Biodiversity & Conservation

Coralline turf communities are described in detail by Hagerman (1968), Dommasnes (1968, 1969), Hicks (1985), Grahame & Hanna (1989), Crisp & Mwaiseje (1989), Bamber (1988) and Bamber & Irving ( 1993). The following information is based the above references and lists of species in the MNCR database (JNCC 1999). Macroalgae including Corallina officinalis, Mastocarpus stellatus, Osmundea pinnatifida and Lomentaria articulata, provide primary productivity either directly to grazing fish and invertebrates or indirectly, to detritivores and decomposers, in the form of detritus and drift algae or as dissolved organic material and other exudates.

Macroalgal species compete for light, space and, to a lesser extent, nutrients, depending on the growth rates, size and reproductive pattern of each species. However, Corallina officinalis probably has a competitive advantage in wave exposed habitats due to their robust coralline fronds and resistant vegetative crustose bases (see Littler & Kauker, 1986).

Corallina officinalis provides substratum for spirorbid worms (e.g. Spirorbis corallinae), epiphytes and periphyton, depending on location, including microflora (e.g. bacteria, blue green algae, diatoms and juvenile larger algae), and interstices and refuges from predation for a variety of small invertebrates (see habitat complexity below).

Amphipods (e.g. Parajassa pelagica and Stenothoe monoculoides), isopods (e.g. Idotea pelagica and Jaera albifrons) and other mesoherbivores graze the epiphytic flora and senescent macroalgal tissue, which may benefit the macroalgal host, and may facilitate dispersal of the propagules of some macroalgal species (Brawley, 1992b; Williams & Seed, 1992). Mesoherbivores also graze the macroalgae but do not normally adversely affect the canopy (Brawley, 1992b).

Grazers of periphyton (bacteria, blue-green algae and diatoms) or epiphytic algae include harpacticoid copepods, small gastropods (e.g. Rissoa spp. and Littorina neglecta.

Macroalgal grazers include limpets e.g. Patella vulgata and Patella ulyssiponensis, juvenile blue-rayed limpets Helcion pelucidum, and gastropods such as Littorina saxatilis and Littorina neglecta.

Coralline algae are probably relatively grazing resistant (Littler & Kauker, 1984) and few species graze the corallines directly except perhaps chitons and limpets of the genus Tectura. Grazers probably benefit the coralline turf by removing epiphytic and ephemeral algae (e.g. Ulva), which could potentially smother the turf.

Suspension feeders include Semibalanus balanoides, the spirorbid Spirorbis corallinae, the sponge Halichondria panicea, juvenile bivalves and interstitial bivalves such as Lasaea adansoni and Turtonia minuta, and the tubiculous amphipod Parajassa pelagica.

Turbellarians, nematodes and halacarid mites are probably interstitial predators on other nematodes, mites, and harpacticoid copepods (Hicks, 1985).

When the biotope is covered by the tide, intertidal fish such as gobies, blennies and clingfish, and the juveniles of larger inshore fish are probably active predators of amphipods, isopod, ostracods and harpacticoid copepods. The physical complexity of the Corallina officinalis turf was reported to offer a refuge from predation for epiphytic invertebrates (Coull & Wells, 1983; Hicks, 1985). Choat & Kingett (1982) did not detect any significant effect on fish predation in exclusion experiments. In harpacticoid copepods, although large numbers were consumed by fish little effect on the population resulted (Hicks, 1980). However, Hicks (1985) noted that considerable evidence of predators regulating prey abundance was available.

The brittlestar Amphipholis squamata probably is a detritivore within the turf.

Red algal turf declines in abundance during the winter months, partly due to die back and abrasion during winter storms. For example, Seapy & Littler (1982) noted that the cover of Corallina officinalis var. chilensis declined in the winter months, growing back in summer and developing a dense cover in autumn in California. Littler et al. (1979) reported a autumn maximum in cover of Corallina officinalis var. chilensis and a summer minimum in cover in San Clement Island, California. In Denmark, fronds of Corallina officinalis were reported to cease growing in summer, sloughed in autumn, and new fronds initiated from crustose, perenniating bases in late winter (Rosenvinge, 1917; cited in Johanssen, 1974). However, in the Bristol Channel, Bamber & Irving (1993) noted that the biomass of Corallina officinalis increased steadily through spring and summer and began to decline after July. Mastocarpus stellatus (as Gigartina stellata) was reported have a perennial holdfast, losing many erect fronds in winter, which grow back in spring (Dixon & Irvine, 1977). Osmundea pinnatifida also shows seasonal variation in growth, expanding its perennial holdfast in June to September, and producing erect fronds from October onwards reaching a maximum in February to May (Maggs & Hommersand, 1993).

Choat & Kingett (1982) reported that the abundance of amphipods in a New Zealand coralline turf habitat peaked in summer and declined to a low in winter, while polychaetes showed a peak of abundance in winter decreasing in summer. But ostracods showed a relatively low abundance throughout the sampling period (Choat & Kingett, 1982). Bamber (1993) examined coralline turf dominated runoffs in the Bristol Channel, and noted that the amphipod Melita palmata and the brittlestar Amphipholis squamata recruited after the summer growth of the coralline turf reaching a peak abundance in autumn. But the small isopod Jaera albifrons recruited to the turf in late winter and the polychaete Platynereis dumerilii showed an erratic pattern of abundance (Bamber & Irving, 1993). However, Bamber & Irving (1983) noted considerable variation in seasonal abundance between sites (runoffs) on the same shore.

This biotope occurs in very wave exposed conditions on horizontal, steep or vertical bedrock subject to wave crash and is composed of species tolerant of wave action. The biotope may develop below the lower limit of the barnacle or mussel belts in wave exposed conditions.

• Corallina officinalis forms a dense carpet or turf on the bedrock and with increasing wave exposure may grow as a cushion like or compact turf (Dommasnes, 1968; Johansen, 1974; Irvine & Chamberlain, 1994).
• Other red algae occur in low abundance depending on wave exposure with Mastocarpus stellatus being the most tolerant, Osmundea pinnatifida slightly less tolerant, while Lomentaria articulata and Palmaria palmata favour shaded or overhanging surfaces. Shaded overhangs may also support Plumaria elegans, Ptilota plumosa and Cladophora rupestris (Lewis, 1964).
• Depressions filled with Osmundea pinnatifida and Corallina officinalis may also support the olive-brown bulbous seaweed Leathesia difformis (Lewis, 1964).
• Large macroalgae such as Himanthalia elongata typically occur at low abundance, their long thongs lying over the coralline turf.
• The interstices formed by the branches of Corallina officinalis support a diverse epiphytic fauna (Dommasnes, 1968, 1969; Hagerman, 1968; Hicks & Coull, 1983; Hicks, 1985; Bamber, 1988; Crisp & Mwaiseje, 1989; Grahame & Hanna, 1989; Bamber & Irving, 1993). The species diversity and abundance of the epiphytic fauna depends the percentage cover of turf, wave exposure, the size of the interstices within the turf, and the build up of sediment. In wave exposure, the build up of sediment is likely to be limited and the close compact, cushion growth form may reduce the diversity of the infauna but provide a better refuge from predation for harpacticoid copepods and ostracods (Dommasnes, 1968, 1969; Seapy & Littler, 1982; Choat & Kingett, 1982; Hicks & Coull, 1983; Hicks, 1985).
• In wave exposed conditions, tubiculous amphipods and isopods are represented by species with well developed claws or gnathopods and strong stout legs and bodies, e.g. the isopods Idotea pelagica and Jaera albifrons, and the amphipods Parajassa pelagica, although Stenothoe monoculoides, Apherusa jurinei and the isopod Ianiropsis breviremis occur irrespective of wave exposure (Dommasnes, 1986, 1969).
• Corallina officinalis provides a substratum for small spirorbids e.g. Spirobis corallinae, which is only found on Corallina officinalis. Increasing density of Spirorbis corallinae was shown to increase the species richness of the epiphytic fauna, especially small species such as Stenothoe monocloides (Crisp & Mwaiseje, 1989) but with increasing wave exposure, the spirorbid is found within the Corallina officinalis turf rather than at its tips and was reported to be absent from the 'most wave exposed' sites (Grahame & Hanna, 1989).
• Wave exposed coralline turf also reported to support Foraminifera, Turbellaria, nematodes, polychaetes (e.g. Platynereis dumerilii and Perinereis cultrifera), the tanaid Tanais cavolinii, halacarid mites, gastropods (e.g. Littorina neglecta, Littorina saxatilis, and Rissoa spp.), juvenile bivalves (e.g. Mytilus edulis, Musculus discors), interstitial bivalves (e.g. Lasaea adansoni and Turtonia minuta) and the small brittlestar Amphipholis squamata (Hagerman, 1968; Dommasnes, 1968, 1969; Bamber & Irving, 1993).
• In gaps in the turf, the surface of the bedrock may be covered with encrusting coralline algae and barnacles such as Semibalanus balanoides, and patrolled by limpets (e.g. Patella ulyssiponensis).

Little information concerning the productivity of coralline turf communities was found. The red algae, algal epiphytes and periphyton provide primary productivity to grazers, while their spores and phytoplankton provide primary productivity to suspension feeders. Bamber & Irving (1993) reported that Corallina officinalis reached a biomass of up to 3.3-6.7 kg/m². Littler et al. (1979) determined the total daily productivity of an intertidal algal population in California, which peaked in autumn at 1.22 gC fixed /m²/day, and declined in winter to a spring low of 0.47 gC fixed /m²/day. Blue-green algae, Corallina officinalis var. chilensis and Egregia menziesii contributed 76% of the total community primary productivity (Littler et al., 1979).

Secondary productivity of the invertebrate fauna may be high and coralline turf may support high abundances of invertebrates. For example, Choat & Kingett (1982) recorded the following numbers of epiphytic fauna: amphipods 1038 / 0.01m²; ostracods 219 /0.01m², and polychaetes 134 /0.01m².

Corallina officinalis has isomorphic sexual (gametophyte) and asexual (sporophyte) stages (see MarLIN review). Settled tetraspores develop into a perennial crustose base, from which the upright, articulate fronds develop. Sporeling formed within 48hrs, a crustose base within 72hrs, fronds being initiated after 3 weeks and the first intergeniculum (segment) formed within 13 weeks (Jones & Moorjani, 1973). Settlement and development of fronds is optimal on rough surfaces but settlement can occur on smooth surfaces (Harlin & Lindbergh, 1977; Wiedeman, pers comm.). Corallina officinalis settled on artificial substrata within 1 week of their placement in the intertidal in New England summer suggesting that recruitment is high (Harlin & Lindbergh, 1977).

The propagules of most macroalgae tend to settle near the parent plant (Schiel & Foster, 1986; Norton, 1992; Holt et al., 1997). For example, the propagules of fucales are large and sink readily and red algal spores and gametes and immotile. Norton (1992) noted that algal spore dispersal is probably determined by currents and turbulent deposition (zygotes or spores being thrown against the substratum). For example, spores of Ulva sp. (as Ulva) have been reported to travel 35km, Phycodrys rubens 5km and Sargassum muticum up to 1km, although most Sargassum muticum spores settle within 2m. The reach of the furthest propagule and useful dispersal range are not the same thing and recruitment usually occurs on a local scale, typically within 10m of the parent plant (Norton, 1992). In clearance studies in the subtidal Kain (1975) noted that on a single block cleared every two months, most biomass belonged to Rhodophyceae in winter, Phaeophyceae in spring and Chlorophyceae in late summer, and concluded that recruitment was dependant on spore availability. For example, spore production in Mastocarpus stellatus is maximum between September to December (Dixon & Irvine, 1977), spores of Osmundea pinnatifida are present in October and December to June (Maggs & Hommersand, 1993), while the spores of Lomentaria articulata are available all year round with a peak in summer (Irvine, 1983).

Recruitment of Patella vulgata fluctuates from year to year and from place to place (Bowman, 1981). Fertilization is external and the larvae are pelagic for up to two weeks before settling on rock at a shell length of about 0.2mm. Winter breeding occurs only in southern England, in the north of Scotland it breeds in August and in north-east England in September. Reproduction is probably similar in Patella ulyssiponensis, except that it may be a protandrous hermaphrodite, spawning in October in south-west Ireland (Fish & Fish, 1996). The larvae of the blue-rayed limpet Helcion pellucidum settle on encrusting corallines and migrate to Mastocarpus stellatus as they grow and finally to Laminaria spp. via Himanthalia elongata (McGrath, 1992; see MarLIN review).

Barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors, such as wind direction and success depends on settlement being followed by a period of favourable weather. Long term surveys have produced clear evidence of barnacle populations responding to climatic changes. During warm periods Chthamalus spp. predominate, whilst Semibalanus balanoides does better during colder spells (Hawkins et al., 1994). Release of Semibalanus balanoides larvae takes place between February and April with peak settlement between April and June.

Many species of mobile epifauna, such as polychaetes have long lived pelagic larvae and/or are highly motile as adults. Gammarid amphipods brood their embryos and offspring but are highly mobile as adults and probably capable of colonizing new habitats from the surrounding area (e.g. see Hyale prevosti review). Similarly, isopods such as Idotea species and Jaera species brood their young. Idotea species are mobile and active swimmers and probably capable to recruiting to new habitats from the surrounding area by adult migration. Jaera albifrons, however, is small and may take longer to move between habitats, and Carvalho (1989) suggested that under normal circumstances movement was probably limited to an area of less than 2m. Hicks (1985) noted that epiphytic harpacticoid copepods lack planktonic dispersive larval stages but are active swimmers, which is therefore the primary mechanism for dispersal and colonization of available habitats. Some species of harpacticoids are capable to moving between low and mid-water levels on the shore with the tide, while in other colonization rates decrease with increasing distance form resident population. Overall immigration and in situ reproduction were thought to maintain equilibrium populations exposed to local extinction, although there may be local spatial variation in abundance (see Hicks, 1985).

The small littorinids Littorina saxatilis and Littorina neglecta are ovoviviparous, releasing miniature adults. Therefore, local recruitment is probably good, whereas long distance recruitment is probably poor. The interstitial bivalve Lasaea adansoni also broods its eggs, releasing miniature adults. However, Martel & Chia (1991b) reported bysso-pelagic or mucus rafting in small bivalves and gastropods in the intertidal, and suggested that drifting may be an effective mean of dispersal at the local scale, even for species that produce miniature adult offspring. The gastropod Rissoa parva lays eggs capsules, from which hatch veliger larvae with a prolonged pelagic life and potentially good dispersal capability (Fish & Fish, 1996).

The epiphytic species diversity of the coralline turf is dependant on the Corallina officinalis cover and its growth form (Dommasnes, 1968, 1969; Seapy & Littler, 1982; Crisp & Mwaiseje, 1989). Corallina officinalis was shown to settle on artificial substrata within one week of their placement in the intertidal in New England summer suggesting that recruitment is high (Harlin & Lindbergh, 1977). New fronds of Corallina officinalis appeared on sterilised plots within six months and 10% cover was reached with 12 months (Littler & Kauker, 1984). In experimental plots, up to 15% cover of Corallina officinalis fronds returned within 3 months after removal of fronds and all other epiflora/fauna (Littler & Kauker, 1984). Bamber & Irving (1993) reported that new plants grew back in scraped transects within 12 months, although the resistant crustose bases were probably not removed. New crustose bases may recruit and develop quickly the formation of new fronds from these bases and recovery of original cover may take longer. Once a coralline turf has developed it will probably be colonized by epiphytic invertebrates such as harpacticoids, amphipods and isopods relatively quickly from the surrounding area. Therefore, the biotope would be recognizeable once the coralline turf has regrown, which is likely to be within a few months if the resistant crustose bases remain. Recruitment of red algae is probably equally rapid, and once the algal turf has developed most of the epiphytic invertebrates would colonize quickly, although some species e.g. small brooding gastropods would take longer.

None entered