ex c SCI Black Abalone Survey Report 2016 2019.pdf

Investigations into recruitment enhancement and recovery of black abalone (Haliotis cracherodii) on San Clemente Island

Nathaniel Fletcher, Laura Anderson, Kate Melanson, and Pete Raimondi UC Santa Cruz

Prepared for:

Commander, U.S. Pacific Fleet

Submitted to:

Naval Facilities Engineering Command (NAVFAC), Southwest, under Cooperative Agreement No. W9126G-15-2-0017

Final May 2021

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Suggested Citation:

Fletcher, N., L. Anderson, K. Melanson, and P. Raimondi. 2021. Investigations into recruitment enhancement and recovery of black abalone (Haliotis cracherodii) on San Clemente Island.

Report to U.S. Navy.

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Contents Introduction

Methods

Results

Discussion

References

Appendix A

Appendix B

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Introduction

Massive and sudden declines of dominant species can fundamentally alter the composition and structure of the communities in which they reside. Disease and overharvesting are two increasingly important factors responsible for mass mortalities of species across the globe (Harvell et al. 1999; Jackson et al. 2001; Harvell et al. 2002). Predicting the recovery of these valuable species is difficult, however, because it requires a comprehensive understanding of a number of variables that are hard to assess even individually. These variables include environmental conditions that support high reproductive success and recruitment, availability of appropriate habitat for settling juveniles, and life history and demographic traits of the species (e.g. regional density, sex ratio, size and age specific fecundity and survivorship, and larval dispersal). Recovery of a species may be inhibited by constraints imposed by one or more of these variables – either additively or synergistically. These combined forces may act against the recovery of a species in decline, resulting in a failure not only of the species, but also of the ecological community that relies on the species. Often, the only successful way to restore the species and ecological community may be through intervention and restoration.

Black abalone (Haliotis cracherodii) is a large, long-lived marine gastropod that was once a dominant species in rocky intertidal communities along the California coast. Since the mid- 1980s, black abalone have experienced mass mortalities due to infection by a bacterial pathogen (Candidatus Xenohaliotis californiensis) that leads to a fatal wasting disease called “withering syndrome” (WS). The disease affects the animal’s digestive system and leads to starvation and shrinking of the animal’s foot until it can no longer adhere to the substratum and the animal dies (Friedman et al. 2000).

The symptoms of the disease are associated with warming of oceanic water during El Niño Southern Oscillation (ENSO) periods or localized warming events, where disease transmission is accelerated (Raimondi et al. 2002). Over the last 30 to 40 years, the symptomatic distribution of the disease has progressed northward from southern California to its current “demographic front” near southern Big Sur. “Demographic front” is used to describe the progression of WS symptoms because pathological and microbiological work has shown the pathogen is present in most (if not all) extant populations of black abalone (e.g. Friedman and Finley 2003). The first massive die-offs due to WS occurred on the Channel Islands in 1983-1986 (1983-1984 ENSO event), and by 1992 the disease was observed by researchers from the University of California Santa Cruz (UCSC) near Point Conception. The symptomatic progression of WS moved to the southern boundary of the Big Sur coastline during the 1997-1998 ENSO event. In areas symptomatically impacted by the northward progression of the disease, mortality was >90% (Lafferty & Kuris 1993), leading to a population crash typically associated with very little subsequent recruitment of new individuals (Richards and Davis 1993). The impact of WS on black abalone populations was so severe that in 2009 the National Marine Fisheries Service (NMFS) listed the species as Endangered under the Endangered Species Act (ESA).

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Prior to the impact of WS, black abalone were extremely abundant on the Channel Islands, including San Clemente Island (SCI). SCI is the southernmost and fourth largest of the eight California Channel Islands (Figure 1). The island has been owned and operated by the United States Navy since 1934. In 2011, NMFS designated Critical Habitat for black abalone but provided an exclusion (referred to as 76 FR 66806) for SCI based on determinations that the Navy’s Integrated Natural Resource Management Plan (INRMP) provides benefits to black abalone. The Navy has subsequently supported several surveys of black abalone on the island.

An initial population assessment was conducted in 2011-2012 and estimated the total remaining population of black abalone on SCI to be between 91 and 344 individuals (Raimondi et al. 2012). Additional abalone habitat surveys were conducted in 2013 to fill spatial gaps in the population assessment survey and to better understand the extent of essential recruitment habitat. Juvenile black abalone were not found during any of these surveys, indicating that recovery of black abalone on SCI has been impeded by a lack of recruitment of new individuals.

In addition to a lack of recruitment on SCI, there is also concern that the remaining adult population may have been impacted by recent anomalous warm water events, including the 2014-2015 marine heatwave, during which there were positive temperature anomalies of 2-4 C° in the eastern Pacific (Figure 2). Any impact to the population would further reduce the likelihood of local reproduction and impede the recovery of black abalone on this island.

Recovery of a species after massive population declines requires successful recruitment of new individuals into areas where local populations were impacted. Recruitment is dependent on both an available supply of new individuals and specific environmental conditions required to induce settlement. Successful recruitment is often dependent on the presence of healthy, conspecific adult populations. Lack of recruitment following loss of adult black abalone from WS could be due to at least one of the following mechanisms: 1) the density of adults is too low for successful local reproduction and (assuming recruitment is local) local replenishment via settlement of new individuals cannot be effective; 2) the disease is still present, so new individuals cannot survive regardless of whether they were locally or distantly produced; and 3) the lack of a healthy adult population that maintains suitable recruitment habitat has resulted in a fundamental change to the community and a resultant decrease in suitable habitat for recruitment. When considering actions that support the recovery of black abalone, this last mechanism provides an opportunity for habitat restoration that may enhance recruitment.

Adult abalone maintain suitable recruitment habitat of algal crusts and bare rock through movement and grazing of the substrate, especially in crevices (Morris et al. 1980). When adults decline and are removed from crevice habitats, other organisms can settle in these crevices and alter the community in a way that limits the amount of available habitat for abalone recruitment (Miner et al. 2006). Actively clearing habitat of fouling organisms to restore that habitat to conditions consistent with a health adult population may help support successful recruitment of new individuals.

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Figure 1. Regional map showing the location of San Clemente Island.

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Figure 2. Eastern Pacific sea surface temperature anomaly for 9/20/2014 (top), 11/20/2014 (middle), and 1/20/2015 (bottom).

Tem p eratu re an o m aly: d egrees C

(relative to p erio d

-1

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To support recovery of black abalone on SCI, habitat recruitment studies were implemented on SCI in 2015 to: 1) restore and maintain recruitment habitat and assess recruitment to this habitat, and 2) enhance local recruitment through the use of Abalone Recruitment Modules (ARMs). Additionally, this project was designed to assess climate associated impacts and the outlook for recovery of black abalone on SCI through monitoring of a set of known individuals or focal population. In 2019, NMFS released a Final Recovery Plan for Black Abalone and several Recovery Actions identified in the plan relate to the abalone population on SCI. These include 1) monitoring of black abalone populations and abalone health throughout their range, and 2) restoring populations that have experienced mass declines through population enhancement and restoration efforts to enhance recruitment (NMFS 2019). Assessing and enhancing recruitment and documenting changes the focal population on SCI will contribute to the understanding of the species trajectory and potential for recovery under the Final Recovery Plan. This information is also essential to decisions concerning the management of this ESA listed species on SCI and for evaluation of recovery criteria stipulated in the Final Recovery Plan

Methods

Assessment of abalone recruitment to restored habitat

To assess abalone recruitment to restored habitats, two sites were identified (Eel Point and West Cove, Figure 3) on SCI. Within each of those sites, 16 crevices were located that represented suitable abalone habitat (deep crevices in the mid to low intertidal zones). We mapped and numbered the crevices to return to for continued monitoring. In eight of these crevices, we cleared areas of roughly 10 cm x 10 cm by removing other organisms (algae, barnacles, mussels, etc.) with scrapers and wire brushes to create suitable recruitment habitat (i.e., bare rock and crustose coralline algae). The other eight crevices remained uncleared and were used as controls. We returned to the sites 2 to 3 times per year from 2016 through 2019 to monitor the crevices for abalone recruitment (Table 3). Clearings were maintained by re-clearing and removing fouling organisms when needed following this schedule.

Enhancement of local recruitment through the use of ARMs

In addition to restoring recruitment habitat, we attempted to enhance recruitment by providing additional habitat through the use of artificial ARMs. ARMs would also provide a standardized method for monitoring abalone recruitment over time and a potential method for attracting recruits that could be translocated to restored habitat in dense aggregations. Two ARM designs were used: 1) stacked PVC plates and 2) cobble nested in vexar mesh (see photos in Appendix A). PVC plates were 10 cm x 10 cm and each ARM consisted of five plates stacked on 3.5-in bolts and spaced with ¼-in nylon spacers. ARMs were attached to the substrate with 2-in lag screws and concrete wall anchors. Cobble nests consisted of 15 to 20 cobble rocks covered in a 20 cm x 20 cm piece of vexar mesh. The mesh was attached to the substrate with PVC washers, 2-in lag screws, and concrete wall anchors. Eight of each ARM type were deployed at both Eel Point and West Cove.

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We selected eight of the crevices from the 16 initially identified at each site and installed each type of ARM adjacent to these crevices. This resulted in four treatment types consisting of four replicates: crevices with ARMs and clearings; crevices with ARMs and no clearings; crevices with clearings and no ARMs; crevices with neither ARMs nor clearings (control; Table 1). ARMs were monitored for recruits 2 to 3 times per year from 2016 through 2019 (Table 3). Monitoring was conducted by carefully unstacking the PVC plates and removing each cobble from the vexar nest and inspecting each for abalone recruits. Plates and cobble were replaced when sampling was complete.

In addition to monitoring the crevices, clearings, and ARMs at Eel Point and West Cove, site wide searches were conducted for abalone recruits during each visit. This was done to determine if recruitment was occurring at other areas of the site (outside of the crevices and ARMS) and to monitor the status of the known individuals of adult abalone at each site.

Table 1. Treatment types for crevices at Eel Point and West Cove.

Assessment of climate associated impacts and recovery outlook for black abalone

Black abalone population surveys were conducted at a set of focal locations on SCI (Figure 3).

The purpose of these surveys was to relocate any previously documented abalone (those found in the 2011-2013 surveys) and search for new (not previously documented) individuals to assess any change to the population on SCI. Relocated abalone were also assessed for health and condition to determine if any individuals were symptomatic for WS. Results of these surveys were used to determine if there was any potential impact to the population from recent anomalous warm water events including the 2014-2015 marine heatwave (Figure 2).

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These surveys occurred in 2016 and again in 2019 through 2020 (Table 3). We used existing maps, photos, and GPS coordinates to relocate known abalone. We also surveyed extensively in the areas around these known abalone to attempt to locate new abalone. The extent of survey areas was documented with GPS coordinates and tracks. We surveyed all suitable habitat for both the presence of abalone and the quality of habitat within each survey segment at each location. Note that these surveys were based on focal populations that were explicitly set up to assess the population trajectory of the species at SCI. The locations sampled were not random, but rather strategically placed to locate previously documented abalone in order to have enough individuals to determine a rate of change. We note this because in the 2011-2012 surveys we conducted a habitat-based survey of SCI that allowed estimation of the population size at that time (estimated to be between 91-344 individuals, Raimondi et al. 2012). Such an estimate is not possible with the data collected in this project.

All abalone found were counted, sized, assigned a nearest neighbor category, and assessed for health/condition. Nearest neighbor categories refer to how close an individual is to its nearest abalone neighbor (A = touching, B = <10 cm, C = < 1 m, D = <5 m, E = >5 m) and are an important metric for determining if abalone are in dense enough aggregations for successful reproduction. We also recorded the quality of the microhabitat in which each abalone was found. At the completion of each segment, the overall habitat quality of the segment was characterized by estimating the percent of total habitat that was of good, moderate, and poor quality with respect to refuge value and suitability for abalone occupation (Table 2). The location of any new individuals was also documented with photos and GPS coordinates.

Table 2. Black abalone habitat quality rubric. Refuge value is based on level of protection from predation or other disturbance. Suitability for occupation is based on biological features.

Project dates and locations

We selected crevices, established clearings, and deployed ARMs in January 2016. Monitoring and population surveys were conducted from January 2016 to February 2020 (Table 3). Due to a disruption in funding, we did not conduct monitoring or surveys in 2018 and the project was extended into Winter 2019 when ARMs were removed. Additional abalone surveys were conducted in Winter 2020. The full survey schedule is included in Appendix B. Recruitment monitoring and enhancement were conducted at Eel Point and West Cove. Abalone surveys were conducted at a total of eight locations including Eel Point and West Cove (Figure 3).

Detailed locations of survey segments are included in Appendix B.

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Table 3. Project timetable showing dates (month and year) that each project activity was conducted

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Figure 3. Map of abalone survey locations and recruitment enhancement sites on SCI.

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Results

Assessment of abalone recruitment to restored habitat and enhancement of local recruitment through the use of ARMs

We did not observe any black abalone recruitment to crevices or clearings. No abalone recruits were found in the ARMs and we did not observe any recruits during site-wide searches.

Assessment of climate associated impacts and recovery outlook for black abalone

In 2016, six sites along the west coast of SCI were surveyed for previously documented abalone.

A total of 11 abalone were found compared to the 31 abalone that were previously found at these locations in the 2011-2013 surveys (Figure 4, Table 4). Additional surveys were conducted in 2019 and 2020 at eight sites and 2852 meters of shoreline were surveyed for abalone. In the 2019-2020 surveys, 25 abalone were found, whereas a total of 42 individuals were documented in during the 2011-2013 surveys (Figure 4, Table 4). These data show a 65% decline in the number of black abalone found in 2011-2013 surveys and 2016 efforts and a 41% decline between 2011-2013 and 2019-2020 surveys. No signs of WS (abalone with shrunken foot) were observed and all abalone found were in good condition. Although no signs of WS were observed, this decline correlates with the anomalous 2014-2015 warm water event that occurred in the eastern Pacific.

Note that survey areas were selected in order to target previously documented abalone. Due to access and/or conditions, some areas (and abalone) that were surveyed in 2011-2013 could not be surveyed during the 2016 and 2019-2020 efforts (Table 4). More shoreline was surveyed in 2019-2020 than in the 2016 efforts in order to locate any additional abalone at these locations.

(Table 4). Appendix B provides additional details and maps of survey areas and locations of abalone found.

Table 4. 2016 and 2019-2020 abalone survey details. Documented abalone were those that were found and documented during 2011-2013 surveys. *These areas were previously surveyed in 2011-2013 but were not resurveyed due to access restraints.

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Figure 4. Number of abalone documented in 2011-2013 (blue) vs. abalone counts in areas surveyed (red) in 2016 (top) and 2019-2020 (bottom) at eight locations on SCI. Graduation Point and Swat1 were not surveyed in 2016.

As observed in the 2011-2013 island-wide surveys (Raimondi et al. 2012), a disproportionate number of abalone were found in good habitat, relative to the amount of good habitat on the island. Of the 25 abalone found in the 2019-2020 surveys, 19 were found in good habitat and six were found in moderate habitat while only 5.6% of available habitat was classified as good and 33% was classified as moderate (Figure 5). Although most abalone were found in good habitat, abalone density in this habitat was very low across sites.

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Figure 5. Number of abalone found in 2019-2020 by habitat quality (top) and percentage of habitat available (bottom).

Abalone density was calculated by habitat quality and by habitat quality and survey location for the 25 abalone found in 2019-2020. Densities were very low for all locations and habitats (Figures 6 and 7). Mean densities were 0.006 abalone/m2 in good habitat and 0.0003 abalone/m2 in moderate habitat, and were well below numbers believed to be needed for successful reproduction (1 abalone/m2, Miner et al. 2006). Abalone density was highest in good habitat at Eel Point (Figure 7). Of the 25 abalone found in 2019-2020 surveys, all but two were over 100 mm in size. Mean size was 127 mm (Figure 8). No juveniles (<30 mm) were found. All but two abalone were found at least 5 m away from any other abalone.

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Figure 6. Mean abalone density by habitat type (good, moderate, poor), (error bars = standard error).

Figure 7. Abalone density by habitat type (good, moderate, poor) and survey location.

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Figure 8. Abalone size distribution for number (N) of abalone found during 2019-2020 surveys.

Discussion

Black abalone were once abundant throughout southern California and the Channel Islands, including SCI. These populations were decimated by WS throughout the 1980s and 90s. Surveys of the population on SCI have found that the number of black abalone individuals is critically low and there is no evidence that there has been any recovery since initial surveys in 2011- 2013. Instead, it is likely that the population has decreased over this period and this decline correlates with the 2014-2015 anomalous warm water event. This conclusion is based on two results: first, in an assessment of the same locations, the number of abalone found in both 2016 and 2019-2020 surveys was lower than in 2011-2013 efforts. Second, no recruits were found during monitoring at Eel Point and West Cove or in any population survey during the periods of 2016 and 2019-2020. The size distribution of abalone found during these surveys is also skewed towards larger size classes, which is indicative of an older population with a lack of new, younger individuals. This is key and problematic because ultimately recovery of the population is dependent on the recruitment of new individuals.

The recruitment limitation is a result of one or more of the following mechanisms: 1) the density of adults is too low for successful reproduction and, therefore, local recruitment of new individuals; 2) the disease is still present so new individuals that do recruit die before detection;

and 3) the lack of a healthy adult population that passively maintains suitable recruitment habitat through movement and grazing has resulted in a fundamental change to the community

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Our initial and subsequent surveys of the population on SCI have shown that the population density is very low (<1 abalone/m2) even in areas of good habitat where most of the abalone are located. Additionally, all but two abalone were found at least 5 m away from any other abalone. Although black abalone are broadcast spawners, with males and females releasing gametes into the water, it is thought that successful reproduction is not possible if two abalone are >1 m apart or if densities are <1 abalone/m2 (Miner et al. 2006). Because a lack of recruitment habitat may be a contributing factor limiting recruitment (even if larval dispersal is broader than we think), we tested two habitat restoration techniques: 1) habitat restoration to address change in communities following the loss of adults and 2) recruitment enhancement through the use of ARMs. ARMs also had the potential to attract recruits that could be used to “seed” restored habitat.

We did not observe any recruitment to restored habitat (clearings) or to ARMs. Additionally, we did not observe any recruits during site-wide searches or population surveys. There is the potential that artificial ARMs did not provide appropriate habitat for recruits and that they are not suitable for enhancing recruitment. Recruits preferentially settle on crustose coralline algae (Morse et al. 1980, Miner et al. 2006), but there was little growth of crustose coralline algae on the PVC plates and cobble used in ARMs. Other materials, such as stone tiles, may provide a better substrate for crust growth and therefore a better habitat for recruitment. We are currently testing other ARM designs on Santa Cruz Island, where recruitment is higher, with the hope that these designs are effective and could be used to seed juveniles to support recovery.

The other, more likely, factor limiting recovery is that larval availability on SCI is very low or absent. This is supported by our survey findings that show very low adult densities throughout the island and a continued absence of recruits or juvenile abalone. Black abalone larvae do not disperse very far (McShane 1992, Chambers et al. 2005), so recruitment to an island like San Clemente is likely dependent on reproduction from the local adult population. In areas where adult densities are higher, including San Nicolas and Santa Cruz Islands, there is both recruitment and population growth (NMFS 2019, MARINe unpublished data). There is also recruitment to sites on the Big Sur coastline where populations have remained stable and unaffected by WS.

Although we were not able to make an updated population estimate, we did observe a 41% decline of adults at focal locations compared to 2011-2013 surveys. Although no WS was observed, this decline correlates with the 2014-2015 anomalous warm water event that occurred in the eastern Pacific. The decline is problematic as any additional loss of adult abalone is likely to further reduce the likelihood of local reproduction (and subsequent recruitment) and chances for recovery. Future ENSO and warm water events may continue to threaten the populations both on SCI and throughout the species range.

In summary, the result of the surveys reported here show the following:

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1) Black abalone abundance on SCI has likely declined since 2011-2013 and this decline occurred over the period that included the 2014-2015 anomalous warm water event (although no WS was observed)

2) Black abalone local densities are far below levels required for successful reproduction

3) No recruitment sized individuals were found in natural habitat, modified habitat (habitat restored to state suitable for recruitment), or in ARMs

The Final Black Abalone Recovery Plan lists several Recovery Actions that relate to the population on SCI including 1) monitoring of black abalone populations and abalone health throughout their range, and 2) restoring populations that have experienced mass declines through population enhancement and restoration efforts to enhance recruitment. The plan also stipulates several criteria that must be met for black abalone to be downlisted/delisted.

Meeting these criteria is a way to ensure long-term viability of the species. To meet the geographic range criteria, black abalone must be present in all Regions throughout their range including on seven of the eight Channel Islands. Additional criteria for population density, structure, and growth must be met on six of the eight Channel Islands (for delisting). Because black abalone have not been recently observed on Santa Catalina Island (Neuman et al. 2011, Obaza et al. 2016, MARINe unpublished data), the black abalone population on SCI is key to meeting the geographic range recovery criteria of the species and continued restoration efforts are important for recovery.

Ultimately, the primarily passive management measures that we have assessed are unlikely to lead to recovery of the species at SCI and recovery is not likely to occur unless more active recovery strategies are implemented. These strategies could include attempting to aggregate local adults, although this could involve risk of mortality and this is of course problematic when the number of adults is already critically low. Another option would be to translocate juvenile abalone (which have lower translocation risk) from a non-local source with high recruitment (e.g. other Channel Islands) and to aggregate these individuals in high densities to restored (cleared) habitat. The Final Recovery Plan indicates further research is required for both aggregating and translocating abalone to restore and enhance populations. SCI would be a good candidate for such studies and it meets several criteria laid out in the Final Recovery Plan, including: 1) subpopulations that are amenable to repeated assessment; 2) existing data suggesting that population viability is low if left unmanipulated; and 3) minimal predation and poaching pressures (NMFS 2019). We recommend conducting another island-wide population survey to further assess any impacts from WS and recent anomalous warm water events. This would also provide a comprehensive assessment of the population and size structure (including the possibility of finding rare recruits that might have been missed in the recent surveys).

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Appendix A

ARM Design Photos

Figure 1. Stacked Plate ARM design

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Figure 2. Cobble Nest ARM design.

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Appendix B

Abalone Survey Details and Maps