Stephen R. Fegley

Short-term variation in the quantity and quality of seston available to benthic suspension feeders

Recent studies have demonstrated that short-term and small-scale variation in seston availability can have significant effects on individual and population characteristics of benthic suspension feeders. To provide a better understanding of in situ seston dynamics 1–2 cm above the substrate surface we measured hourly variation in seston quantity and composition (total C and N, chlorophyll a , bacteria, energy content, and particle size spectra) over a tidal cycle. Mean seston concentration was significantly lower in water collected during ebb tide than in water sampled during flood tide (37·1 vs. 78·1 mg 1 −1 ). The range of seston concentrations observed in a single tide was almost as great as the range of seston concentrations measured at this site over an entire year in other studies. Particles 2–20 μm in diameter comprised most (>80%) of the volume of the seston throughout the entire tidal cycle. The organic portion of the seston remained fairly constant when tidal velocities increased during flood tide; the seston was not ‘diluted’ by inorganic particles. In general, mean seston concentration for the entire tide (57·1 mg l −1 ) was greater in our study than has been reported in the majority of comparable studies. This may be a consequence of our sampling much closer to the substrate surface. The patterns of variation in seston concentration and quality were not predictable solely from measurements of physical factors responsible for particle suspension (e.g. current speeds, wind speeds).

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

Thirteen monthly measurements of individually marked juvenile (16 mm long) and adult (60 mm long) specimens of Mercenaria mercenaria (L.) from field plots in North Carolina demonstrated similar seasonal patterns in size-adjusted monthly growth rates in shell volume: a large absolute maximum occurred in spring (April or May) with smaller relative maxima in mid summer and late autumn. The ratio of juvenile to adult size-adjusted growth rates in shell volume was nearly constant for ten months but then increased eight-fold in December and January. This growth anomaly between size classes could not be explained by examining dry weights of soma and gonads from additional marked juvenile and adult Mercenaria that were sacrificed monthly. Juveniles differed from adults by possessing negligible gonadal mass on all dates. However, knowledge of monthly changes in adult gonadal mass did not explain a significant amount of the residual variation in the regression of monthly juvenile volumetric growth on monthly adult volumetric growth. Seasonal changes in growth of adult gonadal mass and quarterly examinations of gonad histology both suggested a winter period of negligible gametogenesis followed by a spring burst of intense reproductive activity. The best explanations for the anomalously high volumetric growth of juveniles relative to adults in December and January are: (1) winter availability of a food source accessible only to juveniles or (2) biochemical storage of energy during winter by adults in preparation for the process of rapid gametogenesis in spring. If the latter explanation is correct, adult Mercenaria exhibit a large seasonal change in the allocation of resources between somatic growth and reproduction with maximal allocation to reproduction in winter months before gonad histology and growth of gonadal mass indicate reproductive effort.

Timing, intensity and sources of autumn mortality of adult bay scallops Argopecten irradians concentricus Say

Intensive sampling for the bay scallop Argopecten irradians concentricus Say at five sites in sounds around Cape Lookout, North Carolina, in 1983–1984 demonstrated little change in density of adult (>4 cm in shell height) scallops from August to October in either year but several significant declines from October to December 1983. Because the first sampling interval brackets the period of autumn migration through the North Carolina sounds of the molluscivorous cownose ray Rhinoptera bonasus (Mitchill), a reputed scallop predator, these sampling results imply that cownose rays have little effect on adult bay scallop densities during autumn in North Carolina. Furthermore, eight young-of-the-year cownose rays failed to consume any adult bay scallops when confined for 6 days with 104 tethered adult scallops in a 48-m2 field enclosure. Mortality of tethered scallops within the enclosure, probably caused by predation from whelks Busycon spp., was significantly greater on unvegetated bottom than inside a seagrass meadow, yet did not vary with the presence or absence of epibiotic cover on the scallops top valve. The October–December declines in density of adult scallops preceded the commercial harvest but coincided with the arrival of large numbers of overwintering herring gulls Larus argentatus and ring-billed gulls Larus delawarensis. Field experiments revealed extremely rapid predation by these gulls on adult scallops aerially exposed on intertidal flats and negligible losses for scallops covered by as little as 1–3 cm of water. Gull predation did not vary with epibiotic cover on the scallops. Because adult bay scallops can be shown to emigrate more rapidly from sandflats than from seagrass beds, which are deep enough to avoid aerial exposure on all but the most extreme low tides, it is unclear whether gull predation can explain the full magnitude of observed October–December declines in scallop density. Storms may be necessary to transport enough scallops onto intertidal flats where vulnerability to gulls is enhanced to enable gulls to exert substantial mortality.

Sea level anomalies exacerbate beach erosion

Sea level anomalies are intra-seasonal increases in water level forced by meteorological and oceanographic processes unrelated to storms. The effects of sea level anomalies on beach morphology are unknown but important to constrain because these events have been recognized over large stretches of continental margins. Here, we present beach erosion measurements along Onslow Beach, a barrier island on the U.S. East Coast, in response to a year with frequent sea level anomalies and no major storms. The anomalies enabled extensive erosion, which was similar and in most places greater than the erosion that occurred during a year with a hurricane. These results highlight the importance of sea level anomalies in facilitating coastal erosion and advocate for their inclusion in beach-erosion models and management plans. Sea level anomalies amplify the erosive effects of accelerated sea level rise and changes in storminess associated with global climate change.

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

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 (ρs = 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 (ρs = 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.

Enhancing the potential for population recovery: restoration options for bay scallop populations, Argopecten irradians concentricus, in North Carolina.

ABSTRACT Historically depressed bay scallop populations in North Carolina have retained some capacity to replenish themselves. However, continued abnormally high predation by cownose rays, and growing degradation of seagrass beds may limit bay scallop population recovery. We modified existing methods for protecting spawning adult scallops from cownose rays (stockades) and enhancing scallop set (spat collectors in the natural habitat and in managed shore-side ponds) to determine whether the population growth of bay scallops could be enhanced. We found, with one important exception, that spawner sanctuaries inside stockades could be used to concentrate and protect adult scallops during a time when they are susceptible to ray predation. Spat collector bags proved effective not only in gathering scallop spat but serving as nurseries for juvenile scallop grow-out. The results from our pond experiments were mixed: spat collector bags did not do well in the pond, but an alternative collector design holds promise for making shore-side ponds important sources for inexpensive scallop seed. The simple techniques examined in this study can be used to enhance the potential of bay scallop populations to recover from low abundances, and were applied successfully to enhance North Carolina bay scallops during the two years of this project.

Parahaploposthia thiophilus sp.n. and the Use of Living Specimens in Identification of Acoel Turbellarians

Parahaploposthia thiophilus is described as a new species of the acoel turbellarian family Haploposthiidae. Although P. thiophilus exhibits strong anatomical similarities to other members of the genus Parahaploposthia, notably in the male copulatory organ, the male gonads and the frontal organ, this new species differs from all other members of its genus by the possession of a bursa. We have broadened the generic diagnosis of Parahaploposthia to include this feature, a measure that we prefer to the erection of a new genus based on a character (the bursa) of uncertain validity in the present system of acoel taxonomy. This species description is based primarily on information gleaned from the observation of living specimens by phase contrast microscopy, in order to illustrate the utility of an often neglected method that reveals important information not available from fixed and sectioned specimens, and which also may provide for more rapid and simple identification of acoel turbellarians by nonspecialists.

Fertilization and plant diversity accelerate primary succession and restoration of dune communities

Plant species richness can increase primary production because plants occupy different niches or facilitate each other (“complementarity effects”) or because diverse mixtures have a greater chance of having more productive species (“selection effects”). To determine how complementarity and selection influence dune restoration, we established four types of plant communities [monocultures of sea oats (Uniola paniculata), bitter panicgrass (Panicum amarum) and saltmeadow cordgrass (Spartina patens) and the three-species mixture] under different soil treatments typical of dune restorations (addition of soil organic material, nutrients, both, or neither). This fully factorial design allowed us to determine if plant identity, diversity and soil treatments influenced the yield of both the planted species and species that recruited naturally (volunteers). Planted species responses in monocultures and mixtures varied among soil treatments. The composition of the plantings and soils also influenced the abundance of volunteers. The mixture of the three species had the lowest cover of volunteers. We also found that the effect of diversity on production increased with fertilizer. We partitioned the biodiversity effect into complementarity and selection effects and found that the increase in the diversity effect occurred because increased nutrients decreased dominance by the largest species and increased complementarity among species. Our findings suggest that different planting schemes can be used to meet specific goals of restoration (e.g., accelerate plant recovery while suppressing colonization of non-planted species).

Regional differences in initial settlement and juvenile recruitment of Mya arenaria L. (soft-shell clam) in Maine.

ABSTRACT Clam landings have dramatically decreased in eastern Maine since 1982. Earlier studies demonstrated that densities of 0-y-old individuals of Mya arenaria L. were lower in Washington County on the eastern Maine coast than in Cumberland County on the southern Maine coast. Reduced juvenile recruitment could result from reduced larval abundances, high postsettlement mortality, or a combination of these factors. Attempts to assist recovery of populations experiencing reduced recruitment would vary depending on which combination of factors inhibited recruitment. In this study we measured initial settlement, short-term (<4 wk) postsettlement densities, and longer term (several months) postsettlement densities of 0-y-old juvenile M. arenaria in both eastern and southern Maine. Although there were seasonal and spatial differences, densities of juvenile clams were significantly greater in southern Maine over eastern Maine at each of these life history stages (initial settlement, and early and later postsettlement), generally by one or more orders of magnitude. These results suggest the low number of M. arenaria recruits in eastern Maine is a consequence primarily of reduced densities of larvae in near-shore waters rather than processes affecting postsettlement survival differentially between southern and eastern Maine. Because of the very low abundance of competent clam larvae in eastern Maine, restoration of clam populations there will require intensive efforts, such as seeding mudflats with hatchery-reared juvenile clams and managing subsequent clam survival.

Oil spill response-related injuries on sand beaches: when shoreline treatment extends the impacts beyond the oil

Studies of oil spills on sand beaches have focused traditionally on the effects of shortterm oil exposure, with recovery of sand beach macrobenthic communities occurring within several weeks to several years. The Deepwater Horizon spill resulted in chronic, multi-year re-oiling and up to 4 yr of extensive and often intensive treatments. Of the 965 km of sand beaches that were oiled, shoreline treatment was documented on 683 km. Intensive mechanical treatment was conducted from 9 to 45 mo after the initial oiling on 32.4 km of shoreline in Louisiana, and deep beach excavation/sifting and tilling was conducted along 60.5 km in Louisiana, Alabama, and Florida, often along contiguous lengths of beach. Recovery of sand beach invertebrate communities from the combined effects of oiling and treatment would likely be delayed by 2 to 6 yr after the last response action was completed. We introduce the concept of ‘Response Injury’ categories that reflect both intensity and frequency of beach treatment methods. We use the literature on similar types of disturbances to sand beach communities (foot traffic, vehicular traffic, wrack removal, beach nourishment) to describe the expected impacts. Temporal patterns of responserelated disturbances can affect seasonal recruitment of organisms and the overall rate of ecosystem recovery from both oil exposure and treatment disturbance. This concept provides a framework for specifically assessing response-related impacts in future spills, which has not been considered in previous injury assessments.