Sonia Ibarra and Jodi Pirtle

1
Comparing Kelp Communities on the Inner and Outer
Coasts of Southeast
Alaska Sonia Ibarra1, Jodi Pirtle2, Ginny
Eckert2,3 1 Humboldt State University, 2
University of Alaska Fairbanks, 3 University of
Alaska Southeast, 1 UAS, NSF, Research
Experiences for Undergraduates
Results
Introduction An archipelago of many islands
separates the mainland coast of southeast Alaska
from the outer coast at the open ocean.
Variability in kelp biogeography and community
structure has been observed in southeast Alaska
but is not well documented or directly linked to
habitat or environmental variability. We can
better predict how environmental change will
affect kelp communities in southeast Alaska when
we understand relationships between kelp
communities and the environment. The goal of our
study is to understand how nearshore kelp
communities in southeast Alaska are structured by
habitat and environmental variability.

• Methods
• Conducted SCUBA surveys along 25 m2 transects at
  6 m and 12 m depths.
• Quantified kelp abundance, physical substrate,
  and percent cover of other algal types.
• Measured temperature and salinity of the water
  column using a CTD.
• Analyzed data using the General Linear Model,
  Shannon Diversity Index, and Detrended
  Correspondence Analysis.

Figure 1 Legend
Sacharina subsimplex
Sacharina latissima
Agarum clathratum
Cymathere triplicata
Costaria costata
Laminaria yezoensis
Laminaria setchellii
Nereocystis leutkeana
Sonia and Travis Smith at Kita Island, Sitka
Sound.
Macrocystis integrifolia
Alaria fistulosa
Alaria marginata
Pleurophycus gardneri
Desmarestia ligulata
Desmarestia spp.
Nereocystis leutkeana at Vitskari Rocks, Sitka
Sound.

• Objectives
• Identify and compare patterns of kelp
  biogeography and community structure between the
  outer coast and mainland coast of southeast
  Alaska.
• Link patterns of kelp biogeography and community
  structure to habitat and environmental
  variability.

• Conclusions
• Outer coast kelp communities have higher species
  richness, diversity, and evenness than mainland
  coast communities, which are dominated by three
  species. Abiotic conditions, in addition to
  interspecific interactions, may be driving these
  patterns.
• Environmental variability and habitat affect kelp
  biogeography and community structure. Salinity is
  a major environmental gradient between locations,
  possibly due to increased freshwater runoff at
  the mainland coast, and a lack of open ocean
  exchange.
• Our study improves resolution of kelp
  biogeography and community structure in southeast
  Alaska. Further analysis will incorporate
  additional biological and abiotic factors. Future
  studies of interspecific dynamics will be
  insightful.

Sonia with Laminaria yezoensis, Kita Island,
Sitka Sound.
Figure 1. Kelp density (individuals/m2) along
deep (12 m) and shallow (6 m) transects at sites
on the (a) mainland coast and (b) outer coast of
southeast Alaska. A total of 13 kelp species were
identified. Kelp abundance is significantly
greater at 6 m than 12 m depth (a 0.05 p
0.02), but is not significantly different between
locations.
1
Figure 2. Rank-abundance curve of kelp community
structure by location. Species richness and
diversity are higher at the outer coast (N 12,
H 1.75) than the mainland coast (N 7, H
1.03). The outer coast community has greater
evenness.
Mainland Coast Kelps
Outer Coast Kelps
0.1
Proportional Abundance
0.01
Figure 2
0.001
Macrocystis integrifolia, Echolms Islands, Sitka
Sound.
1
2
3
4
5
6
7
8
9
10
11
12
Rank Abundance
Figure 3. Ordination of sites and kelps along
dimensions 3 and 4 from Detrended Correspondence
Analysis. Vectors are the maximum of significant
environmental gradients (a 0.1) temperature,
salinity, and gradients in boulder and pebble
substrates.
DCA 4 (34 of variability)
Macrocystis integrifolia and Sebastes mystinus,
Kita Island, Sitka Sound.
Nereocystis leutkeana, Symonds Point, Stevens
Passage, Juneau.

• DCA displays three ecological groups
• Mainland 1 lower surface salinity, less pebbles,
  A. fistulosa and Desmarestia spp.
• Mainland 2 higher temperature, lower salinity,
  boulders present, A. clathratum, L. yezoensis, C.
  triplicata.
• Outer Coast higher salinity, pebbles present,
  lower temperature, M. integrifolia, C. costata,
  L. setchellii, and others.

Macrocystis integrifolia, Kita Island,
Sitka Sound.

• Juneau Alaska
• Mainland Coast
• 9 dive sites
• Sitka Sound
• Outer Coast
• 8 dive sites

Acknowledgements This study was undertaken by
Sonia Ibarra while participating in the National
Science Foundation Research Experience for
Undergraduates Program (NSF No. 0553000) at the
University of Alaska Southeast. Sonia would like
to thank Jodi Pirtle, Dr. Ginny Eckert, and Dan
Okamoto for their guidance and support in the
development and follow through of her project.
This research is funded by the American Academy
of Underwater Sciences Kathy Johnston
Scholarship, the Professional Association of
Diving Instructors Aquatic World Awareness,
Responsibility and Education Foundation, and
supported by the University of Alaska Fairbanks
and the Alaska Department of Fish and Game.
DCA 3 (54 of variability)