Species-Habitat Associations in the Benthic Community of the Kelp Forest at Hopkins Marine Station [[4/4 clear, specific, gets at the major ecological questions]]
Astrid Leitner
[[13/14 - Overall Clarity – line-by-line edits provided for the intro only, try to apply these concepts to the rest of the paper and consider in your future work. Your writing style is overall quite easy to read and understand.
· Be sparing in your use of dramatic and flowery language (e.g. “since the dawn of time”, “outstanding”, “incredible”) and beware of superlatives (e.g. the most, best, largest etc.) because these are rarely accurate or truly meaningful.
· Don’t forget to connect the dots between ideas, just because you understand how two ideas presented in adjacent sentences are related, does not mean it’s clear to your reader.]]
Introduction [[16/20 – nicely written and clearly lays out the big picture questions, see comments below for what’s missing]]
Understanding how diversity is maintained within an ecosystem has long been the goal of ecologists. This is a complex and debated topic; however, one of the major processes that ecologists have identified niche partitioning as an important process foras being important to maintaining high diversity is niche partitioning. Niche partitioning maintains high diversity by reducing competition among species: ; instead of competing for the same resource the species use different parts of the same resource or niche, thus functionally dividing the resource between them (Schoener 1974). One key way to study resource partitioning is through habitat association studies. By understanding each organism’s individual habitat, one can begin to piece together how different niches are partitioned throughout the coexisting community. [[this is a nice, clear explanation of niche partitioning, and why it is of interest to ecologists. Look into proper use of colons and semi-colons; semi-colons should be used to separate two related sentences, while colons are used to introduce a series of things.]]
Species-habitat association studies have a long history in both terrestrial and marine ecosystems. For example, Robert Macarthur conducted a classic study highlighting how multiple species of warbler can persist by utilizing different sections of the same tree (Macarthur 1958). Resource partitioning has also been cited as a major cause of the present diversity of rockfishes within the Pacific coast kelp forest ecosystem (Hallacher and Roberts 1985). However, studying habitat associations in marine systems is much more challenging than in terrestrial ecosystems, and therefore, many associations still remain poorly understood. [[this does not DIRECTLY address the novelty of the study, and could be improved if it did]].
The kelp forest ecosystem provides an ideal study system for marine habitat association work due to its incredibly high species and habitat diversity. Moreover, much remains to be explained about the patterns of the benthic communities within kelp forests. We chose to conduct our benthic surveys at Hopkins Marine Station in Pacific Grove California due to the pristine condition of the kelp forest, as a result from of its longstanding protected status. At this site we examined 1) whether observable associations between species and substrates exist 2) whether observable associations between species and relief exist 3) and whether these associations vary in strength.
We hypothesize that organisms are not randomly distributed among different substrates, and patterns do exist between species presence and relief [[these hypotheses could be more clearly defined and articulated]]. Moreover, we hypothesize that these associations would vary in strength for different species.
Methods [[13/18 – missing an attempt to directly relate survey and analysis methods to each hypothesis, but otherwise well structured]]
To test our hypothesis that associations of variable strengths exist between benthic invertebrates and habitat, specifically relief and substrate type, we conducted an observational field study at the Hopkins Marine Station in Pacific Grove, California (36°37'12.3"N 121°54'11.2"W) (Map Figure 1).
The Study System
Our research was conducted in the Hopkins State Marine Reserve, which was previously known as the Hopkins Marine Life Refuge (Jones 1985). Since 1985 the taking of fish, plants, and marine invertebrates has been prohibited, making this an ideal place to study natural occurring habitat associations (Jones 1985). Macrocystis pyrifera, or giant kelp, dominates the kelp forest, and granite is the dominant rock type in this region (Watanabe 1984). [[Should also mention that there are a variety of different substrate types (boulder, bedrock, cobble, sand) and categories of vertical relief which makes it possible to assess species-habitat associations. Also the diversity of sessile benthic species is important for a robust study of species-habitat associations]]
[[You should introduce the specific hypotheses here and explain how your data collection methods will allow you to test each hypothesis. After you’ve explained WHY you did things the way you did, you want to provide a detailed description of methods, including data analysis.]]
Sampling
We collected data from 20 transects running on and offshore off the permanent transect cable at Hopkins marine station, sampling from the 90 meter mark to the 135 meter mark in increments of 5 meters. All transects were 30 m in length and conducted on SCUBA using uniform point contact methodology (henceforth referred to as UPC). In UPC data is collected at uniformly spaced points along a meter tape. At each of these points the species of the primary substrate holder directly under the meter tape is identified and recorded. This makes it possible to survey invertebrates that act as primary substrate holders, which are often impossible to count as individuals.
To collect the UPC data, divers in two man teams conducted two dives at each 5 m increment, the first heading offshore (90° heading) and the second one heading inshore (270° heading). Each transect had a length of 30 m, which was further subdivided into 5m increments. These 5 m increments were sampled at every half-meter with the first diver sampling the first half (points 0, .5, 1, 1.5, and 2 m) and the second diver sampling the second half of each increment (points 2.5,3,3.5,4,4.5, and 5 m). At each point divers identified the substrate as being either bedrock (rock greater than or equal to 1m in extent), boulder (between 10 cm and 1 m), cobble (less than 10 cm), or sand. Additionally, divers classified the relief at each point by noting the maximum elevation change occurring within a 1 m by .5 m rectangle (.5 m to either side of the transect line and .25 m ahead and behind the point). A four point relief scale was used to classify relief: F-flat for relief between 0 and 10 cm, S-shallow from 10 cm to 1 m, M-medium from 1 to 2 m, and H-high for relief greater than 2 m. The presence of a superlayer of drift algae and juvenile Laminariales was noted as well. Finally the species that occurred directly under each point was identified and recorded (or the type of inanimate substrate if there was no biotic organism present). This methodology was repeated for all 5 m increments along each transect.
Analysis
Associations were classified as deviations from the expected values if organisms were distributed on habitats by chance. These associations were then classified as having different strengths. Deviations <-2 and >2 are classified as strong associations, and deviations between 1 and 2 and between -1 and -2 are considered moderate (all others were qualified as weak). A negative deviation meant that the species was found less often on that substrate than would be expected by chance. A positive deviation shows that the organism is found on that particular substrate more frequently than would be expected. Associations for inanimate contacts were noted and calculated but are not discussed in this paper. [[good description of analysis methods]]
Results [[13/16 – this section could be improved if you included all the figures you used to support your written results]]
Habitat Characterization
With our twenty 30 m long transects our sample area was characterized to be mostly sand and bedrock with some boulder and relatively little cobble (Figure 2A). The relief of the survey area was therefore mostly flat and shallow (>80%) with some medium relief and relatively little high relief (Figure 2B).
The flat areas were mostly sand (>66%) and bedrock (18%). The shallow substrate was almost evenly sand, boulder, and bedrock, with bedrock being the largest percentage (44%). Medium relief was mostly boulder and bedrock habitat (37% and 42% respectively). High relief was relatively rare in our survey, and the substrates were almost evenly distributed with the exception of cobble which was also rare in our survey (less than 4%). [[this whole section refers to a figure that you did not include among your figures! Otherwise good discussion of the habitat characterization to set the stage for the other results]]
Species Presence and Substrate Types
For certain species there was indeed a greater association to specific substrate types than would be expected by chance. 18 groups were found to have strong substrate associations (Figure 3).
Notably Diopatra ornate/ Chaetopterus which are both tube worms showed a strong positive association with sand and strong negative associations with all other substrates. Macrocystis pyrifera holdfasts on the other hand showed a strong positive association with bedrock and a strong negative association with sand. [[good level of detail with these examples]]
The strawberry anemone Corynactis californica showed a strong [positive?] association with bedrock. Moreover, the cup corals also showed a strong positive association with bedrock as well as a strong negative association with sand.
Both articulated and encrusting coralline algae showed strong positive associations with hard substrates (boulder, and boulder and bedrock respectively). Almost all the red algae sampled showed some association with a specific substrate type (only turf did not). All groups of red algae sampled, except for lacy red algae, showed strong positive associations with the hard substrates (boulder and bedrock) and strong negative associations with sand. Lacy red algae instead showed a strong positive association with sand.
Colonial tunicates and barnacles both showed strong positive associations with bedrock and strong negative associations with sand. Sponges showed a strong negative association with sand. Bryozoans showed a strong positive association with bedrock.
Moderate strength associations were also found, however these were not included in our results. [[why, insignificant?]]
Species Presence and Relief
For several species in our survey (11), we found patterns of association between species type and relief (Figure 4). Most notably cup corals showed an extreme strong positive association with high relief habitat which is even more notable considering that high relief was only 6% of the surveyed habitat.
Articulated and crustose coralline algae had the same association patterns with strong positive association with medium relief and strong negative associations with flat relief.
The tubeworms Phragmatopoma californica and Diopatra ornate/ Chaetopterus also both showed relief associations. Ornate tubeworms showed a strong positive association with flat relief and a negative association with medium relief. Phragmatopoma, on the other hand showed a strong positive association with the relatively rare high relief.
Several algae also showed associations with specific types of relief. Dictyoneurum californicum showed a strong positive association with shallow relief areas. Of the red algae, leafy algae showed a very strong positive association with medium relief, and like branching and encrusting red algae, it showed a strong negative association with flat relief habitat. [[perhaps you could reduce the level of detail here in the future, or organize it so that it flows better]]
Several moderate strength associations also existed for other groups, but these are not included in the results because we feel that the strong associations are more robust. [[better explanation than in the previous section]]
Difference in Association Strengths
We also hypothesized that there would be a difference in the general strengths of associations. Indeed, of the patterns of associations that were evident in the data, the association strengths were variable for different species. Moreover, some species showed strong associations to specific substrates while others only showed strong associations to certain classes of relief. However, some species showed strong associations to both a specific substrate and a specific relief. For example, both types of coralline algae as well as leafy red algae showed strong associations to medium relief boulder habitats. Cup corals showed a strong association to high relief bedrock habitats. The ornate tube worm Diopatra ornate / Chaetopterus showed strong associations specifically to shallow relief sandy habitats. The summary of strong positive associations can be found in Table 2.
Several groups showed only weak associations. Barnacles showed no relief associations, for example, and general anemones showed no strong substrate associations. [[this whole hypothesis section has an appropriate level of detail.
Discussion
[[18/22 - You have all the essential elements here, but you could potentially go into a little more detail with respect to each of the hypotheses next time around, and use the scientific literature to put your study in the context of past work (i.e. compare your results to other similar studies)]]
With this study we tested three separate hypotheses: 1) Some species in kelp forest ecosystems do associate with certain substrates 2) Associations are also observable between specific species and relief 3) These associations do vary in strength depending on species. All three hypotheses were supported by our data with 15 groups showing strong associations with substrate and 9 groups showing strong associations with relief. 5 groups showed strong associations to both a specific substrate and a specific relief.
All the strong associations noted here make sense in the light of known life history characteristics for these organisms. For example, barnacles showed a strong association to bedrock, which is to be expected knowing that barnacles require hard substrate for attachment and metamorphosis (Buschbaum 2001). Cup corals were found to have strong associations with high relief bedrock habitats, and this group is known to be abundant on vertical rock walls (Bruno and Witman 1996). Live Macrocystis pyrifera holdfasts were found to strongly associate with bedrock as expected because Macrocystis can only persist when attach to stable, hard substrates, and it requires rock substrate to recruit (Deysher et al. 2003, Edwards 2003). The associations between Diopatra ornata / Chaetopterus and low relief, sandy areas have also been noted in previous studies where they are said to dominate sandy regions(Hardy 1973). Therefore the associations found in this study are supported by previous research done on the life histories of the surveyed organisms. This accordance supports the validity of our results.