Size and density data were collected for Nereocystis luetkeana sporophytes from kelp beds in Van Damme Bay, Mendocino County during May, June and July 1990. Length and weight measurements were made on individual plants from

representative size groups collected from depths of 6.1 m and 12.2 m. Mean sporophyte weight was 268 g (SD 393 g), while mean stipe length was 214 cm (SD 275 cm). Densities were determined separately for those plants which had reached the surface and for all plants within the water column. Sixty-five 12.7 m2 surface quadrats yielded mean surface densities of 2.2 (SD 1.5) and 2.7 plants/m2 (SD 1.3) in June and July, respectively. Individual plants were counted within 42 1x5 m plots along benthic transect lines

yielding average densities of 2.7 (SD 4.5) and 5.2 plants/m2 (SD 3.0) in May and July, respectively. Combined density and size data from July 1990 and kelp bed area estimates from fall 1988 for Van Damme Bay yielded a biomass estimate of 640 metric tons distributed over 45.7 hectares.  (15pp.

Barns, Allison

Kalvass, Peter

English

Aquatic Commons

State of California
The Resources Agency
DEPARTMENT OF FISH AND GAME
BULL KELP, NEREOCYSTIS LUETKEANA, ABUNDANCE
IN VAN DAMME BAY, MENDOCINO COUNTY, CALIFORNIA
by
ALLISON BARNS
and
PETER KALVASS
MARINE RESOURCES DIVISION
Administrative Report No. 93-6
1993
Bull Kelp, Nereocystis luetkeana, Abundance
in Van Damme Bay, Mendocino County, California1
by
Allison Barns2
and
Peter Kalvass 3
ABSTRACT
Size and density data were collected for Nereocystis luetkeana sporophytes
from kelp beds in Van Damme Bay, Mendocino County during May, June and July
1990. Length and weight measurements were made on individual plants from
representative size groups collected from depths of 6.1 m and 12.2 m. Mean
sporophyte weight was 268 g (SD 393 g), while mean stipe length was 214 cm
(SD 275 cm). Densities were determined separately for those plants which
had reached the surface and for all plants within the water column. Sixty-
five 12.7 m2 surface quadrats yielded mean surface densities of 2.2 (SD 1.5)
and 2.7 plants/m2 (SD 1.3) in June and July, respectively. Individual
plants were counted within 42 1x5 m plots along benthic transect lines
yielding average densities of 2.7 (SD 4.5) and 5.2 plants/m2 (SD 3.0) in May
and July, respectively. Combined density and size data from July 1990 and
kelp bed area estimates from fall 1988 for Van Damme Bay yielded a biomass
estimate of 640 metric tons distributed over 45.7 hectares.
1 - Marine Resources Administrative Report No. 93-6
2 - Humboldt State Univ., Arcata, CA 95521
3 - CDFG, 19160 S. Harbor Dr., Fort Bragg, CA 95437
i
ACKNOWLEDGMENTS
The authors wish to thank Ian Taniguchi, Catherine Talbot and John
Mello of the Fort Bragg office of the Department of. Fish and Game for their
valuable assistance on this project. We would also like to thank Frank
Henry and Diana Watters for editing this report.
ii
INTRODUCTION
It is a curious phenomenon of fisheries management that species which
are long regarded as possessing little potential for human use may quickly
become an object of considerable economic interest. This may be influenced
by depletion of stocks of related species or simply a desire to explore new
endeavors. Recently, commercial interest in the bull kelp, Nereocystis
luetkeana, has increased in coastal northern California. Commercial abalone
culturists have expressed interest in harvesting bull kelp for use as feed
for their abalone, while others are interested in producing food additives
and fertilizer products from this resource.
The ecological impacts of large-scale harvest of Nereocystis are not
well known. Bull kelp forms extensive canopies which provide shelter and
feeding grounds to bony fishes and invertebrates, including abalone
(Haliotis spp.) and sea urchins (Strongylocentrotus spp.) (Burge and Schultz
1973, Bodkin 1986). In northern California, abalone are sought by sport
divers and red sea urchins support a large commercial fishery. If large-
scale harvest of Nereocystis develops, these economically important
fisheries could be negatively impacted. Beginning in about 1985 in the Fort
Bragg area, bull kelp beds appeared to increase in size and density, based
upon aerial photographic surveys, coincident with intensive harvest of red
sea urchins, a primary macroalgivore, by the commercial fishing industry
(Kalvass, Taniguchi, and Buttolph 1990). Surface canopies apparently peaked
in 1988, possibly reaching their maximum potential. Hobson (1989) has found
evidence that the observed increase in bull kelp may have been a temporary
response to urchin removals within a larger ecological framework, which may
lead to a future reduction in the bull kelp resource. In 1992, northern
California bull kelp recruitment and growth appeared to be both delayed and
reduced, possibly related to anomalously elevated nearshore sea temperatures
coincident with reduced upwelling.
Nereocystis has a recorded range from Point Conception, California to
Shumagin Island, Alaska (Burge and Schultz 1973). It is the dominant
canopy-forming macrophyte in the nearshore waters of northern California.
In addition to possessing a single stipe terminating in a large
pneumatocyst, Nereocystis differs from its relative Laminarian, the
perennial Macrocystis, in that there is no regrowth of damaged tissue once
the upper plant has been destroyed, and only one stipe is produced during
the lifetime of the sporophyte (Nicholson 1970). Nereocystis has an annual
growth and reproductive cycle with sporophyte growth initiation in early
spring, the first sporophytes usually reaching the surface by May, and
typically reaching peak development by September or October. Spores are
produced in fertile patches (sori) on the blades. Mature sori ready to
release spores separate from the blades (Amsler and Neushul 1989). The
first winter storms initiate the break up of bull kelp beds, with the slow
deterioration of beds throughout winter providing drift algae to benthic
macroalgivores (Burge and Schultz 1973). A few stipes may survive through
the winter and it is possible for these old sporophytes to regenerate blades
and again be reproductive (Nicholson 1970, Foreman 1970 in Burge and Shultz
1973) .
The purpose of this study was to estimate the abundance of Nereocystis
luetkeana in a cove near Fort Bragg, California during the late spring/early
summer months and provide baseline density and length/weight data to
2
researchers for use in kelp harvest management planning. Additionally, an
estimate of the maximum potential biomass of Van Damme Bay was made based
upon aerial photographs from the fall of ~988.
STUDY AREA
Bull kelp beds at Van Damme Bay, a cove along the coast of northern
California about ten miles south of Fort Bragg, Mendocino County, were
chosen for the study site since this large cove is easily accessible and
hosts some of the most extensive bull kelp beds in northern California
(Figure ~). Beds in the cove ranged in depth from approximately ~.5 to
~2.2 m.
METHODS
Field Sampling
Benthic Nereocystis Density
Benthic density data was collected in May and July, ~990. SCUBA
2divers examined forty-two, 5 m quadrats at depths of 6.1 and ~2.2 m. Once
inside a selected kelp bed, divers descended to the bottom from the anchored
skiff swimming in a northerly direction until encountering predominantly
rocky substrate. A 30 m transect line, marked at 5 m intervals, was placed
on the substrate in a north/south orientation. Each diver then used a
movable ~ m long PVC pipe attached to the line to mark 1 m x 5 m quadrat
boundaries on each side of the line. All sporophytes in a quadrat which
could be identified as Nereocystis were tallied on a slate carried by each
diver. Sporophytes are not identifiable as Nereocystis until they reach 6-
10 cm total length at which time a vertical line marking the origin of the
first blade division appears (Nicholson 1970). Individual bull.kelp plants
of representative size groups were removed from the substrate for length and
weight measurements. We attempted to remove the plants with as much of the
3
holdfast intact as possible.
Surface NereQQY$tis Density
Surface densities were calculated by counting all bull kelp
pneumatocysts (bulbs) floating within 12.7 m2 (roughly 2.5 x 5 m) quadrats
on the sea surface from an anchored skiff within a study kelp bed. Free
divers held the floating quadrat in place while bulbs were counted from the
boat. Quadrats circled the boat, placed consecutively but not overlapping.
We counted bulbs in 44 quadrats in June and 21 in July, 1990.
Laboratory Analysis
Length and Weight Measurements
Length and weight measurements were combined from 44 Nereocystis
sporophytes collected in May and July, 1990, covering a range of sizes
observed during underwater surveys. The kelp was kept covered in sea water
until measurements were taken at the Department's Marine Laboratory in Fort
Bragg. Total wet weight, stipe length (from insertion into holdfast to tip
of pneumatocyst), blade length (longest blade), total blade weight, number
of blades, and weight of holdfast (if available) were recorded. Figure 2
shows the external structure of a bull kelp sporophyte.
Biomass Estimate
Though peak bed area may not have remained constant from 1988 to 1990,
maximum potential kelp bed area at Van Damme was estimated using a 1988
aerial infrared photographic survey of kelp beds along the Mendocino/Sonoma
county coast of California (Kalvass, Taniguchi and Buttolph 1990) (Figure
1). 1988 appears to have been the peak biomass year for bull kelp based
upon annual aerial photographic surveys begun in the early 1980s. Foreman
(1984) reported no change in bull kelp bed area despite changes in kelp
4
density during a six-year study in British Columbia. A grid system, with
each grid representing 4,356 m2 , was overlaid on a map (scale 1:7700) of the
study area and used to estimate the kelp bed area. Average density and
plant weight were combined with the bed area estimate to calculate the total
biomass of Nereocystis at Van Damme.
RESULTS
Benthic Nereocystis Density
We counted 787 individual Nereocystis sporophytes over 210 m2 of
substrate from two discrete kelp beds. Mean Nereocystis density for the
combined sampling periods was 3.7 plants/m2 (SD 4.1). Mean density in May
was 2.7 plants/m2 (SD 4.5), increasing to 5.2 plants/m2 (SD 3.0) in July.
This increase may in part be attributed to small sporophytes which were not
identified as Nereocystis during the first sampling period. It is also
likely that small bull kelp sporophytes were present during both sampling
periods but not identified as Nereocystis due to their small size. Since
different locations within each bed were surveyed in May and July, the
increased density in July may be due to variation among these locations.
Surface Nereocystis Density
Sixty-five 12.7 m2 surface quadrats were examined. Mean surface
density for the combined sampling periods was 2.7 plants!m2 (SD 1.5). Mean
density for June was 2.1 plants/m2 (SD 1.5), while mean density for July was
2··.7 plants/m2 (SO 1.3).
Length and Weight Measurements
Mean plant weight was 268 g (SO 393). Mean stipe length was 214.1 cm
(SD 275.2). The relationship between plant weight and stipe length is
expressed by the regression formula of y=O.OO+1.02x (Figure 3) ·
5
Biomass Estimate
The maximum potential surface area of bull kelp beds at the Van Damme
study area was estimated to be approximately 457,300 m2 (113 acres) based
upon the fall 1988 aerial photographic survey. Two types of biomass
calculations were made: an estimate of potentially-harvestable kelp based
upon surface counts, and a more inclusive water column estimate based upon
benthic transect counts. July values were used for making the biomass
estimates because they were taken closer to the time of peak biomass
(September/October). We did not sample after July due to time and budget
constraints.
The average surface density in July of 2.7 plants/m2 (SD 1.3)
yielded an estimated potential of 1,234,700 sporophytes for the entire Van
Damme site (the 95\ C.l. ranged from 964,900 to 1,504,500).
Average density from benthic surveys in July of 5.2 plants/m2 (SD
3.0) yielded a potential of 2,378,000 sporophytes for the entire study area,
with a 95\ C.I. from 1,692,000 to 3,059,300. Applying the mean plant weight
of 268 g/plant yields 1,394 g Nereocystis/m2 . The kelp beds at Van Damme
were estimated to contain a biomass potential of 640 metric tons of bull
kelp at 1.4 kg/m2 .
DISCUSSION
Van Damme Bay was estimated to contain a biomass potential of
approximately 640 metric tons of Nereocystis based upon maximum potential
kelp bed area estimates from the fall of 1988. In British Columbia, Foreman
(1984) reported 500,000 mt of bull kelp in 11,600 hectares of bed area, or
4.3 kg/m2 . Burge and schultz (1973) reported Diablo Canyon kelp beds had
about 20.4 mt of bull kelp in an estimated 4,046 m2 bed area, or 5.0 kg/m2 .
The British Columbia beds had three times while Diablo Canyon had about 3.6
6
times the biomass density of Van Damme. Since the present study does not
include data for the fall season of peak biomass, these differences are
perhaps more a reflection of within-season variation rather than true
differences in peak biomass.
Foreman (1984) presented linear regressions of sporophyte weight upon
stipe length for bull kelp from 11 different locations in British Columbia
and at Salt Point in northern California. Regression coefficients varied
from 1.94 to 7.38 compared to our value of 1.02. Our low value probably
reflects a growth strategy in which the plants undergo rapid stipe
elongation initially, apparently in search of light, followed by an increase
in blade biomass. Most of our plant collections were too early in the
season to show the later phase of growth. Growth rates of 6 em/day have
been recorded for bull kelp (Nicholson 1970) .
Bull kelp beds are known to experience year to year fluctuations in
density (Foreman 1984; Burge and Shultz 1973). Foreman (1984) found high
Nereocystis densities correlated with years with low mean annual sea water
temperatures and salinities, though bull kelp has a wide temperature and
salinity tolerance (Vadas 1972 in Foreman 1984). This characteristic, along
with an annual life cycle and rapid growth capability, appears to allow
Nereocystis to inhabit sites not suitable for perennial competitors such as
Macrocystis. It is possible that the present study and the British Columbia
and Diablo Canyon studies mentioned above reflect atypical years. Biomass
estimates for several successive years would be needed to increase accuracy.
Foreman (1984) found no observable deleterious impacts as the result
of his experimental harvests of British Columbia Nereocystis beds. He
suggested that the potential effects of biological and physical factors
7
(i.e. light intensity, temperature and salinity) on yearly fluctuations in
Nereocystis density and standing crop be of primary concern to resource
managers.
Bull kelp canopies serve as shelter and feeding grounds for many bony
fishes and invertebrates. Bodkin (1986) identified 27 species of fish
living in Nereocystis canopies off the central California coast. Bull kelp
is a primary food source for abalone and sea urchins, both of which comprise
important fisheries in the Fort Bragg area. In northern and central
California 400 to 1500 metric tons of abalone were taken annually by sport
fishermen between 1985 and 1989; 77 percent of this effort was in the same
area being considered for kelp harvest (Mendocino and Sonoma counties) (K.
Karpov, California Department of Fish and Game (CDFG), pers. comm.). The
ten year (1980-1989) average of commercial sea urchin landings in Fort Bragg
was 2,372 mt, worth $1,355,000 (CDFG unpub. rpt. 1990).
A 1989 aerial photographic survey revealed that only about 11 percent
of California's canopy forming kelp beds were in Mendocino and Sonoma
counties (Van Wagenen 1990); north of Bodega Bay (Sonoma County), these kelp
beds are almost exclusively comprised of bull kelp. Based upon long-term
subtidal surveys in the vicinity of Van Damme Bay, Hobson (1989) suggest
that as the urchin fishery in northern California stabilizes and subtidal
kelp beds increase their colonization of formerly urchin dominated areas,
there will be a decrease in the bull kelp bed density as lower growing
perennials like Laminaria sp. and Pterygophora californica begin to
outcompete Nereocystis germlings for light and space. The urchin/kelp
dynamic appears to be undergoing a succession of significant magnitude, with
the outcome unclear at this time.
8
LITERATURE CITED
Amsler, C.D., and M. Neushul. 1989. Diel periodicity of spore release
from the kelp Nereocystis luetkeana (Mertens) Postels et Ruprecht.
Journal of Experimental Marine Biology and Ecology, 134:117-127.
Bodkin, J.L. 1986. Fish assemblages in Macrocystis and Nereocystis kelp
forests of central California. Fishery Bulletin, 84(4) :799-808.
Burge, R.T., and S.A. Schultz. 1973. The marine environment in the
vicinity of Diablo Cove with special reference to abalones and bony
fishes. California Department of Fish and Game Marine Resources
Technical Report No. 19, 423 p.
Foreman, R.E. 1970. Physiology, ecology and development of the brown alga
Nereocystis luetkeana (Mertens) P. and R. Ph.D. Dissertation, University
of California, Berkeley. 114 p.
Foreman, R.E. 1984. Studies on Nereocystis growth in British Columbia,
Canada. Hydrobiologia, 116 (117) :325-332.
Hobson, E. 1989. Changes in the nearshore environment attributed to sea
urchin fishery. NMFS-Tiburon Lab. Newsletter, p.2S.
Kalvass, P., I. Taniguchi, and P. Buttolph. 1990. Relative abundance and
size composition of red sea urchin, Strongylocentrotus franciscanus,
populations along the Mendocino and Sonoma county coasts, August 1988.
California Department of Fish and Game, Marine Resources Division,
Administrative Report No. 90-1, 101 p.
Nicholson, N.L. 1970. Field studies on the giant kelp Nereocystis.
Journal of Phycology, 6:177-182.
Vadas, R.L. 1972. Ecological implications of culture studies on
Nereocystis luetkeana. Journal of Phycology, 8:196-203.
Van Wagenen, R. 1990. California coastal kelp resources, summer 1989.
Rev. 1.0. Ecoscan (unpublished).
9
•W.ndoclno Co.
Northerll Caillorllia .
• • • • • II II .
. ..:&5 &: .
.. -----------1------
..... .....
Vall namm. Bay
W'DelociIlO. Co•
._._-----
....
FIGURE 1. Location of Van Damme Bay, California (top). Peak bull kelp production in Van
Dammc Bay, fall of 1988 (bottom). Survey sites are S=surfacc, B=benthic.
5CM
BLADES
IOOCM
HOLDFAST
FIGURE 2. External structure ofNereocystis luetkeana (from Abbott and Hollenberg 1976).
o2000
0
y=O.OO+ 1.02x
1600
R
2
=0.51
-(;)
- 1200I-
:r:
Q
UJ
~
...J 800~
0
I-
400
o 200 400 600 800 1000 1200
STIPE LENGTH (eM)
Figure 3. Linear regression of total plant weight on stipe length of Nereocystis luetkeana from
VanDamme Bay. California.


Bull kelp, Nereocystis luetkeana, abundance in Van Damme Bay, Mendocino County, California

http://aquaticcommons.org/378/1/Admin._report_No._93-6.pdf

Bull kelp, Nereocystis luetkeana, abundance in Van Damme Bay, Mendocino County, California

Abstract

Similar works

Full text

Available Versions

Aquatic Commons