Height: Width of Limpets Across Different Zones on an Exposed Shore

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Rocky Shore Ecology: Holbeck Beach

This study was conducted to deduce whether the height to width ratio of limpets altered across the three main zones on the shore: upper, middle and lower. It was carried out on Holbeck Beach, North Yorkshire, where limpets were measured in all three zones using random sampling. We found a significant difference in the height to width ratio between the upper and lower shore and upper and middle shore. This is due to many factors, including the threat of desiccation and strong waves.

Limpet Patelle VulgataRocky ShoreEcologyHolbeck Beach
Upper ShoreMiddle ShoreLower ShoreCallipers
QuadrentRandom SampleDesiccation

INTRODUCTION

Common limpets, Patella Vulgata, are found, on rocky shores, wherever there is an area firm enough for attachment on rocks, stones and in rock pools. [1] The common limpet is commonly found on Holbeck shore in relatively high abundance. Patella vulgata are in the taxonomic group gastropoda, and the family acmaeidae.

They are abundant on rocky shores of all degrees of wave exposure but a high density of seaweed makes it harder for the Patella Vulgata to attach itself to the rocks, so limpet density is reduced.[2] Patella Vulgata have the ability to use their mucus and their ‘foot’ to clamp down upon the rock with considerable force. This allows them to remain safely attached at all times, despite strong wave action and the threat of desiccation during low tide. When the limpet is fully clamped onto the rock it is almost impossible to remove them.

The common limpet is a temperate species, so is found mainly across Europe, spread from Norway to Portugal. The grey conical shell of Patella Vulgata can reach a width of 6cm and height of 3cm with ridges radiating from the central apex. The muscular foot of the limpet is usually a yellow colour and attached to the smooth interior of its shell.[3] Limpets graze upon algae, which grows upon the rocks where they live. They can scrape the algae with its radula (a tongue coated with many rows of teeth) as they slowly move across the rock surfaces.

The Patella Vulgata always return to the same spot, known as the homing scar, before the tide withdraws. The shells grow to match the contours of the rock in order to form a strong seal, protecting them from desiccation and also predation. They find their way back to the same spot by using chemical cues, finding their own mucus track and following it back to their home point.[4]

Limpets are the prey of a variety of creatures, including seals, fish, shore-birds, starfish and humans. The limpets have two defences: fleeing or clamping down to the rock. They can determine which would be the most effective by detecting chemicals in the environment.

Patella Vulgata have the general lifespan of 10 years but this can be drastically changed by the rate of growth. If there is an excess of food, the limpets grow exceedingly quickly but generally only live for around 3 years. However, if food is sparse, limpets usually grow very slowly but can live up to 20 years. [5]

Patella Vulgata are hermaphrodites and undergo a sex change during their life. At around 9 months they mature as males, but after a couple of years they change sex and become female. Spawning occurs annually, usually during the winter months as it is triggered by rough seas, which disperse the eggs and sperm.[6] The larvae has a pelagic life of about 2 weeks and then settles on rocks at a shell length of about 0.2 mm, usually in rock pools or areas that are constantly damp.

HYPOTHESIS

Our hypothesis states that there will be a difference in the height to width ratio of limpets on different parts of the beach: lower, middle and upper. The null hypothesis states that there will be no difference between the height to width ratio of limpets on different parts of the beach: lower, middle and upper.

METHOD
We visited an exposed rocky shore at Scarborough in order to deduce...
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