413 publications from this institution
Marine communities have served as productive laboratories for the discovery of fundamental processes and mechanisms driving community structure and function (e.g., Paine 1966; Connell 1961; Dayton 1975). Within these communities, inducible responses are ubiquitous; extending from the seafloor to the sea-surface, and from microscopic plankton to charismatic marine megafauna (e.g., Harvell 1990; Toth and Pavia 2007; Hay 2009; Vaughn and Allen 2010). These changes may influence energy and nutrient cycling within and among ecosystems (Hay and Kubanek 2002; Long et al. 2007b). Over the past decade, marine ecologists have begun to demonstrate the often dramatic, cascading consequences of these trait modifications on co-occurring species and thus community structure and function. These trait-mediated indirect interactions (TMIIs) influence trophic cascades (Trussell et al. 2002; Grabowski and Kimbro 2005), competition between herbivores (Denno et al. 2000; Long et al. 2007a, 2011), apparent competition (Schmitt 1987), herbivore population dynamics (Denno et al. 2000), linkage across ecosystems (Nevitt et al. 1995) and energy flow and food chain length (Trussell et al. 2006b). In this chapter we discuss how TMIIs affect marine populations, communities and sometimes ecosystems, and consider the insights that can be gained from understanding and contrasting marine patterns and processes with those occurring in terrestrial or freshwater systems.
We investigated the factors selecting for host—plant specialization and the roles that plant defensive chemistry may play in this process. We studied marine organisms because marine communities contain fewer specialized herbivores than terrestrial communities and, therefore, provide a simplified system for investigating certain aspects of host—plant specialization. Our study focused on the unusual domicile—building and feeding behavior of the amphipod Pseudamphithoides incurvaria, which is the only herbivorous marine amphipod known to specialize on a few closely related seaweeds. P. incurvaria lives in a portable, bivalved domicile that it constructs from the chemically defended brown alga Dictyota bartayresii. Chemical assays indicate that natural populations of Pseudamphithoides construct their domiciles from D. bartayresii even when this alga is rare compared to other Dictyota species and to other related genera in the family Dictyotaceae. In both choice and no—choice tests in the laboratory, Pseudamphithoides built domiciles from and selectively consumed species of Dictyota that produced dictyol—class diterpenes that deter feeding by reef fishes. Other brown seaweeds in the family Dictyotaceae, including a Dictyota species, that did not produce these fish—feeding deterrents were avoided by the amphipod. Amphipods removed from their domiciles were rapidly eaten when presented to predatory fish; amphipods in their normal domiciles were consistently rejected by fish. The defensive value of the domicile appeared to result from specific characteristics of the Dictyota from which it was built, since amphipods forced to build domiciles from the palatable green seaweed Ulva were rapidly eaten when these amphipods, in their domiciles, were exposed to predatory fish. Algal defensive chemistry directly cued domicile building. When the green alga Ulva was treated with pachydictyol—A (the major secondary metabolite produced by Dictyota bartayresii), domicile building by Pseudamphithoides increased in proportion to the concentration of pachydictyol—A. All data collected during this study are consistent with the hypothesis that predator escape and deterrence are primary factors selecting for host specialization by Pseudamphithoides incurvaria. Similar conclusions can be drawn for the limited number of other marine herbivores that are relatively specialized.
Some corals release their gametes all at once, dramatically increasing the chances of any one gamete being fertilized. In a report in this issue, Clifton et al . ( 1116 ) demonstrate that a seaweed, Halimeda , also engages in synchronous spawning. Hay's Perspective discusses the natural history of these seaweeds and their efficient use of time in their growth and reproduction.
An extensive sand plain containing scattered hard substrates dominated by algae adjoins the shallower Galeta reef seaward from a depth of 11-14 m. This sand plain represents a physically marginal habitat where low light and lack of adequate attachment sites limit algal growth and where seasonal physical disturbances (turbidity and sand movement) cause large decreases in algal densities and cover. Light levels are higher and substrate more abundant on the nearby reef slope but species from the sand-plain assemblage rarely occur there. Algae from both reef-slope and sand-plain habitats become light saturated at approximately the same level (75-100 μE/m2 per s) but those from the sand plain were more productive (i.e., more efficient) throughout the range of light levels tested (13-170 μE/m2 per s). Efficient utilization of low light levels allows sand-plain species to survive on the dimly lit bottom but does not prohibit them from occupying areas of high light intensity. During two experimental periods of approximately 6 mo each, plants that settled on monofilament lines at about 3 m deep were 4-20 times more numerous, 6-23 times larger, more than three times as fertile, accumulated 27-400 times as much two-dimensional surface area, and were represented by 3-5 times as many species as algae that recruited at about 9 m deep. Although resources are more plentiful and sand-plain species more fit in shallower reef-slope areas, they are excluded from these habitats by intensive herbivory. It is hypothesized that in the absence of grazing, sand-plain species would competitively exclude reef-slope species from much of the subtidal reef. If this is valid, then reef hervibores, by limiting competitive dominants to refuge areas, are of primary importance in maintaining the large between-habitat diversity typical of shallow Caribbean reef systems.
Relationships among food choice, compensatory feeding, and the consequences for consumer fitness rarely have been quantified. We created foods of varying nutritional quality and evaluated the consequences of compensatory feeding for three sympatric species of amphipods by analyzing food choices, feeding rates, and long-term effects on fitness. Nutritional quality was manipulated by creating low-quality diets from algae (low in protein, nitrogen, and total organic carbon), high-quality diets from commercial fish food (high in protein, nitrogen, and total organic carbon), and intermediate-quality diets from mixtures of those two foods. When high- and low-quality diets were simultaneously offered, the more mobile, non-tube-building amphipods, Gammarus mucronatus and Elasmopus levis, both fed preferentially on the high-quality diet. The more sedentary, tube-building amphipod Ampithoe longimana did not discriminate between these foods. When confined to a single food type, all three species exhibited compensatory feeding on the low-quality diet. Despite compensatory feeding, when Elasmopus levis were cultured on the low-quality food, they experienced reduced survivorship, growth, and fecundity during two successive ovulations, compared to individuals feeding on more nutrient-rich foods. Low-nutrient foods caused similar declines in growth and female gonad size for Gammarus mucronatus. In contrast, the survivorship, growth, and fecundity of Ampithoe longimana was not affected by any of the diets tested. Thus, compensatory feeding allowed the more sedentary species, Ampithoe longimana, to completely circumvent the effects of low nutritional quality, but the same behavior was ineffective for both of the more mobile species, Gammarus mucronatus and Elasmopus levis. The ability of A. longimana to achieve equal fitness by substituting food quantity for food quality may allow this sedentary species to form longer associations with individual host plants, minimize movement among hosts, and thus lower its risk of being detected by predators.
Enemy release and biotic resistance are competing, but not mutually exclusive, hypotheses addressing the success or failure of non-native plants entering a new region. Enemy release predicts that exotic plants become invasive by escaping their co-adapted herbivores and by being unrecognized or unpalatable to native herbivores that have not been selected to consume them. In contrast, biotic resistance predicts that native generalist herbivores will suppress exotic plants that will not have been selected to deter these herbivores. We tested these hypotheses using five generalist herbivores from North or South America and nine confamilial pairs of native and exotic aquatic plants. Four of five herbivores showed 2.4-17.3 fold preferences for exotic over native plants. Three species of South American apple snails (Pomacea sp.) preferred North American over South American macrophytes, while a North American crayfish Procambarus spiculifer preferred South American, Asian, and Australian macrophytes over North American relatives. Apple snails have their center of diversity in South America, but a single species (Pomacea paludosa) occurs in North America. This species, with a South American lineage but a North American distribution, did not differentiate between South American and North American plants. Its preferences correlated with preferences of its South American relatives rather than with preferences of the North American crayfish, consistent with evolutionary inertia due to its South American lineage. Tests of plant traits indicated that the crayfish responded primarily to plant structure, the apple snails primarily to plant chemistry, and that plant protein concentration played no detectable role. Generalist herbivores preferred non-native plants, suggesting that intact guilds of native, generalist herbivores may provide biotic resistance to plant invasions. Past invasions may have been facilitated by removal of native herbivores, introduction of non-native herbivores (which commonly prefer native plants), or both.
Risk of larval mortality is a critical component of models and debates concerning the ecology and evolution of the differing reproductive characteristics exhibited by marine invertebrates. In these discussions, predation often is assumed to be a major source of larval mortality. Despite limited empirical support, most marine larvae are thought to be palatable and broadly susceptible to generalist predators. Previous studies of larval—planktivore interactions have focused primarily on larvae that typically feed, grow, and develop for weeks to months in the plankton. Such planktotrophic species commonly produce large numbers of small larvae that disperse over vast distances. In contrast, the nonfeeding lecithotrophic larvae from sessile invertebrates that brood are often large and conspicuous, lack morphological defenses, and have limited dispersal distances because they typically are competent to settle minutes to hours after spawning. Interactions between lecithotrophic larvae and consumers are not well studied. This has limited the ability of previous authors to test broad generalities about marine larvae. We show that brooded larvae of Caribbean sponges (11 species) and gorgonians (three species) as well as brooded larvae of temperate hydroids (two species) and a bryozoan are unpalatable to co—occurring fishes. In contrast, brooded larvae of temperate ascidians (three species), a temperate sponge, and Caribbean hard corals (three species) are readily consumed by fishes, as are larvae from four of six species of synchronous broadcast—spawning gorgonians from the Florida Keys. Frequencies of survivorship for larvae attacked and rejected by fishes were high and statistically indistinguishable from frequencies for unattacked control larvae. Frequency of metamorphosis (when it occurred) of rejected larvae never differed significantly from that of unattacked control larvae. Assays testing for larval vs. adult chemical defenses for five species with distasteful larvae showed that larvae of all five species were chemically distasteful to fishes, whereas only three of five adult extracts deterred fish feeding. A comparison of larval palatability among chemically rich taxa showed that brooded larvae were significantly more likely to be unpalatable (86% of the species tested) than larvae of broadcasters (33%), and that palatable larvae were rarely released during the day (23%) while unpalatable larvae usually were (89%). Additionally, the frequency of bright coloration was high (60%) for unpalatable larvae and low (0%) for palatable larvae, suggesting that unpalatable larvae often may be aposematically colored. Results of this broad survey cast doubt on the widely accepted notion that virtually all marine larvae are suitable prey for most generalized planktivores. Among species that do not chemically or physically protect larvae against fishes, selection appears to favor the release of larvae at night, or the production of smaller more numerous offspring that grow and develop at sea as a way of escaping consumer—rich benthic habitats. Because distasteful larvae are not similarly constrained, distasteful species should exhibit reproductive and larval characteristics selected more by the fitness—related consequences of larval development mode and dispersal distance than by the necessity of avoiding benthic predators. Production of large larvae and retention of offspring in parental habitats that have proved to be suitable for growth and reproduction have both been proposed as advantageous, but these advantages often were assumed to be offset by losses due to increased larval apparency to fishes. This assumed trade—off is not mandatory because larvae can be defended chemically. Distasteful larvae tend to be conspicuous, localized dispersers that can co—occur with benthic fishes, and yet not be consumed.
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 342:191-196 (2007) - doi:10.3354/meps342191 Propagule pressure of an invasive crab overwhelms native biotic resistance A. L. Hollebone, M. E. Hay* School of Biology, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0230, USA *Corresponding author. Email: mark.hay@biology.gatech.edu ABSTRACT: Over the last decade, the porcelain crab Petrolisthes armatus invaded oyster reefs of Georgia, USA, at mean densities of up to 11000 adults m2. Interactions affecting the invasion are undocumented. We tested the effects of native species richness and composition on invasibility by constructing isolated reef communities with 0, 2, or 4 of the most common native species, by seeding adult P. armatus into a subset of the 4 native species communities and by constructing communities with and without native, predatory mud crabs. At 4 wk, recruitment of P. armatus juveniles to oyster shells lacking native species was 2.75 times greater than to the 2 native species treatment and 3.75 times greater than to the 4 native species treatment. The biotic resistance produced by 2 species of native filter feeders may have occurred due to competition with, or predation on, the settling juveniles of the filter feeding invasive crab. Adding adult porcelain crabs to communities with 4 native species enhanced recruitment by a significant 3-fold, and countered the effects of native biotic resistance. Differences in recruitment at Week 4 were lost by Weeks 8 and 12, when densities of recent recruits reached ~17000 to 34000 crabs m2 across all treatments. Thus, native species richness slows initial invasion, but early colonists stimulate settlement by later ones and produce tremendous propagule pressure that overwhelms the effects of biotic resistance. KEY WORDS: Exotic crab · Invasive species · Marine bioinvasion · Oyster reef · Recruitment · South Atlantic Bight Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.
