Chapter 6: Zonation Rock Species Diversity Study 2011 Hardy Hill Ziz Raskin Zonation Rock Species Diversity Study

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Chapter 6:
Zonation Rock Species Diversity Study 2011

Hardy Hill

Ziz Raskin
Zonation Rock Species Diversity Study

The Zonation rock of Racing Beach is an excellent study sight for an investigation of both of species distribution and diversity, as well as the interactions between the two. In our study we endeavored to determine the distribution of species across both faces of Z rock, as well as the diversity if the intertidal zones and the factors which affect it. Due to Z rocks orientation, with one ocean face and one shore face, wave action is a central consideration in our study of the factors determining diversity and species distribution. Our observations led us to the conclusion that wave action is indeed higher on the ocean face of Z rock. However, contrary to our hypothesis we discovered the greatest diversity in the upper intertidal zone of the shore face. After comparing our data with that collected by DelDonno (2008), we found diversity to have fallen even in our most diverse. The causes of this change remain unclear, however we have hypothesized that they are due either to an increase in wave action, or conversely the process of succession springing from relatively calm and undisturbed conditions.


Racing beach's Zonation rock, with its four faces, large and stable nature, and clear banding pattern, makes it ideal for studying the diversity, structure, and species distribution of intertidal communities across the lower, middle, and upper intertidal range of a rocky shore. Generally, species distribution can be attributed to a number of biotic and abiotic factors; in intertidal communities abiotic factors include desiccation, fluctuation in temperature, wave disturbance, and scouring by sea ice. Biotic factors include predation, competition, and facilitation (Sumich 1992, Bertness 2002). Z rock, with its clear delineation of the upper, middle, and lower intertidal zones provides an excellent case study of species distribution and the effect of biotic and abiotic factors. The distribution of Balanus and Chthamalus in the upper, middle, and lower intertidal zones illustrates this particularly well. The dominance of Balanus in the middle and lower intertidal demonstrates the importance of biotic factors in determining species distribution in ideal environments where morphological dominance becomes more important than hardiness and resistance to harsh conditions such as desiccation and scouring (Menge 1976). However, the presence of Chthamalus in the upper intertidal and Balanus' general absence or decreased presence can be attributed to the importance of abiotic factors in determining species distribution in this zone, where resistance to harsh conditions is more critical to survival than the ability to compete with other organisms.

In addition, the varying conditions organism are exposed to on the shore and ocean face, as well as in the upper, middle, and lower intertidal, makes Z rock an ideal study site for examining the impact of abiotic factors on species diversity. The determining factors affecting diversity are complex. Environmental conditions determine what range of organisms can be sustained, and the age and stability of the community determine whether succession and competition have established clearly dominant species (Wethey 1985). In addition, as was suggested by Connell in 1978, what has been dubbed intermediate disturbance seems to play a role in determining the diversity of a community. In other words, communities where competition (aka. biotic factors) is (are) rigorous, but intermediate environmental disturbances prevent any one species from entirely filling a niche, are the most diverse. While we cannot be sure of the difference in wave action on the shore and ocean faces of Z rock, their respective positions relative to the shore would suggest a significant difference in exposure to wave force, thus making a study of the effects of wave action on species diversity both practical and important for our understanding of Z rock's community. Taking these factors into account we have hypothesized that the we will find the greatest diversity in the middle and lower intertidal zones of the shore face, where abiotic factors are mild enough to allow competition and yet severe enough to prevent the establishment of fully dominant species. It is our belief that conditions in the upper intertidal of the shore face as well as in the upper, middle, and lower intertidal of the ocean face, are too harsh to allow for a variety of organisms to succeed and in turn are mitigating factors to diversity.

The study of Z rock remains relevant from year to year as it allows us to monitor changes in diversity and species distribution which may illuminate the process of succession on Z rock as well as furthering our understanding of intermediate disturbance as it pertains to this study site. We experienced a rather late spring this year and winter storms have apparently been mild. Due to changes in experimental format however, data from the 2010 and 2009 studies is difficult, if not impossible to use, however data from 2008 fit with our experiment design very well and presented some unusual results. In the 2008 study, DelDonno found the greatest diversity in the upper intertidal zone of the ocean face, a fact both contrary to our hypothesis that diversity would be reduced on this face due to overwhelming abiotic factors such as wave force and scouring, as well as being at odds with the standard expectation that diversity will increase as one moves into the middle and lower intertidal zones, which DelDonno in fact found to have far lower diversity on both faces. In an attempt to understand the factors that have led to these peculiar trends in diversity, we will repeat DelDonno's 2008 study with a number of modifications. We will continue to measure wave heights on the two faces of Z rock in the hope of quantifying the wave force that each face is subjected to. In addition to examining wave force and the effects of scouring, we intend to take measurements of areal coverage by juvenile barnacles, which are a clear sign of recent disturbance, as well as bare patches.


Duct tape quadrat (10 cm x 10 cm)

10 cm ruler

Meter stick

Magnifying glass

Waterproof notebook

Peterson Field Guide to the Atlantic Sea Shore


  1. Determine the upper limits of the lower, middle, and upper intertidal zones of the shore and ocean face measured from the bottom using a meter stick placed firmly on the floor at a central location. Use banding patterns to signal the limits of each zone.

  2. Calculate from the upper and lower limit of each respective zone the center of each. For 2011, the numbers were as follows

Shore Face

Upper ≈ 1 meter 58 centimeters

Middle ≈ 1m 45 cm

Lower ≈ 60 cm

Ocean Face

Upper ≈ 1 meter 89 centimeters

Middle ≈ 1 m 74 cm

Lower ≈ 83cm

  1. At the center of each zone take 10 cm x 10 cm quadrats 10 cm apart along the three zones of each face.

  2. In each quadrat estimate the areal coverage (expressed as a percentage) by each barnacle species as well as that of unidentifiable juvenile barnacles, proceed to extrapolate the area left uncovered. For example, a quadrat might be 45% Balanus, 10% Chthamalus, 30% juveniles, and 10% bare.

  3. Record other organisms (Litortina saxatilis, Urosalpinx cinerea, Anachis, etc.) by actual number of individuals within quadrat. Covert these counts to percentage coverage through the formula below

Urosalpinx: 1 individual = 1% coverage

Littorina littorea, Anachis: 10 individuals = 1% coverage

  1. Convert percentage values to decimals and calculate the Shannon Diversity Index using the formula H = Σplnp

  2. Calculate averages for each species and perform t tests were appropriate.

  3. Each day make general observations of the rock and the weather conditions.

  4. Each day measure wave amplitude with meter stick by placing it firmly on the floor at a central location and observing the upper and lower limits of wave height.


General Observations

At first glance, all the intertidal zones of Z Rock blend together, making it difficult to distinguish between them. Balanus, Chthamalus, and juvenile barnacles dominate the rock’s surface but after looking closely at the rock, it becomes clear where the three intertidal zones begin and end because of the location of each species. Another helpful indicator of intertidal zones is amount and size of bare spots where barnacles have been scorned off. Fucus, Littorina saxalitis, and Urosalpinx cinerea are also sprinkled throughout the different zones, although they tend to appear on the shore side of the rock.


The ocean face was coated in juvenile barnacles, especially the lower intertidal zone, which was almost entirely made up of juvenile barnacles. The middle intertidal zone was largely covered by Balanus and juvenile barnacles, while the upper intertidal zone was spotted with Chthamalus and bare spots. There were virtually no Fucus, Littorina saxalitis, or Urosalpinx cinerea found on the ocean side.


The shore side of Z Rock had a significantly less clear division between the middle and upper intertidal zones while the lower intertidal was very distinguishable. The lower intertidal was coated in a thick layer of Fucus, and had a comparable amount of both juvenile barnacles and Balanus. However, the middle and upper intertidal zones were largely Balanus, the deciding factor between the upper and middle intertidal zones for the shore face was roughly where Chthamalus clustered. A major difference between the two zones, was the middle intertidal zone had very little bare spots compared to the upper intertidal which was largely made up of bare spots. The middle and upper intertidal zones also had a fair amount of Littorina Saxatilis.

Table 1 and 2 Figure 1:

The ocean side has about the same average areal coverage of Chthamalus and Balanus but almost no Urosalphinx, Littorina saxatilis, juvenile barnacles, or bare spots. The shore side has a very high average areal coverage of bare spots, similar Chthamalus and Balanus coverage, and virtually no juvenile barnacles, Littorina saxatilis, or Urosalpinx cinerea.

Table 1 and 2 Figure 2:

Balanus dominates the middle intertidal of the shore side and the juvenile barnacles dominate the middle intertidal of the ocean side. There is virtually no littorina saxatilis or urosalpinx cinerea on either ocean side or the shore side, and only a very small average areal coverage of bare spots on the shore side.

Table 1 and 2 Figure 3:

Juvenile barnacles almost exclusively dominate the lower intertidal zone of the ocean side while, the shore side has a relatively balanced average areal coverage between juvenile barnacles, Balanus, and bare spots. There were almost no littorina saxatilis or urosalpinx cinerea found on the lower intertidal zone of the ocean side or shore side.

Table 3 Figure 4:

There is not a large difference in species diversity on the upper and middle intertidal zones of the ocean and shore sides. However, the lower intertidal zone shows a clear difference between the two sides, the shore side has a significantly higher level of diversity than the ocean side.

Table 3 Figure 5:

In general, the ocean side of Z rock had a higher level of species diversity in 2008 than 2011 except for the middle intertidal zone, which was identical.

Table 3 Figure 6:

Both the middle and lower intertidal zones of Z rock’s shore face had a higher level of species diversity in 2011 than 2008 while the level of species diversity in the upper intertidal was higher in 2008 than 2011.

Table 4 Figure 7:

Balanus was almost exclusively found in the middle intertidal zone on the ocean side in 2011 while Balanus had a large presence in all intertidal zones in 2008.

Table 4 Figure 8:

The average percent coverage of Balanus on the shore side was much more similar on the shore side during 2008 and 2011. 2008 had a higher average percent coverage in the upper and middle intertidal while the lower intertidal had a higher percent coverage of Balanus in 2011.

Table 4 Figure 9:

Chthamalus (which was exclusively found on the upper intertidal zone on both the ocean and shore face) had a fairly consistent average percent coverage in 2008 while 2011 had significantly more Chthamalus on the ocean side than the shore side.


We were unable to use data from either 2009 or 2010 due to format changes, inaccessibility of raw data, and alteration in the study procedures; however we were able to compare our data with that from 2008 and noticed significant changes. First, diversity on the Ocean side has fallen in the upper and lower intertidal zones and remained constant in the middle, the decrease in diversity in the upper and lower intertidal are almost identical (Table 3, Figure 5). From the 2008 data, it seems Balanus had a significant presence in the upper intertidal, this presence, as is demonstrated by our data, has dropped off almost entirely. In addition unoccupied space has increased and areal coverage by juveniles (though it was not measured in the 2008 study) is significant (Table 4, Figure 7). This would perhaps suggest that a very harsh winter (or more accurately, series of winters), or a general increase in wave action over the past three years, has pushed the less resilient barnacle out of the harsh upper intertidal, causing the precipitous drop in diversity. As for the drop in the lower intertidal, the data (Table 4) would suggest that it is correlated with the dramatic decrease in Littorina littorea since 2008. From the data collected by DelDonno in 2008, specifically her discovery of vast numbers of Littorina littorea located in the upper, middle, and lower intertidal zones of the shore face and the comparatively small number found on the ocean face, we can perhaps imagine that Littorina littorea are in some way also averse to high wave action, and therefore whatever caused the drop in Balanus population is correlated to the drop in Littorina littorea. Alternativley, if wave action has been relatively mild over the past three years, one could understand the drop in diversity as the result of succession in the upper intertidal. As Connell demonstrated, Balanus often settles in the upper intertidal as larvae but are, over time, pushed out, either by competition with Chthamalus or by the harsh conditions of the upper intertidal. So, if the upper intertidal has remained relatively undisturbed over the past three years, then there is a distinct possibility that the Balanus recorded by DelDonno in 2008 may have been incidental, and in turn have slowly lost coverage in the upper intertidal as a result of the aforementioned environmental constraints. 

Also notable is the fall in diversity in the upper intertidal and rise in the middle and lower zones of the shore face (Table 3, Figure 6). The drop in diversity in the upper intertidal is strangeBalanus and Cthamalus have lost ground since 2008 and Littorina littorea has disappeared completely. Again, two possibilities present themselves, either increased wave action has driven away Littorina littorea and begun to hurt the delicate Balanus in the upper intertidal, or mild abiotic factors have allowed succession to take place and in turn, an incidental Balanus population, recorded in 2008, has lost ground just as Connell observed. The data proves problematic in supporting either of these hypotheses. While Balanus suffered a 4% greater loss of areal coverage than Cthamalus since 2008 (Table 4, Figures 8-9) this could support either succession or an increase in wave action. In addition the decrease in areal coverage by Cthamalus is utterly perplexing and is entirely out of keeping with the notion of succession, but fails to truly provide strong evidence for the alternative. One might see the observed  35% average loss for Balanus in the upper intertidal of the ocean side, 26% greater than the loss on the shore face, as evidence for the wave action hypothesis in that it supports our assumption of greater wave action on the ocean face as well as its impact on barnacle distribution. In addition, the wave action hypothesis can also be applied to the increase in diversity in the lower and middle intertidal, something that cannot be said of succession. Since 2008 Balanus has suffered an approximate 28% loss of areal coverage in the middle intertidal, however there has been a very small, though noticeable increase in Littorina saxatalis since 2008. One could imagine that this increase in Littorina saxatilis is correlated to space being freed up by the scouring of barnacles from the rock face. Finally the increase in diversity in the lower intertidal is utterly perplexing, there has been a slight (5%) increase in Balanus in the lower intertidal, but Urosalpinx and Littorina littorea have both vanished completely, we recommend monitering this in future studies to illuminate the causes of this trend.

This year we found the greatest diversity in the upper intertidal of the shore side, followed by the upper intertidal of the ocean side (Table 3, Figure 4). The lowest diversity was in the lower intertidal zone of the ocean face. Perhaps ocean spray is high enough on the shore face to provide an environment capable of sustaining the desiccation prone. Balanus, but too great on the ocean side for Balanus to withstand the wave action. Looking at the data (Table 4), the nearly even mix of Chthamlaus and Balanus seems to be the main cause of its higher diversity index. If this is the case one might attribute this occupation of the same space to a balance of biotic and abiotic factors. On the ocean side, abiotic factors seem to play too great a role in the upper intertidal for Balanus to maintain a presence, and indeed in the lower and middle intertidal of both faces biotic factors play too great a role to allow the morphologically inferior Chthmalus to achieve any level of penetration. However, the somewhat sheltered upper intertidal of the shore face might just produce a balance of biotic and abiotic factors, allowing both species to remain, but allow neither to become dominant. The exceptionally low diversity of the lower intertidal zone of the ocean face may be due to scouring. This zone was almost completely devoid of mature barnacles, being mostly comprised of Fucus, bare spots, and a crusting of juveniles, all these, save for the presence of Fucus would suggest recent displacement by scouring. However one might also attribute it, along with the relatively low diversity of the lower intertidal zone of the shore face, to the dominance of Fucus, which may, given the condition of the lower intertidal, outcompete Balanus.

While our results did not exactly match our hypothesis, our data does seem to suggest intermediate disturbance as a factor in the greater diversity of the shore face. The moderate, though significant wave action that we hypothesized the shore side to be exposed to, was largely confirmed by our measurements of wave amplitude, as well as our observation of Fucus and Littorina distribution. Coupled with this, our findings concerning diversity on the two faces definitely point to some sort of an interaction between wave force and diversity, though we cannot claim causation. The shocking decrease in diversity in the middle and lower intertidal zones, was the greatest disparate element between our hypothesis and our findings. It is difficult to understand these differences as functions of intermediate disturbance, however it would undoubtedly be an interesting aspect of Z rock's community to study, as we are not the first to come across this peculiar pattern. Included in this study are a number of sources of error. First and foremost is the importance of estimation in the process of taking quadrats, because counting individual barnacles is unreasonable we have expressed their areal coverage as rough estimations in percentage form, the inexactitude of this process is undoubtedly the key source of error in our study. In addition, though hardly as significant as the difficulties posed by estimation, the fact that we spread our data collection over several days may have added to any preexisting inaccuracies in our data. Unfortunately, neither of these problems can be fully addressed without a change in the structure of the study. Our work has shed some light on the issues of succession, intermediate disturbance, and the roles of biotic and biotic factors on species distribution and diversity on Z rock, and the continuation of this study will surely be invaluable for future classes wishing to examine these elements of a rocky intertidal community. 

  1. . Jonsson, Per R., Lena Granhag, Paula S. Moschella, Per Åberg, and Stephen J. Hawkins. "Interactions between Wave Action and Grazing Control the Distribution of Intertidal Macroalgae." Ecological Society of America. 87.5 (2006): pp. 1169-1178 . Print.

  2. Menge, Bruce A. " Organization of the New England Rocky Intertidal Community: Role of Predation, Competition, and Environmental Heterogeneity." Ecological Society of America. 46.4 (1976): pp. 355-393 . Print.

  3. Wethey, David S. " Catastrophe, Extinction, and Species Diversity: A Rocky Intertidal Example." : Ecological Society of America. 66.2 (1985): pp. 445-456 . Print.

  4. Menge, Bruce A. "Generalizing from Experiments: Is Predation Strong or Weak in the New England Rocky Intertidal?." in cooperation with International Association for Ecology. 88.1 (1991): pp. 1-8 . Print.

  5. Bertness, Mark D., George H. Leonard, Jonathan M. Levine, Paul R. Schmidt, and Aubrey O. Ingraham. "Testing the Relative Contribution of Positive and Negative Interactions in Rocky Intertidal Communities." Ecological Society of America. 80.8 (1999): pp. 2711-2726 . Print. 

  6. Gosner, Kenneth L. A Field Guide to the Atlantic Seashore: From the Bay of Fundy to Cape Hatteras . 1. Boston: Houghton Mifflin Harcourt, 1999. Print.

  7. Sumich, James L. An Introduction to the Biology of Marine Life . 8. Sudbury, MA: Jones & Bartlett Publishers, 1992. Print.

  8. Bertness, Mark D. The Ecology of Atlantic Shorelines . 1. Sunderland, MA: Sinauer Associates Inc, 2002. Print.









Figure 9




Table 3


2011, chapter 6, pg.

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