Biology Reference
In-Depth Information
grow and thus provide a long-lasting food source for herbivorous passengers. The
floating thalli of, e.g.,
M. pyrifera
even continue to reproduce while afloat, thereby
acting as successful spore carriers, dispersing over hundreds of kilometers (Macaya
et al.
2005
; Hern
´
ndez-Carmona et al.
2006
). Thus, floating rafts facilitate population
connectivity and expansion of geographic ranges of the floating algae themselves and
of associated organisms. Winds and ocean currents mainly determine the floating
directions, velocities, and distances that algae can cover.
17.5.1 Floating Velocities and Trajectories
Driven by the major oceanic currents, floating algae are transported across the
world's oceans. While ocean currents determine large-scale algal movements,
strong winds largely influence algal dispersal on a regional scale. Overall both
forces in combination determine algal trajectories and velocities (Thiel and Gutow
2005a
and references therein).
Following patches of
M. pyrifera
, Harrold and Lisin (
1989
) showed that rafts
within Monterey Bay (California) occasionally move very slowly and at other times
can advance very fast (0.2-2.3 km h
1
). Within the southern California Bight a
similar trend was observed by Hobday (
2000b
) for satellite-tracked drifters. Very
high velocities of up to 0.8 km h
1
have also been reported for algae floating in
southern Japan (Segawa et al.
1962
; Yoshida
1963
), which are probably related to
the prevailing current velocities (Thiel and Gutow
2005a
).
Trajectories of floating algae and their associated organisms closely follow the
directions of the major current systems (Thiel and Gutow
2005a
). For instance,
Helmuth et al. (
1994
), who sampled
M. pyrifera
rafts, underlined the importance of
the West Wind Drift in the Southern Ocean in transporting algae in eastward
direction between South America and sub-Antarctic islands (see also Chap.
14
by
Huovinen and G´mez). A similar route in the West Wind Drift had been reported
for
D. antarctica
(Smith
2002
). Along the Chilean Pacific coast, within the
Humboldt Current, floating seaweeds are generally displaced towards the north
(Macaya et al.
2005
) but southward movements are also observed occasionally. In
the N Pacific, Hobday (
2000b
) underlined that floating
M. pyrifera
are transported
in southward direction within the Californian Current. These observations confirm
that algal rafts together with their passengers are transported with the main oceanic
currents, both across vast areas of open ocean and over extensive distances in
alongshore direction.
17.5.2 Connectivity of Populations
There is increasing evidence from molecular studies confirming population con-
nectivity of floating seaweeds and their associated fauna (e.g., Thiel and Haye
2006
