Matt Cravens
10/11/2011
Determining the effectiveness of qualitative sampling as a means for studying species abundance in a central California kelp forest
Introduction:
Determining species abundances is an important aspect of ecological research because it can give indications on the relative health of a community (Kraznov 2006). It can also be a baseline to measure the effects of disturbances on communities (Ebeling et al. 1985). Though a broad term, in this paper ‘species abundance’ will refer the amount of individuals of a species within a given area (Chiarucci 1999). Macrocystis pyriferadominated kelp forests are sites of immense biodiversity and abundance but are also subject to many natural fluctuations and disturbances (Edwards 2004, Ebeling et al. 1985) which makes it a good location to research the composition and abundance of the community. In this study, we determined species abundance of common species of the algae, invert, and fish taxa found in a central California kelp bed at the Hopkins Marine Sanctuary using a qualitative survey method.
As opposed to a quantitative method, qualitative sampling is a method of sampling that is a non-numerical way of assessing data, using terms such as “rare” or “common”. Quantitative surveying uses exact numbers and counting to assess the focus of the survey. Qualitative surveying is more likely to vary based on the discretion of the researcher and is also less numerically exact as opposed to quantitative sampling (Deneka & Hornbach 1996). However the qualitative method is effective in giving a researcher a time efficient estimate of species abundances and is accurate if the guidelines for determining abundances are strictly outlined. Qualitative surveys are also especially appealing for research done by the use of SCUBA in sub tidal zones because there is a strong time constraint due to the amount of air in a diver’s tank and the variability of the environment. Qualitative surveying is a quick and less tedious way of gathering data on a community as opposed to quantitative surveying (Carr & Raimondi 2011).
Despite this study being a survey of species abundance at the Hopkins Marine Sanctuary kelp forest, the main focus of our study is to examine the effectiveness of qualitative sampling as a means for ecological research. More specifically we want to find answers to the questions: 1) What differences occurred between buddy pair individuals in their sampling and what could have caused the differences and 2) What species seem to be relatively good candidates for qualitative surveying and what characteristics make them such good candidates?
Methods:
This study was performed at the Hopkins Marine Laboratory kelp forest in Pacific Grove, CA. Common species from the algae, invertebrate, and fish taxa were examined for their abundance. Sampling was performed on SCUBA. Buddy pairs were each given a meter mark every 5 meters along a black cable that runs through the kelp forest, parallel to shore. Buddy pairs rolled out a 30 m transect tape while recording species abundances on a scale of 1 (not present), 2 (rare), 3 (present), 4 (common), and 5 (abundant) on both the deep (offshore) and the shallow (on shore) side of the cable. The range of sampling was not determined, that is divers were not told how far to look (width of transect) while sampling along their transect. Also, no indication was given about what constituted the categories of “rare”, “present”, “common”, and “abundant”.The data collected was then analyzed using a variance component analysis which compared the variation in species abundance based on three factors: buddy pair differences, depth, and meter mark along the cable. The data was then analyzed by comparing the percentage of buddy groups that disagreed on whether a species was present or absent.
Results:
The mean species abundances of the species sampled are shown in Fig. 1. The variance component analysis[jf1] shown in Fig. 2 shows that ~37% in variance of species abundance was attributed to difference between individuals in a buddy pair in their sampling, ~23% of the variance was attributed to depth and ~40% of the variance in data was attributed to the meter mark divers sampled on along the cable. Fig.3 shows the variance analysis based on taxa and shows that, especially in the case of invertebrates (50%), buddy differences in data recording played a huge part in the variance of species abundance recorded (~15% for fish and ~40% for algae). Furthermore, the presence/absence analysis of buddy disagreement (Fig. 4) showed that with 14 species, 30% of the buddy pairs had disagreements on whether or not the species was even present along the transect.
Discussion:
The results of the mean abundance of species are skewed because of the fact that ~37% of the variance in data is due to the fact that buddy pairs disagreed on the abundance of species. To have a relatively accurate survey of species abundance, buddy variance needs to be low. This result was not surprising to me, not because the qualitative method was used to sample, but because the instructions to the researching divers were very broad and guidelines in the rating of species were not explained. As reported above, while sampling, divers were not told how wide their survey along the transect should be. So, for example, in some buddy pairs one buddy may have only been sampling one side of the meter tape, while the other buddy may have been sampling both sides of the meter tape. Furthermore, the ratings for species abundance (1-5) were not outlined well, so divers may have had varying opinions on what could be considered common (a rating of 4) and what could be considered present (a rating of 3) and even more so the abundance scale of species varies drastically from species to species. For instance, Asterina miniata (commonly known as the bat star)is a very common central Californian starfish (Newman 1922) as opposed to Semicossyphus pulcher(commonly known as the California sheephead), which is considered less common as you move north along the CA coast. If a diver were to record only 1[jf2]A. miniata and 1 S. pulcher along a transect, the numerical significance of each is extremely different. Only seeing one bat star in a place where bat stars are very common means that it should be recorded as a 2 (rare) however seeing a sheephead in an area where sheepheads aren’t usually found means that it should be given a higher rating such as a 3 (present). This could have been another area where disagreements could have arisen between buddy pairs. Instead it should have been outlined what is considered a 2, a 3, etc. for each species so that the confusion would be avoided and the data more accurate. These two issues have no reflection on the efficiency of the qualitative method, but rather that the surveyinstructions were not very clear so it was easier for differences to arise between dive buddies during the sampling. Furthermore, the percent disagreement graph based on presence/absence of species (Fig. 4) shows how disagreement between buddies was high (over 30% in 14 cases)even in determining if a species was present or not. Again, this may not have been a reflection of the qualitative method, but rather based upon the fact that divers did not have a clear guideline in the width of their sampling.
I feel that this survey is inconclusive in determining what species are good candidates for qualitative surveys. Even though in the results species such as Macrocystis pyrifera and Asterina A. miniata had no variance in buddy pairs based on absence/ presence, this is simply because in a kelp forest in central California, these species are almost always present. To determine more thoroughly what species are good candidates for qualitative sampling and overall whether the qualitative method is an efficient research method for determining species abundance, another study must be done in which divers are given clear instructions on 1) How wide their survey must be along the transect and 2) The scale at which to judge species abundances. Overall, the qualitative method can provide just as accurate data as the quantitative method. However, as with any research study, it must be outlined clearly so that less discrepancy is created when performing the research and accurate data can be generated.
Figures:
Figure 1: Mean Abundances abundance for eachof species, divided by taxa (Scale of 1-5 as explained in Methods).
Figure 2: Variance component analysis, Variance (%) compared to source. Be more clear in your legend. Variance component analysis of WHAT?
Figure 3: Variance Component analysis by taxa. Variance (%) compared to source. Be more cleart and complete. Hit the main points, figures should be stand alone.
Fish Algae Invertebrates
Figure 4: Percentage of buddy pairs that disagreed in the presence/absence of a species
Works Cited:
Carr, M. and P. Raimondi. Qualitative sampling-Kelp forest ecology-First field survey. Internet.
(2011)
Chiarucci, A. et al. Cover versus biomass as an estimate of species abundance: does it make a difference
to the conclusions? Journal of Vegetative Science 10, 35-42 (1999)
Deneka, T. and D.J. Hornbach. A comparison of a qualitative and a quantitative collection method for
examining freshwater mussel assemblages. Journal of the North American Benthological Society 15, 587-596 (1996)
Ebeling, A.W. et al. Severe storm disturbances and reversal of community structure in a southern ddddddCalifornian kelp forest. Marine Biology 84, 287-294 (1985)
Edwards, M. Estimating scale-dependency in disturbance impacts: El Niños and giant kelp forests in the ddddddnortheast Pacific. Oecologia 138. 436-447 (2003)
Kraznov, B.R. et al. Is Abundance a Species Attribute? An example with haematophagous ectoparasites.
Oecologia150, 132-140 (2006)
Newman, H.H. An experimental analysis of asymmetry in the starfish, Patiria miniata. Biological Bulletin
45, 1-9 (1922)
Results (25)
__2__/4 Figure legends Accurate
__2__/4 Figure Legends well composed (complete and concise)
__4__/5 Results organized according to questions
__4__/4 Graphs presented in a logical order, case made for the order
__4__/4 Grammar, sentence structure and spelling
__3__/4 Clarity and conciseness of writing
Discussion (25)
__7__/9 How well did they answer the questions they present in the Intro?
1)__2__/3 Discuss the results from the specific to the general.
2)__3__/3 Do these results surprise you? In other words, is the qualitative method more or less reliable than you thought it would be, and do you think that degree of reliability (which can be assessed based on relative difference between buddies) implies anything about accuracy?
3)__2__/3 Do you think the qualitative sampling approach is appropriate for describing trends of species abundances through time? Explain your answer
__3__/3 Grammar and Spelling
__2__/2 General Thoughtfulness
__2__/3 Clarity and conciseness
__4__/5 Organization of discussion
__3__/3 Context and Bigger Picture
General Notes:
[jf1]Not: Shown in Figure 1. Make your statement and follow with (Figure 1). Refer to the guidelines for a description of how to reference figures
[jf2]Spell numbers to ten