Chrysophyceae on vertical upper littoral fringe soft rock
Ecological and functional relationships
The supralittoral lies above high water springs, and is influenced by wave wash, splash and spray. The mobile fauna will vary with the tide and wave exposure with marine intertidal species further up the shore at high tide and mobile species of terrestrial origin foraging down the shore as the tide recedes only to return to the top of the shore as the tide returns. Other species of terrestrial origin, notably mites (acarids), and some spring tails (Collumbola) seek refuge is cracks and crevices at high tide.
Chrysophyceae, Haptophyceae, blue-green algae (Cyanobacteria) and fine filamentous green algae (Chlorophycota) are primary producers, converting sunlight and simple inorganics to biomass.
Grazers and browsers feed on unicellular green algae (Chrysophyceae), lichens, and fine filamentous green algae, e.g. the sea slater Ligia oceanica, the bristletail Petrobius maritimus, the small periwinkle Melarhaphne neritoides and some acarid mites (Nicholls, 1931; Joosse, 1976; Roth & Brown, 1976; Pugh & King, 1988; Carefoot & Taylor, 1995; Bücking, 1998).
Detritus may accumulate in pits or crevices and is fed on by detritivores such as acarid mites.
Predators include mites (acarids), centipedes of terrestrial or intertidal origin (e.g. Strigamia maritima, which may take isopods, amphipods and periwinkles), and terrestrial or maritime spiders (Roth & Brown, 1976; Pugh & King, 1988).
The sea slater (Ligia oceanica) may also act as a scavenger (Nicholls, 1931).
Several species are probably more active at night (e.g. Ligia oceanica) to avoid predation by foraging birds. Anand (1937a,b&c) originally described the 'Chrysophyceae' communities of soft chalk cliffs but several species (e.g. Apistonema sp. and Chrysotila sp.) are now described under Haptophyceae (Fowler & Tittley, 1993; van den Hoek et al., 1995), however, the term 'Chrysophyceae' mat or belt is still used.
Seasonal and longer term change
Tittley & Shaw (1980) suggested that Apistonema sp. changed little with season. In winter, the mucilaginous 'Chrysophyceae' mat may be punctuated by light brown or white patches caused by frost. Chrysotila stipitata (Haptophyceae) community develops in winter but in summer may dry and peel off, being restricted to shaded, moist locations. The primary 'Chrysophyceae' community, dominated by Apistonema carterae is best developed in winter but present all year round but in prolonged exposure to sunlight and high temperatures in summer when the seas are calm (low humidity) may result in drying of the mat, which cracks and curls up (Anand, 1937b; Plate IV B). In winter, the mucilaginous mat may be covered by the filamentous growth of Ulothrix sp., and in spring and summer the mat may support numerous species of diatom. Cyanobacteria (e.g. Calothrix sp. and Schizothrix fritschii) are more common in summer. The Rivularia atra belt (see habitat complexity) is best developed in winter but dies back in summer. The growth of the fine green filamentous algae Pseudendoclonium submarinum (previously described by Anand as Endoderma perforans) is favoured in winter (Anand, 1937b; Tittley & Shaw, 1980; Burrows, 1991).
No information concerning seasonal changes in the associated fauna was found.
Habitat structure and complexity
This biotope occurs in the supralittoral of soft vertical rock cliffs, above the high water of springs tides, and replaces the Verrucaria maura
communities typically found on hard rock substrata. Supralittoral algal communities show a distinct zonation pattern (Anand 1937a,b,&c; Magne, 1974; Tittley & Shaw, 1980). The height of the supralittoral zone and, hence, the height of each individual algal band (or zone) is dependant on moisture and humidity. Moisture or humidity are dependent on the height reached by wave wash, splash and spray and, therefore, on the degree of hence wave exposure, the porosity of the rock, and the drying forces of wind and sunlight and hence, the north or south aspect of the cliff face. For example, on wave exposed North Atlantic headlands the supralittoral may reach 50-60 ft (ca 15-18m) above mean high water springs tides (MHWS) but only reach 4-5 ft (ca 1-1.5m) above on sheltered shores (Lewis, 1964).
The surface of the soft rock provides complexity to the habitat in the form of pits or crevices that retain moisture and may be punctuated by tunnels and caves. Chrysophyceae and Haptophyceae are single celled (unicellular) microalgae more usually found in planktonic communities. The Chrysophyceae and Haptophyceae found in soft rock communities form a thallus of algal cells bound by mucilage or filaments of mucilage (Anand, 1937a; van den Hoek et al.
, 1995). Anand (1937a,b&c) described five main communities of Chrysophyceae, Haptophyceae and Cyanobacteria associated with the 'Chrysophyceae' mat.
(down the shore from the yellow and grey lichen belt)
- An upper belt (45cm or more high) of the fine green filamentous algae Pseudendoclonium submarinum (previously described by Anand as Endoderma perforans), filaments of which penetrate the loose rock and give the rock face a green hue. The Pseudendoclonium submarinum belt may reach 8-10m above high water, more in caves and recesses where the waves break and spray reaches higher.
A lower belt of 'Chrysophyceae' communities, forming an orange, light or dark brownish mucilaginous mat. The mucilaginous mat grows over a layer of Pseudendoclonium submarinum that grows endophytically within the 'Chrysophyceae' mat, from which it may protrude. Alternating layers of green algae within the brown Chrysophyceae may form, depending on season.
The 'Chrysophyceae' belt is dominated by Apistonema carterae, commonly with Thallochrysis litoralis and Gloeochrysis maritima. Chrysotila stipitata (Haptophyceae) may form a separate 'Chrysophyceae' community, especially in the winter months.
Several species of blue-green algae (Cyanobacteria) live endophytically within the 'Chrysophyceae' mat forming layers of black or dark brown growth within the mucilaginous mat, e.g. the Calothrix sp. community. Schizothrix fritschii (Cyanobacteria), however, may form erect branched bundles of a yellowish or green olive colour on the surface of the mat.
- A band of Rivularia atra (Cyanobacteria) may occur between the bottom of the 'Chrysophyceae' belt and the top of the Ulva sp. zone (Anand, 1937a,b&c; Tittley & Shaw, 1980; Burrows, 1991).
In the winter months the mucilaginous mat may be covered by the fine, felt like growth of the green algae Ulothrix sp.
The lower limit of this biotope is delimited by a band dominated by Ulva sp. (see MLR.Eph).
The 'Chrysophyceae' belt is found near the entrance but its vertical extent is increased and it may extend for 6 -8m from the floor in well illuminated caves The dominant species vary with light intensity and hence, distance into the cave (Anand, 1937b). Pseudendoclonium submarinum
(described as Endoderma perforans
) penetrates the surface of the mucilaginous mat giving it a green colour. Pseudendoclonium submarinum
becomes more prominent in vertical extent in caves than on open cliffs. Anand (1937b) describes three algal communities specific to soft rock caves.
The Chrysophyceae, Haptophyceae, the associated Chlorophycota and Cyanobacteria provide primary production within this biotope. However, no further information was found.
Chrysophyceae and Haptophyceae reproduce predominantly by asexual reproduction. Flagellate zoospores may also be produced. The Haptophyta Chrysotlia lamellosa is predominately benthic but the motile flagellate part of the life-cycle is an abundant member of the phytoplankton, previously described as Isochrysis maritima. The fine, filamentous green algae found in this biotope produce motile zoospores and swarmers. While Cyanobacteria do not form flagellate cells, they are ubiquitous. Hence, the algae species within this biotope have a high potential for dispersal, depending on local currents.
Therefore, it is likely that recolonization of soft rock cliffs would be relatively rapid, probably occurring within a year. Tittley & Shaw (1980) noted that Apistonema sp. was replaced by Entophysalis sp. (Cyanobacteria) on sea walls and that hard, impervious rock substrata supported different algae communities to those of soft, porous rock substrata. This was probably dependent o the moisture retained by the porous rock surface, e.g. chalk and the ability of algal spores to settle and stick to rough rather than smooth surfaces (Tittley & Shaw, 1980).
Time for community to reach maturity
Little information was found. The 'Chrysophyceae' communities develop in winter, with Cyanobacteria developing in spring and summer, suggesting a seasonal cycle. Therefore, it is likely that the community would reach maturity within a year.
With the exception of the studies indicated above, the ecology of soft rock algal communities has received little attention.
This review can be cited as follows:
Chrysophyceae on vertical upper littoral fringe soft rock.
Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line].
Plymouth: Marine Biological Association of the United Kingdom.
Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=121&code=1997>