The Incredible Coral Reef: August 2015

One more way to look at the species in a coral reef would be to look at their age-structure pyramids. Basically, these graphs show how much of an individual is living at each certain age. For example, many of the fish when they are young do not survive, therefore few make it to adulthood and old age. The age-structure pyramid would look something along the lines of this:

However, it is usually very hard to create these graphs for marine animals, any animal in fact, because of a lack of research and the difficulty of collecting this data. Age-structure pyramids are more often used to represent human populations.

Monday, August 17, 2015

Coral Reef Populations

In general, the populations of the coral reef are declining. One of the large reasons for this is because of acidification and acid rain caused by the increased carbon dioxide in the air from combustion of fossil fuels. The reason acidification can be so devastating for a reef is because the extra carbon effects the growth of shells and harms the shelled organisms. It also causes coral bleaching, which kills the coral and the home for the thousands of fish inhabiting the reef. See below.

Other types of ways to identify population growths is logistic versus exponential growth. Exponential growth is the theory that with no carrying capacity, which is determined by both population dependent factors and population independent factors, the species will grow exponentially. However, the more realistic growth curve is logistic because most species do have a carrying capacity in their habitat. Logistic curves show that the population levels out once the capacity is reached. Fish can reach their capacity through a limited amount of shelter for homes or a limited amount of prey, for example.

Sunday, August 16, 2015

The Other Types of Species

There are many other types of species in a coral reef, but all of them can be put under two categories: r-selected and k-selected species. R-selected species are those who produce a large number of offspring for better survival chances, do not have maternal care for the young produced, and have short growth periods and life-spans. One example of an r-selected species living in a coral reef would be, as a matter of fact, coral. Coral is actually very small organisms called coral polyps that reproduce many thousands of other polyps per year to form a colony. They can either do this sexually or asexually. When they die, they leave their calcium carbonate shell so that more coral polyps can form on top of them.

On the contrary, a k-selected species generally has a long lifespan, have longer maturation rates, reproduce less, and care for their young (humans are a k-selected species). On a coral reef, a dolphin is a k-selected species because they have a very long lifespan (40-50 years), care for their young, have a longer maturation period, and produce fewer offspring. They are migrant within a coral reef (venture in and out); the majority of species living in a coral reef are r-selected species.

The Keystone Species

There are three main types of species that I am going to identify for a coral reef. First and foremost, a keystone species. Keystone species are those that maintain the "status quo" of the ecosystem, such that if they were removed the ecosystem would be at risk of drastic changes, which could ultimately destroy the ecosystem. One keystone species of a coral reef that I would like to identify is the shark. The shark eats carnivorous fish, and without this regulation the population of herbivorous fish that eat algae and plankton would decrease. This causes an increase in algae which outcompete corals. Without corals, well, there would be no coral reef.

Symbiotic Relationships

First things first, there are three types of symbiotic relationships: mutualism, commensalism, and parasitism, all of which are found within a coral reef. Mutualism is when two organisms both benefit from their relationship, such as zooxanthellae and coral polyps. Zooxanthellae provide the coral polyps with an energy source through photosynthesis to build coral structures, while the coral provides the zooxanthellae with shelter.

Commensalism, which is when one species benefits from their relationship while the other is unaffected, can be found in the relationship between a pearl fish and a sea cucumber. The pearl fish uses the sea cucumber's anus as a hiding spot from predators; the sea cucumber is oddly unaffected by this action.

Lastly, parasitism is when one species uses another as shelter or for a food source and is harmed in the process, such as when a trematode hosts on a snail and uses it for reproduction. So, instead of the snail producing more snails, it produces more trematodes. This means that the snail’s reproduction is harmed for life.

The Food Web: Predators and Their Prey

The food web of a coral reef goes as follows: primary producers, such as phytoplankton and algae, are consumed by primary consumers such as small fish or shrimp. Then, those small fish are eaten by larger fish. Those larger fish are then eaten by the top predators (sharks!). Refer to the diagram below for a closer look.

One specific predator/prey relationship not found on this chart is that of a barracuda to a mullet, pictured below:

Biodiversity

The biodiversity of a coral reef is pretty straightforward: It is extremely high. In fact, many scientists believe that coral reefs are the highest center for biodiversity on the planet, passing tropical rainforests! Although reefs cover less than one percent of the ocean, they are responsible for around 25 percent of all marine life known on earth. For example, coral reefs make the home for 4,000 species of fish alone. In total, millions of species call the coral reef their home.

The Carbon Cycle (Reef Style)

The carbon cycle in a coral reef is an extremely large part of the ecosystem. Essentially, carbon dioxide (g) that is formed by combustion of fossil fuels dissolves into the ocean water. Then, the phytoplankton, seagrasses, and algae take in the carbon dioxide as a part of photosynthesis to produce oxygen, and in turn the oxygen is used by consumers to breathe. The carbon dioxide they breathe out can either transform back to air or stay dissolved for the use of producers. When the animal dies, they sink to the bottom and are recycled by decomposers. Eventually, they can become part of the carbon fossil which is then brought up for anthropogenic use. This is the organic part of the carbon cycle. The inorganic part in coral reefs includes calcification, or the building of shells. Calcium ions and carbonate combine to form calcium carbonate, the building block of shells for organisms like clams and mussels.

The Limiting Factors

Now, to get an idea of the living conditions of a coral reef, we are going to go through the abiotic and biotic factors of this ecosystem. Abiotic limiting factors include salinity of the water, temperature, depth, waves, and translucency. In coral reefs, salinity levels range from 34 to 37 parts per thousand. Temperature usually never gets below 20℃ or above 28℃, which means that almost all reefs are located in between 30°N and 30°S. Coral reefs also form where there are waves crashing because waves bring in nutrients and plankton that are vital for a reef to thrive, and these areas are usually no deeper than 45 meters. Lastly, the water must be clear enough for light to get through to wherever the reef is because it relies on phytoplankton's and algae's photosynthesis as its main source of energy. PH (around 8.4) is another factor, any changes in pH can drastically change/harm the reef environment.

Next, the biotic limiting factors of the coral reef. Biotic factors have to do with living things; for example how many sharks there are to control the populations of fish, or how much phytoplankton there is to produce enough energy for the rest of the food chain. In addition, biotic factors of a reef can be the amount of coral (coral is living), since coral forms a home for a large majority of the animals. If there is only so many coral structures, only so many fish can make a home there. Biotic limiting factors are largely predator/prey related. Either the amount of predators can control a prey population, or the amount of prey available can also control the predator population.

Thursday, August 13, 2015

The Different Types of Reefs

To start off our exploration of the coral reef, let us first identify the three different types of reefs. First, perhaps the most well-known around the world is the barrier reef (Great Barrier Reef, AUS!) that is separated from the shore by a channel or lagoon.

Next, there are fringing reefs, such as those in the Bahamas. The particular fringing reef pictured below is off of the coast of Israel. Fringing reefs have very little space between them in the shoreline or practically sprout up off the shoreline.

Lastly, atoll reefs completely surround a lagoon. They are often formed over old volcano tips and are found mostly in the Pacific Ocean. Well, there ya have it! Next, we will go into the abiotic and biotic factors of these incredibly diverse reefs. Check back soon!