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1 Introduction: SCUBA Kelp Report

The importance of large seaweeds, or macroalgae, in coastal ecosystems cannot be understated. Distributed worldwide, they form the base of many marine food webs, provide habitat for a diverse collection of species across many life stages, and comprise some of the most productive marine ecosystems in our oceans (Duarte 2017; Lefcheck et al. 2019; Seitz et al. 2014; Krause-Jensen and Duarte 2016). Macroalgae form mosaics of habitat above the tide line, as well as in deeper subtidal waters. In Oregon there are more than 50 common low intertidal and subtidal macroalgal species that are used as shelter or food by ecologically and commercially important species including rockfish, salmon, sea urchins, and abalone (Lefcheck et al. 2019; Seitz et al. 2014; Krieg, Menge, and Lubchenco 2019).

While much research has described the diversity and ecology of intertidal macroalgae in Oregon, there has been relatively little investigation into subtidal macroalgal communities, which potentially comprise a large portion of the habitable coastline (B. A. Menge et al. 2005; B. Menge et al. 1993; Bracken and Nielsen 2004). This is due, in large part, to the logistical difficulties of accessing near-shore submerged habitat exposed to the open ocean. Assumptions about subtidal macroalgal diversity in Oregon have therefore been primarily based on intertidal algal observations across the coast, which are much more robust and have been summarized in numerous places (Krieg, Menge, and Lubchenco 2019). Prior to the formation of the Oregon Marine Reserves monitoring program in 2010, the only data available on subtidal macroalgal communities came from disparate sources. These data included approximately 50 SCUBA surveys by the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) from 2001-2004 (Carr et al. 2020), a contracted benthic resources summary by The Port Orford Ocean Resources Team (POORT) and ODFW in 2009, and satellite imagery targeting canopy-forming kelps in Oregon collected semimonthly since 1984 that has only recently been synthesized (Hamilton et al. 2020). The remote-sensing data synthesis in particular is useful as it provides a continuous record of kelp cover on the Oregon Coast for the last 35 years, however, it targets only the large canopy forming kelp Nereocystis luetkeana leaving many sub-canopy species unaccounted for. While these historical surveys capture snapshots of algal communities on a broad scale, they lack continuity in the case of the PISCO data, algal abundance in the POORT report (presence/absence only), and assemblage-level accounting in the case of the satellite data. What is needed is a continuous, fine-scale multi-species inventory of subtidal algal resources along the Oregon Coast.

Although global canopy kelps are in decline, there is evidence that Oregon’s canopy kelp communities have increased in area since 2014, or at least remained stable (Krumhansl et al. 2016; Hamilton et al. 2020). Yet the state and trajectory of Oregon’s subtidal algal communities which are associated with these canopy kelps is unknown. Warming sea surface temperatures and increasing sea urchin populations have been linked with large-scale macroalgal declines on the West Coast (Rogers-Bennett and Catton 2019). This speaks to an urgency to characterize our local macroalgal populations, as Oregon is in the transition zone between recently decimated kelp populations to the south, and more stable populations to the north (Beas-Luna et al. 2020; Pfister, Berry, and Mumford 2017). In addition, macroalgal communities have been shown to have differential responses to upwelling depending on the strength and duration of the event (Hessing-Lewis and Hacker 2013). As patterns of upwelling along the Oregon coast continue to shift with climate change, it is vital to implement long-term, targeted monitoring of Oregon’s subtidal algal resources to inform the state of these valuable macroalgal communities and how they might respond (Rykaczewski et al. 2015).

The goal of the ODFW Marine Reserves Ecological Monitoring program is to provide such long-term monitoring to track changing nearshore communities over time. The reserves were put in place with the expectation of preserving biodiversity and resilience of the coastal ecosystem. While systems such as these have been effective for fish and invertebrate communities in many areas around the world, less is known about their effects on macroalgal assemblages (Molloy, McLean, and Côté 2009; Halpern 2003). Studies suggest that it may be difficult to detect community-wide algal trends even over a decade or more of protection, although targeting focal species may provide more answers than simply considering total biomass or other gross indicators of production (Medrano et al. 2020; Barrett, Buxton, and Edgar 2009).

As a first step to implementing long-term monitoring of the marine reserves’ and associated comparison areas’ marine flora and fauna, ODFW contracted CA-based PISCO divers to start benthic SCUBA surveys in 2010 and 2011 at the Redfish Rocks and Otter Rock Marine Reserves. These surveys included a targeted kelp swath survey – focused on commonly observed kelp species (brown algaes) - and a benthic habitat survey (uniform point count (UPC)) focused on broad structural groups of mostly red algaes). After this initial survey effort, it was determined that contracting PISCO to conduct future surveys was not a feasible long-term strategy, so ODFW worked with PISCO and local partners to build a volunteer dive program in Oregon based on PISCO methods. Starting in 2013, the Oregon Marine Reserves (ORMR) volunteer dive team began collecting monitoring data targeting macroalgae, fish, and other associated invertebrates. The Marine Reserve Program and local partners have worked hard to sustain the pool of well-trained volunteer divers that currently collect data at four of the five marine reserve (Cape Perpetua has no hard bottom habitat in diveable depths).

The data summarized in this report are from the kelp swath surveys, for data on benthic habitat and cover from UPC surveys, please see the SCUBA habitat and cover appendices for the Redfish Rocks, Otter Rock, Cascade Head and Cape Falcon Marine Reserves. The kelp swath surveys target several common taxa identified to genera or species level including: Alaria marginata, Costaria costata, Desmarestia sp., Saccharina latissima, Laminaria setchellii, Nereocystis luetkeana, Pleurophycus gardneri, and Pterygophora californica. Of these, the OFDW Marine Reserves program selected Nereocystis luetkeana and Pterygophora californica as focal species based on their ecological, economic or management importance. For more information please refer to the (Update) Methods Appendix detailing focal species selection. These data are a starting point to describe diversity, abundance, and distribution of subtidal Oregon kelps, however, they are limited in their descriptions due to the depths, spatial extent, and temporally irregular intervals at which they were conducted.

1.1 Knowledge Gaps

Given the dearth of information available on the diversity and distribution of subtidal macroalgal communities along the Oregon Coast, there are several key knowledge gaps that can be prioritized to provide information as a starting place to create a clearer picture of the state of these communities. These gaps include:

1. The abundance and distribution of key subtidal macroalgae. This includes canopy kelps as well as perennial sub-canopy species.
2. The stability of macroalgal abundance and distribution through time. Where do we find macroalgae, and are assemblages of species consistent across years?
3. Associations between fish, invertebrates, and macroalgal habitats. Do we see associated changes in animal communities associated with macroalgae? Do these associations change across space and through time?
4. The overall diversity of subtidal macroalgae. What is the overall diversity of all subtidal macroalgae in Oregon?
5. The oceanographic, climatic, and ecological factors controlling macroalgal diversity, composition, and abundance. There are many potential drivers of macroalgal community state that are likely operating across multiple scales (Lamy et al. 2018; Conser and Shanks 2019).

The first three gaps are being partially addressed by by the OR Marine Reserves monitoring program, though methods can be streamlined, augmented, and targeted from lessons learned since monitoring of the reserves began. The last two are opportunities for future work that could be addressed though various means, including ‘bio-blitz’-style survey efforts, DNA analysis, and modeling.

1.2 Research Questions

• What kelp species have been observed at each marine reserve and comparison area?
• How have these kelp communities changed over time?

2 Takeaways

Here we present the major takeaways from our SCUBA kelp swath analyses across Oregon’s Marine Reserves.

All targeted kelp swath species have been observed across the marine reserves, but their presence varied among sites and years.

Over the course of the Marine Reserve Monitoring Program all major groups of kelps targeted–including ‘focal species’ (N. luetkeana, P. californica) and other species of interest (Desmarestia sp., C. costata, L. setchellii, S. latissima, and A. marginata)–were detected, although the detection of those species varied among marine reserves, comparison areas, and years. The highest total counts of kelps within a marine reserve totaled across all years were found at Otter Rock, followed by Redfish Rocks and Cascade Head. No kelps were detected at Cape Falcon. P. californica and A. marginata are found almost exclusively in the shallow subtidal <10 meters depth so it’s not surprising that they were not frequently detected at any of the sites.

Monitoring data suggest declines over time, but likely attributable to methodological shifts, not true biological changes.

Summary data from both the Redfish Rocks Marine Reserve and Otter Rock Marine Reserve suggest precipitous kelp declines between 2011 and later survey years. However, the low detection rate of kelp in later years and generally shallower transects (half the depth at Otter Rock) in earlier years (2010-2011) do not allow us to rule out methodological differences causing the declines observed. In general, a decline was detected at Cascade Head as well, but the low counts of kelps, even in earlier years, do not allow us to draw any conclusions. No kelps were detected at Cape Falcon in any survey so trends cannot be determined. At the Otter Rock Marine Reserve, the early PISCO surveys counted 3,136 kelp observations over two years, whereas the later two survey years counted only 107 individuals. If we compare the early two years to the later two years, we noted a difference in average transect depth, where the 2010-2011 transects were on average five meters shallower than the 2017-2019 transects. At Redfish Rocks Marine Reserve, we also observe very low detection rates of kelp in the later two years of surveys (2015, 2019), compared to the earlier years (2010, 2011). While the differences in depth between these years was not significant, safety concerns of diving in the open ocean limited access to kelp beds in these later years (L. Aylesworth, pers.comm). It is possible that the results may reflect a genuine decline in N. luetkeana in both regions, though other regional data on N. luetkeana populations through 2018 suggests they are increasing or stable, indicating there may be methodological differences at play (Hamilton et al. 2020). Furthermore, there are no observations in the literature of any decline on the order of what is observed in the data, if these were indeed true biological declines. Macroalgal communities up until 2010 had been fairly stable in estuaries across Oregon, though macroalgae are sensitive to temperature and the marine heatwave of 2015 could have negatively impacted these populations (Hessing-Lewis and Hacker 2013; Straub et al. 2019), this is not supported by other regional N. luetkeana data (Hamilton et al. 2020).

Adapting SCUBA surveys to open ocean conditions in Oregon limits our ability to survey prime subtidal kelp habitat.

On the surface, it appears there was a drastic decline in kelp detection between initial survey efforts and subsequent survey years for all sites except Cape Falcon where no kelp was detected. However, with the transition from the PISCO dive team to an Oregon-based volunteer dive team, surveys were adjusted for safety concerns around live-boating in nearshore conditions. This resulted in requiring a down-line divers must use to descend/ascend, avoiding the shallowest target depth (5 m), and avoiding N. luetkeana beds. Algal communities are concentrated in the shallows to access light for photosynthesis; surveys in later years moved away from targeting the shallower 5 m depths at which we’d expect to find dense nearshore macroalgal communities along the Oregon coast. Of the remaining two target depths (12.5 and 20 m) only one of those has the potential for algae communities as the photic zone is frequently shallower than 20 m during summer months (Steneck and Dethier 1994; Small and Menzies 1981). Safety concerns of diving at such shallow depths in exposed open ocean environments, and the requirement to maintain contact with a descent line limited access to prime subtidal algal habitats at some sites occasionally, and at other sites entirely.

These safety restrictions led to targeting the edges of N. luetkeana beds or other hard bottom substrate without N. luetkeana beds at the Otter Rock and Redfish Rocks Marine Reserves. The implementation of monitoring efforts at the Cascade Head Marine Reserve (2014) and Cape Falcon Marine Reserve (2016) provided additional challenges, as these sites are not known to contain the rich N. luetkeana beds of the other two marine reserve sites, and targeting the edge of such beds was not possible. These factors combined with the irregular sampling intervals and randomly stratified transect locations make it difficult to draw any conclusions about the state of kelp populations over time.

For these reasons, the program is not currently able to detect change over time in kelp communities apart from generalized presence/absence metrics. These data should be considered snapshots of limited transects at a particular place in time, though they provide a starting place for future survey work.

While abiotic characteristics are generally similar between reserves and comparison areas, more data is necessary to assess the suitability from a kelp perspective.

From the kelp monitoring data we cannot say whether or not the comparison areas are appropriate reference sites for assessing change over time at the marine reserves. The ODFW Marine Reserves program did select comparison areas based on similar abiotic conditions (depth range, size, habitat types, oceanographic conditions), but further data is required to determine if comparison areas are appropriate from a kelp perspective.

While methodological shifts in kelp monitoring proved to be challenging for analyses, data provides a ‘snapshot’ of subtidal kelps in Oregon.

The challenges of our kelp data have been outlined above, but we were able to collect some baseline data that provides a snapshot of more rarely sampled kelps, especially subcanopy kelps. With the recommendations below our program aims to improve the consistency of our kelp data collection.

2.1 Recommendations

A move towards permanent transects for kelp surveys is needed to confidently detect future trends in brown algae with SCUBA surveys.

Algal communities can be ephemeral, and random stratified selection of survey sites, particularly those that encompass substrate that we would not expect to have associated macroalgal communities, may not be representative of the population dynamics at play. Therefore, the installation of several permanent transects along appropriate substrate (i.e. - bedrock, consolidated rock) in extant kelp habitat will allow temporal variation to be tracked. These can be supplemented occasionally by additional surveys for annual ‘snapshots’ of the community.

Eliminate 20 m kelp surveys, reconsider adding 5 m sites where appropriate.

Kelp communities are concentrated in the shallows to access light for photosynthesis. The depths of the surveys (5 m, 12.5 m, 20m) only capture two depth contours at which we’d expect to find dense nearshore macroalgal communities along the Oregon coast (5 m, 12.5 m), as the photic zone is frequently shallower than 20 m during summer months (Steneck and Dethier 1994; Small and Menzies 1981). To address this shortcoming, more shallow surveys should be conducted to access the likely range of canopy, and subcanopy kelp Additionally, future analysis could focus on 12.5 m data only to explore trends, with this depth-bin having the most overlap between PISCO and ODFW surveys.

Conduct surveys during peak of kelp production season (July – August).

The lack of consistent sampling across years poses a challenge in detecting patterns of kelp community dynamics. Surveys along permanent transects should be conducted at a minimum of once per year, preferably at the peak of macroalgal production season (June-August) as is standard in other macroalgal monitoring programs (Byrnes and Reed 2018; Pfister, Berry, and Mumford 2017) to ensure more comparability from year to year and increases the likelihood of sampling the full kelp community.

Consider adding in UAV surveys at Redfish Rocks and Otter Rock Marine Reserves to improve tracking of the focal species, N. luetkeana.

Additional surveys of N. luetkeana, one of the ‘focal’ species identified by ODFW for monitoring, can also be tracked using unmanned aerial vehicle (UAV, aka drone) technology. Drones have become and increasingly affordable and reliable way to quantify canopy kelps such as N. luetkeana in nearshore areas (Tait et al. 2019; Thompson 2021). These remote sensing techniques has also been used to monitor many types of marine vegetation and can be accomplished by surface crew concurrently with SCUBA transects and other shore- or boat-based surveys.

3 SCUBA Kelp Methods

3.1 Field Surveys

All dive surveys were conducted from a boat within the Oregon Marine Reserve System and in associated comparison areas. The overall survey design for the initial surveys consists of multiple survey sites on shallow (< 20m depth) rocky reef habitat within each reserve area and corresponding comparison sites outside of the reserve. Comparison areas outside of each reserve were chosen based on similar depths, habitat, size, oceanographic conditions and historical fishing pressure similar to each reserve. For more detail on the selection of comparison areas please see the SCUBA Methods Appendix. In 2013, PISCO methods and datasheets were modified to adjust for common Oregon species, frequently challenging sea states, and safety needs given the volunteer diver team (avoiding shallower depths, avoiding kelp bed locations, and requiring downlines).

Kelp swath surveys were conducted concurrently with invertebrate and benthic habitat and cover surveys where depths of 12.5 and 20 m were targeted . Once the site was located with GPS, a video lander was deployed from the boat with a buoyed downline. Divers would descend on the downline and use the lander as the anchor-point for their transect tapes (a required OSU safety requirement). A visibility check was conducted on each dive with a minimum acceptable visibility of 1 m. A 30 m transect was laid along contiguous rocky substrate following the depth contour of interest and following the natural curves of the substrate. Transect depths were kept within 1.5 m of the target depth and any changes in substrate type were noted during data collection. Transects did not overlap with other transects and the surveys were aborted if more than 5 continuous meters of sand were encountered. Divers noted all algal species of interest within 1 m on either side of the transect including:

• Nereocystis luetkeana (>1 m stipe length)
• Pterygophora californica (>30 cm stipe length)
• Pleurophycus gardneri (>30 cm stipe length)
• Laminaria setchellii / Saccharina latissima¹ (>30 cm stipe length)
• Costaria costata (any size)
• Desmarestia sp. (any size)
• Alaria marginata (any size)

Algae were subsampled if encountered in excess of 30 individuals per 10 m-swath segment. Subsampling ended at the completion of each swath column (i.e., every 10m), and regular counting resumed.

3.2 Data Analysis

All data used in this analysis were complete 30 meter transects (i.e. equal area surveyed), thus abundance is explored at as counts. Survey effort and basic abundance relationships among sites, years, and species were visualized in boxplots and tables. Higher-level statistical analysis proved difficult due to the sparse nature of the data (zero-rich dataset) and irregular sampling intervals (skipped years, unbalanced sampling effort). While simple statistical comparisons were made between dive parameters with ANOVA and post-hoc Tukey tests, any higher-level analyses with factors of interest (site, year, reserve vs. comparison area) could only be achieved by pooling data sets or comparing data that were not statistically robust, which was not a realistic or informative line of inquiry. As such, descriptive visualizations were created to suggest trends and provide a starting point for future survey design refinement. Because we adapted original PISCO protocols for long-term use in Oregon nearshore water, we decided to test data collected with the original PISCO protocol against those collected with the modified Oregon Marine Reserves (ORMR) method. To determine if overall mean transect depth was different between the protocols among sites a multi-way ANOVA was run. Significant differences in site-specific depths were detected using a post-hoc Tukey test. All survey and species counts were visualized in R using the tidyverse, gt, and viridis packages (R Core Team 2020; Iannone, Cheng, and Schloerke 2020; Wickham et al. 2019; Garnier et al. 2021).

4 SCUBA Kelp Results

4.1 Data Overview

Between 2010 and 2019 there were a total of 254 kelp swath survey transects completed in the Oregon Marine Reserves and associated comparison areas (Table 1). Kelp was counted on 102 of the 254 total transects (~40% overall detection rate) at every site except Cape Falcon, where no kelp was detected.

Reserves and their associated comparison areas were surveyed annually on a rotating basis. Three of the reserves have four years of survey data (Redfish Rocks (2010, 2011, 2015, 2019); Otter Rock (2010, 2011, 2017, 2019); Cascade Head (2013, 2014, 2017, 2018)), and despite several efforts over multiple years, only one year of survey data is available for Cape Falcon (2017). Kelp transects within a single reserve and comparison area ranged from 1-31 in a single year, with an average of 20 transects conducted per site on years when it was surveyed.

4.1.1 Protocol Comparison

The PISCO team conducted 70 kelp surveys between 2010 and 2011, while the OR Marine Reserve (ORMR) dive team conducted 184 surveys between 2013 and 2019. Overall, kelp was detected on 67 of the PISCO surveys (96% detection) and 35 of the ORMR surveys (19% detection). The PISCO surveys were also shallower on average by 3.9 m, and an interaction between protocol followed and site surveyed was detected (ODFW: 14.5 m, PISCO: 10.6 m; Figure 1; multi-way ANOVA, F(3, 240) = 5.28, p < 0.01; see Data By Site).

Table 1: Number of SCUBA kelp swath transects per year across all regions including marine reserves and comparison areas completed as part of Marine Reserves Ecological Monitoring. All surveys conducted in 2010-2011 followed original PISCO dive protocols. Those from 2013 onwards followed a modified ORMR protocol.

Fig. 1: Average depth of kelp swath transects between ODFW and PISCO survey teams.

4.2 Data By Site

4.2.1 Redfish Rocks

4.2.1.1 Survey Maps

4.2.1.1.1 Redfish Rocks Marine Reserve

Fig. 2: Map of SCUBA transect locations at Redfish Rocks Marine Reserve

4.2.1.1.2 Humbug Comparison Area

Fig. 2: Map of SCUBA transect locations at Humbug Comparison Area

4.2.1.2 Results

A total of 75 kelp transects were conducted at Redfish Rocks, and Humbug Comparison Area over four years (2010, 2011, 2015, 2019; Table 2, Figure 3).

Table 2: Total number of SCUBA kelp swath transects conducted in Redfish Rocks Marine Reserve and Humbug Comparison Area between 2010 and 2019.

Fig. 3: Total SCUBA kelp swath surveys conducted by year in the Redfish Rocks Marine Reserve (dark blue), and Humbug Comparison Area (lighter blue).

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4.2.1.2.1 Protocol Comparison

Mean depths of PISCO and ORMR protocols differed between the marine reserve and comparison area, though none of these differences were statistically significant (Table 3).

Table 3: Mean depth of SCUBA kelp swath transects conducted with PISCO protocols (2010, 2011) and modified OR (ORMR) protocols (2015, 2019). None of the depth comparisons between protocols or sites were statistically significant (post-hoc Tukey, p > 0.05).

Across all years and protocols the focal species N. luetkeana was the most abundant alga of all species surveyed within the Redfish Rocks Marine Reserve and in the Humbug Comparison Area (Figure 4). Focal species P. californica was detected also in three of the four survey years, along with associated species L. setchellii and P. gardneri. No kelp was detected inside or outside the reserve in 2019.

Fig. 4: Kelp species counts observed in the Redfish Marine Rocks Reserve and Humbug Comparison Area (combined) by year.

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4.2.1.3 Takeaways

Mean depth of transects did not differ significantly between the PISCO and ORMR surveys.

The focal species N. luetkeana and P. californica, along with other common species P. gardneri and L. setchellii were detected in the marine reserve between 2010-2015, but not detected at all in 2019. Observations in the comparison area followed a similar pattern.

Observed declines in N. luetkeana may be due to methodological differences between the PISCO and ORMR surveys. Specifically the avoidance of N. luetkeana beds by ORMR due to safety considerations.

The focal species N. luetkeana was found in relatively high abundance within the Redfish Rocks Marine Reserve in 2010 and 2011 along with associated species P. gardneri and L. setchellii, although L. setchellii was found less frequently in 2011 with a total decline in detection of 76% (Table 4, Figure 5). Focal species P. californica peaked in 2015 with 139 individuals counted, but was not detected at all in the following survey year of 2019. In fact, no kelp was detected at Redfish Rocks Marine Reserve at all in 2019.

Table 4: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Redfish Rocks Marine Reserve by year. Total counts are summed across 30 m transects.

A total count of 1013 individual N. luetkeana were found in the Humbug Comparison Area in 2011, the second highest detection of N. luetkeana across all years and sites second only to Otter Rock Marine Reserve in the same year, and the highest count within a comparison area (Table 5, Figure 5). Algal detection was reduced greatly in 2015 and 2019, similar to the marine reserve, however none of the focal species P. californica was detected in Humbug Comparison Areas as it was in the marine reserve. Overall, kelp detection between the marine reserve and comparison areas tended to be species-specific in terms of abundance within and across years. The only consistent pattern was the drastic reduction in detection between 2010/11 and 2015/19. The common species Desmarestia sp. was also detected in small quantities in 2015/19.

Table 5: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Humbug Comparison Area by year. Total counts are summed across 30 m transects.

Fig. 5: Kelp species counts observed in Redfish Rocks Marine Reserve and Humbug Comparison Area from SCUBA kelp swath surveys by year. Total counts are summed across 30 m transects.

4.2.2 Otter Rock

4.2.2.1 Survey Maps

4.2.2.1.1 Otter Rock

Fig. 6: Map of SCUBA transect locations at Otter Rock Marine Reserve

4.2.2.2 Results

A total of 63 transects were conducted at Otter Rock over four years of survey effort (2010, 2011, 2017, 2019; Table 6, Figure 7).

Table 6: Total number of SCUBA kelp swath transects conducted in Otter Rock Marine Reserve and Cape Foulweather Comparison Area between 2010 and 2019.

Fig. 7: Total SCUBA kelp swath surveys conducted by year in the Otter Rock Marine Reserve (dark blue), and Cape Foulweather Comparison Area (lighter blue).

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4.2.2.2.1 Protocol Comparison

Mean depths of PISCO and ODFW transects differed significantly among the Marine Reserve and Comparison Area transects. PISCO transects were reliably shallower than the ODFW transects with a mean difference of 5.57 m within the Marine Reserve (n = 41) and 7.05 m in the Cape Foulweather Comparison Area (n = 22; Table 7).

Table 7: Mean depth of kelp surveys conducted at Otter Rock by PISCO (2010, 2011) and modified OR (ORMR) protocols (2017, 2019). Depths between teams were different in both the Marine Reserve and Comparison Area (post-hoc Tukey, ** p < 0.001, *** p < 0.0001).

Across all years the common species L. setchellii and S. latissima were the most consistently detected at Otter Rock, while focal species P. californica and N. luetkeana were the most abundant overall in 2010 and 2011 (Fig 8). This was also the only site where the alga Costaria costata was found inside or outside the Marine Reserve system.

Fig. 8: Kelp species counts observed in the Otter Rock Marine Reserve and Cape Foulweather Comparison Area (combined) by year.

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4.2.2.3 Takeaways

Transect depths were significantly shallower using the PISCO protocol (2010, 2011) by 5.57 m and 7.05 m in the marine reserve and comparison area respectively.

The Cape Foulweather Comparison Area was the only site among all the regions surveyed where the alga Costaria costata was detected (2011, 2019).

Kelp detection was greater by an order of magnitude in the marine reserve than in the associated comparison area in 2011. This was driven primarily by N. luetkeana and P. californica. While detection remained higher within the marine reserve in 2017 and 2019, overall counts were greatly reduced.

Inside the Otter Rock Marine Reserve the focal species P. californica was detected in every survey year. Likewise, the common alga P. gardneri was also detected each year, albeit in much lower quantities (Table 8, Figure 9). Within the marine reserve N. luetkeana was detected at its highest level with a count of 1702 individuals across 14 transects. The alga Desmarestia sp. was also detected in 2017.

Table 8: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Otter Rock Marine Reserve by year. Total counts are summed across 30 m transects.

In the Cape Foulweather Comparison Area both N. luetkeana and P. californica were detected in 2011, though P. californica was detected at lower levels than in the marine reserve the same year (Table 9, Figure 9). Only a single observation of P. californica was made in 2017 and 2019, and N. luetkeana was not detected at all after 2011. Other species including P. gardneri, Desmarestia sp., C. costata, L. setchellii, and S. latissima were detected at very low level sporadically across the 2011 and 2019 survey years. No kelp whatsoever was detected at Cape Foulweather Comparison Area in 2017.

Table 9: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Cape Foulweather Comparison Area by year. Total counts are summed across 30 m transects.

Fig. 9: Kelp species counts observed in Otter Rock Marine Reserve and Cape Foulweather Comparison Area from SCUBA algal swath surveys by year. Total counts are summed across 30 m transects.

4.2.3 Cascade Head

4.2.3.1 Survey Maps

4.2.3.1.1 Cascade Head Marine Reserve

Fig. 10: Map of SCUBA transect locations at Cascade Head Marine Reserve

4.2.3.1.2 Schooner Creek Comparison Area

Fig. 10: Map of SCUBA transect locations at Schooner Creek Comparison Area

4.2.3.1.3 Cavalier Comparison Area

Fig. 10: Map of SCUBA transect locations at Cavalier Comparison Area

4.2.3.2 Results

A total of 88 transects were conducted at Cascade Head over four years of sampling effort (2013, 2014, 2017, 2018; Table 10, Figure 11).

Table 10: Total number of kelp transects conducted in Cascade Head Marine Reserve and Schooner Creek and Cavalier Comparison Areas between 2013 and 2018.

Fig. 11: Total SCUBA kelp swath surveys conducted by year in the Cascade Head Marine Reserve (dark blue), and comparison areas (lighter blue).

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4.2.3.2.1 Protocol Comparison

Cascade Head Marine Reserve and associated comparison areas were not surveyed with the original PISCO protocols as other sites in 2010 and 2011. To detect if there are mean differences in transect depths across years, ODFW transects were binned into either a 2013-2014 or 2017-2018 category. These binned year groups were tested for differences in the same way as the PISCO and ORMR protocols in other marine reserves and comparison areas. Mean depths of ODFW transects differed significantly across years, but not across sites within years (Table 11). The 2013-2014 transects were 3.98 m shallower on average than the 2017-2018 transects.

Table 11: Mean depth of kelp surveys conducted at Cascade Head by the Marine Reserve Research Dive Team (ORMR) binned into 2013-2014 and 2017-2018 groups. Mean depth was different between years, but not among sites (ANOVA, df = 1, F = 14.010, ** p < 0.001).

Across all years inside and outside the Cascade Head Marine Reserve the most common kelp detected were Desmarestia sp., L. setchellii, N. luetkeana, and P. gardneri (Figure 12). Both focal species (N luetkeana and P. californica) were only detected in 2017, and a gradual decrease in overall detection of all kelp can be seen between 2013 and 2018.

Fig. 12: Kelp species counts observed in the Cascade Head Reserve and comparison areas (combined) by year.

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4.2.3.3 Takeaways

Surveys were consistenly shallower in 2013-2014 than in 2017-2018, though no clear pattern in kelp detection other than an overall decline in 2018 was apparent.

The focal species N. luetkeana and P. californica were only detected in the region in 2017 within the marine reserve.

The alga Desmarestia sp. was detected at the highest rate across all years and regions within the Cavalier Comparison Area at 71 individuals counted in 2013.

Within the Cascade Head Marine Reserve the focal species N. luetkeana and P. californica were only detected in 2017, while the other algae P. gardneri and L. setchellii/S. latissima were only detected in small quantities in 2014/17 and 2017/18 respectively (Table 12; Figure 13). N. luetkeana had the highest detection count at 45, which was found on just two transects. No other kelp species were detected in any survey year.

Table 12: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Cascade Head Marine Reserve by year. Total counts are summed across 30 m transects.

The only species detected at the Cavalier and Schooner Creek Comparison Areas were P. gardneri, Desmarestia sp., L. setchelli/S. latissima (Table 13, Figure 13). Detection rate were generally higher in 2013-14 with 150 total counts of kelp across all comparison areas, but only 2 detections in 2017-18.

Table 13: Abundance of focal species (N. luetkeana, P. californica) and other common kelp from SCUBA swath surveys within the Cavalier and Schooner Creek Comparison Areas by year. Total counts are summed across 30 m transects.

Figure 13: Kelp species counts observed in Cascade Head Marine Reserve and associated comparison areas from SCUBA kelp swath surveys by year. Total counts are summed across 30 m transects.

4.2.4 Cape Falcon

4.2.4.1 Survey Maps

4.2.4.1.1 Cape Falcon Marine Reserve

Fig. 14: Map of SCUBA transect locations at Cape Falcon Marine Reserve

4.2.4.1.2 Low Fishing Pressure Comparison Area

Fig. 14: Map of SCUBA transect locations at Low Fishing Pressure Comparison Area

4.2.4.1.3 Moderate Fishing Pressure Comparison Area

Fig. 14: Map of SCUBA transect locations at Moderate Fishing Pressure Comparison Area

4.2.4.1.4 High Fishing Pressure Comparison Area

Fig. 14: Map of SCUBA transect locations at High Fishing Pressure Comparison Area

4.2.4.2 Results

A total of 28 transects were conducted at Cape Falcon over one year of sampling effort (2017; Table 14, Figure 15), despite multiple attempts over several years to reach the Marine Reserve and comparison areas.

Table 14: Total number of SCUBA kelp swath transects conducted in Cape Falcon Marine Reserve and Low Fishing Pressure and Moderate Fishing Pressure Comparison Areas since surveys began.

Fig. 15: Total SCUBA kelp swath surveys conducted by year in the Cape Falcon Marine Reserve (dark blue), and associated comparison areas (lighter blue).

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4.2.4.2.1 Protocol Comparison

Mean depths of transects were not significantly different among the marine reserve and comparison area transects with an overall mean depth of 14.2 m (Table 15).

Table 15: Mean depth of kelp surveys conducted at Cape Falcon by the Marine Reserve Research Dive Team (ORMR) separated into the Marine Reserve and associated comparison areas. Mean depth was not different among the marine reserve and comparison areas (post-hoc Tukey Test, p > 0.05).

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4.2.4.3 Takeaways

Due to the logistical difficulties of accessing Cape Falcon by SCUBA, kelp swath surveys were only conducted in 2017 within the marine reserve and at associated comparison areas.

Although 28 SCUBA kelp swath surveys were conducted in the region, no kelp was detected on any transect.

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1. Recorded as S. groenlandica, updated for current taxonomy (Lane et al. 2006).↩︎