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Western Range Extension for Nereocystis luetkeana in the North Pacific Ocean

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Abstract

Discovery of a bed of Nereocystis luetkeana (Mertens f.) Postels et Ruprecht extends the known range of this species to Umnak Island, about 100 km west of Unalaska Island in the eastern Aleutians. This abrupt range termination cannot be correlated with similarly abrupt changes in environmental parameters, but light limitation is suggested as the most likely factor limiting the distribution of Nereocystis. The range of Nereocystis may fluctuate according to long term cycles, as do the ranges of other kelps in the northeastern Pacific Ocean.
Mi11er and Estes: Western range extension lor Nereotl'stis luetkeana in thc north Pacific 535
Botanica Marina
Vol. 32. pp. 535-538, 1989
western Range Extension for lr{ereocystis luetkeana
in the North Pacific Ocean
K. A. Iv{iller and J. A. Estes*
Llniversity Herbarium, university o/ CatiJbrnia, Berkeley, Cali/ornia 94720' Lr's.4.
* U.,S. Fish and Witettife Seryice,lnstitute of Marine Slutlies, Llniversitv- o.f California, Santa Crtrz, Califurniu
95064, U.S.A.
(Accepted 1 July 1989)
Abstract
Discovery of a bed of Nereocy-stis luetkeana (Mertens f.) Postels el Ruprecht extends the known range of this
species to Umnak Island, about 100 km west of Unalaska Island in the eastern Aleutians. This abrupt range
tirmination cannot be correlated with similarly abrupt changes in environmental parameters, but light
limitation is suggested as the most likely factor limiting the distribution of Nereoi',i s/rs. The range of ly'er eocystis
may fluctuate according to long term cycles, as do the ranges of other kelps in the northeastern Pacific Ocean'
Introduction
The western distributional boundary of the annual
kelp Nereoc.vstis luetkeana (Mertens f.) Postels el Ru-
precht (Lessoniaceae, Laminariales) is variously re-
corded as Unalaska Island, Alaska (53.19'N'
161"25'W; e.g., Druehl 19'70, Lindstrom 1917,
Hawkes et al. 1978, Scagel et al. 1987) or the Shu-
magin Islands, Alaska (50'5'N, 159"45'W; e' g', Vadas
1912, Abbott and Hollenberg 1976) (Fig' 1)' The
occurrence of attached populations has not been sub-
stantiated west of Unalaska Island, although drift
plants have been sighted throughout the Aleutian
chain to Attu Island (Lebednik and Palmisano 19ll;
our own observations and voucher specimen UC
1569901 from Chichagof Harbor, Attu Island), the
Commander Islands (Kardakova-Prezhentsova 1 938)'
the Kuril Islands (Abbott and Hollenberg 1976) and
Japan (Kawashima 1986)'
Observations
During a five week cruise in June-July 1987, we did
not observe attached plants from Attu Island through
the Islands of the Four Mountains, but on 11 July
1987. at the southwest end of Umnak Island, Alaska,
we saw what we believe to be the westernmost pop-
ulation of Nereocl'slls. We anchored and dove at
52'51.57'N, 168'56.87'W (Fig. 1, diamond symbol)'
This site is 2 degrees (about 100 km) west of Unalaska
Island, and the l{ereot'.vstis bed extended at least
several kilometers farther to the west. The bed con-
sisted of mature plants growing in depths of 6 - 12 m,
forming a substantial surface canopy. Two juvenile
plants (10 cm tall) were seen. Most pneumatocysts
exceeded 15 cm in diameter; stipes were up to 12 m
long, and blades, also up to 12 m long, bore fertile
sori. Upper portions of the stipes were heavily epi-
phytized with meter long thalli of reproducrive Por-
phyra nereotTslis Anderson and other algae. The low-
relief bottom was dominated by filter-feeding inver-
tebrates, especially encrusting sponges and barnacles'
The kelps Laminaria groenlandica Rosenvinge and L'
yezoensis Miyabe were well-developed, but the red
algal understory was depauperate. The predatory gas-
tropod Thais lamellosa (Gmelin 1791) and the pred-
atory asteroids Pycnopodia helianthoides (Brandt
1835) and Orthosterias kohleri (de Loriol 1897) were
common. From the faunal composition of this com-
536 Miller and Estes: Western range cxtension for Nereot'y.rtis luetkeana in thc north Pacific
Fig. 1. The Aleutian Islands (insert shows position of the Alcutian chain with respect to the mainland). Black diamond indicates
site of the Nereocystis bed off Umnak Island.
munity and the absence of Alaria fistulosaPostels et
Ruprecht, we infer that this site is exposed to swells
and currents passing through the adjacent Samalga
Pass (between Umnak and the Islands of the Four
Mountains).
Discussion
The large size and the maturity ol these Nereocystis
plants and their epiphytes were surprising. Hawkes
(1981) described the seasonal occurrence of Nereo-
cystis in Barkley Sound on the west side ol Vancouver
Island, Canada (48"50'N, 125'11'W). There, sporo-
phytes appear at the beginning of March and reach
the surface by July, at which time stipe elongation is
reduced. Epiphytes appear in August and increase in
abundance through the winter. Porphyra nereocystis
appears in late November or early December and is
reproductive from January to July. Most of lhe ltler-
eocystis population is carried away by winter storms.
Porphyra present in spring and summer is epiphytic
on Nereocyslrs surviving from the previous year.
Nereocysti,s sporophytes in the Umnak population
may have either started growing earlier or they grew
more quickly than those in the Vancouver Island
population; their summer condition seemed to be
equivalent to the fall and winter condition of the more
southern plants. Alternatively, the entire population
may be composed of second-year plants (holdovers
from the previous season). This situation is unlikely,
however, as most plants appeared to be similar in size
and maturity, and no cohort of younger plants was
seen. Because we were able to observe this population
only once, we cannot confirm this apparent difference
in seasonal development, but can suggest that the
Umnak population, like those farther south, is essen-
tially annual with some plants persisting into a second
year.
We are intrigued by the abrupt termination of Ner-
eocy,stis east of Samalga Pass and the exuberant
expression ol growth and reproduction in this popu-
lation on the margin of the species' geographic range.
Two explanations are generally given for such a pat-
tern:
1) further expansion westward is limited by a barrier
to dispersal or
2) habitats to the west are physically or biologically
unsuitable for growth andf or reproduction.
Although we noted high-velocity currents in Samalga
Pass that might prevent I{ereocystis from successfully
dispersing west to the Islands of the Four Mountains,
the broad distribution of apparently healthy drift
plants at islands as far west as the Kuril and Japanese
archipelagos argues against the dispersal barrier hy-
pothesis.
Seawater temperature gradients are often correlated
with changes in plant distribution, especially latitu-
dinal (e.g., Setchell 1920). Liining and Freshwater
(1988) concluded that a species' upper temperature
limit was a conservative taxonomic trait and deter-
mines the southern limits of its distribution. Usins
Miller and Estes: Western range extension lor Nereocystis luetkeana in the north Pacific 537
net positive photosynthesis as a criterion for survival,
they lound that l{ereocyslrs sporophytes were able to
survive one week at temperatures ranging from
- 1.5 'C to 18 'C. Vadas (1912) showed, through cul-
ture studies, that the eflective temperature limits for
reproduction in Nereor:ysrrs sporophytes and game-
tophytes are 3 'C and 1l '''C. It seems unlikely that
diflerences in sea water temperature sulficient to limit
reproduction in lVereocyslls occur over the less than
20 km separating the west end of Umnak Island and
the Islands of the Four Mountains, especially since
the Kuroshio current moderates seawater tempera-
tures through most of the year along the Aleutian
chain (McAlister and Favorite 1977).
Yadas (1972) also demonstrated that temperature has
less effect than light intensity on the growth and
development of gametophytes and young sporo-
phytes, and that the total quantity of light (intensity
x photoperiod) is the most important factor in the
development of both phases. He correlated maximum
growth with periods of maximum light availability.
Although summer days are long at 50.N, the western
Aleutians are extremely foggy, especially during sum-
mer (Armstrcng 1977), and light levels are low. A1-
though Wheeler et al. (1984) demonstrated that l/er-
eocystis can utilize low levels of light for photosyn-
thesis, Duncan and Foreman (1980) reported that
stipe elongation in Nereocystis is a phytochrome-me-
diated response to far-red illumination. Fog may con-
tribute to a reduction in light quality as well as quan-
tity sufficient to inhibit stipe elongation. Thus, .Ay'er-
eocystis may be light-limited west of Umnak Pass,
especially at the time of its early growth, when tem-
peratures are also low (McAlister and Favorite 1977).
Alaria fistulosa, a canopy-forming kelp, is competi-
tively subordinate to the dense community of peren-
nial stipitate Laminaria species in the Aleutians (Day-
ton 1975). Nereocystis is also a poor competitor for
substrate. Cowen et al. (1982) stated that the annual
Nereocystis replaces the perennial Macrocystls only
when Macrocysrls is removed by storms. In California
and Washinglon, I\,trereocyslls is an opportunistic col-
onizer in sea urchin-dominated areas that lack per-
ennial algal cover (other than encrusting corallines)
and tend to have high light levels (e.g., troster 1982).
Still, the increase in sea urchin-dominated habitats in
the Aleutians since the extirpation of sea otters (e. g.
Estes 1977) has not promoted the western spread of
l{ereocystis.
Environmental and biotic factors not considered here
or elsewhere must influence seaweed distributions in
this interesting region. The geographic range of Ma-
crocystis integrifolia Bory (Lessoniaceae) agrees
closely with that of l,{ereocystrs (Foster and Schiel
1985) and may be maintained by similar mechanisms,
as yet unknown. Our sighting of l{ereocystls at Um-
nak may represent evidence that the endpoint of the
range of Nereocystis in Alaska fluctuates according
to seasonal or larger cycles, as do those of Macrocystis
pyri/bra (Linnaeus) C. Agardh in Baja California,
Mexico (Foster and Schiel 1985) and Alariafistulosa
in southeast Alaska and northern British Columbia
(Widdowson 7964, L. Druehl, personal communica-
tion). In light of the difficulty of defining, either
descriptively or experimentally, mechanisms that
structure the geographic range of a given species, we
recognize that the maintenance of distributional limits
is a dynamic evolutionary process acting on the pop-
ulation level, rather than a hxed, specific attribute of
any individual plant.
Acknowledgements
We thank Drs P. Silva, R. Moe, D. Garbary, L.
Druehl and a reviewer lor the U. S. Fish and Wildlife
Service for critically reading this manuscript, and Dr
L. Vorobik lor preparing the illustration. We are also
grateful for support from N. S. F. Polar Biology and
Medicine Grant DPP-8421362 to C. Simenstad, D.
Duggins, and J. Estes; the crew of the P.IY Alpha
Helix; the U. S. Coast Guard (Kodiak Air Station,
17th District); and the U. S. Fish and Wildlife Service,
Alaska Maritime Refuge (Kodiak Island, Aleutian
units).
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... Indeed, floating rafts of Macrocystis pyrifera are commonly observed along the west coasts of North and South America (Dayton et al., 1984;Dayton, 1985;Hobday, 2000;Macaya et al., 2005;Hernández-Carmona et al., 2006;Rothäusler et al., 2009;Hinojosa et al., 2010;Macaya and Zuccarello, 2010), where they have been identified as important long distance dispersal vectors (Batista et al., 2018). Similarly, drifting Nereocystis leutkeana with reproductive sporophylls have been observed cast on the beach and floating near the coast of Shemya Island in the Aleutian Archipelago, which is approximately 1,170 kilometers to the west of the western range limit of the species at Unmak Island, Alaska (Miller and Estes, 1989). However, Nereocystis leutkeana has yet to establish large sporophytes to the west of Unmak Island, which may be due to constraints posed on its microscopic life stages (Miller and Estes, 1989; discussed below). ...
... Similarly, drifting Nereocystis leutkeana with reproductive sporophylls have been observed cast on the beach and floating near the coast of Shemya Island in the Aleutian Archipelago, which is approximately 1,170 kilometers to the west of the western range limit of the species at Unmak Island, Alaska (Miller and Estes, 1989). However, Nereocystis leutkeana has yet to establish large sporophytes to the west of Unmak Island, which may be due to constraints posed on its microscopic life stages (Miller and Estes, 1989; discussed below). Nereocystis leutkeana sporophytes have also been observed drifting along the coast of Oregon, USA where they have been identified as an important vector for the colonization of associated flora and fauna (Kidder, 2006). ...
... On a longitudinal gradient, Miller and Estes (1989) observed that the western range limit of Nereocystis leutkeana in the Aleutian Islands was set at Unmak Island, just to the east of the Samalga Pass. While they did not determine the factors that set this range limit, they did hypothesize that it was likely due, at least in part, to the ability of its microscopic stages to reproduce under the lower light conditions that are established by the heavier cloud and fog cover to the west. ...
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... Consequently, the pass marks a transition where many offshore species, such as demersal fish and deep water faunal communities, reach their range limits and where the structure and productivity of pelagic food webs markedly differ on opposing sides of the pass (Sinclair & Zeppelin, 2002;Coyle, 2005;Jahncke et al., 2005;Logerwell et al., 2005). The pass also coincides with a transition in the community structure of many species of coastal fishes, in particular cods and greenlings (Konar et al., 2015), and marks where the forest-forming bull kelp, Nereocystis luetkeana, experiences its western range limit (Miller & Estes, 1989). Three explanations have been suggested to explain these abrupt changes in ecosystems at Samalga Pass: 1) differences in pass width and depth to the east and west; 2) water masses with differing physical and chemical properties to the east and west; and 3) an east to west change from large land masses on a wide continental shelf to small land masses on a narrow shelf . ...
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... Although the species' ranges overlap throughout much of coastal Alaska, the southern extent E. fistulosa occurs in southeastern Alaska while the distribution of N. luetkeana extends further south (i.e., into warmer waters) to Point Conception, California. The western extent of N. luetkeana occurs at Samalga Pass near the base of the Aleutian Islands in southwestern Alaska, while the range of E. fistulosa continues west (i.e., into colder waters) along the Aleutian Archipelago to the islands north of Japan (Miller and Estes 1989). While both species form dense surface canopies, they have dissimilar morphologies, with E. fistulosa producing a single large blade that extends from the benthos to the sea surface and provides substantial midwater and surface structure, and N. luetkeana producing a single thin stipe that provides little mid-water structure but numerous blades at or near the surface that provide substantial structure in the upper few meters of the water column ( Fig. 1). ...
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Interactions in the Marine Benthos - edited by Stephen J. Hawkins August 2019
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