Larvae from afar colonize deep-sea hydrothermal vents after a catastrophic eruption

Abstract

The planktonic larval stage is a critical component of life history in marine benthic species because it confers the ability to disperse, potentially connecting remote populations and leading to colonization of new sites. Larval-mediated connectivity is particularly intriguing in deep-sea hydrothermal vent communities, where the habitat is patchy, transient, and often separated by tens or hundreds of kilometers. A recent catastrophic eruption at vents near 9 degrees 50'N on the East Pacific Rise created a natural clearance experiment and provided an opportunity to study larval supply in the absence of local source populations. Previous field observations have suggested that established vent populations may retain larvae and be largely self-sustaining. If this hypothesis is correct, the removal of local populations should result in a dramatic change in the flux, and possibly species composition, of settling larvae. Fortuitously, monitoring of larval supply and colonization at the site had been established before the eruption and resumed shortly afterward. We detected a striking change in species composition of larvae and colonists after the eruption, most notably the appearance of the gastropod Ctenopelta porifera, an immigrant from possibly more than 300 km away, and the disappearance of a suite of species that formerly had been prominent. This switch demonstrates that larval supply can change markedly after removal of local source populations, enabling recolonization via immigrants from distant sites with different species composition. Population connectivity at this site appears to be temporally variable, depending not only on stochasticity in larval supply, but also on the presence of resident populations.

Full text

Larvae from afar colonize deep-sea hydrothermal
vents after a catastrophic eruption
Lauren S. Mullineaux
1
, Diane K. Adams
2
, Susan W. Mills, and Stace E. Beaulieu
Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
Edited by David Karl, University of Hawaii, Honolulu, HI, and approved March 4, 2010 (received for review November 13, 2009)
The planktonic larval stage is a critical component of life history in
marine benthic species because it confers the ability to disperse,
potentially connecting remote populations and leading to colonization
of new sites. Larval-mediated connectivity is particularly intriguing in
deep-sea hydrothermal vent communities, where the habitat is patchy,
transient, and often separated by tens or hundreds of kilometers. A
recent catastrophic eruption at vents near 9°50′N on the East Pacific
Rise created a natural clearance experiment and provided an opportu-
nity to study larval supply in the absence of local source populations.
Previous field observations have suggested that established vent pop-
ulations may retain larvae and be largely self-sustaining. If this hypoth-
esis is correct, the removal of local populations should result in a
dramatic change in the flux, and possibly species composition, of set-
tling larvae. Fortuitously, monitoring of larval supply and colonization
at the site had been established before the eruption and resumed
shortly afterward. We detected a striking change in species composi-
tion of larvae and colonists after the eruption, most notably the
appearance of the gastropod Ctenopelta porifera, an immigrant from
possibly more than 300 km away, and the disappearance of a suite of
species that formerly had been prominent. This switch demonstrates
that larval supply can change markedly after removal of local source
populations, enabling recolonization via immigrants from distant sites
with different species composition. Population connectivity at this site
appears to be temporally variable, depending not only on stochasticity
in larval supply, but also on the presence of resident populations.
larval dispersal
|
population connectivity
|
Ctenopelta
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Lepetodrilus
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East Pacific Rise
In marine benthic systems, dispersal in a planktonic larval stage
influences the dynamics and spatial structure of populations and
can be critical for regional persistence of species. It is informative
to consider these systems in the framework of metapopulation
theory (1) as a balance between extinction and dispersal-mediated
colonization. The extent to which a local marine population is
open (i.e., the proportion of recruits that come from other locales)
may increase its resilience to perturbation (2, 3), but recruitment
of progeny back into the natal site also contributes to persistence
(4). Larval dispersal between deep-sea hydrothermal vent com-
munities is an intriguing topic in this context because the habitat is
spatially disjunct and populations are subject to local extinctions.
A major challenge to solving questions of population openness
(connectivity) in marine systems, however, is determining whether
the source of each recruit is local or remote because the larvae are
difficult to track. Consequently, fundamental questions about how
vent populations persist and what physical and biological pro-
cesses control their connectivity remain unresolved despite more
than three decades of research (5).
Population genetic studies indicate that specific currents or
topographic features may constitute barriers to dispersal between
widely separated vents (6–9), but, on scales of tens to even a
hundred kilometers, populations of many species show little
genetic differentiation (8, 10, 11). On these small scales, the lack of
significant increase in genetic differentiation with separation dis-
tance has been interpreted to mean that larvae are supplied in a
well-mixed pool (12). Although larvae of some vent species have
the potential to disperse long distances (13, 14), larval patchiness
in the field (15, 16), enhanced larval supply directly downstream of
source populations (17), and hydrodynamic analyses (18) suggest
that larval retention may occur near natal sites. It is possible that
these populations are largely self-sustaining on ecological time
scales and maintain high apparent genetic connectivity through
infrequent exchange of individuals over long periods.
A recent catastrophic eruption at vents near 9°50′N on the East
Pacific Rise (EPR) created a natural clearance experiment and
allowed us to study larval connectivity after the removal of local
populations. Such perturbations are common along the fast-
spreading EPR, where tectonic and magmatic events cause vents
to open and close on decadal time scales (19). Since the discovery
of vents at this site, researchers have detected two major eruptions,
one in 1991 (20) and a second (the subject of the present study) in
2006 (21). The latter eruption introduced a major perturbation
into local vent communities. New lava emerged between 9°46′and
9°56′N and reached as far as 2 km off axis (22) (Fig. 1), paving over
existing vent communities. The precise timing of lava extrusion is
uncertain; estimates vary from late 2005 to January 2006 (21).
Although the lava eradicated invertebrate communities, it did not
plug all of the vents, and hydrothermal fluids (on which the com-
munities depend) continued to flow from many of the orifices
established before the eruption. One community survived at the
southern margin of the eruption (V-vent at 9°47′N); the species
composition there did not change detectably after the eruption
(authors’visual surveys) and was similar to pre-eruption faunas at
the paved-over vents. To the north, a single colonized vent has
been reported at 10°08′N (23), but its status at the time of the
eruption is unknown. No other colonized vents are known between
9°56′N and the Clipperton Transform Fault (10°13′N).
This large-scale removal of vent populations provided us with an
opportunity to address questions about larval supply and recoloni-
zation at vents where initially there was no local larval source. This
was possible only because we had been monitoring larval supply and
colonization near 9°50′N before the eruption (24) and were able to
mobilize quickly afterward to resume sampling. If larvae were typ-
ically supplied to these EPR vents in a well-mixed, time-invariant
larval pool (12), we would expect little influence of the eruption on
larval supply and early recolonizationto be determined primarily by
responses to conditions in the benthic environment. If,instead, local
populations had been an important contributor to supply (17), we
would expect a reduction in larval abundance after the eruption and
distinct differences in species composition, depending on which
remote source populations contributed immigrants. This altered
pool of larval immigrants would constitute the pioneer colonists and
potentially direct the trajectory of subsequent succession. Our
specific objectives in this study were to determine whether larval
Author contributions: L.S.M., D.K.A., S.W.M., and S.E.B . designed research, performed
research, contributed new analytic tools, analyzed data, and wrote the paper.
This article is a PNAS Direct Submission.
1
To whom correspondence should be addressed. E-mail: lmullineaux@whoi.edu.
2
Present address: National Institutes of Health, National Institute of Dental and Cranio-
facial Research, Bethesda, MD 20982.
This article conta ins supporting info rmation online at ww w.pnas.org/cg i/content/full /
0913187107/DCSupplemental.
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supply changed significantly after the eruption and to explore the
effects of this supply on recolonization.
Results
The species composition of larvae supplied to vents after the
eruption differed markedly from that before (Fig. 2 and Table S1).
Although supply of the abundant larval gastropod species varied
substantially between cup intervals, all but one (Gorgoleptis emar-
ginatus) arrived at a consistently different rate after the eruption
than before (P<0.05, MANOVA and ANOVA, Systat v. 11; Table
S2). Supply of Cyathermia naticoides,Lepetodrilus spp., Gorgoleptis
spiralis,andBathymargarites symplector declined significantly after
the eruption, despite the continued presence of potential source
populations within 6 km to the south at V-vent. In contrast, Cte-
nopelta porifera, whichhad been virtually absent before the eruption
[only a single individual in the 2004–2005 trap samples and one in a
2004 pump sample (25)] was supplied in significantly higher num-
bers afterward. During a few intervals of the larval sampling series,
the change insupply of some species over several weeks was as high,
or higher,than the difference in meansupply between pre- andpost-
eruption. When such a change occurs simultaneously across multi-
ple species (e.g., the decrease in supply observed after pre-eruption
interval 11, or after post-eruption interval 1; Fig. 2), it is likely
associated with mesoscale hydrodynamic transport processes (24)
that are unrelated to the eruption.
The post-eruption change was detectable in larvae of rare spe-
cies as well; 14 of 27 larval gastropod taxa present at East Wall
before the eruption were not found at P-vent afterward (Table S1).
These differences in species composition are apparent in a non-
metric multidimensional scaling analysis (nMDS) (Systat v. 11)
(Fig. 3A). Other groups also showed large changes in supply after
the eruption (e.g., an increase in crabs Bythograea microps and
Bythograea thermydron)(Table S1).
Species composition of colonists also changed distinctly after
the eruption. Most surprising was the appearance of C. porifera
(Fig. 4A) because it had never been reported before in the benthos
from this segment of the EPR. The limpet Lepetodrilus tevnianus
also was prominent in the hot environment after the eruption,
whereas previously common species including Lepetodrilus ele-
vatus,Lepetodrilus pustulosus, and Rhynchopelta concentrica were
absent. The temperatures at P-vent (post-eruption) were similar to
those at Tica (pre-eruption), so elevated temperatures do not
appear to be responsible for these differences, although it is pos-
sible that chemistry differed. On surfaces in the warm environ-
ment, L. tevnianus was prominent after the eruption (Fig. 4B),
whereas diverse species present before the eruption (Bathy-
margarites symplector,Lepetodrilus ovalis,L. pustulosus, Clypeo-
sectus delectus, Gorgoleptis spiralis) had disappeared. The distinct
Fig. 1. Locations of vents and sample sites on the East Pacific Rise in the
region of the eruption. Symbols designate vent sites (yellow circles), sediment
traps (inverted triangles), and colonization experiments (squares) (blue = pre-
eruption, red = post-eruption). Blue line outlines the extent of lava extruded
in the 2005–2006 eruption (22). Bathymetry of ridge (53) is contoured at 10-m
intervals. Map courtesy of S. A. Soule.
A
B
C
D
E
F
Fig. 2. Larval supply measured in sediment traps. Traps sampled before the
eruption (November 25, 2004, to April 21, 2005, at 7-day intervals; blue bars)
near East Wall vent and after (July 1 to November 4, 2006; 6-day intervals;
red bars) near P-vent. Supply (daily downward flux of larvae into 0.5-m
2
trap
opening) displayed for the six most abundant species/groups at either site
that also were found as colonists: (A)Cyathermia naticoides,(B)Lepetodrilus
spp; (C)Gorgoleptis spiralis,(D)Bathymargarites symplector,(E)Gorgoleptis
emarginatus,(F)Ctenopelta porifera. Mean flux of each species except
G. emarginatus changed significantly (P<0.05, MANOVA and ANOVA; Table
S2) after the eruption. Larval individuals of the five described lepetodrilid
species in this region (Lepetodrilus elevatus, L. pustulosus, L. ovalis, L. cris-
tatus, and L. tevnianus) were not distinguishable morphologically.
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differences in overall species composition, including rare species,
before and after the eruption are apparent in nMDS analysis of
gastropod colonists (Fig. 3B).
The dramatic increase in larval supply of C. porifera after the
eruption coincided with its appearance as a colonist (Fig. 4). Other
species (e.g., B. symplector,C. naticoides,G. spiralis,R. concentrica)
also showed a post-eruption change in larval supply that corre-
sponded with change in colonist abundance (Tables S1 and S3).
Unfortunately, we could not tell whether changes in larvae of
individual lepetodrilid species (Lepetodrilus spp.) coincided with
changes in the associated colonists because the larvae are not
morphologically distinguishable at the species level. We suspect that
larvae in this group predominantly represented predisturbance
species (L. elevatus, L. pustulosus, L. ovalis) before the eruption and
the postdisturbance pioneer (L. tevnianus) afterward, but molecular
genetic identifications are needed for confirmation.
Discussion
The marked change in species composition of larval supply and
colonists after the 2005–2006 eruption is consistent with a scenario
in which pioneer species from remote populations were able to
colonize successfully at 9°50′N only after the resident populations
(and their larvae) had been eliminated. The observed changes are
not consistent witha model of recolonization via a well-mixed larval
pool, from which larval supply would be relatively unaffected by
elimination of local populations. Clearly, the disturbance strongly
affected larval supply in the local region. Surprisingly, the source
of pioneer colonists did not appear to be the nearest established
communities, such as V-vent (at 9°47′N) or other sites to the south
whose faunal composition resembled the pre-eruption commun-
ities at 9°50′N. Instead, at least one prominent pioneer species,
Ctenopelta porifera, arrived from possibly more than 300 km away,
where vents at 13°N host the only known populations.
The post-eruption change in larvae and colonists could have
developed through two different mechanisms, initiated either by
altered larval supply or settlement responses to the altered envi-
ronmental conditions. The first case might be expected if larval
supply in the disturbed region declined precipitously directly after
the eruption. This “larval vacuum,”caused by elimination of local
populations, could open the sites to settlement of highly dispersive,
but perhaps competitively inferior, immigrant species from remote
regions that typically are not able to infiltrate established pre-
eruption communities. The particular species of pioneers depends
on which larvae are available in the interval shortly after the erup-
tion, as influenced by time-variant transport processes (17), or
spawning cycles (26). This type of postdisturbance colonization
scenario, contingent on supply of new pioneers, has been observed
in a variety of marine and terrestrial environments (27–29). Our
larval flux measurements, initiated roughly 6 months after the main
seismic event in January 2006, and possibly even longer after the
main lava extrusion, did not measure supply in the first few months
after the eruption. A pilot set of larval samples (Fig. S1) collected in
the eruption region during May to June 2006 did reveal very low
fluxes (averaging <1day
−1
), but those results must be interpreted
carefully because the collectors were located several hundred
meters away from vents, where larval abundances are known to be
reduced (16). Nevertheless, we think the altered supply scenariois a
likely one, given prior evidence of local larval supplyat this site (17),
and the observations 6 months after the eruption of reduced fluxes
of many predisturbance species.
An alternative possibility is that environmental conditions
changed so drastically after the eruption that predisturbance
species were not able to settle and survive, even if they were sup-
plied as larvae. In this case, larval supply may or may not have
declined directly after the eruption, but only species adapted to the
new thermal or chemical conditions were able to colonize as pio-
neers. The chemical composition of hydrothermal fluids at some
EPR vent sites are known to have changed after the eruption (30)
and may have altered habitat suitability for select species. The
structural habitat also changed, with Tevnia jerichonana replacing
Riftia pachyptila as the main foundation tubeworm species, possi-
bly facilitating establishment of associated gastropod species such
as L. tevnianus. Environmental conditions at vents are known to
correlate with distribution of some species (31, 32), and with faunal
changes over time (33). Investigations of species’tolerances to
specific thermal and chemical habitats in the post-eruption sites
are underway, but it is not yet known whether the gastropod spe-
cies that were so prominent before the eruption are able to tolerate
the post-eruption conditions. It is quite possible that altered larval
supply and environmental tolerances both contributed to the
faunal changes observed after the eruption.
The increase in larval supply of postdisturbance species after the
eruption suggests that once the pioneers became established and
reproductively mature they bolstered overall local larval supply to
near pre-eruption levels. Although no broad survey of reproductive
maturity was attempted, many of the gastropod colonists collected
in November 2006 were larger than the minimum size of repro-
ductive maturity, and mature gonads were observed in C. porifera
and L. tevnianus.
Continued observations of the vent communities will show
whether the post-eruption change in species composition persists
and results in an ecological regime shift or is simply an early stage
in succession that will transition back to the pre-eruption state. If
local populations dominate larval supply, the established species
may pre-empt occasional immigrants of other species from remote
-2 -1 0 1 2
Dimension-1
-2
-1
0
1
2
2-noisnemiD
Larvae
-2 -1 0 1 2
Dimension-1
-2
-1
0
1
2
2-noisnemiD
TY_W2
TY_W1
TY_W3
P_H3
P_H2
P_H1
WH_W2
WH_H2
TA_ H2
WH_W3
WH_H1
WH_H1
WH_W2
TA_ H3
TA_ H1
Colonists
A
B
P4
P16
P8
P2
P7
P5
P17
P3
P19
P6
P1
P21
P9
P15
P14
P10
P18
P13
P12
P11
P20
E6
E8
E5 E7
E9
E2
E10
E13 E12
E11
E14
E4
E16
E1
E3
E18
E21
E17
E15
E20
E19
Fig. 3. nMDS of species composition of larvae and colonists. The proximity
of samples corresponds to the similarity in their species composition. Analysis
conducted on Pearson correlation of fourth-root transformed abundance.
(A) Larvae (excluding polychaetes) in sediment traps before (blue dots) and
after (red dots) eruption; label designates site (E = East Wall, P = P-vent) and
cup interval; Kruskal stress = 0.15. (B) Colonists (gastropods only) on blocks
before the eruption (blue dots) and on sandwiches after (red dots); label
designates site (WH = Worm Hole, TA = Tica; TY = Ty/Io, P = P-vent), envi-
ronment (H = hot, W = warm), and replicate; Kruskal stress = 0.073. Mean
species or species-group abundances listed in Table S3.
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locales or from neighboring sites to the south with predisturbance
faunas. Alternatively, if fluid chemical conditions revert to pre-
eruption levels or if pioneers make the habitat more suitable for
other species, the faunal communities may develop through a
successional sequence as immigrants outcompete the initial col-
onists. Successional observations from the previous (1991) erup-
tion cycle described a transition in the large, structure-forming
species from the tubeworms T. jerichonana to R. pachyptila and
eventually to the mussel Bathymodiolus thermophilus (33) that was
attributed to changes in environmental conditions. Before the
2006 eruption, most 9°50′N vent sites hosted R. pachyptila, indi-
cating a mid- to late stage of succession (16). Although changes in
gastropod species composition also occur during succession at
vents (34, 35), no clear sequence of species replacement has been
observed, and the pioneer gastropod colonists after the 1991
eruption did not include C. porifera or L. tevnianus (36). Deter-
ministic succession is found in terrestrial meadows and temperate
forests (28, 37), both quite stable systems where disturbance time
scales are long relative to species’generation times. In contrast,
the EPR vents are a system where disturbance occurs at intervals
approaching species’generation times. The inclusion of larval
measurements through the 2006 eruption will allow future inves-
tigation of whether larval/propagule availability influences suc-
cession at vents, as it does in many other frequently disturbed
marine and terrestrial communities (27, 38, 39). The extensive,
coordinated history of observations in the 9°50′N EPR region and
the ongoing monitoring there make it a truly unique site for studies
of ecosystem response to disturbance.
Our results show that vent populations on the EPR are, as
expected, connected by larval dispersal, but specific populations
cannot be consistently characterized as open or closed. Once a
catastrophic disturbance eliminates the community at a vent, the
site becomes open to colonization via larvae from remote pop-
ulations, possibly as far as 300 km away. After the site has become
colonized, however, larvae from the local populations appear to
dominate as potential recruits. This alternation between open and
closed condition is quite different from the situation in more stable
marine environments where interdisturbance period is long com-
pared to species’generation times, and connectivity is more likely
to depend on population growth rates and transport processes
than disturbance.
Although the magnitude of connectivity at these vents appears to
depend strongly on the frequency of disturbance, the species com-
position of pioneer larvae is likely subject to temporally variable
currents, as demonstrated for coastal habitats (40). One con-
sequence of stochasticity in larval supply, and episodic opening of
vent sites to new colonists, is the potential for occasional exchange
between far distant sites, as was observed for C. porifera in the
present study. Such an exchange could explain the high genetic
connectivity reported for many vent species (12, 41), even in cases
where most larvae are retained locally between disturbances.
Studies of immigration and succession at transient, geographically
separated, vents on the EPR contribute to our understanding of vent
systems in a metapopulation context (42) as they have in terrestrial
volcanic systems (43, 44). In these highly disturbed systems, the
important question may not be whether populations are open or
A
B
C
Fig. 4. Species composition of vent gastropod colonists and larvae. All gastropods were identified to species except larval and small juvenile Lepetodrilus,
which could only be identified to genus. Jagged line separates pre- (Left) and post-eruption (Right) samples. (A) Colonists in hot vent environment before
eruption at Worm Hole and Tica vents and after eruption at P-vent. Values are average relative abundances (±SE; n= 3) of seven most common species or
species groups (those >2% of all vent gastropods at any of three sites). (B) Colonists in warm vent environment before eruption at Worm Hole and after
eruption near Ty/Io vent. Values are average relative abundances (±SE; n= 3) of six most abundant species/groups (those >2% of all vent gastropods at either
of two sites). (C) Larval supply in sediment traps before eruption at East Wall and Choo Choo vents and after eruption at P-vent. Values are average relative
abundances (±SE; n= 21) of six most common species/groups that are also found as colonists.
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closed (45) but instead how often they become open and for how long.
This temporal variation in connectivity has important implications for
predicting effects of natural perturbations, or anthropogenic impacts
such as seafloor mineral mining, ecotourism, or bioprospecting.
Materials and Methods
Larvae were collected in McLane PARFLUX Mark 78H-21 time-series sediment
traps with a 0.5-m
2
collecting area. Particles dropped into collection cups filled
with 20% dimethyl sulfoxidein saturated saltsolution (46) as a preservative. Pre-
eruptiontraps were positionedinto the axialtrough near vents by lowering on a
wire from shipboard into a seafloor navigation network (17). These traps sam-
pled at East Wall and Choo Choo vents (Fig. 1) on 7-day intervals between
November 25, 2004, and April 21, 2005 (24). Following the eruption, a rapid-
response cruise was launched in July 2006 aboard the R/V Atlantis. A trap was
positioned near P-vent by submersible (Fig. 1), sampling on a 6-day interval
between July 1 and November 4, 2006. P-vent was selected as a nearby alter-
native to East Wall, which was no longer venting vigorously, and Choo Choo,
which had shut down. On recovery, samples from the traps were maintained at
approximately4 °C until the larvae(molluscs, polychaetes,and crustaceans)were
sorted and identified morphologically (47) under a dissecting microscope to the
lowest taxonomic level possible (e.g., species level for most gastropods). The
traps collect larvae that are swimming or sinking downward, and flux into the
trap is considered an indicator of larval supply to the benthos (25, 48).
The East Wall, Choo Choo, and P-vent traps were located directly in the
axial trough within 50 m of active vents. Three other traps were deployed
after the eruption near Tica and Bio9 (starting May 16, 2006, at 2-day
intervals) and Ty/Io (starting July 1, 2006, at 6-day intervals) (Fig. 1) but lacked
precise navigation and were positioned out of the trough. Larvae from these
traps were not used in primary analyses because larval abundance may be
reduced outside the trough (16).
Colonists (larvae that had settled and metamorphosed) were collected on
experimental surfacesdeployed by the submersible Alvinin vent sites for 4- to 5-
month durations. The surfaces were placed into two distinct environments in
inhabited, diffuse-flow vents. The “hot”environment was characterized by the
presenceof tubeworms, vigorous flow, and maximum temperatures up to 30 °C.
The “warm”environment lacked tubeworms and had moderate flow with
temperatures less than7 °C. These environments correspond respectively to the
vestimentiferan and bivalve/suspension-feeder zones ofprevious studies at this
site (35). In the 9°50′N region, species composition at different vents typically is
similar within a zone, but varies substantially between zones (33, 35, 49). Sur-
faces usedto quantify pre-eruption colonistswere selected froma largersample
set from this region of the EPR (35, 49, 50) to match as closely as possible the
deployment intervals and environmental and faunal characteristics of the post-
eruptionsites. They included surfacesplaced at Worm Hole ventfrom November
1994 to April 1995 in hot (temperatures at surfaces of 1.9–10.9 °C) and warm
(1.8–2.1 °C) environments and at Tica vent from December 1999 to May 2000 in
hot (18.0–26.3 °C) environments (Fig. 1). Neither site supported abundant mus-
sels, which were absent in post-eruption communities and are known to influ-
ence colonization (51). Species abundances in the different environments from
thesepre-eruptioncolonizationsamples are representativeof those in the larger
sample set. Post-eruption surfaces were deployed between July and November
2006 in the hot (23.2–26.7 °C) environment at P-vent and warm (2.2–6.5 °C)
environment at a site near Ty/Io vent. These sites were selected because they
were venting vigorously and were sufficiently large to accommodate replicate
experimental surfaces; Worm Hole hadshut down before the eruption and Tica
was not visited on the eruption-response cruise due to time limitations. For all
colonization surfaces, the thermal environment was measured with a temper-
atureprobe on deploymentand recovery at thebase of the surface. On recovery,
they wereplaced in individual collection compartmentsfor transport backto the
ship. On shipboard,surfaces and their attached colonists werepreserved in 80%
ethanol,as were any detached individuals from the compartment retained on a
63-μm sieve. In the la boratory , each surface was examined under a dissecting
microscope and all metazoan colonists (including detached individuals >1mm)
were enumerated and identified. Gastropods only were used in subsequent
analyses because methods of identification and quantification were consistent
across all samples for those species.
The colonization surfaces used before the eruption were basalt blocks, 10 cm
on a side. Those used after the eruption were “sandwiches”of six Lexan plastic
plates, each 0.64 cm thick and separated from each other by 0.95 cm to provide
additional surface area within a 1,000-cm
3
volume. Many vent species settle
onto plastic surfaces (52), so we did not expect this change in surface com-
position to greatly alter species composition of colonists, especially over a
period of months. To evaluate this assumption, we compared gastropod col-
onists between basalt blocks and Lexan sandwiches in a simultaneous, later
deployment (November 2006 to January 2007) at Tica vent. nMDS analysis
showed that dissimilarities based on species composition were no greater
between surface types than within a type and that composition on both blocks
and sandwiches was similar to that on sandwiches deployed earlier in com-
parable thermal habitat (Fig. S2). However, the surface area of sandwiches was
more than twice the area of basalt blocks; because this difference potentially
influences absolute abundance of colonists, we compare relative abundances
between pre- and post-eruption deployments.
Larval supply was compared between pre- and post-eruption periods using
MANOVA followed by univariate ANOVA (Systat v. 11; Table S2) for the six most
abundant species at either site that were also found on colonization surfaces.
Because sequential intervals in the time series were used as replicates, auto-
correlation analysis (Matlab 7.1) was used to evaluate independence. Sig-
nificant autocorrelation (P<0.05) with a 1-step lag was detected in at least one
record for three taxa (C. naticoides,G. spiralis, and G. emarginatus)and
autocorrelation with a two-step lag was detected for Lepetodrilus spp. In each
of these cases, when the ANOVA was repeated with subsampled records to
avoid autocorrelation (every second or every third sample interval as appro-
priate) no changes in significance were found (P<0.05 level). Differences in
community composition were examined with nMDS of larval abundance in
trap samples (Systat v. 11), using Pearson correlations of fourth root trans-
formed values to emphasize rare taxa. Polychaetes were not included because
their preservation was poor in some samples. For visual clarity, only the East
Wall samples were plotted from the pre-eruption collections (when Choo
Choo samples are added, they cluster near East Wall positions). Colonist
community composition (gastropods only) was examined similarly with nMDS.
ACKNOWLEDGMENTS. We are grateful for help at sea from K. Buckman,
D. Fornari, A. Fusaro, I. Garcia Berdeal, B. Govenar, B. Hogue, R. Jackson,
C. Strasser, T. Shank, S. Worrilow, and to the Captains and crew, Alvin group,
and Chief Scientists (M. Lilley, C. Vetriani, K. Von Damm, and A. Thurnherr)
during Atlantis cruises AT11-20, 11-26, 15-06, and 15-12, and the Captain,
crew, and Chief Scientist (J. Cowen) of the New Horizon rapid response cruise.
S. Bayer examined gastropod specimens for reproductive maturity, S. A. Soule
provided a base topographic map of the eruption area, and two anonymous
reviewers contributed useful comments. Principal investigators in the LADDER
project (W. Lavelle, J. Ledwell, D. McGillicuddy, and A. Thurnherr) were
instrumental in facilitating this project and provided input during numerous
discussions. Support was provided by National Science Foundation Grants
OCE-969105, OCE-9712233, and OCE-0424953, Woods Hole Oceanographic
Institution grantsfrom Deep OceanExploration Instituteand the OceanVenture
Fund, a National Defense Science and Engineering Graduate Fellowship to
D.A., and the Woods Hole Oceanographic Institution Jannasch Chair for Excel-
lence in Oceanography to L.M.
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