10.5061/DRYAD.V6WWPZGQX
Lamb, Robert
0000-0001-8652-9906
Brown University
Smith, Franz
Brown University
Witman, Jon
Brown University
Consumer mobility predicts impacts of herbivory across a wave stress gradient
Dryad
dataset
2020
2019-10-02T00:00:00Z
2019-10-02T00:00:00Z
en
3379445 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Environmental stress impedes predation and herbivory by limiting the
ability of animals to search for and consume prey. We tested the
contingency of this relationship on consumer traits, and specifically
hypothesized that herbivore mobility relative to the return time of
limiting environmental stress would predict consumer effects. We examined
how wave-induced water motion affects marine communities via herbivory by
highly mobile (fish) versus slow moving (pencil urchin) consumers at two
wave-sheltered and two wave-exposed rocky subtidal locations in the
Galapagos Islands. The exposed locations experienced 99th percentile flow
speeds that were 2-5 times greater than sheltered locations, with mean
flow speeds >33 cm/s vs <16 cm/s, 2-7 times higher standing
macroalgal cover and 2-3 times lower cover of crustose coralline algae
than the sheltered locations. As predicted by the Environmental Stress
Hypothesis (ESH), there was a negative relationship between mean flow
speed and urchin abundance and herbivory rates on Ulva spp. algal feeding
assays. In contrast, the biomass of surgeonfishes (Acanthuridae) and
parrotfishes (Labridae- Scarinae) was positively correlated with mean flow
speed. Ulva assays were consumed at equal rates by fish at exposed and
sheltered locations, indicating continued herbivory even when flow speeds
surpassed maximum reported swimming speeds at a rate of 1-2 times per
minute. Modeled variation in fish species richness revealed minimal
effects of diversity on herbivory rates at flow speeds <40 cm/s,
when all species were capable of foraging, and above 120 cm/s, when no
species could forage, while increasing diversity maximized herbivory rates
at flow speeds of 40 – 120 cm/s. Two-month herbivore exclusion experiments
during warm and cool seasons revealed that macroalgal biomass was
positively correlated with flow speed. Fish limited macroalgal development
by 65-91% at one exposed location but not the second, and by 70% at the
two sheltered locations. In contrast, pencil urchins did not affect algal
communities at either exposed location, but reduced macroalgae by 87%
relative to controls at both sheltered locations. We propose an extension
of the ESH that is contingent upon mobility to explain species-specific
changes in feeding rates and consumer effects on benthic communities
across environmental gradients.