ICES Journal of Marine Science, 59: S330–S337. 2002
doi:10.1006/jmsc.2002.1290, available online at http://www.idealibrary.com on
Effects of El Niño events on natural kelp beds and artificial reefs
in southern California
Robert S. Grove, Karel Zabloudil, Tim Norall, and
Lawrence Deysher
Grove, R. S., Zabloudil, K., Norall, T., and Deysher, L. 2002. Effects of El Niño
events on natural kelp beds and artificial reefs in southern California. – ICES Journal
of Marine Science, 59: S330–S337.
Since 1978, bottom characteristics and giant kelp (Macrocystis pyrifera) population
dynamics of three historically productive natural kelp beds located south of San
Clemente, California, have been monitored on a semi-annual basis using diver
observations, sidescan sonar, and downlooking sonar. Aerial photographs of the
kelp-bed surface canopies have been recorded annually since 1968. Since 1981, studies
have been intermittently performed on the Pendleton Artificial Reef. Ecological studies
were also conducted pre- and post-1997–1998 El Niño and qualitatively from 1994 to
1999 at the Mission Beach Artificial Reef. El Niño events have been associated with
catastrophic ecological conditions in the southern California nearshore zone that may
have significant influence on both reef structure and reef community. The variation of
kelp populations in the three natural kelp beds is reviewed relative to recent El Niño
events, local wave climate, local sea surface temperatures, and regional precipitation.
The local temperature and precipitation data show that El Niño periods have had
varying and non-consistent effects with respect to kelp growth. Yet, periods of low kelp
density appear to be related to extended periods of above normal sea surface
temperatures and increased precipitation generally associated with El Niño events.
Examination of artificial reef data from the standpoint of substrate and kelp
persistence through the latest 1997–1998 El Niño event revealed effects that are
consistent with natural kelp bed information. The population dynamics of natural kelp
beds through various El Niño periods indicate that the range of kelp density
fluctuations over time on an artificial reef designed for kelp can be expected to be quite
high.
2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.
All rights reserved.
Keywords: artificial reefs, El Niño events, kelp beds, mitigation, sonar surveys,
southern California.
Accepted 15 March 2002.
R. S. Grove: Southern California Edison Company, 2244 Walnut Grove Ave., Rosemead,
California 91770, USA; tel: +1 626/302-9735; fax: +1 626/302-9730; e-mail:
[email protected]. K. Zabloudil, T. Norall: EcoSystem Management Associates, Inc.,
2270 Camino Vida Roble, Suite L, Carlsbad, California 92009, USA; tel: +1 760/4388682; fax: +1 760/438-8684; e-mail: [email protected]. L. Deysher: Ocean
Imaging, 201 Lomas Santa Fe Drive, Suite 370, Solana Beach, California 92075, USA;
tel: +1 858/792-8529; fax: +1 858/792-8761; e-mail: [email protected]
Introduction
Kelp forests are an important ecological feature along
the southern California coast. These nearshore habitats
are dominated by the giant kelp (Macrocystis pyrifera), a
brown alga forming structurally complex, species-rich,
and highly productive habitat (North, 1971; Mann,
1973; Gerard, 1976; Carter et al., 1985; Dayton, 1985).
Fish and invertebrates have substantially higher standing stocks in kelp forests compared with the flat sandy
1054–3139/02/0S0330+08 $35.00/0
bottom common to the nearshore zone (Foster and
Schiel, 1985; DeMartini and Roberts, 1990).
Viable kelp beds of Macrocystis form surface canopies
that range in areal extent from 0.1 ha, as seen in small
north San Diego County beds, to 600 ha in the largest
bed at Point Loma, City of San Diego (North and
Curtis, 1998). The 24 kelp beds of San Diego and
Orange Counties in southern California have been
monitored since the 1960s (North, 1971; North et al.,
1993; North and Curtis, 1998). Most of these beds are
2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.
Effects of El Niño events on natural kelp beds and artificial reefs in southern California
located on low-relief hard bottom substrate consisting of
either cobble and boulder fields, outcroppings of bed
rock, or on smaller cobble and silt-stone substrate areas
on the sandy bottom.
The construction of artificial reefs that target the
enhancement of kelp communities has been suggested as
a means of mitigating human-induced impacts to natural kelp forests in southern California. The first experimental reef designed to test the efficacy of improving
kelp habitat and constructed in 1980 was the high-relief
(3–5 m off bottom) Pendleton Artificial Reef (Grove,
1982; Grant et al., 1982). Kelp has not flourished or
persisted on this reef (Carter et al., 1985). The creation
of new kelp forests using low-relief (0.5–1.5 m off bottom) artificial reefs is now being tested (Deysher et al.,
1998) by scattering hard substrata (a single layer of
quarry rocks and/or broken concrete) in sandy bottom
areas in the appropriate depth zone (10–18 m).
A complicating and possibly dominant factor in
assessing the performance of artificial kelp reefs is the
influence of large-scale weather patterns that are influenced strongly by El Niño/La Niña cycles. El Niño
events have been identified as influencing catastrophic
conditions in the southern California nearshore zone
that can have significant influence on both the structure
and community of reefs (Dayton and Tegner, 1984;
Dean and Jacobsen, 1986; Tegner and Dayton, 1987).
La Niña events result in cooler and calmer conditions
that may be more favourable for kelp. Since 1978,
bottom characteristics and Macrocystis population
dynamics of three historically productive natural kelp
beds located south of San Clemente (Figure 1) have been
monitored on a semi-annual basis using diver observations, aerial photography, sidescan sonar, and downlooking sonar techniques. In addition, studies have been
performed on the nearby high-relief Pendleton Artificial
Reef. Additional qualitative studies were conducted
from 1994 to 1999 at the Mission Beach Artificial Reef,
which was built off San Diego in 1991. Ecological
studies focused specifically on the influence of the 1997–
1998 El Niño. The Mission Beach reef is the only
artificial reef that has developed a long-term kelp population. We present data from these studies on the effects
of El Niño/La Niña cycles on kelp distribution on
natural reefs and on artificial reefs.
Study sites
The three natural reefs persistently supporting kelp in
the San Clemente study area are the San Mateo, San
Onofre, and Barn kelp beds (Figure 1). These kelp beds
are located in water depths of 10–18 m and have ranged
in size from 0 to 100 ha each since 1980 (North et al.,
1993; North and Curtis, 1998).
120°
119°
118°
S331
117°W
Santa Barbara
San Miguel Is.
34°N
Santa Rosa Is.
Los Angeles
Santa Cruz Is.
Santa Catalina Is.
San Nicolas Is.
San Clemente
Pendleton Artificial Reef
Oceanside
Mission Beach
Artificial Reef
33°
San Clemente Is.
San
Diego
C
al
ifo
rn
ia
San
Clemente
San Mateo
Point
SONGS
San Mateo
Kelp
Diffusers
San Onofre
Kelp 9
N
2000
0
2000 4000 m
19
m
m
Pendleton
Artificial Reef
BARN
Kelp
Figure 1. Setting of the San Onofre Area Kelp Beds, Pendleton
Artificial Reef, the San Onofre Nuclear Generating Station
(SONGS) Diffuser Cooling System near the City of San
Clemente, and the Mission Beach Artificial Reef adjacent to the
City of San Diego, California, USA.
The Pendleton Artificial Reef was built in August–
September 1980 using 9100 t of quarry rock (Grant
et al., 1982). The rock averaged 0.3–1.2 m in size, typical
of material used to construct breakwaters. The reef
consists of 8 modules situated on a featureless sand
bottom at 14 m depth (MLLW). The reef (approximately 1 ha) is located south of San Clemente (Figure 1)
at 3320N 11731W. The modules are approximately
3013 m with heights between 3 and 5 m. The
8 modules are spaced approximately 20 m apart.
The Mission Beach Kelp Artificial Reef, constructed
in October 1991, consists of a low profile (0.3–1.5 m off
bottom) field of broken concrete obtained from local
demolition projects. The material is said to consist of
slabs 15–21 cm thick, 1.2–1.8 m wide, and 0.6–1.9 m
long. The amount of concrete is estimated to be at least
1800 t, and possibly more. The material was barged
offshore and dumped on a gently sloping sand bottom in
15–18 m depth (Figure 1). The reef (about 1.7 ha) lies
about midway between the Point Loma and La Jolla
kelp forests, and the nearest natural hard substrate (and
kelp population) is approximately 3 km to the south at
Point Loma.
S332
R. S. Grove et al.
Methods
The three natural reefs have been routinely surveyed for
kelp abundance since 1968 using an aerial photography
method to document surface canopy area (North et al.,
1993), and by sonar between 1978 and 1998. The sonar
method consisted of two different systems: sidescan and
downlooking sonar (Zabloudil et al., 1991). Seafloor
substrate boundaries and relative kelp densities are
defined with the sidescan sonar data. The downlooking
sonar serves to collect bottom contour changes and kelp
frond and plant density information. Diver surveys were
used to ground-truth and calibrate the sonar records.
The Pendleton Artificial Reef was surveyed for kelp
using diver transects from 1981 through 1986 (Wilson
and Lewis, 1991). These surveys resulted in a quantitative description of kelp coverage on a per square metre
basis. The reef has been periodically monitored by the
California Department of Fish and Game Artificial Reef
Program dive team between 1989 and 1998. A sonar
survey was performed in 1999 using the sonar methods
described above.
Sidescan sonar surveys of the Mission Beach Artificial
Reef were performed in 1995, and 1997 and 1998,
before and after the latest El Niño event. These surveys
were used to compare the coverage of reef substrate.
Diver surveys have also been conducted on this reef.
Qualitative observations were performed from 1994
through 1996 by the California Department of Fish and
Game. In 1997 and 1998, diver surveys were performed
along a series of 30-m-long transects at a random
selection of sites within the reef and provided quantitative data on substrate, kelp, and invertebrate distributions within the reef. A total of 12 transects were
compared over time for coverage of concrete and
densities of plants and invertebrates.
Oceanographic data were obtained from the NOAA
Coastal Ocean Program. NOAA’s Climate Diagnostics
Center routinely follows El Niño phenomena as they
periodically develop in the eastern half of the equatorial
Pacific. La Niña events, abnormally cold sea surface
temperatures in the eastern half of the equatorial Pacific,
which are the opposite of El Niño events, are also
tracked. This periodic series of events is termed the
Southern Oscillation, and consists of an east–west
atmospheric pressure seesaw that directly affects tropical
weather around the globe, and has direct influences on
southern California nearshore waters. The Climate
Diagnostic Center monitors the coupled oceanicatmospheric character of the El Niño events and
Southern Oscillation phenomenon (ENSO) by estimating an ENSO index based on the main six observed
variables over the tropical Pacific: sea-level pressure, the
east–west and north–south components of the surface
wind, sea surface temperatures, and total amount
of cloudiness. Positive index values represent warm
El Niño phases and negative values represent cold
La Niña phases. The ENSO index depictions of tropical
oceanographic events are compared to local southern
California oceanographic and meteorological conditions
that are recorded routinely at the Scripps Institution of
Oceanography, as well as at the San Clemente pier, and
in San Diego (precipitation).
Results
El Niño events
Based on the multivariate ENSO index, there have been
four significant El Niño events since 1980: 1982–1983,
1986–1987, 1991–1992, and 1997–1998. A time-line of
temperature data (Figure 2) shows the El Niño periods
as positive temperature anomalies, and the lingering
thermal effects after the events have dissipated in the
equatorial Eastern Pacific. Figure 2 also shows the
ENSO index for the seven historic El Niño events since
1950, the 1982–1983 event being the largest one, followed by the 1997–1998 event that had two peaks just
below the 1982–1983 peak. The other two El Niños since
the kelp studies were initiated were smaller (1991–1992
and 1986–1987). Figure 2 also shows the ENSO index
for the seven strongest La Niña events since 1949. The
1998+ event has been one of the strongest, followed by
events in 1988–1989, 1975–1976, 1972–1973, and 1970–
1971. Southern California oceanographic data demonstrate that the El Niño/La Niña cycles appear to have
a direct influence on the regional oceanographic and
climatological picture (Figure 3). Positive temperature
anomalies in the San Clemente pier temperature records
correspond directly to the 1997–1998 and the early 1990s
El Niño periods, with some local-effect delay to the large
1982–1983 event. However, there is no relationship at all
to the 1987–1988 El Niño.
Natural kelp beds
The fluctuation of kelp coverage in the three natural
reefs was determined from sonar records and plotted as
total number of plants in each bed (Figure 3). In
comparing these with seasonal precipitation data and
local sea surface temperature anomalies, the five wettest
seasons during the period 1980–1998 (1983, 1991, 1993,
1995, and 1998) were associated with sharp declines in
all three kelp beds. Positive temperature anomalies
correlate less with declining kelp growth, except for the
large El Niño effects of 1997–1998.
These beds were further assessed using surface canopy
area as calculated from aerial photographs (Figure 4).
These results show that the area of the canopy was
reduced dramatically by the 1997–1998 El Niño, somewhat reduced by the early 1990s and 1982–1983 El Niño,
and dramatically increased in the 1989 La Niña. The
Effects of El Niño events on natural kelp beds and artificial reefs in southern California
S333
Figure 2. Temperature anomalies in C according to the ENSO index, 1950–1998, and El Niño and La Niña Events, 1949–1998
(from NOAA-CIRES Climate Diagnostics Center).
R. S. Grove et al.
4
3
600
SST anomaly
San Diego precipitation
550
SST anomalies (°C)
500
2
450
400
1
350
0
300
–1
250
200
–2
150
100
–3
San Diego precipitation (mm)
S334
50
–4
300 000
No. of adult kelp plants
250 000
0
SOK
SMK
BARN
200 000
150 000
100 000
50 000
0
1980
1982
1984
19865
1988
1990
Year
1992
1994
1996
1998
2000
Figure 3. San Clemente Pier sea surface temperature anomalies, 1980–1998 (based on 1965–1997), San Diego precipitation, and the
number of adult kelp plants at three natural kelp bed reefs (San Mateo, San Onofre, and Barn Kelp).
1989 increase appears to be a function of an unprecedented series of natural events: an unusually severe
storm on 18 January 1988 dislodged most of the adult
kelp plants along the coast that were just recovering
from the 1986–1987 El Niño and also created an abundance of bare substrate within the nearshore zone by
moving large amounts of sand (North and Curtis, 1998).
The availability of bare substrate allowed high recruitment of kelp plants and the La Niña conditions in 1989
stimulated the growth and survival of these new recruits
and resulted in the largest kelp bed sizes observed in
historical records (North et al., 1993; North and Curtis,
1998).
In a statistical analysis of the El Niño effect on kelp
populations, both number of kelp plants and percent
change in these numbers were correlated with sea surface
temperature (SST) and SST anomalies. The SST values
were computed by taking the average of the values 9 and
12 months earlier. The reasoning was that the effects of
temperature are probably integrated by the plant and
should emerge as a perturbation in the population only
after a certain lag period. The resulting trend of decreasing kelp plants with increasing temperature anomalies
was not significant and is therefore not shown. However,
the general picture emerging from the assessment of kelp
plant plots is a predominant influence of episodic
recruitment events during short periods of favourable
conditions. Recruitment events may occur during El
Niño periods but usually they do not. Still, during the
major El Niño periods from 1980 to the present, kelp
populations in the three natural beds surveyed were
substantially reduced.
Pendleton Artificial Reef
Periodic transect surveys on the Pendleton Artificial
Reef from 1982 to 1984 to assess the status of transplanted kelp and to monitor natural recruitment
revealed only intermittent kelp at very low densities
(0.005 plants m 2; Wilson et al., 1991). The qualitative
surveys in the 1990s showed some limited kelp around
Effects of El Niño events on natural kelp beds and artificial reefs in southern California
Table 1. Summary of mean bottom cover (%) of exposed
concrete and plant densities (N 10 2 m 2) of Macrocystis
pyrifera along twelve 30-m transects on the Mission Beach
Artificial Reef during pre- and post-1997–1998 El Niño
Surveys.
1
0.9
0.8
S335
San Mateo Pt
San Onofre
0.7
Pre-
Post-
% change
Mean bottom cover
46.2% 46.9%
Adult (>8 fronds)
6.0
0.6
Sub-adult (<8 fronds, >1-m long) 29.6
1.5
Juvenile (<1-m long)
7.2
0.0
+0.7%
5.4
28.1
7.2
km
2
0.6
0.5
0.4
0.3
0.2
0.1
0
1965 1970 1975
1980 1985 1990
Year
1995 2000
Figure 4. Kelp bed surface canopy coverage (km2) in San
Onofre and San Mateo kelp beds, 1967 to 1998 (from North
and Curtis, 1998).
the edges and on the reef modules, but no persistent kelp
populations.
Mission Beach Kelp Artificial Reef
The Mission Beach Kelp Artificial Reef was first surveyed in November 1994, three years after its construction. This initial qualitative survey showed that a dense
population of Macrocystis pyrifera had developed with
fronds reaching the surface. During the first quantitative
survey in 1995, a diverse and abundant algal population
was observed with adult Macrocystis densities similar to
those observed in natural kelp beds. Populations of the
kelps Laminaria farlowii and Pelagophycus porra were
also found. The Pelagophycus populations were unusual
in that they usually only occur in deeper (25 m) water at
the outer edges of the Point Loma and La Jolla kelp
beds. Subsequent surveys in June and December 1996
showed that the Macrocystis populations were still
persisting at relatively high densities.
Between 25 August and 2 October 1997 (pre-El Niño),
a total of 32 transects were surveyed by divers. A subset
of 12 transects, representing those with the highest
percentage cover of concrete, was chosen from the initial
set for re-survey during the spring of 1998 (post-El
Niño) and the data for this sub-set are compared in
Table 1. The largest single decline in substrate cover was
a 20% drop along one particular transect from 37% to
17%. The average for all transects, however, showed
basically no change. The estimates of concrete cover
made by the diver survey and those from sidescan sonar
surveys showed good agreement. For example, five diver
transects in areas where sidescan sonar indicated 50% to
80% cover had a mean coverage of 69%. The one diver
transect in the sonar’s 30% to 50% class had a coverage
of 40%.
In contrast to the substrate surveys, the pre- and
post-El Niño surveys showed that Macrocystis densities
were reduced severely (Table 1). Continuing qualitative
diver surveys indicate that individual healthy kelp plants
are persistently present.
Discussion
Kelp population dynamics exhibit complex relationships
among many factors, including light levels, temperature,
nutrients, and wave energy. El Niño events generally
affect these factors in ways that decrease kelp recruitment and increase mortality. For example, higher than
normal water temperatures are associated with low
nutrient conditions (Zimmerman and Kremer, 1984)
that adversely affect adult growth and cause higher than
normal adult mortality (North et al., 1982) and decrease
the likelihood of recruitment of sporophytes (Deysher
and Dean, 1986).
Kelp density estimates and surface canopy area data
point to a relationship between major El Niño/La Niña
cycles and changes in kelp on natural and artificial reefs
in southern California. Specifically, major El Niño
events appear to be associated with decreases in kelp
populations. However, there may be a threshold level
because little effect is observed for the minor El Niño
events.
El Niño events can be manifest in ways other than
elevated temperature and reduced nutrients. Kelp beds
appear to have reduced recruitment and reduced kelp
growth in years with excessive precipitation. This might
be caused by greater turbidity in nearshore waters owing
to increased run-off, and leading to reduced light levels
or increased sediment loading.
The kelp records also provide evidence that La Niña
events, such as seen in 1989, may have positive effects on
kelp growth, especially when preceded by a severe storm
event ripping out much of the competing marine growth
and clearing the way for a favourable recruitment episode. The cooler and more nutrient-rich water usually
associated with the La Niña periods provides a good
environment for the growth and survival of both
juvenile and adult plants.
S336
R. S. Grove et al.
The high-relief Pendleton Artificial Reef has not persistently supported kelp and has not been favourably
affected by either the 1989 or 1999 La Niña events. In
contrast, the low-relief Mission Beach Artificial Reef,
the only artificial reef persistently to support giant kelp,
appears to respond to the El Niño/La Niña events
similarly to natural kelp beds. Prior to 1997, there had
been speculation that a major El Niño event would
eliminate kelp from this reef and that the concrete
substrate might become buried in the sand bottom.
Although the reef lost most of its kelp during the winter
storms of the 1997–1998 El Niño event, kelp seems to be
recovering as the 1998–1999 La Niña progresses and the
hard substrate of the reef has shown little change.
There appear to be a number of reasons why there
was no strong correlation between the ENSO index and
kelp abundance: (1) El Niños vary in both duration and
amplitude; (2) El Niños are only one factor of many that
effect kelp populations; (3) time-lags between an El Niño
and the manifestation of its effects may vary as a
function of its duration and amplitude; and (4) conditions immediately preceding and following each El Niño
episode, i.e. the sequencing of La Niña–El Niño–La
Nada (=normal) conditions, critically affects overall
kelp response.
The effect of event timing is well illustrated by the
different responses of kelp populations in the San Diego
and Santa Barbara regions to the 1982 El Niño storms.
These storms caused large declines in Macrocystis populations in the Pt. Loma kelp bed (Dayton and Tegner,
1984), but the same storms had apparent beneficial
effects for Macrocystis on Naples reef in the Santa
Barbara area (Ebling et al., 1985). Bottom surge generated by the storms cleared urchin populations from
Naples reef that had previously removed most of the
kelp. The loss of urchins allowed recruitment of a new
kelp population on the reef.
The effects of island shadowing on the intensity of El
Niño storm wave intensities (Pawka et al., 1984) also has
the potential to create localized differences in storm
effects on kelp populations.
Acknowledgements
We thank Dr Wheeler North for his unceasing enthusiasm and dedicated work with kelp, his data and insights
used herein, his encouragement, and his thoughtful
review of this manuscript. We dedicate this paper to
Karel Zabloudil, our esteemed co-author who passed
away this past year.
References
Carter, J. W., Jessee, W. N., Foster, M. S., and Carpenter,
A. L. 1985. Management of artificial reefs designed to
support natural communities. Bulletin of Marine Science, 37:
114–127.
Dayton, P. K. 1985. Ecology of kelp communities. Annual
Review Ecology and Systematics, 16: 215–245.
Dayton, P. K., and Tegner, M. J. 1984. Catastrophic storms,
El Niño, and patch stability in a southern kelp forest
community. Science, 224: 283–285.
Dean, T. A., and Jacobsen, F. R. 1986. Nutrient-limited growth
of juvenile kelp, Macrocystis pyrifera, during the 1982–
1984 El Niño in southern California. Marine Biology, 90:
597–601.
Demartini, E. E., and Roberts, D. A. 1990. Effects of giant kelp
(Macrocystis) on the density and abundance of fishes in a
cobble-bottom kelp forest. Bulletin of Marine Science, 46:
287–300.
Deysher, L. E., and Dean, T. A. 1986. Interactive effects of light
and temperature on sporophyte production in the giant kelp,
Macrocystis pyrifera. Marine Biology, 93: 17–20.
Deysher, L., Dean, T. A., Grove, R., and Jahn, A. 1998. An
experimental reef program to test designs of an artificial reef
for kelp mitigation. Gulf of Mexico Science, 16: 64–72.
Ebling, A. W., Laur, D. R., and Rowley, R. J. 1985. Severe
storm disturbance and reversal of community structure in
a southern California kelp forest. Marine Biology, 84: 287–
294.
Foster, M. S., and Schiel, D. R. 1985. The ecology of giant kelp
forests in California: a community profile. U.S. Fish and
Wildlife Service Biology Reports, 85(7.2). 152 pp.
Gerard, V. G. 1976. Some aspects of material dynamics and
energy flow in a kelp forest in Monterey Bay, California.
PhD Dissertation, University of California, Santa Cruz, CA,
USA. 173 pp.
Grant, J. J., Wilson, K. C., Grover, A., and Togstad, H. 1982.
Early development of Pendleton Artificial Reef. Marine
Fisheries Review, 44: 53–60.
Grove, R. S. 1982. Artificial reefs as a resource management option for siting coastal power stations in southern
California. Marine Fisheries Review, 44: 24–27.
Mann, K. H. 1973. Seaweeds: their productivity and strategy
for growth. Science, 182: 975–980.
North, W. J. 1971. The biology of giant kelp beds (Macrocystis)
in California. Nova Hedwigia, 32: 1–600.
North, W. J., and Curtis, M. D. 1998. Status of the Kelp Beds
1997–1998. Report presented to the San Diego Regional
Water Quality Control Board (Region Nine). MBC Applied
Environmental Sciences, Costa Mesa, California. 100 pp.
North, W. J., Gerard, V., and Kuwabara, J. 1982. Synthetic
and degradative processes in marine macrophytes. In
Proceedings of a Conference Held at Bamfield Marine
Station, Bamfield, Vancouver Island, British Columbia,
16–18 May 1980, pp. 247–262. Ed. by L. M. W. Srivastava.
de Gruyter, Berlin.
North, W. J., James, D. E., and Jones, L. G. 1993. History of
kelp beds (Macrocystis) in Orange and San Diego and
counties, California. Hydrobiologia, 260/261: 277–283.
Pawka, S. A., Inman, D. L., and Guza, R. T. 1984. Island
sheltering of surface gravity waves: model and experiment.
Continental Shelf Research, 3: 35–53.
Seymour, R. J., Tegner, M. J., Dayton, P. K., and Parnell,
P. E. 1989. Storm wave induced mortality of giant kelp,
Macrocystis pyrifera, in southern California. Estuarine,
Coastal and Shelf Science, 28: 277–292.
Tegner, M. J., and Dayton, P. K. 1987. El Niño effects on
southern California kelp forest communities. Advances in
Ecological Research, 17: 243–279.
Wilson, K. C., and Lewis, R. D. 1991. Report of Pendleton
Artificial Reef with recommendations for constructing a kelp
Effects of El Niño events on natural kelp beds and artificial reefs in southern California
reef. California Dept. of Fish and Game, Presented to
Southern California Edison. 42 pp.
Zabloudil, K., Reitzel, J., Schroeter, S., Dixon, J., Dean, T.,
and Norall, T. 1991. Sonar mapping of giant kelp density and
distribution. In Proceedings of Coastal Zone 91, pp. 391–406.
Ed. by O. Magoon, V. Tipte, H. Converse, and L. T. Tobin.
S337
American Society of Civil Engineering, Doc. 0-87262/88,
Long Beach, CA, USA.
Zimmerman, R. C., and Kremer, J. N. 1984. Episodic nutrient
supply to a kelp forest ecosystem in southern California.
Journal of Marine Research, 42: 591–604.