Rocky Shore Ecosystems

A rocky shore is usually a high-energy shoreline (compared to areas of coastal accretion), with high erosive forces stemming from waves, wind and tide.The shore is the transition between marine and terrestrial environments, and creates a habitat wherein neither fully marine nor terrestrial organisms can flourish; emersion and dessication is stressful to marine organisms, while immersion is stressful to terrestrial creatures. The transitional gradient seen between the two dissimilar environments creates an intertidal zone with notable zones, although the effects of wave splash and spray extend beyond High Spring Tide Level, meaning the gradient between marine and terrestrial is not entirely embraced. In British shores, sheltered shores are often dominated by fucoids, macroalgae, whilst exposed shores are dominated by barnacles and mussels.

 Fetch describes the distance of open water across which the predominant wind blows; this builds up energy in the form of waves, and the energy determines whether a sandy or rocky shore develops. 

In polar regions, crevices and hollows are formed in the rock by ice scrapes and are the only areas in which organisms can survive, unless they migrate to the sublittoral zone. Deep freezing and summer thaw both create harsh environments. In tropical regions, higher light intensities, temperatures and dessication at low tide are incredibly hostile towards macroscopic algae; it is below the Mean Low Tide Level biodiversity climbs.

Zonation

Competition for resources and the environmental conditions are the two factors responsible for zonation; it is a manifestation of resource-partitioning among potentially competing species,a nd linear zones reflect the linear nature fo the environmental gradient. For sessile, sedentary organisms, several physical factors determine the extent of suitable microclimes;

• The slope of the shore determines the amount of suitable rock surface
• Tidal amplitude will affect wetting and submergence
• Greater wave action will push the zonal boundaries further upshore
• Shore aspect will affect the amount of drying out at low tide, and shaded slopes will remain damp for longer than sunny slopes. 

Macroalgae

Higher competition is experienced here, and macroalgae such as Liminaria digitata are found growing from a holdfast; a stipe developes and branches out in to fronds, which are composed of the lamina, thallus and blade. They are adapted to minimise water loss with a mucilaginous coating and channelled thallus. All macroalgae must be submerged to photosynthesise efficiently, and some species have bladders for buoyancy. They grow through meristematic cell division at the algal apex, and reproduction uses haploid gametophytes, which produce gametes that combine to form a diploid zygote. This grows in to a diploid organism. Meiosis in the sporophyte leads to the production of the haploid spores that may be flagellate, and grow in to gametophytes. Macroalgae may also be monoecious (self-fertilising), although are generally dioecious, releasing sperm/spores at high tide. Macroalgae reproductive cycles are connected to a temperature threshold and have lunar cycles!

Zonation at Bembridge rocky shore, Isle of Wight (http://www.medinavalleycentre.org.uk/resource/bembridge-marine-life/).

Animals

Consumers include the porifera (sponges), anthozoa (soft corals), annelids (worms) and pycnogonida (ticks and mites), bryozoa (colonialists), crustacea, mollusca and echinodermata (starfish). Increasing mobility on a rocky shore would reduce the effects of physical environmental stress on zonation, which may be influenced more by the distribution of protective microhabitats or food supply. 

Molluscs: These include the gastropods; topshells, limpets and winkles. Trochidae (topshells) such as Monodonta spp. or Gibbula spp., exhibit a tooth and have mother-of-pearl inners. Patellidae such as Patella spp., and Andsates pellucida are blue-rayed limpets. Littorinidae are primarily Littorina littorea and Melaraphe neritoides, and are shelled organisms, soft-bodied with a muscular foot. 

The operculum is a piece of shell that seals the arpeture when the organism retreats inside, to prevent water loss and protect from predators. A larger shell surface area with ridges minimises heat loss and increases the enzyme tolerance to fluctuating temperatures. The camoflage and position on the sea shore decreases the chance of predation. Most molluscs are dioecious, and the larvae are planktonic, named veliger larvae. 

Crustacea: This includes the cirripedia; barnacles such as Cthalamus montagui and Semibalanus balenoides, and the decapoda such as Cancer pagarus. Cyprids of both settle on suitable substrate throughout the intertidal zone down to the sublittoral zone. Semibalanus balenoides cyprids can cement down their antennules in 20 minutes. However, they are incredibly intolerant to dessication, and have a calcareous plate system to improve resistance, and close over the aperture during emersion. They are well adapted to temperature variation, with enzymes capable of tolerating high temperatures. Cement glands facilitate fastenings to the rocky substratum, where they feed on plankton and detritus. They also have huge penises that fall off after sex. 

Indicator Species

Pelvetia cannaliculata is found in the Mean High Tide Level and is characterised by its surface mucilage, channelled fronds, and enzymes/pigments resistant to high temperature. 

Fucus spiralis is found in the eulittoral zone, with a higher tolerance to dessication, but a slower growth rate. It is easily out-competed by Fucus vesiculosis and Fucus serratus. 

Littorina saxatilis is a large-ridged top-shell, well-adapted to low temperatures, with an operculum and thick shell, and they are found in rocky crags. 

Fucus versiculosis is found in the upper eulittoral zone and is tolerant to heat shock, but not as well as Pelvetia cannaliculata. It is further out-competed by Fucus serratus. 

Chondrus crispus is found in the low intertidal zone as a dominant competitively superior species.

Space on the substratum is an essential resource for sedentary organisms, and may be provided by the rock surface or biological surfaces (secondary space); it is non-renewable since once occupied, no more space is forthcoming. Food resources by contrast are renewable, so is not so fixed in extent, imposing a limit to the number of sessile individuals able to occupy a zone. Therefore, space is the most essential resource and can quickly become both a physical and biological limitation; for instance, reduced area for attachment, deformed growth, undercutting or smothering, alongside reduced light accessibility, algal films reducing growth and reduced reproductive output.  

Human exploitation 

Intertidal plants and animals are harvested commercially; consider the Concolepas concholepas fishery in central Chile. They farm a carnivorous gastropod whose diet consists of mussels and barnacles, and grows to a size large enough for human consumption. Where C. concholepas was fenced off from farmers and allowed to function normally in the community structure, the previously mussel-dominated rocky shore became cleared to allow colonisation of barnacles and macroalgae. Mussel domination in Chile is the result of human exploitation; both fishermen and C. concholepas are keystone species controlling the community of these rocky shores. 

                              

In New South Wales, shore fishes are caught using intertidal ascidians, crabs and gastropods for bait; following this decimation it has been concluded that sanctuaries excluding people from the shore may significantly improve adjacent fisheries and preserve breeding populations of the exploited invertebrates. 

Renewal of secondary space and of non-hierarchal competition 

Physical and biological disturbances are incredibly important for maintaining species diversity; sedentary organisms form linear, competitive hierarchies, and space is a non-renewable, limiting resource. Undisturbed, such a system would eventually lead to monopoly.

Fucus serratus grows prolifically on sheltered shores, supporting epifaunal communities with a high biodiversity, controlled by the summer growth of the plant, which replenishes the substratuma vailable by up to 75% every year. 

Patch dynamics 

A rocky shore often exhibits 'patchiness' within zones. It is nested in the population distribution on a scale of kilometres, and different biological/physical factors will operate on the different spacial scales. The patch mosaics within zones reflect varying forms of space occupation by intertidal organisms, and as patches become bigger, colonisation from immigration between patches will likely occur.