Chapter 1: The Rocky Intertidal: Disturbance and Diversity Pirates of the Intertidal: On stranger Tides. By: Connor Rooks and Austin Grace.

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1 Chapter 1: The Rocky Intertidal: Disturbance and Diversity Pirates of the Intertidal: On stranger Tides By: Connor Rooks and Austin Grace Introduction Abstract In our study, we investigated the intermediate disturbance hypothesis and its effects within the rocky intertidal zone. The intermediate disturbance hypothesis states that areas that experience an intermediate amount of ecological disturbance will be more diverse than those that receive a lot or little to none. We applied this concept to the rocky intertidal and studied a cove and its wave action. We placed our quadrats throughout the cove and then divided them up by their distance from the shore. We also took the wave heights by row of quadrats and used that to measure the disturbance. While our data suggested that the zones of intermediate disturbance had the highest levels of diversity, the results were not statistically significant. For our study on Hurricane Island, we continued research on the intermediate disturbance hypothesis that was explored by two students in this class last year. This hypothesis states that local species diversity will be highest in areas where there is ecological disturbance that is neither too rare nor too frequent. The intermediate disturbance hypothesis predicts that too little disturbance will increase competitive exclusion and limit some species and too much disturbance eliminates species incapable of rapid re colonization (1). Figure 1 shows what the species diversity should be as disturbance increases according to the intermediate disturbance hypothesis. There are a number of ways to measure disturbance, but for the intertidal area that we studied, we measured ecological disturbance through wave height in order to simplify the measures of disturbance; however, we acknowledge that there are other factors that contribute to an area s level of disturbance. When Malik Kuziwa 17 and Noah Wass 16 studied the IDH last year, they measured disturbance as rock size over wave height. Their study also differed from ours because they looked at a few sites in the intertidal area around Hurricane Island and Two Bush Island whereas we just looked at one location. Statistical analysis of their results revealed that their results were significant; however, they did not have enough data to conclusively say the rocky intertidal followed the IDH (5). We hope to establish a measure of disturbance, so students in future years students can have a consistent way of measuring disturbance consistent with our study. We think this is important because diversity can help measure the health of the island. In 1979, Wayne P. Sousa looked into wave disturbance on intertidal boulder fields on the coast of Southern California. This study looked more into the different sizes of boulders in the intertidal zone and the diversity on them. They hypothesised that the intermediate sized boulders would have the highest levels of diversity because during the winter storms of the area, the small boulders would receive too much disturbance and the larger boulders wouldn t receive enough disturbance to foster a rich ecosystem. This study found that of their three classification sizes of boulders, the intermediate sized boulders had the highest levels of 1

2 diversity. This was because the smaller boulders were tossed around too much by the storms of winter which destroyed the life that was on them. And on the opposite end of the spectrum, the largest rocks didn t get moved around and therefore didn t receive the same level of turnover which exposes them to more nutrients and clears off some of the more dominant species, which further promotes diversity. The rocks in the middle, the intermediate sized boulders of intermediate disturbance had the highest levels of diversity (3). These boulders were moved around less than the small boulders but enough to maintain higher levels of diversity than the large boulders. This study supports our hypothesis because they looked at areas of low intermediate and high disturbance and found that the area of intermediate disturbance had the highest level of diversity. Materials List Figure 1: What the Intermediate disturbance hypothesis PVC Quadrat.25m Wind gauge Compass A Field Guide to the Atlantic Seashore: From the Bay of Fundy to Cape Hatteras (3) meter measuring tape Calculator 2 1 meter measuring sticks A bucket for holding materials when we leave for the field Thermometer Masking tape Waterproof pen or pencil Waterproof paper 2

3 Laptop equipped with Excel Procedure 1. Determine the locations of the transects, noting the disturbance for each. Inlet GPS Location: 19T , Two Bush Island Transect Location: 12m total transect running along the edge of the inlet, with transects branching out horizontally every two meters, measuring another transect and recording a quadrat every 0.5 meters. Figure 2: A bird s eye view of our inlet, with Vinalhaven in the background. Notice how our transects get progressively farther out into the ocean, so that the rocks dissipate the waves, creating multiple sections with different disturbance, in terms of wave height. 2. Record the abiotic features of each transect. Take one wind reading for the whole area, and take the wave height for each transect. Also record any major landscape features. For instance, there was a large rock near transect two that blocked much of the wave action, so be sure to note accordingly. 3

4 3. Record the contents of each quadrat, pushing aside non holdfast seaweed, and differentiating between different species and animals. We saw three types of snails: dog whelks, periwinkles, and flat periwinkles, but we classified them as Littorina.sp. and Nucella lapillus. The most prevalent organisms we encountered were: Figures 3A: Littorina littorea, one of the most common species we found. Figure 3B: Nucella lapillus, another common species in the rocky intertidal at Two Bush Island. Figure 3C: Littorina Obtusata, a somewhat common organism we found. 4. Consolidate different quadrat data into average values, and compare the different transect values and their respective shannon index values. Transect # Wave Height

5 Avg. Shannon Disturbance Level* LOW LOW MEDIUM MEDIUM HIGH HIGH Figure 4: Although we were not able to distinguish a clear disturbance with wave height, we took qualitative observations about each location during the data collection phase, so we are using the qualitative observations to differentiate disturbance. Figure 5: Location of research. Note the location of our inlet is in the rocky intertidal, requiring that we conduct our research during the hours of low tide. 5

6 Figures 6A and 6B: Shells of Littorina littorea and Littorina obtusata, respectively. We often found upwards of 80 shells which made it hard to differentiate between Littorina obtusata, so we consolidated them into Littorina.Sp. Figure 7: Transects with Intermediate disturbance tend to have higher Shannon Index Values than transects with low or high disturbance. When we averaged the different disturbances, our T test returned a p value greater than

7 Figure 8: Medium Disturbance transects have higher Shannon Index Values than low and high disturbance transects. There was no significant difference between low and medium disturbance, and high and medium disturbance. Discussion While there were some sources of error in our data collection, we feel like the data showed a suggestive connection between intermediate disturbance and higher Shannon Index diversity values. Figure 6 showed that the average Shannon Index value for the medium disturbance was higher than both the high and low disturbance diversity values. In Figure 7, although our classifications of disturbance were qualitative observations, the intermediate disturbance values are higher than the respective low and high disturbance values. Although we are unable to conclude that the intermediate hypothesis is consistent in the rocky intertidal of Hurricane Island, we believe the data suggests that it is true. We would like more data to be collected in order to confirm our hypothesis, but we believe this is a significant start. As we were looking for potential areas to study, we noticed a few things about the intertidal. One of the most notable, was the presence of Dogwhelk nests, where a group of dogwhelks would crowd around a nest of eggs, perhaps to protect the eggs from the waves of the intertidal or predators. We would often find these in crevices of two rocks, and they would have very high populations of dogwhelks relative to the observed density. Two of our classmates Sara Pratt (18) and Julianna Rick (17) studied these types of snails(6). Along with the location of the dogwhelk nests, we also noticed that the coralline algae was often only found in the subtidal zone, where the water was always present, thus the algae was always submerged in the water. These were just some of the informal observations we made at the intertidal, and we would be excited to study these trends more often. In fact, one important note that can be drawn from this study is the functionality of the inlet as an area for further study. With differing wave heights, multiple species, and different depths, the inlet could be studied as a microcosm of differing disturbances. To continue this study there are a few key changes that should be made. This was 7

8 originally a goal of our study, but it could be a study of its own; establishing a more exact way to measure wave height. This is complicated because our method was very crude and mostly left to our observations. The problem with measuring wave heights in such a short period of time is that one even slightly more wavy day could totally throw off the data, or even year over year, just one stormy year could throw off the data. One suggestion I d give is to have a collection of wind and wave height data from the same spot on the island every year independent of the projects, although could construct a wind rose, which would be helpful. This could be done for more than wind and wave height but if there was a general table of data that students could compare their data to and use to help prove their studies it s possible some of these projects may have had more statistically significant results. Another factor that could be helpful for studies of this nature, would be finding a wind rose for Hurricane Island. We looked for one but did not find one; there should be one for Vinalhaven, (the island across the bay) but we would need to do more research to conclude whether this would be useful information or not. This also leads to another topic that would be interesting to explore is the effect of wind. When we discussed wind with Marilyn she said we should just ignore it for now, but wind has a large effect on waves and potentially an effect on diversity. A wind rose could address this, especially if the data was available for numerous years; however, we were not able to get the relevant wind rose, but it is possible the Hurricane Island Foundation collects the data. CSW students could also explore the difference between the windward and leeward sides of the rocky intertidal, as a way to measure disturbance and diversity. For instance, in figure 5, there is a visible protected (right) and exposed (left) side of the intertidal; these two sites could be compared as they would inevitably have different levels of disturbance. 8

9 Bibliography: (1) Wilkinson, David M. The Disturbing History of Intermediate Disturbance. Oikos, vol. 84, no. 1, 1999, pp JSTOR, (2) Gosner, Kenneth L. A Field Guide to the Atlantic Seashore: From the Bay of Fundy to Cape Hatteras. Boston: Houghton Mifflin, Print. (3) Sousa, Wayne. "Ecology of Disturbance." Teaching Issues and Experiments In Ecology. Charlene D'Avanzo and the Ecological Society of America, 22 Feb Web. 6 June < >. (4) "Diversity II." Home. UC Boulder, n.d. Web. 06 June (5) Malik Kuziwa and Noah Wass, 2016 (6) Julianna Rick and Sara Pratt,