Towards A More Balanced View of Marine Ecosystems
C.H. Greene and R. Ji
Ocean Resources and Ecosystems Program, Cornell University, Ithaca, NY 14853 USA
Summary: Frank et al. (2011) hypothesize that the Scotian Shelf ecosystem’s
dynamics are governed by top-down forcing, predator-prey role reversals, and a
trophic cascade extending from demersal predatory fish, especially cod, down to the
level of nutrients (Frank et al., 2005; 2011). Greene and Pershing (2007) called into
question the underlying assumption of an extended trophic cascade. They argued that
while top-down forcing can be important at higher trophic levels in many Northwest
Atlantic Shelf ecosystems, its impacts on zooplankton, phytoplankton, and nutrients
are minor or nonexistent. Instead, they argued that lower trophic-level dynamics in
these ecosystems are governed by climate-associated, bottom-up forcing. Observations
over the past three decades (Greene et al., 2008; MERCINA, 2012) are consistent with
predictions from the climate-forcing hypothesis proposed by Greene and Pershing
(2007), while those from the past decade (MERCINA, 2012) demonstrate that the
trophic cascade hypothesis as proposed by Frank et al. (2005) should be rejected. A
closer examination of these observations also calls into question Frank and colleagues
more recent hypothesis of ecosystem recovery in the Northwest Atlantic being
governed by the oscillatory, runaway consumption dynamics of the forage fish
complex (Frank et al. 2011). Recent modeling efforts by Ji and colleagues are
attempting to tease out the elements of top-down and bottom-up control in Northwest
Atlantic Shelf ecosystems. The modeling result suggests that, for certain copepod
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species (e.g. Pseudocalanus spp. and Centropages typicus), besides bottom-up, topdown control by their predators plays a significant role. This result supports a
balanced view of processes controlling zooplankton population dynamics.
References
Frank, K.T., Petrie, B., Fisher, J.A.D., and Leggett, W.C. (2011) Transient dynamics of an
altered large marine ecosystem. Nature 477: 86-89.
Frank, K.T., Petrie, B., Choi, J.S., and Leggett, W.C. (2005) Trophic cascades in a formerly
cod-dominated ecosystem. Science 308: 1621-1623.
Greene, C.H., and Pershing, A.J. (2007) Climate drives sea change, Science 315: 10841085.
Greene, C.H., Pershing, A.J., Cronin, T.M., and Cecci, N. (2008) Arctic climate change
and its impacts on the ecology of the North Atlantic. Ecology 89(11) Supplement 2008:
S24-S38.
MERCINA. (2012) Recent Arctic climate change and its remote forcing of Northwest
Atlantic shelf ecosystems. Oceanography 25(3): 208-213.
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