Community unity: Experimental evidence for meiofauna and macrofauna

The response of two different size classes of marine benthos, macrofauna and meiofauna, to manipulation of disturbance/predation and size specific utilization of biogenic structural refuges by each benthic size category were studied in an intertidal sandflat in Virginia. A field investigation was conducted during August and September 1980 in the same Diopatra tube system which Woodin (1978; 1981) previously utilized for macrofauna I experiments. Predator/disturber exclusion cages were employed to experimentally evaluate changes in patterns of abundance of both meiofauna and macrofauna in areas of varying Diopatra tube densities (0, 1, 3 or 6 Diopatra 0.01 m–2). Samples were collected for macrofauna and meiofauna in areas immediately adjacent to tubes (= inner) and in outer areas with no tubes present from all treatment (caged or uncaged) and tube density (0, 1, 3, 6) combinations after 2 and 4 weeks. A significant increase in total macrofaunal polychaetes, nematodes and copepods was recorded inside cages after 2 and 4 weeks. Those species which were numerically abundant in control sites were also dominant inside cages. Adult densities of the bivalve, Gemma gemma increased inside cages after 2 weeks but declined dramatically after 4 weeks. Juvenile Gemma abundances, unlike those of the adults, increased inside enclosures after both 2 and 4 weeks. Along with the density increases noted in cages, a variety of main effects (i.e., tube number or position) and interactions were revealed, but these were not consistent even among benthos of similar sizes. Although densities of both meiofauna and selected macrofauna increased over similar time scales in response to predator/disturber exclusion, their spatial patterns and relationships with tubes were highly variable. Our analyses of spatial patterns of macrofauna and meiofauna in caged and uncaged sites do not fit our a priori predictions necessary to support a refuge hypothesis for all meiofauna and macrofauna by Diopatra tubes. The discrepancies between the findings of this study and earlier reports of macrofaunal utilization of Diopatra tube-caps as refuges may be related to yearly changes in community composition and/or predator/disturber activity or possibly the time scale of experiments reported here. We suggest that simultaneous monitoring of various size classes from soft-bottom communities, coupled with field experimentation, would provide valuable insight into the relative importance of forces organizing soft-bottom assemblages

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

Process-specific cues for recruitment in sedimentary environments: Geochemical signals?

The most biologically and geochemically active marine sediments are characterized by steep chemical gradients within the top centimeters of sediment (Berner, 1980). A common feature of these environments is disruptions of surface sediments by both physical and biotic forces. Growth and mortality rates for new recruits are affected by many of these surface perturbations. At the same time, these disturbances also impose a discontinuity in concentration across the sediment-water interface, and accordingly, a change in surface chemistry. In this paper we present evidence that the cue used by juveniles to distinguish between recently disturbed and undisturbed surfaces may be disruption of geochemical gradients that are typical of nearshore benthic systems. New juveniles exposed to ammonium concentrations typical of disturbed surface sediments exhibit behaviors consistent with rejection of the habitat. Conversely, new juveniles placed onto sediments containing ammonium levels typical of undisturbed surficial sediments rapidly initiate burrowing activity, a sign of acceptability. We also present a numerical model, which assesses the dynamics of small-scale chemical shifts that accompany sediment disruption, to determine (a) what is the magnitude of surface chemistry changes associated with disturbance (i.e. what is the signal strength)? and (b) what are the spatial and temporal scales associated with the return to the undisturbed condition ( recovery )? Model results show that the signal strength, and the return to acceptable conditions, are strongly influenced by the initial gradient. Model predictions of the time required to recover indicate that times to recovery are longer than the interval between disturbance events, but are of the same temporal scale (minutes to hours). Thus, our results suggest that the dynamics of surficial gradients provide a strong signal over appropriate time scales that may reveal the intensity of disturbance and the likelihood of mortality for juveniles. As such, transport-reaction processes which govern porewater concentrations in surficial sediments may also play a role in recruitment processes

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

The assimilation and retention of carbon in upland heath plant communities typical of contrasting management regimes : a 13C tracer study

Peer reviewedPublisher PD

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

Intermittent bioirrigation and oxygen dynamics in permeable sediments: An experimental and modeling study of three tellinid bivalves

To explore the dynamic nature of geochemical conditions in bioirrigated marine permeable sediments, we studied the hydraulic activity of three tellinacean bivalve molluscs (the Pacific species Macoma nasuta and Macomona liliana, and the northern Atlantic and Pacific species Macoma balthica). We combined porewater pressure sensing, time-lapse photography and oxygen imaging to quantify the durations and frequencies of tellinid irrigation activity and the associated oxygen dynamics in the sediment. Porewater pressure records of all tellinids were dominated by intermittent porewater pressurization, induced by periodic water injection into the sediment through their excurrent siphons, which resulted in intermittent oxygen supply to subsurface sediments. The irrigation (two–12 minutes long) and intervals between subsequent irrigation bouts (1.5–13 minutes) varied among tellinid species and individual sizes. For large M. liliana and M. nasuta, the average intervals between irrigation bouts were sufficiently long (10 minutes and four minutes, respectively) to allow complete oxygen consumption in between irrigation bouts in all tested sediment types. Irrigation patterns of smaller conspecifics and the smaller species M. balthica were characterized by significantly shorter separation of irrigation bouts, which resulted in more continuous oxygenation of the sediment. Transport-reaction modeling confirmed these species- and size-specific geochemical signatures and indicated that the geochemical character of the sediment is largely conditioned by the interplay between temporal irrigation patterns and sedimentary oxygen consumption rates. For large tellinids, model simulations indicated that oscillatory rather than stationary geochemical conditions are prevalent in a wide range of sediment types, with oxic pockets collapsing completely between periods of active irrigation. Based on the model results we developed analytical approximations that allow estimation of spatio-temporal characteristics of sediment oxygenation for a wide range of sediment types and infaunal activity patterns. Our results emphasize the need to consider the intermittent nature of bioirrigation when studying the geochemical impact of infauna in permeable sediments

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