Biodiversity & Conservation

The terrestrial animal and plant communities of Phragmites reed beds have been well studied (Haslam, 1972; Ranwell, 1972; Haslam, 1978; Fuller, 1982; Cowie et al., 1992; Ditlhogo et al., 1992; Fojt & Foster, 1992; Ward, 1992; Rodwell, 1995; Hawke & José, 1996), while the aquatic community, especially invertebrates, has been less well studied (Arnold & Ormerod, 1997) and the benthic infauna are poorly known (Connor et al. 1997a). In the information that follows inferences concerning ecological relationships have been made from other aquatic communities (see £IMU.NVC_A12£ or £IMS.Rup£) where appropriate. Phragmites australis forms extensive perennial systems of rhizomes that bind, oxygenate and stabilize the sediment.

The rhizomes, litter and upright stems of Phragmites australis provide a substratum for a wide variety of microalgae, macroalgae, aquatic invertebrates, terrestrial invertebrates and amphibians, and substratum and nesting material for some birds (e.g. the reed warbler Acrocephalus scirpaceus and the bittern Botaurus stellaris) and the harvest mouse (Micromys minutus).

Phragmites australis and other aquatic macrophytes or helophytes (e.g. the common marsh bedstraw Galium palustre, bogbean Menyanthes trifoliata, and the spear-leaved orache Atriplex prostrata) provide primary productivity within the biotope and are fed on by numerous phytophagous insects.

Phragmites australis is fed on directly by numerous species of Lepidoptera (butterflies and moths), Diptera (flies), Hymenoptera (bees and wasps), Coleoptera (beetles), Homoptera (true bugs and aphids), and Acari (mites). Notable examples include, the large wainscot Rhizedra lutosa, the twin-spotted wainscot Archanara geminipunctata, Fenn's wainscot Photedes brevilinea, the reed leopard moth Phragmataecia castaneae, the gall forming midge Giraudiella inclusa, gall-forming flies e.g. Lipura spp., and aphids such as Hyalopterus pruni (for details see Haslam, 1972; Ditlhogo et al., 1992; Tscharntke, 1992, 1999; Fojt & Foster, 1992; Hawke & José, 1996; Drake, 1998).

Short, young shoots or rhizomes of Phragmites australis may be grazed by sheep, deer, water voles, some species of wild birds (e.g. Canada or grey lag geese) (Haslam, 1972, Hawke & José,1992; Rodwell, 1995).

Additional primary productivity is provided by benthic microalgae (Wainright et al., 2000), microalgal (e.g. blue-green algae and diatoms) periphyton and epiphytes growing on the stems of Phragmites australis (Müller, 1999), a mat of filamentous algae (e.g. Ulva prolifera and Cladophora spp.) in more saline situations and, when present, stoneworts (e.g. Chara aspera and Lamprothamnium papulosum) (Connor et al., 1997a).

Decomposition of leaves and stems, especially in autumn and winter, support a detrital food chain within the biotope and probably also provide primary productivity to deeper water and the strandline. Wainright et al. (2000) suggested that Phragmites australis contributed secondary productivity to aquatic food webs in tidal marshes (see productivity below).

The most important role in the food chain for isopods (e.g. the water louse Asellus aquaticus, the isopod Sphaeroma rugicauda and the wood louse Philoscia vittata) and gammarids (e.g. Orchestia spp., Gammarus zaddachi and Gammarus duebeni) is the break down of decomposing leaves, stems and other plant material into fine particles of detritus suitable for suspension and deposit feeders and microbes in the detrital food chain (Hawke & José, 1996; Arnold & Ormerod, 1997; Fell et al., 1998). Other decomposers include midge larvae, nematodes, oligochaetes (e.g. Heterochaeta costata) and Collembella (spring tails).

The periphyton, epiphytes and algal mats may be grazed by gastropods (e.g. Hydrobia ulvae and Potamopyrgus spp.), amphipods (e.g. Gammarus salinus and other Gammarus species), isopods (probably Jaera spp., and Idotea spp.), probably mysids (Mauchline, 1980), and tadpoles where present.

Suspension feeders filter both phytoplankton and detritus (organic particulates), for example amphipods (e.g. Corophium volutator), the mysids, the epiphytic bryozoan Conopeum seurati where present (see Bamber et al., 2001), and some polychaetes (e.g. Hediste diversicolor).

Surface and infaunal deposit feeders probably include oligochaetes (e.g. Heterochaeta costata), amphipods (e.g. Corophium volutator), and chironomid larvae.

Small aquatic invertebrates and fish fry or larvae are probably preyed on by small mobile predators such as dragonfly larvae, water boatmen (e.g. Sigara spp.), mysids, shrimp (e.g. Crangon crangon), and small fish such as sticklebacks e.g. Gasterosteus aculeatus).

The larva of the silky wainscot Chilodes maritimus preys on the pupae of other reed moths.

Other fish such as the gobies and the eel Anguilla anguilla are generalist predators.

Mysids, shrimp (e.g. Crangon crangon or Palaemonetes varians) and crabs probably act a scavengers within the biotope.

The terrestrial and aquatic macroinvertebrate population probably supports a variety of fish species, which enter the habitat from shallow water or with the tide, and a variety of bird species from the surrounding area.

Small fish such as sticklebacks, minnow, fish fry, together with frogs may be important food sources for the bittern or grey heron (Hawke & José, 1996).

Terrestrial insects are probably food sources for frogs, birds and small mammals, both within the reed bed and the surrounding area. For example, chironomids (midges) are an important food source for warblers and bearded tit (Panurus biarmicus), while aphids are an important food for migratory warblers, e.g. the sedge warbler Acrocephalus schoenobaenus. Water voles and water shrews are common on ditches and the harvest mouse may reach high numbers in reed beds feeding on insects in summer and seed (including Phragmites seed) in winter (Hawke & José, 1996).

Where present the otter (Lutra lutra) may feed on frogs and fish, while the grass snake (Natrix natrix) feeds primarily on frogs (Hawke & José, 1996).

Competition
In saline and brackish conditions Phragmites australis competes with other halophytic plants e.g. cord grasses Spartina spp. at its seaward limit, where conditions favour Spartina species (Ranwell, 1972). In drier areas of marsh Phragmites may be out-competed by bulrush Typha latifolia, the common club rush Schoenoplectus lacustris, Buck's horn plantain Plantago coronopus or the slender sedge Carex lasiocarpa (Haslam, 1972). However, in areas of habitat disturbance, where for example Spartina spp. is removed, Phragmites may invade the habitat (Amsberry et al., 2000). Once established, Phragmites australis is tall and a dominant competitor for light, so that dense stands of the common reed tend to be species poor in other plant species (Haslam, 1972; Rodwell, 1995; Bertness et al., 2002). But Phragmites itself may be suppressed by shading (Haslam, 1972), presumably by shrub and trees (e.g. alder or willow carr) at the inland edge of the shore.

Phragmites australis is an rhizomatous perennial producing annual aerial shoots that die back in winter. Young shoots begin to emerge from late March to late April for about 1-3 months (depending on conditions), reaching maximum shoot density by June to July (Haslam, 1972; Rodwell, 1995). Large buds shoot first producing larger, taller shoots that are more likely to flower than the later, smaller and shorter shoots. Shoot growth is curtailed by cooler temperatures after September. Inflorescences emerge from shoots between late July and early August and flower about a month later. Fruit develop in November and seeds are shed through winter and spring. During summer, nutrients are cycled to the rhizomes, accompanied by renewed growth of the horizontal rhizome system. In late summer, as underground food reserves reach a maximum, the rhizomes produce horizontal shoots that turn up to the surface of the substratum, forming dormant buds. Most buds form before winter ready to produce the new growth of aerial shoots in the following season. As summer progresses the aerial stems harden and leaves begin to die so that by January most leaves have fallen and stems are dead and brittle. Stems can remain standing for 2-3 years, after which they break close to the surface of the ground leaving a stubble and a litter of fallen stems (Haslam, 1972; Rodwell, 1995).

Phragmites australis first flowers after 3-4 years in moderately good conditions and individual rhizomes live for only 3-6 years, dying from behind (Haslam, 1972). However, the Phragmites community can be very long-lived if not disturbed, and vegetative clones of Phragmites australis can be up to 1000 years old (Rudescu et al., 1965 cited in Rodwell, 1995).

Growth of filamentous algae and algal mats is greatest in the summer months. The aquatic and terrestrial invertebrate populations probably vary seasonally, peaking in numbers during spring and summer when the aerial shoots are growing. Some species over-winter as pupae in the dead stems of the common reed e.g. the reed leopard moth Phragmataecia castaneae, while others probably use the reed as an attachment for their pupae. Gall forming midges over-winter in the galls formed on Phragmites (Tscharntke, 1992), emerging to infest summer shoots of the reed.

The aquatic invertebrates of Phragmites reed beds may show similar seasonal change to those reported in Potamogeton and Myriophyllum beds in Portugal (see IMU.NVC_A12) (Cunha & Moreira, 1995). They reported that polychaetes showed little seasonal changes in abundance while molluscs and leeches showed high densities in spring to summer but low numbers or even absence in autumn to winter. Crustaceans (e.g. gammarids) were most abundant in autumn, while insects were rare but abundant in winter and summer. Oligochaetes were most abundant in winter, although some species of oligochaete were also abundant in spring. Seasonal changes in the macrofauna was related to seasonal changes in temperature, dissolved oxygen, tidal regime and low or high rainfall and hence freshwater runoff and salinity (Cunha & Moreira, 1995).

Phragmites reed beds may be grazed by Canada and grey lag geese in spring, while other species e.g. warblers use reed beds as pre-migration feeding areas. Reed beds are used by numerous nesting birds in the spring and summer mating season, e.g. the bearded tit, reed warbler, bittern and the marsh harrier (Fuller, 1982; Hawke & José 1996).

The leaves and stems of Phragmites australis provide substratum and refuge for several species, while the rhizome and root system stabilize the sediment, and transport of oxygen from the stems, including dead stems, to the roots oxygenates the sediment in the vicinity of the roots (the rhizophere) changing the local redox potential, sediment chemistry and oxygen levels. Phragmites reed beds are an important component of emergent vegetation communities, and may occur near the waters edge in ditches and estuaries or as landward part of the hydrosere above saltmarsh habitats. Therefore, the complexity of the habitat and its species composition will vary both within and between locations. Variation in salinity within the reed bed adds complexity and variation in dominance by invertebrates or fish of marine origin rather than invertebrates and fish of terrestrial or freshwater origin (see Arnold & Ormerod, 1997). The gross structure a British reed bed is given by Hawke & José, (1996; Figure 1). The finer structure of the habitat with respect to invertebrates is probably similar to other aquatic macrophyte habitats e.g. Ruppia spp. communities (see IMS.Rup) . The reed bed probably comprises the following components (adapted from Verhoeven & van Vierssen,1978; Verhoeven 1980a; van Vierssen & Verhoeven, 1983, and Hawke & José, 1996).

• Phragmites australis and other associated aquatic macrophytes or macroalgae (see Rodwell, 1995);
• mats of filamentous algae, e.g. Cladophora spp., and Ulva spp., that harbour high densities of invertebrates e.g. aquatic insects, chironomid larvae, amphipods, and copepods (Verhoeven & van Vierssen, 1978; Verhoeven 1980a; van Vierssen & Verhoeven, 1983);
• epiphytic species attached to the plants e.g. diatoms, filamentous diatoms, blue green algae, bacteria, and fungi (Haslam, 1972; Müller, 1999);
• temporary epiphytic species, e.g. aquatic insects;
• species depositing eggs on Phragmites and other macrophytes, e.g. insects, hydrobids, and some fish;
• species living in tubes attached to plants, e.g. the amphipod Corophium volutator;
• species creeping over plants and other hard substrata but not the sediment, e.g. amphipods, isopods, gastropods, and insect larvae;
• species creeping over plants and the sediment bottom, e.g. Hydrobia spp. and Potamopyrgus spp.;
• benthic infauna, e.g. oligochaetes, the polychaete Hediste diversicolor, the amphipod Corophium volutator, and chironomids (Arnold & Ormerod, 1997);
• mobile aquatic species occurring within the vegetation and the surrounding area, e.g. shrimps, crabs, mysids, gobies, and eels that probably vary with the tidal or emergence regime (Verhoeven & van Vierssen, 1978; Verhoeven 1980a; van Vierssen & Verhoeven, 1983);
• mobile species in the vegetation canopy, e.g. phytophagous insects, roosting birds, nesting birds and mammals (Fuller, 1982; Tscharntke, 1992; 1999; Hawke & José, 1996; Arnold & Ormerod, 1997), and
• an accumulated litter layer which provides nesting material for nesting species and shelter for other species e.g. hunting beetles and frogs.

In salt marsh habitats, Phragmites australis dominated communities represent the landward extreme of the hydrosere from pioneer salt marsh communities, through Puccinellia maritima communities (see LMU.NVC_SM13) to the higher or upper marsh. As the marsh becomes dryer, the Phragmites dominated communities give way to alder or willow carr (see Packham & Willis, 1997). In more brackish or freshwaters, Phragmites may lead the transition from submerged aquatic plants (see IMS.Rup and IMU.NVC_A12) to emergent vascular plants. The reader is directed to Rodwell (2000) for further information on saltmarsh communities and Rodwell (1995) for further information on aquatic plant communities.

Primary productivity
Phragmites australis communities are amongst the most productive swamp communities (Rodwell, 1995). In Britain, mono-dominant stands of the common reed reach modal densities of over 100 shoots /m² but vary between 200 shorter shoots/m² or 30 shoots /m² (Rodwell, 1995). Above ground productivity was estimated to be as high as 100-150 tonnes/ha of standing crop in the Tay Estuary in a poor (cool) growing year in 1978 (Ingram et al., 1980), while other studies reported a standing crop of up to 1kg/m² and occasionally 2 kg/m² (Haslam, 1972; Rodwell, 1995). Rodewald-Rudescu (1974; cited in Ingram et al., 1980) suggested that only one third of total production was above ground, providing an estimated total productivity of reed biomass in the Tay Estuary in 1978 of about 300-450 tonnes/ha (Ingram et al., 1980). Haslam (1972) suggested that in fairly good to optimal stands total biomass may reach 10-40 tonnes/ha, although at least 36% and up to 96% of the biomass was below ground. Additional primary productivity derives from phytoplankton, periphyton, epiphytes and benthic microalgae, macroalgal mats within the bed as well as other vascular plants. Benthic microalgal productivity was reduced in Phragmites beds in comparison to salt marsh communities, and phytoplankton was of less importance in the brackish marshes of Delaware Bay (Wainwright et al., 2000).

Secondary productivity
Phragmites australis, macroalgae and microalgae supports consumers such as grazing gastropods and phytophagous insects, while its litter supports a wide variety of secondary consumers, including e.g. gammarid amphipods, isopods, chironomids, and bacteria. Wainwright et al., 2000 estimated that in Delaware Bay reed beds, Phragmites australis supported 73% of secondary productivity. Phragmites litter, resultant detritus, organic particulates and dissolved organic matter probably contribute to the wider aquatic food chain (Lee, 1990; Wainright et al., 2000). A summary of the net production and detritus dynamics in Mai Po Marshes, Hong Kong was given by Lee (1990).

The reed beds support a high biomass of terrestrial and aquatic invertebrates that provide secondary production further up the food chain (see ecological relationships). For example, Warren et al (2001) reported densities of ca 176/m² of Orchestia grillus and Philoscia vittata in tidal marshes of the Lower Connecticut river. Tscharntke (1999) reported insect densities, depending on emergence (dry vs. wet) and degree of damage by Archanara geminipuncta, of ca 140-269/m² for the gall inducing midge Giraudiella inclusa, ca 495-1618/m² for the gall inducing midge Lasioptera hungarica, and ca 6-13/m² for the twin-spotted wainscot Archanara geminipuncta in German reed beds. In Burry Inlet reed swamps, Arnold & Ormerod (1997) identified six communities of aquatic invertebrates that varied between ca 100 and 350 total invertebrate abundance (no of individuals collected).

Phragmites australis flowers in late August to early September, fruits ripen by November and seed are dispersed during winter and spring. Flowers are wind pollinated and each inflorescence may produce up to ca 1000 seeds. But fertility varies from 1-55%, depending on year, location, weather, and probably genetic variation between clones of Phragmites. Dispersal varies from 1-5 or 40% from same site in consecutive years (see Haslam 1972). The seed is plumed and dispersal is usually by wind, although birds nesting in the reed beds may also transport seed when collecting nesting material. Unshed seed may fall with the inflorescence only to be dispersed by water or man (Haslam, 1972).

Seed germination is variable and usually poor in the field, especially on organic soils (e.g. peat and within reed beds). Germination occurs over a wide range of temperatures, is slower at lower temperatures (ca 10-30 °C) and stopped by frost. The effect of water varies, some worker suggesting sowing at or below water level, other reporting germination in 1.5m of water and other no germination in 5 or 15cm of water and increased germination with drying. Germination also varies with salinity. In addition, seedlings are killed by frost, damaged by saline conditions, leave die underwater and may be stunted on organic soils, preferring mineral soils or muds with a flow of nutrient rich water (Haslam, 1972). Overall, sexual reproduction by seed is limited and seedlings are rarely observed in the field, except in new habitats devoid of other macrophytes (e.g. resulting form disturbance). However, propagation by seed is probably adequate to the long-lived clones of Phragmites (Haslam, 1972).

Vegetation reproduction by clonal spread of horizontal rhizomes is probably more important to the maintenance and expansion of established beds. Once established the Phragmites produces horizontal rhizomes that spread across the surface producing new vertical shoots and roots at each internode (Hawke & José, 1996). Hawke & José (1996) reported expansion rates of 1-10m per year, sometimes faster, depending on temperature and water depth. Amsberry et al. (2000) noted that underground rhizomes spread horizontally about 1-1.5m per year. Pieces of rhizome may be transported by water or man (but die at sea) and may act as an effective mode of dispersal. Cutting of rhizomes, stems and shoots are used to propagate reed beds and fragments of the common reed would probably root in the wild if they arrived on suitable substrata.

Other species
The microalgae and filamentous macroalgae found within the biotope are wide-spread and ubiquitous, producing numerous spores, and can colonize rapidly. Similarly, bryozoans such as Conopeum seurati probably produce numerous but short lived pelagic larvae, so that local recruitment from adjacent populations is probably rapid. For example, Electra crustulenta is probably adapted to rapid growth and reproduction (r-selected), capable of colonizing ephemeral habitats, but may also be long lived in ideal conditions (Hayward & Ryland, 1998). In settlement studies, Electra crustulenta recruited to plates within 5 -6months of deployment (Sandrock et al., 1991). Boström & Bonsdorff (2000) examined the colonization of artificial seagrass beds by invertebrates. They reported colonization by abundant nematodes, oligochaetes, chironomids, copepods, juvenile Macoma baltica and the polychaete Pygospio elegans within 33-43 days. Disturbance by strong winds after 43 days resulted in a marked increase in the abundance of species by day 57, except for Pygospio elegans. They noted that settlement of pelagic larvae was less important than bedload transport, resuspension and passive rafting of juveniles from the surrounding area in colonization of their artificial habitats. The above observation suggests that most aquatic macrobenthic species in reed beds may recruit rapidly.

Mobile species, such as the gammarids, small gastropods and mysids are probably able to recruit and colonize available habitats from the surrounding area. Hydrobid molluscs produce pelagic larvae capable of considerable dispersal and may also colonize new habitats by rafting. Coleoptera (beetles), Odonata (dragonflies) and Heteroptera (true-bugs), with adults capable of flight, will probably be able to colonize available habitats relatively quickly once established, although the ability to fly varies between species (van Vierssen & Verhoeven, 1983). For example, the aphid Hyalopterus pruni colonizes reed beds annually in summer, although it reaches its highest densities at the edges of reedbeds, before migrating to its main host cherry trees (Prunus sp.). The larvae of the twin-spotted wainscot Archanara geminipunctadamages thick shoots and induces thinner side shoots (Tscharntke, 1992). Several, species are dependant on the shoot damage or side shoots induced by the twin-spotted wainscot. For example, the gall forming midge Lasioptera arundinis, gall forming flies (Lipara lucens and Lipara ruftitarsis) benefit from the additional thin side shoots, while some species of fly (Chloropidae) feed on the droppings of the twin-spotted wainscot (Tscharntke, 1992, 1999). Therefore, their recruitment is dependant on the presence of the twin-spotted wainscot, which itself demonstrates a flush and crash life cycle every 3-4 years (Tscharntke, 1992).

The stickleback Gasterosteus aculeatus may be associated with reed beds. The males set up a territory and build nests, in which the female lays eggs that are subsequently fertilized and guarded by the males (Fishbase, 2000). The abundance of vegetation provided by the reed bed and its associated algal mats probably provides nesting material for the males and a refuge for developing juveniles. While associated with this biotope, sticklebacks are mobile species capable of colonizing the habitat from adjacent areas or the open sea. Similarly, amphibians, reptiles and birds are highly mobile and probably recruit to the habitat rapidly from the surrounding areas.

Once established expansion of a reed bed may be relatively rapid. For example, at Hickling, Norfolk an area of derelict grazing marsh was bunded to allow colonization by the common reed, and a closed stand of reed formed over 50ha within 5 years. Colonization by associated mobile species is probably rapid. Cunha & Moreira (1995, Figure 9) noted that peak abundance of molluscs, leeches and insects in pondweed beds occurred in spring and summer, probably coincident with the peak of macrophyte biomass, while oligochaete and crustacean abundance peaked during late autumn and winter probably coincident with decomposition of senescent macrophytes. Their observation suggest that the species richness and density of aquatic invertebrates fluctuates seasonally with macrophyte abundance or decomposition, suggesting that different invertebrate groups can colonize the pondweed beds readily, depending on season. Similarly, terrestrial insects can potentially colonize the reed bed rapidly on a seasonal or annual basis. Tscharnkte (1992) noted that the species richness of reed bed habitat depended on the age, stability and size. For example, a 2ha habitat could support 180,000 twin-spotted wainscot during outbreaks but could not persist, being dependent on rapid recruitment from neighbouring populations. The larvae of the reed leopard moth spends two years within the stems of Phragmites, while the twin-spotted wainscot over-winters as eggs on stems and pupates within thick stems of reed, both therefore, requiring established and stable beds. Small stands of stressed plants are likely to be better habitats for gall forming midges, gall forming flies, and the aphid Hyalopterus pruni. Bird species vary in their needs but conservation (i.e. viable populations) of most of the bird species found in reed beds requires stands of at least 2ha. For example, the reed warbler breeds in reed patches >1600m², the marsh warbler and reed bunting breed along edges of stands >9000m², while the great reed warbler (Acrocephalus arundinis) prefers watersides of reed belts >21,000m² (Tscharntke, 1992). The litter layer is often used by bearded tits which prefer to nest amongst dead stem. Nesting reed warblers were reported to occupy cut areas rapidly, and after one years growth of reed nests were recorded at densities of 20/ha increasing to 35-40/ha within 2-3 years. Therefore, the development of the terrestrial community is dependant on the size of the reed bed and hence the time taken for it to develop. The species richness of the aquatic invertebrate community and decomposers is probably also dependant on the build up of litter within the bed.

None entered.