Pete Raimondi, Mark Carr

Sertic 1

Maya Sertic

Pete Raimondi, Mark Carr

Kelp Forest Ecology

October 18, 2011

Total = 4+24+ 44+40+…

Lit Cited=6

[4] The Effects of Site Exposure on Algal, Invertebrate, and Fish Communities at Point Lobos and Hopkins Marine Sanctuaries

Abstract [24]

[4]Many of the current theories shaping our understanding of marine ecology were born out of spatial comparisons between different sites within a given ecosystem.We were interested in evaluating [4] the effects of turbulence on kelp forest communities within Macrocystis-dominated kelp forests found in central California.We compared 2 sites, Hopkins and Point Lobos, which are similar in most abiotic [4] traits except for their relative exposure to the ocean. While Hopkins is known to be a site unusually well protected from disturbances in the open ocean, Point Lobos is more exposed to turbulent winter storms.[4] To compare the effects that differences in exposure to the ocean have on kelp forest communities, we compared the species compositions of Hopkins and Point Lobos with respect to site and day by with quantitatively collecting surveys of abundance data for 29 species along transects. We found that the [4] species compositions foralgae and invertebrates varied by site, whilethe species composition for fish showed greater variance between different sampling days due to their greater mobility. Fish abundance was also the only category which showed an interaction between site and day. We conclude that [4] exposure to the open ocean does influence the species assemblage at a given site, but that different taxa react to turbulence on different time scales.

Introduction [44]

In trying to detect patterns in nature, ecologists have identified and defined different ecosystems based on the specific biotic and abiotic factors that characterize them. While differences between ecosystems are generally well-defined because their unique traits are used to describe them, differences within ecosystems are variable and notas well defined.It is these differences within ecosystems that researchers study in order to test their hypotheses about the processes responsible for different ecological patterns.

[4, 4]]Many of the current theories shaping our understanding of marine ecology were born out of spatial comparisons between different sites within a given ecosystem. Kelp forests in particular have been used in many studies using spatial comparisons.A comparison of coves inhabited by sea otters and uninhabited by sea otters in the Aleutian Islands helped develop the theory of keystone predators and top-down trophic interactions (Duggins 1980). A comparison of coves exposed to and protected from killer whales in the Aleutian Iislands led to the understanding that transient species can play a key role in community structure (Estes et al. 1998). A comparison of 90 sites from Baja California to Central California revealed that large disturbances, such as El Nino, cause a shift in the factors controlling kelp abundance from within-site local factors to large-scale regional factors (Edwards 2004). A comparison of MPAs and fishing grounds around Tasmania suggested that large individuals in a population fulfill roles in community structure that smaller individuals cannot (Ling et al. 2009). These studies along with many others have helped marine scientists identify the processes that create patterns in kelp forest ecosystems, which has led to a better understanding of community structure and function within kelp forests.

[4, 4]We were interested in the effects that exposure to the open ocean has on community composition in central California kelp forests. Water turbulence and turbidity areis known to shape kelp forests in different regions along the California coast. In relatively calm waters in Central and Southern California, Macrocystis is the prominent canopy-forming alga. This kelp is fast-growing and forms a thick canopy that shades out and can inhibit the growth of other algal species (Reed and Foster 1984). However, it is sensitive to turbulence, and dislodges during more severe winter storms. In northern California, the severity of winter storms limits the distribution of Macrocystis. (Dayton et al. 1984). We were interested in evaluating the effects of turbulence on kelp forest communities within Macrocystis-dominated kelp forests found in central California.

[4]We compared two2 sites, Hopkins and Point Lobos, which are similar in most abiotic traits except that, while Hopkins is known to be a site unusually well protected from disturbances in the open ocean, Point Lobos is more exposed (although this has not been directly testedcompared). To compare the effects that differences in exposure to the ocean have on kelp forest communities, we compared the species compositions of Hopkins and Point Lobos with respect to the following questions: 1) Is there a difference in species composition between Hopkins and Point Lobos? 2) Is there a difference in species composition from day to day for either site? 3) Is there an interaction effect between site and day? To answer these questions, we quantitatively collected abundance data for 29 species at both sites on 2 days. [citations= 4, sci names= 4, quality= 4, length= 4, organization= 4]

Methods [40]

[4]To study the differences in species composition at Hopkins and Point Lobos, we did a conducted quantitative observational surveysstudy, in which we counted the number of individuals for 9 fish species, 7 algal species, and 13 invertebrate species along transects using SCUBA(fig. Table 1). [lists are tables, not figures]

We sampled abundances for the same 29 fish, algae, and invertebrate species at both Hopkins and Point Lobos. Different species were chosen for different reasons. Most of the species we chose to sample are considered characteristic of central Californian kelp forests. We chose some species because they are known to occur at Point Lobos but are not characteristic of the central coast (such as Eisenia). More importantly, we wanted to have a diverse group of sessile and motile species, large and small species, as well as species whose life histories represent open and closed populations. A diverse group of species can help us expand our analysis to include organisms that were not studied but function in a similar way to those that were studied.

Study Sites[12, including spp descriptions above]

Hopkins Marine Station is located at the east end of Lovers Point Marine Reserve and faces east into the Monterey Bay. We did our sampling at the far east end of the marine station, just beyond the offshore rocky outcrop. This area is well protected from the wave action of the open ocean. The water temperature was 54°F on both days. [you should look up and include the lat and lon for the site… has become standard for site descriptions]

We collected our composition data for Point Lobos at the mouth of Whaler’s Cove, a north-facing cove at the southern edge of Carmel Bay, 10 miles south of Hopkins (fig.Figure 2, SIMoN). The cove itself is highly protected from the ocean (Lovejoy 1996), while the mouth of the cove (often referred to as middle reef) is more exposed to the ocean. The water temperature was 51°F on both days; it is typical for the water temperature at Point Lobos to be cooler than at Hopkins (P. Raimondi, pers. comm.).

Otherwise, these two sites are similar to one another. At both sites, the substrate is composed of granite outcrops and boulders interspersed with sandy patches (Paddock and Estes 2000). Both sites are no-take zones in marine protected areas, which means that the species compositions at the sites are not affected by fisheries. [nice citations!! 4]

Are there differences in species composition and abundance by site? [4]

We expected predicted that differences in site exposure would lead to variation in species composition between sites. To test this hypothesis, we estimated the density (number of individuals per 60m2) collected species abundance datavisually observed along 30m transects. At each site, the transects were laid out parallel to one another and perpendicular to a main transect running roughly from north to south. At Hopkins, we laid out seven 30m transects off the main cable at 90° and seven at 270°. The transects were 10m apart from one another. At Point Lobos, we sampled along 14 transects set 5m apart from each other, all pointing headed 90°.We ensured that the variation in transect placement at the two sites did not affect our data by comparing the depth profiles of our dives. Although our transects spanned a greater total distance from east to west at Hopkins (60m) than at Point Lobos (30m), the depth gradients at both sites were not steep, creating a similar depth profile for the 2 sites (fig.Figure 3).

At both sites, we surveyed the most motile organisms, fish, while reeling out the meter tape to avoid disturbing them and potentially affecting our data collection. Paired divers [[I go with this instead of “buddies”… sounds like their just a little too close]] counted fish separately on adjacentEach diver counted fish in a 1m wide by 2m high by 2m long volume (60m3) of water (total volume per transect= 120m3). Each fish was counted only once, regardless of whether it travelled between buddies’ volume parametersone diver’s sampling volume to the other’s. We counted invertebrates and algae in a 1m swath as we returned to the main cable. We counted the number of stipes for each Macrocystis pyrifera plant in our swaths.

We used permanovas PERMANOVAs to test whether there was a real difference in the relative densities of species composition between sites.Data were The permanovas were then 4th root transformed for the analysis to obtain information aboutestimate the percent dissimilarity between sites and the contributions of each species to the dissimilarity. We used permanovas to analyze the differences between sites due to all species combined as well as for each taxon individually (algae, invertebrates, and fish).

[What about generating MDS plots to examine for differences in the structure of each assemblage??]

Are there differences in species composition and abundance within each site from day to day?

We expected not to findpredicted no significant differences in species compositionthe relative density of speciesat each site on the two2 days sampled because of the short time period in between the two2 sampling days. We hypothesized that any variation in species composition with respect to time would be due to differences in fish composition because fish are far more mobile than any of the other species we sampled.

To control for variation in species composition from day to day, we sampled on two2 days, October 11 and October 13, 2011, using the sampling methods described above. [that sentence doesn’t make sense, also… give sampling dates up in the beginning of the Methods section.. same with the following two sentences.] We chose to sample in October, when the kelp forests have had a full summer to regrow from the previous winter’s storms, but before the onset of this year’s storms. Thus, the two sites should be the most similar at this time of year. While the first sampling day was calm and overcast, the second day was sunny with large swell. We used permanovas and their transformations (described above) for all species combined and for each taxon to analyze the differences within sites between days. We also used Variance Components Analysis to assess the relative contributions of 2 potential sources of variance, site and day, to our estimates of fish, algae, and invertebrate abundance. [actually, what this analyses does is compare dates within and across sites… tests for a general “day effect” regardless of site just like the “site effect” is first tested between sites by combining both dates . Then, the next section uses the PERMANOVA to test whether the sites differed in their day-to-day differences (the “site by time” interaction).

Is there an interaction between site and day? Better yet… Do any differences between sites differ between days?

We hypothesized that we may find an interaction between site and day for motile organisms such as fish (mostly affected by fish).To answer this question we analyzed the same permanova as above for an interaction between site and day effects. We also tested for an interaction between site and day for each individual taxon.

Results

The total dissimilarity between Hopkins and Point Lobos was 73%. Overall, we found a strong difference between sites, and no difference within sites between days, but when we separated out analyses by taxa, we found that fish actually varied by day rather than by site.

Differences in species composition by site

For all species combined, there was a strong effect of site on species composition (Fig. 4, permanova: site effect, P=0.001). However, only algae and invertebrates strongly contributed to the difference between sites. Balanophyllia elegans’s contribution to the difference between sites was by far the strongest (31.54%), followed by Pterygophora californica (12.34%).

We found a strong effect of site on the species composition of the algal assemblage (Fig. 5, permanova: site effect, P=0.001). While Pterygophora was the most common algae found at Point Lobos, it was absent at Hopkins, which made its contribution to differences in algae assemblage the strongest (29.43%). Similarly, Eisenia was only found at Point Lobos, although it did not contribute strongly to the difference between sites (8.22%), likely because it was not very common at Point Lobos. At Hopkins, Chondracanthus corymbifera had the highest abundance, and both Dictyoneurum and Dictyoneuropsis were present, but these species were rare or absent at Point Lobos. Macrocystis, which formed the kelp canopy at both sites, was the only algae with similar abundances at both sites (Fig. 6). However, individual Macrocystis plants at Hopkins had more stipes than plants at Point Lobos (Fig 7, Permanova: site effect, P=0.000022).

There was also a difference in invertebrate composition between the 2 sites (Permanova: site effect, P=0.001). Similar species assemblages were seen at both sites, but their abundances differed between sites. Balanophyllia elegans and Asterina miniata were the most abundant species in both sites, but there were many more Balanophyllia individuals at Hopkins than there were at Point Lobos. Pachycerianthus fimbriatus was only seen at Hopkins, and Urticina lofotensis was only seen at Point Lobos (Fig. 8).

Fish composition did not vary by site (Fig. 9, Permanova: site effect, P=0.319). On average, less than 0.5 individuals of any species were seen on each transect, suggesting very low fish densities. Kelp rockfish (Sebastes atrovirens) were the most common fish seen at each site, while gopher rockfish (Sebastes carnatus) and black and yellow rockfish (Sebastes chrysolmelas) were rare at both sites (Fig. 10).

Differences in species composition by day

For all species combined, there was no effect of day on species composition at either site (Fig. 4, permanova: day effect, P=0.382). An evaluation of each taxon individually shows that all of the variance in algae and invertebrate composition is explained by differences in site. However, a higher percent of the variance in fish composition is explained by day than by site (Fig. 11). While algae and invertebrates did not vary by sampling day (Algae: Permanova: P=0.724, Invertebrates: Permanova: P=0.505), fish composition did vary by sampling day ( Fish: permanova: P=0.043). There were a lot fewer fish seen at either site on the second day than on the first day, although this difference was especially apparent at Point Lobos (Fig. 10).

Was there a species interaction by site and day?

Overall, there was no interaction between site and day for all species combined. There was also no species interaction between site and day for algae (algae permanova: site by day, P=0.926) or invertebrates (invertebrate permanova: site by day, P=0.569). There was, however, an interaction between site and day for fish composition (fish permanova: site by day, P=0.015).

Discussion

Although we did not directly test the exposure of the two sites to the open ocean, our results and observations strongly suggest that Point Lobos is in fact more exposed than Hopkins. Whaler’s Cove is unprotected from the north, making it exposed to the swells that commonly come from the north-west. The cooler water temperature is likely due to greater water movement, and mixing of the cold bottom temperatures with the surface water. Our observation that Macrocystis plant at Point Lobos have fewer stipes on average suggests that the plants are ripped out more often, and therefore smaller in size. Finally, an observational comparison of swell at Point Lobos and at Hopkins on the second sampling day made it very clear that Point Lobos was less protected from ocean turbulence than Hopkins (although the storm that occurred on October 12 was not strong enough itself to rip out Macrocystis plants between the 2 sampling days).

Wave exposure does impact community structure in a kelp forest, but it doesn’t impact all taxa equally. There were differences in species compositions of sessile invertebrates and algae between the sites, but these differences in composition did not vary from day to day, suggesting that wave exposure impacts their abundances over a larger time scale. However, fish composition, and abundance especially, did vary from day to day, showing that fish are affected by environmental conditions on a much shorter time scale. We suggest that turbulent conditions cause fish to go into hiding, and thus, fewer fish are seen in the open along transects