of those untouched.

That the pollution of the soil affects the flora would seem proved by the fact that I have failed to get Chcetomorpha linzim, which exists in masses in Wakering ditches, to establish itself in the Leigh Marsh ditches, the Wakering ditches being " clean," the Leigh ones polluted ; but it is possible, however, that evaporation in the Wakering ditches, which are well inland, and the clear water produce the conditions essential to life, as Chcetomorphu likes, and can endure, very high salinity, bright light, and heat *,

The condition of the mud must also affect to some extent the rnollusca and worms which live in it. I have seen the shells of Paludastrina d v m quite red with rust f. As a matter of fact, the predominant colour of the shells of these molluscs is reddish. A t various places in the Leigh ditches I have seen both the bottom and the vegetation very rusty, and in Shelford Creek, Foulness side, there were patches where rust was actually oozing away at the surface, though, delving with a trowel under the patches, I failed to disclose any spring or anything other than ordinary surface drainage. On the Leigh open mud-fiats old tube-casts of worms where the soil is denuded after storms stand out of the surface as iron sand, and iron pyrites is quite common in the form of nodules and finger-like shapes.

I n these enclosed ditches in hot weather an incessant struggle exists for oxygen. The weed, especially Vuucheria, the nether masses of which are almost always buried in putrid mud, grows luxuriantly in the .hot sunshine and rapidly evaporating water, which, brackish a t first, becomes very salt at last. The plant in masses turns reddish, then pale yellow, and dies, poisoning most of the life which i t had previously helped to preserve. At Wakering I have seen large eels lying with more than half their bodies out of water which was red (2 with alga or rust) and stinking. When pushed back into the water they crawled out again. A t Leigh, in the artificial ditches I have seen Gasterosteus lying dead in hcndreds from the same cause, yet in the putrid mud hundreds of PffiEtdestrina ventrosa were still alive and apparently unharmed. Crustacea are not noticed on such occasions; either they withdraw in time, or their bodies are not noticeable 2.

It will be noticed that the observations recorded above refer to the putrefaction of vegetation ; yet also great loss of life takes place through high salinity and desiccation. The Mollusca generally do not appear able to sustain high salinities. I have seen in the middle of Havengore Island a large colony of Curdium edule dead (1921) through high salinity, the water not otherwise being bad, and I have also seen in the ditches, recently cleaned, large masses of Ch~tomo7yhu linum in a rapidly reducing quantity of crystal-clear wtter of the high salinity with numbers of Gasterosteus (3-spined) striving to find a way out of the water in vain.

I n one case a t least it is interesting to note that an aquatic animal exposed to tho danger involved in the periodic drying-up of its habitat apparently survives in great numbers because it has acquired amphibious habits. This form is Puludestrina ulvvce, which, in my experience, has a definite objection to continuous immersion in water.

I think that wherever this mollusc occurs i t will be discovered to spend a t least 20 hoursof the 24 in direct contact with air, even if it must be moist air. If it is in tidal water i t will be found thus long, uncovered. If in stngnant water; it will crawl out and sometimes remains out so long as to die. Littorzwa r d i s perishes in the same fashion occasionally. I n artificial conditions it crawls

* Perhaps the absence of iron from the cleansed ditches is also a factor, t vuaucheria in my jars apparently caused a heavy deposit of rust to collect on the glass

wherever a piece of limestone touched it ; and mud from Shelford creek leaves a line of rust on the glass of the jar containing it at the h e of the surface of the mud.

$ I have, on the other hand, found numbers of Stratiomy larv= at Wakering living amid putrescent vegetation, and Corophium lives under similar conditions a t Leigh.

52*

806 NR. F. J. LAMBBRT : ANIMAL LIFE IN

out and attaches itself by a film. In nature i t would probably be recalled t o activity by rain, which would moisten the film and cause the mollusc to drop on damp ground and so recuperate *.

In a normal way rain is received in these ditches so gradual1.y as not to cause great harm. As a matter of fact, it does not appear to be obnoxious to many creatures to which tap water would be fatal t. Starfishes on sandbanks and mudbanks and Actiniu ‘mese,nbryffinthemum on rock, Nereids in mud, besides Irucoids, Enteromorphu, and other plants, must often be literally deluged with it- yet they survive.

It is doubtful whether non-saline water ever reaches the ditches in sufficient masses to be fatal to the fauna. The creatures disliking a low salinity usually have time to retire to the sea-wall, where, it is conceivable, they may be washed out to sea through the sluices. A case of very great biological interest in this connection exists in the dammed portion of New England creek, Essex. Originally a free passage from the Tliames to the Crouch via the Roach, and receiving water and animal life from both directions, it has been dammed at each end of the island by order of the War Office. The western end was designed for a sluice, which, when made, could not be used for fear of washing away the ‘‘ footings.” It has, therefore, been definitely sealed, and the creek, full of truly marine creatures, is now a lake taking the dminnge(not purely fresh, owing t o the island having been “ drowned” for so long, since 1897) of the island. It contains Flounders and other flatfish (some kiiown to be still alive), Oysters, Sabellu, Tunicates, Nereids, Cvepidtda, Anaphitrite, Whelks, Crabs, and probably many other forms, inclitdiug bivalves. The water is very brackish. It would be very interesting to know if this fauna is still alive, but a proper dredge would be necessary, with a boat (at present there) and War Office permission.

At Hadleigh Marsh many of the cross ditches on the south side and all on the north side of the railway are now fresh water, with a purely freshwater fauna, except in the case mentioned a t Benfleet (Kearsey Marsh). Water Grasses abound with Rushes, Water Jzanmiculus, Callitriche, Mosses, Lemna, Potanzogeton, Juncus and Artindo, but no Anachavis, though I attempted its introduction out of curiosity. Of animals, I have found Dytiscus, Gasterosteus (3-spined and 10- spined), Dragonfly larva, Caddis, Mayfly Iarvs, Bloodworms (Fubifez), Eels, etc.- a true freshwater fauna and flora.

As will be fieen, the life in the brackish ditches will be largely seasonal, and, as regards the marine forms, somewhat dependent on the time when certain species come close into the coasts. The main ditch, neier becomihg dry and oakud, but receiving each title at least a modicum of new water, becomes R factor in the distribution of the species.

V. NOTES ON THE LEIGII DITCHES. I n MI-. G. C. Robson’s pzper on the succession of Paludestrimz t~lvcje and

wentrosffi (Ann. & Mag. Nat. Hist. 1920) appear lists of the fauna and flora of the Leigh ditches. As he states, they are not complete. The forms recorded in my notes for these ditches may be added to Robson’s lists :-

(1) 2/4/1922. Examined main ditch, Leigh Marsh j found a few Gobies only, no Prawns or Sticklebacks ; found specimens of Alde&z naodestu and Limapontia nigrffi (first time for 2 years).

(2) 29/4/22. Main (Dyke) ditch ; Palmmonetes varians, Qobius mihutus, Spheroma rugicorda.

* In South Africa (Durban) a mollusc, probably Cerithidea, climbs out of the mud and up the stems of the mangroves, remaining suspended in thousands from the undersidea of the branches until they eventually drop off dead.

t Fresh water is stated to kill Starfish instantly, and rtnemones are likewise destroyed by it to my knowledge.

THE MARSH DITCHES OF THE THAMES ESTUARY. $07

(3) 28/5/22. Main ditch ; Pakernon squilla, small 3-spined Sticklebacks, also a few of breeding size, S. rugicorda and a few sewatus (rarer), 1 Eel (3 inches), no Gobies, no Corophiurn, millions of Paludestrii~a-in proportion, 150 UlvGe t o 15 veiatrosa.

(4) 3/3/23. Searched Leigh main ditch for Corophiunz j found none ; G. minutzts and a few largish Sticltlebncks found. Afterwards went to side ditch (west) for larva! of Chameleon-fly, but found none. Brought up mud containing Aldevia niodestci and two S. rugicorda.

(5) 24/3/23. Visited main ditch, Leigh ; found G. ntiiautus, Stickleback, S. rugicorda, and Idotea, Gut no Corophizcnt ; noted bed of ditch black and rotten, with patches of grey fungus.

Visited Leigh main ditch and side ditches ; saw no Corophium ; found large Sticklebacks, Gobies, Idotea, P. varians i n numbers in side ditches, with beetles and four 1mvE like Leacher Jackets, but not apparently the l a rw of Dronefly (Rat-tail larvze).

Vaucheria i n plenty, animal life scarce; P. varians, a few Sticklebacks, 1’. veizt~osa i n abundance, mostly floating. Obtained a water-boatmsri (A’ofonecta) and Hydrophihs ; saw no Stratiomnys larva: nor pupz ; nothing but P. ae3ztrosa on weed pulled up.

(8) 13/1/29. Visited main ditch Leigh, high tide, but very little water coming through sluice. Surface of ditch covered with th in film of ice; no trace of animals save worms and Scrobiculuria from their tubes ; shrunken and crinkled Ulvcz the only weed.

(6) 2/4/23.

(7) 4/3/23. Rode t o Wakering and examined ditches.

Ditch filled with refuse.

Thus it will be seen the inhabitants generally of the marine ditches a re a8

PISCES.. . . . . MOLLUSCS .

VERMES . . . CBUS~ACEA. Carciiizts ninrnas, Idoten, Ganiniams, Spheronza, Corophium,

INSECTS . . . Hydrophilus, Strationys, Dipterous flies, Notonecta. PLANTS . . . Ulva luctuca, host to Paludestrina u h z , Paucheria marina, host to

P. veiitrosa, Chatomorpha linuna, host to Littorii~a riidis var. teizebroscc, Enteromorpha, host t o Alderia niodesta, Limnpontia nigra (and at Slielford Creek to P. zc lv~) . Ruppia nzciritima (to which a Dipterous fly larva attaches itself). Xchlerochroo naaritima ,

fnllows :- Gcf,sterosLeits (3-spined), Gobitcs iniitutus, and Eel. Sm o b i c d ~ i c ~ . C(crcliicnz, P u l ~ m ilnd eeiztrosa, Littorina iwlis vnr.

Ncreis diversicaloi. ant1 peluyica, Nematoda tenehosa (W;ilming), A. nzodestcc, and Linzupoiitia itigra.

Palcemoiietes va~icci~s, P. squilla.

The Corophiztm mentioned are exceedingly interesting, being gargantuan for t h e species. I have never met with them on .flats of the Estuary, which contain t h e 3-inch vertical burrows of untold myriads of the small variety of Corophium. Of the large variety t h e British Museum possesses one specimen (from Hastings), and Stratford Essex Museum three specimens (from Leigh main ditch). It is quite probable tha t no more will be obtained from the la t ter station. To such extent had the inferior antenna1 legs developed t h a t it was impossible for t h e creatures to swim normally, and they rolled over and over i n progressing. They werevisible in one month only of t h e year (April), when they could be seen swimming and moving along the bottom. I have never been fully satibfied as t o whether they were indigenous t o the main ditch or were annual introductions through t h e sluice, bu t I am inclined to believe tha t the former is correct.

They were never abundant.

808 ANIMAL LIFE IN THE M A R S 5 DlTCHEk OF THE THALMEB ESTUARY.

VI. SUMMARY. 1. The formation of the marsh ditches on the Essex side of the Thames

estuary is described. 2. An account is given of the progressive reclamation of the marshland and

its conversion into arable, and the effect of these processes on the aquatic organisms contained in the drainage ditches of the marsh.

3. The effect of various kinds of organic polliltion which occur regularly each year during the hot weather and of periodic changes in salinity are discussed in detail, and the seasonal change in animal life is described.

4. Detailed notes on the seasonal changes and faunal succession in the brackish pitches at Leigh are given.

F? 2 . 5. 1930, MIDD1ETON.PI. I .

THE ECOLOGY OF T H E AMERICAN GREY SQUIRREL (SCIURUS CAROLINENSIS GMELIN) IN THE BRITISH ISLES.

P. 2 . S. 1930, MIDDLETON. PI. I I .

THE ECOLOGY OF THE AMERICAN GREY SQUIRREL (SCIURUS CAROLINENSIS GMELIN) IN THE BRITISH ISLES.

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