PATTERNS OF DISTRIBUTION OF ACTINIA EQUINA

BASED ON ABIOTIC AND BIOTIC FACTORS IN

STARESO HARBOR AND SURROUNDING COVES

M. J. DAVIS1, N. ALCARAZ1, J. COSSABOON1, H. KROM1, A. GOMEZ1

1 School of Biological Sciences, University of California, Santa Cruz 3

Abstract Factors that influence Actinia equina distribution along a stretch of coastline near Calvi, France were explored over the month of October in 2010. The distribution of the species with regards to depth and nearest neighbor was surveyed and other species within their community were identified and quantified. The correlation between A. equina allocation and light exposure was also recorded, as well as the relationship between algal line height and anemone depth. We observed these parameters using observational surveys, quadrats, plankton tows, and light meter readings. It was observed that they were aggregated in a clumped distribution. Community composition, notably percent coverage of encrusting coralline algae, erect coralline algae, and fucas, varied significantly between A. equina-specific and randomly selected quadrats. There was a higher density of planktonic organisms observed at night, and we found that light intensity did not have a correlation with their distribution. At locations where the upper limit of algal growth decreased in depth, the average depth of anemones also decreased.

INTRODUCTION

The distribution of a species within its environment is important in understanding the structure, function, and ecology of ecosystems. Knowing the distribution and role of a species is also helpful for conservation purposes and to prevent human encroachment on currently occupied habitats. Many biotic and abiotic factors influence dispersal of organisms, including predator-prey interactions, primary productivity, and climate. Species allocate themselves to an area that is most beneficial to their needs and survival by occupying their specified niche. It is a constant struggle for many organisms to adapt to a constantly changing environment. In rocky intertidal habitats, competition for space is thought to drive the distribution of many sessile species. Wave action, food availability, predation, and desiccation are other obstacles for species inhabiting intertidal zones. Actinia equina, a species of sea anemone, are commonly found in such habitats as those on the rocky coastline of Corsica, France in the Bay of Calvi. Actinia equina attach their pedal foot to hard substrates, expose their tentacles primarily at night, reproduce by both cloning and sexual reproduction involving a plaktonic larval stage, and mostly stationary with the exception of some slow lateral movement (Quicke and Brace,

1983). Their relative abundance and sedentary lifestyle made them an ideal candidate to study factors influencing distribution in the intertidal.

While snorkeling in the harbor and adjacent coves, we noticed that A. equina were commonly found in the intertidal zone, rarely had their tentacles exposed (were “open”) during the day, and were often distributed in a clumped order. We also noticed that there was a higher density of anemones present at the south coast of the STARESO compound compared to the north coast.

The goal of this project was to understand what factors influenced distribution of A. equina. To do so, we addressed the following hypotheses:

1. There is an observable pattern to the distribution of anemones, along with a negative correlation between pedal foot size and likelihood to aggregate. 2. The community structures are different at sites containing A. equina versus randomly chosen sites along the coast. Also, each cove will have a unique community structure due to varying factors within a cove. 3. There is a difference between the density of planktonic organisms at night and during the day, and there is a relationship between this possible food source's time dependent density and the temporal exposure of tentacles by the anemones. 4. There is a significant correlation between the depth of individual A. equina and the upper limit of algae growth. 5. Actinia equina density is related to light exposure intensity.

Our predicted results are: 1. The anemones were not randomly dispersed along the cove walls and smaller anemones would be settled closer to neighbors than larger anemones. 2. Areas where anemones were present would contain less algal cover and coexisting species. Wave action and geography also varied within each cove, resulting in contrasting variation and abundance of species. 3. The abundance of food present at night exceeded the amount available during the day. This is correlated with the period of tentacle exposure of A. equina. 4. If the upper algal growth limit is closer to the surface, the corresponding anemones are found closer to the surface as well. 5. A higher density of anemones is correlated to areas of lower light

intensity.

MATERIAL & METHODS Our study was conducted on the northwestern coast of Corsica, France, at the STARESO marine research station near Calvi. Our observational data was collected in the intertidal to subtidal zone of four small coves south of the STARESO harbor during the month of October. There is little to no habitat disturbance from human impact within the harbor and surrounding coves. Actinia equina (Order Actiniaria, Suborder Nyantheae, Family Actinidae) are

a common species of sea anemone, also known as the beadlet anemone (Perrin, 1997). They are found throughout the Atlantic and Mediterranean coasts of Europe, extending all the way to northern Africa (Sole-Cava and Thorpe, 1987). These anemones are omnivorous suspension feeders that eat organic detritus found in the water column (Chintiroglou and Koukouras, 1992). It was observed that they live in close proximity to several algal species, but primarily attach directly to bare substrate devoid of algal growth. Our research aims to examine the distribution patterns and behavior of A. equina that may give us insight to the factors affecting their dispersal.

Patterns of A. equina Distribution We conducted a census of A. equina within the first four southern coves of

STARESO as well as a small area to the north in order to test the hypothesis that there is a substantial distribution pattern shared between each cove. The data we collected included each anemone's position along a transect line, as well as their size, depth, and the distance to their nearest neighbor. A one hundred meter transect tape was extended along the cove walls, with one person holding the base, and another person working their way along the wall. Every time an anemone was encountered, another individual with their dive slate recorded its position. After their position was recorded, calipers and a meter stick were used to measure size and depth. We noted whether they were solitary or aggregated in a cluster. An individual was considered to be solitary if it was further than twenty centimeters from any other neighbor anemone. Within each cove, we restarted our transect line when the angle of the wall shifted, which could have created different conditions for the anemones. All of this data collected was be used to determine the distribution pattern of A. equina.

The Relationship Between A. equina and Community Composition

Quadrats were used to test the hypothesis that community structure varied between areas containing and areas devoid of A. equina. First, five sites in each cove were chosen by randomly selecting a 50 sq. cm area centered around one A. equina individual. Within each quadrat, we quantified and classified all other organisms including other anemones, invertebrates, and algal species. The number of individual animals was counted and percent algal cover was calculated. We then repeated the process at five random spots in each cove without taking the presence of A. equina into account. The data was then used to compare community structures with or without A. equina present, as well as species compositions within and between coves.

Diurnal Cycle Associated with Planktonic Organisms

We hypothesized that there would be higher planktonic organism abundance during the night at the surface compared to the morning due to previous knowledge of the deep scattering layer. Plankton tows were conducted to quantify the amount of plankton in the water column at a selected site during the morning and at night.

At 9am, we took a 120 meter tow at the surface as well as a depth of two meters along a straight horizontal wall in cove three. We repeated this procedure at 9pm, assuming that the deep scattering layer would have moved onshore. These four samples were analyzed in a lab using a microscope. We focused on counting the total numbers of organisms present. Data collected was used to observe a relationship between planktonic density and the behavior of A. equina to open primarily at night.

Algal Growth Limit vs. A. equina Depth To test the hypothesis that algal line depth was correlated with the depth of

A. equina, we used a meter stick to measure the depth of the upper algal growth limit and the depth of corresponding A. equina individuals. This was repeated at ten randomized sites on each wall of the four coves. We then calculated the difference between each algal limit and A. equina depth in hopes of identifying a relationship. An increase in the upper algae growth limit and a resulting decrease in A. equina depth would suggest a positive correlation.

The Relationship Between Light Levels and A. equina Distribution To test the hypothesis that the distribution of A. equina is related to light exposure, each cove was first separated into walls whose faces were fairly consistent in their vertical hard substrate. We then measured the length of each wall and counted anemone abundance, which gave us the density of A. equina for each wall.

Then a light meter (set to record lumens on two second intervals) was exposed at 5-10 randomized sites on each wall about .25m below the surface (where a majority of the A. equina were found) for 30-50 seconds. This data was compiled, outlying values were discarded, and each wall was given an average lumen and light exposure rating. The densities were then compared to the light exposure ratings. If the density of A. equina increased as light exposure decreased, we could conclude that A. equina were more densely distributed at lower light levels.

RESULTS

Patterns of A. equina Distribution A census was taken of 343 individual A. equina and the data revealed a statistically significant pattern. We rearranged our data into five different categories including; size of the focal individual, size of the nearest neighbor, distance to the nearest neighbor, depth of the focal, and depth of the nearest neighbor. A Poisson distribution test affirmed that anemones followed a clumped distribution pattern. In Figure 1, the black curve indicates the expected number of individuals against their nearest neighbor distances if a random distribution were present. The purple curve represents the actual observed distribution of A. equina, and because it is centered to the left of the black expected curve (indicating closer actual nearest neighbor distances), it can be assumed that the A. equina were aggregated in a clumped distribution. Using a Kolmogorov-Smirnov One-Sample Test under a

Poisson(34.26) Distribution yielded a p-value of 0.0, indicating that our results were statistically significant. This data was then incorporated into a bar graph as seen in Figure 2, which illustrates that small individuals tended to have mainly small or medium-sized neighbors, while medium individuals were noted to aggregate around all sizes of anemones. Larger individuals were found to be located around mainly medium-sized neighbors, however were least likely to be found in a cluster. Using a Pearson Chi-Square, we found that the p-value was 0.0 for the data used in Figure 2, indicating our results can be considered statistically significant.

Figure 1. The black curve represents a frequency distribution based on A. equina mean nearest neighbor distance. The purple curve above shows that the nearest neighbor distance of A. equina was closer than expected given a random distribution.

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Figure 2. The percentage of large, medium, and small A. equina versus the size of their nearest neighbor.

The Relationship Between A. equina and Community Distribution

The results from the quadrats revealed a considerable difference in community structure when we compared A. equina-specific sites to those randomly chosen. An ANOVA test was used to calculate p-values for each treatment. Though there was a statistically significant difference between A. equina-specific site and random site composition (indicated by a p-value of 0.001) , these differences across the four coves did not vary significantly (indicated by a p-value of 0.514). It was found that the average dissimilarity in species abundance and composition between the random and A. equina-specific sites was 72.39% as seen in Figure 3. Encrusting and erect coralline algae, as well as purple fuzzy algae, were the main contributors to the observable dissimilarity between the two types of quadrats, as seen in Figure 4. These three species were overall the least variable, further confirming the significant dissimilarity between the sites containing A. equina and those randomly observed. Coves 1, 3, and 4 were found to share similar composition, while Cove 2 and the harbor had significantly different community structures.

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Resemblance: S17 Bray Curtis similarity

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Figure 3. The green triangles represent the community structures of the A. equina-

specific sites, while the blue triangles represent the sites that were randomly

selected.

Figure 4. The red bars represent the species abundance in the A. equina specific

quadrat sites, while the purple bars represent the species abundance found

within the randomly selected quadrats.

Diurnal Cycle Associated with Planktonic Organisms Our tows yielded an abundance of plankton at night that exceeded the amount

present during the day, as seen in Figure 5. The total number of planktonic organisms

present in seven drops of seawater were observed under a microscope for each of the four

samples.

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Figure 5. Four total plankton tows were performed; two in the morning at the surface and at a depth of 2 meters, and two at night at the surface and at

a depth of 2 meters. Light blue bars represent samples taken at the surface; red bars represent samples collected at depth.

Algal Growth Limit vs. A. equina Depth

A positive correlation between the upper algal growth limit and the corresponding depth of A. equina was observed. With a p-value of 0.002, we can conclude that the data supports a statistically significant relationship. As the upper algal growth limit increased, corresponding A equina were found at shallower depths indicating a positive correlation, as seen in Figure 6. On average, it was found that the algal line would begin about nine centimeters below an anemone, as seen in Figure 7.

Bivariate Fit of Depth of Algae By Depth of Actinia

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Figure 6. As the upper algal growth limit increases, the height of Actinia increases.

Distributions Distance Between Actinia and Algae

Figure 7. This histogram displays a normal distribution for the differences (in

centimeters) between individual A. equina and the top of the algal line.

The Relationship Between Light Exposure and A. equina Distribution The results from the light exposure data and analysis with the density of A. equina showed that there is not a statistically significant correlation between the two. The examination yielded a p-value of 0.5 percent, which forces us to reject our hypothesis and assume that there is no relationship between A. equina density and light exposure.

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Figure 8. The relationship between anemone density and light intensity.

Discussion

From the data collected over the course of four weeks at STARESO field station in the Bay of Calvi Corsica, we were able to observe various biotic and abiotic factors correlated with the spatial distribution of A. equina. From our completed census we can conclude that this species of anemone demonstrated a clumped pattern of dispersal. We suspected that the anemones' reproductive cycle, including cloning and sexual reproduction with a planktonic larval stage, could account for their clustered settlement pattern. Young anemones are known to be brooded inside the gastric cavity off an adult anemone, and once ejected are known to settle nearby (Quicke and Brace, 1983). They mainly reproduce asexually through cloning, however the presence of gonads in the adults and genetic variation are both evidence of sexual reproduction (Orr et al., 1982). The environmental variability of the coves may also present an explanation for their preference to locate in groups due to certain niches being advantageous to occupy, therefore many aggregate in the same area.

The community structures of sites containing A. equina versus those not containing anemones were noticeably different in composition and abundance of species. Sites with no anemones yielded considerably higher concentrations of encrusting coralline algae, as well as more barnacles, suggesting a competition for space between A. equina and these species. In A. equina-specific quadrats, erect coralline algae was found to be the most common neighbor species. Coves 1, 3, and 4 shared considerable similarities, while Cove 2 and the harbor were remarkably different from the other coves, as well as each other. This may suggest that the first, third, and fourth cove share such similar species composition due to similarities in abiotic factors such as lower wave action and deeper total depth. We suspect that Cove 2 had a significantly unique community structure due to its higher level of wave action, wider geographical structure, longer coastline, shallower overall depth, and higher levels of exposure to direct sunlight. The harbor yielded different results compared to the other coves most likely due to the presence of man-made structures such as the rock piles lining the driveway, as well as the least amount of direct sunlight and shallowest total depths. There was also considerably less wave action within the harbor due to the protection provided from the jetty.

The plankton tows revealed that significantly more plankton were present in the water column at night, which may suggest that A. equina open primarily at night due to increased food availability, though experimentation would be necessary for confirmation.

The algal limit line data showed that there is a positive correlation between the upper algal growth limit and A. equina depth. As the upper limit of algal growth increases, the average depth of A. equina decreases suggesting that the algae may be one of A. equina's main competitors for space, though further experimentation is necessary. We can predict within a 95% confidence interval that an individual A.

equina is 6.2-11.7cm above the upper algal growth line. The results of the light exposure data yielded a p-value that was too high to

accept our hypothesis and we therefore must conclude that there was no correlation between light exposure and A. equina density. This suggest that their lack of evasion to sun exposure is attributed to their evolutionary advances aiding their resistance to desiccation due to heat and light exposure. Our high amount of samples strengthened out observational analysis. A. equina had a high resistance towards desiccation and could withstand high light exposure.

Our census proved to be an efficient mode of data collection for testing the hypothesis that there was a pattern in A. equina distribution. The different parameters collected for each individual provided a broad spectrum of observational data. Environmental factors such as weather and ocean conditions could have caused inconsistencies in our census, as well as time of day, slight tidal changes, and limited geographical range. Due to lack of experimentation, we could not make any assumption about the anemones optimal niche.

The use of quadrats to observe community structure was beneficial because we were able to observe and record which species were present with A. equina on the shared rocky substrate. However, the quadrats only pin-pointed a small portion of the overall cove community, therefore there was space for inaccuracy in the assumption that other possible sites within the same cove would have the same species composition. The plankton tows allowed us to see the higher abundance of planktonic organisms at night versus during the day, supporting our hypothesis for a correlation between food available and the nature of A. equina to open at night. However, the difference of two meters in depth between the morning and nighttime tows was not significant in identifying vast differences in abundance of organisms. The abundance of data in our observational analysis involving the upper algal limit and corresponding A. equina depths allowed us to get accurate results. Errors, however small, may have been involved in acquiring depths due to wave action and changing tides. The light exposure observation also gave us a lot of data, however the designated walls were large and had varying light intensities, which could have affected the data.

The overall goal of our project was to identify a clear distribution pattern and community structure of Actinia equina, while also investigating associations with their nocturnal behavior. Since there is little research done on A. equina, our method of data acquisition can be used as a template to increase knowledge on the distribution of this species of anemone. Previous research indicated that these anemones are a solitary species, however our data contradicted these findings. This may suggest that A. equina clones and ejected sexually reproduced juveniles travel little from the parent or nurturing individual, which results in a clumped distribution. Also, our analysis suggest that the presence of anemones may influence immediate community structure or A. equina may be opportunists and their distribution may be affected by space competition with other sedentary species. Future research can be done to determine what their optimal habitat conditions are,

and whether or not they actually compete/are affected by other sedentary species. Additionally, tests can be performed to discover if algal species out compete anemones at lower depths, or why A. equina favor living at the surface. This cornucopia of knowledge would be beneficial to the field of marine biology because of their role withing the rocky intertidal coast of the Mediterranean.

Works Cited

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Anemone Species, Anemonia viridis (Forskål), Actinia equina (Linnaeus) and

Cereus pedunculatus (Pennant)." Helgoland Marine Research 46.1 (1992): 53-68.

Orr, J., J. P. Thorp, and M. A. Carter. "Biochemical Genetic Confirmation of the Asexual

Reproduction of Brooded Offspring in the Sea Anemone Actinia Equina." Marine

Ecology Progress Series 7 (1982): 227-29

Perrin, M.C., J.P. Thorpe, and A.M. Sole-Cava. "Population Structuring, Gene Dispersal

and Reproduction in the Actinia Equina Species Group." Oceanography and

Marine Biology: an Annual Review (1999): 129-52.

Quicke, D. L. J., and R. C. Brace. "Phenotypic and Genotypic Spacing within an

Aggregation of the Anemone, Actinia Equina." Journal of the Marine Biological

Association of the United Kingdom (1983): 493-515.

Sole-Cava, A. M., and J. P. Thorpe. "Netic Evidence for the Reproductive Isolation of

Green Sea Anemone Actinia Prasina Gosse from Common Intertidal Beadlet

Anemone Actinia Equina (L.)." Marine Ecology 38 (1987): 225-29.