distributions and patterns of organisms on the rocky shore

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  • 7/22/2019 Distributions and Patterns of Organisms on the Rocky Shore

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    Distributions and Patterns of Organisms on the Rocky Shore

    Aim: To observe and sample organisms on the Rocky Shore, and to discern any patterns of distributions

    and possible reasons for this.

    Method:

    1. Identify the high water mark (HWM) on the shore (this is easier to measure because it has the mosttidal exposure).

    2. Choose 5 or more rock pools to observe, preferably at different distances from the HWM3. Using string lines, measure the distance from the HWM to the rock pool you are observing.4. Look into each pool and identify all the organisms present, record this in a data table, and state

    whether this organism is; absent, present, common, or abundant (qualitative data).

    5. Repeat this for each of the 5 or more rock pool you are observing.

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    Data Table of Results:

    ORGANSIM 5m 15m 20m 26m 35m 40m

    Green

    Anemone

    P C

    Sea Star C

    Neptunes

    Necklace

    A P A C C C

    Strap

    Weed

    P P

    Cushion

    Star

    C C

    Chiton P P P P

    Brown

    Periwinkle

    P

    Cats Eye

    Snail

    C A C

    ZigzagWeed

    P P

    Encrusting

    Sponge

    P

    Sponge

    (golf ball)

    A

    Limpets A C

    Mossweed A

    Glass

    Shrimp

    P

    Large Crab P PIntestine

    Weed

    A C

    Shore Crab C

    Absent: A

    Present: P

    Common: C

    Abundant: A

    The organisms

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    Discussion:

    There were seventeen different species that were observed in the various rock pools along the Rocky

    Shore, from 5m to 40m from the high water mark.

    The most widely spread and common organism was probably Neptunes Necklace, as it was present in allrock pools from 5m to 40m from the high water mark. However after gathering data from the rock pools, it

    was mentioned that maybe not all the Neptunes Necklace observed was in fact alive, but the seaweed was

    still present in nearly all the rock pools observed, so this data will be counted as accurate. This widespread

    amount of Neptunes Necklace indicates a wide tolerance range, and could also indicate that Neptunes

    Necklace has a commensal interspecific relationship with other organisms on the Rocky Shore. This could

    be because the mats of Neptunes Necklace formed on the surface of several rock pools (such as the rock

    pool at the 5m mark), form a protective moist habitat from the sun at low tide, possibly benefitting other

    organisms such as molluscs or crustaceans (who are in danger of dessication at low tide) and leaving this

    seaweed seemingly unaffected.

    An example of this could be the unusually wide spread of Chiton (compared to other organisms on the

    Rocky Shore) which was present close to the high water mark (15m) as well as further away (40m). This

    could mean Neptunes Necklace does indeed provide a habitat for this mollusc that allows it to be so

    widespread compared to other organisms. However there is no obvious correlation between the numbers

    of chiton and regularly widespread amount Neptunes necklace, and, though there could be other factors

    that apply, limpets and other such molluscs do not follow this pattern.

    Limpets were found to be abundant and common at 15m and 20m from the highwater mark, and there

    could be a correlation between this and the very low amount of organisms present in the zone of the

    Rocky Shore. At 15m where the limpets were abundant there were no other organisms found apart from

    low levels of chiton, and a low amount of Neptunes Necklace. A correlation observed is at the 15m limpets

    are abundant whereas Neptunes necklace is present (this is the only time this seaweed has been observed

    as less than common), but at 5m and 20m as the level of limpets decrease, Neptunes Necklace increases

    to abundant. This could mean that something the limpet does causes Neptunes Necklace to decrease, as

    well as causing a lack of other organisms, such as feeding on other organisms food supply, or it could just

    mean limpets are in their optimum range in this zone, whereas other organisms are not because of some

    change in an abiotic factor such as salinity or temperature.

    Another observation about chitons was that there seemed to be a correlation between these molluscs and

    Intestine Weed. Where there was abundant and common numbers of the weed (5m and 27m

    respectively), there were no limpets, and vice versa. This also links in with the pattern of limpets, because

    chitons and limpets both seem to be abundant in the same zone, (15-20m from highwater mark). This

    suggests that in this zone there is a plentiful food supply for these molluscs (they are both filter feeders), or

    there is some other factor that makes this an ideal habitat for them, that isnt ideal for intestine weed.

    The rock pool with the highest amount of organisms was at 40m from the high water mark. This included

    everything from seaweed to sponges to crabs to snails and starfish. From this we can suggest that a lot of

    the organisms living on the Rocky Shore probably prefer less exposure to sunlight (because of the danger

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    of dessication), or that their food supply prefer less exposure, and so these organisms must also make their

    habitat where their food supply is. This would explain the large variety of organisms at the 40m from

    highwater mark, and also how a lot of the organisms are similarly abundant or less abundant at the 35m-

    40m mark, and then are not observed in any other rock pools. This could be a exploitative relationship

    between predator and prey, where s the food supply increases the number of a particular predator will

    also increase.

    There was also an extreme value with the zigzag weed, which was found in the rock pools 5m and 40m

    from the highwater mark, but not in the rock pools between these. No other organism recorded follows

    this pattern so it is hard to discern the reason for this. It was likely an error, as the tolerance range of an

    organism should not usually go from one extreme to the other, as has happened here.

    The only other organism just living close to the high water mark was the shore crab, and this could be

    because its food source is intestine or zigzag weed, which was also present close to the high water mark. It

    could also be because it has a higher tolerance range for light and exposure to light, and so survives where

    possible predators (such as those organisms whos habitat is 35m-40m away from the high water mark) donot, making it easier for these shore crabs to survive.

    Conclusion:

    From the observations about the distribution of the organisms in the Discussion, the most logical

    conclusion is that the tolerance and optimum range of many organisms on the Rocky Shore is around the

    35m-40m from the highwater mark, probably because of abiotic factors such as the length of time exposed

    to light, or the lower temperature of the water further away from the highwater mark. Biotic factors alsoadd to this, for example some organisms such as snails or crabs might only feed on organisms whos

    habitat is between 35m-40m from the highwater mark, and so must live in that zone as well. Other

    organisms, such as limpet or chitons, might also prevent other organisms from living in the one that suits

    their tolerance and optimum range, for example by eating all the food supply (ie an organism might

    compete for the same niche as limpets and lose, and so must stay in the 35m-40m zone). Lastly, there are

    some organisms that were observed close or moderately close to the high water mark, but this was mostly

    Neptunes Necklace, which was present in every rock pool. Other organisms close to the high water mark

    were the shore crab, which has probably adapted to survive in an area where there are not many

    predators, and its possible food source, the intestine and zigzag weeds. However most of the organismswere observed between the 35m-40m from high water mark.