The Rocky Shore has one of the most extreme environments due to abiotic factors constantly changing. Organisms living there must learn to adapt to the constant changes in order to survive, the main factor causing zonation being tidal movement because it causes air exposure. The species I have been researching are the Black Nerite and the Encrusting Coralline Algae because they are distributed in the same zone.
Black Nerite
Zonation is when species distribution falls into horizontal bands across a habitat due to biotic and abiotic conditions, the main one bring tidal movement. The Black Nerite (Nerita melanotragus) are marine snails or molluscs with either a black or dark grey shell. From my kite diagrams and data from Te Raekaihou Point we can see that Black Nerite are mostly found in mid to low tide. The data shows that the first sightings of the organisms were 5 meters from the high tide mark and for the next few meters away from the tide there were zero Black nerite on the rocky shore. However, more Black Nerite were found at 9 meters from the high tide mark which is around mid to low tide. We can also see from the kite diagram that the Black Nerite live at the bottom of the rock pools and boulders where there is the most water and shelter. The Black Nerite avoid sunlight and heat as much as possible to prevent drying out and desiccating.
Encrusting Coralline Algae
Encrusting Coralline algae are found in the mid to lower zones of the rocky shore. Our research and data collection at the rocky shore showed that the algae was spotted living 5 meters and 9 meters from the high tide, the exact same as the Black Nerite species. This proves that they share a zonation pattern because they are found in the same areas meaning they have similar tolerance levels to environmental factors. Tidal movement causes this distribution pattern because the Algae requires exposure to sunlight for photosynthesis in order to grow and survive. Encrusting Coralline Algae produces calcium carbonate within its cell walls which causes it to crust over and become cement-like. This allows it to grow in areas where weaker algaes cannot because it’s hard skeleton can withstand strong tides and harsh winds, both of which are common at the rocky shore.
The changing tides will affect the Black Nerite because it will be exposed to air one minute and submerged in water the next so it will need to adapt to this environment. Exposure to air, wind and sun would bring on desiccation while being submerged in water could sweep the nerite off the rocks and out to sea where it would die. Marine organisms avoid desiccation because if they dry up they will die from dehydration. Desiccation will affect the behaviour of Black Nerite because they will choose carefully where exactly to live on the rocks depending on their tolerance to air/light exposure. To avoid desiccation Black Nerite often cluster together in groups to limit their surface area from being in direct sunlight. Another way for Black Nerite to prevent desiccation is by attaching themselves to surfaces that are vertical/ have a steep slope. On a flat horizontal rock surface they would be fully exposed to the sun however on a greater slant the organisms will absorb less sunlight and heat. They are also most commonly found in pools or rocks which are virtually always damp in order to stay hydrated and to stop from drying out. They can also hide in crevices, in or under seaweed or hang under rocks in the shadows to avoid winds which would increase water loss. However competition for living space comes in as a problem for these especially shaded and protected areas.
An environmental factor that would affect Encrusting Coralline Algae is light because it utilizes energy from the sun for photosynthesis which requires light energy, water and carbon dioxide. The Algae will grow where they get sufficient amounts of sunlight to turn into energy and therefore thrive. So while Black Nerite attempts to avoid sunlight so that they don’t dessicate, Encrusting Coralline Algae demands it.
The Black Nerite is a primary consumer of seaweeds and algae which creates living space for more plants to grow. It has inherited many adaptations to help them survive in the constant changing environment at the rocky shore. One structural way to combat desiccation was to adapt by having a flap known as the Operculum which traps water inside the shell. The heavy and tough shell also prevents desiccation and protects them from predators because it keeps the light and sun from penetrating through the shell and into the organism which will dry it out. Another adaptation is the Black Nerite creates slime to keep itself moist. Encrusting Coralline Algae creates a cement like protection over the sea bed, coral reefs and rocks which helps to bind and stabilise the habitat. The interrelationships between the Black Nerite species and Encrusting Coralline Algae is that the Black Nerite feed/ graze off the Algae so the Algae is a primary producer of a good food source and therefore helps the Nerite survive. Encrusting Coralline Algae contains calcium carbonate which discourages grazing from most marine organisms but also encourages marine invertebrates to settle around it (they are also important to the global carbon cycle). Luckily the Black Nerite have a hardened mouth and are one of the few species which can munch on the hard Algae, therefore making the Algae an important food source for Black Nerites. The Algae can also be used a micro habitat and refuge for juvenile Black Nerite while the Nerite don’t benefit the Algae at all except for possibly eating other seaweeds around it so that it has more living space.
The Black Nerite and Encrusted Coralline Algae link because the Black Nerite feeds off the Algae for energy and nutrients. Both the Algae and Black Nerite are found in the same zone (mid to low tide or the intertidal zone) which we know from the data we collected. One of the reasons for this particular distribution could be because the Nerite move towards the Algae because they eat them, and like most organisms, choose to live where food is most easily accessible. The Nerites have a structural adaptation where their gills enable them to get oxygen from water when they are in the mid tide zone so that they can be submerged in the ocean and feed off the Algae – which usually stay submerged as well. This adaptation allows them to survive in the intertidal zone for food resource reasons because that is where the Algae live and the Nerite often need to be able to access their food underwater. Nerites also have an adaptation where they have a strong foot so that they can stick to rocks in harsh tides. This is again useful for when they are in mid tide and need to eat the algae with a structure called a radula which is used for scraping the Coralline Algae off the rocks without falling off and being pushed around by the tides.
Gause’s principle states that no two species with identical ecological niches can survive in the same area for a long period of time because one will outcompete the other, causing the outcompeted species’ population to significantly decrease. Black Nerite and Encrusting Coralline Algae have different Niches because one is a mollusc and a primary consumer and the other is a plant species and is a primary producer. Therefore they can both thrive in the same zone because they are not competing for the same food or living space because Black Nerite eat Algae and can also live on it. For example however, Black nerite and Limpets have similar niches and compete for living space and food. The data we collected from Te Raekaihou Point showed that where one species was found, the other was not which proves Gause’s theory that organisms with similar niches will distribute to areas where they are not competing for resources. The data also shows that there are many more Limpets than Black Nerite which concludes that Nerite are being outcompeted by Limpets because they cannot completely avoid each other seeing as they all need to live on the rocky shore.