Publications

Associational Plant Defenses and the Maintenance of Species Diversity: Turning Competitors Into Accomplices

The palatable plants investigated in this study gained significant protection from herbivores by associating with abundant competitors that were less susceptible to herbivory. When herbivores were excluded, palatable species associated with unpalatable ones grew at only 14%-19% of the rate of palatable plants separated from unpalatable ones. When herbivores were present, however, palatable species appeared to depend completely on unpalatable competitors to provide microsites of reduced herbivory to prevent grazers from causing local extinction of the preferred species. For the species studied here, the cost of being associated with a larger, unpalatable competitor was much less than the cost of increased consumption in the absence of that competitor. Under these conditions, one competitor can have a strong positive effect on another. Associational defenses can provide an unappreciated mechanism for maintaining species richness within communities that are dominated by one or a few major species. In this community, increases in the abundance of common late-successional competitors led to increases, not decreases, in the abundance and number of other species and to retention, not exclusion, of early-successional species.

Induced chemical defenses in a freshwater macrophyte suppress herbivore fitness and the growth of associated microbes

Growth and survival of mature Sargassum polycystum fronds in crowded and isolated habitats

Feeding and growth of native, invasive and non-invasive alien apple snails (Ampullariidae) in the United States: Invasives eat more and grow more

Callophycoic Acids and Callophycols from the Fijian Red Alga <i>Callophycus serratus</i>

Callophycoic acids A-H (1-8) and callophycols A and B (9 and 10) were isolated from extracts of the Fijian red alga Callophycus serratus, and identified by NMR, X-ray, and mass spectral analyses. These natural products represent four novel carbon skeletons, providing the first examples of diterpene-benzoic acids and diterpene-phenols in macroalgae. Compounds 1-10 exhibited antibacterial, antimalarial, and anticancer activity, although they are less bioactive than diterpene-benzoate macrolides previously isolated from this red alga.

Benthic cover data from six sites in Viti Levu, Fiji from 2010-2012 (Killer Seaweeds project)

Benthic cover data from six

Ecological leads for natural product discovery: novel sesquiterpene hydroquinones from the red macroalga Peyssonnelia sp.

Faculty Opinions recommendation of Larval sensory abilities and mechanisms of habitat selection of a coral reef fish during settlement.

Sensory abilities and preferences exhibited by mobile larvae during their transition to juvenile habitats can establish spatial heterogeneity that drives subsequent species interactions and dynamics of populations. We conducted a series of laboratory and field experiments using coral reef fish larvae (Chromis viridis) to determine: ecological determinants of settlement choice (conspecifics vs. heterospecifics vs. coral substrates); sensory mechanisms (visual, acoustic/vibratory, olfactory) underlying settlement choice; and sensory abilities (effective detection distances of habitat) under field conditions. C. viridis larvae responded positively to visual, acoustic/vibratory, and olfactory cues expressed by conspecifics. Overall, larvae chose compartments of experimental arenas containing conspecifics in 75% of trials, and failed to show any significant directional responses to heterospecifics or coral substrates. In field trials, C. viridis larvae detected reefs containing conspecifics using visual and/or acoustic/vibratory cues at distances <75 cm; detection distances increased to <375 cm when olfactory capacity was present (particularly for reefs located up-current). We conducted high performance liquid chromatography (HPLC) analyses of seawater containing C. viridis juveniles and isolated high concentrations of several organic compounds. Subsequent laboratory trials demonstrated that C. viridis larvae responded positively to only one of these organic compounds. This compound was characterized by a weak polarity and was detected at 230 nm with a 31-min retention time in HPLC. Overall, our results suggest that fishes may use a range of sensory mechanisms effective over different spatial scales to detect and choose settlement sites, and species-specific cues may play a vital role in establishment of spatial patterns at settlement. PMID: 15647903

Size matters: Predator outbreaks threaten foundation species in small Marine Protected Areas

The unanticipated impacts of consumers in fragmented habitats are frequently a challenge for ecosystem management. On Indo-Pacific coral reefs, crown-of-thorns sea stars (Acanthaster spp.) are coral predators whose outbreaks cause precipitous coral decline. Across large spatial scales, Acanthaster densities are lower in large no-take Marine Protected Areas (MPAs) and reefs subject to limited human exploitation. However, using a combination of observational and manipulative experiments, we found that Acanthaster densities within a network of small, no-take MPAs on reef flats in Fiji were ~2-3.4 times greater inside MPAs than in adjacent fished areas and ~2-2.5 times greater than the upper threshold density indicative of an outbreak. This appeared to result from selective Acanthaster migration to the coral-rich MPAs from fished areas that are coral-poor and dominated by macroalgae. Small MPAs can dramatically increase the cover of foundation species like corals, but may selectively attract coral predators like Acanthaster due to greater food densities within MPAs or because the MPAs are too small to support Acanthaster enemies. As coral cover increases, their chemical and visual cues may concentrate Acanthaster to outbreak densities that cause coral demise, compromising the value of small MPAs. An understanding of predator dynamics as a function of habitat type, size, and fragmentation needs to be incorporated into MPA design and management.

Seaweed-Coral Interactions: Variance in Seaweed Allelopathy, Coral Susceptibility, and Potential Effects on Coral Resilience

Tropical reefs are in global decline with seaweeds commonly replacing corals. Negative associations between macroalgae and corals are well documented, but the mechanisms involved, the dynamics of the interactions, and variance in effects of different macroalgal-coral pairings are poorly investigated. We assessed the frequency, magnitude, and dynamics of macroalgal-coral competition involving allelopathic and non-allelopathic macroalgae on three, spatially grouped pairs of no-take Marine Protected Areas (MPAs) and non-MPAs in Fiji. In non-MPAs, biomass of herbivorous fishes was 70-80% lower, macroalgal cover 4-9 fold higher, macroalgal-coral contacts 5-15 fold more frequent and 23-67 fold more extensive (measured as % of colony margin contacted by macroalgae), and coral cover 51-68% lower than in MPAs. Coral contacts with allelopathic macroalgae occurred less frequently than expected by chance across all sites, while contact with non-allelopathic macroalgae tended to occur more frequently than expected. Transplants of allelopathic macroalgae (Chlorodesmis fastigiata and Galaxaura filamentosa) against coral edges inflicted damage to Acropora aspera and Pocillopora damicornis more rapidly and extensively than to Porites cylindrica and Porites lobata, which appeared more resistant to these macroalgae. Montipora digitata experienced intermediate damage. Extent of damage from macroalgal contact was independent of coral colony size for each of the 10 macroalgal-coral pairings we established. When natural contacts with Galaxaura filamentosa were removed in the field, recovery was rapid for Porites lobata, but Pocillopora damicornis did not recover and damage continued to expand. As macroalgae increase on overfished tropical reefs, allelopathy could produce feedbacks that suppress coral resilience, prevent coral recovery, and promote the stability of algal beds in habitats previously available to corals.

INTEGRATING PREY DEFENSIVE TRAITS: CONTRASTS OF MARINE WORMS FROM TEMPERATE AND TROPICAL HABITATS

Marine worms are speciose and numerically prominent members of marine communities where they play critical roles in trophic interactions and in affecting biogeochemical cycles. Despite the ecological importance of this group, little is known about their palatability to, and defenses against, consumers. In addition, most studies of prey defenses in marine organisms have focused on overt, sessile species: few studies have investigated more mobile and behaviorally complex species that could potentially be integrating predator deterrents with refuge use and other escape behaviors. To increase our understanding of consequences of defensive traits among mobile marine prey, we surveyed the palatability of 81 species of worms from the Caribbean and warm-temperate western Atlantic. Thirty-seven percent of the species were unpalatable. Worms with differentially exposed body portions commonly defended exposed feeding appendages with chemical or structural deterrents, while palatable and undefended bodies remained sheltered within structural refuges. Unpalatable worms tended to be brightly colored and sedentary, exposed to epibenthic predators, and to occupy hard substrates. Palatable worms tended to be drab, to live in structural refuges from consumers, to be mobile, and to inhabit unconsolidated sediments. Overall, taxonomy (Sabellidae and Terebellidae) and color were the traits most strongly associated with unpalatability. Unpalatable species appeared less constrained by predation and freer to forage for long periods on higher quality surface sediments or on other invertebrates at the sediment surface (thus, potentially influencing the distribution and abundance of other species). In contrast, palatable species appeared more constrained by predation risk. They fed on lower quality subsurface sediments and foraged at times or locations where consumers were less active. These ecological patterns may be generalized to other soft-bodied prey, such as caterpillars, which show similar trends regarding palatability and lifestyle.

Ukubuyisana: Reconciliation in South Africa

Gene expression patterns of the coral Acropora millepora in response to contact with macroalgae

Faculty Opinions recommendation of Restoration of seagrass habitat leads to rapid recovery of coastal ecosystem services.

There have been increasing attempts to reverse habitat degradation through active restoration, but few large-scale successes are reported to guide these efforts. Here, we report outcomes from a unique and very successful seagrass restoration project: Since 1999, over 70 million seeds of a marine angiosperm, eelgrass (Zostera marina), have been broadcast into mid-western Atlantic coastal lagoons, leading to recovery of 3612 ha of seagrass. Well-developed meadows now foster productive and diverse animal communities, sequester substantial stocks of carbon and nitrogen, and have prompted a parallel restoration for bay scallops (Argopecten irradians) Restored ecosystem services are approaching historic levels, but we also note that managers value services differently today than they did nine decades ago, emphasizing regulating in addition to provisioning services. Thus, this study serves as a blueprint for restoring and maintaining healthy ecosystems to safeguard multiple benefits, including co-benefits that may emerge as management priorities over time.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: 33028530

Intergenerational effects of macroalgae on a reef coral: major declines in larval survival but subtle changes in microbiomes

Tropical reefs are shifting from coral to macroalgal dominance, with macroalgae suppressing coral recovery, potentially via effects on coral microbiomes. Understanding how macroalgae affect corals and their microbiomes requires comparing algae- versus coral-dominated reefs without confounding aspects of time and geography. We compared survival, settlement, and post-settlement survival of larvae, as well as the microbiomes of larvae and adults, of the Pacific coral <i>Pocillopora damicornis</i> between an Marine Protected Area (MPA) dominated by corals versus an adjacent fished area dominated by macroalgae. Microbiome composition in adult coral, larval coral, and seawater did not differ between the MPA and fished area. However, microbiomes of adult coral were more variable in the fished area and Vibrionaceae bacteria, including strains most closely related to the pathogen <i>Vibrio shilonii</i>, were significantly enriched, but rare, in adult and larval coral from the fished area. Larvae from the macroalgae-dominated area exhibited higher pre-settlement mortality and reduced settlement compared to those from the coral-dominated area. Juveniles planted into a coral-dominated area survived better than those placed into a fished area dominated by macroalgae. Differential survival depended on whether macroalgae were immediately adjacent to juvenile coral rather than on traits of the areas <i>per se</i>. Contrary to our expectations, coral microbiomes were relatively uniform at the community level despite dramatic differences in macroalgal cover between the MPA (~2% cover) and fished (~90%) area. Reducing macroalgae may elicit declines in rare but potentially harmful microbes in coral and their larvae, as well as positive intergenerational effects on offspring survival.

Chemical defense in the seaweed Ochtodes secundiramea (Montagne) Howe (Rhodophyta): effects of its monoterpenoid components upon diverse coral-reef herbivores

Disentangling the impacts of macroalgae on corals via effects on their microbiomes

Tropical reefs are commonly transitioning from coral to macroalgal dominance, but the role of macroalgae in coral decline remains inadequately understood. A growing body of research suggests that algae may harm corals via disruptions to the homeostasis of the coral holobiont, including resident microbial communities, but the processes that mediate these potential microbial effects and the spatial scales at which they operate are uncertain. Resolving the relative importance and context dependencies of microbially-mediated algal-coral competition is critical for understanding and predicting coral dynamics as reefs further degrade. In this review, we examine the current state of knowledge surrounding algal impacts on corals via disruption of their microbiomes, with a particular focus on the mechanisms hypothesized to mediate microbial effects, the scales at which they are thought to operate, and the evidence from laboratory- and field-based studies for their existence and ecological relevance in the wild. Lastly, we highlight challenges for further advancing the field.