del mar boat basin eelgrass mitigation and … month eelgrass survey.pdf · pre-dredge eelgrass...

Submitted to:

Southern California Edison CompanySan Onofre Nuclear Generating Station

San Clemente, California 92672

Submitted by:

MBC Applied Environmental SciencesCosta Mesa, California 92626

October 2010

DEL MAR BOAT BASIN

EELGRASS MITIGATION AND RESTORATION PROJECT FOR

SONGS STEAM GENERATOR REPLACEMENT

TWO-YEAR PROGRESS REPORT

PROJECT STAFF

Southern California Edison

Brian Metz

MBC Applied Environmental Sciences

Project Manager — M. D. Curtis

Marine Scientists

D. S. BeckM. D. CurtisR. H. MooreM. R. PavlickJ. S. SloanJ. N. Smith

MBC Applied Environmental Sciences, 3000 Red Hill Ave., Costa Mesa, CA 92626

DEL MAR BOAT BASINEELGRASS MITIGATION AND RESTORATION PROJECT FOR

SONGS STEAM GENERATOR REPLACEMENT TWO-YEAR PROGRESS REPORT

INTRODUCTION

A two-year post-transplant eelgrass mitigation survey was conducted on 7 October 2010of the eelgrass transplant area prepared for the Southern California Edison (SCE) Company’s SanOnofre Generating Station steam generator replacement project. As part of the transport efforts toreplace steam generators for San Onofre Units 2 and 3, the new steam generators were shippedfrom the Port of Los Angeles via barge to the Del Mar Boat Basin at Marine Corps Base CampPendleton (MCBCP). The area chosen to offload the generators, however, was too shallow andrequired dredging to insure sufficient depth for the offloading operations (Figure 1).

URS Eelgrass Survey. The area to be dredged was previously surveyed in 2008 and wasknown to have patches of eelgrass (Zostera marina) in the area of potential effect (APE) (URS2008).

Mitigation Plan and Caulerpa Survey. Following state and federal regulations requiringno further net loss of eelgrass in California (Southern California Eelgrass Mitigation Policy - SCEMP,NMFS 2005) and companion regulations designed to stop the spread of the invasive species

Figure 1. Location of the study area with transects.

SCE - 2010 Del Mar Boat Basin Eelgrass Mitigation Project - Two-Year Post Transplant Report 2


Caulerpa taxifolia (CDF&G 2002), a survey for both eelgrass and Caulerpa was undertaken as partof the final mitigation plan (MBC 2008a). It required the removal and transplant of eelgrass into anearby area of Del Mar Boat Basin.

Pre-Dredge Eelgrass Survey. A pre-dredge survey of the APE was conducted on 3September 2008 for eelgrass and Caulerpa. Eelgrass, as expected, but no Caulerpa, was found inthe APE (MBC 2008a). Eelgrass was, however, found at a slightly higher coverage (109 m2) thanpreviously detected in the basin. As directed in the SCEMP, a revised mitigation plan was preparedthat indicated that the higher total of 109 m2 of impacted eelgrass was to be replaced at a 1.2:1 ratiowhich would require a minimum cumulative new coverage of 131 m2. The SCEMP strongly suggestsusing a higher density of eelgrass transplants than required to maximize the opportunity for successand provide a safety margin; therefore, a total of 153 bundles of eelgrass were to be transplantedat one per meter square densities which would result in a replacement ratio of 1.4:1.

Eelgrass Transplant. An acceptable eelgrass mitigation area was found in an area nearbywith small patches of existing eelgrass between relatively large open areas that indicated the barrenpatches between the small eelgrass patches might support a transplant. The area selected wasdemarcated via GPS coordinates (MBC 2008b, Table 1, Figure 2); within these coordinates a total

Table 1. Global Positioning System (GPS) latitude / longitude of eelgrass mitigation site.

Station Designation Location Latitude Longitude

M1 Southeast (End 50-m Transect) 33° 13.131 N 117° 24.096 W

M2 Northeast Corner 33° 13.133 N 117° 24.100 W

M3 Northern Diagonal 33° 13.121 N 117° 24.121 W

M4 Southwest Corner 33° 13.116 N 117° 24.127 W

M5 Northwest Corner 33° 13.119 N 117° 24.126 W

M6 End 30-m Transect Line 33° 13.124 N 117° 24.107 W

M7 End 15-m Transect Line 33° 13.121 N 117° 24.116 W

Figure 2. Del Mar Boat Basin Eelgrass Transplant.



of 28 m2 of existing eelgrass was found. However, there was an additional 22 m2 of eelgrass outsideof the demarcated transplant area that was near the transplant area, or a total of 50 m2 of nativeeelgrass in the immediate area of the transplant. Again, as directed in the SCEMP, all eelgrass thatwould have been lost to dredging in the APE was salvaged by biologist-divers who harvested andtransplanted the eelgrass to the previously prepared mitigation area. The transplant was conductedon 3 September 2008 just prior to the dredging (MBC 2008b). As planned, the total area planted was153 m2 at a density of approximately 12.5 turions per bundle (Table 2).

Table 2. Mitigation and Reference Bed Turion Densities and Coverage, 7 October 2010.

Survey Type Dredge /

TransplantMonitoring

Mitigation bedarea coverage

(m2)

Mitigationbed turion

density(per m2)

Referencebed

coverageand % of

25-mtransects

Referencebed turion

density (Per m2)

% coverageof 129 (179)m2 requiredtransplantarea (134{184} m2

after 6-2010)

Mitigationbed as a %of reference

bed density

Transplant Sep08

153 + 50 12.5 (15.9 m)63.6

64 119% 14.7

Post-Dredge Oct08

148 + 50 18.1 (14.6 m)58.5

106 115% 21.3

Post-Transplant Mar 09 (6-mo)

138 + 50 66.8 (13.6 m)54.4

102 108% 65.5

Post-Transplant Sept 09 (1-yr)

159 + 50 131.6 (15.8 m)63.5

201 123% 65.5

Post-Transplant Oct 10 (2-yr)

438 + 50 177.6 (22.8 m)91.1

276 326% 64.3

Post-Dredge Survey. A post-dredge survey conducted on 23 October 2008 confirmed thatthe loss of eelgrass from dredging was consistent with the revised mitigation plan, and though severalsmall patches of eelgrass were found following the dredging, only about 2 m2 of eelgrass appearedlikely to survive the offloading operations (MBC 2008c). Therefore, utilizing a loss of 107 m2 ofeelgrass coverage, a transplant of 128.4 m2 (129 m2) was required for this project; an amount about20% less than this was actually planted allowing a small leeway for any loss due to transplant shock.During the post-dredge survey, quadrats placed over 20 existing turion eelgrass bundles (theindividual bundles were still readily distinguishable at seven weeks post-transplant as they had notyet commingled with each other) were recorded and densities were found to have increased sinceinitial transplanting in September 2008, from 12.5 turions to 18 turions (Table 2, MBC 2008c).

Six-Month Post-Transplant Survey. At the six-month post-transplant survey, all areas ofthe transplant site were searched. It was determined that 138 m2 of eelgrass remained in themitigation area with many of the turion bundles having expanded greatly, but that 15 m2 of eelgrasswas missing. The 28 m2 of preexisting eelgrass within the mitigation site and the additional 22 m2 (50m2 total) of eelgrass outside growing near the original boundaries had begun to coalesce with themitigation eelgrass at the site (Table 2). The missing eelgrass was concentrated in the shallower areaat the northwest edge of the site. However, the total remaining eelgrass was in excess of the 129 m2

required and, on the plus side, the eelgrass had grown and turions were filling in about one half ofeach meter square planting area. The density of 20 eelgrass turion bundles (still distinguishable) wasrecorded during the six-month survey on 25 March 2009; turion densities had increased more than5-fold to almost 67 turions per m2 (Table 2, MBC 2009a).



One-Year Post-Transplant Survey. At one-year post transplant, the narrow band of eelgrasshad grown beyond the boundaries of the individual planting units and had commingled with eelgrassoriginally found in that location. Therefore, a 50-m long transect was placed on bottom in the originalposition of the northeast and southwest offshore corners of the transplant (Table 1). Line transectswere conducted perpendicular to shore at intervals of 2.5 m using the transect line as the mid-pointof the line transects. It was determined from the 21 line transects averaging 3.74 m long each that187 m2 of eelgrass remained in the mitigation area with many of the turion bundles having expandedgreatly (Figure 3). As there were 28 m2 of eelgrass in the area prior to the transplant of 153 turionbundles, the mitigation eelgrass in the transplant area had grown from that observed in March 2009of 138 m2 to 159 m2 of additional eelgrass (MBC 2009a, 2009b). Eelgrass densities at the mitigationsite (which had commingled with that of native eelgrass at the site) had increased greatly to 132turions per one m2 (Table 2, MBC 2009b). Although there had been die back of eelgrass on thesouthwest portion of the site in the shallower area, the area expanded on the northeast portionespecially in an offshore direction.

Interim Dredge Eelgrass and Caulerpa Survey. By mid-2010 it was determined thatportions of the dredged area in front of the offloading platform had filled in and were in need of minordredging to depth specifications for offloading the barge carrying the SCE Unit 3 steam generatorsscheduled to arrive in September 2010. As all eelgrass had been previously removed from the originaldredge site and had been fully mitigated, permission was granted to remove any existing eelgrassat risk and place into the adjoining mitigation site. An interim pre-dredge survey of the APE wasconducted on 8 June 2010 for eelgrass and Caulerpa. Small patches of eelgrass, but no Caulerpa,were found (the majority) on the slopes of the dredged area. The total amount of eelgrass found inthe survey area was about 12.75 m2. A total of 5.25 m2 of eelgrass was within or very close to theproposed dredge area and would have resulted in its probable loss from remedial dredging. Theseeelgrass turions were removed and transplanted to the southwest end of the mitigation site. Asmentioned, the survey area encompassed a greater area than that of the APE. The other 7.5 m2 ofeelgrass coverage was found outside of the APE and was sufficiently removed from the proposeddredge location that it was unlikely to be affected as a result of direct or indirect impacts. Theadditional 5.25 m2 added to the previously required 128.4 m2 of eelgrass mitigation brought the newtotal of required eelgrass replacement to slightly less than 134 m2 (MBC 2010).

METHODS

Mitigation Site. Using GPS coordinates of the eelgrass mitigation site, tape measures, and0.125 m2 quadrats, the restoration site was re-occupied on 7 October 2010 (Figure 2). Although thetransect was originally 50-m long, eelgrass was planted outside of these boundaries during theinterim survey, and new growth from the transplanted eelgrass had expanded to the east and westand especially south in an offshore direction. Therefore, a transect line of 64-m (56 m and 8 m)length was required to encompass the entire eelgrass bed (MBC 2010). Eelgrass was found bothabove (shoreward) and below (bayward) the transect line with ends at M4 and M1 (Table 1,Figure 2). Perpendicular line transects to the limits of eelgrass growth were conducted at 2-mintervals along the 64-m long transect (8 m south and 56 m north of the 0 m mark laid parallel to the

-4

-2

0

2

4

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 35.0 37.5 40.0 42.5 45.0 47.5 50.0

above

below

Transect Length (m)

Wid

th (

m)

Figure 3. Width in m of eelgrass transects along 50-m transect line depicting eelgrass growth above andbelow the transect line. Del Mar Boat Basin One-Year Post Transplant.



roughly rectangular shaped eelgrass transplant area. Density was determined by counting turionsin 20 randomly placed 0.125 m2 quadrats throughout the transplant area.

Reference Site. The reference site was surveyed at the same time intervals as required atthe mitigation site in order to compare its density with that of the mitigation site. The reference sitewas surveyed and eelgrass coverage and density was determined using a 25-m transect and 0.125m2 quadrats.

RESULTS

At two-years post transplant, the narrow band of eelgrass had grown beyond the boundariesof the original eelgrass mitigation area and was found deeper than during the one-year survey. It wasno longer possible to distinguish the original eelgrass inside and adjacent to the mitigation area fromthat of the transplanted mitigation eelgrass. There were 28 m2 of eelgrass in the area prior to thetransplant and 22 m2 adjacent to the area, so the eelgrass in the mitigation area needed to cover atleast 50 m2 plus the 134 m2 required for the mitigation, a total of 184 m2 of eelgrass. Therefore, inorder to encompass all of the eelgrass, a 64-m long transect was placed on bottom in the originalposition of the northeast and southwest corners of the transplant, but extending an additional 8 mwest of the line and 6 meters east of the original 50-m transect line. Line transects were conductedperpendicular to shore at intervals of 2 m using the transect line as the mid-point of the perpendicularline transects (Figure 4). In all 33 perpendicular transects were conducted. Vegetated portions of thetransects ranged from 0 to 12.8 m long and averaged 7.63 m each and indicated a total eelgrasscoverage of 488 m2 (Table 2). As there was 50 m2 of pre-existing eelgrass present at the site andholes were found in the eelgrass bed totaling 30.6 m2, the transplanted area had grown from 209m2 present at the site during the first year survey (MBC 2009), to 438.4 m2 in October 2010(Table 2). Eelgrass densities at the mitigation site (which were commingled with that of nativeeelgrass at the site) had increased from 131.6 at the one-year survey to 177.6 turions per one m2

(Table 2, Appendix A). Although there had been die back of eelgrass on the southwest portion ofthe site in the shallower area, the area expanded on the northeast portion, especially in an offshoredirection.

Reference Site. A reference eelgrass bed located a few hundred meters from the transplantsite and situated at the same depth and current regime was selected for comparison with thetransplanted bed (Figure 5). The reference site was surveyed following the completion of thetransplanting at the mitigation site and was again surveyed during the post-dredge survey in October2008, during the six-month post-transplant survey in March 2009, during the one-year survey inSeptember 2009, and during the present survey October 2010 (Table 3). At the initiation of theproject, reference eelgrass bed turion densities averaged 64 per 1.0 m2 and eelgrass coverageaveraged 15.9 m per 25-m transect (Table 3, MBC 2008b). At the post-dredge survey in October2008, eelgrass coverage decreased slightly, while density increased; eelgrass coverage averaged

-10

-8

-6

-4

-2

0

2

4

6

8

-8 -6 -4 -2 0 2 4 6 8

10

12

14

16

18

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

above

below

Transect Length (m)

Wid

th (

m)

Figure 4. Width in meters of eelgrass transects above and below 64-m transect line.



Table 3. Reference Site Eelgrass Survey, 7 October 2010.

Mid-TransectLatitude / Longitude

33o13.166 /117o24.055

33o13.169 /117o24.044

33o13.167 /117o24.028

AverageCoverage

(m)

AverageDensity (m2)

Transect T-1 25-m T-2 25-m T-3 25-m 25-m -

Inshore depth -0.25 ft MLLW -1.25 ft MLLW -1.0 ft MLLW -0.83 ftMLLW

-

Offshore depth -3.5 ft MLLW -5.6 ft MLLW -4.5 ft MLLW -4.5 ftMLLW

-

Coverage (m)Sept 2008

16.4 12.0 19.3 15.9 64

Coverage (m)Oct 2008

13.2 12.7 18.0 14.6 106

Coverage (m)Mar 2009

7.5 12.3 21.0 13.6 102

Coverage (m)Sept 2009

14.3 10.6 22.7 15.9 201

Coverage (m)Oct 2010

15.3 21.7 31.3 22.8 276

Figure 5. Eelgrass transects at the control bed.



14.6 m per 25-m transect and densities averaged 106 turions per 1.0 m2. At the six-months post-transplant survey in March 2009, eelgrass at the reference site again decreased in coverage slightly(losing coverage in the western portion of the bed and gaining in the eastern portion) to 13.6 m per25-m transect and also decreased in density very slightly to 102 turions per 1.0 m2. The one-yearpost-transplant survey in September 2009 found that eelgrass at the reference site increased incoverage from 13.6 to 15.9 m and also increased in density to almost double that found in March(102 turions) to 201 turions per 1.0 m2. At the 2-year survey, both density and coverage increasedby about 37%. The reference bed increased to an average of 22.8 m coverage of the three 25-mtransects (transect T3 was actually 31.3 m long) while turion density increased from 201 to 276 perm2 (Table 3, Appendix A).

SUCCESS CRITERIA

Success criteria for the transplantation (as found in the SCEMP) will be based on"comparison of vegetation coverage (area) and density (turions per square meter) between theproject and mitigation sites" (NMFS 1991). The "extent of vegetated cover is defined as that areawhere eelgrass is present and where gaps in coverage are less than one meter between individualturion clusters.” The criteria are defined by time following completion of transplantation as listedbelow.

• A minimum of 70% coverage and 30% density after the first year.

• A minimum of 85% areal coverage and 70% density after the second year.

• A sustained 100% areal coverage and 85% density for the third through seventhyears.

Therefore, based on the criteria stated in the SCEMP, the eelgrass transplant at the mitigation siteis a success at the end of year two, far exceeding project mitigation expectations of 85% coverage(coverage was 326%) and density was greater than 70% (at 277%) of initial density of the referencesite).

DISCUSSION

The site continues to develop at a pace commensurate with other eelgrass mitigationprojects (MBC 1995, 2000, and 2005). All the observations of the biologist-diver surveyors wouldsuggest that the site will ultimately be successful. It is apparent that environmental conditions werevery unusual during the past year (a La Niña developed which generally brings cooler temperaturesand nutrients to southern California waters) and especially beneficial to the eelgrass beds. Hencea three-fold increase in the size of the eelgrass beds from that of one year previous. Most of the newgrowth took place offshore of the previously existing eelgrass bed which indicates thatphotosynthetically available light was not limiting during the past year allowing eelgrass to colonizedeeper areas of Del Mar Boat Basin. This was evident during the interim survey in June 2010,although not immediately recognized, as eelgrass was found growing in small patches during thatsurvey in the dredge area where depths would not have typically supported eelgrass due to lightlimitations (MBC 2010). Some of the differences noted between the one- and two-year surveyscould be the differing intervals for the perpendicular transects; the 2-m transect intervals could haveresolved the eelgrass bed perimeter better than the 2.5-m perpendicular transects the yearprevious. However, as the average eelgrass transect was 7.63 m at two-years post-transplant, anincrease of more than 100% from the 3.73-m long transects noted at one-year post transplant, it isunlikely the difference could have been more than a small fraction of the increase noted. Becauseof the relatively unusual conditions of the past year, it would be expected that there will be somelosses as oceanographic conditions presumably return to a more average regime. Therefore, it islikely that the large gains seen at two-years post transplant will decrease as eelgrass retreats fromsome of the deeper areas where it is now growing.



LITERATURE CITED

CDF&G. 2002. Caulerpa Control Protocol. Prepared by California Department of Fish and Gameand National Marine Fisheries Service (Version 3.0, adopted March 12, 2007). 7 p.

MBC Applied Environmental Sciences. 1995. Three month post-transplant eelgrass survey East SkiIsland, Mission Bay. Prepared for the City of San Diego, Parks and Recreation Dept. 5 p.

MBC Applied Environmental Sciences. 2000. 2000 Monitoring and Biological Assessment Report forCity of San Diego Mission Bay Eelgrass Transplants, Mission Bay, San Diego, California.Prepared for the City of San Diego, Parks and Recreation Dept., San Diego, CA. 28 p.

MBC Applied Environmental Sciences and RECON Environmental, Inc. 2005. U.S. Army Corps ofEngineers Upper Newport Bay eelgrass mitigation project - One year monitoring report.Prepared for U.S. Army Corps of Engineers, Los Angeles District, Los Angeles, CA. ContractNo. DACW09-02-D-0023. 6 p. + Appendix.

MBC Applied Environmental Sciences. 2008a. Del Mar Boat Basin Pre-dredge Eelgrass andCaulerpa Survey for San Onofre Nuclear Generating Station Steam Generator ReplacementProject, September 2008. Prepared for Southern California Edison Company San OnofreNuclear Generating Station. 5 p. + Appendix.

MBC Applied Environmental Sciences. 2008b. Del Mar Boat Basin Eelgrass Mitigation andRestoration Report for the SONGS Steam Generator Replacement Project, September 2008.Prepared for Southern California Edison Company San Onofre Nuclear Generating Station.8 p.

MBC Applied Environmental Sciences. 2008c. Del Mar Boat Basin Post-dredge Eelgrass andCaulerpa Survey for SONGS Steam Generator Replacement Project, October 2008.Prepared for Southern California Edison Company San Onofre Nuclear Generating Station.4 p.

MBC Applied Environmental Sciences. 2009a. Del Mar Boat Basin Eelgrass Mitigation andRestoration Project Six-Month Progress Report. March 2009. Prepared for SouthernCalifornia Edison Company San Onofre Nuclear Generating Station. 5 p.

MBC Applied Environmental Sciences. 2009b. Del Mar Boat Basin Eelgrass Mitigation andRestoration Project One-Year Progress Report. September 2009. Prepared for SouthernCalifornia Edison Company San Onofre Nuclear Generating Station. 5 p.

MBC Applied Environmental Sciences. 2010. Del Mar Boat Basin (Interim) Pre-dredge Eelgrass andCaulerpa Survey and Mitigation Project For San Onofre Unit 3 Steam GeneratorReplacement. Prepared for Southern California Edison Company San Onofre NuclearGenerating Station. 4 p.

NMFS. 2005. Southern California Eelgrass Mitigation Policy. Prepared by National Marine FisheriesService and California Department of Fish and Game. Revision 11, 30 August 2005. 8 p.

URS. 2008. Eelgrass Transplantation Plan for the Songs Steam Generator Replacement Projecton Marine Corps Base Camp Pendleton. Prepared for Southern California EdisonCompany, San Onofre Nuclear Generating Station, PO Box 128, San Clemente, CA 92672.Prepared by URS, 1615 Murray Canyon Road, Suite 1000, San Diego, CA 92108. 13 p. +Appendix.

APPENDIX A

Eelgrass parameters mitigation and reference sites

T-1 T-2 T-3 Average

15.3 21.7 31.3 22.8

depth 7 ft 11 ft 12 ft

time 1130 1135 1140

Average

Mitigation Site Turion Densities 0.125 m2

( m2 )

24 23 17 33 21

20 19 19 28 18 177.6

Average

Reference Site Turion Densities 0.125 m2

( m2 )

41 33 22 38 30

49 27 38 31 36 276.0

Transect length (m)

Reference Site

Appendix A. Eelgrass parameters mitigation and reference sites.

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