Microhabitat Distributions of Juvenile Hydrothermal Vent Gastropods•
A thesis submitted to the faculty of
San Francisco State University
In partial fulfillment of
The requirements for
The degree
Master of Science
In
Marine Science
by
Patricia Ann McMillan
San Francisco, California
November 2003
© Copyright by
Patricia Ann McMillan
2003
Microhabitat Distributions of Juvenile Hydrothermal Vent Gastropods
Patricia Ann McMillan
San Francisco State University
2003
Early gastropod settlement patterns around a hydrothermal vent at 9°50' N East
Pacific Rise were determined and compared to the distribution of adults of the
same species. Post-settlement processes were also examined by deploying
caged and uncaged settling blocks. These blocks were deployed in 4 different
zones at the vent site for a 5-month period. The zones were characterized by
different intensities of hydrothermal influence.
Juvenile (<1mm) gastropods
were identified and counted from the blocks. The most abundant species were
Lepetodri/us spp., Eulepetopsis vitrea, C/ypeosectus delectus and Gorgofeptis
sp. (C/ypeosectus and Gorgoleptis were combined due to morphological
similarity). The number of juvenile Lepetodrifus spp. was higher in the area of
high hydrothermal influence compared to no influence. There was a significant
difference between adult and juvenile distributions for Lepetodrilus spp. and
Cfypeopsectus!Gorgoleptis across all zones. Juvenile Eufepetopsis vitrea were
more abundant on the caged than the uncaged blocks. These data suggest
that initial settlement patterns of vent gastropods are modified by postsettlement processes for Lepetodrilus spp. and CfypeopsectusfGorgolepUs.
•·
ACKNOWLEDGMENTS
I would like to thank:
•
•
•
•
Dr. Stacy Kim for her enthusiasm, assistance and encouragement.
Dr. Nicholas Welschmeyer, Dr. Kenneth Coale, Dr. J. Timothy
Pennington, and Dr. Kenneth Johnson for their encouragement,
comments and suggestions on this manuscript.
Dr. Lauren Mullineaux and Susan Mills for providing me the samples
and their assistance.
MBARI for their technical support.
I am also very grateful to:
•
•
•
•
•
•
•
•
•
"
The faulty, staff and student of Moss Landing Marine Labs for their
support.
Kimberly Puglise for all her help and support during our time at MLML
Dr. Wiebke Ziebis for her friendship, support and reviewing of this
manuscript
Christine Whitcraft for her support and many reviews of this
manuscript.
Donna Drazenovich, Maureen Shea, Val Growney, Sandy Krebsbach,
and Bonnie Becker for their friendship and encouragement.
Dr. Lisa Levin and her lab for their support.
Dr. Paul Hyde, Dr. Sabina Wallach and Dr. Jean Mefferd for the gift of
life!
My friends for their continued support and encouragement
My family for being themselves and always asking, "So how's the
thesis going?"
My husband Tom for his love, support and patience during this
endeavor.
My funding sources:
•
•
Dr. Earl H. Myers and Ethel M. Myers Oceanographic and Marine
Biology Trust
David and Lucille Packard Grant for Graduate Research and Travel
v
TABLE OF CONTENTS
List of Tables ............................................vii
List of Figures...........................................viii
Introduction ............................................. 1
The Physical Setting: Vent Geology ..................... 2
Vent Biology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Dispersal Mechanisms (to disperse or not) ............... 8
Settlement Cues and Recruitment . . . . . . . . . . . . . . . . . . . . . 10
General Gastropod Biology and Adult Distribution ......... 12
Method ................................................ 15
Statistical Analyses ................................. 19
Results ................................................ 20
Juveniles......................................... 21
Juveniles vs. Adults ................................ 22
Discussion ............................................. 23
Dispersal potential. ................................. 24
Juvenile distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Role of predation ...................................28
Juvenile vs. Adult distribution ......................... 29
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Literature Cited ......................................... 33
vi
LIST OF TABLES
Page
Table
1.
Generalize description of hydrothermal vent zones at EPR . .42
2.
Identified juvenile hydrothermal vent gastropod species .... 43
3.
Statistical results of ANOVA .......................... 44
4.
Statistical results of a priori ANOVA .................... 45
vii
LIST OF FIGURES
Figure
1.
Page
Generalized diagram of zonation pattern at an EPR black
smoker vent site . . . ........................... 46
2.
Study site . . . ..................................... 4 7
3.
Deployment of settling substrate . . . . . . . . .............. 48
4.
Major species identified .............................. 49
5.
Other species id entiffed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.
Distribution of adult and juvenile Lepetodrilus spp ......... 51
7.
Distribution of adult and juvenile Clypeosectus delectus and
Gorgoleptis sp. . .................................52
8.
Distribution of adult and juvenile Eu/epetopsis vitrea ....... 53
viii
Introduction
Larval settlement and post-settlement processes have been
studied in the rocky intertidal (e.g. Connell 1961, 1972). As space
becomes available, opportunistic species colonize thereby creating an
environment for subsequent species. The post-settlement processes
such as space competition, migration, and predation that structure the
rocky intertidal communities may also structure hydrothermal vent
communities. This scenario may be analogous to that at hydrothermal
vents. The ability in the rocky intertidal to do manipulative experiments
and thus observe daily changes is much easier. However at
hydrothermal vents, the ability to remove fauna from areas within the
vent habitat and daily observations are not feasible. Therefore, the
knowledge obtained from the rocky intertidal studies may provide
insight into larval settlement and post-settlement processes at
hydrothermal vents. This study exams settlement through the use of
settling blocks to determine settlement patterns of hydrothermal vent
gastropods compared to adult distributions of the same species and
physical (geological) setting.
1
The Physical Setting: Vent Geology
Hydrothermal vents occur at diverging plate boundaries, where
plates of the earth's crust are spreading apart. As the plates move, hot
magma rises to fill in the gaps.
The rising magma is not evenly
distributed but is focused in disjunct fissures from which the lava may
be extruded.
The young crust is very porous, and a "hydrothermal
circulation" develops where cold seawater penetrates cracks and
fissures in the rock. This water is heated by the hot rocks and magma
before reemerging at the surface.
This hot hydrothermal fluid is
enriched in reduced chemical compounds (sulfur species) and with
some metals (e.g. iron, copper, zinc). When it exits the sea floor and
mixes with the surrounding cold and alkaline seawater, "black smoker"
plumes can form by the precipitation of metal sulfides.
Columnar
chimneys typical of hydrothermal vents on the East Pacific Rise can
grow around the fluid outlet starting by the precipitation of anhydrite
(calcium sulfate) and its manifestation in sheaths (Tivey 1995).
The bulk of evidence indicates that the spreading rate at the
mid-ocean ridges is proportional to the heat flux and influences the
distance between vents and the length of time a vent is active.
In
general, the faster the spreading rate, the more closely spaced and
2
ephemeral the vents are.
At slow spreading ridges (Mid-Atlantic
Ridge, MAR}, vents are 10's to 1000's of km apart (Grassle 1986;
Seyfried and Mottl 1995) and may remain active for hundreds of years
(Kim 1996). At fast spreading ridges (East Pacific Rise, EPR}, the
vents are 10's to 100's of m apart and may last 10 - 100 years
(Mullineaux 1994; Kim 1996). Recent investigations on Gakkel Ridge,
an ultraslow-spreading ridge in the Arctic Ocean, have found more
active vents than would be expected; these were localized near
volcanic centers (Edmonds et al. 2003).
This recent evidence
suggests that the distance between vents may not be directly related to
the spreading rate.
A unique feature at hydrothermal vents is that reduced sulfur
species, as well as reduced metals that are expelled with the
hydrothermal fluid, provide an energy source for chemoautotrophic
bacterial growth. Free-living or symbiotic sulfur-oxidizing bacteria are
important primary producers in vent environments (Fowler and
Tunnicliffe 1997).
They fix carbon through oxidation of reduced
chemical species found in vent fluid and can provide food for higher
taxa which thrive in amazing abundance at many vents. The
endosymbionts associated with clams or tubeworms similarly provide
3
their hosts with nourishment. As the symbionts require sulfide for their
energy metabolism, the hosts are restricted to the vent areas.
Surrounding individual black smokers on the East Pacific Rise
were five distinct faunal zones. A general diagram of this zonation
pattern is in Figure 1.
The zone closest to the vent opening was
characterized by very high temperatures (-250°C) dominated by
alvinellid polychaetes (Hessler et al. 1985; Mullineaux et al. in press;
Van Dover and Hessler 1990). However, in my research this zone was
not investigated, as it is very difficult to perform experiments here. A
summary table describing the zones is in Table 1. The first zone (z1)
considered in this thesis was characterized by high flow and high
temperatures, elevated sulfide levels (up to 330 J.!M), and low but
variable oxygen levels (Johnson et al. 1988).
The predominant
organisms in this zone were vestimentiferan tubeworms (e.g., Riftia
pachyptila). The second zone (z2) was characterized by a moderate to
low diffuse flow, and temperature a few degrees above ambient
(Hessler and Smithey 1983; Hessler et al. 1988).
This area was
mostly colonized by bivalves (mussels and clams). The third zone (z3)
had low flow and a temperature at most a few tenths of a degree
above ambient (Hessler and Smithey 1983). The sulfide levels were
4
low, and oxygen levels were high. The organisms that reside here
were primarily suspension feeders, typically serpulid worms.
The
fourth zone (z4) was outside the vent field and was characterized by
ambient temperature, sulfide and oxygen levels. The organisms that
resided here were typical deep-sea fauna. The approximate spatial
range from zone 1 to zone 4 is 3 to 20 meters.
The spatial structuring of animal or plant communities in distinct
zonation patterns is controlled by physical, biological or chemical
variables and their interactions.
The more familiar zonation in the
rocky intertidal zone can, to some extent, be regarded as an analogue
to the zonation pattern of vent environments. In the intertidal, benthic
communities are also often controlled by extreme variables and
structured along desiccation and temperature gradients.
Other
important factors for species survival and thus community structure are
biological interactions, for example, predation.
This interaction of
physical, chemical and biological forces structures all ecosystems.
The purpose of the present work is to examine potential biological and
physical interactions in the vent community by examining the pattern of
larval settlement, and corresponding adult distributions, across the
physicalfchemical gradient characteristic of the vent zones.
5
Vent Biology
The isolation and distances between hydrothermal sites have
always provoked discussion on the larval dispersal, settlement and
recruitment of the mostly endemic and sessile species found near
vents.
The vent environment includes unique microhabitats with
equally unique species that thrive in this extreme environment The
environmental factors of temperature, oxygen availability and sulfide
concentration are dramatically different at hydrothermal vent sites than
at the rest of the ocean floor (Johnson et al. 1994).
Two life history features should influence larval dispersal
patterns of vent species: larval developmental mode and larval life
span.
The first. larval development mode, varies widely for vent
endemic
taxa.
Some
mytilid
mussel
larvae
have
demersal
development (Lutz et al. 1980). Other bivalve larvae have been found
near the surface of the oceans over vents (Berg and Van Dover 1987).
Bouchet and Waren (1994) found evidence of ontogenetic migration to
the surface in planktotrophic larvae of vent gastropods including
Phymorhynchus (turrid), Shinkailepas (limpet), and Alviniconcha and
Desbruyeresia spp. ("hairy snail").
6
Larvae of vestimentiferans are
lecithotrophic (Marsh et al. 2001), although it is unknown where they
develop.
Thus, the larvae of vent dwelling organisms vary widely,
probably along with their dispersal patterns. The evolutionary benefits
of these differing strategies for vent organisms are at present unclear.
The second life history feature, larval life span, depends partly
on whether larvae are planktotrophic or lecithotrophic. Planktotrophic
larvae feed on the microplankton in the water column where an
adequate food supply can extend survival for long periods of time
(Hessler and Kaharl 1995). However, microplankton is generally most
abundant at the surface and rare at depth (Fuhrman et al. 1989), so
many planktotrophic vent larvae may swim to the surface to feed then
return to the deep-sea to settle.
Conversely, some mytilid mussel
larvae are both planktotrophic and demersal; such larvae apparently
feed in the benthic boundary layer near vents (Lutz et al. 1980).
Lecithotrophic larvae do not feed but instead are provisioned
with yolk that provides nourishment during development Larvae of
vestimentiferans are lecithotrophic (Marsh et al. 2001 ).
Recently,
Marsh et al. (2001) fertilized and reared the vestimentiferan, Riftia
pachyptila, at in situ temperature and pressure in the lab. Based on
their results, they estimate a metabolic larval lifespan to be 38 days.
7
Since it is generally believed that food supply is restricted in
deep water, it makes sense that most vent species would produce nonplanktotrophic larvae (Lutz 1988; Gustafson and Lutz 1994) even
though such larvae probably have shorter life spans and thus more
limited dispersal potential than planktotrophic larvae.
Still, several
studies have shown that some lecithotrophic larvae absorb dissolved
organic matter (DOM) (Jaeckle and Manahan 1989a & 1989b;
Manahan 1990; Shilling and Manahan 1994). The absorption of DOM
could extend the survival of larvae of vent organisms, allowing for
greater dispersal distance. In addition, the cold ambient water of the
deep-sea may lower the metabolic rate of the larvae, thereby
extending time in the water before settling (Boidron-Metairon 1995;
Mullineaux and France 1995; Craddock et al. 1997).
Dispersal Mechanisms (To disperse or not)
Dispersal distance depends on the flow field as well as larval
survival time.
Flows may act to retain larvae near the parent
population or may transport larvae to new sites.
A positive
consequence of retention is ensuring a suitable habitat to settle in
while a disadvantage is that gene flow is limited. An advantage of long
8
distance dispersal is potential colonization of new vent fields and
enhanced gene flow between vent fields.
A disadvantage is larval
loss.
Since hydrothermal vents are a patchy habitat, larval retention
or an ability to return to suitable habitat would seem advantageous.
The larvae of vent organisms may be retained near their originating
vent if they remain in near bottom flows. The currents moving along
the ridge axis have a mean velocity of <2 cm/s, although speeds of up
to 15 cm/s were recorded at 10°N EPR over a 3 day period (reviewed
in Mullineaux and France 1995). The currents move cross-axis at
roughly between 2 and 5 cm/s (Kim and Mullineaux 1998). The overall
elliptical flow pattern would cause larvae to be retained near the
originating vent site.
A similar patchy habitat, estuarine systems, may provide insight
into another potential larval retention mechanism through larval
behavior. In estuaries, larvae vertically migrate in the water column
with the tide; during ebb tide the larvae migrate lower in the water
column to prevent being washed out to sea, and at flood tide, the
larvae migrate higher in the water column to move further into the
estuary (Cronin and Forward 1982; 1986).
9
At hydrothermal vents,
mesoscale eddies (e.g. Taylor caps) can retain a water mass in the
proximity of the region of origin for weeks to months (Mullineaux 1994).
As discussed above, the currents may also transport the larvae off the
ridge axis. The effect of these currents and eddies would depend upon
when the larvae were released. Larval vertical migration, as observed
in estuaries, could also affect the distribution of larvae of hydrothermal
vent species.
Another long distance dispersal mechanism may be vent
plumes. Plumes are the result of the release of hot buoyant fluid. As
the fluid ascends, this flow creates eddies that entrain the ambient
water and particulate matter, including organisms and larvae (Kim et
al. 1994; Helfrich and Speer 1995; Lupton 1995; Speer and Helfrich
1995). The plume rises until mixing with ambient water and cooling
make it neutrally buoyant, at which point it spreads laterally. Larvae
may be entrained and thus transported upwards via the plume, then
advected horizontally in ambient currents (Mullineaux 1994).
Settlement Cues and Recruitment
For species with planktonic and thus widely-dispersing larvae,
settlement cues are thought to be especially important, and the
10
physico-chemical factors that are distinctive near vents could be
potential settling cues.
However, the relatively small habitat targets
and often harsh conditions that characterize hydrothermal sites must
also make settlement in the vent habitat a challenge to the larvae of
vent endemics.
Nevertheless,
successful
recruitment
to
this
ephemeral and widely spaced habitat must depend on the dispersal of
larvae and their subsequent successful settlement.
The cues for larval settlement in vent communities are still
largely unknown.
Larval settlement may be triggered by water
temperature (Lutz et al. 1970; Mullineaux et al. 1997; Fisher 1998).
With increasing water temperature, the concentrations of silicate and
sulfide also increase with concomitant decreases in oxygen levels
(Johnson et al. 1986).
Another settlement cue may be the
concentration of sulfides in the water.
Some organisms need high
levels for symbionts; others would avoid it due to toxicity. Settlement
cues in other systems include light (Koback 2001; Strasser et al.
1999), gravity, conspecifics (Koback 2001), substrate type (Gutierrez
1998), and flow dynamics.
Several
recruitment
studies
have
been
conducted
at
Van Dover et al. (1988) and
hydrothermal vent communities.
11
Mullineaux et al. (1998) conducted studies at the EPR and Tunnicliffe
(1990) conducted a study a Juan de Fuca Ridge. Van Dover et al.
compared recruitment within and outside the vent area at 21°N. This
study used shale as a settling substrate and found more settlement
within the vent area. The Mullineaux et al. study was at 9°N and used
natural basalt obtained near 18°N. This was a comparison between
two vent zones at two vent sites 1km apart. They found settlement in
both zones with one species, Lepetodrilus elevantus, at both sites.
Tunnicliffe deployed slate arrays and a time-lapse camera. Recovery
resulted in loss of many of the mobile species.
However, visual
observation showed that Lepetodrilus fucensis heavily populated
several of the plates.
General Gastropod Biology and Adult Distribution
The larval development mode of several hydrothermal vent
gastropod species has been deduced from the larval shell (Lutz et al
1984; Lutz 1988; Gustafson and Lutz 1994). Four specific species of
interest in this study, Lepetodrilus spp. Clypeosectus delectus,
Gorgoleptis spp. and Eulepetopsis vitrea, have been inferred to
12
produce lecithotrophic larvae. The food source for these species is
microbial films.
Physical characteristics vary with each species.
spp. larvae have a length of 120- 200
~-tm.
Lepetodrl/us
and the adult size range is
6 - 20 mm, depending on the species. One species is known to be
sexually mature at 1/3 of its maximum length (Gustafson and Lutz
Clypeosectus delectus larvae have a maximum diameter of
1994).
200
~-tm.
and an adult size range is 5 - 8 mm (Gustafson and Lutz
1994). Depending on the species of Gorgo/eptis, the larvae have a
maximum length of 120- 130 11m and an adult size range of 3-9 mm
(Gustafson and Lutz 1994). The larvae shell of Eulepetopsis vitrea has
a maximum length of 400 11m and is often lost on adults (Gustafson
and Lutz 1994). The adult can be up to 17 mm.
The adult distribution patterns are also species specific.
Lepetodrilus spp. has been found mostly in collections from Riftia in
the Vestimentiferan zone (Mclean 1988). In a study by Mullineaux,
Peterson, and Fisher (in press), adult Lepetodrllus spp. were found in
all zones of hydrothermal vent influence with decreasing abundance
further away from a central smoker. For C/ypeosectus delectus and
13
Gorgoleptis spp., a general habitat for both these species is unknown
(Mclean 1988, 1989b). However, Mullineaux et al. (in press), found
the highest concentrations in the Vestimentiferan zone (z1) and the
Suspension zone (z3). Adults were in all areas of vent influence but in
very low abundance in the Bivalve zone (z2). Eulepetopsis vitrea has
been found on basalt substrate, mussels, and a few individuals from
washings of vestimentiferan tubewonms (Mclean 1990).
In the
Mullineaux et al. study (in press), the adults were found in all areas of
vent influence.
The purpose of this study was to compare the influence of
environmental factors on larval settlement of gastropods in the four
distinct zones, as well as to investigate the impact of predation on
juvenile survival and thus adult community structure.
This study
examined settlement patterns to artificial substrata to address the
following questions:
1) What is the zonal/habitat distribution of juvenile gastropods at
9°50'N EPR?
2) How does juvenile distribution compare to that of the adults
(size >1 mm) of the same species?
14
3) Do settlement (larval choice) or post-settlement processes (e.g.
predation) have a greater influence on adult distribution?
Methods and Materials
The study was carried out at 9°50' N on the East Pacific Rise
(EPR) at the East Wall site (Figure 2), where several studies have
been conducted by Mullineaux et al. (1998; 2000; in press}.
To
determine the early recruitment patterns of vent fauna, settling
substrates of basalt, a natural substrate at vents, were deployed. The
basalt was acquired from a quarry in Washington State (Interstate
Rock Products). The basalt blocks were 10 em on a side with buoyant
polypropylene handles looped through a small hole in one corner that
facilitated deployment and retrieval.
The blocks were placed in four zones via the submersible Alvin
on November 1994 and retrieved in April 1995 to determine the early
settlement patterns. The zones were defined as: (1) vigorous diffuse
hydrothermal flow, identified by tubeworms; (2) moderate to low levels
15
of diffuse fluid hydrothermal flow, identified by bivalves; (3) very tow or
no detectable hydrothermal flow, identified by suspension-feeders; and
(4) no exposure to vent flow, identified by non-vent species.
The
above zones will be referred to as z1 - Vestimentiferan, z2 - Bivalve, z3
- Suspension, and z4 - Periphery, respectively.
Six replicate basalt blocks were placed in each zone; three with
cages and three without cages (Figure 3) (in zone 2, only two of the
caged blocks were retrieved). The cages were designed to exclude
large predators such as crabs, the octopods, and fishes (Mullineaux
1996; 1997; Micheli et al. 2002).
Cages were constructed of 7 mm
plastic mesh in a 20 em cube with the settling blocks suspended in the
center of the cage with plastic cable ties to prevent abrasion of the
recruits (Mullineaux et al. 1997). The mesh size was selected to keep
out major predators and not become blocked by microbial growth.
Mullineaux (1997) previously conducted a cage control experiment to
determine whether there was a hydrodynamic effect of the cages on
recruitment. The cage controls consisted of basalt blocks elevated 2-{l
em above the seafloor with one side of the cage mesh missing. They
found no significant difference in animal abundance between cages
16
and cage controls indicating that caging did not appear to affect
settlement (Mullineaux et al. 1997).
During retrieval, the settlement blocks were placed into isolated
individual slots in a sealed collection box for transport to the surface.
Upon arrival at the surface, the organisms were removed from the
blocks and the transport slot and passed through a 63J1m sieve to
retain any individuals that may have detached during transport.
Organisms were preserved in 80% ethanoL
Mullineaux et al.
(2000,
in
press) identified
the most
conspicuous organisms obtained from the blocks. This included
gastropods >1mm; their data are used here for comparisons. Small
juvenile gastropods remained unidentified even though they were often
the most abundant taxa. These gastropods are the subjects of this
study.
The terminology that I will use is that all individual gastropods
that are less than 1mm will be referred to as juveniles. This
encompasses both post-larvae and juveniles with growth beyond the
larval shell. Since the blocks were deployed for only 5-months, it could
not be determined if larvae settled 5 minutes or 4.9 months before
retrieval.
Results
concerning
settlement
17
were
inferred
from
examination of the juveniles <1 mm.
adults,
and
Larger animals were termed
their abundances were previously determined
by
Mullineaux et aL (in press).
The small gastropods (<1mm) were sorted under a dissecting
microscope using 50x to 70x magnification.
identification was made at this level.
Whenever possible,
However, in cases where the
shell-sculpting pattern on the juvenile gastropods was indiscernible, a
scanning electron microscope (SEM) was used.
The organisms were prepared for SEM by coating with goldpalladium using a Pelco SC-7 sputter coater under 0.02 mbar of
pressure.
Both an lSI WB6 and a Philips XL40 SEM were used for
analysis, and each produced equivalent images.
Digital images of
each gastropod were saved and used for identification based on the
morphology of the protoconch (larval shell).
The species level
identifications were made using taxonomic guides of Mullineaux et al.
(1996), Waren and Bouchet (1989; 1993) and Mclean (1988; 1989a;
1989b; 1990).
18
Statistical analvses
Analyses were run for the most abundant juvenile gastropods
encountered, Lepetodrilus spp., Eulepetopsis vitrea, and a combination
of G/ypeosectus delectus
Gorgo/eptis) (Figure 4).
inability
to
distinguish
and
Gorgoleptis
sp.
(C/ypeosectus/
The latter group was combined due the
between
them
(i.e.
similar
juvenile
morphologies).
Parametric 2-way model 1 ANOVA was run using SYSTAT 9.0
on rank transformed count data (S. Bros pers. comm.) at a.=0.05. The
ANOVA was used to determine if there were differences between
zones (Vestimentiferan (z1), Bivalve (z2), Suspension (z3), and
Periphery (z4)), between treatments (caged and uncaged), and
interactions between zones and treatment.
When a statistically
significant difference was found, an a priori ANOVA was performed
using the ranked count data (S. Bros pers. comm.). The number of
comparisons that can be done for a priori tests is limited to 'a - 1'
where 'a' is the number of levels for the independent variable (i.e.
zones). This analysis was limited to three comparisons. The three
most interesting comparisons between zones were chosen.
19
The
statistical significance levels are reported without adjustment due to
low replication.
To determine if there was a difference between adult and
juvenile distribution across zones, Chi-square goodness of fit tests
were run. Each species was examined separately across all zones.
The juvenile distribution pattern was set as the expected distribution
with a=0.05 for df=3.
Results
Juveniles of eight different gastropod species were identified in
this study (Table 2). Images of these species appear in Figures 4 and
5. Lepetodrilus spp., Eulepetopsis vitrea, Clypeosectus delectus and
Gorgoleptis sp. (Figure 4) were in high abundances and statistical
analyses were performed on these species.
Cyathermia naticoides,
Melanodrymia sp., Peltospira sp., and Rhynchopelta concentrica
(Figure 5) were found in very low abundances, eight specimens total.
These numbers were so low that statistical tests could not be
20
performed, and trends could not be distinguished. Many specimens
remained unidentified (- 21 %) because the shells were in small pieces,
the protoconch had been etched beyond recognition, or the shells had
become decalcified.
Juveniles
Caging effects v.aried by species (Table 3).
Only for
Eu/epetopsis vitrea, was there a significant cage effect, with more
settlers on caged blocks (Table 3).
The cages provided protection
from predation, a post-settlement process. These limpets are larger
than the other species in this study and therefore potentially more
"visible" to predators as larvae or recent settlers.
There were no
significant cage effects for Lepetodri/us spp. and C/ypeosectusl
Gorgoleptis, so the juvenile patterns observed in the different zones
presumably are not affected by post-settlement predation for these
three species.
The abundance of juvenile Lepetodri/us spp. varied by zone.
There was a significant higher abundance of juvenile Lepetodri/us spp.
in the Vestimentiferan (z1) zone than in the Periphery (z4) zone (fable
4). The lower abundance of these young animals away from vents
21
suggests that characteristics of the vent habitat attract settlers.
Eulepetopsis vitrea and ClypeosectusiGorgoleptis juvenile abundances
were not different across zones (Table 3), suggesting that larvae of
these three species settle indiscriminately across the four zones.
There were no interactions between zone and treatment.
Juveniles vs. Adults
A Chi-square goodness of fit test tested for overall differences in
abundance of adults versus juveniles.
For Lepetodrilus spp., there
was a statistically significant difference between the adults and
juveniles across zones, (x.2=461.781, (p<0.001 )), with adults more
abundant in Vestimentiferan (z1) zone and Bivalve (z2) zone but less
abundant in Suspension (z3) zone (Figure 6).
For Clypeosectusl
Gorgoleptis, the comparison of the distribution patterns between adults
and juveniles also showed that there was a significant difference
(·l=539.552, (p<0.001)), with adults more abundant in Vestimentiferan
(z1) zone and Bivalve (z2) zone but less abundant in Suspension (z3)
zone (Figure 7). In Eulepetopsis vitrea, no difference was observed
2
(x. =0.052, (p=0.996)) (Figure 8).
22
Discussion
This study provides insight into the early settlement patterns for
hydrothermal vent gastropods, as reflected in the distribution of small
juveniles on introduced substrate. The gastropods, Lepetodrilus spp.,
Clypeosectus/Gorgoleptis,
and
Eulepetopsis
vitrea
all
produce
lecithotrophic larvae, but which exhibit differential settlement success
across the vent spatial gradient (Figures 6-8). The short deployment
time of 5-months for the settlement blocks was a useful approach to
investigate these patterns.
In the deep-sea, cost limitations require
that experimental manipulations involve a balance between replication
and bottom time. Although limited in the number of replicates of caged
and uncaged treatment blocks, this experiment was still sufficient to
provide insight into the role of predation early in the settler's life. At
this vent site, East Wall on the East Pacific Rise, the settlement
patterns were different for each gastropod species.
23
Dispersal potential
The gastropods, Lepetodrilus spp., Clypeosectus/Gorgofeptis,
and Euiepetopsis vitrea, analyzed in this study have been implied to
produce lecithotrophic larvae (Lutz et al. 1984; Lutz 1988; Gustafson
and Lutz 1994). This development mode may well provide the ability
for these larvae to disperse long distances or disperse then return to
the same vent site. Marsh et al. (2001) estimated the larval lifespan of
Riftia pachyptiia to be 38 days. Kim and Mullineaux (1998) found most
vent gastropod larvae in the near bottom (within 15m above bottom),
both inside and outside the axial ridge. At heights of 10- 45m above
bottom, they also observed gastropod larvae.
Potential dispersal mechanisms include hydrothermal plumes,
currents, or mesoscale eddies, as discussed earlier.
Hydrothermal
vent plumes ascend entraining ambient water until the water mass
becomes
neutrally buoyant which
then
spreads out laterally.
Mesoscale eddies formed by the rising plume and the Coriolis effect
can break away from the plume and remain a coherent water mass
while moving away (reviewed in Van Dover 2000).
Currents are
constrained by the ridge crest topography and flow up and down the
24
ridge axis. If larvae get into these different flow patterns, they have the
ability to be transported to a different area or retained.
Vents are temporally ephemeral. They senesce, disappear and
new ones appear. The larvae that are in the water column must be at
least occasionally available to settle these new sites.
The actual
mechanisms of colonization at new sites are still unknown.
New tools, such as genetic testing, may provide some insight
into larval dispersal distances. For two of the species in this study,
Lepetodrilus spp. and Eulepetopsis vitrea, genetic testing has been
successfully applied to determine that these species have long
distance dispersal (Vrijenhoek 1997; Vrijenhoek et al. 1998). Won et
al. (2003) have also found that the diverging oceanic flows that cross
mid-ocean ridges apparently isolate the sections on either side. This
results in genetic differences within the same species on each side of
the ridge axis.
Juvenile distribution
The zonation of the communities at hydrothermal vents has
been compared to rocky intertidal zonation. Near the smoker opening,
high levels of sulfides favor species that contain symbionts. These
25
symbionts utilize the sulfides, and energetically support the host
organisms. At vents, the harshest physical conditions co-occur with
the most abundant energy source.
Conversely, in the intertidal, the
harshest physical conditions are high in the intertidal above the low
intertidal areas of high food availability. More organisms settle at lower
levels of the shoreline than at the upper levels (Connell 1972; Menge
and Branch 2001) where the organisms are least impacted by wave
exposure and desiccation.
The opposing trends - more settlement in
the physically stressful area near vents versus more settlement in the
physically benign area in the intertidal - indicate that some factor other
than physical stress is influencing settlement. Lepetodrilus spp. settled
predominately in the Vestimentiferan zone (z1); the most stressful
environment.
Clypeosectus/Gorgoleptis
settled
mainly
in
the
Suspension zone (z3) which Eulepetopsis vitrea had no preference.
Food availability is a factor that is high near vents and lower in the
intertidal, and may be controlling settlement in both these habitats. For
Lepetodrilus spp., another factor may be that it contains a symbiont. A
species of Lepetodrilus at Juan de Fuca Ridge was found to multiple
ways to obtain nourishment which included grazing, a symbiont or a
combination of the two (Fox et al. 2002).
26
Another factor affecting distribution is space competition, which
is observed in many communities. In the intertidal, organisms actively
remove other organisms (Benedetti-Cecchi 2000) or passively crowd
out others (Connell, 1961 ). At hydrothermal vents, Micheli et al. (2002)
suggest that new settlers may be dislodged from the substrate by the
grazing of previous settlers or adults. The grazing also removes a food
source, surface-attached microbes (Hessler and Smithey 1983; Van
Dover and Fry 1994). In the present experiment, the deployed basalt
blocks were initially completely bare. This represents a maximum of
space availability and surface for the development of a microbial film,
the first step in microhabitat creation. This then offers maximum space
and food availability and therefore maximum settlement yield. For 5months, there were an average of eight gastropods/block of both
adults and juveniles. The size range of these gastropods was <1mm
to 20mm. Therefore, space competition may not have been a factor in
these experiments.
Although not statistically significant, there was an interesting
trend of low or no settlement in the Bivalve (z2) zone. This lack of
settlement suggests that biotic forces may be contributing not only to
post-settlement mortality but also to settlement patterns themselves.
27
Lenihan et al. (2001) have shown that recruitment to mussel patches at
vents is lower than in areas with no mussels.
In aquatic systems,
Dreissena polymorpha (zebra mussel), is found in dense beds similar
to those at hydrothermal vents. Though no studies on clearance rates
have been done on vent mussels, studies have been conducted on
Dreissena polymorpha.
Pace et al. (1998) have reported zebra
mussels reducing zooplankton biomass by >70%. This would suggest
that vent mussels could consume larvae as they pass over.
Role of predation
After settlement,
predators
may
reduce
abundances
of
juveniles. In this study, predation was a factor only for Eulepetopsis
vitrea as there were more in the caged blocks.
An interesting
observation is that a large number of gastropods from zone 1 caged
blocks remained unidentified. Dominant predators have been shown in
the intertidal to play a role in community structure (Menge and Branch
2001). Mobile predators have an impact at vents (Micheli et al. 2002).
Micheli et al. (2002) and Mullineaux et al. (in press) showed through
gut analysis of the vent fish, Thermarces cerberus, that it is a major
predator of gastropods.
Mullineaux et al. (in press) observed an
28
increase in abundance of gastropods in cages that excluded T.
cerberus.
Other predators include crabs and octopods. The size of
mesh, 7 mm, used for the cages in this study effectively blocked these
predators. Although the cages excluded predators, they also provided
an additional surface for microbial film to develop. Therefore, more
food was likely available on the caged blocks, which may have
produced a cage effect However, Mullineaux et al. (1997) found no
cage effect when comparing cage and cage control blocks utilizing the
same caging design. Predation was statistically significant only for the
species with the largest juvenile (Eulepetopsis vitrea). The large size
may make them more obvious to predators.
Adult vs. Juvenile distribution
Lepetodrilus spp. and Clypeosectus/Gorgoleptis (the smallest
juveniles) showed no effect of predation in the caging experiment
However, there was a significant difference between adults and
juveniles for Lepetodrilus spp. and Clypeosectus!Gorgoleptis. There
was a trend, for both species, of more juveniles in the Suspension (z3)
zone. This suggests that migration and/or mortality were affecting the
29
observed distribution. Both these mechanisms can be influenced by
predation, habitat unsuitability or space competition.
Migration between blocks or zones would allow species to find
the appropriate microhabitat where they could survive. In this study, it
was not specifically investigated whether these gastropods migrate
between the zones. However, Mullineaux et al. (unpub. data) showed
no change is distribution for Lepetodrilus spp. and Glypeosectusl
Gorgoleptis at the time intervals of 8- and 13-months. This suggests
that within a 5-month time period, these gastropods found the
appropriate habitat and remained there.
Food availability may also affect survival and therefore the
observed species distributions.
The amount of food available (e.g.
microbial mat) differs in each zone.
There is a gradient with the
highest concentration of microbes in the Vestimentiferan (z1) zone and
a general decrease away from the vent smoker.
Conclusion
Juvenile gastropods occurred in all areas of vent influence but
rarely in the Periphery zone (z4). For Lepetodrilus spp. there was a
30
decrease in juvenile abundances between the Vestimentiferan (z1)
zone and Periphery (z4) zone, suggesting variable characteristics (e.g.
chemical or food availability) within the vent habitat enhance
settlement for this species in the Vestimentiferan (z1) zone. Significant
differences in abundance of adults and juveniles were found for
Lepetodrilus spp. and Clypeosectus!Gorgoleptis (more juveniles in z3
and more adults in z1 and z2) suggesting that post-settlement
processes (e.g. predation or migration) were superimposed on the
initial settlement response to vent habitat to create the adult
distribution patterns.
There was also a significant positive caging
effect found for Eulepetopsis vitrea suggesting that, especially in this
species, predation influenced adult distributions.
This study addressed post-settlement processes that have been
shown to affect distribution patterns.
The results raised additional
questions concerning pre-settlement processes. First, the observation
of low juvenile abundances in the Bivalve zone led to the question of
what impact the mussels have on larval settlement in that zone.
Secondly, this study demonstrated that settlement occurred in zones of
hydrothermal influence, raising the question of what are the cues for
larval settlement.
Finally, the actual mechanism(s) for how larvae
31
disperse remain unknown; specifically, are the larvae retained; do they
disperse then return to the same vent; or do they disperse to distant
vents?
In combination with research on these potential future
directions, the post-settlement questions addressed in this study are
important to increase our understanding of settlement at new vent
sites.
32
literature Cited
Benedetti-Cecchi, L. 2000. Predicting direct and indirect interactions
during succession in a mid-littoral rocky shore assemblage.
Ecological Monographs, 70(1), pp. 45-72.
Berg Jr., C. J. and C.L. Van Dover. 1987. Benthopelagic
macrozooplankton communities at and near deep-sea
hydrothermal vents in the eastern Pacific Ocean and the Gulf of
California. Deep-Sea Res. 34(3), pp. 379-401.
Boidron-Metairon, I. F. 1995. Larval nutrition. In Ecology of Marine
Invertebrate Larvae. Editor: L McEdward. CRC Press, pp.
223-248.
Bouchet, P. and A. Waren. 1994. Ontogenetic migration and dispersal
of deep-sea gastropod larvae. In Reproduction, larval biology
and recruitment of the deep-sea benthos. Editors: C. M. Young,
and K.J. Eckelbarger. Columbia University Press, pp. 98-117.
Connell, J.H .. 1961. The influence of interspecific competition and
other factors on the distribution of the barnacle Chthamalus
stellatus. Ecology 42(4), pp. 710-723.
Connell, J.H .. 1972. Community interactions on marine rocky intertidal
shores. Annual Reviews of Ecology and Systematics 3, pp. 169172.
Craddock, C., D. R A. Lutz, and R C. Vrijenhock. 1997. Patterns of
dispersal and larval development of archaeogastropod limpets
at hydrothermal vents in the eastern Pacific. J. Exp. Mar. Bioi.
Ecol., 210, pp. 37-51.
Cronin, T. W. and RB. Forward Jr.. 1982. Tidally timed behavior:
Effects on larval distributions in estuaries. In Estuarine
Comparisons. Editor: V. S. Kennedy. New York, Academic
Press, pp. 505-520.
33
Cronin, T. W. and R.B. Forward Jr.. 1986. Vertical migration cycles of
crab larvae and their role in dispersal. Bulletin of Marine
Science 39(2), pp. 192-201.
Edmonds, H.H., P.J. Michael, E.T. Baker, D.P. Connelly, J.E. Snow,
C.H. Langmuir, H.J.B. Dick, R. Muhe, C.R. German, and D.W.
Graham. 2003. Discovery of abundant hydrothermal venting on
the ultraslow-spreading Gakkel ridge in the Arctic Ocean.
Nature 421, pp. 252-256.
Fisher, C.R .. 1998. Temperature and sulphide tolerance of
hydrothermal vent fauna. Cah. Bioi. Mar., 39, pp. 283-286.
Fowler, C. M. R. and V. Tunnicliffe. 1997. Hydrothermal vent
communities and plate tectonics. Endeavour 21(4). pp. 164-168.
Fox, M .• S.K. Juniper, H. Vali. 2002. Chemoautotrophy as a possible
nutritional source in the hydrothermal vent limpet Lepetodrilus
fucensis. Cah. Bioi. Mar. 43, pp. 371-376.
Fuhrman, J.A.. T.D. Sleeter, C.A. Carlson, L.M. Proctor. 1989.
Dominance of bacterial biomass in the Sargasso Sea and its
ecological implications. Marine Ecology Progress Series 57,
pp. 207-217.
Grassle, J. F.. 1986. The ecology of deep-sea hydrothermal vent
communities. Advances in Marine Biology. Editors: J. H. S.
Blaxter and A. J. Southward. London, Academic Press, pp.
301-362.
Gustafson R.G. and R.A. Lutz. 1994. Molluscan life history traits at
deep-sea hydrothermal vents and cold methane/sulfide seeps.
In Reproduction, larval biology and recruitment of the deep-sea
benthos. Editors: C. M. Young, and KJ. Eckelbarger.
Columbia University Press, pp. 76-97.
34
Gutierrez, L.. 1998. Habitat selection by recruits establishes local
patterns of adult distribution in two species of damselfishes:
Stegastes dorsopunicans and S. planifrons. Oecologia 115,
pp. 268-277
Helfrich, K.R. and KG. Speer. 1995. Oceanic hydrothermal
circulation: mesoscale and basin-scale flow. In Seafloor
Hydrothermal Systems: Physical, Chemical, Biological, and
Geological Interactions. Editors: S.E. Humphris,
R. A. Zierenberg, L.S. Mullineaux, and R. E. Thompson.
Geophysical Monograph 91, pp. 347-356.
Hessler, R.R. and V.A. Kaharl. 1995. The deep-sea hydrothermal vent
community: An overview. In Seafloor Hydrothermal Systems:
Physical, Chemical, Biological, and Geological Interactions.
Editors: S.E. Humphris, R. A Zierenberg, LS. Mullineaux, and
R. E. Thompson. Geophysical Monograph 91, pp. 72-84.
Hessler, R. R. and W.M. Smithey, Jr.. 1983. The distribution and
community Structure of megafauna at the Galapagos Rift
hydrothermal vents. In Hydrothermal Processes at Seafloor
Spreading Centers. Editors: P.A. Rona, L. Laubier, and K.L.
Smith, Jr.. New York, Plenum Press, pp. 735-770.
Hessler, R. R., W.M. Smithey, MA Boudrias, C.H. Keller, RA Lutz,
and J.J. Childress. 1988. Temporal changes in megafauna at
the Rose Garden hydrothermal vent (Galapagos Rift; eastern
tropical Pacific). Deep-Sea Res. 35(10/11), pp. 1681-1709.
Hessler, R. R., W.M. Smithey and C.H. Keller. 1985. Spatial and
temporal variation of giant clams, tubeworms and mussels at
deep-sea hydrothermal vents. In Hydrothermal Vents of the
Eastern Pacific: an Overview. Editor: M.L Jones. Bull. Bioi.
Soc. Wash. 6 pp. 411-428.
Jaeckle, W.B. and D.T. Manahan. 1989a. Feeding by a "nonfeeding"
larva: uptake of dissolved amino acids from seawater by
lecithotrophic larvae of the gastropod Haliotis rufescens. Mar.
Bioi., 103, pp. 87-94.
35
Jaeckle, W.B. and D.T. Manahan. 1989b. Growth and energy balance
during development of a lecithotrophic molluscan larva (Ha/iotis
rufescens). Bioi. Bull., 177, pp. 237-246.
Johnson, KS., C. L Beehler, C.M. Sakamoto-Amold, and J.J.
Childress. 1986. In-situ measurements of chemical distribution
in a deep-sea hydrothermal vent field. Science, 231, pp. 11391141.
Johnson, KS., J.J. Childress, C.L. Beehler, and C.L. Sakamoto. 1994.
Biogeochemistry of hydrothermal vent mussel communities: the
deep-sea analogue to the intertidal zone. Deep-Sea Res. I,
41{7), pp. 993-1011.
Johnson, K.S., J.J. Childress, R.R. Hessler, C.M. Sakamoto-Arnold,
and C. L. Beehler. 1988. In-situ measurements of chemical
distribution in a deep-sea hydrothermal vent field. Deep-Sea
Res., 35(10/11), pp.1723-1744.
Kim, S.L.. 1996. Larval dispersal between hydrothermal vent habitats.
PhD. Dissertation, Woods Hole Oceanographic Institute.
118 pp ..
Kim, S.L., and L.S. Mullineaux. 1998. Distribution and near-bottom
transport oflarvae and other plankton at hydrothermal vents.
Deep-Sea Res. II, 45 (1-3), pp. 423-440.
Kim, S.L., L.S. Mullineaux and K.R. Helfrich. 1994. Larval dispersal
via entrainment into hydrothermal vent plumes. J. Geophys.
Res .• 99, pp. 12,655-12,665.
Koback, J .. 2001. Light, gravity, and conspecifics as cues to site
selection and attachment behaviour of juvenile and adult
Dreissena polymorpha Pallas, 1771. J. Moll. Stud., 67, pp.183189.
36
Lenihan, H.S., L.S. Mullineaux, S.W. Mills, C.R. Fisher, C.H. Peterson,
and F. Micheli. 2001. Species interactions in vent
communities: Evidence of larval settlement inhibition through
suspension-feeding. LARVE Results Symposium.
Lutz, R.A.. 1988. Dispersal of organisms at deep-sea hydrothermal
vents: A review. Oceano!. Acta. Special volume, pp. 23-29.
Lutz, R.A., H. Hidu, and K.G. Drobeck. 1970. Acute temperature
increase as a stimulus to settling in the American oyster,
Crassostrea virginica (Gmelin). Proc. Natl. Shell. Assoc., 60, pp.
68-71.
Lutz, R.A., D. Jablonski, D.C. Rhoads, and RD. Turner. 1980. Larval
dispersal of a deep-sea hydrothermal vent bivalve from the
Galapagos Rift. Mar. Bioi., 57, pp. 127-133.
Lutz, RA., D. Jablonski, and RD. Turner. 1984. Larval dispersal at
deep-sea hydrothermal vents. Science, 226, pp. 1451-1453.
Lupton, J.E.. 1995. Hydrothermal plumes: near and far field. In
Seafloor Hydrothermal Systems: Physical, Chemical, Biological,
and Geological Interactions. Editors: S.E. Humphris,
R. A. Zierenberg, L.S. Mullineaux, and R E. Thompson.
Geophysical Monograph 91, pp. 317-346.
Manahan D. L.. 1990. Adaptations by invertebrate larvae for nutrient
acquisition from seawater. Amer. Zool. 30, pp.147-160.
Marsh, A.G., L.S. Mullineaux, C.M. Young, D.T. Manahan. 2001.
Larval dispersal potential of the tubeworm Riftia pachypti/a at
deep-sea hydrothermal vents. Nature 411(6833), pp. 77-80.
Mclean, J.H .. 1988. New archaeogastropod limpets from hydrothermal
vents; Superfamily Lepetrodrilacea I. Systematic Descriptions.
Phil. Trans. R. Soc. Lond. B, 319, p 1-32.
37
Mclean, J.H .. 1989a. New archaeogastropod limpets from
hydrothermal vents; new family Peltospiridae, new superfamily
Peltospiracea. Zool. Scr., 18(1}, p 49-66.
Mclean, J.H .. 1989b. New slit-limpets (Scissurellacea and
Fissurellacea} from hydrothermal vents. Part 1. Systematic
descriptions and comparisons based on shell and radular
characters. Contributions in Science, 407, pp. 1-29.
Mclean, J.H .. 1990. Neolepetopsidae, a new docoglossate limpet
family from hydrothermal vents and its relevance to
patellogastropod evolution. J. Zool. Land., 222, p 485-528.
Menge, B.A., and G.M. Branch. 2001. Rocky intertidal communities.
In Marine Community Ecology. Editors: M.D. Bertness, S.D.
Gaines, and M.E. Hay. Sinwaer Associates, Inc., pp.221-251.
Micheli, F., C.H. Peterson, L.S. Mullineaux, C.R. Fisher, S.W. Mills,
G. Sancho, G.A. Johnson, and H.S. Lenihan. 2002. Predation
structures communities at deep-sea hydrothermal vents.
Ecological Monographs, 73(2}, pp.365-382.
Mullineaux, L.S .. 1994. Larval dispersal in mesoscale flows. In
Reproduction, larval biology and recruitment of the deep-sea
benthos. Editors: C. M. Young, and K.J. Eckelbarger.
Columbia University Press, pp. 201-222.
Mullineaux, L.S., C.R. Fisher, C.H. Peterson, and S.W. Schaeffer.
2000. Tubeworm succession at hydrothermal vents: use of
biogenic cues to reduce habitat selection error?. Oecologia
123, pp. 275-284.
Mullineaux, L.S., and S.C. France. 1995. Dispersal mechanisms of
deep-sea hydrothermal vent fauna. (In Seafloor Hydrothermal
Systems: Physical, Chemical, Biological, and Geological
Interactions. Editors: S.E. Humphris, R. A. Zierenberg, L.S.
Mullineaux, and R. E. Thompson) Geophysical Monograph 91,
pp. 408-424.
38
Mullineaux, L.S., S.L. Kim, A. Pooley, and R.A. Lutz. 1996.
Identification of archaeogastropod laNae from a hydrothermal
vent community. Mar. Bioi., 124, pp. 551-560.
Mullineaux, L.S., S.W. Mills, and E. Goldman. 1998. Recruitment
variation during a pilot colonization study of hydrothermal vents
(9°50' N, East Pacific Rise). Deep-Sea Res. II, 45(1-3) pp. 441-
464.
Mullineaux, L.S., C.H. Peterson, and C.R. Fisher. 1997. Community
Development and Structure at Hydrothermal Vents: Life After
Recruitment. Proposal
Mullineaux, L.S., C.H. Peterson, F. Micheli, S.W. Mills. In press.
Seasonal mechanism varies along in hydrothermal fluid flux at
deep-sea vents. Ecological Monographs,
Pace, M.L., S.E.G. Findlay, and D. Fischer. 1988. Effects of an
invasive bivalve on the zooplankton community of the Hudson
River. Freshwater Biology, 39(1) pp. 103-116.
Seyfried Jr., W.E. and M.J. Mottl. 1995. Geologic setting and chemistry
of deep-sea hydrothermal vents. In The Microbiology of Deep
Sea Hydrothermal Vents. Editors: D. M. Karl. New York, CRC
Press, pp. 1-34.
Shilling, F.M. and D.T. Manahan. 1994. Energy metabolism and
amino acid transport during early development of Antarctic and
temperate echinoderms. Bioi. Bull., 187, pp. 398-407.
Speer, K.G. and K.R. Helfrich. 1995. Hydrothermal plumes: a review of
flow and fluxes. /n: Hydrothermal Vents and Processes.
Editors: L.M. Parson, C.L. Walker, and D.R Dixon. London:
The Geological Society, pp. 373-385.
Strasser, M., M. Walensky, K. Reise. 1999. Juvenile-adult distribution
of the bivalve Mya arenaria on intertidal flats in the Wadden
Sea: why are there so few year classes? Helgol. Mar. Res., 53,
pp. 45-55.
39
Tivey, M.K.. Modeling chimney growth and associated fluid flow at
seafloor hydrothermal vent sites. In Seafloor Hydrothermal
Systems: Physical, Chemical, Biological, and Geological
Interactions. Editors: S.E. Humphris, R. A. Nierenberg,
LS. Mullineaux, and R. E. Thompson. Geophysical Monograph
91, pp. 158-177.
Tunnicliffe, V .. 1990. Observations on the effects of sampling on
hydrothermal vent habitat and fauna of axial seamount, Juan de
Fuca Ridge. J. Geophys. Res., 95{B8), pp. 12,961-12,966.
Van Dover, C.L.. 2000. Ecology of deep-sea hydrothermal vents.
New Jersey: Princeton University Press, 424 pp..
Van Dover, C.L, C.J. Berg and RD. Turner. 1988. Recruitment of
marine invertebrates to hard substrates at deep-sea
hydrothermal vents on the East Pacific Rise and Galapagos
spreading center. Deep-Sea Res., 35 {10111), pp. 1833-1849.
Van Dover, C.L. and Brian Fry. 1994. Microorganisms as food
resources at deep-sea hydrothermal vents. Limnol. Oceanogr.,
39(1 ), pp. 51-57.
Van Dover, C.L and R.R. Hessler. 1990. Spatial variation in faunal
composition of hydrothermal vent communities on the East
Pacific Rise and Galapagos Spreading Center. In: Gorda
Ridge: A Seafloor Spreading Center in the United States
Exclusive Economic Zone. Editor: G.R. McMurray. New York:
Springer-Verlag, pp. 253-264.
Vrijenhoek, R.C .. 1997. Gene flow and genetic diversity in naturally
fragmented metapopulations of deep-sea hydrothermal vent
animals. J. Heredity, 88, pp. 285-293.
Vrijenhoek, RC., T. Shank, and RA Lutz. 1998. Gene flow and
dispersal in deep-sea hydrothermal vent animals. Cah. Bioi.
Mar., 39, pp. 363-366.
40
Won, Y., C.R. Young, RA Lutz, R.C. Vrijenhoek. 2003. Dispersal
barriers and isolation among deep-sea mussel populations
(Mytilidae: Bathymodiolus} form eastern Pacific hydrothermal
vents. Molecular Ecology, 12, pp. 169-184.
Waren, A. and P. Bouchet. 1989. New gastropods from East Pacific
hydrothermal vents. Zool. Scr., 18(1}, pp. 67-102.
Waren, A. and P. Bouchet. 1993. New records, species, genera, and
a new family of gastropods from hydrothermal vents and
hydrocarbon seeps. Zool. Scr., 22(1}, pp. 1-90.
41
Table 1. Generalized descriptions of hydrothermal vent zones at East Pacific Rise. ** Zone is not
sampled in this study due to difficulty in performing experiments here.
Zone#
Zone
Temp°C
Sulfide J.tm
-250
0**
Oxygen !J.m
Dominant Organisms
0
Alvinellid polychaetes
1
Vestimentiferan
Up to 30
Up to 330
>25-0
Riftia pachyptila
2
Bivalve
2.3-7
27- 150
75-25
Mussels and clams
3
Suspension
2-2.3
0-27
110- 75
Serpulid worms
4
Periphery
2
0
-110
Deep-sea fauna
42
Table 2. Identified juvenile hydrothermal vent gastropod species (in order of abundance) which
settled from November 1994 to Apri11995 at East Wall vent site. The numbers are the Individuals of
each species in each zone and deployment type.
Species
Zones
Vestimeniferan
Bivalve
Suspension
Caged
Uncaged
Caged
Uncaged
Caged
Uncaged
264
5
78
1
1
Melanodrymia sp.
1
Cyathermia natacoides
1
250
623
4
2
1
36
59
Eulepetopsis vitrea
533
48
3
Lepetodrilus spp.
Clypeosectus!Gorgoleptis
3
Unidentified
Caged
Uncaged
1
1
1
Peltospira sp.
Rhynchopelta concentrica
Periphery
1
415
12
11
43
51
9
Table 3. Statistical results of ANOVA for comparison between zones (Vestimeniferan, Bivalve,
Suspension, and Periphery) and for treatment effects (caged vs. uncaged) of the juveniles. The
symbol • denotes significance at the 0.05 level.
Species
Lepetodri/us spp.
Effect
Zone
Treatment
Zone*Treatment
Error
ss
df
MS
F
p
354.533
0.708
112.533
456.458
3
1
3
15
118.178
0.708
37.511
30.431
3.884
0.023
1.233
0.031+
0.881
0.333
C/ypeosectus!Gorgoleptis
Zone
Treatment
Zone*T reatment
Error
192.018
20.745
20.965
366.000
3
1
3
15
64.006
20.745
6.988
24.400
2.623
0.850
0.286
0.089
0.371
0.834
Eu/epetopsis vitrea
Zone
Treatment
Zone*Treatment
Error
103.695
164.414
121.748
259.292
3
1
3
15
34.565
164.414
40.583
17.286
2.000
9.511
2.348
0.157
44
o.oos•
0.114
Table 4. Statistical results of a priori ANOVA for comparison between zones of the juveniles.
V=Vestimeniferan; B=Bivalve; S=Suspension; P=Perlphery. The symbol+ denotes significance at the
O.OSievel.
Species
Lepetodrilus spp.
Zone Effect
Vvs. B
Vvs.S
Vvs. P
Error
ss
df
MS
63.375
102.083
352.083
456.458
1
1
1
15
63.375
102.083
352.083
30.431
45
F
2.083
3.355
11.570
p
0.170
0.087
0.004+
Zonation of resident fauna
Vestimen!iferan
Bivalve
Suspension-feeder
Periphery
Figure 1. Generalized diagram of zonation pattern at an East Pacific Rise black smoker vent site.
(Modified from Mullineaux at al. in press)
46
Biovent
East Wall
Worm Hole
9°48' +---------- ' - - - - - - - . . , - - - - - - !
104°18'36" 104°17'24"
104°16'12"
Figure 2. East Wall vent site at 9°50'N East Pacific Rise between the Clipperton (C) and Sequieros
(S) fracture zones (from Mullineaux et al., 2000). Arrow denotes study site.
47
in
;(yt.>ec•sectu's delectus D) Gorgoleptis sp..
49
Figure 5.
B) Me,lar.lod'rvtnia sp. C) Peltospira sp. D) Rhynchopelta concentrica.
50
11!11
Juvenile D Adult
200
100
~i
0
v
s
B
p
Zone
figure 6. Distribution of adult and juvenile Lepetodrilus spp. across zones. V=Vestlmeniferan;
B=Bivaive; S=Suspension; P=Peripheii'Y. !Error bars indicate standard errol'S.
51
22 5 - --
~-~---
-
~ --~-----------
Juvenile D Adult
150 -,
0
v
s
B
p
Zone
Figure 7. Distribution of adult and juvenile Clypeosectus delectus and Gorgoleptis sp. across zones.
V=Vestimeniferan; IB=Bivaive; S=Suspension; P=Periphery. Error b;:us indicate standard errors.
52
1.5
llftl Juvenile o Adult
0.0
v
s
8
p
Zone
Figure 8. Distribution of adult and juvenile Eulepetopsis vitrea across zones. V=Vestimeniferan;
B=Bivalve; S=Suspension; P=Periphery. Error bars indicate standard errors.
53