The fish Sarpa salpa (L.) is one of the main macroherbivores in the western Mediterranean. Through direct and indirect mechanisms, this herbivore can exert significant control on the structure and ...functional dynamics of seagrass beds and macroalgae. Past research has suggested nutritional quality of their diet influences S. salpa herbivory, with the fish feeding more intensively and exerting greater top down control on macrophytes with higher internal nutrient contents. However recent findings have questioned this notion and shown that herbivores do not preferentially feed on macrophytes with higher nutrient contents, but rather feed on a wide variety of them with no apparent selectivity. To contribute to this debate, we conducted a field fertilization experiment where we enriched leaves of the seagrass Posidonia oceanica, a staple diet for S. salpa, and examined the response by the herbivore. These responses included quantification of leaf consumption in fertilized and non-fertilized/control plots within the bed, and food choice assays where fertilized and non-fertilized/control leaves were simultaneously offered to the herbivore. Despite the duration of leaf exposure to herbivores (30 days) and abundant schools of S. salpa observed around the plots, leaf consumption was generally low in the plots examined. Consumption was not higher on fertilized than on non-fertilized leaves. Food choice experiments did not show strong evidence for selectivity of enriched leaves. These results add to a recent body of work reporting a broad generalist feeding behavior by S. salpa with no clear selectivity for seagrass with higher nutrient content. In concert, this and other studies suggest S. salpa is often generalist consumers not only dictated by diet nutrient content but by complex interactions between other traits of nutritional quality, habitat heterogeneity within their ample foraging area, and responses to predation risk.
The complex structure of seagrass beds provides increased protection for prey compared to unvegetated substrates. Additionally, most studies support the notion that predation intensity is negatively ...correlated with seagrass density. However, virtually every study to previously test this idea has used the same number of predators and prey across a gradient of seagrass density treatments. This design ignores another well-established fact: invertebrate and fish abundance increase with increasing seagrass density. Therefore, it makes sense to carry out predation experiments that increase the number of both predators and prey as seagrass density increases. Outdoor tank experiments (7 density treatments: 0 to 3000 leaves m–2) were carried out using artificial seagrass units modeled after turtlegrassThalassia testudinumand field mesocosm experiments (4 density treatments: 0 to 3000 leaves m–2) in livingT. testudinumin Big Lagoon (Florida, USA). In these experiments the absolute number of predators (the pinfishLagodon rhomboides) and prey (grass shrimpPalaemonetes pugio) were increased with increasing seagrass density. Both experiments yielded similar results: the only significant difference in predation rate was between the unvegetated treatment and the seagrass treatments as a group. These results suggest that dense seagrass does not necessarily provide increased protection for prey organisms.
We investigated the interaction between epiphyte-grazer abundance and eutrophication to assess the relative importance of top-down and bottom-up effects in subtropical seagrass meadows. In field ...experiments using a cageless technique to control amphipod abundance, we measured the effects of grazing and nutrient supply on the growth and productivity of shoalgrass Halodule wrightii and its epiphytes at both protected and wave exposed sites. Amphipod removal at the protected site resulted in 70% greater epiphyte loads on shoalgrass leaves and a 36% reduction in leaf biomass after 10 wk. At the wave-exposed site, where amphipod abundance was consistently low, we found no significant effects of grazer presence or nutrients on epiphyte load or leaf biomass. Average leaf length, however, was significantly reduced in nitrogen-enriched plots. Our results indicate that natural densities of amphipods can reduce seagrass loss by controlling epiphytes.
Doppler weather radar imaging enabled the rapid recovery of the Sutter's Mill meteorite after a rare 4-kiloton of TNT—equivalent asteroid impact over the foothills of the Sierra Nevada in northern ...California. The recovered meteorites survived a record high-speed entry of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets (Tisserand's parameter = 2.8 ± 0.3). Sutter's Mill is a regolith breccia composed of CM (Mighei)—type carbonaceous chondrite and highly reduced xenolithic materials. It exhibits considerable diversity of mineralogy, petrography, and isotope and organic chemistry, resulting from a complex formation history of the parent body surface. That diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to C-class asteroids are interpreted.
Tropicalization Regional environmental conditions in the Big Bend are dominated by atmospheric forcing and watershed input, as the wide continental shelf tends to limit oceanic upwelling, waves and ...tides, and seasonal discharge from the Apalachicola and other rivers delivers vast freshwater plumes high in chromophoric dissolved organic matter (CDOM), nutrients, tannins and chlorophyll a (Morey et al., 2017). ...coral species, such as Acropora palmata, have been recorded in the Flower Gardens reefs of the northwestern GoM (Precht and Aronson, 2004) at a latitude and depth previously unknown. In the Big Bend Area, where the shallow shelf restricts ocean mixing, the warming is expected to be particularly severe, with SST increases of nearly 4°C during the summer and fall (Liu et al., 2015). ...increased frequency of drought conditions in the American Southeast (Pederson et al., 2012) coupled with groundwater withdrawal by growing human populations in the Suwannee River and adjacent basins will likely lead to reduced discharge of relatively cold water from springs and rivers (Hensley and Cohen, 2017), further alleviating cold stress to nearshore environments. Seasonal wind patterns (Morey et al., 2003, 2017; Todd et al., 2014) and simulated drifter experiments (Johnson et al., 2017) suggest periodic connectivity to the Florida Middle Grounds, FKNMS and to a lesser extent the Flower Garden Banks, a luxuriant reef system in the northwestern GoM (Figure 1A). ...reefs should be seeded by a supply of coral larvae spawned by the massive and plating corals (genera:
Can habitat restoration be redundant? Geraldi, Nathan R.; Powers, Sean P.; Heck, Kenneth L. ...
Marine ecology. Progress series,
09/2009, Letnik:
389
Journal Article
Recenzirano
Odprti dostop
Expectations of ecological and fisheries benefits of habitat restoration are commonly used to justify its high financial cost; however, few empirical studies that rigorously test these expectations ...exist. Here, we describe the results of a study designed to quantify the effects of restoring oyster reefs in marsh tidal creeks on the mobile macrofauna. We used a before/after control/impact (BACI) design in which fishes and crustaceans within 6 tidal creeks were sampled 7× before and 14× after the addition of live oyster reefs to 3 of the tidal creeks. We detected no significant effects of the addition of oyster reefs on the overall fish or crustacean assemblages within the tidal creeks, and a weak positive effect on the abundance of demersal fishes. These results challenge current predictions that restoration of oyster reefs will result in an increase in mobile fauna. Our findings of no increase in mobile fauna may have resulted from the functional redundancy of a nearby biogenic habitat because reefs were placed in tidal creeks that were surrounded by dense salt marsh. We conclude that a positive correlation between mobile fauna and oyster habitat is not automatic, and that the role of the surrounding landscape is important in predicting the response of transient fish and crustaceans to oyster reef restoration.
Climate change is impacting marine ecosystem community dynamics on a global scale. While many have assessed direct effects of climate change, indirect effects on marine ecosystems produced by biotic ...interactions remain poorly understood. For example, warming-induced range expansions and increased consumption rates of herbivores can lead to significant and unexpected changes in seagrass-dominated ecosystems. To better understand the threats tropicalization presents for the functioning of turtlegrass (
Thalassia testudinum
) meadows, we focused on the extensive turtlegrass beds of St. Joseph Bay, Florida in the northern Gulf of Mexico, a location with increasing numbers of tropically-associated green turtles. Our goals were to investigate experimentally how different grazing rates (natural and simulated),including high levels reflective of green turtle herbivory, coupled with nutrient supply, might alter turtlegrass structure and functioning in a higher latitude, subtropical turtlegrass meadow. We found that 4 months of varying levels of herbivory did not affect turtlegrass productivity, while 7 months of herbivory reduced percent cover, and 10 months reduced shoot density. Nutrient additions had few important effects. Ten months into the study, a massive recruitment of the herbivorous sea urchin (
Lytechinus variegatus
), whose densities reached 19 urchins/m
2
completely overgrazed our study area and a large portion of the lush turtlegrass meadows of St. Joseph Bay. While local turtlegrass overgrazing had been previously noted at these urchin densities, a total loss of seagrass in such a large area has rarely ever been recorded. Overgrazing of the kind we observed, likely a result of both urchin and increasing green turtle grazing, can result in the loss of many key ecosystem services. As tropicalization continues, understanding how changes in biotic interactions, such as increased herbivory, affect higher latitude seagrass meadows will be necessary for their proper management and conservation.
The importance of habitat factors in designing marine reserves and evaluating their performance over time has been regularly documented. Over three biennial sampling periods, we examined the effects ...of vegetated coverage and habitat diversity (i.e., patchiness) on fish density, community composition, and species-specific patterns along a gradient of protection from harvest in the shallow Spanish southern Mediterranean, including portions of the Tabarca marine reserve. With the exception of two herbivores (Sarpa salpa and Symphodus tinca), vegetated cover did not significantly affect fish densities, while habitat diversity was an influential factor across all three sampling periods. Overall, fish density was more positively associated with more continuous vegetated or unvegetated habitats, and was greatest in areas of highest protection (Tabarca II – Isla Nao site). These patterns were usually observed for four abundant fish species (Boops boops, Chromis chromis, Oblada melanura, and S. salpa). Fish community composition was distinct in the most protected portion of the Tabarca reserve, where it was also most stable. Our findings align with previous investigations of the Tabarca reserve and its surrounding areas, and demonstrate its continued effectiveness in conserving fish biomass and habitat. Together with effective management, marine reserves can facilitate greater species abundance, more stable biological communities, and resilient ecosystems.
The induction of morphological, physiological and chemical defenses against herbivory is well known in seaweeds, but relatively unstudied in seagrasses. To determine if grazing history affected ...turtlegrass (Thalassia testudinum) palatability, choice and no choice feeding experiments were conducted with turtlegrass and the variegated sea urchin (Lytechinus variegatus) from two north Florida bays, and turtlegrass and bucktooth parrotfish (Sparisoma radians) from the Florida Keys. Results of choice experiments indicated that urchins exhibited a weak preference for ungrazed turtlegrass. Parrotfish, alternatively, consumed more ungrazed than grazed turtlegrass when only offered one tissue type, but when offered a choice, preferred grazed turtlegrass. The mechanisms underlying urchin feeding behaviors remain unresolved, as analyses of total reactive phenolics, nutrients and tissue toughness did not indicate that any of these factors significantly influenced results over the time scale tested. Parrotfish feeding patterns, however, were likely driven by total reactive phenolic content of turtlegrass. Effectiveness of induced defenses may be grazer-specific and dependent on the feeding mode and chemoreceptive abilities of the grazer.
► We tested whether prior grazing affects consumption of turtlegrass. ► Urchins preferred ungrazed turtlegrass. ► Parrotfish preferred grazed turtlegrass. ► The mechanisms behind urchin feeding behaviors remain unresolved. ► Parrotfish feeding was likely driven by turtlegrass phenolic content.
Herbivory on Mediterranean seagrass species is generally low compared to consumption of some other temperate and tropical species of seagrasses. In this study we: (1) investigate the feeding ...preference of the two dominant Mediterranean seagrass herbivores, the sea urchin Paracentrotus lividus and the fish Sarpa salpa, on Posidonia oceanica and Cymodocea nodosa and (2) elucidate the role of epiphytes in herbivore choices. We assessed consumption rates by tethering seagrass shoots, and preferences by food choice experiments with the following paired combinations: 1) Epiphytized leaves of both C. nodosa vs. P. oceanica (CE vs PE); 2) Non-epiphytized leaves of C. nodosa vs. P. oceanica (CNE vs. PNE); 3) Epiphytized vs non-epiphytized leaves of C. nodosa (CE vs. CNE) and 4) Epiphytized vs non-epiphytized leaves of P. oceanica (PE vs PNE). We found that preference for C. nodosa was weak for S. salpa, but strong for P. lividus, the species responsible for most consumption at our study. Overall both herbivores showed preference for epiphytized leaves. The higher nutritional quality of C. nodosa leaves and epiphytes together with the high coverage and diversity of the epiphyte community found on its leaves help explain the higher levels of herbivory recorded on epiphyted leaves of C. nodosa. Other factors such as seagrass accessibility, herbivore mobility and size, and behavioral responses to predation risks, may also affect the intensity of seagrass herbivory, and studies addressing the interactions with these factors are needed to improve our understanding of the nature, extent and implications of herbivory in coastal ecosystems.
•We investigate herbivory on Posidonia oceanica and Cymodocea nodosa.•Paracentrotus lividus was responsible for most consumption in the seagrass bed.•Preference for C. nodosa was weak for Sarpa salpa, but strong for P. lividus.•Both herbivores showed preference for epiphytized leaves.•Nutritional quality and epiphyte community may influence herbivory on C. nodosa.
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