Zonation On Rocky Shore Essay Research Paper

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The seashore is a

habitat that contains a wide range of microhabitats and ecological niches for

different creatures. This is mainly due to the effects of the tides that rise

and fall twice each day. Tides are the vertical movement of water in a

periodical oscillation of the sea due to the gravitational pull of the sun and

moon. The tides are on a semi-diurnal cycle so there are two high tides and two

low tides each day. Due to the orbit of the moon the tides also have a monthly

cycle. This creates neap (very low) and spring (very high) tides. The seashore

can be divided into several zones which are illustrated on the diagram below:

Key: EHWS = Extreme High Water Spring (MHWS = Mean High Water Spring) MHWN =

Mean High Water Neap (MTL = Mid Tide Level) MLWN = Mean Low Water Neap ELWS =

Extreme Low Water Spring (MLWS = Mean Low Water Spring) CD = Chart datum The

Supralittoral Zone: This is the highest zone on the shore and lies above the

EHWS mark and therefore is never covered by seawater. However it may be

occasionally be spray wetted. Because of this it is mainly inhabited by

terrestrial species such as lichen that can live in areas of very high

salinity. The Littoral (Intertidal) Zone: This zone is the area that is covered

and uncovered by the tides and therefore organisms that live here must be able

to tolerate a large range of conditions. It can be further divided into the

Littoral Fringe and the Eulittoral zone. The Littoral Fringe (Splash Zone): This

part of the Littoral zone lies above the area that is completely submerged by

the sea in normal conditions. However it is frequently covered by splash from

waves and so is far more marine in character that the Supralittoral Zone.

Lichens still dominate this zone but some species of periwinkles and topshells

may graze them. The Eulittoral Zone: This zone is the area of the beach that is

regularly submerged by the tides and can be divided into three more zones the

upper middle and lower shores. It shows the greatest species diversity of any

of the zones. The Upper Shore: This region of the shore lies between the EHWS

and MHWN marks and so is only immersed during spring tides. Because of this

organisms that live here must be adapted to survive long periods of desiccation.

The two seaweeds that are the most common here Fucus spiralis and Pelvetia

canaliculata have adaptations to survive in this area. The Middle Shore: This

region of the shore lies between the MHWN and MLWN marks and will be submerged

for half of every day even during neap tides. The most common seaweed in this

zone Fucus vesiculosus. Mussel beds will form and both limpets and periwinkles

will graze the rocks. Sea anemones and crabs are residents of this zone. The

Lower Shore: This region of the shore lies between the MLWN and ELWS marks and

will be submerged for most of each day even during neap tides. The most

important seaweed in this area is Fucus serratus which will form large zones

wherever suitable. It shows the greatest species diversity of any zone on the

seashore. The Sublittoral Zone: This part of the shore lies below the ELWS mark

and is therefore never uncovered by the sea. There are many types of organism

found on the rocky shore. The two main photosynthetic organisms are the lichens

and the macroalgae or seaweeds. Lichen are the main organisms found in the

splash zone and come in three distinct types; crustose foliose and fruiticose.

Crustose lichens form a thin crust on the rock surface and are impossible to

remove without damage. Foliose lichens are leafy lichens that are not as firmly

attached to the rocks. Fruiticose lichens extent vertically from the rock

surface and can sometimes be confused with mosses and small grasses. The leafy

part of a lichen is known as the thallus. Seaweeds are primarily divided by

colour into brown red and green groups. Most marine seaweeds are brown

seaweeds with fewer red species and even fewer green species. The three main

parts of a seaweed are: 1. Frond (lamina thallus blade) (often broad and flat)

2. Stipe region (often long and cylindrical) 3. Basal attachment (holdfast) The

frond or thallus is the site of most of the photosynthetic activity in the

organism and also contains the reproductive organs. The stipe region can act

either as a structural support a storage organ or as a transport network

within the organism. The role of the holdfast is to anchor the seaweed securely

to the substrate it lives on. The holdfast must be strong enough to resist the

strong pull of the waves and tides on the seaweed. The size and strength of the

holdfast varies between species. The main heterotrophic organisms of the

seashore are the molluscs. The most common molluscs are the gastropods

(periwinkles limpets and topshells) and the mussels. Periwinkles have coiled

shells and a circular operculum (a small retractable piece of shell used to

cover the opening of the shell when the snail is inside.). They average about

15mm in length and are the most common group of gastropods on the seashore.

Topshells are very similar to periwinkles but have an oval operculum and tend

to be slightly smaller. There are fewer species of topshells than periwinkles on

a rocky shore. Limpets have a conical shell with no operculum and are much

larger than either periwinkles or topshells. Mussels have two shells and are

fixed to a single location in adult life. They can form large groups on the

rocky shore. Describe LOWER SHORE There was only one species of seaweed found in

the lower shore Fucus serratus and it was very abundant. However several

species of animal were found such as Gibbula cineraria Littorina obtusata

Littorina littorea limpets (Patella spp.) and mussels (Myttilus edulis). Of

those Gibbula cineraria was the most abundant. Fucus serratus: This species of

brown seaweed (Phaoephyta) was found only below the MLWN mark in stations 10 11

and 12. It was most common in station 11 (40% cover) but there was not a lot of

difference in the distributions between these three stations. Fucus serratus is

a medium sized marine seaweed with a flattened branched thallus with a small

stipe for support and a small holdfast. At the ends of the thalli there are

small swollen areas called receptacles which contain many conceptacles in

which gamete production occurs. There are many air bladders on Fucus serratus

which cause it to float when submerged. As the name suggests Fucus serratus has

a thallus with serrated saw-like edges. Gibbula cineraria: This species of

topshell was found mainly in the lower shore below the MLWN mark (stations

10 11 and 12) and in station 9 (just above the MLWN mark). It was evenly

distributed across stations 9 10 and 11 with similar numbers in each quadrat

(between 40 and 50 individuals per quadrat). It was far less common in station

12 where only two individuals were found. Gibbula cineraria is a relatively

large snail at just over 15-mm. It was a pale grey in colour and was found

beneath seaweeds such as Fucus serratus and Fucus vesiculosus. MIDDLE SHORE

Several species of seaweed were recorded in the middle shore. Fucus vesiculosus

Ascophyllum nodosum and Polysiphona lanosa were all found and Fucus vesiculosus

was the most abundant. Many animal species were recorded such as Gibbula

umbilicalis G. cineraria Littorina saxatalis L. obtusata L. littorea

limpets (Patella spp.) and mussels (Myttilus edulis). Of these Gibbula cineraria

was the most abundant. Fucus vesiculosus: This seaweed was found mainly in the

middle shore between the MLWN and MHWN marks (stations 7 8 and 9) but also in

station 6 (just above the MHWN mark). There was a much lower density in stations

6 7 and 8 (between 3 and 12%) than in station 9 where the percentage cover was

30%. Fucus vesiculosus is similar to Fucus serratus (see above) with a

flattened branched thallus and air bladders but lacks the serrated edges of

Fucus serratus. Littorina obtusata agg.: This species of periwinkle was found in

the middle shore (stations 7 8 and 9) and the lower upper shore (station 6). It

was also recorded in station 12 at the lower end of the lower shore. It had the

highest population density in the middle shore (between 32 and 38 individuals

per metre) with a similar density in station 6. It was far less abundant in

station 12 with only 12 individuals recorded. Littorina obtusata agg. is a

small flat periwinkle mainly found on the underside of seaweeds such as Fucus

vesiculosus Fucus spiralis and Ascophyllum nodosum where it mimics air

bladders. It comes in a wide range of colour but most individuals are a dark

olive green to match the seaweeds they live on. UPPER SHORE Again several

species of seaweed were recorded in this zone such as Fucus vesiculosus F.

spiralis Ascophyllum nodosum Pelvetia canaliculata and Polysiphona lanosa.

Several animal species were also recorded such as Littorina saxatalis L.

obtusata and limpets (Patella spp.) Pelvetia canaliculata: This seaweed was

found in station 4 only (at the very upper limit of the littoral zone just

below the EHWS mark) but was very abundant covering 70% of the quadrat.

Pelvetia canaliculata has narrow thalli that are channelled and curl up into

loose rings. It is browny red in colour and has no air bladders for support.

Littorina saxatalis: This species of periwinkle was found across the whole upper

shore (stations 4 5 and 6) and at the top of the middle shore (station 7). It

was most abundant at the top of its range in station 4 where 141 individuals

were recorded. It became less and less abundant down the beach at the bottom of

its range in station 7 where only 20 individuals were recorded. Littorina

saxatalis is a medium-sized periwinkle about 16-mm long. It has a ridged shell

that is orange-brown in colour and is commonly found in crevices and cracks on

the upper shore. SPLASH ZONE The only plants found in the splash zone where

lichens such as Verrucaria maura Xanthoria parientina Ramalina siliquosa

Lecanora atra and Ochrolechia parella. No animal species were recorded in this

zone. Xanthoria parientina: This species of foliose lichen was found throughout

the splash zone (stations 1 2 and 3) and was the largest range out of all the

lichens. It was not very abundant in each quadrat never covering more than 8%

of the area (station 3) and some times as little as 1% (station 2). Xanthoria

parientina is a foliose lichen which means it is only loosely attached to the

rock and has large thalli. It was orangey yellow in colour. Explain The

environmental gradient on the seashore is constantly changing. This means that

there are a wide range of habitats to be found over a relatively small distance.

The wide range of species found on the seashore is due to the wide range of

habitats and conditions found there. Species can only be adapted to a small

range of conditions so as the conditions on the seashore change so do the

species found there. There are a number of factors that determine the specific

conditions of an area. These factors can be either biotic or abiotic. Biotic

factors are factors such as competition for resources predator/prey

relationships etc. Abiotic factors are factors like temperature relief

climate etc. The abiotic factors that affect a rocky shore are: Desiccation:

all the species found on the shore are marine species so spending time out of

water is stressful to them as immersion in seawater provides them with food

oxygen water for photosynthesis and is needed for reproduction. Desiccation is

worse on the upper shore as it is exposed for the longest time but also

affects the middle shore. Temperature: Seawater remains at a far more constant

temperature that the land (seawater varies between 5? and 15? Celsius

whereas the land temperature varies between below freezing in winter and 30? C

plus in summer) so species that are immersed in seawater for long periods of

time are buffered against large temperature changes. The temperature of the

surroundings also affects the rate of metabolism; very cold conditions will slow

it down whereas very high temperatures may denature vital enzymes. Again

temperature change is a worse problem on the upper and middle shores than on the

lower shore. Wave action: The action of powerful waves can dislodge many

species so those that live on the middle shore (where wave action is at its

most powerful) must be adapted to survive very rough conditions. Wave action

also increases the humidity of an area and so can help to reduce desiccation.

Light: Light is needed for photosynthesis and all seaweeds must be immersed in

water for this to occur. Water filters off some of the wavelengths of light and

reduces the intensity that reaches the seaweeds. To maximise the light that does

reach them red and brown seaweeds have accessory pigments that help to absorb

different wavelengths of light. These accessory pigments mask the green

chlorophyll in red and brown seaweeds and they take the colour of the accessory

pigment that they utilise. Other factors: the above factors are the main abiotic

factors but others are also present. The aspect of a slope affects the

temperature and rate at which water evaporates so south facing slopes are

warmer but dry faster while north facing slopes are cooler and damper. The

steepness of a slope also affects the rate at which it drains as a steeper

slope drains faster than a shallower one so desiccation is more of a problem.

The turbidity or cloudiness of seawater (due to plankton sewage and other

detritus) can affect the intensity of light reaching submerged seaweeds. Another

factor is the seepage of freshwater onto the shore. Many seaweeds cannot

tolerate salinity changes so other species that can tolerate such changes will

inhabit these areas. The biotic factors that affect the rocky shore tend to

affect the lower limits at which a species may live. The biotic factors that

affect the distribution of organisms on the rocky shore are: Food supply: All

organisms need food to survive and so can only flourish in areas in which they

can find food. Many species that are found on the seashore left the sea in

search of food supplies. For organisms such as barnacles which depend on food

carried by the waves far more food will be found in the intertidal zone that at

the bottom of the sea. Predation: Many species also live on the seashore in an

attempt to evade marine predators such as fish crabs lobsters etc that are

far more common in the sea than on the shore. Organisms will also try to live as

far up the shore as possible in order to avoid their less well adapted

predators. Predation is an important factor regulating the population of many

organisms. Reproduction: Most marine organisms still rely on the sea for

reproduction so animal species such as crabs may migrate lower down the shore

in order to release their gametes. Seaweeds and non-mobile animals must rely on

the tides to submerge them before releasing their gametes. Competition: This is

the most important biotic factor determining the distribution of species on the

seashore. There are two types of competition interspecific (between two

different species) and intraspecific (between individuals of the same species).

Organisms compete for all the resources that are in short supply. On the

seashore most resources are in short supply so organisms compete for space

food and light. Only species that are very efficient in utilising in demand

resources will flourish and survive. Eventually the will competitively exclude

other species or members of their own species. Despite the more stressful

conditions further up the shore species live as far above the ELWS mark as

possible in an attempt to avoid competition with other species. For example

Fucus spiralis is very well adapted to surviving long periods out of water so

it is found in the upper shore. It is not found in the middle and lower shores

because competition with other species of seaweeds such as Fucus vesiculosus and

Fucus serratus prevents them from surviving so no specimens are found. Species

can adapt to these different factors in three ways. They can adapt in physical

physiological or behavioural ways. Physical adaptations are those that modify

the external appearance of an organism physiological adaptations are those that

modify the internal organisation of an organism and behavioural adaptations are

those that modify the behavioural of an organism. Those species that are best

adapted to take advantage of a set of conditions will do far better than those

that are not adapted will. This survival of the fittest leads to wide diversity

of species found on the seashore. The main factor affecting the species found in

the splash zone is that although it lies above the EHWS mark and is therefore

never covered by the sea it is regularly covered in salt spray from waves and

the wind. This prevents many terrestrial species from living there as they

cannot tolerate areas of high salinity. This means that lichens such as

Xanthoria parientina that can tolerate such conditions are the dominant

species. No marine seaweeds can live in this zone as they all require regular

immersion in seawater and this does not occur above the EHWS mark. However

small periwinkles may occasionally graze on the lichens found here. The main

factors affecting the upper shore are the highly variable temperature and the

amount of desiccation that organisms have to endure as a result of their

infrequent immersion in the sea. However wave action and the light that reaches

seaweeds are not major factors are waves do not cover this area regularly and

even when it is submerged it is not submerged deeply so the light is not

affected. Pelvetia canaliculata is adapted to survive long periods of

desiccation as it is coated in thick mucilage which reduces water loss. The

thick mucilage layer also helps to regulate the temperature of the seaweed. It

has channelled fronds which helps reduce the surface area of the fronds that

are exposed to the air. The enzymes and pigments found within it are also

resistant to sudden temperature change so it is well adapted to live on the

upper shore. However it is not found further down the shore due to competition

with other seaweeds. Littorina saxatalis can cope with low temperatures far

better than it can with high temperatures so it has a ridged shell surface to

increase its surface are and therefore the amount of heat that it radiates. This

helps the snail maintain a constant body temperature so its enzymes are not

denatured. It has a tight fitting operculum which helps to seal in moisture

within the snail thus reducing desiccation. All of the main abiotic factors

affect the Middle Shore. Wave action is very strong on the middle shore so any

creatures that live here must be able to withstand this. Desiccation and

temperature change are also important factors as the middle shore is regularly

exposed to the air. The main seaweed found in the middle shore is Fucus

vesiculosus which has thick mucilage to conserve water. The enzymes and

pigments within are also able to withstand a certain amount of temperature

shock though not as much as those found in Pelvetia canaliculata. It is very

firmly attached to the substrate material and so is able to withstand the wave

action. Grazing by limpets and periwinkles is not a major problem on this shore

so the seaweed cover is very abundant. It is not found in the upper shore as it

cannot cope with the extremes of temperature and the lack of water in that zone.

It does not inhabit the lower shore in an attempt to avoid competition with

Fucus serratus. Littorina obtusata can withstand the moderate amounts of

desiccation and temperature change on the middle shore by closing its operculum

to seal in moisture and by resting under seaweeds to insulate it. It does not

have the ridged shell of Littorina saxatalis so it cannot radiate heat as

efficiently and therefore cannot survive on the upper shore. By remaining on the

middle shore Littorina obtusata can avoid predators such as dog whelks that

live further down the shore. However 12 Littorina obtusata were recorded in

12th station just above the ELWS mark which is very unusual as they are

normally out competed by lower shore snails such as Gibbula cineraria in that

region. The conditions on the lower shore are most like those in the sea. The

organisms that inhabit this zone cannot tolerate large amounts of desiccation or

temperature change so they are not found further up the beach. As they are

submerged for long periods the amount of light reaching the seaweeds is an

important factor and only those with the appropriate accessory pigments can

survive here. Predation is far more of a problem for the animals that live here.

Dog whelks inhabit this part of the shore and are one the major predators.

Because it is submerged for so long predation from fish is another danger

animals living here face. Fucus serratus is very efficient at using the

resources that are in short supply so it out competes other species such as

Fucus vesiculosus and Pelvetia canaliculata. However rapid temperature changes

destroy the photosynthetic pigments in its cells so it is not found further up

the shore. It is brown in colour and so is very well adapted for taking

advantage of all the available wavelengths of light that reach it. Gibbula

cineraria cannot tolerate desiccation or temperature change very well so it does

not inhabit the upper of middle shore. However it is very good at maximising

the resources around it so it out competes other species of snails such as

Littorina saxatalis. It has a thicker shell than many other snails and so is

more difficult for predators to eat. Limitations The method that was followed

had a number of limitations that lead to anomalous results (such as finding

Littorina obtusata in the twelfth station). The limitations affecting the

results were: ? The misidentification of species. Many of species found looked

very similar and so misidentification could have affected the results. The

misidentification of species would lead to species being miscounted or being

recorded in stations where they are not normally found. The correct species

would not be recorded and this again would affect the results. This limitation

affected the periwinkles and topshells more that the other groups as they are

the most physiologically similar. ? Species or specimens being miscounted or

missed altogether. Due to the thick seaweed cover on the shore it is possible

that many of the periwinkles and topshells where either miscounted (as

individuals were covered up) or missed altogether. Quadrats containing many

cracks or crevices or large rocks which organisms could hide under also made

it more difficult to be confident that every specimen had been recorded leading

to inaccurate results. ? Quadrats being placed in the wrong location. It would

have been easy for errors to have been made while cross-staffing new locations

for quadrats which would lead to species being recorded at the wrong heights

and in the wrong zones. This would make it harder to draw meaningful conclusions

from the results. ? Quadrats placed on uneven ground. The shore that was

surveyed was very rocky and so quadrats were occasionally placed overhanging

other areas. This lead to larger areas being surveyed as the slopes were

surveyed as well as the flat ground. The same problem occurred when large rocks

were within the quadrats as the top bottom and sides of the rock were

surveyed again leading to large areas. This could lead to abnormally high

results as a larger area was surveyed than normal which would make it harder

to draw conclusions from the results. ? Animals moving around. The majority of

the animal species recorded are mobile and so could move around while being

counted leading to inaccurate results or could have been found far from their

niche distorting the results. The animals could move into a quadrat leading to

higher results or move out of a quadrat leading to lower results than would be

expected. It is also possible that animals could have been counted twice which

would increase the results. All of these limitations would affect the accuracy

of the results making it harder to draw meaningful conclusions. Biological

Significance An organism can only survive in a particular habitat if it is well

adapted to that habitat. If a organism arrives in a habitat to which it is not

adapted then it will be either killed outright by the conditions there (e.g.

extreme temperature changes in upper shore kill any Fucus serratus spores that

germinate there); or out-competed by other better adapted species (e.g.

Littorina saxatalis is not found further down the shore because it would be out

competed by other Littorina species). If a species is very well adapted to a

particular habitat then it can make maximum use of the resources there and

competitively exclude any less well-adapted species. It will therefore become

one of the most abundant species in that habitat. Species become adapted to new

habitats as mutations randomly occur in the population. The majority of these

mutations will have no affect on how well adapted the organism is (e.g. a human

being born with webbed toes) some will make it less well adapted (e.g. a bright

white lion is born and is unable to be camouflaged against its prey and so

starves) and others may make an organism better adapted to its habitat (e.g. a

giraffe is born with a longer neck and so can reach more food). Those organisms

that are better adapted to their environment will be more successful than those

that are less well adapted and will have more offspring and so pass on their

genes to more individuals. If a disaster occurs and resources are in very short

supply those organisms that are better adapted will be more likely to survive

and pass on their genes. Eventually a new species will be formed with every

individual being better adapted. When this occurs the original species may

become extinct (e.g. all the giraffes with short necks) or continue surviving

if the new species is adapted to take advantage of a different habitat (e.g. a

new seaweed evolves that can survive higher up the shore). This process is known

as survival of the fittest and it increases species diversity as new species

are constantly evolving. This can be seen on a miniature scale on the rocky

shore where many different species have evolved to take advantage of the many

different ecological niches available. My results show that each species is only

found on a small area of the shore an area that it ha evolved to be adapted to

and one where it is the most successful species. This process of evolution is

constantly occurring producing better and better-adapted species for many

different ecological niches. It occurs all over the globe in many different

habitats forming many new species.