Community Structure and Quantitative Sampling
Brett Banka
Abstract
This study was conducted to examine the effects of temporal and spatial differences in two kelp forest systems and how these effects influence community structure. This study examined the effect of swell exposure and how wave energy influences the community structure of two kelp forest systems. The two sites we examined included Hopkins Reef at Hopkins Marine Station characterized by low swell exposure in comparison to Whalers Cove at Point Lobos characterized by increased swell exposure. This study posed three questions: 1) Is there a difference in species composition between Hopkins and Point Lobos? 2) Is there a difference in species composition between days? and 3) Does the interaction effect of both site and sampling day affect species composition?
Introduction
This study was conducted to examine the effects of temporal and spatial differences in two kelp forest systems and how these effects influence community structure. This study examined species diversity and species composition within kelp forests, which are important characteristics that define community structure (Cain et al. 2008). By examining community structure, ecologists can infer the stability and resilience of biological systems and how they may respond to environmental and biological disturbance (Steneck et al. 2002). Kelp forests communities are strongly influenced by their physical and biological environment (Steneck et al. 2002). Water motion is an important environmental mechanism that structures kelp forest ecosystems (Cowen et al. 1982). This study examined the effect of swell exposure and how wave energy influences the community structure of two kelp forest systems. The two sites we examined included Hopkins Reef at Hopkins Marine Station characterized by low swell exposure in comparison to Whalers Cove at Point Lobos characterized by increased swell exposure. This study posed three questions: 1) Is there a difference in species composition between Hopkins and Point Lobos? 2) Is there a difference in species composition between days? and 3) Does the interaction effect of both site and sampling day affect species composition?
This study used observational quantitative field sampling methods to determine the distribution and composition of 33 target species among three taxa (algae, fish, and invertebrates) that characterize central California temperate kelp forest ecosystems (Table 1). These species were examined because they are readily available to count and are representative species of kelp forest communities. The two sites surveyed (Hopkins and Lobos) are representative of contrasting energy gradients of two differing kelp forest systems. Marine reserve sites such as Hopkins and Point Lobos contain kelp forests that are ideal to study because they are not confined by the effects of fishing and allow us to examine specific natural effects particularly swell exposure that we hypothesize is responsible for driving spatial and temporal variation of species abundance and distribution in these communities.
Methods
General Approach
This quantitative sampling study was conducted to determine if the community structure and species composition among three taxa (algae, fish, and invertebrates) differed between two kelp forest sites(Hopkins and Point Lobos). This study investigated the sources of variability in our collection of data including variability between sites, sampling day, and the combined interaction effect of site and day. This variability was then used to analyze the adequacy of our sampling methods by examining the number of days data was collected, the number of transects, and the ability to effectively sample the species used in these surveys.
Surveys were conducted at Hopkins and Point Lobos to assess species composition and species abundance at each site to determine overall community structure. Data was collected by divers on SCUBA at 5m mark intervals along a transect line. At each marker, dive teams used meter tapes to deploy two 30m belt transects. Data was collected in 10m intervals along a (30m long x 2m wide x 2m high) swath. Data was collected quantitatively to measure the abundance of 33 target species (Table 1). These data were analyzed using multidimensional scaling plots to measure difference in species composition and difference in taxa between both sites. PERMANOVA analysis was used to measure the variability in species composition and variability between taxa for each site.
Study System
This study was conducted at Hopkins Reef at Hopkins Marine Station in Monterey, CA (36°37'16.15"N Latitude, 121°54'6.28"W Longitude) and Whalers Cove at Point Lobos in Carmel, CA (36°31'17.77"NLatitude, 121°56'20.70"W Longitude). Data was collected on two sampling days between 0900 and 1100 on October 22, 2011 in low swell conditions and October 13, 2011 in intensified swell conditions.
Image 1) Map of Hopkins Marine Station and Point Lobos on Monterey Penninsula
Image 2) Hopkins Reef site at Hopkins Marine Station
Image 3) Whalers Cove site at Point Lobos
The Hopkins and Point Lobos surveys were conducted in subtidal temperate marine kelp forests dominated by the giant kelp Macrocystis pyrifera (Watanabe 1984). The substrate composition of these sites is composed of granite boulders and shell-fragment rubble that supports macroalgal communities and the fish and invertebrates they contain (Watanabe 1984). This study aimed to examine the difference in species composition between these two sites by using quantitative sampling to measure the abundance and distribution of 6 species of algae, 9 species of fish, and 13 species of invertebrates at Hopkins and Point Lobos (Table 1). We hypothesized that the community structure and species composition would differ due to the difference in swell and wave energy between the swell protected location at Hopkins in comparison to a less swell protected location at Point Lobos.
Is there a difference in species composition between Hopkins and Point Lobos?
Our null hypothesis states there is no difference in species composition between Hopkins and Point Lobos. To measure the difference in species composition between sites, data was collected as indicated in the general approach. Amultidimensional scaling plotwas used to indicate this difference by measuring similarities between sites for all species. P-values less than 0.005 were used to signify dissimilarities between sites to reject the null hypothesis.
Does the difference in species composition between Hopkins and Point Lobos vary by taxa?
Our null hypothesis states that the difference in species composition between Hopkins and Point Lobos does not vary by taxa (algae, fish, and invertebrates). To measure the difference in species composition, data was collected as indicated in the general approach. A multidimensional scaling plot was used to indicate this difference by measuring similarities between sites for each taxa. P-values less than 0.005 were used to signify dissimilarities between sites to reject the null hypothesis.
Is there a difference in species composition between days?
Our null hypothesis states that there is no difference in species composition between days. To measure the difference in species composition between days, data was collected as indicated in the general approach. PERMANOVA analysis was used to indicate the difference in species composition between days. P-values less than 0.005 were used to determine statistical significance to reject the null hypothesis.
Does the difference in species composition between days vary by taxa?
Our null hypothesis states the difference in species composition between days does not vary by taxa (algae, fish, and invertebrates). To measure the difference in species composition between days that varies by taxa, data was collected as indicated in the general approach. PERMANOVA analysis was used to indicate if the difference in species composition varied by taxa. P-values less than 0.005 were used to determine statistical significance to reject the null hypothesis.
Do both site and sampling day affect species composition by interaction effect?
Our null hypothesis states that site and sampling day do not affect species composition by interaction effect. To measure the difference in how site and sampling day affect species composition by interaction effect, data was collected as indicated in the general approach. PERMANOVA analysis was used to indicate if both site and sampling day affected species composition by interaction effect. P-values less than 0.005 were used to determine statistical significance to reject the null hypothesis.
Does the interaction effect betweensite and sampling day vary by taxa?
Our null hypothesis states that interaction between site and sampling day does not vary by taxa (algae, fish, and invertebrates). To measure if the interaction effect between site and sampling day varied by taxa, data was collected as indicated in the general approach. PERMANOVA analysis was used to indicate if the interaction effect between site and sampling day varied by taxa. P-values less than 0.005 were used to determine statistical significance to reject the null hypothesis.
Algae and Plants1) Cystoseira osmundacea
2) Gigartina corymbifera
3) Dictyoneurum californicum
4) Macrocystis pyrifera
5) Dictyonueropsis reticulata
6) Phyllospadix spp. (sea grass)
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)
Invertebrates
1) Asterina miniata (bat star)
2) Pycnopodia helianthoides (sun star)
3) Pisaster brevispinus (short spined star)
4) Pisaster giganteus (great spined star)
5) Urticina picivora (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
Table 1) Target Species List
Results
Is there a difference in species composition between Hopkins and Point Lobos?
Figure 1) Multidimensional scaling plot of all species Give us some details, otherwise we don’t know what we are looking at. What are triangles and what do the numbers mean?
This multidimensional scaling plot of all species signifies significance not exactly : it is a graphical depiction of the data. Permanava is the statistic in difference in species composition between Hopkins and Point Lobos with a P-value of 0.001 (Table 1).
Does the difference in species composition between Hopkins and Point Lobos vary by taxa?
Figure 2) Multidimensional scaling plot of algae same comment
This multidimensional scaling plot of algae signifies significance in difference in species composition of algal assemblage between sites with a P-value of 0.001 (Table 1).
Figure 3) Multidimensional scaling plot of fish
This multidimensional scaling plot signifies no difference in fish assemblage between sites. There is a statistically significant interaction effect considering sampling day and site effects with a P-value of 0.015 (Table 1).
Figure 4) Multidimensional scaling plot of invertebrates
This multidimensional scaling plot signifies a significant difference in invertebrate assemblage between sites with a P-value of 0.001 (Table 1).
Table 1) PERMANOVA table of results
Is there a difference in species composition between days?
Figure 5) Algal species abundance by sample day
The mean number of abundance for algal species between sites is similar in both sampling days. The bar graphs indicate similarities among all seven species represented.
Figure 6) Fish species abundance by sample day
The mean number of abundance for each fish species between sites is not consistent for both sampling days. Mean fish abundances were higher on sampling day one than day two and there is no consistency in mean fish abundance for each sampling day.
Figure 8) Invertebrate species abundance by sample day
The mean number of abundance of invertebrate species is similar between sampling days. The bar charts indicate consistency in abundance of invertebrate species for both sampling days.
Do both site and sampling day affect species composition by interaction effect?
Figure 9) Percent source of variance explained by taxa
There is an interaction effect combining sampling day and site that is responsible for the variance for fish assemblages.
The permanova is the test for interaction. It would have been good to indicate the species that contributed to the statistical differences.
Discussion
Is there a difference in species composition between Hopkins and Point Lobos?
We found a strong effect of site on the overall species composition between Hopkins and Point Lobos (Figure 1). This result rejects the null hypothesis. The difference in species composition between these two sites may be due to the different gradient in swell exposure ultimately affecting community structure. This is almost inseparable from the results section. This is your opportunity to discuss possible mechanisms. For example, what species contributed to this difference? Why would you expect them to be differentially affected by wave exposure?
Does the difference in species composition between Hopkins and Point Lobos vary by taxa?
We found a strong site effect on species composition that varied by taxa for algae and invertebrates but not for fish. This result rejects the null hypothesis. The difference in species composition by site may be due to difference in swell exposure at each site.
Is there a difference in species composition between days?
There is no difference in overall species composition between days. This result rejects the null hypothesis.
Does the difference in species composition between days vary by taxa?
There is a difference in species composition between days for fish but not as significant as the combined interaction effect. This result rejects the null hypothesis for algae and invertebrates. Day and site conditions are responsible for the difference in mean abundance of fishes observed, day one experienced low swell conditions and day two experienced intensified swell conditions.
Do both site and sampling day affect species composition by interaction effect?
We found no interaction effect on species composition. This result fails to reject the null hypothesis.
Does the interaction effect between site and sampling day vary by taxa?
We found a strong interaction effect on the fish assemblages between site and day combined. This result may be due to the effect of different conditions on different days where swell intensity inversely affects fish species abundances.
You also need to finish up with some overarching message. Implications, applications, suggestions for future research.
See general comments
References
Cain et al. 2008 The nature of communities. Pages 322-326 Ecology
Cowen et al. The maintenance of community structure in a central California giant kelp forest. Elsevier Biomedical Press64:189-201
Steneck et al. 2002 Kelp forest ecosystems: biodiversity, resilience, and future. Environmental Conservation29:436-459
Watanabe, James M. 1984 The influence of recruitment, competition, and benthic predation on spatialdistributions of three species of kelp forest gastropods (Trochidae: Tegula). Ecology 64:920-936
Results (25)
__3__/4 Figure legends Accurate
__2__/4 Figure Legends well composed (complete and concise)
__5__/5 Results organized according to questions
__3__/4 Graphs presented in a logical order, case made for the order
__3__/4 Grammar, sentence structure and spelling
__3__/4 Clarity and conciseness of writing
Discussion (25)
____/11 How well did they answer the questions they present in the Intro?
1)__1__/2 Discuss the results from the specific to the general.
2)__1__/3 Answered question about how sites differ in community composition?
3)__1__/3 Assessed sources of variation and made a strong case for whether we are able to detect differences among sites.
4)__1__/3 Presented sound logic as to why certain taxa or species were sampled well.
__2__/2 Grammar and Spelling
__2__/3 General Thoughtfulness
__1__/2 Clarity and conciseness
__3__/5 Organization of discussion
__0__/2 Context and Bigger Picture
General Notes: Your discussion is very weak for the following reasons.
1)You do not need to include subheadings in the discussion, it can be OK, but often the discussion will not follow the same strictly categorical structure of the methods and results.
2) You do not expand on any of the results in the discussion, making it essentially another version of the results.
3)You backed yourself into a corner because you did not provide any detail results in the results section. Simply stating that there are differences is not interesting. WHAT species contributed to those differences and WHY do you think they differed?
If this is not clear, I recommend you find myself, another TA or instructor to go over this. I say this because it will be very important that you understand this for the final paper.