Hydrobiologia 471: 133–142, 2002.
L. Watling & M. Risk (eds), Biology of Cold Water Corals.
©2002 Kluwer Academic Publishers. Printed in the Netherlands.
Axial rod growth and age estimation of the sea pen,
Halipteris willemoesi Kölliker
Matthew T. Wilson1,AllenH.Andrews
2, Annette L. Brown1& Erik E. Cordes3
1National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE,
Seattle, WA 98115, U.S.A.
Tel: (206) 526-6522. Fax: (206) 526-6723. E-mail: email@example.com
2Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA 95039, U.S.A.
Tel: (831) 632-4400
3Pennsylvania State University, Biology Department, 208 Mueller Lab, University Park, PA 16802, U.S.A.
Tel: (814) 863-8360
Key words: Pennatulacea, age, growth, axial rod, lead-210, radium-226
Halipteris willemoesi is a large octocoral commonly found in the Bering Sea. It is a member of a ubiquitous group
of benthic cnidarians called sea pens (Octocorallia: Pennatulacea). Sea pens have a skeletal structure, the axial rod,
that in cross section exhibits growth rings. Pairs of adjacent rings, or ring couplets, were assumed to be annuli
and were used to estimate the age and growth of H. willemoesi. Twelve axial rods, extracted from H. willemoesi
collected in the Bering Sea, were selected to represent small (25–29 cm total length), medium (97–130 cm TL)
and large (152–167 cm TL) colonies. Each rod resembled a tapered dowel; the thickest part (0.90–6.75 mm in
diameter) was at about 5–10% of total length from the base tip, the distal part was more graduallytapered than was
the base. The number of ring couplets increased with rod size indicating their utility in estimating age and growth.
Estimated age among rods was based on couplet counts at the thickest part of each rod; the average estimated age
(±SE) was 7.1 ±0.7, 19.3 ±0.5, and 44.3 ±2.0 yr for small, medium and large-size rods, respectively. Based on
these estimated ages, average growth rate in total length was 3.9 ±0.2, 6.1 ±0.3, and 3.6 ±0.1 cm yr−1for small,
medium, and large-size colonies. The average annual increase in maximum rod diameter among all colonies was
0.145 ±0.003 SE mm yr−1; therefore, age prediction from maximum rod diameter was calculated (estimated age
(yr) = 7.0 ∗(maximum rod diameter, mm) −0.2; R2= 0.99). At maximum diameter, the average couplet width was
relatively constant among the three colony sizes (0.072 ±0.05 mm). X-ray diffraction and electron microprobe
analyses revealed that the inorganic portion of the rod is composed of a high-magnesium calcite. Radiometric
validation of these age and growth rate estimates was attempted, but high amounts of exogenous 210Pb precluded
using the disequilibria of 210Pb:226Ra. Instead, 210Pb activities were measured in a series of cores extracted along
the axial rod. These activities ranged from 0.691 ±0.036 (SE) to 2.76 ±0.13 dpm g−1, but there was no pattern of
decay along the length of the rod; therefore, the growth rates and corresponding ages could not be validated. Based
on estimated age from ring couplet counts, growth in total rod length is slow at ﬁrst, fastest at medium size, and
slows toward maximum size, with an estimated longevity approaching 50 yr.
Sea pens and whips (Octocorallia: Pennatulacea) are
colonial organisms that inhabit soft-bottom areas over
a broad range of depths (intertidal – 6200 m) in all
oceans (Williams, 1995, 1999). They can form vast
forest-like patches of biogenic habitat that may play
an important role as ﬁsh habitat (Krieger, 1993). Each
colony stands erect and is secured to the sea ﬂoor
by peristaltic burrowing of the peduncle, a slightly
swollen basal (proximal) part of the ﬂeshy tissue. The
upper or distal part, the rachis, is populated with feed-
ing polyps (autozooids). Sea pens are considered to
be sessile (Williams, 1999), but movement by detach-
ing, drifting, and re-attaching has been noted in the
shallow-water species Ptilosarcus gurneyi (Birkeland,
1974) and Renilla kollikeri (Kastendiek, 1976), and
the deep-water sea pen Umbellula lindahli (Flores,
1999). Despite this potential for movement, sea pens
may contain useful records of environmental condi-
tions stored in the skeletal tissues.
The endoskeleton of sea pens is a simple un-
branched structure called an axial rod. The axial rod of
the sea pen Veretillum cynomorium consists of a matrix
of longitudinally oriented collagen ﬁbrils embedded in
columns of calcite that radiate out from a nodular core
(Franc & Chassagne, 1974; Ledger & Franc, 1978).
At the base (inferior) end, a calciﬁcation gradient ex-
ists between the non-calciﬁed tip and the rest of the
rod. The autoradiography (3H-proline labeling) res-
ults of Franc et al. (1985) indicate that deposits are
made onto the rod exterior; the interior is closed to de-
position. Chia & Crawford (1977) found evidence of
initial axial rod formation in P. gurneyi primary polyps
soon after settlement of the planula. Birkeland (1974)
found that growth rings in the axial rods of young
sea pens (P. gurneyi) were formed annually, based
on observed growth, and averaged 0.1 mm in width.
Some colonies were estimated to be 15 years old based
on rod diameter but, because of core degeneration,
these estimates remain unvalidated. Linear extension
rates and radiometric age determination provide evid-
ence that skeletal growth rings in other octocorals
are formed annually (Grigg, 1974; Szmant-Froelich,
1974; Andrews et al., 2002).
In September 1997, numerous large sea pens
(Halipteris willemoesi) were collected as bycatch dur-
ing bottom-trawl sampling in the Bering Sea prompt-
ing an investigation of the structure of the axial rod
as a tool for determining age. Transverse sections re-
vealed many growth rings in the axial rods indicating
that H. willemoesi colonies may be slow growing and
long lived; therefore, anthropogenic disturbance or re-
moval of sea pen ‘forests’ could have a lasting effect
on the structure of soft-bottom communities. In addi-
tion, chronologically ordered sequences of ring widths
may be useful for constructing a history of variation in
the surrounding environment. This concept is suppor-
ted by studies on other organismsthat indicate skeletal
microstructure can be used as a record of age and en-
vironmental variability; for example trees (Stokes &
Smiley, 1996), ﬁsh (Woodbury, 1999), bivalves (Cer-
rato, 2000), and other colonial anthozoans (Druffel et
al., 1995; Cole et al., 2000; Andrews et al., 2002; Risk
et al., 2002). Despite the cosmopolitan distribution and
large size of H. willemoesi (Williams, 1995), we found
no literature describing colony age or the growth of its
axial rod. Therefore, the focus of this study was to:
(1) describe the structure of different-size axial rods;
(2) estimate colony age from axial rod ring counts;
(3) create growth models from estimated ages; and 4)
attempt to validate colony age and growth estimates
using radiometric age validation.
Material and methods
Twelve H. willemoesi colonies were selected from
two trawl samples collected in the eastern Bering Sea
(Fig. 1). Species identiﬁcation was based on the re-
cent revision of the order Pennatulacea (Williams,
1995). Colonies were selected by total rod length to
form three size groups (small, 25–29 cm; medium,
98–130 cm; large, 153–167 cm) consisting of four
colonies each (Table 1). The largest colonies were
from Pribilof Canyon (11 September 1997, 56◦16.8
N, 169◦25.8W, 248 m depth, 3.5◦C bottom temp.),
the others were collected farther northwest (28 July
1998, 60◦0.6 N, 177◦56.4W, 142 m, 2.0◦C). Soft
tissue surrounding the axial rod was easily removed
because it was securely attached only to the rod base.
Each rod was allowed to dry for 1 month at room
temperature before measuring and sectioning. Rod
diameter along the full length of each rod was meas-
ured with a micrometer to the nearest 0.05 mm. Cross
sections were cut at set distances from the base tip with
a diamond blade saw and mounted onto slides with LR
White resin. Each mounted section was ground down
to a thickness of approximately 0.3 mm using 320 and
600 grit wet/dry sand paper and coated with immer-
sion oil for viewing. Sections were viewed through a
dissecting microscope with transmitted light to make
all counts and measurements at a magniﬁcation of 16
times. Although higher magniﬁcation revealed rings
nested within rings, these ﬁner rings were often hard
to distinguish. Growth rings were evident as couplets,
each consisting of one translucent and one adjacent
For each cross section, the number of couplets was
counted three non-consecutive times. In addition, ra-
dial measurements of cross sections of the rod base
were made to quantify and construct a longitudinal
view of the thickness of a core of smooth rings and
the overlaying layer of rough material. These measure-
Table 1. Axial rod measurements and age estimates at maximum rod diameter for twelve Halipteris willemoesi colonies collected
in the eastern Bering Sea, with calculated total length and diameter growth rates
Size-group Total Maximum Average increment Estimated age Length growth Diameter growth
and colony length (cm) diameter (mm) width (mm)a(yr ±SD)brate (cm yr−1)crate (mm yr−1)d
BS-G 25.3 0.90 0.075 6.0 ±1.0 4.21 0.150
BS-E 26.2 0.95 0.079 6.0 ±1.7 4.36 0.158
BS-F 29.0 1.15 0.075 7.7 ±1.2 3.78 0.150
BS-H 29.3 1.05 0.060 8.7 ±0.6 3.38 0.121
BS-D 97.8 2.55 0.070 18.3 ±0.6 5.33 0.139
BS-B 118.4 2.80 0.074 19.0 ±1.0 6.23 0.147
BS-A 124.4 2.85 0.075 19.0 ±2.6 6.54 0.150
BS-C 130.3 3.05 0.074 20.7 ±2.1 6.30 0.148
PC-C 152.6 5.85 0.073 40.0 ±5.3 3.81 0.146
PC-D 156.9 6.35 0.076 41.7 ±2.1 3.76 0.152
PC-B 162.6 6.75 0.072 47.0 ±1.7 3.45 0.144
PC-A 166.7 6.40 0.066 48.3 ±1.5 3.44 0.132
aCalculated as half the diameter divided by increment count.
bTriplicate count of the growth increments resulting in an average age at the maximum rod diameter.
cTotal length divided by the estimated age.
dMaximum diameter divided by the estimated age.
ments were also repeated three non-consecutive times.
Triplicate counts and measurements were averaged be-
fore calculating the average and standard error (SE) for
each rod size group and cross-section position. Cross-
section positions were constant within each size group
and were determined by distance from the base tip.
Average couplet width was calculated as one-half rod
diameter divided by couplet count.
Rod length and diameter measurements and
growth increment counts (estimated age) were used to
estimate growth rates. In addition, growth rates were
calculated for the change in colony size, from small
to medium and from medium to large, by dividing the
difference of the average rod lengths by the difference
of the average estimated age.
To gain a better understanding of the composition
and structure of the carbonate matrix, X-ray diffrac-
tion was performed at the Department of Geology and
Geophysics at the University of Alaska, Fairbanks.
To attempt a validation of age and growth es-
timates, a radiometric age-validation technique was
applied to the calciﬁed axial rod among and within
colonies. Skeletal material from three sea pen colonies
was used in these analyses. Whole and core skeletal
material from one colony was used in a preliminary
analysis to determine the levels of 210Pb and 226Ra.
Core material at the center of the rod was exposed
when the rod exterior was removed using a milling
machine. The result was a 1-mm diameter, 3-cm long
core estimated to be the ﬁrst few years of growth. Ex-
tracted samples were cleaned and processed for 210Pb
and 226Ra using well established protocol as described
by Andrews et al. (1999 a, b). Two approaches were
utilized to attempt to validate age and growth. First,
to determine radiometric age using the disequilibria
of 210Pb and 226Ra, core material from the thickest,
and presumably oldest, part of the axial rod in two
colonies was analyzed. The aim of this approach was
to age individual cores using the disequilibria of 210Pb
and 226Ra. Second, core material at locations along
the axial rod (base to tip) was analyzed for 210Pb only.
The aim of this approach was to measure the decay
of 210Pb activity along the rod from the apical tip to
near the base tip that presumably corresponds with a
The axial rods of H. willemoesi resembled a thin
tapered dowel, and extended the length of the colony
(Fig. 1). The upper part of the rod was white, well
Figure 1. Twelve intact Halipteris willemoesi colonies from the Bering Sea (left of meter stick) next to the twelve axial rods from similar-size
colonies. The cleaned rods on the right were used to describe rod structure, and to estimate colony age and growth rate.
calciﬁed, and smooth and circular in cross section
(Fig. 2A). Soft tissue easily sloughedoff this part. The
lower part, hereafter referred to as the base, comprised
about 10% of the total rod length and differed from
the upper part by having a rough exterior and by be-
ing irregular in cross section (Fig. 2B). Except at its
very tip, which was brown and pliable when wet, the
base was also white and well calciﬁed. Soft tissue was
securely attached to the base, particularly the tip.
Transverse sections of the rod base revealed that
the rough material overlays a core of smooth, con-
centric growth rings that are similar in cross-section
appearance to the rings in the upper part of the rod
(Fig. 2). Series of radial measurements of this core
were used to construct longitudinal views to show how
core thickness decreases toward the base tip (Fig. 3).
Comparing core thickness among different size rods
helps to illustrate how the rod base may grow. Assum-
ing no structural variation after deposition, the core of
small rods corresponds in thickness to the lower part
of the core in large rods indicating that the youngest
part of large rods is probably close to the base tip.
Rod shape was similar among the different size
groups (Fig. 4A). From the point of maximum dia-
meter, rod thickness decreased sharply before as-
suming a more gradual taper to the apical tip. The
distance from the base tip to the point of maximum
rod diameter increased with rod size. As a percent
of total length, however, this distance was about 5–
10% regardless of size group. Maximum rod diameter
was similar among the four rods in each size group
(Table 1). The average maximum thickness for small,
Figure 2. Photographs (32×) of transverse sections of an axial rod taken in the distal part at 25 cm from the basal tip (A), and in the basal part
at 5 cm (B) from the basal tip. The axial rod, 167 cm total length, was from a Halipteris willemoesi colony collected in the Bering Sea. The
arrow points to the interface within the rod base between the inner core of smooth, concentric increments, and the outer rough material (scale
bar = 1 mm).
medium, and large rods was 1.01 mm ±0.06 (SE),
2.81 mm ±0.10, and 6.34 mm ±0.19, respectively.
The number of couplets per cross section changed
with rod diameter (Fig. 4A, B). For each rod, max-
imum couplet count occurred at the maximum rod
diameter. Among the rods examined, the average
count at maximum diameter increased with rod size
(Table 1): small, 7.1 ±0.7 (SE); medium, 19.3 ±0.5;
and large, 44.3 ±2.0. These counts are assumed to
indicate colony age in years; thus, the maximum es-
timated age for the largest colony, 167 cm total length,
was 48.3 ±1.5 SD yr.
Assuming an annual rate of couplet formation, the
estimated annual growth rate in colony length varied
with rod size, whereas change in diameter was near
constant (Table 1). Total colony length divided by
the average estimated age resulted in average annual
growth rates of 3.9 ±0.2 (SE), 6.1 ±0.3, and 3.6 ±
0.1 cm yr−1for small, medium, and large-size colon-
ies, respectively. Estimated growth rates calculated for
change in size, from small to medium and medium
to large, also varied as the rod increased in length.
Growth estimates from small to medium colony size
was 7.42 cm yr−1and 1.68 cm yr−1from medium
to large. Estimated annual increase in rod maximum
diameter varied little among colonies (small, 0.145
±0.008 (SE); medium, 0.146 ±0.002; and large, 0.144
±0.004 mm yr−1) reﬂecting low among-group vari-
ability in mean couplet width. The average annual
increase in rod maximum diameter among all colon-
ies was estimated to be 0.145 ±0.003 SE mm yr−1.
This relationship was used to estimate an age predic-
tion model using maximum rod diameter (estimated
age (yr) = 7.0∗(maximum rod diameter, mm) - 0.2;
R2= 0.99). The average width of each couplet was
somewhat variable along the rod for all sizes (0.128
±0.013 mm; Fig. 4C), particularly at the base and
apex which reﬂects our observation that the innermost
couplets tend to be relatively wide. At maximum dia-
meter, the average increment width was near constant
among the three colony sizes (0.072 ±0.050 mm;
The X-ray diffraction analysis of the axial rod in-
dicated the carbonate structure is a high-magnesium
calcite. Magnesium comprised 3–4 weight percent of
the carbonate. Sodium was present at 1–1.5 weight
Figure 3. Measurements from cross sections taken throughout the
base of twelve axial rods of Halipteris willemoesi were used to
calculate the average (±SE) radius of the inner core (dotted line,
Fig 2B) and the average (±SE) total rod radius (solid line) for each
size group (four rods per group, Table 1). For each size group, su-
perimposed plots of these two measurements versus cross section
position along the rod (distance from the base tip) illustrate how
core radius and thickness of the rough outer material varies longit-
udinally, and that the core extends to the basal tip regardless of rod
size. Position along the rod is scaled so that zero (solid horizontal
bar) corresponds with the probable relative position of the seaﬂoor
Radiometric results indicated that 210Pb activities
were relatively high and that exogenous 210Pb was
present in all samples except one (Table 2). Whole
and cored samples had 210Pb activities that exceeded
the activity of 226Ra in 7 out of 8 samples. The one
sample that had a 210Pb activity (0.0229 ±0.0022
dpm/g) that was lower than 226Ra activity (0.121 ±
0.0013 dpm/g) allowed for the calculation of an age
from the disequilibrium of 210Pb:226Ra. The result was
5.7 yr (1.7–10.2 yr range) for that colony.The next set
of 5 samples from colonies 2 and 3, all of which were
cores, had 210Pb:226Ra ratios that exceeded 1.0. There-
fore, the ageable sample was thought to be anomalous
and the method of disequilibria dating was dropped.
Figure 4. Average diameter (A) and growth increment count (B)
from along the axial rods of small (n=4), medium (n=4), and large
(n=4) Halipteris willemoesi colonies collected in the Bering Sea.
Average increment width (C) was calculated as one-half diameter
divided by increment count. Vertical bars indicate the standard error
of the mean.
The alternate approach to determining a growth
rate was to pursue the decay of 210Pb over the length
of the colony (Andrews et al., 2002). In general, 210Pb
activity in cores taken from near the basal and apical
tips was high relative to activity in the middle of the
rod. The range of activities for the 8 core samples
taken from colony 3 ranged from 0.692 ±0.036 to
2.76 ±0.13 dpm/g. No growth rate or age was de-
termined because the 210Pb activities did not follow a
consistent pattern over the length of the colony.
Knowledge of structural and temporal growth are im-
portant factors in understanding the life history of
organisms like coral whose structure provides hab-
itat for other species (i.e., biogenic habitat), and in
understanding how skeletal structures may record en-
vironmental variability. In situ observations indicate
that H. willemoesi, or similar species, stand erect on
the sea ﬂoor with the peduncle, which corresponds to
the base of the axial rod (Fig. 1), embedded in sed-
Table 2. Results from the radiometric analysis of axial rod sections (whole or core) taken from three H. willemoesi colonies
collected in the eastern Bering Sea.
Colony Distance Sample type Sample Activity of Sigma Activity of Sigma 210Pb:226 Ra
(cm)a(whole/core) weight (g) 210Pb (dpm/g) (1 SE) 226Ra (dpm/g) (1 SE) activity ratio
1 11.6 Whole 0.699b1.79 0.12 0.125 0.001 14.3
11.6 Whole 0.699b1.92 0.10 0.125 0.001 15.4
16.7 Wholec0.7244 0.0229 0.0022 0.121 0.001 0.19
2 (PC-C) 13.1dCore 0.1543 0.875 0.033 0.147 0.002 5.95
18.2dCore 0.1711 0.728 0.028 0.132 0.002 5.52
3 (PC-B) 11.6 Core 0.0691 0.917 0.050 0.157 0.001 5.84
16.7 Core 0.0700 0.773 0.045 0.149 0.006 5.19
24.4 Core 0.0313 0.715 0.055 0.178 0.044 4.02
52.3 Core 0.0633 0.727 0.041 N.P. – –
77.7 Core 0.0415 0.774 0.046 N.P. – –
103.1 Core 0.0702 0.692 0.036 N.P. – –
128.5 Core 0.0600 1.03 0.050 N.P. – –
156.4 Core 0.0200 2.76 0.13 N.P. – –
N.P. Not processed
aDistance from basal end to the center of each section.
bSame sample for 226Ra analysis, split for 210Pb analysis.
cSmall amount of exterior removed by grinding.
dSample length was 6 cm.
iments (Krieger, 1993). The rough part of the base
corresponds to secure attachments between the rod
and the surrounding soft tissue. In contrast, the up-
per part of the rod may be smooth so that the soft
tissue better slides along it as the colony ﬂexes in
near-bottom currents. Based on cross sections through
the base, the rough material overlays a core of well
deﬁned rings resembling the distal, above-sediment,
part of the colony (Fig. 2).
As with P. guerneyi (Chia & Crawford, 1973), H.
willemoesi probably begin to burrow into the sediment
as newly settled planula larvae. The axial rod probably
forms early after settlement (Chia & Crawford, 1977),
but exactly when is unclear. With development, each
colony probably burrows deeper to better anchor and
support itself. We believe that depositions onto the rod
above the seaﬂoor surface result in smooth concentric
rings and that lower depositions result in the rough
material. Thus, the two layers of the base (Fig. 3)
can be explained by rough material being deposited
onto the rod as burrowing by the colony draws the rod
farther into the sediment. The core of smooth rings at
the base tip is difﬁcult to explain unless the tip is the
ﬁrst-formed part of the rod. The relatively thin cover-
ing of rough material over this core at the tip probably
results from relatively little material being deposited
onto the tip during subsequent growth. Deposits onto
the remaining parts of the rod must therefore cause
it to thicken and elongate. This is relevant to ring-
count age estimates because our couplet counts at the
maximum diameter of axial rods from large colonies
(ca. 160 cm total length) probably did not include the
youngest part of the rod, perhaps the ﬁrst couple of
growth rings were missed.
Average width of growth-ring couplets was nearly
constant in cross sections of the axial rod. This was es-
pecially true for determinations made at the maximum
diameter of the rod (Table 1). The calculated average
width of the couplets (0.072 ±0.005 mm) was similar
to the result from a study on the axialrod of the sea pen
Ptilosarcus gurneyi (0.1 mm), a shallow-water species
Age, estimated from counts of ring couplets, was
similar within size groups and was used to determ-
ine growth rates (Table 1). The average growth rate
for each colony indicated that growth was fastest for
the medium sized colonies (97.8–130.3 cm), slower
in the small size class (25.3–29.3 cm), and slowest
for largest sizes (152.6–166.7 cm). Calculated interval
growth, small to medium size and medium to large
size, clearly indicated that growth was rapid (7.42 cm
yr−1) from an average length of 27.5 cm to 117.7 cm.
Interval growth from 117.7 cm to 159.7 cm was slower
at 1.68 cm yr−1.
The growth pattern in length indicates slow ini-
tial growth followed by rapid growth at intermediate
rod size progressing towards an asymptotic length.
This is similar to growth models used in other stud-
ies of octocoral growth. Velimirov (1975) used a
sigmoidal function to describe the growth of the Medi-
terranean gorgonian Eunicella cavolinii, which ap-
proached asymptotic size at approximately 15 years.
Cordes et al. (2001) used a Gompertz function to
model the growth of the deep-sea alcyonacean An-
thomastus ritteri, which reached an asymptotic size
between 30 and 35 years. Although neither study
formed conclusions about the maximum age for these
colonies, the ages estimated for asymptotic size for A.
ritteri were similar to the maximum ages reported in
this study. No growth model was applied to the data
for H. willemoesi because few length intervals were
In contrast to the rate of growth in length, the
rate of growth in diameter was nearly constant des-
pite differences in rod size. An age prediction equa-
tion was developed based on maximum rod diameter
(estimated age (yr) = 7.0∗(maximum rod diameter,
mm) – 0.2, R2= 0.99). This relationship needs to
be further reinforced, however, because of the low
number of samples (n = 12). Assuming the age estim-
ates are valid, this relationship could be used in age
composition monitoring of trawl bycatch.
Radiometric age determination using the disequi-
libria of 210Pb:226Ra and the decay of 210Pb was un-
successful in establishing a validation of age or growth
rate estimates for H. willemoesi.Inonesample,an
age estimate of 5.7 yr (1.7–10.2yr range) was determ-
ined for a colony (Table 2). This estimate, however,
is suspect because subsequent samples had 210Pb and
210Pb:226Ra activity ratios that exceeded 1.0 (Table 2).
These high activity ratios indicate an accumulation of
210Pb from an exogenous source. Because all 210Pb
must result from the decay of 226Ra for the technique
to work (Burton et al. 1999), the presence of exo-
genous 210Pb in these samples precluded the use of
measured 210Pb:226Ra activity ratios as an indicator of
An alternate approach using the decay of 210Pb
over the length of a coral colony was successfully
applied to red tree coral (Primnoa resedaeformis;An-
drews et al., 2002). The approach was successful for
P. resedaeformis because the activities of 210Pb in a
series of core samples (material from the inner part of
the skeleton when viewed in cross section) from near
the apical tip to near the base followed the expected
decay pattern and allowed for growth rate estimation
and validation of annual growth rings. This approach
was applied to one sea pen colony (PC-B), but was
unsuccessful because the activity of 210Pb from near
the apical tip to near the basal tip did not follow a
consistent reduction in activity (Table 2). This may in-
dicate that 210Pb was taken up by the colony unequally
throughout life, which may be a reﬂection of either
environmental variability or a violation of the closed
system assumption (Burton et al., 1999).
It is increasingly common to ﬁnd that deep-sea
organisms can attain ages that are on the order of dec-
ades to hundreds of years (Andrews et al., 1999a; Kas-
telle et al., 2000; Andrews et al., 2001; Cailliet et al.,
2001). The patterns of growth in their skeletal tissues
may therefore reﬂect long histories of environmental
variability such as the seasonal ﬂux of particulate mat-
ter. This ﬂux has been linked to reproductive cycles
in some deep-sea organisms (Valiela, 1984), but not
deep-sea pennatulids (Rice et al., 1992; Tyler et al.,
1995; Eckelbarger, 1998). Furthermore, the longevity
of these organisms and the biogenic habitat they may
provide to other species makes it essential that ﬁshing-
related impacts be studied in detail (Krieger, 1993;
Auster & Langton, 1999; Freese et al., 1999), par-
ticularly as ﬁshing activities reach greater depths and
ﬁsh stocks decline. This perspective on ﬁshing-related
impacts has been mandated in management practices
in 1996 with the Sustainable Fisheries Act, where un-
derstanding and protection of essential ﬁsh habitat has
become paramount (Rosenburg et al., 2000).
Future efforts using other methods, such as ﬂuoro-
chemical marking and linear extension rates may
provide validated estimates of age and growth rates for
H. willemoesi. It remains to be seen if the growth rates
and age estimates determined in this study are accur-
ate; however, in light of their importance as biogenic
habitat, it is prudent to take heed of the high estimated
longevity of H. willemoesi, which may approach or
exceed 50 years.
We gratefully appreciate help from many people on
this project. At NOAA, Alaska Fisheries Science Cen-
ter, Seattle, WA, Jerry Hoff and Bob Lauth collec-
ted the sea pens, Craig Kastelle generously shared
his knowledge of ageing hard biogenic tissues, and
Kevin Bailey and Art Kendall reviewed earlier ver-
sions of this manuscript. At the California Academy
of Sciences, San Francisco, CA, Gary Williams kindly
provided much advice on sea pen identiﬁcation. Spe-
cial thanks to the organizers of the First International
Symposium on Deep Sea Corals in Halifax, Nova
Scotia, where this research was presented. This re-
search was sponsored in part by the NOAA Coastal
Ocean Program and is contribution FOCI-B394 to
Fisheries-Oceanography Coordinated Investigations.
Radiometric and compositional analyses performed in
this study was funded by a grant through the Uni-
versity of Alaska, Fairbanks, North Paciﬁc Marine
Research Initiative from the U.S. Geological Sur-
vey grant 99HQGR0103, designated for research in
the North Paciﬁc Ocean and Bering Sea. Additional
thanks to Melissa Mahoney, Gregor Cailliet, and Ken-
neth Coale for assistance with the radiometric portion
of this study and editorial assistance; thanks to Ken-
neth Severin at University of Alaska, Fairbanks in the
Department of Geology and Geophysics for the XRD
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