Supplement 1. Summary of terrestrial studies demonstrating tritrophic interactions that were incl... more Supplement 1. Summary of terrestrial studies demonstrating tritrophic interactions that were included in our survey. Studies are arranged alphabetically by the last name of the lead author
Journal of Experimental Marine Biology and Ecology, 2013
Although geographic variation in algal-herbivore interactions should be common, our appreciation ... more Although geographic variation in algal-herbivore interactions should be common, our appreciation of such variation remains incomplete. For example, feeding choice assays examining variation in palatability of algae typically compare multiple algal species or genera from a single location or a single alga from multiple locations. Unfortunately, most studies have not compared the interaction of herbivores with multiple algae from multiple locations, thus tests of variation of relative palatability are lacking. To examine spatial variation in algal palatability we determined the feeding preferences of the periwinkle snail Littorina littorea when offered multiple algal genera at the same time from two regions in choice assays. Multi-choice experiments were repeated throughout the year to examine temporal variation in feeding preferences. Consistent with previous studies, L. littorea preferred to feed on ephemeral algae compared to perennial species. Importantly, the relative palatability of the two ephemeral genera, Ulva and Porphyra, varied greatly between regions and seasons. Under certain conditions, Ulva only represented 24% of consumed algal wet mass in choice assays, while under other conditions, Ulva was eaten almost exclusively. Preferences for Ulva or Porphyra were unrelated to differences in morphology. Variation in the relative palatability of algae could influence consumer behavior leading to shifts in algal communities across broad geographic scales.
Communities are influenced by multiple stressors that can interact in surprising ways, yet trampl... more Communities are influenced by multiple stressors that can interact in surprising ways, yet trampling studies typically ignore other sources of disturbance. While there is some evidence that disturbed communities may resist trampling because of species shifts, we lack an understanding of how previous disturbance interacts with trampling in monospecific stands. Furthermore, recent studies emphasized experimental trampling additions with assumed ecological realism. We monitored barnacle cover in unmanipulated and experimentally disturbed plots at 2 sites separated by only 300 m and with disparate levels of human visitation. During the summer, barnacle cover increased by 6 and 15% at the less-visited site but decreased by 5 and 4% at the heavily visited site (unmanipulated and disturbed plots, respectively). Interestingly, the influence of site on barnacle cover was greater in disturbed than in unmanipulated plots. New recruits represented a greater proportion of the barnacles at the heavily visited site. Neither plot slope nor predator abundance differed between these sites. To isolate the influence of trampling on barnacles, we monitored barnacle cover in caged, human exclusion plots and in uncaged controls at both sites. Summer barnacle cover increased in all treatments except in uncaged plots at the heavily visited site. During 9 paired surveys coinciding with the exclusion experiment, as many as 70 humans (km -1 shoreline h -1 ) entered the intertidal zone of the heavily visited site but no one did so at the less-visited site. Given that (1) visitation was the dominant factor explaining differences in barnacle cover between the 2 sites, and (2) caging enhanced barnacle cover only at the heavily visited site, we conclude that previous disturbance mediated the effects of human trampling on barnacle populations, with more disturbed plots displaying greater trampling vulnerability.
Interactions between grazers and autotrophs are complex, including both top-down consumptive and ... more Interactions between grazers and autotrophs are complex, including both top-down consumptive and bottom-up facilitative effects of grazers. Thus, in addition to consuming autotrophs, herbivores can also enhance autotroph biomass by recycling limiting nutrients, thereby increasing nutrient availability. Here, we evaluated these consumptive and facilitative interactions between snails (Littorina littorea) and seaweeds (Fucus vesiculosus and Ulva lactuca) on a rocky shore. We partitioned herbivores' total effects on seaweeds into their consumptive and facilitative effects and evaluated how community context (the presence of another seaweed species) modified the effects of Littorina on a focal seaweed species. Ulva, the more palatable species, enhanced the facilitative effects of Littorina on Fucus. Ulva did not modify the consumptive effect of Littorina on Fucus. Taken together, the consumptive and facilitative effects of snails on Fucus in the presence of Ulva balanced each other,...
Communities are influenced by multiple stressors that can interact in surprising ways, yet trampl... more Communities are influenced by multiple stressors that can interact in surprising ways, yet trampling studies typically ignore other sources of disturbance. While there is some evidence that disturbed communities may resist trampling because of species shifts, we lack an understanding of how previous disturbance interacts with trampling in monospecific stands. Furthermore, recent studies emphasized experimental trampling additions with assumed ecological realism. We monitored barnacle cover in unmanipulated and experimentally disturbed plots at 2 sites separated by only 300 m and with disparate levels of human visitation. During the summer, barnacle cover increased by 6 and 15% at the less-visited site but decreased by 5 and 4% at the heavily visited site (unmanipulated and disturbed plots, respectively). Interestingly, the influence of site on barnacle cover was greater in disturbed than in unmanipulated plots. New recruits represented a greater proportion of the barnacles at the heavily visited site. Neither plot slope nor predator abundance differed between these sites. To isolate the influence of trampling on barnacles, we monitored barnacle cover in caged, human exclusion plots and in uncaged controls at both sites. Summer barnacle cover increased in all treatments except in uncaged plots at the heavily visited site. During 9 paired surveys coinciding with the exclusion experiment, as many as 70 humans (km −1 shoreline h −1 ) entered the intertidal zone of the heavily visited site but no one did so at the less-visited site. Given that (1) visitation was the dominant factor explaining differences in barnacle cover between the 2 sites, and (2) caging enhanced barnacle cover only at the heavily visited site, we conclude that previous disturbance mediated the effects of human trampling on barnacle populations, with more disturbed plots displaying greater trampling vulnerability.
Terrestrial insect predators and parasitoids commonly use volatile plant compounds released durin... more Terrestrial insect predators and parasitoids commonly use volatile plant compounds released during grazing to find living herbivorous prey (i.e. tritrophic signaling). Because few studies have tested for tritrophic signaling in marine organisms, it is unclear if marine predators commonly use these fluid-borne cues to find living herbivore prey, especially under realistic settings. Such interactions might occur in the ocean because marine predators often use chemosensory-based foraging, and herbivore-induced production of defensive chemistry is common in some algal taxa. To examine the ability of predators to find live herbivores using waterborne chemical cues from grazed algae, we tested the responses of marine predators to several baits using in situ trapping and video experiments. We tested the attractiveness of chemical cues released by (1) Macrocystis pyrifera and Ulva sp. actively grazed by herbivores for short-or longterm periods, (2) crushed herbivores, (3) positive controls containing fish carrion, or (4) negative controls. Most predators trapped and filmed were spiny lobsters Panulirus interruptus. Under realistic field conditions, chemical cues from actively grazed algae with live herbivores failed to attract predators, but chemical cues from crushed herbivores and fish carrion were highly attractive. Thus, while marine predators like lobsters may utilize fluid-borne chemical cues to find dead or injured prey, such cues appear less important for finding live herbivore prey. Our literature review of 142 terrestrial studies revealed that tritrophic cues were unrelated to diet breadth of predators or herbivores and that most examples of terrestrial tritrophic signaling contained parasitoid predators. We additionally found that similar field studies in natural, non-agricultural settings such as ours are lacking even in better-studied terrestrial food webs, where they represent only 3% of manipulative experiments.
Interactions between grazers and autotrophs are complex, including both top-down consumptive and ... more Interactions between grazers and autotrophs are complex, including both top-down consumptive and bottom-up facilitative effects of grazers. Thus, in addition to consuming autotrophs, herbivores can also enhance autotroph biomass by recycling limiting nutrients, thereby increasing nutrient availability. Here, we evaluated these consumptive and facilitative interactions between snails (Littorina littorea) and seaweeds (Fucus vesiculosus and Ulva lactuca) on a rocky shore. We partitioned herbivores' total effects on seaweeds into their consumptive and facilitative effects and evaluated how community context (the presence of another seaweed species) modified the effects of Littorina on a focal seaweed species. Ulva, the more palatable species, enhanced the facilitative effects of Littorina on Fucus. Ulva did not modify the consumptive effect of Littorina on Fucus. Taken together, the consumptive and facilitative effects of snails on Fucus in the presence of Ulva balanced each other, resulting in no net effect of Littorina on Fucus. In contrast, the only effect of Fucus on Ulva was to enhance consumptive effects of Littorina on Ulva. Our results highlight the necessity of considering both consumptive and facilitative effects of herbivores on multiple autotroph species in order to gain a mechanistic understanding of grazers' top-down and bottom-up roles in structuring communities.
The United States Navy (USN) is currently demonstrating the viability of environmentally sustaina... more The United States Navy (USN) is currently demonstrating the viability of environmentally sustainable alternative fuels to power its fleet comprised of aircraft and ships. As with any fuel used in a maritime setting, there is potential for introduction into the environment through transport, storage, and spills. However, while alternative fuels are often presumed to be eco-friendly relative to conventional petroleum-based fuels, their environmental fate and effects on marine environments are essentially unknown. Here, standard laboratory-based toxicity experiments were conducted for two alternative fuels, jet fuel derived from Camelina sativa (wild flax) seeds (HRJ5) and diesel fuel derived from algae (HRD76), and two conventional counterparts, jet fuel (JP5) and ship diesel (F76). Initial toxicity tests performed on water-accommodated fractions (WAF) from neat fuels partitioned into seawater, using four standard marine species in acute and chronic/sublethal tests, indicate that the alternative fuels are significantly less toxic to marine organisms.
Supplement 1. Summary of terrestrial studies demonstrating tritrophic interactions that were incl... more Supplement 1. Summary of terrestrial studies demonstrating tritrophic interactions that were included in our survey. Studies are arranged alphabetically by the last name of the lead author
Journal of Experimental Marine Biology and Ecology, 2013
Although geographic variation in algal-herbivore interactions should be common, our appreciation ... more Although geographic variation in algal-herbivore interactions should be common, our appreciation of such variation remains incomplete. For example, feeding choice assays examining variation in palatability of algae typically compare multiple algal species or genera from a single location or a single alga from multiple locations. Unfortunately, most studies have not compared the interaction of herbivores with multiple algae from multiple locations, thus tests of variation of relative palatability are lacking. To examine spatial variation in algal palatability we determined the feeding preferences of the periwinkle snail Littorina littorea when offered multiple algal genera at the same time from two regions in choice assays. Multi-choice experiments were repeated throughout the year to examine temporal variation in feeding preferences. Consistent with previous studies, L. littorea preferred to feed on ephemeral algae compared to perennial species. Importantly, the relative palatability of the two ephemeral genera, Ulva and Porphyra, varied greatly between regions and seasons. Under certain conditions, Ulva only represented 24% of consumed algal wet mass in choice assays, while under other conditions, Ulva was eaten almost exclusively. Preferences for Ulva or Porphyra were unrelated to differences in morphology. Variation in the relative palatability of algae could influence consumer behavior leading to shifts in algal communities across broad geographic scales.
Communities are influenced by multiple stressors that can interact in surprising ways, yet trampl... more Communities are influenced by multiple stressors that can interact in surprising ways, yet trampling studies typically ignore other sources of disturbance. While there is some evidence that disturbed communities may resist trampling because of species shifts, we lack an understanding of how previous disturbance interacts with trampling in monospecific stands. Furthermore, recent studies emphasized experimental trampling additions with assumed ecological realism. We monitored barnacle cover in unmanipulated and experimentally disturbed plots at 2 sites separated by only 300 m and with disparate levels of human visitation. During the summer, barnacle cover increased by 6 and 15% at the less-visited site but decreased by 5 and 4% at the heavily visited site (unmanipulated and disturbed plots, respectively). Interestingly, the influence of site on barnacle cover was greater in disturbed than in unmanipulated plots. New recruits represented a greater proportion of the barnacles at the heavily visited site. Neither plot slope nor predator abundance differed between these sites. To isolate the influence of trampling on barnacles, we monitored barnacle cover in caged, human exclusion plots and in uncaged controls at both sites. Summer barnacle cover increased in all treatments except in uncaged plots at the heavily visited site. During 9 paired surveys coinciding with the exclusion experiment, as many as 70 humans (km -1 shoreline h -1 ) entered the intertidal zone of the heavily visited site but no one did so at the less-visited site. Given that (1) visitation was the dominant factor explaining differences in barnacle cover between the 2 sites, and (2) caging enhanced barnacle cover only at the heavily visited site, we conclude that previous disturbance mediated the effects of human trampling on barnacle populations, with more disturbed plots displaying greater trampling vulnerability.
Interactions between grazers and autotrophs are complex, including both top-down consumptive and ... more Interactions between grazers and autotrophs are complex, including both top-down consumptive and bottom-up facilitative effects of grazers. Thus, in addition to consuming autotrophs, herbivores can also enhance autotroph biomass by recycling limiting nutrients, thereby increasing nutrient availability. Here, we evaluated these consumptive and facilitative interactions between snails (Littorina littorea) and seaweeds (Fucus vesiculosus and Ulva lactuca) on a rocky shore. We partitioned herbivores' total effects on seaweeds into their consumptive and facilitative effects and evaluated how community context (the presence of another seaweed species) modified the effects of Littorina on a focal seaweed species. Ulva, the more palatable species, enhanced the facilitative effects of Littorina on Fucus. Ulva did not modify the consumptive effect of Littorina on Fucus. Taken together, the consumptive and facilitative effects of snails on Fucus in the presence of Ulva balanced each other,...
Communities are influenced by multiple stressors that can interact in surprising ways, yet trampl... more Communities are influenced by multiple stressors that can interact in surprising ways, yet trampling studies typically ignore other sources of disturbance. While there is some evidence that disturbed communities may resist trampling because of species shifts, we lack an understanding of how previous disturbance interacts with trampling in monospecific stands. Furthermore, recent studies emphasized experimental trampling additions with assumed ecological realism. We monitored barnacle cover in unmanipulated and experimentally disturbed plots at 2 sites separated by only 300 m and with disparate levels of human visitation. During the summer, barnacle cover increased by 6 and 15% at the less-visited site but decreased by 5 and 4% at the heavily visited site (unmanipulated and disturbed plots, respectively). Interestingly, the influence of site on barnacle cover was greater in disturbed than in unmanipulated plots. New recruits represented a greater proportion of the barnacles at the heavily visited site. Neither plot slope nor predator abundance differed between these sites. To isolate the influence of trampling on barnacles, we monitored barnacle cover in caged, human exclusion plots and in uncaged controls at both sites. Summer barnacle cover increased in all treatments except in uncaged plots at the heavily visited site. During 9 paired surveys coinciding with the exclusion experiment, as many as 70 humans (km −1 shoreline h −1 ) entered the intertidal zone of the heavily visited site but no one did so at the less-visited site. Given that (1) visitation was the dominant factor explaining differences in barnacle cover between the 2 sites, and (2) caging enhanced barnacle cover only at the heavily visited site, we conclude that previous disturbance mediated the effects of human trampling on barnacle populations, with more disturbed plots displaying greater trampling vulnerability.
Terrestrial insect predators and parasitoids commonly use volatile plant compounds released durin... more Terrestrial insect predators and parasitoids commonly use volatile plant compounds released during grazing to find living herbivorous prey (i.e. tritrophic signaling). Because few studies have tested for tritrophic signaling in marine organisms, it is unclear if marine predators commonly use these fluid-borne cues to find living herbivore prey, especially under realistic settings. Such interactions might occur in the ocean because marine predators often use chemosensory-based foraging, and herbivore-induced production of defensive chemistry is common in some algal taxa. To examine the ability of predators to find live herbivores using waterborne chemical cues from grazed algae, we tested the responses of marine predators to several baits using in situ trapping and video experiments. We tested the attractiveness of chemical cues released by (1) Macrocystis pyrifera and Ulva sp. actively grazed by herbivores for short-or longterm periods, (2) crushed herbivores, (3) positive controls containing fish carrion, or (4) negative controls. Most predators trapped and filmed were spiny lobsters Panulirus interruptus. Under realistic field conditions, chemical cues from actively grazed algae with live herbivores failed to attract predators, but chemical cues from crushed herbivores and fish carrion were highly attractive. Thus, while marine predators like lobsters may utilize fluid-borne chemical cues to find dead or injured prey, such cues appear less important for finding live herbivore prey. Our literature review of 142 terrestrial studies revealed that tritrophic cues were unrelated to diet breadth of predators or herbivores and that most examples of terrestrial tritrophic signaling contained parasitoid predators. We additionally found that similar field studies in natural, non-agricultural settings such as ours are lacking even in better-studied terrestrial food webs, where they represent only 3% of manipulative experiments.
Interactions between grazers and autotrophs are complex, including both top-down consumptive and ... more Interactions between grazers and autotrophs are complex, including both top-down consumptive and bottom-up facilitative effects of grazers. Thus, in addition to consuming autotrophs, herbivores can also enhance autotroph biomass by recycling limiting nutrients, thereby increasing nutrient availability. Here, we evaluated these consumptive and facilitative interactions between snails (Littorina littorea) and seaweeds (Fucus vesiculosus and Ulva lactuca) on a rocky shore. We partitioned herbivores' total effects on seaweeds into their consumptive and facilitative effects and evaluated how community context (the presence of another seaweed species) modified the effects of Littorina on a focal seaweed species. Ulva, the more palatable species, enhanced the facilitative effects of Littorina on Fucus. Ulva did not modify the consumptive effect of Littorina on Fucus. Taken together, the consumptive and facilitative effects of snails on Fucus in the presence of Ulva balanced each other, resulting in no net effect of Littorina on Fucus. In contrast, the only effect of Fucus on Ulva was to enhance consumptive effects of Littorina on Ulva. Our results highlight the necessity of considering both consumptive and facilitative effects of herbivores on multiple autotroph species in order to gain a mechanistic understanding of grazers' top-down and bottom-up roles in structuring communities.
The United States Navy (USN) is currently demonstrating the viability of environmentally sustaina... more The United States Navy (USN) is currently demonstrating the viability of environmentally sustainable alternative fuels to power its fleet comprised of aircraft and ships. As with any fuel used in a maritime setting, there is potential for introduction into the environment through transport, storage, and spills. However, while alternative fuels are often presumed to be eco-friendly relative to conventional petroleum-based fuels, their environmental fate and effects on marine environments are essentially unknown. Here, standard laboratory-based toxicity experiments were conducted for two alternative fuels, jet fuel derived from Camelina sativa (wild flax) seeds (HRJ5) and diesel fuel derived from algae (HRD76), and two conventional counterparts, jet fuel (JP5) and ship diesel (F76). Initial toxicity tests performed on water-accommodated fractions (WAF) from neat fuels partitioned into seawater, using four standard marine species in acute and chronic/sublethal tests, indicate that the alternative fuels are significantly less toxic to marine organisms.
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