Ecological consequences of mechanical harvesting of clams

A field experiment was performed in 1,225 m2 plots in each of two shallow estuarine habitats, a seagrass bed and a sand flat. in Back Sound, North Carolina (USA), to test the impact of clam raking and two different intensities of mechanical harvesting of clams ("clam kicking") for up to 4 years on 11 hard clam, Mercenaria mercenaria, recruitment, 2) seagrass biomass, 3) the density of benthic macroinvertebrates, and 4) the density of bay scallops, Argopecten irradians. The removal of adult hard clams with the contingent sediment disturbance had ambiguous effects on the recruitment of hard clams: in the sand flat recruitment tended to be lower (but not significantly) in intense-clam-kicking matrices than in controls, whereas in seagrass recruitment of hard clams did not not show a clear response to treatment. In the raking and light-clam-kicking matrices, seagrass biomass fell immediately by ≌25% below controls but full recovery occurred within a year. In the intense-clam-kicking matrices, seagrass biomass fell by ≌65% below levels expected from controls; recovery did not begin until more than 2 years passed, and seagrass biomass was still ≌35% lower than predicted from controls 4 years later. Clam harvest did not affect either the density or species composition of small benthic macroinvertebrates from sediment cores, probably because of their rapid capacity for recolonization and generally short life spans. In all treatments, densities of benthic macroinvertebrates (mostly polychaetes) were substantially higher in the seagrass than in the sand flat during October samplings but equal during March samplings. Bay scallop density declined with declining seagrass biomass across harvest treatments, but the intense-clamkicking matrices contained even fewer bay scallops than their seagrass biomass would predict, perhaps because of enhanced patchiness of the remaining seagrass. The relative inertia of the change in seagrass biomass following extensive destruction in the intensely kicked matrices suggests that seagrass replanting may be an extremely important means of returning disturbed, unvegetated areas to seagrass systems. Emergence during summer of a between-habitat gradient in infaunal densities (higher in seagrass than in sand) supports the hypothesis that seagrass provides a partial prey refuge for infaunal invertebrates. The failure of the benthic macroinvertebrate density to respond to clam harvest treatments in both sand flats and seagrass beds implies that the polychaetes which dominate recover rapidly from disturbance and are probably not adversely affected by clam harvest. The negative and long-lasting impact ofintense hard clam harvest on seagrass biomass with its effects on other fisheries, including bay scallops, implies that hard clam fisheries should be managed to minimize the intensity of harvest within seagrass beds

Diagnostic PCR can be used to illuminate meiofaunal diets and trophic relationships

Analysis of the meiofaunal food web is hampered because few prey have features that persist long enough in a predator’s digestive tract to allow identification to species. Hence, at least for platyhelminth predators, direct observations of prey preference are almost nonexistent, and where they occur, prey identification is often limited to phylum. Studies using an in vitro approach are rare because they are extremely time-consuming and are subject to the criticism that predators removed from their natural environment may exhibit altered behaviors. Although PCR-based approaches have achieved wide application in food-web analysis, their application to meiofaunal flatworms suffers from a number of limitations. Most importantly, the microscopic size of both the predator and prey does not allow for removal of prey material from the digestive tract of the predator, and thus the challenge is to amplify prey sequences in the presence of large quantities of predator sequence. Here, we report on the successful use of prey-taxon-specific primers in diagnostic PCR to identify, to species level, specific prey items of 13 species of meiofaunal flatworms. Extension of this method will allow, for the first time, the development of a species-level understanding of trophic interactions among the meiofauna

SEASONAL ALLOCATION OF RESOURCES TO GROWTH OF SHELL, SOMA, AND GONADS IN MERCENARIA MERCENARIA

Volume: 171Start Page: 597End Page: 61

Environmental Correlates of Tardigrade Community Structure in Mosses and Lichens in the Great Smoky Mountains National Park (Tennessee and North Carolina, USA)

A major inventory of tardigrades in the Great Smoky Mountains National Park was conducted and we compared tardigrade species composition in moss and lichen samples and analysed environmental correlates of tardigrade community structure. We also compared these tardigrades with those collected from soil. The basic dataset from tree mosses and lichens consisted of 336 samples, 9200 individuals and 43 species. The supplemental dataset from rock mosses and lichens consisted of 29 samples, 811 individuals, and 41 species. Collectively, there were 57 species present in mosses and lichens. Eleven species were found uniquely on rock habitats. Two-way ANOVAs for various community metrics showed no significant differences between substrate (moss versus lichen) or height (ground level versus breast height); however, there were significant differences between ATBI plots. Tardigrade communities were not significantly different between mosses and lichens, but soil tardigrade communities were quite distinct from these moss/lichen communities. We analysed the impact of 17 environmental variables on community structure using partition tree analyses. SOx deposition explained most of the variation in species richness and evenness in moss tardigrades. Forest disturbance regime had the greatest impact on abundance in lichen tardigrades. Other environmental factors influencing community structure are discussed

Addition of juvenile oysters fails to enhance oyster reef development in Pamlico Sound

Oyster reefs are one of the most depleted and degraded marine habitats worldwide. To reverse the current oyster reef declines, governmental and private organizations have invested substantial resources into oyster restoration. Restoration primarily consists of deploying hard substrate. If oyster recruitment is thought to be limited, hatchery-raised juvenile oysters are set on the hard substrate. These costly setting efforts are carried out despite limited information on whether seed oysters accelerate reef development and, if so, how oyster size and time of deployment maximize oyster survival. North Carolina, USA, has established subtidal oyster sanctuaries in Pamlico Sound using marl mounds and hatchery-raised juvenile oysters set on recycled shell. We experimentally manipulated marl mounds at 3 sanctuaries differing abiotically and biotically during summer 2010 and varied recycled shell and seed presence, seed size, and shell and seed deployment date. Although oyster settlement varied spatially, natural recruitment swamped any measurable effect of seeding. Our findings, in combination with information from 3 additional sanctuaries seeded in 2006 and 2008, indicate that seeding does not enhance oyster reef restoration efforts in Pamlico Sound. Financial resources used for oyster seed would be better used to increase the amount of substrate for oyster settlement. Although our results may not apply to areas with less natural oyster recruitment, our study highlights the need to quantify basic ecological processes on appropriate spatiotemporal scales to optimize restoration actions. Analogous information should underlie restoration planning for other biogenic habitats like seagrass meadows and coral reefs

Prey Distribution, Physical Habitat Features, and Guild Traits Interact to Produce Contrasting Shorebird Assemblages among Foraging Patches

<div><p>Worldwide declines in shorebird populations, driven largely by habitat loss and degradation, motivate environmental managers to preserve and restore the critical coastal habitats on which these birds depend. Effective habitat management requires an understanding of the factors that determine habitat use and value to shorebirds, extending from individuals to the entire community. While investigating the factors that influenced shorebird foraging distributions among neighboring intertidal sand flats, we built upon species-level understandings of individual-based, small-scale foraging decisions to develop more comprehensive guild- and community-level insights. We found that densities and community composition of foraging shorebirds varied substantially among elevations within some tidal flats and among five flats despite their proximity (all located within a 400-m stretch of natural, unmodified inlet shoreline). Non-dimensional multivariate analyses revealed that the changing composition of the shorebird community among flats and tidal elevations correlated significantly (ρ_s = 0.56) with the spatial structure of the benthic invertebrate prey community. Sediment grain-sizes affected shorebird community spatial patterns indirectly by influencing benthic macroinvertebrate community compositions. Furthermore, combining sediment and macroinvertebrate information produced a 27% increase in correlation (ρ_s = 0.71) with shorebird assemblage patterns over the correlation of the bird community with the macroinvertebrate community alone. Beyond its indirect effects acting through prey distributions, granulometry of the flats influenced shorebird foraging directly by modifying prey availability. Our study highlights the importance of habitat heterogeneity, showing that no single patch type was ideal for the entire shorebird community. Generally, shorebird density and diversity were greatest at lower elevations on flats when they became exposed; these areas are at risk from human intervention by inlet sand mining, construction of groins and jetties that divert sediments from flats, and installation of seawalls on inlet shorelines that induce erosion of flats.</p> </div

Oyster abundance on subtidal reefs depends on predation, location, and experimental duration

Predation affects community structure and functioning within marine habitats. Predator–prey interactions can change through space and time. Documenting how these interactions change is essential to improve our understanding of food web dynamics and to enhance our ability to manage preferred species. In this study, our goals were to determine whether the density of subtidal oysters (Crassostrea virginica) differed spatially by looking at three separate restored oyster sanctuaries within Pamlico Sound (North Carolina, USA), whether oyster density changed over an interval of 16 months, and whether oyster density was related to the presence of different-sized predators by using an experimental approach. Multiple exclusion treatments were used in situ to exclude, selectively, different predator guilds from consuming oysters. Predator densities were also measured both within experimental treatments and on the restored oyster reefs by using multiple survey techniques. We found that oyster abundance differed among the four sample dates over the 16-month study and differed among the three sites. Mud crabs—one of the smallest predators measured—had the greatest predator biomass per unit of area, but the presence of other predators was largely site-dependent. Oyster abundance was affected by the exclusion of all predators, but this was dependent on sample date and location, which may suggest that mud crabs were the only predator to reduce oyster abundance in this study. In addition, large predators may have affected small predators, such as mud crabs and oyster drills, which were more abundant in treatments where large predators were excluded. The strongest evidence for top-down effects on oyster reefs occurred at one of the three field sites at the first and final sampling time, suggesting that predator effects are complex, as well as spatially and temporally variable. Field experiments that assess variables through time and at multiple locations are needed as this information could improve the success of oyster reef conservation and restoration efforts.Funding was provided by the National Estuarine Research Reserve System (NOAA) to Nathan R. Geraldi and a North Carolina Coastal Recreational Fishing License Grant awarded to Charles H. Peterson. Project partially supported by the Juan del la Cierva Incorperacion grant number IJC2018036527 I to AA

Predominant foraging modes of all observed shorebird species.

<p>Predominant foraging modes of all observed shorebird species.</p

Flat use by shorebird foraging guild.

<p>Percentages are flat-specific. All tidal stages combined.</p