413 publications from this institution
Presented at The ecology of deep and shallow coral reefs : results of a workshop on coral reef ecology held by the American Society of Zoologists, Philadelphia, Pennsylvania, December 1983
Herbivory is a critical process that underpins coral reef structure and function. Parrotfishes play significant roles in the herbivore guild by removing macroalgae, promoting coral settlement and growth, producing sediment by bioeroding carbonate substrates, and preying on corals. This chapter addresses patterns in functional variation among parrotfishes and how species of parrotfishes are either complementary or redundant to other members of the herbivore guild. Herbivore and parrotfish diversity is critical for maintaining ecosystem function because herbivores differ in sensitivity to algal chemical, morphological, and structural defenses. In addition to complex patterns in complementarity in diet selection, parrotfish species are diverse in their spatial foraging patterns, life history strategies, habitat use, and responses to predators. This functional variation and complementarity within parrotfishes and among other herbivorous species results in important positive impacts of herbivore diversity on coral reefs. Increasing parrotfish and herbivorous fish diversity often results in increased macroalgal consumption and increased success of corals. Thus, the complementary roles that parrotfishes play are important for the ecosystem function of coral reefs.
For five decades, Jim A. Estes studied sea otters in the Aleutian archipelago of Alaska, discovering how otters structured entire communities. By consuming sea urchins, otters released kelp from herbivory, kelp beds flourished, and kelps sheltered a diversity of fishes, and invertebrates. When otters were extirpated by paleohumans, modern humans, or killer whales, urchins proliferated, reduced kelp forests to “urchin barrens,” and species-rich assemblages of fishes and invertebrates were lost. These losses affected seals, eagles, sea gulls, fishes, and sea stars that depended on these prey as well as adjacent habitats that had been nourished by exported kelp production. Jim’s research became the poster child for keystone species, trophic cascades, and the critical role of predators in structuring ecosystems. Similar discoveries followed in freshwaters, forests, and grasslands.
Indirect biotic effects arising from multispecies interactions can alter the structure and function of ecological communities—often in surprising ways that can vary in direction and magnitude. On Pacific coral reefs, predation by the crown-of-thorns sea star, Acanthaster planci , is associated with broad-scale losses of coral cover and increases of macroalgal cover. Macroalgal blooms increase coral–macroalgal competition and can generate further coral decline. However, using a combination of manipulative field experiments and observations, we demonstrate that macroalgae, such as Sargassum polycystum , produce associational refuges for corals and dramatically reduce their consumption by Acanthaster . Thus, as Acanthaster densities increase, macroalgae can become coral mutualists, despite being competitors that significantly suppress coral growth. Field feeding experiments revealed that the protective effects of macroalgae were strong enough to cause Acanthaster to consume low-preference corals instead of high-preference corals surrounded by macroalgae. This highlights the context-dependent nature of coral–algal interactions when consumers are common. Macroalgal creation of associational refuges from Acanthaster predation may have important implications for the structure, function and resilience of reef communities subject to an increasing number of biotic disturbances.
Many seaweeds produce chemicals that deter feedlng by fishes and sea urchins.A growing body of evidence suggests that small, relatively immobile herbivores (mesograzers) such as amphpods, polychaetes, and ascoglossan gastropods are often unaffected by these compounds and may preferentially consume seaweeds that are chemically defended from fishes.We tested this hypothesis by examining the responses of reef fishes and amphipods to a mutture of 2 C,, hydrocarbons, &ctyopterenes A and B, produced by the Canbbean brown alga D~ctyopteris delicatula.This alga was intermediate in preference for reef fishes, and the dictyopterenes reduced fish grazing by a significant 40 %.In contrast, D. delicatula was highly preferred by a muted-species group of amphipods and the dlctyopterenes had no effect on their feeding Despite the tendency for mesograzers to selectively consume some seaweeds that are chemically deterrent to fishes, true specialization by these or other marine herbivores appears to be rare in companson with terrestnal systems.Plant-dwelling amphipods at our study site in the Grenadine Islands were found on, and consumed a variety of, macrophytes; they were not restrict~vely specialized to D. delicatula.Many terrestnal insects are very specialized feeders, sequester toxins from theu food plants, and use these as duect defenses against predation.In contrast, sequestenng of seaweed toxlns by marine mesograzers appears to be relahvely rare.However, the indirect advantage of llving on seaweeds that are not eaten by fishes may be considerable.We hypothesize that mesograzers living on plants chemically defended from fishes wlll experience less predation than those living on plants preferred by fishes.
Predation is believed to be a major source of mortality for larvae of benthic invertebrates, but the palatability of larvae commonly found in the water column has rarely been assessed. Larval palatability assays were conducted by collecting live invertebrate larvae from a temperate field site and offering them to a suite of common predators (the fishes Lagodon rhomboides, Leiostomus xanthurus, and Monacanthus hispidus and the hard coral Oculina arbuscula). By crushing larvae that were rejected intact and re-offering them to predators, it was possible to distinguish between defenses based on morphological and chemical characteristics of the larvae. Additionally, abundance data were collected for taxonomic groups of larvae at our sampling location. The majority of invertebrate larvae were palatable to consumers. Most predators readily consumed polychaete larvae, barnacle nauplii, bivalve veligers, shrimp zoeae, crab megalopae, phoronid actinotrochs, and hemichordate tornaria (which together accounted for 65% of meroplankton abundance), suggesting that these larvae lacked effective morphological or chemical defenses. Against at least 1 fish predator, a significant number of gastropod veligers, barnacle cyprids, crab zoeae, and stomatopod larvae (which accounted for 34% of meroplankton abundance) appeared to be morphologically defended. Larvae from these groups tended to be rejected whole, but were consumed by fishes once they were crushed. A significant number of nemertean pilidia, asteroid bipinnaria, and cnidarian planulae (which accounted for only 0.2% of meroplankton abundance) were rejected both whole and crushed, suggesting that some species or individuals within these taxa may be chemically defended. Thus, the majority of larvae from this assemblage of temperate meroplankton lacked physical or chemical defenses against potential predators (3 fishes and 1 cnidarian). Among the remaining larvae, physical resistance to predators was much more common than chemical resistance.
In North Carolina, the decorator crab Libinia dubia camouflages almost exclusively with the chemically noxious alga Dictyota menstrualis. By placing this alga on its carapace, the crab behaviorally sequesters the defensive chemicals of the plant and gains protection from omnivorous consumers. However, Dictyota is absent north of North Carolina, whereas Libinia occurs as far north as New England. Crabs from three northern locations where Dictyota is absent (Rhode Island, Connecticut, and New Jersey) camouflaged to match their environment, rather than selectively accumulating any one species. When D. menstrualis was offered to crabs from northern sites, they did not distinguish between it and other seaweeds for camouflage, whereas crabs from Alabama and two locations in North Carolina used D. menstrualis almost exclusively. In addition, in winter and spring, when Dictyota was seasonally absent in North Carolina, Libinia selectively camouflaged with the sun sponge Hymeniacidon heliophila, which was chemically unpalatable to local fishes. Thus, southern crabs were consistent specialists on chemically defended species for camouflage, while northern crabs were more generalized. The geographic shift in crab behavior away from specialization coincides with a reported decrease in both total predation pressure and the frequency of omnivorous consumers. These shifts in the nature and intensity of predation pressure may favor different camouflage strategies (generalist vs. specialist), contributing to the observed geographic differences in camouflage behavior.
Numerous small sedentary herbivores (mesograzers such as amphipods, small crabs, and gastropods) are resistant to seaweed secondary metabolites that deter larger, more mobile herbivorous fishes. In addition, specialist mesograzers experience reduced predation from fishes when living on seaweeds that produce these compounds. In this study we tested the hypothesis that generalist, as opposed to specialist, mesograzers can also benefit from reduced predation when they occupy chemically defended plants.
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 134:37-47 (1996) - doi:10.3354/meps134037 Responses of temperate reef fishes to alterations in algal structure and species composition Levin PS, Hay ME Reef habitats in the South Atlantic Bight comprise only a small proportion of the available benthic habitat, but support enormous densities of fishes, invertebrates, and algae. Because these reefs are distant from shore and in deeper waters (usually >20 m), we know very little about the factors affecting the distribution of fishes or the structure of fish assemblages on these reefs. Our goal in this study was to determine how variance in macroalgal structure and species composition on reefs off the coast of North Carolina affects reef fishes. Manipulations of algal density and species composition in artificially created 1.5 m2 plots indicated that: (1) patches with Sargassum filipendula had greater numbers and higher species richness of reef fishes than patches without algae; (2) fishes responded to variability in Sargassum density with high fish abundance in patches with higher algal density, but this response varied among fish species; (3) greater numbers of individuals and species of fish used Sargassum patches compared to patches of 2 other brown algae common in this region (Zonaria and Dictyopteris); (4) fish densities were higher in patches with taller algae and greater percent cover of algae. Many of the fishes using experimental patches were small, young-of-the-year individuals. Our results indicate that variability in the structure of seaweed beds on reefs in the South Atlantic Bight can influence the distribution and abundance of reef fishes. Although the algal beds in the South Atlantic Bight are more diminutive and less extensive than kelp beds of cold temperate waters, they may be a critical habitat for juvenile reef fishes in this region, and the algal species dominating the beds will have a large effect on their value as juvenile habitat. Reef fish . Temperate reef . Habitat structure . Macroalgae . South Atlantic Bight . North Carolina . Sargassum . Recruitment Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 134. Publication date: April 25, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.
Tydemania expeditionis Weber–van Bosse (Udoteaceae) is a weakly calcified green alga. In the present paper, liquid chromatography coupled with photodiode array detection and electrospray mass spectrometry was developed to identify the fingerprint components. A total of four triterpenoid sulfates and three hydroxy fatty acids in the ethyl acetate fraction of the crude extract were structurally characterized on the basis of retention time, online UV spectrum, and mass fragmentation pattern. Furthermore, a detailed liquid chromatography–mass spectrometry analysis revealed two new hydroxy fatty acids, which were then prepared and characterized by extensive nuclear magnetic resonance (NMR) analyses. The proposed method provides a scientific and technical platform for the rapid identification of triterpenoid sulfates and hydroxy fatty acids in similar marine algae and terrestrial plants. Copyright © 2011 John Wiley & Sons, Ltd.
