Predators mediate above- vs. belowground herbivory in
a salt marsh crab
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204 USA
Citation: Vu, H. D., and S. C. Pennings. 2018. Predators mediate above- vs. belowground herbivory in a salt marsh crab.
Ecosphere 9(2):e02107. 10.1002/ecs2.2107
Predators can signiﬁcantly affect prey by removing prey individuals and by changing prey
behavior. The tradeoff between foraging behavior and predation risk may result in a trophic cascade that
can have important effects on ecosystem processes. For herbivores that can feed both above- and below-
ground, it is likely that predation risk affects the location of feeding. We tested whether two species of
predatory marsh crabs affected feeding behavior of the herbivorous crab, Sesarma reticulatum. We found
that predatory crabs could kill or injure Sesarma and that Sesarma did less damage to its food plant Spartina
alterniﬂora in the presence of the more dangerous predator. Sesarma prefers to feed on and grows better on
belowground rhizomes than aboveground leaves; however, the costs of digging burrows to access rhi-
zomes lead to higher mortality if it is the only diet option. The location of feeding did not affect total bio-
mass of S. alterniﬂora. For Sesarma, a choice in feeding location allows the crabs the behavioral ﬂexibility to
balance the risks of predation, the nutritional beneﬁt of feeding belowground, and the survival costs of
belowground feeding. Similar tradeoffs are likely to increase the success of other herbivores that can feed
both above- and belowground.
Key words: aboveground herbivory; belowground herbivory; crab herbivory; Eurytium; non-consumptive effects;
Panopeus; predator–prey interactions; Sesarma; Spartina.
Received 19 December 2017; accepted 26 December 2017. Corresponding Editor: Hunter S. Lenihan.
Copyright: © 2018 Vu and Pennings. This is an open access article under the terms of the Creative Commons Attribution
License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Predators can affect prey directly by killing
them or indirectly by altering prey behavior.
Direct consumption of prey can strongly affect
prey densities in marine (Estes et al. 1998) estuar-
ine (Altieri et al. 2012) and terrestrial (Ripple
et al. 2014) environments. However, there is
growing evidence that indirect effects of preda-
tors can have equal effects on the structure and
function of ecosystems even when prey densities
do not change (Preisser et al. 2005, Heithaus
et al. 2007, Davidson et al. 2014).
Indirect effects of predators are important
because prey are under considerable pressure to
detect and avoid predators. The fear of predators
can alter the prey’s behavior and feeding patterns,
with consequent effects on the prey’sresources
(Ripple et al. 2001, Rizzari et al. 2014). In the case
of herbivores, predation risks can alter foraging
behavior, thereby affecting plant diversity, produc-
tivity, nutrient exchange, and trophic energy trans-
fer (Godin 1990, Schmitz et al. 2008, Grifﬁnetal.
2011). For example, increased predation pressure
from large predators in Yellowstone National Park
altered the locations where elk grazed, leading to
changes in aspen sapling survival rate (Fortin et al.
2005, Beschta and Ripple 2010).
Herbivores that feed both above- and below-
ground might alter where they feed in response
to predators. For example, pocket gophers can
feed on leaves or roots, but are exposed to preda-
tors when feeding aboveground (Douglas 1969,
Feldhamer et al. 2003). Seasonal variation in