7 Rocky Shore Communities Described as inhospitable environmentExposure to the Elements e.g. Wind and Wave ActionLack of ShelterIce (geographical location)But in some cases Very Rich Diversity of Organisms
8 Rocky Shore Communities Zonation (horizontal banding)Plants and AnimalsUniversal Patterns IdentifiedA dark belt of brown seaweeds, a white belt of barnacles and a black belt of lichens dominate the lower, middle and upper shore levels respectively.
9 Rocky Shore Communities Notice that the flora are dominated by brown seaweeds. At the bottom of the shore, exposed to air only during short periods of low water during Spring tides, are 'kelps' or laminarians: in this case, species of the genus Laminaria which can grow to several metres in length; a tough stipe supports a floppy frond. Above this, between MLW and MHW, the main seaweeds are 'wracks' or fucoids, especially species of the genus Fucus but also Ascophyllum nodosum and Pelvetia canaliculata . Seaweed size tends to grow smaller towards the top of the shore. This is in part a result of tougher conditions here, but also a result of interactions amongst species.
10 Rocky Shore Communities Where do red and green seaweeds fit into the picture of zonation? According to an old theory, the zonation of seaweeds was a response to the changing colour of light penetrating the sea. Thus green seaweeds were found at the top of the shore, where average water cover was small and light close to white; brown seaweeds at greater depth, adapted to green light; and red seaweeds at greatest depth, adapted to the prevailing blue colour of light penetrating here. However, a better explanation is this. Red seaweeds are less tolerant of dessication and less good at competing with brown seaweeds on shores on the west coast of Scotland, so they tend to be found as an understory, or in rock pools, or growing on other seaweeds. Green seaweeds such as Enteromorpha are not very resistant to dessication and are heavily grazed, but they can grow quickly, and seem to fluorish in regions of nutrient enrichment - e.g. where sewage pipes cross the beach.
12 Rocky Shore Communities Communities vary from shore to shore despite vertical zonationWave exposureZonation more obvious where fewer plants e.g. barnaclesBallantine’s scale (figure)
13 Rocky Shore Communities Sheltered versus exposed (protection versus wave action)Increasing exposure – brown algae to barnacles, mussels and red algaeIn-between shores – mosaic of fucoids, barnacles and bare rockPattern varies around the World though
14 Rocky Shore Communities Also differences in vertical zones with different exposures (Figure 3.2)Distributions of flora and fauna are not just the result of physical factorsWave forces are responsible for some organisms but not for all
15 Rocky Shore Communities Differences in environment e.g. water temperature and turbiditySome organisms exist in more than one type of environment, but show physical differences in size and form e.g. kelp, algae etc…Physical and biological factors are responsible
16 Rocky Shore Communities Wave action both influences structure and community composition by eliminating organisms that can not withstand the waves, but also alters the balance of competition, predation, and grazing pressuresDifficult to devise a general ‘model’Other factors that need to be taken into account are: rock type and texture etc….Localised features such as crevices, gullies, caves etc.
18 Rocky Shore Communities Littoral ecosystemsFood websTwo examples provided by Little and Kitching (Figures 8.1a and b)Show how communities work – albeit simplifiedProvides a basis for questions to be askedAre communities stable or changeable?
22 Rocky Shore Communities On sheltered shores algal-dominated communities are stableModerately exposed shores are much more variableExposed shores show little overall variation but small scale mosaic patterns change frequently
23 Rocky Shore Communities The changes that take place are deemed to be a combination of both physical and biological interactionsDisturbance lies at the root of the changeFor example, wave action leads to physical removalMobile ice in different climates; desiccation; Sand Scour etc…Result is often a mosaic community
24 Rocky Shore Communities Competition also influences the community structureInterspecies interactions affect succession and therefore structuring of communitiesCompetition for space, foodBalance between physical and biological factors
25 Rocky Shore Communities Also Predation, Grazing and RecruitmentPaine’s hypothesis of ‘Keystone Species’ that can ‘free up space’ for othersBut... not all predators are dominant because of recruitment of prey; physiological limitations of predator; prey may have refuge from predator; resistance to predator (chemicals or behaviour patterns)
26 Rocky Shore Communities Grazing – different because it is a different process and involves different speciesRecruitment – miniature adults important in the density of populations e.g. larval supply
27 Rocky Shore Communities Macroalgae and MicroalgaeDominate on some shoresBrown, green and redBlue-green, diatoms etc.Microalgae more important in the food chain than macroalgaeMicroalgae have high rate of production
28 Rocky Shore Communities Distribution varies according to exposed shore etc. and also locallyExposed shore less evident than sheltered shoreVariety of species always increases towards the sub-littoral zoneGreen algae less abundant: Enteromorpha, Ulva, Cladophora
29 Rocky Shore Communities Primary production of algae is substantialEaten by grazers (but less of the larger sizes)Large plants end up as detritusAlgal defences: growing out of reach; temporal escape (growing or fruiting when grazing pressure is least); deter grazers through structural adaptations; chemical
30 Rocky Shore Communities Brown AlgaeFucoids and Laminarians or KelpsDifferent habitat and distributionLaminarians are affected by wave action, competition and sea urchins
31 Rocky Shore Communities Green AlgaeEnteromorpha for example occurs anywhere on the shore, but usually high-shore, Ulva on the lower shore, as is CladophoraGenerally sheltered environmentsVery frequent and rapid reproduction aids colonization
32 Rocky Shore Communities Red AlgaeVery varied form: frondose and branching, filamentous, encrustingLive low on the shore (but some at top)Some live in tidal poolsLike brown and green algae contain chlorophyll a, but also red pigments – phycoerythrins (absorb blue and green light)
33 Rocky Shore Communities MicroalgaeProvides most of the food that the limpets, winkles, topshells and other herbivores survive onEvidence of vertical zonationDifferent diatom assemblages on different substrateEffects of grazers at different times of the year
34 Rocky Shore Communities Grazers or HerbivoresLive algaeDead algae (detritus) are detritivoresMolluscan grazers most prominent on rocky shoresMajor control on algal vegetationLower shore – sea urchinsMesograzers – amphipods and isopods overallLimpets and Winkles and many others specialise in intertidal life
35 Rocky Shore Communities Grazers may determine community structureIntertidalSubtidalLimpets: widespread, at all intertidal levels, adaptable, strong, resist wave attack and predators, demonstrate homing and territoriality, different feeding timesCan be affected by desiccationPredators deterred by Stomping and Mushrooming
36 Rocky Shore Communities WinklesCommon around the worldVery adaptableEvidence of ZonationPreference for algal foodsOthers are: Topshells, Mesograzers (amphipods and isopods), Sea Urchins
37 Rocky Shore Communities Suspension FeedersBarnacles and bivalves (mussels) on wave-exposed shoresLargely sessileMany others around the worldMany man-made substrates – docks, ship hulls, offshore platformsFouling communities
38 Rocky Shore Communities Rocky shores suspension feeders are sessileDepends on local conditions for supply of food and nutrientsTolerate conditions of flow, wave action, desiccation,Mussels, Barnacles, Polychaetes, Sea Anemones,
39 Rocky Shore Communities Interaction between speciesFor example, efficiency of grazers e.g. limpetsCompetitionBut differences exist between sheltered and exposed shores
40 Rocky Shore Communities Habitat-modifying, dominant species such as algaes, seagrass, corals, and mussels are known as ''foundation species' or 'ecosystem engineers' because they provide habitat for a high diversity of species.This is achieved through increasing the heterogeneity of habitat, reducing the water flow, stabilising the substrate, increasing sedimentation, reducing light, and providing substrate for species to live on.
42 Rocky Shore Communities Another example of the effects of grazing is illustrated by following the events that occurred after the Torrey Canyon oil spill in England in Beaches were treated with 10, 000 tonnes of oil dispersants, which proved, however, more toxic than the oil to most sea-shore life. Most animals on the shore were killed, imcluding many Patella (limpets) which were normally present in large numbers. There followed a settlement of the green seaweeds Ulva and Enteromorpha spp. During the late summer and autumn of 1967, Fucus vesiculosus began to appear, and in places the large brown seaweeds Laminaria digitata and Himanthalia grew m further upshore than normal. Animal life was still reduced in number during 1968, but a few barnacles settle in areas free from Fucus. Patella settled and removed much of the Fucus in , and there was a return to the limpet-barnacle community by
45 Rocky Shore Communities BENEDDETTI-CECCHI, L. (2001). Variability in abundance of algae and invertebrates at different spatial scales on rocky shores. Marine Ecology Progress Series 215,BROEKHUYSEN, G.J. (1940). A preliminary investigation of the importance of desiccation, temperature and salinity as factors controlling the vertical distribution of certain intertidal marine gastropods in False Bay, South Africa. Transaction of the Royal Society of South Africa 28,GIBBONS, M.J. (1988). The impact of wave exposure on the meiofauna of Gelidium pristoides (Turner) Keutzing (Gelidiales: Rhodophyta). Estuarine, Coastal and Shelf Science 27,GIBBONS, M.J. & GRIFFITHS, C.L. (2000). A comparison of macrofaunal and meiofaunal distribution and standing stock across a rocky shore, with an estimate of their productivities. Marine Biology 93,POVEY, A. & KEOUGH, M.J. (1991). Effect of trampling on plant and animals populations on rocky shores. Oikos 61,SOUTHWARD, A.J. (1958). The zonation of plants and animals on rocky sea shores. Biological Reviews 33,P.G. Moore and R. Seed (editor), The Ecology of Rocky Coasts: Essays Presented to J.R. LewisGeorge A Knox. The Ecology of Seashores. CRC Press 2000 Brosnan, D.M. and Crumrine, L.L. (1994) Effects of human trampling on marine rocky shore communities. J. Exp. Mar. Biol. Ecol., 177,
Your consent to our cookies if you continue to use this website.