T . Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
93
the captured crab in McMurray et al. 1984, n 5 138 crab, all , 10 mm CL; in Stevens
and MacIntosh 1991, n 5 36 crab, , 16 mm CL. Calculations only included tows in
which age 0 1 red king crab were caught ‘successful’ tows, assuming that all
unsuccessful tows were conducted in non-nursery habitat. As such, the resultant estimates should: a overestimate catch rates if unsuccessful tows were conducted within
nursery habitat, or b underestimate catch rates if successful tows were not completely contained within appropriate habitat.
3. Results
3.1. Dive transects and suction dredge surveys Early benthic phase EBP; cryptic individuals generally
, 1.5 years post-settlement red king crabs were found only in the most physically complex substrates during both
transect surveys and suction dredge sampling. A total of eight EBP crabs, estimated to be approximately 15 months post-settlement, were found during dive transects: five
crabs in the rocky rubble at Indian Point, three beneath a piece of corrugated fiberglass roofing material in the sand shell-hash along the east shore of Auke Cape, and none in
the muddy silt bottom in Auke Nu Cove. In both 1997 and 1998, the only crabs located via suction dredge were found at Indian Point 1997: n
5 4, average density 5 2.061.1
22
individuals m , estimated age
5 10 months post-settlement, average size 5 6.960.1
22
mm CL; 1998: n 5 4, average density 5 2.061.3 individuals m , estimated age 5 11
months post-settlement, average size 5 10.160.5 mm CL. These results are comparable
to those reported by Sundberg and Clausen 1977 in Cook Inlet Tables 2 and 3. Densities were much higher than reported for the southeast Bering Sea, presumably due
to more efficient sampling methods used in this study.
3.2. Larval collection Results of ANOVA indicate that differences in larval supply, expressed as the average
number of larvae and postlarvae per collector, were apparent between sites Table 4. Pair-wise comparisons of larval supply at each site, at the 5 level of significance, yield
the following groupings: S5 . S3 5 S4 . S2 5 D1 5 D3. In general, the greatest
abundance of glaucothoe occurred in shallow water along the east side of the Cape. Larval supply was highest over muddy silt bottom in Auke Nu Cove S5 and was at
intermediate levels at East Shore S4 and Indian Point S3. Larval supply was lowest on the western shore of Auke Cape S2 and at 20 m depth D1, D3.
Larval abundance within collectors did not vary significantly over time during the study df
5 2, P 5 0.1807; Fig. 3. The lack of temporal variation suggests that the majority of settlement had already occurred by late-June and that collectors were
effective in retaining settled individuals over the study period. This is further supported by examining the size composition of larval post-larval king crab populations within the
collectors during each sampling period Fig. 4. While the collectors sampled earliest were populated primarily by glaucothoe, only 7.2 of the crab collected in mid-July
94 T
. Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109 Table 2
Density of EBP red king crab located at the Indian Point nursery habitat in this study compared to data from other researchers in Cook Inlet and the southeast Bering Sea. Levels observed in this study are similar to those
observed by Sundberg and Clausen 1977. Much lower densities observed in the southeast Bering Sea are probably due to much less effective sampling methods
Authors Crab age, in years
Gear used Estimated population
22
location study season
density [ crab m This study
late 0 1
diver-operated suction dredge 1997: 2.0
61.1 Southeast Alaska
May 1998: 2.0
61.3 Sundberg and Clausen 1977
1 A diver-operated suction dredge
A1.33 61.47
Cook inlet August–Sept
B hand collection of erect Bryozoa B 1.95 error unreported;
21
5 Flustrellidra sp. by divers 3.85 crabs kg
of Flustrellidra, wet weight
McMurray et al. 1984 1 to 2 1
A rock dredge 0.9m 3 0.4m rigid
A 0.037 60.057
Southeast Bering Sea April–Sept
frame, net mesh-size not reported B try net 5.4 m head-rope length,
B 0.0021 60.0032
net mesh-size not reported Stevens and McIntosh 1991
1 to 2 1 beam trawl 3.0 m
3 0.6m rigid 0.00066
60.00059 Southeast Bering Sea
May–June frame, 12 mm stretch-mesh cod end
were at this stage of development, and by late-July no glaucothoe were present. Inspection of the larval post-larval size-distributions Fig. 4 suggests that over half of
the post-larvae sampled in late-July had reached the second instar, indicating little new settlement, but retention and growth of individuals that had settled earlier. The
interaction of sampling period
3 site on larval abundance showed no statistically significant trend df
5 8, P 5 0.0535. 3.3. Early post-settlement habitat use
In order to facilitate comparison of results on use of early post-settlement habitat with the suction-dredge sampling, we report postlarval population densities normalized as the
number of settlers per square meter of pail area. Postlarval density patterns were site-specific, as well as temporally structured Fig. 5. Significantly detectable abun-
dances of settled crabs were found in both the rocky rubble at Indian Point and the shell-hash at East Shore during all sampling periods East Shore, t
5 36.9898, P 0.001; Indian Point, t
5 25.7380, P 0.001 while no glaucothoe or postlarvae were detected at any time in muddy silt at Auke Nu Cove. With respect to East Shore and
Indian Point, differences in postlarval density varied significantly between the two sites and between sampling periods Table 5. Throughout time, postlarval crab density in
rocky rubble habitat was approximately three times greater than in sand shell-hash substrate rocky rubble
. sand shell-hash . muddy silt; see Fig. 5. Densities were significantly higher during mid-July than at any other time, after which they fell to levels
similar to initial, late-June densities and remained at those levels into mid-September. In addition to age 0
1 crab, a total of four age 1 1 individuals were found in
T . Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
95 Table 3
Substrate characteristics and biogenic associations reported for early benthic phase red king crab age 0 to 2
1 in this study, and by other researchers throughout the Gulf of Alaska and Bering Sea
a
Authors Sampling method
Biogenic correlates Substrate correlates
Southeast Alaska: This study
suction dredge, none apparent
rocky rubble, cobble diver transects,
shell-hash settlement pails
Karinen 1985 diver observation
none reported shale, slate,
overlapping debris Freese and Babcock 1989
diver observation none reported
shale, cobble, gravel, pebble
Cook inlet Kodiak: Sundberg and Clausen 1977
suction dredge, Spn, Bryo
5 Flsp Dnsp, ‘‘coarse substrate’’ shell,
bottom skimmer Hydr, RdAl
cobble, boulder Powell and Nickerson 1965
diver observation Kelp, SSt, possibly Barn
rock crevices, pilings Dew 1990, 1991,
diver observation SSt
5 Et Aa, Anem 5 Ms pilings
Dew et al. 1992 Southeast Bering Sea:
Anonymous 1959 commercial tangle net
Hydr; fouling organisms not reported
McMurray et al. 1984 try net, rock dredge
Bryo, TPly, SSt 5 Aa,
gravel Urch
5 Sd Stevens and MacIntosh 1991
beam trawl beam trawl
not reported Kamchatka:
Orlov 1964 net not described
Algae 5 Ansp. Srsp
not reported Vinogradov 1968
Sigsby trawl, Hydr, RdAl, SSt
5 Lpsp not reported
diver observation Rodin 1985
not reported Spn, Hydr, Echn
not reported
a
Biota abbreviated as follows: Spn 5 sponge; Bryo 5 bryozoan; Hydr 5 hydroid; RdAl 5 red algae; SSt 5
sea star; Barn 5 barnacle; Anem 5 anemone; TPly 5 tubicolous polychaete; Urch 5 sea urchin; Echn 5
echinoderm; Flsp .
5 Fustrellidra sp.; Dnsp 5 Dendrobeania sp.; Et 5 Evasterias troschelii; Aa 5 Asterias amurensis; Lpsp
5 Leptasterias sp.; Ms 5 Metridium senile; Sd 5 Strongylocentrotus droebachiensis; Ansp 5 Ahnfeltia sp.; Srsp
5 Sargassum sp.
settlement pails at Indian Point over the course of the experiment. These individuals had apparently moved into the pails from the surrounding substrate, indicating a temporal
overlap in nursery usage by the 1996 and 1997 cohorts. Age 1 1 crab ranged in size
from 8.35 to 15.50 mm CL, with larger individuals found later in the summer Fig. 6.
Table 4 Summary results of 2-factor ANOVA testing the effects of date and site on combined larval plus postlarval red
king crab densities observed in larval collectors Source
df SS
MS F-value
P Date
2 24.7167
12.3583 1.7576
0.1807 Site
5 1478.7167
295.7433 0.4206
0.0001 Interaction
8 115.6500
14.4563 2.0560
0.0535 Residual
64 450.0000
7.0312
96 T
. Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
Fig. 3. Abundance of red king crab in larval collectors deployed at 7 sites around Auke Cape. No data were available for site S1 in late June and mid-July due to loss of collectors. Abundance was not determined at deep
sites in late July; collectors at deep sites were devoid of crabs in mid-July. Error bars represent one standard error about the mean. Statistical tests indicate three groupings with regard to post-larval abundance: S5
. S3 S4
. S2 Dl D3.
3.4. Substrate characteristics Indian Point is characterized primarily by rocky cover, a feature which is much
reduced at East Shore and essentially absent from Auke Nu Cove Fig. 7. Approximate- ly 80 of the bottom at Indian Point is large, loose cobble, rocky rubble and boulder.
These are angular rock fragments measuring approximately ten centimeters to a meter in maximum diameter and even the sediments underlying this surface layer are laden with
larger particles such as cobble and pebble, which comprise more than half of the overall sediment composition Fig. 8. In contrast, the only large surface cover items at Auke
Nu Cove are shells and shell fragments that represent less than 2 of the total cover Fig. 7. While grain-size analyses indicate that nearly 10 of the sediment at Auke Nu
Cove is comprised of cobble-sized particles and nearly 20 is pebble-sized, these particles are almost completely submerged in fine sediment Fig. 8 making them
unavailable as cover for settling glaucothoe. The East Shore site represents a transition between the former two habitats Figs. 7, 8. A small amount of rock and shell is found
at the surface, and sediments are coarser in texture than at Auke Nu Cove. East Shore is
T . Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
97
Fig. 4. Size and instar composition of red king crab glaucothoe and early benthic instars from larval collectors, late June through late July. Data from all sites are pooled for late June and mid-July. Late July depicts only
crab from the Auke Nu Cove site, since post-larvae from the other sites were not measured, being retained for use in separate behavioral experiments.
98 T
. Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
2
Fig. 5. Age 0 1 red king crab densities normalized as number meter at the three primary study sites as
observed in settlement pails open symbols during the summer of 1997, and in situ by suction dredge closed symbols the following spring, bars represent one standard error about the mean. Population densities were
significantly higher in mid-July than on all other dates; differences between sites are also significant at the 0.05 level see Table 4.
typified by a more even mix of particle sizes with substantial amounts of coarse sand and ‘pebble’, much of which is actually crushed shell of various sizes.
It is important to note that none of the sites were substantially colonized by vertically protruding ‘erect’ epibiota. Percent-cover estimates for epifauna at each site were as
follows: Indian
Point 5 0.260.2, East Shore 5 0.260.1, Auke Nu Cove 5
0.02 60.03. Epifaunal cover at Indian Point was comprised primarily of anemones.
Protruding bivalve siphons and a single bryzoan colony occurred at East Shore. At Auke Nu Cove a single ascidian was the only erect epibiont noted. At Indian Point, three
species of brachiopod Laqueus californianus, Terabratalia transversa, and Hemithiris psittacea were also observed, but since they were found exclusively on the underside of
rocks they do not appear in these percent cover estimates. However, their overall cover seemed similarly low.
Epiphytic cover was more site-dependent. None appeared in the quadrat photos from East Shore and Auke Nu Cove. At Indian Point, kelps Laminaria spp. and Agarum
T . Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
99 Table 5
Summary results of Poisson regression analyses testing the effects of site and sampling date on densities of post-settlement red king crab in settlement pails. The t-statistics associated with the site variable compare
early-post settlement survival rates at East Shore to that at Indian Point. In an attempt to resolve all significant differences between between sites, the model was run multiple times with respect to date. Reported here are
the results comparing each date to mid-July configuration A and to mid-September configuration B. These indicate that post-settlement densities during mid-July were different from all other dates, and that late June,
late July, and mid-September were not significantly different from one another
Independent Estimated
Standard t-statistic
variable coefficient
error Site:
a
East Shore 2 1.06947
0.35226 2 3.0598
Sampling date model configuration A:
a
late June 2 1.48396
0.49902 2 2.97377
a
late July 2 1.0 1397
0.41793 2 2.42614
a
mid-September 2 1.01397
0.41822 2 2.42451
Sampling date model configuration B: late June
0.03698 0.51763
0.07144
a
mid-July 0.95327
0.43925 2.17020
late July 2 0.2507 1
0.55642 2 0.45057
a
Significant at the 0.05 level.
clathrum were a common member of the community. They appeared in quadrat photos
22
at a density of 4.7 63.2 holdfasts m . Their total percent cover was not calculated for
the following reasons: 1 kelp cover is seasonally variable and relatively low at 12 m
Fig. 6. Size of age 0 1 red king crab collected from settlement pails closed symbols and suction dredge
quadrats open symbols in 1997 circles and 1998 triangles. Estimated ages are based on a settlement date of June 30th, consistent with the larval settlement patterns observed during 1997. The dashed line is a linear
2
regression through the points line equation: y 5 0.070x 2 16.87; r 5 0.94 and has been included only to
highlight that larger individuals were collected later in the summer.
100 T
. Loher, D.A. Armstrong J. Exp. Mar. Biol. Ecol. 245 2000 83 –109
Fig. 7. Percent cover of the three major substrate types rock, shell, and sediment at each of the three primary study sites. Error bars represent one standard error about the mean.
depth during the spring and early summer when red king crab glaucothoe are settling, and, 2 in order to maintain consistancy between the settlement pails, kelp was avoided
when filling them with substrate. Thus, densities at the site did not reflect experimental conditions within the pails. Of the 31 settlement pails retrieved, only 4 contained kelp
while 17 contained early post-settlement red king crab.
4. Discussion
