Sabellaria spinulosa with kelp and red seaweeds on sand-influenced infralittoral rock
Ecological and functional relationships
Sabellaria spinulosa colonize scoured rock rapidly and may be sufficiently dense to prevent the settlement or attachment of other species to the substratum, although the crust itself may act as a substratum for other fauna and flora.
Sabellaria spinulosa requires suspended sand grains in order to form its tubes; reef communities therefore, only occur in turbid areas where sand is placed into suspension by water movement.
Kelps are major primary producers, up to 90% of kelp production enters the detrital food web and kelp is probably a major contributor of organic carbon to surrounding communities (Birkett et al. 1998b).
Kelp fronds, stipes and holdfasts provide substrata for distinct communities of species, some of which are found only or especially on kelp plants. Kelp holdfasts provide both substrata and refugia for a huge diversity of macroinvertebrates. Kelp beds are diverse species rich habitats and over 1,800 species have been recorded in the UK kelp biotopes (Birkett et al. 1998b).
Epiphytes and understorey algae are grazed by a variety of amphipods, isopods and gastropods, e.g. Littorina spp., Acmaea spp., Haliotis tuberculata, Aplysia and rissoid gastropods (Birkett et al., 1988b).
Sabellaria spinulosa and other associated organisms in the biotope, may be an important source of food for the pink shrimp Pandalas montagui. The biotope may also be an important feeding ground for fish.
Suspension feeders, such as Sabellaria spinulosa, Ophiothrix fragilis, sponges, bryozoans and ascidians are the dominant fauna in the biotope. The top shell Gibbula cineraria is the only common grazer in the biotope although Echinus esculentus is also sometimes present. The anemone Urticina felina is a passive carnivore, waiting to trap animals that stumble into its tentacles.
Although not present in large numbers in the biotope Echinus esculentus can have an influence in the biotope. The species graze the under-canopy and understorey algae, including juvenile kelp sporophytes, together with epiphytes and epifauna on the lower reaches of the laminarian stipe. Wave action and abrasion between stipes probably knocks urchins off the upper stipe. It is likely that urchins will graze the Sabellaria spinulosa. Sea urchin grazing may maintain the patchy and species rich understorey epiflora/fauna by preventing dominant species from becoming established.
Seasonal and longer term change
- Sabellaria spinulosa is a fast growing annual species and crusts up to 2-3cm thick can develop within one growing season. High recruitment of Sabellaria spinulosa may result in 'reinforcement' of the crust of tubes on the substratum. Reproductive seasonality of Sabellaria spinulosa is unclear, but spawning probably occurs largely over winter and settlement in early spring (Holt et al., 1998).
- New blades of Laminaria hyperborea grow in winter between the meristem and the old blade, which is shed in early spring or summer together with associated species growing on its surface. Larger and older plants become liable to removal by wave action and storms due to their size and weakening by grazers such as Helcion pellucidum. Loss of older plants results in more light reaching the understorey, temporarily permitting growth of algae including Laminaria hyperborea sporelings.
- Many species of red algae are perennial exhibiting strong seasonal patterns of growth and reproduction. Delesseria sanguinea, for example, produces new blades in February and grows to full size by May - June becoming increasing battered or torn and the lamina are reduced to midribs by December (Maggs & Hommersand 1993).
- Several other species, including hydroids, are annuals and abundance may show seasonal changes.
Habitat structure and complexity
The crusts of Sabellaria spinulosa
appear to have a considerable influence on community structure by providing a single species sheet that may be unstable for other species to attach to. The development of a diverse community may be dependent on space being made in the Sabellaria
crust and other species settling on the rock. Diversity on crusts is not high. It might be that the richest communities occur where Sabellaria
is not dominant. This is in contrast to Sabellaria spinulosa
reefs on mobile substrata such as cobbles and pebbles which are stabilised by the crusts and often have a higher diversity and abundance of fauna than nearby areas (George & Warwick, 1985) with fauna such as sponges, ascidians, hydroids and bryozoans attached to the crust. The presence of kelp plants, and other algae, contribute to increases in structural complexity as the fronds, stipe and holdfast provide substratum and shelter for a great diversity and abundance of epiphytic algae and sessile fauna.
Productivity in the biotope is a mixture of primary and secondary productivity. Kelps are the major primary producers in UK marine coastal waters producing nearly 75 % of the net carbon fixed annually on the shoreline of the coastal euphotic zone (Birkett et al
. 1998b). Kelp plants produce 2.7 times their standing biomass per year. Kelp detritus, as broken plant tissue, particles and dissolved organic material supports soft bottom communities outside the kelp bed itself. The kelps reduce ambient levels of nutrients, although this may not be significant in exposed sites, but increase levels of particulate and dissolved organic matter within the bed. However, kelp abundance, and hence productivity is not as high in the MIR.SabKR biotope as some other infralittoral biotopes (e.g. see EIR.LhypR). Many of the other species in the biotope, such as Sabellaria spinulosa
and Ophiothrix fragilis
, are suspension feeders feeding on detritus and phytoplankton.
Most species present in the MIR.SabKR biotope possess a planktonic stage (gamete, spore or larvae) which float in the plankton before settling and metamorphosing into the adult form. This provides the potential for dispersal over considerable distances allowing many of the species in the biotope to rapidly colonize new areas that become available such as in the gaps often created by storms. The recruitment processes of key characteristic or dominant species are described here.
- Recruitment of Sabellaria spinulosa can be very variable. The larvae of Sabellaria spinulosa spend between six weeks and two months in the plankton (Wilson, 1970b) and so dispersal range is likely to be considerable. Larvae are strongly stimulated to settle by cement secretions of adult or newly settled individuals. In the absence of suitable stimulation metamorphosis and settlement occurs but always more slowly. High recruitment of Sabellaria spinulosa may result in 'reinforcement' of the crusts of tubes on the substratum.
- Laminaria hyperborea produces vast numbers of spores, however they need to settle and form gametophytes within about 1 mm of each other to ensure fertilisation and therefore may suffer from dilution effects over distance. Gametophytes can survive darkness and develop in the low light levels under the canopy. However, young sporelings develop slowly in low light. Loss of older plants provides the opportunity to develop into adult plants. Most young sporophytes (germlings) appear in spring but can appear all year round depending on conditions (Birkett et al. 1998b).
- Rhodophyceae have non flagellate, and non-motile spores that stick on contact with the substratum. Norton (1992) noted that algal spore dispersal is probably determined by currents and turbulent deposition. However, red algae produce large numbers of spores that may settle close to the adult especially where currents are reduced by an algal turf or in kelp forests.
- Reproductive types of Lithophyllum incrustans occur from October to April but tail-off into summer. It has been calculated that 1 mm x 1mm of reproductive thallus produces 17.5 million bispores per year with average settlement of only 55 sporelings/year (Edyvean & Ford, 1984). However, spores will settle and new colonies will arise rapidly on bare substratum although growth rate is slow (2-7 mm per annum - see Irvine & Chamberlain, 1994).
- Some characterizing species may not recruit so readily, for instance the larvae of Urticina felina inhabits the water column, but is not considered to be truly pelagic and probably has limited dispersal abilities (Solé-Cava et al., 1994).
Time for community to reach maturity
seems in many cases to acts as a fast growing annual and early colonizer, but on more stable reefs the animals seem to be able to live for a few years. A typical life span for the littoral Sabellaria alveolata
living in colonies forming reefs on bedrock in Duckpool was 4-5 years (Wilson, 1971). Areas where Sabellaria spinulosa
had been lost due to winter storms appeared to recolonize quickly up to the maximum observed crust thickness (2.4cm) during the following summer (R. Holt pers. comm. cited in Holt et al
., 1998). Linke (1951) reported that spawning of intertidal Sabellaria spinulosa
reefs in the southern North Sea took place during the first and second years. Thus, in ideal conditions, sexual maturity of Sabellaria spinulosa
is probably reached within the first year. The algae in the biotope are also likely to reach maturity fairly rapidly. Experimental clearance experiments in the Isle of Man (Kain 1975; Kain, 1979) showed that Laminaria hyperborea
returned to near control levels of biomass within 3 years at 0.8 m and the species reaches sexual maturity at between 2 and 6 years of age. Sivertsen (1991 cited in Birkett et al
. 1998b), showed that kelp populations stabilise about 4-5 years after harvesting. However, many of the other species, the anemone Urticina felina
and coralline algae for example, within the reef matrix are slow growing and long-lived with a very low turnover rate. Lithophyllum incrustans
in particular is very slow growing (2-7 mm per annum) and colonies may be up to 30 years old (Irvine & Chamberlain, 1994). Species diversity on the Sabellaria
crust is likely to increase with age of the reef so although most components of the biotope can reach maturity within several years full community diversity and complexity is likely to take much longer.
This review can be cited as follows:
Sabellaria spinulosa with kelp and red seaweeds on sand-influenced infralittoral 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=144&code=1997>