Oceanography | Vol. 38, No. 2
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corrosive fluids is used to monitor, in real time, the soundscape
at the site for extended periods of time. For example, PAM was
applied successfully to the detection and classification of explo
sive events at volcanically active sites (Chadwick et al., 2008).
Different features of the sounds produced by venting are
related to the physical mechanisms producing the sounds.
These, in turn, are influenced by physical parameters such as
flow rate, chimney height, sound speed, and cavity size (Little
et al., 1990; Crone et al., 2006; Smith and Barclay, 2023). Studies
aimed at establishing the connection between these parameters
and the sounds produced can, in principle, enable the contin
uous, remote, long-term monitoring and investigation of flow
rates, growth, and other aspects of the vents via PAM.
To explore the potential of PAM, ONC deployed a hydro
phone at MEF in 2018, and then upgraded the installation to a
four-element array in 2023. Additionally, Dalhousie University’s
Deep Acoustic Lander (Figure 4) was deployed and recovered
in 2021 and 2023, further augmenting the time series (Smith
and Barclay, 2023). Though still in its infancy, this study has
already detected a large number of transient (i.e., of duration
measurable in seconds or less), often impulsive, sounds char
acterizing the soundscape at MEF. These include chimney col
lapses, waterborne signals associated with earthquakes, and a
number of other sounds whose origins are being investigated.
A recent study reports that numerous such signals were cap
tured by ONC’s hydrophones during the major seismic event of
March 5–6, 2024. Through the investigation of power spectral
density, ambient-noise coherence, and cross-correlation with
other sensors at MEF, the same study highlighted other, longer-
term changes in the MEF soundscape that may be associated
with changes to the venting activity resulting from the increased
seismicity in the region (Smith and Barclay, 2024).
Finally, PAM is also being explored as a tool for environmen
tal impact assessment. Some marine organisms may use acoustic
cues to select settlement locations around hydrothermal vents
(Eggleston et al., 2016). Industrial activities, such as shipping
and deep-sea mining, can potentially interfere with the local eco
system by introducing changes in the soundscape, even though
they may be located at significant distances (Chen et al., 2021).
Understanding of the local soundscape relevant to the biological
activity of a site is an important component of an effective envi
ronmental impact mitigation strategy (Lin et al., 2019).
VENT BIOLOGY
Numerous biological studies utilizing video imagery and sam
ples collected from ROVs and submersibles have been con
ducted at Endeavour. They focused on describing the benthic
assemblages inhabiting a range of hydrothermal vent condi
tions, from those on high-temperature black smoker chimneys
to those sustained by broadly spread diffusive flows (Sarrazin
et al., 1997; Tunnicliffe et al., 1997; Lelièvre et al., 2018; Murdock
et al., 2021). The early studies of hydrothermal vent systems
described a specialized fauna characterized by low species diver
sity, high biomass, and high levels of endemicity (i.e., species
only occurring at vent environments; Tunnicliffe and Fowler,
1996; reviewed in Van Dover, 2000).
A key characteristic of typical vent fauna is successful asso
ciations between chemoautotrophic, symbiotic microorganisms
and their macroinvertebrate hosts (Lonsdale, 1977; Corliss et al.,
1979). Utilizing the chemical energy from sulfur, hydrogen,
iron, and methane, vent microorganisms fix carbon not only in
symbiont associations with host species but also as free-living
cells or in extensive bacterial mats (Dick, 2019). Host-symbiont
associations often achieve high densities and biomass surround
ing the areas of hydrothermal fluid flow. At the Endeavour
vents, the most conspicuous and abundant vent fauna assem
blages are comprised of the siboglinid polychaete tubeworm
Ridgeia piscesae, alvinelid polychaetes Paralvinella sulfincola
(sulfide worm) and Paralvinella palmiiformis (palm worm), the
limpet Lepetodrilus fucensis, and many other species of snails
(Figure 5a-d, Sarrazin et al., 1997). Studies to date have inven
toried close to 60 vent-associated species at Endeavour, with
12 endemic species not occurring anywhere else in the world
(Fisheries and Oceans Canada, 2010). Sampling of macrofauna
associated with tubeworm bushes near the Grotto edifice alone
revealed up to 31 species occurring in substrate patches of less
than 0.1 m2, and it highlighted the importance of keystone
species such as R. piscesae in creating habitat complexity that
enhances local biodiversity (Lelièvre et al., 2018).
The roles of microbial diversity and production in con
trolling large-scale nutrient elemental cycling and ecosystem
function have also been topics of studies based on the frequent
sampling at Endeavour. Samples of diffusive sulfidic vent fluids
helped to quantify microbial production pathways (denitrifica
tion, anammox, and dissimilatory nitrate reduction to ammo
nium), aiding global estimates of nitrogen (N) removal rates
to the subsurface biosphere that represent 2.5%–3.5% of total
marine N loss (Bourbonnais et al., 2012). Microbes were also
the focus of a number of studies examining vent fauna host-
symbiont relationships and population structure. The tubeworm
Ridgeia piscesae, a keystone species, was found to have the same
phylotype Gammaproteobacteria symbiont (Ca. Endorifitia
persephone) as six other tubeworm species in the Eastern Pacific,
revealing high levels of interconnectivity between the Northeast
Pacific and the East Pacific Rise vents (Perez and Juniper, 2016).
However, the same authors later uncovered multiple genotypes
within E. persephone making up the symbiont assemblages
of R. piscesae and argued that this genetic diversity could be
an important predictor of resilience to environmental change
(Perez and Juniper, 2017).
Since the installation of seafloor cables and platforms in the
axial valley of the Endeavour Segment in 2010, in situ instru
ments and sensors, including time-lapse video imagery, have
been providing new insights into the environmental controls