Matt Cravens
10/30/2011
Differences in community structure of two central California kelp forests stemming from exposure levels to the open ocean environment
Abstract:
Comparing differences in community structure based upon time and space are important parts of ecological field studies. It gives insight into the processes that structure an ecosystem. In our study we compared the differences in species composition between a kelp forest at Point Lobos Marine Reserve and a kelp forest off of Hopkins Marine Station. The studies were also performed on two different days to determine temporal differences in species composition. We investigated whether exposure to the open ocean caused differences in the community structure using surveys of common central California kelp forest species as indications of variance. Our survey found that exposure did play a role in the community structure between the two sites, however there were temporal differences in fish species abundances, which were attributed to the mobility of fish and the worsening of conditions from the first to the second day of sampling.
Introduction:
Spatial comparisons of community structure are a key aspect of ecological study because they provide insight into the biotic and abiotic processes that structure communities (Samways, 1990). Past studies show that community structure varies when different factors (biotic and abiotic) are acting upon them such as the presence of an apex predator (Duggins et al. 1989), a change in temperature ( Schiel et al. 2004), and disturbances such as ENSO events (Edwards 2006). Our study aims to determine how the level of exposure to outside disturbances affects the relative community structure of an ecosystem.
Kelp forests ecosystems are strong candidates for this type of study because they have a rich and diverse community structure and it is theorized that this structure changes based on its exposure to the greater ocean environment (Carr et al. 2011). We compared two such forests, one off the coast of Hopkins Marine Station and another in Whaler’s Cove within the Point Lobos Marine Sanctuary. We chose to survey these sites because they differ in their exposure to the greater ocean environment. Hopkins is a very protected forest, while the kelp forest at Point Lobos is more susceptible to the rough turbulence of the open ocean (Watanabe, 1984). To see whether exposure had an effect on the community structure of the two kelp forests, we performed quantitative surveys of common central California kelp forest species on two different days at each of the sites to answer the questions: 1) Is there a difference between community structure (species composition) between Hopkins and Point Lobos and does this difference vary between the components of the community sampled (fish, algae, and invertebrates)? , 2)Is there a difference in species composition based on the sampling day and does this difference vary between the components of the community sampled?, and 3) Is there a difference in species composition based on the interaction effect of samplesite and sample dayand does this difference vary between the components of the community sampled? Our research showed that invertebrates and algae species had different abundances based on site, while fish abundance did not vary based on site, but rather it varied based on the sampling day. The variance in algae and invertebrate based on site is most likely attributed to the differences in exposure to the two sites. The differences in fish based on sampling day are mainly a factor of the day-to-day variability of fish derived from their high mobility as opposed to algae and invertebrates which are not very mobile.
Methods:
Sample Site
To study the impacts of exposure on community structure, we compared species abundances at a kelp forest in Point Lobos Marine Reserve and a kelp forest off of Hopkins Marine Station. Surveys were conducted on SCUBA along transects that ran off a permanent cable at Hopkins and a temporary meter tape at Point Lobos, and were performed on two different days, October 11, 2011 and October 13, 2011, to also see the effects of temporal variation on species abundances. The kelp forest at Point Lobos is located in Whaler’s cove (36° 31’ 14.18’’ N 121° 56’ 21.96’’ W). The forest is on a rocky reef surrounded by sandy bottom, the cove itself is very exposed to the northwest. The kelp forest off Hopkins Marine Station is a well protected rocky reef located at 36° 37’ 13.70’’ N 121° 54’ 7.03’’ W. The species surveyed were fish, algaeand invertebrates that are commonly found in a kelp forest along central California (Fig. 6). The mobility, sizeand abundances of species varied and thus influenced their relative abundance.
Is there a difference in species composition between Hopkins and Point Lobos?
To test if there is a difference in community structure between Hopkins and Lobos, we performed surveys along transects and recorded the abundances of species present. For algae and invertebrates, we counted the planar number of species in a 2 m by 30m transect and recorded the amounts, also we counted the number of Macrocystis pyrifera stipes for everyM. pyrifera individual that was counted. For surveying the abundances of fish, we counted the number of individuals per unit volume (2m x 2m) for 30 meters. We took the total number of individuals counted and calculated the mean amount of each species per transect. The results were then analyzed using a PERMANOVA test to calculate whether the variance in species abundance for all species was attributed to sample site, sample day, or the interaction effect of site and day. To determine whether variance was attributed to site, the site effect P value would need to be <.05.
Does the difference in species composition between sites vary between fish, algae, and invertebrates?
To determine whether the difference in species composition varies between the 3 components of the community surveyed (fish, algae, and invertebrates), we graphed the mean abundance data collected by the methods discussed above comparing it to the site and the day it was sampled to show which species varied most based on site. We then analyzed the data with a PERMANOVA test for each specific community component. This test would reveal which individual components varied based on site, again a P value <.05 would mean that the variability of the community component was attributed to the site.
Is there a difference in species composition between the days sampled?
To determine whether species composition differed between the two days we sampled on (October 11,2011 and October 13, 2011), the mean abundances of the species at both sites were collected using the methods explained above and were analyzed using a PERMANOVA test. The abundances were compared between the two days and a P value was calculated to determine if there were differences on a temporal scale. Again, if the P value is below .05, this means that there was a difference based on the days the surveys took place.
Does the difference in species composition between days vary between fish, algae, and invertebrates?
To determine whether the difference in species composition between days varies between the three components of the community that were surveyed, we graphed the mean abundance data. This data wascollected by the survey methods discussed above, comparing these means to the site and the day they were sampled on to show which species varied by day. Furthermore, we analyzed each of the community components using a PERMANOVA test, comparing the abundances to the days they were sampled and generating a P value which would determine whether each component differed based on day. Again, if the P value is below .05, this would mean that there was a difference based on the day surveyed for the community component.
Does the interaction effect of both site and sampling day cause differences species composition?
To determine if there was a difference in species composition from the interaction effect of both the site and the day sampled, we used the mean abundances collected using the methods discussed above and analyzed them with a PERMANOVA test which generated a P value. If the P value is below .05 for the species, then it impliesthat there is a difference in species composition from the interaction effect of both site and day sampled. This means that if a site is sampled over long term, the composition of species would change over time.
Does the difference in species composition from interaction effect vary between fish, algae, and invertebrates?
To determine whether the difference in species composition from interaction effect of site and day varied between the three components of the community, we analyzed the community components individually in a PERMANOVA test to generate P values for each component showing how much of a difference interaction effect has on each of the three components. Again, if the P value was below .05, the differences in species composition due to interaction effect are significant.
Results: Any result requiring a single line does not require a subheading. That said there are results that support this conclusion that you did not include. HOW were they different?
Is there a difference in species composition between Hopkins and Point Lobos?
There was a significant difference between Hopkins and Point Lobos for all species (PERMANOVA, site P value = .0001, Fig. 1). Lead into this next paragraph with: , but not all taxa responded similarly…
Does this difference in species composition between Hopkins and Point Lobos vary between fish, algae, and invertebrates?
For fish, there was no significant variance in composition between site review how stats are reported…this is close! (PERMANOVA, fish site P value = .319, Fig. 1). On the other hand, invertebrates and algae both had significant variance in composition between site (PERMANOVA, invertebrate site P value = .0001, Algae site P value = .0001, Fig. 1). The species that showed the most difference for invertebrates between sites was Balanophyllia elegans. Small differences were shown between sites for Pisaster giganteus, Calliostoma ligulatum, and Pachycerianthus fimbriatus(Fig. 2). Algae had many species that differed between sites which gives insight [jf1]into a difference in understory algae composition (Fig. 3). These species included: Chondracanthus corymbifera, Cystoseira osmundacea, Dictyoneuropsis reticulata, Dictyoneurum californicum, Eisenia arborea, and Pterygophora californica. Furthermore, the number of stipes per Macrocystis pyrifera individuals differed significantly from Hopkins to Point Lobos, with Hopkins having more stipes per M. pyrifera individual (PERMANOVA, stipe per individual by site P value = .000022, Fig. 5).
Is there a difference in species composition based on the days sampled?
There was not a difference in species composition as a whole based on the days sampled (October 11, 2011 and October 13, 2011) (PERMANOVA, all species sample day P value = .382, Fig. 1). Include the Permanova as a table.
Does this difference in species composition between days sampled vary between fish, algae, and invertebrates?
For algae and invertebrates, the differences based on day were insignificant (PERMANOVA, invert sample day P value = .505, algae sample day P value = .724, Fig. 1). However, fish differed significantly based on the sample day (PERMANOVA, fish sample day P value = 0.043, Fig. 1). These differences were seen in every species, major ones being: Sybastes Sebastes mytinus, Seybastes atrovirens, Embiotoca lateralis, and Embiotoca jacksoni(Fig. 4).
Does the interaction effect of both site and sampling day [jf2]cause differences species composition? Subheadings should refer to the general question.
There was not a difference in species composition as a whole based on the interaction effect of site and sampling day (PERMANOVA, all species site and sample day P value = .375, Fig. 1).
Does the difference in species composition from interaction effect vary between fish, algae, and invertebrates?
For algae and invertebrates, there was no difference in species composition based on the interaction effect of site and sampling day (PERMANOVA, inverts site and sample day P value = .569, algae site and sample day P value = .926, Fig. 1). However, fish species did differ from the interaction effect (PERMANOVA, fish site and sample day P value = .015, Fig. 1). This means that both the site and the time period we sampled had large differences in fish species that were sampled.
Discussion:
Start with a general statement to put these results in context. Our study reveals that there is a difference in abundance of species between Hopkins and Point Lobos, and we believe that this difference is highly dependent on the difference in wave disturbance that each site experiences. This is evidenced by the differences in algal composition between the two sites. At Point Lobos, the primary components of the understory are Pterygophora californica and Eisenia arborea. Both species are composed of a thick single stipe (in the case of P. californica, the stipe is hard and woody) and are very hydrodynamic, thus they are found more often in open coastal regions (Dayton et al. 1992, Edwards & Matson 2006). Furthermore, when we compared the number of stipes per individual between Macrocystis pyrifera at the two sites, individuals at Point Lobos had a much lower number of stipes per individual than at Hopkins. This also is evidence towards the effects of exposure playing a role in species abundance differences. M. pyrifera is a species with poor hydrodynamics and large surface area (Raimondi 2011). Thus, it would be logical that in an area with high wave disturbance such as Point Lobos there would be a lower number of stipes, which would decrease the overall drag of the individual. As opposed to Hopkins where there is very little disturbance to have a high number of stipes per individual because hydrodynamics is not a limiting factor.
As shown in the results, fish species did not vary based on site. Rather they differed based on the day of the sampling. This is attributed to the mobility of fish and the difference in conditions between the two days. First off, fish are relatively mobile taxa compared to invertebrates and algae, so they will vary in local locations from day to day even if conditions are exactly the same. However, the two sampling days were drastically different. On day 1 (October 11, 2011), visibility was very high at both sample sites and the swell was minimal, however on day 2 (October 13, 2011), visibility was very low and swell had increased greatly (NOAA 2011). The worsening of conditions paired with the relative mobility of fish would cause significant variance between the species abundances based on sample day. To compensate for high variation in the abundance of fishes and low power to detect differences between Hopkins and Pt Lobos, determine whether there is an actual difference in fish species abundances between Point Lobos and Hopkins, we would have to conduct many more days of sampling so that day to day variance would not skew our numbers.
Overall, exposure is shown[jf3] to have caused a difference in species abundances between Hopkins Marine Station kelp forest and a kelp forest at Point Lobos. Algae and Invertebrates played the main role in the species differences. I believe that [jf4]there is a difference in fish species between the two sites, however, many more days of sampling would be needed to prove this hypothesis.
Figures[jf5]:
All speciesPERMANOVA table of Results
Source / df / SS / MS / Pseudo-F / P(perm)
Site / 1 / 11844 / 11844 / 13.852 / 0.001
Sampling_Day / 1 / 896 / 896 / 1.0479 / 0.382
SitexSampling_Day / 1 / 941.24 / 941.24 / 1.1008 / 0.375
Res / 27 / 23086 / 855.05
Total / 30 / 37258
Algae
PERMANOVA table of results
Source / df / SS / MS / Pseudo-F / P(perm)
Si / 1 / 21931 / 21931 / 37.805 / 0.001
Sa / 1 / 240.52 / 240.52 / 0.41461 / 0.724
SixSa / 1 / 3.6189 / 3.6189 / 6.24E-03 / 0.926
Res / 28 / 16243 / 580.1
Total / 31 / 38689
Fish
PERMANOVA table of results
Source / df / SS / MS / Pseudo-F / P(perm)
Si / 1 / 2536.3 / 2536.3 / 1.2145 / 0.319
Sa / 1 / 5585.9 / 5585.9 / 2.6749 / 0.043
SixSa / 1 / 7831.7 / 7831.7 / 3.7503 / 0.015
Res / 23 / 48030 / 2088.3
Total / 26 / 65415
Inverts
PERMANOVA table of results
Source / df / SS / MS / Pseudo-F / P(perm)
Si / 1 / 4671.9 / 4671.9 / 4.943 / 0.001
Sa / 1 / 805.32 / 805.32 / 0.85204 / 0.505
SixSa / 1 / 708.82 / 708.82 / 0.74994 / 0.569
Res / 26 / 24574 / 945.16
Total / 29 / 30999
Figure 1: PERMANOVA results of variance based on Site (Si), Sample Day (Sa), and interaction effect between site and Sample day (SixSa) for all species, fish taxa individually, invertebrate taxa individually, and algae taxa individually.
Figure 2: Differences in species abundances for invertebrates (right y –axis by bottom x-axis) between sample day (left y-axis) and sample site (upper x-axis)
Figure 3: Differences Abundances of algal species sampled in 60m2 transects at Hopkins (left panels) and Pt Lobos (right panels) on date 1 (top panels) and date 2 (bottom panels). See this…much more clear. in species abundances for algae (right y –axis by bottom x-axis) between sample day (left y-axis) and sample site (upper x-axis)
Figure 4: Differences in species abundances for fish (right y –axis by bottom x-axis) between sample day (left y-axis) and sample site (upper x-axis) same comments
Figure TABLE! 5: PERMANOVA for M. pyrifera stipes per individual. Shows the variance between sample day, sample site, and the interaction effect of sample site and sample day.
Taxa: ALGAE1) Cystoseira osmundacea
2) Chondracanthus corymbifera
3) Dictyoneurum californicum (no mid-rib)
4) Macrocystis pyrifera
5) Dictyonueropsis reticulata (mid-rib)
6) Pterygophora californica
7) Eisenia arborea
Taxa: FISHES
1) Oxylebius pictus (painted greenling)
2) Hexagrammos decagrammus (kelp greenling)
3) Sebastes mystinus (blue rockfish)
4) Sebastes carnatus (gopher rockfish)
5) Sebastes chrysomelas (blk/ylw rockfish)
6) Sebastes atrovirens (kelp rockfish)
7) Embiotoca jacksoni (black surfperch)
8) Embiotoca lateralis (striped surfperch)
9) Damalichthys vacca (pile perch)
Taxa: INVERTEBRATES
1) Patiria miniata ( bat star)
2) Pycnopodia helianthoides (sun star)
3) Pisaster brevispinus (short spined star)
4) Pisaster giganteus (great spined star)
5) Urticina piscivora (fish eating anemone)
6) Urticina lofotensis (white-spotted anem.)
7) Pachycerianthus fimbriatus (sand anem.)
8) Balanophyllia elegans (cup coral)
9) Tethya aurantia (ball sponge)
10) Calliostoma ligatum (ring topped snail)
11) Loxorhynchus grandis (sheep crab)
12) Haliotis rufescens (red abalone)
13) Strongylocentrotus fransiscanus
Figure 6: Common Central CA species sampled in our survey.