1. Rocky Shore Communities
MR2505
Lecture 3

2. Rocky Shore Communities

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Described as inhospitable environment
Exposure to the Elements e.g. Wind and Wave Action
Lack of Shelter
Ice (geographical location)
But in some cases Very Rich Diversity of Organisms

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Zonation (horizontal banding)
Plants and Animals
Universal Patterns Identified
A 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.

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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.

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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.

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Communities vary from shore to shore despite vertical zonation
Wave exposure
Zonation more obvious where fewer plants e.g. barnacles
Ballantine’s scale (figure)

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Sheltered versus exposed (protection versus wave action)
Increasing exposure – brown algae to barnacles, mussels and red algae
In-between shores – mosaic of fucoids, barnacles and bare rock
Pattern varies around the World though

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Also differences in vertical zones with different exposures (Figure 3.2)
Distributions of flora and fauna are not just the result of physical factors
Wave forces are responsible for some organisms but not for all

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Differences in environment e.g. water temperature and turbidity
Some 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

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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 pressures
Difficult 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.

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Unique environments include:
fast flowing water;
submersion;
reduced illumination;
reduced salinity

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Littoral ecosystems
Food webs
Two examples provided by Little and Kitching (Figures 8.1a and b)
Show how communities work – albeit simplified
Provides a basis for questions to be asked
Are communities stable or changeable?

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On sheltered shores algal-dominated communities are stable
Moderately exposed shores are much more variable
Exposed shores show little overall variation but small scale mosaic patterns change frequently

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The changes that take place are deemed to be a combination of both physical and biological interactions
Disturbance lies at the root of the change
For example, wave action leads to physical removal
Mobile ice in different climates; desiccation; Sand Scour etc…
Result is often a mosaic community

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Competition also influences the community structure
Interspecies interactions affect succession and therefore structuring of communities
Competition for space, food
Balance between physical and biological factors

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Also Predation, Grazing and Recruitment
Paine’s hypothesis of ‘Keystone Species’ that can ‘free up space’ for others
But... 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)

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Grazing – different because it is a different process and involves different species
Recruitment – miniature adults important in the density of populations e.g. larval supply

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Macroalgae and Microalgae
Dominate on some shores
Brown, green and red
Blue-green, diatoms etc.
Microalgae more important in the food chain than macroalgae
Microalgae have high rate of production

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Distribution varies according to exposed shore etc. and also locally
Exposed shore less evident than sheltered shore
Variety of species always increases towards the sub-littoral zone
Green algae less abundant: Enteromorpha, Ulva, Cladophora

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Primary production of algae is substantial
Eaten by grazers (but less of the larger sizes)
Large plants end up as detritus
Algal defences: growing out of reach; temporal escape (growing or fruiting when grazing pressure is least); deter grazers through structural adaptations; chemical

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Brown Algae
Fucoids and Laminarians or Kelps
Different habitat and distribution
Laminarians are affected by wave action, competition and sea urchins

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Green Algae
Enteromorpha for example occurs anywhere on the shore, but usually high-shore, Ulva on the lower shore, as is Cladophora
Generally sheltered environments
Very frequent and rapid reproduction aids colonization

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Red Algae
Very varied form: frondose and branching, filamentous, encrusting
Live low on the shore (but some at top)
Some live in tidal pools
Like brown and green algae contain chlorophyll a, but also red pigments – phycoerythrins (absorb blue and green light)

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Microalgae
Provides most of the food that the limpets, winkles, topshells and other herbivores survive on
Evidence of vertical zonation
Different diatom assemblages on different substrate
Effects of grazers at different times of the year

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Grazers or Herbivores
Live algae
Dead algae (detritus) are detritivores
Molluscan grazers most prominent on rocky shores
Major control on algal vegetation
Lower shore – sea urchins
Mesograzers – amphipods and isopods overall
Limpets and Winkles and many others specialise in intertidal life

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Grazers may determine community structure
Intertidal
Subtidal
Limpets: widespread, at all intertidal levels, adaptable, strong, resist wave attack and predators, demonstrate homing and territoriality, different feeding times
Can be affected by desiccation
Predators deterred by Stomping and Mushrooming

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Winkles
Common around the world
Very adaptable
Evidence of Zonation
Preference for algal foods
Others are: Topshells, Mesograzers (amphipods and isopods), Sea Urchins

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Suspension Feeders
Barnacles and bivalves (mussels) on wave-exposed shores
Largely sessile
Many others around the world
Many man-made substrates – docks, ship hulls, offshore platforms
Fouling communities

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Rocky shores suspension feeders are sessile
Depends on local conditions for supply of food and nutrients
Tolerate conditions of flow, wave action, desiccation,
Mussels, Barnacles, Polychaetes, Sea Anemones,

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Interaction between species
For example, efficiency of grazers e.g. limpets
Competition
But differences exist between sheltered and exposed shores

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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.

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Impact of man
Trampling
Pollution (sewage, heat)
Oil Spills
Oil Cleanups
Sea Level Rise / Climate Change

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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

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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,
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George 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,