How is primary productivity affected by water depth in coral reef ecosystems in the Redang Island?

Transcription

1 How is primary productivity affected by water depth in coral reef ecosystems in the Redang Island? Word count: 3903 Subject: Biology Candidate number:

2 Abstract This experiment is about primary productivity and which organisms in the water play a role in showing the productivity of the water. Productivity in my case is the amount of dissolved oxygen in the water, by seeing precisely at what depth the primary productivity was greatest at, I used a method called the dark and light bottle method, this was done by collecting samples at depths: 0 meters and 9 meters, given that at 9 meters there was a reef. After collecting the samples I placed the two containers containing the same water from the same depth, one in a black back pack (dark environment) and one under the sun by the beach, after 3 hours, I checked the amount of dissolved oxygen with a probe and collected the data on a graph to see whether or not there was an increase in the productivity of the water over the 3 hours or if there was no difference at all. I found that the water at the surface had no change or may have had a little decrease in the productivity and as for the productivity of the water at 9 meters; there was a slight increase in productivity. What I found was not the only part that was important, what else was important was to investigate hypothetically what factors would affect the productivity in the water in my scenario. 2

3 Table of Contents Page number Subtitle 4 - Introduction: Over view of coral reef, Symbiotic relationships, types of fish, 5 - Introduction: Productivity of water, organisms in water, processes organisms undergo 6 - Introduction: What primary productivity is, how it can be calculated - Research question 7 - Variables - Controlled Variables 8 - Controlled Variables 9 - Materials 10 - Data collection: Dissolved oxygen at surface, light and dark 3 hours 11 - Data collection: Dissolved oxygen at 9 meters, light and dark 3 hours 12 - Data collection: ph 13 - Discussion 14 - Discussion 15 - Discussion and factors that affect primary productivity: Refraction of light 16 - Discussion and factors that affect primary productivity: Refraction of light and ph 17 - Discussion and factors that affect primary productivity: ph 18 - Discussion and factors that affect primary productivity: ph and Upwelling 19 - Discussion and factors that affect primary productivity: Upwelling 20 - Reflection 21 - Reflection 22 - Citations 3

4 Thomas Schipper Supervisor: Mr.Ogle Introduction Coral reefs are a complex, interconnected, City as some may say, providing shelter and a home to about 25 percent of the total marine life. Coral reefs also contain many vital relationships due to the high productivity created by a type of algae called Zooxanthellae which is located inside the coral polyp sacs (Which are part of the corals). One of the sources researched gave a great overview of the relationship between zooxanthellae (photosynthetic organisms in the water, type of algae) that work with polyps. It states that zooxanthellae fix large amounts of carbon, part of which they pass on to their host polyp. This carbon is largely in the form of glycerol but also includes glucose and alanine. These chemical products are used by the polyp for its metabolic functions or as building blocks in the manufacture of proteins, fats and carbohydrates. The symbiotic algae also enhance the coral s ability to synthesize calcium carbonate (Lalli,C.M pp ). Not only that, but fish depend heavily on the coral reefs, not only because it s their home and it provides good shelter and protection, but it also is a great source of food for them. There are three categories of fish, each indicating what they eat, firstly we have: polyp- feeders. Polyp- feeders use their forceps- like mouths to remove individual coral polyps, but do so without damaging the underlying coral skeleton, mucous- feeders fish that eat mucous let off by the coral. And skeletal- feeders corallivores scrape the coral surface and in doing so damage the underlying skeleton. It has been seen that the repair of the coral reef when 4

5 damaged has been extended due to the skeletal feeders that destroy the coral skeleton along with the surface tissue, the dependency of these types of fish on the coral illustrate a non symbiotic relationship where the fish benefit from the host in this case the coral and the coral doesn t benefit from the fish. The symbiotic relationship between the Algae and the coral itself is important given that, without algae (zooxanthellae), corals turn white because zooxanthellae give corals their color. White, unhealthy corals are called bleached. Bleached corals are weak and less able to combat disease (West, J.M), so it is clear that their relationship is very important and dependent. But, what I will be focusing on in this experiment will not be the productivity of the coral, but of the water itself. The most important photosynthetic eukaryotes are the diatoms, which is a type of phytoplankton, in which undergo photosynthesis in which they contain green pigments called chlorophyll. This is where the sunlight is absorbed and lets out oxygen and food, which is usually nitrogen, phosphorus, potassium, iron, these are very limited, but these are vital for consumers. Overall, diatoms contribute about 40% of the primary production, and thus produce almost ¼ of the oxygen we breathe. Although in some areas they produce only a small part of the photosynthetic biomass, in some regions of the ocean, they can fix the same amount of carbon per day as a forest of terrestrial plants. There are hundreds of thousands species of diatoms, which makes them the most abundant photosynthetic group after angiosperms (Phaeodactylum Tricornutum). Importance of diatoms: Carbon fixation and acquisition of nutrients and their assimilation. But, how do we know where the phytoplankton will be? Given that coral reefs live off light and light is the reason productivity is possible, phytoplankton will be all around the reef or closer to the surface, due to the fact it can absorb more light. As a result, overall, it can be more productive in 5

6 giving other organisms what they need to survive. An important point to remember is that light plays a vital role in photosynthesis and since these organisms depend on light: This plays a role with the depth of the coral as well, given that the deeper you go in the water, the less light there will be, so identifying zones of productivity and correlating it with light and depth will be two important variables to examine in my experiment. Primary productivity of an ecosystem is defined as the rate at which organic materials (carbon- containing compounds) are stored. Only those organisms possessing photosynthetic pigments can utilize sunlight to create new organic compounds from simple inorganic substances. Green plants obtain carbon for carbohydrate synthesis from the carbon dioxide in the water or in the air according to the basic equation for photosynthesis: (Primary productivity) 6CO2 + 6H2O > C6H12O6 + 6O2 Research question How is primary productivity affected by water depth in coral reef ecosystems in the Redang Island? Variables Independent Variable Dependent variable Water depth (m) Ph, conductivity, Dissolved oxygen 6

7 Controlled variables Reason for controlling Method Collecting the water When collecting water I ensured that people collected the water at 3 depths: Surface (0m), 9m. When observing the other divers and how they collected the water particularly at 9m they To resolve this issue, my proposed method was to collect the water when the bottle is level with the diving watch, this will reduce most uncertainties but there are still some errors here. But overall, this method is more effective because you will be off by inches rather than one fourth of a meter. weren t collecting the water at exactly those specific depths but rather, would collect at 9.6m rather than 9m. This can effect my results in the way that the light intensity may be weaker if its.6 m deeper, and then when I measure the productivity of this sample, it will seem to be more or less productive. Weather This can be a problem given that my experiment is very dependent among light intensity, because it was cloudy at the time of the dive, less light is exposed to the water, To ensure that the weather is not cloudy, even though we cannot precisely predict the weather, it is important on the day of the dive, to check what the weather forecast is expected to be, and to see if the experiment should be run on that dive or if not, run it maybe the 7

8 Dark and light method: The bag was not dark enough containing the bottle therefore the productivity is lessoned and my aim was to measure almost optimal productivity of the water. It is important to control this given that the bottles in the dark are like a benchmark when comparing it to the productivity of the light bottles, so with that said, I saw the my bag was not dark enough when closed which means that light managed to enter the bag, which means that the water would still be productive rather than neutral which is a problem because I needed the dark bottle to be neutral so I could compare it to water that is productive (in the light) next day or another dive later that day. To avoid this mistake, I should ve gotten used the same bag but maybe gotten also a thick blanket and wrapped it around the bag and then placed the bag in a dark area, such as a cabinet, this would eliminate the chance of light managing to enter the bag through the cracks. 8

9 Materials (For light and dark method): 1x ph probe 1x Dissolved oxygen probe 1x Conductivity probe 6 clear bottles per group of 3(Collecting samples at surface and at 9 meters) Computer with program to collect data Back pack (Dark environment) Exposed area to lots of light (Light environment) Timer 9

10 Data collection: Surface (0m) Dissolved Oxygen: 5.4 mg/l (Min) 5.6 mg/l (Max) Table 1: Dark 3 hours 5.5 mg/l (Max) 5.3 mg/l (Min) Table 2: Light 3 hours 10

11 (9m) Dissolved Oxygen 4.9 mg/l (Min) 5.2 mg/l (Max) Table 3: Dark 3 hours 5.3 mg/l (Min) 5.5 mg/l (Max) Table 4: Light 3 hours 11

12 ph Values between 7 and 8 Table 5: ph 12

13 Discussion: Looking at table 1 and 2 we could see that there was actually a decrease in productivity in the water itself, this could lead to the question, does this mean that there is no productivity in the water at the surface? After some research I found that (Figure 1), due to the impoverishment of low latitude surface waters in N and P, the productivity of the low latitude ocean is typically described as Figure 1 nutrient limited. However, limitation by light is also at work (Figure 2). As one descends from sunlit but nutrient- deplete surface waters, the nutrient concentrations of the water rise, but light drops off.(vinogradov, M. E) To summarize, the water in which I collected my data in, was nutrient limited, therefore less oxygen was produced which was expected, given that, if we look at the two graphs (Table 1 and Table 2) above that were collected at the surface and were kept in the dark and light for 3 hours. There was a decrease or no productivity in the water, this was because the water is exposed to too much sunlight. Does this hint that maybe too much 13

14 light intensity denatures the photosynthetic organisms? This turned out to be a false statement because if there is a low light intensity for example, a higher temperature will compensate for that and the formation of oxygen in these organisms will still occur. On the other hand, as we look at the other two graphs, taking samples at 9m (Table 3 and Table 4), given that it was next to a coral reef, that may have had an impact on the amount of oxygen in the water, the depth in which the samples were taken was very good in the sense that there was a balance with the sufficient enough light and a sufficient amount of nutrients. When you take a look at both data pairs you can see that the data collected at the surface actually had more mg/l of dissolved oxygen than the 9 meter data set, this refutes what is supposed to happen because after researching I found that (Looking at figure 2), the concentration of dissolved oxygen in Figure 2 surface water is controlled by temperature and has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved oxygen concentration is high. In summer and fall, when the water temperature is high, the dissolved- oxygen concentration is low. Dissolved- oxygen concentrations fluctuate with water temperature seasonally as well as diurnally. (Swanson, H.A.) What is clear to that statement is that because I collected the samples 14

15 around autumn time, the dissolved oxygen amount should be higher, which is what my data shows. Although this refutes my thought about having more oxygen in the surface of the water, it was worth researching what I have found because I learnt that seasons have an impact on the amount of oxygen in the surface of the water. Although this makes sense, what I want to find out is why there is not much dissolved oxygen around 9 meters, which brings me to investigate the following factors: Refraction of light Looking at (Tables: 1 and 2) it is clear that there was more photosynthetic organisms at the surface than there was at 9 meters. But why is this? Looking more closely I not only realized that I was not close enough to the coral reef itself to capture a sample; but also the time of day had a great impact on the concentration of dinoflagellates in my samples; given that using the concentration of these organisms alter drastically throughout the day because they are exposed to more light. There are also many surface effects when light passes through. As the light comes from a less dense medium for example the air and enters a more dense medium (In this case water), the light emitted is partly reflected back towards space, and also enters the water. But this all depends on the shape of the water. The amount of light that is reflected upwards depends on the season (position of the sun on the earth) and also the shape of the sea itself, if it s smooth or very rough. For example, typically a rough sea will absorb more light whereas a mirror like sea reflects more. (Floor Anthoni, J) 15

16 In my case, looking at figure 3 this indicates the theoretical loss due to reflection. The left side of the figure indicates the suns position and on the right side of the figure it shows how much light is expected to be reflected. In my case the water was mirror like, so already there is less light traveling to 9 meters where I collected my samples. Also, the samples were collected around 4 pm which means that the light reflectance is quite significant and at 9 meters it is noticeable that there is not much light being absorbed or reaching to that depth. Looking at the figure, at 30 o, the Figure 3 reflection and the transmitted light is quite small which can explain why there were more photosynthetic organisms at the surface than there was at 9 meters. ph The ph scale ranges from 0-14, 14 being most basic and 0 being most acidic. Each whole ph value above 7 is ten times more basic, for example a ph value of 8 is ten times more basic than a ph value of 7. Looking at table 5 it is clear that the water is alkaline reaching PH values between 7 and 8. How does this contribute towards primary productivity? Ocean acidification may also 16

17 impact primary production if ocean ph falls below the point where carbonate dissolution occurs. Carbonate dissolution is stating that as higher levels of CO2 are absorbed into the oceans, fewer carbonate ions (CO3 2- ) are available for organisms such as corals, clams, sea urchins and plankton to produce their calcium carbonate shells and skeletons. (Hoegh- Guldberg, O) When the ocean acidity increases, it has been seen that the time at which reef- building corals produce their personal skeletons decreases, and sometimes their shells start to dissolve when carbonate concentration falls too low. It has been said that by the middle of this century, coral reefs may erode faster than they can be built as a result of ocean acidification. This is because with a lower ph it will mean that it is harder for phytoplankton to maintain their protective shells, and with that being said they will die off and less oxygen will be available in the underwater ecosystem, which kills other organisms, and overtime this will cause a very drastic change to the food chain. The problem comes into place when primary producers have a calcified shell, including diatoms, which play a major role in coastal food webs, will be removed from the pool of producers ( Hoegh- Guldberg, O). This will have a great impact on primary consumers and eventually other species of fish will die from this because they rely on these organisms for food. Phytoplankton removes large amounts of Co2 from the earth s atmosphere when they photosynthesize- turning sunlight into organic matter. This process results in C02 being 17

18 taken out of the atmosphere. Decreases in primary productivity are likely to further increase Co2 levels, which ultimately enhance ocean warming and acidification. In my case, the water I collected data from was alkaline so as for this I did not suffer from this problem, however, if I did collect samples in an ocean environment where acidification is very prominent, then my results would be drastically different from what I have. I chose to include this factor because as stated before, we are destroying our environment and the coral reefs are already seen to be suffering from human impact. Upwelling Another important factor that may have affected my results is upwelling; upwelling is the process in which nutrient rich subsurface deep water ascends to the surface of the ocean. Upwelling is caused by favorable persistent ocean surface winds (Kempler, Steven) After researching, I learnt that upwelling is a factor of growth for photosynthetic organisms that consume mostly nitrate and phosphate. It also uses dissolved Co2 and light energy from the sun to produce organic compounds. Regions where upwelling is common, the primary production is high. 18

19 Ekman transport: This is more of a complex factor, however, it helps me conclude why more nutrients (dissolved oxygen) was present on the surface. The Ekman spiral (Figure 4) indicates that each layer moving is deflected to the right of the overlying layers movement; hence, the direction of water movement changes with Figure 4 increasing depth. In an ideal case, a steady wind blowing across an ocean of unlimited depth and extent causes surface waters to move at an angle of 45 degrees to the right of the wind in the Northern hemisphere. (Ocean in Motion: Ekman Transport Background) Each successive layer moves more toward the right and at a slower speed. In my case, this is not a problem given that I collected my samples in a tropical nutrient limited environment. On the other hand if I were to, hypothetically, collect samples in Alaska, a cold environment, there would be more phytoplankton in the water. As the water is nutrient rich this also explains the reason why the water is cold and how the upwelling that happens makes the water cold. The water at the surface is nutrient rich because all the cold water from the sea bottom and rich nutrients move up to the surface. A nutrient rich surface means high levels of productivity and is a great fishing ground. However, it is still possible that the nutrients may have moved up because of the Ekman transport theory and could explain the nutrient rich surface present in my case. 19

20 Conclusion: This experiment was very hard to do given that, with limited knowledge I suffered through many uncertainties and it overall affected my data. This experiment is not only hard for me but for scientists as well in the way that, you have to be very precise. Also, to see good demonstrations of primary productivity will be very hard because when you do this experiment it relies on so many factors, time of day, time of year, water temperature and many other factors that will, and have, manipulated my data. It takes much more advanced equipment to actually get a substantial reading and draw a valid conclusion. What was also very difficult was the fact that the probes were very hard to calibrate and most likely gave inaccurate readings, which therefore changed my graph. This also taught me the importance of minimizing uncertainties for example, making sure that I took a correct reading of the water collected, right after I got the sample out of the water, things like that effected my overall result, but to be fair, I am quite happy with what I got because this experiment like I have mentioned multiple times, is very difficult and hard to do. Not only that, but the knowledge I gained researching about this experiment was very complex and looking at so many factors that can alter the productivity in the water was very interesting. Also, seeing how the ocean is a complex city like place, it is really fascinating getting the chance to learn about new organisms and how they work in their ecosystem, something I have never seen or heard about before. Furthermore, managing to understand complex factors like I have mentioned that alter the productivity of the water was exceptional, for example, the Ekman transport was a great concept that took some time to understand but was very useful in discussing my results. As for doing the experiment myself, I was not aware of any of these factors and now that I have researched more about this topic it is 20

21 very fascinating to learn things that you may have never thought of before. Looking deeper into the topic and observing how scientists underwent their tests to look at primary productivity in water was clear to be very complex and required strong background information and very advanced equipment to collect the data. What I found very interesting was upwelling, if I were ever to do another experiment on primary productivity, I would really be fascinated in going to Alaska so that I could test how the nutrients move upwards. However, learning about the theory is very interesting because like I have mentioned, before starting this experiment I had very limited knowledge on the topic itself and now my view of the ocean has become more open. As a high school student, this experiment did teach me a lot about the marine life and how it works, in the way it s symbiotic and all organisms work together. However, what I did not mention was what we as humans are doing to destroy all these corals, we depend upon the sea in many factors and the thoughts of loosing the underwater beauty and loosing all these creatures will be devastating to many people across the world especially the ones who appreciate and enjoy diving like myself. 21

22 Citations: 1. Floor Anthoni, J. "Water and Light." N.p., n.d. Web. 20 Aug Hoegh- Guldberg, O. "Decalcification." Climate Change. N.p., n.d. Web. 05 Oct Kempler, Steven. "Upwelling and Phytoplankton Productivity." GES DISC. NASA, 8 May Web. 16 Nov Lalli, C.M., and T. Parsons Biological Oceanography: An Introduction. Oxford: Butterworth- Heinemann Ltd. pp "Phaeodactylum Tricornutum." tricornutum,463.html. Centre Centre National De Séquençage De Séquençage, n.d. Web. 15 July "Primary Productivity." Primary Productivity. N.p., 26 Sept Web. 15 Nov Swanson, H.A. "Water Properties: Dissolved Oxygen." USGS. N.p., n.d. Web. 10 July Vinogradov, M. E. Oceanology: Biological Productivity of the Ocean. 6th ed. Vol. 3. Woods Hole, MA: U.S. Dep. of Commerce, Southampton. Web. 10 Jan West, J.M. "Coral Reefs and Climate Change - How Does Climate Change Affect Coral Reefs - Teach Ocean Science." Coral Reefs and Climate Change - How Does Climate Change Affect Coral Reefs - Teach Ocean Science. N.p., 203. Web. 04 Oct