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Herbivory has a profound effect on seaweeds in both temperate and tropical communities (11, 17, 21, 33, 43, 47, 80, 124). This is especially true on coral reefs where 60-97% (11, 42) of the total seaweed production may be removed by herbivores. To persist in marine communities, seaweeds must escape, deter, or tolerate herbivory. The ecological and evolutionary importance of spatial and temporal escapes has been extensively studied for seaweeds and adequately reviewed in the recent literature (33, 45, 47, 71, 80). The ability of seaweeds to tolerate herbivory has received limited attention. On coral reefs, rapidly growing filamentous algae are heavily grazed, but the algae quickly replace these losses and appear to be dependent upon herbivores to prevent their habitat from being overgrown by larger but less herbivoretolerant species (11, 71). Additionally, several seaweeds have spores or vegetative portions that can withstand gut passage; in some cases this significantly increases the growth rates of the newly settled spores (6, 122). These types of seaweeds may be considered herbivore tolerant. Although numerous seaweed characteristics can deter some herbivores, the effects of morphology and chemistry have been studied most thoroughly. The

Diterpene alcohols produced by the brown seaweed Dictyota menstrualis deter feeding by numerous species of abundant herbivores. Here we show that these same compound also may prevent fouling organisms from colonizing the surface of this alga. In the field, Dictyota menstrualis plants were less frequently and less heavily fouled than any of the other common seaweed species investigated. In laboratory assays, larvae of the common fouling bryozoan Bugula neritina failed to settle on Dictyota even though they contacted its surface as often as they contacted the surface of a preferred host alga. Rejection occurred only after direct contact with the alga's surface. Rejection of Dictyota was not mediated by water—borne chemical cues or by surface wettability (a physical property of the surface that can affect fouling). The lipid—soluble extract from surface rubbings of Dictyota inhibited larval settlement when placed on other surfaces and contained the diterpene alcohols pachydictyol A and dictyol E. Larvae exposed to these compounds experienced mortality, abnormal development, or reduced rates of development. Although the potential for chemically mediated coevolution between plants and herbivores has been the focus of scores of previous investigations, such coevolution will depend on selection altering the chemical defenses of the plant following the evolution of resistance by herbivores. Such a reciprocal response will be constrained if compounds play multiple roles that are ecologically important. Dictyota produces secondary metabolites that are broadly defensive against a wide variety of consumers and fouling organisms. Although certain consumers may evolve resistance to these metabolites, it is unclear that feeding by these consumers will result in reciprocal responses from the plant. We suggest that coevolved interactions may be uncommon, and that many interactions that appear to be coevolved may result from fortuitous and opportunistic preadaptations.

A table showing mean ash-free dry mass per worm volume for palatable and unpalatable worms and worm body parts.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 364:87-95 (2008) - DOI: https://doi.org/10.3354/meps07504 A specialist detritivore links Spartina alterniflora to salt marsh food webs John D. Parker1,2,*, Joseph P. Montoya1, Mark E. Hay1 1School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332, USA 2Present address: Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland 21037, USA *Email: parkerj@si.edu ABSTRACT: Because most plant production is subject to senescence and is eventually consumed by detritivores, the factors that drive detritivore diet choice are pivotal to the flow of energy and materials through food webs. Here, we investigated the common salt marsh amphipod Gammarus palustris, which is a habitat specialist that feeds specifically on the dead leaves of its living host plant, salt marsh cordgrass Spartina alterniflora. Restricted use and consumption of dead S. alterniflora was reinforced by superior amphipod performance (survival, size, and sexual development) on dead S. alterniflora relative to other diets, and was driven at least in part by amphipods being physically able to feed on soft, decaying plant tissues but not live, turgid tissues. Stable isotopes from field surveys and laboratory assimilation assays suggest that amphipods also feed on S. alterniflora in the field, and that the important marsh fish Fundulus hetroclitus feeds on amphipods. Thus, consumption of G. palustris by F. heteroclitus may be an important trophic pathway linking cordgrass production to nearshore food webs. Importantly, direct isotopic analyses of amphipods and their known food sources demonstrated substantial deviation of observed fractionation factors from idealized standards. This suggests caution when using idealized trophic shifts to describe food web linkages, and a renewed focus on assimilation assays to determine the realized fractionation of dietary isotopes. KEY WORDS: Spartina alterniflora · Detritus · Stable isotopes · Food webs Full text in pdf format PreviousNextCite this article as: Parker JD, Montoya JP, Hay ME (2008) A specialist detritivore links Spartina alterniflora to salt marsh food webs. Mar Ecol Prog Ser 364:87-95. https://doi.org/10.3354/meps07504 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 364. Online publication date: July 29, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Herbivores often specialize on particular hosts that provide both food and shelter from natural enemies. It is thus often unclear whether a plant's value as a food or its value as a safe shelter has played a larger role in selecting for specialization. Decorator crabs offer a novel opportunity to investigate the relative effects of diet vs. natural enemies in selecting for specialization because these crabs place plant "shelter" on their backs as camouflage but need not use these plants as food, thus decoupling the plant's value as a food from its value as a shelter. In this study, we show that juveniles of the decorator crab Libinia dubia selectively decorate with the chemically defended brown alga Dictyota menstrualis but treat this plant as a low-preference food. Common omnivorous fishes that are potential predators of Libinia avoid consuming Dictyota due to the alga's potent chemical defenses. In the field, juvenile crabs decorated with Dictyota experience significantly less predation than crabs decorated with an alga that is not chemically noxious to local fishes, and the Dictyota metabolite that most strongly deters feeding by fishes is the specific metabolite that determines decoration choice by this crab. Thus, by behaviorally sequestering defenses from this chemically noxious plant, these small crabs reduce their susceptibility to predation. In the presence of predators, juvenile crabs reduce their rate of feeding, but not of decorating, suggesting that antipredator behavior such as decorating takes precedence over feeding. In addition, only juvenile crabs that are of a size that can be consumed by local fishes decorate at all. Adult crabs that have carapace widths exceeding the gape size of co-occurring fishes do not decorate in either the field or the laboratory. Apparently predation, rather than diet selection, drives decoration specialization in Libinia, highlighting how indirect effects of plant secondary chemistry can impact herbivore behavior, ecology, and evolution.

The mass mortality of acroporid corals has transformed Caribbean reefs from coral- to macroalgal-dominated habitats since systematic monitoring began in the 1970s. Declines have been attributed to overfishing, pollution, sea urchin and coral disease, and climate change, but the mechanisms are unresolved due to the dearth of pre-1970s data. We used paleoecological, historical, and survey data to track Acropora presence and dominance throughout the Caribbean from the prehuman period to present. Declines in dominance from prehuman values first occurred in the 1950s for Acropora palmata and the 1960s for Acropora cervicornis, decades before outbreaks of acroporid disease or bleaching. We compared trends in Acropora dominance since 1950 to potential regional and local drivers. Human population negatively affected and consumption of fertilizer for agriculture positively affected A. palmata dominance, the latter likely due to lower human presence in agricultural areas. The earlier, local roots of Caribbean Acropora declines highlight the urgency of mitigating local human impacts.Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). PMID: 32426458

Abstract The omnivorous crayfish Procambarus clarkii fed selectively on several species of macrophytes, preferring delicate fresh plants that had filamentous or finely-branched architectures. When the macrophytes were dried, powdered, and reconstituted into an alginate gel (thus eliminating among-species differences in physical characteristics), crayfish preferences were altered; previously tough plants that were high in nitrogen and protein were preferred over previously delicate plants that were low in nitrogen and protein. Even though plant structure influences feeding decision of crayfish, the structurally identical macrophyte gels were fed upon differently, demonstrating that nonstructural traits are important feeding determinants. However, plant tissue constituents such as nitrogen, protein, phenolics, lignin, cellulose, or ash were not significantly correlated with feeding preferences. Two high-nitrogen plants that were avoided by crayfish as fresh and as reconstituted tissue (Nuphar luteum macrophyllum and Alternanthera philoxeroides) possessed extracts that reduced crayfish feeding in laboratory assays, demonstrating that macrophyte metabolites can deter some herbivores. As is often observed with large generalist herbivores and omnivores in terrestrial and marine systems, the freshwater crayfish made feeding decisions based upon multiple plant cues (structure, nutrition, chemical defenses).