In a recent Marine Ecology class, students were asked to stay still, underwater, on SCUBA, for half an hour, focusing their observations on one specific area of reef. They then wrote underwater essays on their dive slates, addressing the prompt: Why (or why not) is there so much life on this area of reef. Enjoy these examples: deeply thoughtful analyses written deep under water…
by Chapin Atwood:

I arrived at my patch of coral reef and sank to my knees as I began to watch all the components of this ecosystem react. Watching the fish, busily flipping their tales around pieces of coral reef and sponges, I was amazed at the beauty of this small piece of reef. This reef looked very healthy with life bursting out of it.

After a few moments of enjoying its beauty, I began to study the components of the coral reef in depth. I began by looking at the biotic factors of the reef, such as the different types of sponges and algae and fish species. I noticed large patches of Encrusting sponges as well as the Rope sponges and Tube sponges. All of these species of sponges have a similar niche in the ecosystem, to filter the water and take out nutrients and oxygen from the water. They get their food by filtering the water, which means that they are heterotrophs because they amass organic matter from other sources. I noticed the small holes on each of these sponges, placed in different places for the different species. These holes were the oscula, in which the filtered water came out of. When looking closely at some of the Encrusting sponges, I noticed this layer of green algae that covered the sponge. I wondered what its name was? I also wondered if it has a severe effect on the health of the coral reef? I looked closely at a Flamingo Tongue that was attached to a Sea Fan coral, and Peter pointed out to me how the Flamingo Tongue was eating part of this soft coral, causing parts of it around it to begin to deteriorate. I thought that was really interesting, to see the physical effect that the Flamingo Tongue had on this species of soft coral.

I then began to notice the species of fish; the majority of them were swarming the top of the coral reef. Some of the species that I recognized right away were the Blue Chromis, the Bicolor Damselfish, and the Fairy Basslet. The Blue Chromis and the Bicolor Damselfish were hovering at the top of the reef, but it wasn’t until I looked under the overhang of the reef that I noticed the Fairy Basslet swimming at the bottom of the reef. Is there a specific reason that only the Fairy Basslet were swimming at the bottom, under the overhang of the reef? I also noticed many Yellowtail Snappers that were swimming by the coral reef. Is there a reason that these Yellowtail Snapper don’t stick to one specific patch of coral, while the other fish do? This was a question that I had as I watched all of these species of fish interact with their ecosystem. There was one species of fish, with a yellow black and white stripe on it, that I would like to know the name of because I saw many of them swimming around my patch of coral.

After studying many of the biotic species on my patch of reef, I began to notice the abiotic factors that contribute greatly to the health of this marine ecosystem. Some of these factors were sunlight, water temperature, depth, and terrain conditions. The marine community was heavily lit with sunlight, as it was only between 35-38 feet underwater and the water was very clear. The sunlight shined directly down onto the reef, illuminating many of the beautiful colors. The water temperature is something that I think could affect a marine ecosystem because it could correlate to the species of fish that are present on the reef. Depth could also contribute to the different species on or at a reef. The terrain of the ocean ground is a large abiotic factor of coral reef. Surrounding the patch of coral reef I examined was all sand, creating the nutrient poor conditions – oligotrophic – in which corals thrive in.

Through spending time studying the different parts of this marine ecosystem, I realized that I knew much more then I thought I had known. This gave me excitement to continue to learn about these coral reefs, and all the different components of them that make them such sustainable marine ecosystems. My area of reef was so full of life because of all the different components I explained. In combining all of these aspects of an ecosystem, they come together to create a healthy and vibrant patch of coral reef.

By Pheobe Shaw:

Biodiversity in an area is determined by many abiotic and biotic factors. The relationships between organisms, both autotrophic and heterotrophic, are essential components that contribute to the overall success of an ecosystem. Each individual organism has a niche, or role, in the ecosystem, which must be performed for the community to be successful. We were given the opportunity in marine ecology class to further explore up close the importance of these aspects of an ecosystem and experience how they interact and relate to each other.

As we dove down towards the sand and swan closer and closer to the scattered, more specifically patch, reefs, the abundance of life was magnified right before our eyes. The reefs were scattered with hundreds of plants, corals, and algae and surrounded by countless different species of fish. Our specific area of the reef was just at the edge of a very large, tall patch reef. The arch of the structure created a formation similar to a shelf, under which fish and coral dwelled. The most discernable abiotic factor of the reef that allowed for such large amounts and such a vast variety of life to live there was the plentiful supply of sunlight. Being only roughly thirty-five feet below the surface, large amounts of sunlight were able to reach almost all areas of the patch reefs. The large amounts of sunlight allowed for great amounts of primary producers, or autotrophs, which can photosynthesize and supply food and oxygen for other species to thrive on. As a result of the successful environment for autotrophic organisms, greater biodiversity exists in the area because there is so much energy and food supply being generated by primary producers. Some of the many autotrophic organisms we noticed were Mermaid’s Shaving Brush and Oatmeal Algae, as well as many other plant and coral species that we were unable to identify.

The coral species were very diverse and abundant in the area. In my understanding, this is largely do the shallow depth and resulting amounts of sunlight. Given that corals are composite organisms, meaning they are both part animal and part plant, they rely partly on the algae living in the coral polyps to provide nutrients. The large amounts of sunlight allow the algae to perform photosynthesis efficiently and fulfill their part of their symbiotic relationship with the coral successfully. This makes this particular reef a near ideal habitat for coral. I noticed many large plate corals growing on the edge of the shelf. They appeared to be overlapping each other, which led me to conclude that there is a great deal of interspecific and intraspecific competition between organisms for sunlight considering there are so many autotrophic organisms living in the same area. The large amounts of sunlight and overall ideal habitat for coral was reflected through the fact that I noticed no coral bleaching in my area, implying that the zooxanthellae algae are receiving sufficient sunlight. There were also a large variety of sponges, such as ball sponge, rope sponge, and even encrusting sponge. These organisms, along with Christmas Tree Worms, which were also plentiful in the area, filter the water, keeping the reef a healthy and balanced ecosystem.

The large amounts of these many diverse autotrophic species serve as the base of the food chain and allow for the existence of many heterotrophic species. Among the ones identified at this patch reef were Bicolor Damselfish, Blue Chromis, Queen Angelfish, Grey Angelfish, Blue Tang, Stoplight Parrotfish, Sergeant Major, and many other very small species of fish. Both the Parrotfish and Angelfish were notably feeding on algae around the reef, implying that their niche is regulating the algae population and keeping it from overgrowing and overtaking the reef. Another heterotrophic organism that was noticeable was a very large grouper that remained in the darker, shaded waters under the reef’s ledge. I was not able to determine why he was behaving in such a way or whether it held any significance. Another behavior that led to curiosity on my part was the large amounts of tiny, silver fish that hovered over the reef and rarely moved. I was not able to determine what the purpose of this behavior was or even if their was any importance to it. One of the evident biotic factors in the area was the presence of a lingering lionfish. Given that this species is invasive and very destructive to reef’s fish population, it can be concluded that its existence in this ecosystem is a significant limiting factor to the life in the area.

Overall, the area of the reef we observed contained a large variety and abundance of life forms. The biotic and abiotic factors of the area made it a successful area for growth and life, but also provided limitations that keep populations and conditions in balance. Some of these factors were even harmful, and could potentially deplete populations and the amount of life in the area. However, overall the biodiversity in the reef was clearly evident and included a wide variety of life forms and species.

by Spencer Goodwin:

The part of the reef I chose is teeming with life. From where I kneel I can see at least 5 different species of sea fans, uncountable corals, stoplight parrotfish, a sharpnose puffer, some yellowtail snapper, a queen parrotfish, a couple of sergeant majors, schoolmaster snappers, and a ton of tiny unidentifiable fish.

The sea fans reside in the brightest part of the reef, on the tops and walls of the coral heads where they can receive the most light. On the one nearest to me I can see two flamingo tongues grazing. They are leaving a trail behind them that makes the sea fan look a little paler than the area in front of them. I am next to an overhang, and under it, in the shade I can see many different species of fish, algae, and corals. The coral underneath the overhang seems as if it is being cleaned or fed on by some sort of mid-sized fish. The fish is a shade of orange, has huge eyes, very distinct dorsal spines, and an exceptionally long forked tail. There is no light under here, so I wonder how the coral can survive without any sunlight to feed the algae on the polyps. Perhaps it has something to do with the fish around it? Are they somehow giving the coral the energy it needs to survive in this dark place? Also under the overhang is an interesting type of plant that highly resembles a fern. It grows from the top and hangs down like vines. It is a bright green color, has circular leaves, and I can see that some of the leaves are starting to encrust. Again, how can this plant survive under here? Another flamingo tongue is on the floor on a patch of dead coral. Unlike the other two, its mantle is not showing its spots. I turn it over to see the bottom of it, and I can see inside. The flamingo tongue inside of its mantle almost seems to have a zebra print on it.

A lionfish just passed in front of my face, less than a foot away. He has all of his spines completely spread out making for a truly impressive sight. As he glides under the overhang it’s fascinating to watch how all of the random fish down there give him such a wide berth. As he swims through schools of tiny fish, they part and make it appear as if the lionfish has a bubble of fish surrounding him. I think this part of the reef is so alive because all of the food chain resides here. From the corals and the algae on the corals to the fish that eat the algae and the fish that eat the fish, they are all present. There are plenty of spots for smaller fish to find shelter from predators, and there are also plenty of spots for predators to wait until their next meal swims by. As I take a quick last glance at my surroundings, I see a queen angelfish pecking at the reef, presumably eating the algae, and I see some blue chromises grabbing floating particles. I think the reason this part of the reef is so alive is that this is fish Eden. What more could a fish ask for?