Quantifying Spatial Patterns of Overgrowth in Epibenthic Communities

A method is presented that allows rapid and accurate measurement of changes in the spatial pattern of space occupation in encrusting organisms. The boundaries of organisms are represented as polygons, and geometric difference calculations are used to establish the perimeters of the areas gained or vacated between sampling dates. The influence of interspecific interactions on occupation of space is also quantified: geometric intersection calculations are used to define the perimeters of the areas gained or lost in overgrowth interactions. A method is presented for estimating the sampling frequency necessary for detection of significant changes in occupation of space. The method provides a means of quantifying not only changes in percent cover and diversity but also the dynamics of colony movement and the rates and outcomes of competitive interactions

Settlement and Early Post-Settlement Survival of Sessile Marine Invertebrates on Topographically Complex Surfaces: The Importance of Refuge Dimensions and Adult Morphology

We predicted that both refuge dimension and growth form would influence settlement and short-term post-settlement success (≤7 d) of sessile marine invertebrates that live attached to hard substrata in low energy environments. Individuals with unlimited attachment to the substrata should rapidly be protected by their growth form, thus decreasing their need to settle in refuges and limiting the length of time any locations on heterogeneous substrata act as refuges. Alternatively, organisms with limited attachment to the substrata should remain susceptible to the causes of mortality for a longer time, and as a result should settle in high quality refuges (sites that protect individuals from competitors, predators or physical disturbance events until either a size refuge or reproductive maturity is obtained). Results agreed with these predictions for 4 species of invertebrates examined on both the topographically complex surface of the solitary ascidian Styela plicata (hereafter Styela) and on settlement plates with uniformly spaced roughness elements that mimicked the heights of roughness elements (2.0 and 5.0 rnm) found on Styela in Beaufort, North Carollna, USA. On all surfaces, the 2 species with limited attachment to the substrata, Balanus sp. (aclonal, solitary) and Bugula neritina (clonal, arborescent), settled almost exclusively in the location that provided individuals with the best refuge: the crevices formed where the bases of roughness elements intersect with the flat surfaces. Additionally, when roughness elements of various heights were present (Styela, range: 0 6 to 8.8 mm), intermediate size roughness elements (2.0 ˂ x ≤15.0 mm) were picked over 72% of the time. Settlement locations and locations where survival were enhanced were less consistent for the 2 species with unlimited attachment to the substrata: a clonal, encrusting form (Schjzoporella errata) and a clonal stolon-mat form (Tubularia crocea). Fewer individuals of these 2 species settled on roughness elements on Styela and when they did, they were not restricted to the bases of the roughness elements. On the plate surfaces, most settlement did occur in crevices, but both species grew away from this location within days and short-term survival was not consistently greater in this location. Additional trials were run on plates with pits of the same maximum dimensions as the tested roughness elements (2.0 and 5.0 mm depth) to see if crevices and pits provide refuges of equal quality for newly settled individuals. Only survival of Balanus sp. recruits was greatest in both crevices and pits. Evidence for active choice of settlement location comes from consistent results in trials in which some larvae settled in greater numbers on specific size roughness elements on Styela and in areas of high erosion. Overall, these results show that one must be very cautious when generalizing about refuge quality on heterogeneous surfaces, and to determine if a location is a spatial refuge, it is critical to consider: (1) the dimensions of the larva, (2) the relative dimensions of the individual and potential refuge location at any point in time from the moment settlement occurred, and (3) the growth form of the individual which is related to its need for protection from biotic and abiotic sources of mortality

Modeling interactions of browsing predation, infaunal activity and recruitment in marine soft-sediment habitats

In marine soft-sediment habitats, the sediment surface is altered by activities of sediment dwellers (infauna). Such biogenic disturbance can influence recruitment success if settling larvae and juveniles avoid disturbed sites or if juveniles die as a result of disturbance after settling. Because infauna commonly lose exposed body parts to browsing predators and disturb less sediment as a result, we developed a simulation model to examine the interactions between browsing predation, infaunal adult activity, and recruitment. Sediment disturbance in the model was based on data for the polychaete Abarenicola pacifica. We simulated the activity of two general types of predators: prey nippers, which damaged adults only, and sediment biters, which damaged adults and consumed settled juveniles. As both types of predation rates increased, habitat rejection by settlers decreased, but juvenile mortality increased as settlers landing near damaged adults were killed when those adults resumed activity. When prey nippers were active, the interaction between predation and infaunal activity determined recruitment success, and juvenile mortality was highest at intermediate predation rates. When sediment biters were active, they controlled recruitment success by directly consuming larvae. At low adult worm densities, habitat rejection by settlers and juvenile mortality were both low, and browsing predation did not affect recruitment success. At higher adult densities, net recruitment success increased with the rate of predation by prey nippers (the magnitude of increase depended on bite rate and the length of time juveniles were susceptible to mortality), but it was never enhanced by sediment biters

Global intercomparison of hyper-resolution ECOSTRESS coastal sea surface temperature measurements from the space station with VIIRS-N20

The ECOSTRESS multi-channel thermal radiometer on the Space Station has an unprecedented spatial resolution of 70 m and a return time of hours to 5 days. It resolves details of oceanographic features not detectable in imagery from MODIS or VIIRS, and has open-ocean coverage, unlike Landsat. We calibrated two years of ECOSTRESS sea surface temperature observations with L2 data from VIIRS-N20 (2019–2020) worldwide but especially focused on important upwelling systems currently undergoing climate change forcing. Unlike operational SST products from VIIRS-N20, the ECOSTRESS surface temperature algorithm does not use a regression approach to determine temperature, but solves a set of simultaneous equations based on first principles for both surface temperature and emissivity. We compared ECOSTRESS ocean temperatures to well-calibrated clear sky satellite measurements from VIIRS-N20. Data comparisons were constrained to those within 90 min of one another using co-located clear sky VIIRS and ECOSTRESS pixels. ECOSTRESS ocean temperatures have a consistent 1.01 °C negative bias relative to VIIRS-N20, although deviation in brightness temperatures within the 10.49 and 12.01 µm bands were much smaller. As an alternative, we compared the performance of NOAA, NASA, and U.S. Navy operational split-window SST regression algorithms taking into consideration the statistical limitations imposed by intrinsic SST spatial autocorrelation and applying corrections on brightness temperatures. We conclude that standard bias-correction methods using already validated and well-known algorithms can be applied to ECOSTRESS SST data, yielding highly accurate products of ultra-high spatial resolution for studies of biological and physical oceanography in a time when these are needed to properly evaluate regional and even local impacts of climate change.National Aeronautics and Space Administration | Ref. 80NSSC20K007

Effect of Harvest and Effective Population Size on Genetic Diversity in a Striped Bass Population

A major factor that contributes to loss of genetic variation in natural populations is a small effective population size. In species with a complex life history that involves overlapping generations and delayed maturity, the impact of infrequent annual reproductive bottlenecks is likely to be small because effective population size is defined by the number of individuals contributing to a generation and not to a single year-class. The striped bass Morone saxatilis is a longlived species with overlapping generations and age structure, whose recreational and commercial importance has made it a target of intense harvest.We analyzed allele frequency fluctuation among juvenile year classes of the Santee–Cooper, South Carolina, population from 1990 through 1994 with three independently segregating polymorphic nuclear DNA loci to examine genetic drift and estimate the number of breeders each year. Significant fluctuations in allele frequencies among juvenile year-classes were observed, and most of the variation was attributed to a small number of parents in 1992. The potential impact of this year-class is likely to be low because 1992 was a poor recruitment year, and striped bass have multiple opportunities to breed. However, high adult mortality due to fishing may increase the impact of the 1992 year-class by decreasing the number of adult age-classes in this population. Thus, high exploitation in species with overlapping generations can reduce the long-term effective population size by abrogating the possibility of multiple breeding opportunities

The effect of fiddler crab burrowing on sediment mixing and radionuclide profiles along a topographic gradient in a southeastern salt marsh

Fiddler crabs are one of the principal agents of bioturbation in intertidal salt marshes. The physical, chemical, and biological properties of sediments can be modified by fiddler crab burrowing activity. This study examined the effect of fiddler crab burrowing on sediment reworking and the distributions of 210Pb and 137Cs in salt marsh sediments at North Inlet Estuary, South Carolina. Fiddler crab burrow density, turnover, and volume were measured along a transect from the forest to the creek bank. Burrow density ranged between 40 and 300 burrows m-2 with highest densities at the creek bank. Sediment reworking is related to burrow turnover, density and size. Sediment reworking rates ranged between 4.4 × 103 and 5.7 × 104 cm3 m-2 y-1. Excess 210Pb and 137Cs profiles indicated that fiddler crab burrowing mixed the top 8 to 15 cm of sediment. Direct field measurements of burrow density, turnover, and size were used as input to a modified version of the regeneration model of Gardner et al. (1987) to assess the effect of fiddler crab bioturbation on 210Pb profiles. The modification takes into account the filling of abandoned fiddler crab burrows from both the infilling of surface sediment and the collapse of burrow walls. Model results were in good agreement with the observed 210Pb distributions in the sediments. Overall the results of this study suggest that fiddler crabs directly influence sediment composition and biogeochemical cycles in salt marsh systems

Experimenting with ecosystem interaction networks in search of threshold potentials in real-world marine ecosystems

Thresholds profoundly affect our understanding and management of ecosystem dynamics, but we have yet to develop practical techniques to assess the risk that thresholds will be crossed. Combining ecological knowledge of critical system interdependencies with a large-scale experiment, we tested for breaks in the ecosystem interaction network to identify threshold potential in real-world ecosystem dynamics. Our experiment with the bivalves Macomona liliana and Austrovenus stutchburyi on marine sandflats in New Zealand demonstrated that reductions in incident sunlight changed the interaction network between sediment biogeochemical fluxes, productivity, and macrofauna. By demonstrating loss of positive feedbacks and changes in the architecture of the network, we provide mechanistic evidence that stressors lead to break points in dynamics, which theory predicts predispose a system to a critical transition

Responses to salinity stress in bivalves: Evidence of ontogenetic changes in energetic physiology on Cerastoderma edule

Estuarine bivalves are especially susceptible to salinity fluctuations. Stage-specific sensibilities may influence the structure and spatial distribution of the populations. Here we investigate differences on the energetic strategy of thread drifters (3–4 mm) and sedentary settlers (9–10 mm) of Cerastoderma edule over a wide range of salinities. Several physiological indicators (clearance, respiration and excretion rates, O:N) were measured during acute (2 days) and acclimated responses (7 days of exposure) for both size classes. Our results revealed a common lethal limit for both developmental stages (Salinity 15) but a larger physiological plasticity of thread drifters than sedentary settlers. Acclimation processes in drifters were initiated after 2 days of exposure and they achieved complete acclimation by day 7. Sedentary settlers delay acclimation and at day 7 feeding activity had not resumed and energetic losses through respiration and excretion were higher at the lowest salinity treatment. Different responses facing salinity stress might be related to differences in habitat of each stage. For sedentary settlers which occupy relatively stable niches, energy optimisation include delaying the initiation of the energetically expensive acclimation processes while drifters which occupy less stable environments require a more flexible process which allow them to optimize energy acquisition as fast as possible.Ministerio de Economía y Competitividad | Ref. CTM2014–51935-RXunta de Galicia | Ref. POS-B/2016/032Xunta de Galicia | Ref. GRC2013–00

Predation risk increases in estuarine bivalves stressed by low salinity

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGSalinity drops in estuaries after heavy rains are expected to increase in frequency and intensity over the next decades, with physiological and ecological consequences for the inhabitant organisms. It was investigated whether low salinity stress increases predation risk on three relevant commercial bivalves in Europe. In laboratory, juveniles of Venerupis corrugata, Cerastoderma edule, and the introduced Ruditapes philippinarum were subjected to low salinities (5, 10 and control 35) during two consecutive days and, afterwards, exposed to one of two common predators in the shellfish beds: the shore crab Carcinus maenas and the gastropod Bolinus brandaris, a non-indigenous species present in some Galician shellfish beds. Two types of choice experiment were done: one offering each predator one prey species previously exposed to one of the three salinities, and the other offering each predator the three prey species at the same time, previously exposed to one of the three salinities. Consumption of both predators and predatory behaviour of C. maenas (handling time, rejections, consumption rate) were measured. Predation rates and foraging behaviour differed, with B. brandaris being more generalist than C. maenas. Still, both predators consumed significantly more stressed (salinity 5 and 10) than non-stressed prey. The overall consumption of the native species C. edule and V. corrugata was greater than that of R. philippinarum, likely due to their vulnerability to low salinity and physical traits (e.g., thinner shell, valve gape). Increasing precipitations can alter salinity gradients in shellfish beds, and thus affect the population dynamics of harvested bivalves via predator–prey interactions.Ministerio de Economía y Competitividad | Ref. CTM2014-51935-RMinisterio de Economía y Competitividad | Ref. BES-2015-074211Xunta de Galicia | Ref. GRC2013-00