Oceanography | Vol. 38, No. 2
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only possible direction of transport is westward via the TPD
(Figure 1). Thus, driftwood in Rijpfjorden will more than likely
originate east of Svalbard.
The Rijpfjorden log was heavily colonized with living spec
imens of different sizes of the wood-boring mollusk Xyloredo
nooi (Figure 1). Rijpfjorden is a north-facing fjord that has an
annual extended ice cover consistently dominated by Arctic
water masses (Berge et al., 2009). The bottom temperature in
the region remains at –1.8°C throughout the year (Cottier et al.,
2021, 2022). The second record of X. nooi was documented in
the wood recovered from Smeerenburgfjord (Figure 1).
The two Svalbard fjords represent very contrasting oceano
graphic environments. While the north-facing Rijpfjorden is
characterized by Arctic water masses, Smeerenburg, like other
west-facing fjords on the main island of Spitsbergen, is strongly
influenced by warm Atlantic water (Berge et al., 2005). Although
there are no direct measurements of bottom temperatures in
Smeerenburg, continuous measurements in Kongsfjorden,
another open fjord strongly affected by Atlantic water masses
just south of Smeerenburg, exhibited bottom temperatures rang
ing between 1.5° and 3.0°C in late June 2009 (Cottier et al., 2021,
2022). As a consequence, the fauna in the two fjords are very dis
similar, as seen, for example, in the fish fauna (Nahrgang et al.,
2014; Jordà-Molina et al., 2023). Unlike in Rijpfjorden, only frag
ments of a log were collected in Smeerenburg, and no living spec
imens (just empty shells) were found. And unlike Rijpfjorden,
Smeerenburg rarely freezes over, as it is strongly influenced by
Atlantic water flowing northward through the Fram Strait, enter
ing the Arctic northwest of Svalbard (Ingvaldsen et al., 2024).
Driftwood and Wood-Boring Organisms
There are two families of bivalves (Teredinidae and Xylo
phagaidae) that are able to settle on and digest wood or other
vegetation in the marine environment. As larval stages of species
belonging to these groups undergo metamorphosis, they begin
to bore into and eat the wood in which they settle (Voight, 2015).
Through a molecular phylogenetic study, Distel et al. (2011)
found the two to be a monophyletic taxon. Many species belong
ing to the Xylophagaidae are poorly known, and many inhabit the
deep sea. Hence, based on their common ancestry, information
and status about their biology are in many cases only assumed or
deducted, rather than based on detailed biological studies.
The bivalves of the Xylophagaidae occur from a few meters
below low tide to more than 7,000 m depth (Turner 1972, 2002),
boring into wood sunken to the seafloor using toothed ridges
on their anterior shells and ingesting wood fragments (Purchon,
1941). They are considered the sole wood borers at depths
greater than 200 m (Turner, 1972). A wood fall represents a mas
sive energy input and can be compared to a whale fall on the
seafloor (Ristova, et al., 2017; McClain et al., 2025). However,
the energy in the wood is trapped in cellulose that most organ
isms are incapable of digesting. To access this energy, bottom
dwellers are dependent on organisms such as X. nooi to digest
the cellulose. In addition, wood-boring mollusks may also con
tain symbiont bacteria that enable fixation of nitrogen as well as
cellulose digestion (Goodell et al., 2024). By sustaining the wood
fall communities, wood-boring mollusks in the deep sea fill a
role comparable to grazers in the euphotic zone (Turner, 2002;
O’Connor et al., 2014; Voight, 2015).
In the Northeast Atlantic, Xyloredo is represented by X. nooi
known from deep, cold waters and from deep fjord areas
(Turner, 1972; Voight, 2022). A separate undescribed species
was found in widespread localities in the Bay of Biscay and at the
Haakon Mosby Mud Volcano in the northern Norwegian Sea
(Romano et al., 2020). There is no direct evidence confirming
that Xyloredo species specifically release gametes into the water
column for external fertilization. Most research on shipworms
in general (family Teredinidae) suggests that external fertiliza
tion is a common reproductive strategy, but this has not been
explicitly confirmed for Xyloredo. Given the diversity of repro
ductive strategies among shipworms, such as brooding larvae
internally in some species, it is possible that Xyloredo exhibits
unique or unstudied reproductive adaptations. Further research
is needed to clarify the reproductive biology of Xyloredo, includ
ing the mechanisms of gamete release and fertilization.
Because the size and maturity of the specimens found inside
the Rijpfjorden log were distinctly heterogeneous, the demo
graphic structure of the bivalves indicates either local recruit
ment and reproduction or multiple recruitment events inside
the fjord. One end of the log carried clear indications of hav
ing been buried in anoxic sediments, also suggesting that the log
had been partially submerged in Rijpfjorden for several years.
This, and the fact that several juvenile specimens of X. nooi were
found inside the log, strongly suggest local recruitment and/
or reproduction. Although we cannot rule out the possibility
of multiple recruitment events while the log was moving, this
cannot explain the presence of juvenile specimens inside the
log after several years in Rijpfjorden. As the reproductive biol
ogy of Xyloredo species remains uncertain, it is not possible to
unequivocally assess how recruitment might have occurred
in Rijpfjorden. Importantly, however, both possible events (or
a combination of the two) challenge our status of knowledge
regarding the Arctic marine benthic fauna.
Transpolar Drift
For a Siberian larch that grew in the Yenisei region until the
beginning of the last century to end up in a fjord on Svalbard
(Figure 1), the only mode of transport is by the TPD (Häggblom,
1982). In 1884, the Norwegian researcher and explorer Fridtjof
Nansen came across newspaper reports that fragments of the
hull of the steam bark Jeannette had been found on the east
coast of Greenland. He knew that this ship had been frozen
into the sea ice and wrecked off the New Siberian Islands three
years earlier, during an attempt by the US Arctic Expedition