Seaweed communities on the artificial coastline of south eastern England by Suffolk Naturalists' Society

SEAWEED COMMUNITIES ON THE ARTIFICIAL COASTLINE OF SOUTH EASTERN ENGLAND 1. RECLAIMED SALINE WETLAND AND ESTUARIES IAN TITTLEY

The coastline of south eastern England between northern Kent and Suffolk comprises a complex of estuaries. Since the last glaciation these have undergone considerable changes in coastal configuration, largely due to the effects of rising sea level on soft coastal strata. Man has long inhabited this region and has attempted to stabilise the coastline, originally to prevent flooding, but more recently to improve the coastal environment for industrial, agricultural and amenity uses. Early attempts at sea-wall construction relied on local naturally available materials, usually earth walls with seaward sides stone-pitched. Modern structures employ concrete paving or stepping on the seaward faces; this ensures stability, imperviousness and resistance to abrasion (Minikin, 1963; Barnes, 1977). These and other additions such as groynes and pilings, slipways and quays have created new or alternative habitats for plants and animals. Published accounts of the benthic algal Vegetation on seawalls in the reclaimed wetlands of south eastern England are scant; they include: Price, et al. (1977), Lincolnshire; Chapman (1937), Norfolk; Milligan (1963), Blackwater estuary, Essex; Nisbet (1960), Skippers Island, Essex; Clarke and Tittley (1980), Seasalter, north Kent. The importance of this habitat in England has generally been undervalued; sea-walls in the Netherlands by contrast, have been comprehensively studied (den Hartog, 1959). This project records algal communities on artificial structures and identifies the main differences between these and those in saltmarsh; it augments recent studies in riverine (Tittley, 1985) and open-sea habitats (Tittley, in press). Sites selected for investigation were located in Suffolk, Essex, Kent and Sussex (Figure 1). The north Kent coast site was a wetland area designated by IUCN as internationally important; many of the others of were national or local importance for conservation. Artificial shores were mainly concrete, sometimes boulders, giving way at lower levels to extensive mud-flats. One site (Felixstowe ferry) was a wooden breakwater. Study-areas in adjacent saltmarsh were usually Puccinellia (Common saltmarsh grass) turf, Spartina (Common cord-grass) or Halimione (Sea-purslane) stands.

Methods Algal cover at all artificial sites was studied by belt-transect. Species were sampled and recorded at intervals of 50mm along the transect and at 5 points 100mm apart across the transect; sampling intervals along the transect were extended to 100mm on the more gently sloping and extensive Burnham and Canvey walls, and to 300mm intervals at Upnor. Natural habitats were investigated by sampling 50 points (five 100mm apart, across; ten 50mm apart, down) in a placed 0-25m 2 quadrat.

Trans. Suffolk Nat. Soc. 21

SEAWEED ON THE ARTIFICIAL COASTLINE OF S.E. ENGLAND

Species recorded Overall, 42 species (14 Chlorophyta, 13 Phaeophyta and 15 Rhodophyta) were recorded on sea-walls (Table 2). Only 17 species were from saltmarshes (Table 3); twelve were common to both habitats. The cyanophyte Entophysalis deusta occurred sporadically on sea-walls. Chlorophyta were predominant in the saltmarsh and on natural shores, whilst Phaeophyta predominated on man-made structures. Natural shores The general pattern of algae in saltmarsh is illustrated by the North Kent site (13). A green algal mat of Blidingia minima, Enteromorpha intestinalis/ prolifera (Gut-laver) and the red Bostrychia scorpioides among a horizontal turf of Puccinellia maritima (Huds.) Pari. Saltpans contained additionally E. flexuosa and Cladophora sp. Extensive E. intestinalis/prolifera and occasional Pilayella littoralis grew on the vertical wave eroded clay face and clay Trans. Suffolk Nat. Soc. 21

Suffolk

Natural

History,

Vol. 21

Table 1 Sites Location 1. Southwold (R. Blyth) Suffolk 2. Orford (R. Aide) Suffolk 3. Waldringfield (R. Deben) Suffolk 4. Felixstowe ferry (R. Deben) Suffolk 5. Chelmondiston (R. Orwell) Suffolk 6. Mistley (R. Stour) Essex 7. Brightlingsea (R. Colne) Essex 8. Bradwell (R. Blackwater) Essex 9. Burnham (R. Crouch) Essex 10. Canvey (R. Thames) Essex 11. Grain (R. Thames) Kent 12. Upnor (R. Medway) Kent 13. Harty Ferry (R. Swale) Kent 14. Rye Harbour (R. Rother) Sussex

investigated

Structure

Natural substrate

Sloping embankment of concrete and boulders Sloping embankment of concrete and boulders Concrete quayside and slipways Wooden breakwater

Saltmarsh, mud

Brick wall, slipway, boulders Concrete quayside, wood pilings, boulders Stepped concrete wall

Saltmarsh, shingle, sand, mud Saltmarsh, mud

Sloping embankment of concrete and boulders pitched with bitumen Sloping embankment of concrete and boulders pitched with bitumen Sloping embankment of concrete and boulders pitched with bitumen Sloping concrete embankment Concrete slipway

Saltmarsh; mud

Saltmarsh, mud Saltmarsh, shingle, mud Saltmarsh; shingle beach

Saltmarsh; mud

Saltmarsh; mud Saltmarsh; shingle beach; mud Saltmarsh, mud

(a) Concrete sea-wall, lower limestone boulders (b) boulder causeway Sloping concrete Saltmarsh; sand beach; embankment mud

b o u l d e r s at t h e f o o t of t h e s a l t m a r s h ; a small n u m b e r of Fucus ( W r a c k ) g e r m l i n g s g r e w a m o n g t h e l a t t e r a l g a e . T h e m u d f o r e s h o r e w a s d e v o i d of m a c r o a l g a e . Similar c o m m u n i t i e s b u t w i t h o u t B. scorpioides were recorded in s a l t m a r s h turf at m o s t o t h e r sites. T h e filamentous r e d Polysiphonia macrocarpa w a s e l s e w h e r e w i d e s p r e a d o n e r o d i n g clay f a c e s . In Halimione s t a n d s B. minima a n d Catenella caespitosa g r e w epiphytically o n u p p e r a n d l o w e r H. portulacoides b r a n c h e s r e s p e c t i v e l y , while Enteromorpha spp., a n d B. scorpioides g r e w o n m o i s t soil b e n e a t h . T h e largely n a t u r a l b a n k s of t h e R i v e r O r w e l l in t h e C h e l m i n d s t o n e a r e a s u p p o r t e d Enteromorpha and Vaucheria m a t s a m o n g Zostera ( E e l - g r a s s ) s p . ; t h e l a r g e r b r o w n s Fucus spiralis ( S p i r a l - w r a c k ) , Petalonia fascia a n d Scytosiphon lomentaria grew a m o n g Spartina. R a r e l y , m a t u r e F. spiralis g r e w a t t a c h e d t o h a l o p h y t e rhizomes.

Trans. Suffolk

Nat. Soc. 21

SEAWEED ON THE ARTIFICIAL COASTLINE OF S.E. ENGLAND

Artificial shores Four main bands of algae were detected on sea-walls (Figure 2, Table 4): (1) A supralittoral band of the cyanophyte and/or small green algae. (2) A lower, wider band of Blidingia minima around high tide level. An extensive cover of larger fucoid algae below high water level of neap tides could be separated into: (3) an upper band of Fucus spiralis-, beneath which were green algae such as Ulothrix spp., Urospora spp. and Enteromorpha spp.; (4) a low band and dense cover of F. vesiculosus (Bladder-wrack) and Ascophyllum nodosum (Knotted-wrack) occasionally with the obligate epiphyte Polysiphonia lanosa, over a patchy understory of small green, brown and red algae such as Audouinella purpurea, Callithamnion hookeri, Ca caespitosa, Chondrus crispus (Carragheen-Moss), Cladostephus spon Cladophora rupestris (Blanket-weed), Gelidiumpusillum, Pilayella litto Polysiphonia macrocarpa, Sphacelaria radicans and Viva (Sea-lettuce). Although a generally consistent pattern of zonation was recorded at most sites (Table 4), the greatest Variation was seen at supralittoral levels where three distinct bands were detected. The green algae Prasiola stipitata and Urospora wormskioldii were the dominant species at Southwold and Brightlingsea respectively, while the cyanophyte Entophysalis deusta was predominant at Orford, Grain, Upnor and Rye; elsewhere this level was bare of algae. Other deviations from the pattern of zonation described above were open bands of Rhizoclonium riparium and Enteromorpha spp. below th band of Blidingia on the wooden structure at Felixstowe ferry; a narrow band of Pelvetia canaliculata (Channelled-wrack), at Rye, above and mixed with that of Fucus spiralis. Discussion Several factors are important in determining the occurrence of macroalgae at outer estuarine sites. These are, the availability of substrate for attachment, the variable salinity and the extreme turbidity of the water. As to substrate, large areas of intertidal wetland are of soft mud or silt and are not usually colonised by macroalgae except for occasional Enteromorpha mats and Vaucheria patches (e.g. site 6). Algal Vegetation of natural habitats was clearly different from that on artificial surfaces. At all sites a very distinct pattern of zonation on walls, characterised by brown algae, contrasted with a mosaic of largely green algae in saltmarshes. The composition of brown algal wall communities resembled those in similar habitats in adjacent counties and continent (cf. den Hartog, 1959; Price et al., 1977) although species diversity was reduced in comparison to open-sea sites (Tittley, in press; see also below). The brown algal communities of outer estuaries also contrasted with green-algal dominated communities on walls in the inner, less saline reaches of estuaries (Tittley, 1985; Tittley & Price, 1977). The least obvious and most variable components of the sea-wall Vegetation, and not present in marshes, were the uppermost (supralittoral) communities. Two of the three detected, characterised by Prasiola stipitata and Trans. Suffolk Nat. Soc. 21

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Suffolk Natural History, Vol. 21 Table 3 Algae recordedfrom

saltmarshes

Chlorophyta Acrosiphonia centralis Blidingia minima Cladophora sp. Enteromorpha flexuosa (Wulf, ex Roth) J. Ag E. intestinalis/prolifera* E. torta Rhizoclonium riparium Ulothrix flacca Urospora penicilliformis * For the purposes of the present paper these species are treated as a single entity. Phaeophyta Ectocarpus fasciculatus Harv. Fucus spiralis Petalonia fascia Pilayella littoralis Scytosiphon lomentaria Rhodophyta Catenella caespitosa Bostrychia scorpioides (Huds.) Mont. Polysiphonia macrocarpa Xanthophyceae Vauchaeria spp.

Urospora wormskioldii, occur widely on rocky shores in western Britain and on sea-walls in the Netherlands; the occurrence of P. stipitata at Southwold may reflect local nitrogen-rich pollution. The band forming cyanophyte Entophysalis deusta is less common on western shores but widespread on concrete structures at open-sea sites in the southern North Sea (den Hartog, 1959; Tittley, in press). A distinct feature of the green algal Vegetation on most sea-walls was the desiccation tolerant Blidingia minima at littoral fringe levels, corresponding to its occurrence in the higher, drier regions of saltmarsh. Its consistent presence as an open band, particularly on concrete, conflicts with Lewis's (1964) observations of Blidingia as an ephemeral species on northern and western shores of Britain. Enteromorpha spp. found only once as an open band (on porous wood, Felixstowe ferry) otherwise grows beneath fucoids where sufficient moisture is available. The most obvious difference in Vegetation was the abundance of mature fucoids on sea-walls. Fucoids differ from saltmarsh species in being large in size, perennial, and requiring a firm substrate for attachment. Fucus spiralis and F. vesiculosus were as frequent and widespread as they are on natural rocky and open-sea artificial shores. Ascophyllum nodosum is widespread on Atlantic shores but only sporadic in the southern North Sea; sea-walls have

S E A W E E D ON THE ARTIFICIAL COASTLINE OF S . E . ENGLAND

enabled this fucoid to spread in eastern England. Pelvetia canaliculata is also now less rare in eastern England occurring additionally on sea-walls at Rye (this survey) and Boston Häven in the Wash (Price et al., 1977). The infrequence of F. serratus (Serrated-wrack) and absence of Laminaria spp. (Kelp) probably reflects both a lack of suitable substrate at low shore levels and occasional significant reductions in salinity. The poor underflora beneath the cover of fucoids (both in numbers of species and their individual luxuriance) is because many red and brown algae are not able to tolerate even the temporary reductions in salinity likely to occur in the outer parts of estuaries. Most of the species recorded here were those noted by Tittley and Price (1977) as tolerant of fluctuating salinities in the outer Thames estuary. The occurrence of underflora species Audouinella purpurea, Callithamnion hookeri, Chondrus crispus, Cladostephus spongiosus and Gelidium pusillum represent local incursions since they have never been found in saltmarshes. These and Cladophora rupestris, Pilayella littoralis, Polysiphonia macrocarpa and Sphacelaria radicans, suggest some

Prasiola

i i Ü

stipitata

Blidingia

minima

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vesiculosus

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III

Ullliimillii lllillnlll

. ii iii.iiiiii intestinalis/proiifera

ILL Ulva

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lactuca

Base

Zonation of algae on sea wall Southwold, Suffolk. 0 > 5 indicates frequency (corresponding to points across the transect). Hatched lines indicate touches of fronds; continuous lines touches of holdfasts. cHWS indicates an estimation of high water, spring tides, level.

Suffolk Natural History, Vol. 21 Table 4 Algal

zonation

<e Oll c

2 3 ££

OD _ c sa b u. 3 sj IS o c ^ J -a c a. S f f l f f l B ü O D I I O i

«O Ö Z

oim^t'nôfôoô

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BAND(ZONE) Entophysalis Prasiola Urospora Blidingia Rhizoclonium Pelvetia Fucus spiralis Enteromorpha Fucus vesiculosus Ascophyllum Small reds Ulva

A A

A A A A A A A A A A

A A A A A A A

A A A A A A A A A A A

A A A A A A A A A A

similarity of underflora communities to those on natural rocky and open-sea artificial shores. Rapid cycles of growth and reproduction probably enabled small brown and red species such as P. littoralis, and P. macrocarpa to survive on transient clay as well as the more usual rock surfaces. The red alga Bostrychia scorpioides is widely known in saltmarshes and sometimes occurs on rock substrates in tidal rivers (Lewis, 1964). Its absence from sea-walls on the east coast may be due to a lack of sufficiently shaded situations. Catenella caespitosa, by contrast, was an underflora constituent in both habitats. Most other algae listed only for natural habitats (Table 3, except Enteromorpha flexuosa) occur in rocky situations elsewhere (cf. den Hartog, 1959; Tittley, in press). A saltmarsh algal habitat lost as a result of reclamation is saltpans; these formations and their flora in certain respects correspond to pools on a rocky shore. Since sea-walls normally have relatively even surfaces, recolonisation by pool species is prevented. Changes in flora and fauna following the reclamation of saltmarsh have been investigated at few places (Petch, 1906 - H u m b e r estuary (Yorkshire); Price et al., 1977, - Wash (Lincolnshire); Lambert, 1930 and Myers, 1954 -

SEAWEED ON THE ARTIFICIAL CO ASTLINE OF S.E. ENGLAND

Thames estuary (Essex); Side, 1973, - Thames estuary (Kent)) and only briefly mention algae. While Side (1973) noted the disappearance of Enteromorpha spp. from saltings, Lambert (1930) and Petch (1906) recorded the survival of Ulva, Enteromorpha and Chaetomorpha in brackish ditches after their closure to the sea. No reference was made to the development of algal Vegetation on the seaward faces of sea-walls. Price et al. (1977) identified on the Lincolnshire coast differences between the algal Vegetation of marsh and sea-walls closely resembling those reported here. The present and few previously published field studies have demonstrated a broadly similar pattern of algal zonation on outer estuarine sea-walls throughout south eastern England. This uniformity relates to overall similarities in wall-design, materials used and ecological conditions. Introduction of fresh, stable substrate to an area where the natural substrate is soft or unstable represents a major environmental change. Thus what is essentially a rocky shore environment has extensively replaced natural saline wetland with the consequent loss of specialised communities. This may have wider ecological implications since, for example, green algae are a major component of wildfowl diet. The importance of these changes in character of the benthic algal flora of south eastern England has generally been overlooked. Acknowledgements Dr I. Ridge (Open University), Dr R. L. Fletcher (Portsmouth Polytechnic) and Mr J. H. Price (British Museum, Natural History) for their help and encouragement in many ways. References Barnes, R. S. K. (1977). The Coastline. A contribution to our understanding ofits ecology andphysiography in relation to land-use and management and thepressures to which it is subject. London: John Wiley & Sons. Chapman, V. J. (1937). A revision of the marine algae of Norfolk. Bot. J. Linn. Soc. 51, 205. Clarke, G. C. S. & Tittley, I. (1980). A botanical survey of the South Swale Nature Reserve. Trans. Kent Fld. Club 8, 51. Hartog, C. den (1959). The epilithic algal communities occurring along the coast of the Netherlands. Wentia 1 , 1 . Lambert, F. J. (1930). Animal life in the marsh ditches of the Thames estuary. Proc. zool. Soc. Lond. 1930, 801. Lewis, J. (1964). The ecology of rocky shores. London: English Universities Press. Milligan, G. M. (1965). The seaweeds of the Blackwater estuary. Essex Nat. 31, 309. Minikin, R. R. (1963). Winds, waves and maritime structures Studies in harbour making and the protection ofcoasts. London: Griffin. Myers, J. E. (1954). A survey and comparison of the natural and inned saltmarsh at Leigh on Sea, Essex. Essex Nat. 29,154.

Suffolk Natural History, Vol. 21

Nisbet, R . H . (1960). Marine biology at Skippers Island. Essex Nat. 30, 247. Petch, T. (1906). Notes on the reclaimed land of the H u m b e r district. Trans. Hullscient. Fld. Nats. Club, 3, 221. Price, J. H . , Tittley, I. & Honey S. I. (1977). The benthic marine algal flora of Lincolnshire and Cambridgeshire: a preliminary survey. Naturalist, Hull 102, Part 1 , 3 ; Part 2, 91. Side, T. (1973). Vegetational changes at Egypt Bay following the exclusion of tidal water. Trans. Kent Fld. Club 5, 60. Tittley, I. (1985). Zonation and seasonality of estuarine Benthic algae: artificial embankments in the River Thames. Botanica Mar. 2 8 , 1 . Tittley, I. (in press).. Seaweed communities on the artificial coastline of south eastern England 2. Open-sea sites. Trans. Kent Fld. Club. Tittley, I. & Price J. H . (1977). The marine algae of the tidal Thames. Lond. Nat. 56, 10. Ian Tittley, Botany D e p a r t m e n t , British Museum (Natural History), Cromwell R o a d , London, SW7 5BD.

Unusual Fungus from Brightwell In the autumn of 1984 Mrs E . Coe of Brightwell, Ipswich brought to Ipswich Museum a fungus that she had found growing in her garden and along an adjacent woodland edge. It consisted of a network of white branches forming a hollow ball about tennis ball size. The branches were covered in dark olive green slime and it had a very strong, unpleasant smell. This fruiting body arose f r o m an 'egg stage'. These characters pointed to it being related to the Stinkhorn, Phallus impudicus Pers., however, no mention of it could be found in any of the Standard reference books and it baffled local mycologists. The preserved specimen and a photograph were, therefore, sent to D r Derek Reid of the Royal Botanic Gardens, Kew. H e identified it as Illeodictyon cibarius Tul., a species from the Southern Hemisphere which is found in Australasia and South America. It appears to have been introduced accidently to Britain and has previously only been recorded f r o m Surrey, where it was first reported in 1956 in a garden in H a m p t o n (Reid & Dring, 1964). It has since spread locally to the Thames Ditton area. Mrs Coe remembers seeing the fungus in previous years and there is good reason to believe this is a completely separate introduction that is now well established in the area. The specimen has been retained at Kew. Reid, D . A . & Dring, D . M. (1964). Trans. Brit. Myc. Soc. 47, 293. Carol A . Green The M u s e u m , High Street, Ipswich IP1 3 Q H

Trans. Suffolk Nat. Soc. 21