The ECOSTRESS multi-channel thermal radiometer on the Space Station has an unprecedented spatial ... more 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.
Ocean warming and acidification affect species populations, but how interactions within communiti... more Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remains poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioral plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam's feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most likely due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioral changes of key species.
Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to... more Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to the cooler sea temperatures associated with them. It has been suggested that global warming could lead to enhanced sea surface cooling in EBUS via the intensification of upwelling-favorable winds. Conversely, increased stratification and the widespread warming of the world's oceans could drive these systems in the opposite direction. These competing mechanisms hold the potential for driving the thermal envelopes of EBUS toward -or away from -the thermal envelopes found outside EBUS, with likely contrasting implications for biodiversity conservation in each scenario. Here we characterize the patterns of net sea surface warming rates over more than three decades throughout the global ocean to evaluate if waters inside EBUS are changing differently from those outside EBUS. Results point to a trend of reduced warming inside EBUS, especially along the nearshore. We found that reduced net warming was prevalent in Pacific EBUS but restricted in Atlantic EBUS. In contrast, net warming in the coastal ocean outside EBUS was pervasive and generally associated with proximity to land. Our results suggest that EBUS have been responding to climate change differently from the rest of the global ocean, potentially buffering coastal biomes from decades of global warming.
Intertidal organisms are often assumed to live close to their thermal limits, and have emerged as... more Intertidal organisms are often assumed to live close to their thermal limits, and have emerged as potential early indicators of the effects of climate change. We compared our survey of the 2004-2006 geographic distribution of the barnacle Semibalanus
Journal of Experimental Marine Biology and Ecology, Mar 1, 2000
This study investigates how the presence of symbiotic crabs (Pinnixa chaetopterana or Polyonyx gi... more This study investigates how the presence of symbiotic crabs (Pinnixa chaetopterana or Polyonyx gibbesi) in the tubes of the polychaete Chaetopterus variopedatus affects the worms' pumping activity and growth rates under laboratory and field conditions. In the field, worms whose tubes are inhabited by Pinnixa beat their fan segments significantly more frequently than do worms hosting Polyonyx, but other measures of pumping activity do not differ according to symbiont species. In the lab, worms tend to move water through their tubes at higher rates when crabs are present. In 7-month laboratory experiments, growth rates of worms hosting either species of crab did not differ from growth rates of worms without crab symbionts. Although worms hosting Polyonyx are, on average, significantly larger than worms hosting Pinnixa, this appears to be due to competition between the crab species for hosts and not due to differential effects on host growth. Unlike the crabs in this study, pea crab species inhabiting bivalves are known to have strong deleterious effects on host growth and reproduction, suggesting that the evolution of virulence in symbiotic interactions is dependent upon specific ecological context.
Aim Ecosystem engineering polychaetes in the genus Diopatra are undergoing range shifts in wester... more Aim Ecosystem engineering polychaetes in the genus Diopatra are undergoing range shifts in western Europe. Here we: (1) assess the species diversity underlying these shifts; (2) link biogeographic patterns to sea surface temperature patterns; and (3) predict possible ecosystem-level outcomes of Diopatra's northward expansion. Methods We use molecular phylogenetic and morphological evidence to assess species diversity and biogeographic ranges. Using regression tree analyses, we assess thermal limits for two Diopatra species. We compare biogeographic patterns with historical sea surface temperature patterns to draw links between range shifts and climate change. Finally, we review published data to predict potential ecological changes as Diopatra invades new habitats. The native Diopatra neapolitana range has contracted 130 km to the south. A cryptogenic species, Diopatra sp. A, has extended the northern limit of the genus 350 km to the southern Brittany Peninsula. Both shifts can be explained by historical sea surface temperature anomalies. The Diopatra sp. A expansion is predicted to continue into the English Channel and the North Sea, introducing large tube structures to sheltered sedimentary habitats that currently lack such structures. As climate change intensifies, the sediment-stabilizing Diopatra sp. A will invade habitats dominated by the bioturbating lugworm Arenicola marina. The resulting interaction between functionally different ecosystem engineers will probably cause ecological changes in northern European coastal waters. Existing data for Diopatra species and arenicolids suggest that the diversity and biomass of macroalgae, vascular plants, infauna and epibenthic fauna may increase, while microbial activity may decrease. Net changes in productivity will depend on the relative rates of these changes.
The interactions between the intertidal barnacles Semibalanus (Balanus) balanoides and Chthamalus... more The interactions between the intertidal barnacles Semibalanus (Balanus) balanoides and Chthamalus fragilis were examined in order to determine whether the factors which influence local zonation in the intertidal also contribute to the establishment of geographic limits. Both physical and biotic factors influence intertidal zonation at the northern limit of Chthamalus in New England. On sloping surfaces Semibalanus died at all shore levels higher than mid tide level, apparently as a result of desiccation associated with high summer temperatures. Chthamalus settlement occurred at all shore levels above mean tide level, and postsettlement mortality apparently restricts Chthamalus to high shore locations where Semibalanus growth and survival is inhibited. North of the northern limit of Chthamalus, Semibalanus does not suffer summer heat death, so it occupies the zone where Chthamalus would have a refuge from competition further south. The northern limit of Chthamalus is set not by factors directly related to cold acting on Chthamalus. Rather the northern limit appears to be set by cold which allows the dominant competitor to exclude Chthamalus from its refuge zone. South of the northern limit the competitor, Semibalanus, is excluded from the high shore by high summer temperatures.
In the following decade(s), a set of satellite missions carrying thermal infrared (TIR) imagers w... more In the following decade(s), a set of satellite missions carrying thermal infrared (TIR) imagers with a relatively high noise equivalent differential temperature (NEdT) are expected, e.g., the high resolution TIR imagers flying on the future Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment (TRISHNA), Land Surface Temperature Monitoring (LSTM) and NASA-JPL/ASI Surface Biology and Geology Thermal (SBG) missions or the secondary payload on board the ESA Earth Explorer 10 Harmony. The instruments on board these missions are expected to be characterized by an NEdT of 0.1 K. In order to reduce the impact of radiometric noise on the retrieved sea surface temperature (SST), this study investigates the possibility of applying a multi-pixel atmospheric correction based on the hypotheses that (i) the spatial variability scales of radiatively active atmospheric variables are, on average, larger than those of the SST and (ii) the effect of atmosphere is accounted for via the split window (SW) difference. Based on 32 Sentinel 3 SLSTR case studies selected in oceanic regions where SST features are mainly driven by meso to sub-mesoscale turbulence (e.g., corresponding to major western boundary currents), this study documents that the local spatial variability of the SW difference term on the scale of 3 × 3 km 2 is comparable with the noise associated with the SW difference. Similarly, the power spectra of the SW term are shown to have, for small scales, the behavior of white noise spectra. On this basis, we suggest to average the SW term and to use it for the atmospheric correction procedure to reduce the impact of radiometric noise. In principle, this methodology can be applied on proper scales that can be dynamically defined for each pixel. The applicability of our findings to high-resolution TIR missions is discussed and an example of an application to ECOSTRESS data is reported.
Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We exp... more Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We expected these activities to generate low-frequency pressure waves that would propagate through sediments and be detectable at some distance from the source. Pressure sensors in intertidal sediments recorded large-amplitude porewater pressure signals. Laboratory recordings of single individuals allowed us to identify characteristic signals of arenicolid and nereidid polychaetes and tellinid bivalves. In the bivalve Macoma nasuta, these high-amplitude signals were associated with burrowing, expulsion of pseudofeces, and siphon relocation. In the polychaetes Neanthes brandti and Abarenicola pacifica, the high-amplitude pressure signals were associated with burrowing, burrow construction, burrow ventilation, and defecation. These signals were detectable in the field at distances of at least 20 cm. Since the waveforms are species-specific as well as activity-specific, they may provide a mechanism for prey detection, for predator avoidance, for competitor detection, and perhaps even for mate detection.
In marine sediments, many of the processes associated with high post-settlement mortality of infa... more In marine sediments, many of the processes associated with high post-settlement mortality of infauna have similar effects on the sediment surface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments reported here tested the ability of new juvenile infauna to discriminate between undisturbed and recently disturbed sediment surfaces (i.e.. subsurface sediment exposed). Recently settled juveniles of two polychaete species (Nereis vexillosa and Arenicola cristata) and one bivalve species (Alercenaria mercenaria) were exposed to simulated erosional and mixing events as well as to fresh feces. burrow tailings, and feeding tracks. Where the disturbance buried or removed several millimeters of the sediment surface, the time to initiate burrowing or the percentage of individuals failing to burrow increased significantly over times and percentages for juveniles on undisturbed surfaces. In all cases the results were consistent with the hypothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old. For example. 51% of nereid juveniles did not burrow when placed on subsurface sediments, whereas 100% burrowed into surface sediments; their average burrowing time on surface sediments was 29.3s compared with 109.7s on fecal mounds of arenicolid polychaetes or 106.1 s on burrow tailings ofthalassinid crustaceans. Individuals that did not indicate acceptance of a sediment surface by burrowing were all rapidly eroded from the surface in the presence of flow. Erosion of nonburrowing individuals occurred within 90 s of initiation of flow. Burrowing individuals were not eroded. The decision as to the acceptability of a sediment was made within 30 s. These data imply that
Synopsis Biogenic forces alter sediment characteristics along several axes with important consequ... more Synopsis Biogenic forces alter sediment characteristics along several axes with important consequences for structure of benthic communities. The usual axes discussed are those of sediment stabilization versus resuspension and mobile versus temporally persistent organisms. A third axis of bioadvection is typically subsumed within the others. Here we argue that given the complex fluid dynamics resulting from the bidirectional forces that organisms exert on porewater, bioadvection needs to be examined separately. The probable major players in generation of bioadvection are described with impacts on transport both of materials and heat. Illustrations are given of the bidirectionality of bioadvection and the resultant changes in oxygenation either surficially or at depth, as well as of heat transport both laterally within the sediment and vertically.
The symbiosis with zooxanthellae among tridacnid bivalve molluscs has been examined in order to a... more The symbiosis with zooxanthellae among tridacnid bivalve molluscs has been examined in order to assess the morphological relation of the algae to the hosts' tissues and the dynamics of the interactions between the algae and the clams. Light and electron microscopic evidence indicates that the zooxanthellae located in the haemal sinuses of the hypertrophied siphon are intercellular in all six tridacnid species studied. The algae pass from the siphonal tissues to the alimentary tract from which they are voided as feces. Many of the defecated symbionts are morphologically intact and photosynthetically functional. The concretions in the kidneys of tridacnids, previously thought to be the indigestible remains of zooxanthellae, are identified as phosphorite deposits, which are not unique to tridacnids. Analyses of photosynthesis-radiant flux relations in Tridacna maxima indicate that over 24 h the algae produce more oxygen than is consumed by the association, and estimates suggest that the algae may contribute more than 50% of the animals' metabolic carbon requirements.
Catastrophe, Extinction, and Species Diversity: A Rocky Intertidal Example
Ecology, Apr 1, 1985
Geographically widespread episodes of catastrophic mortality affect local species di- versity. Se... more Geographically widespread episodes of catastrophic mortality affect local species di- versity. Sea ice has been a frequent catastrophic mortality agent on rocky shores in New England during the historical past. Empirical demographic data and the historical record of winters with sea ice were used in a population projection model of intertidal barnacles. Projections indicate that animals that live exclusively in the zone affected by ice would have become extinct under the conditions of sea ice disturbance that have existed in New England during the past 300 yr. This may explain the absence from New England of abundant, large, long-lived species with delayed reproduction that are restricted to the mid to low intertidal zone. Such species are common elsewhere in the world on shores unaffected by ice. Given the cyclic nature of the postglacial climate, global patterns of species richness may be influenced by climatically induced extinction pressures of this kind.
The physicochemical environment can strongly constrain the outcome of ecological interactions suc... more The physicochemical environment can strongly constrain the outcome of ecological interactions such as predation, mating, and competition. This is especially true of processes mediated by the sense of olfaction, because wind and water currents control the dispersal of odor signals and act as ancillary cues during odor plume following. In the field, we examined how variations in the physical and chemical properties of odor plumes would alter the foraging behavior of the blue crab Callinectes sapidus, a common predator/ scavenger in tidal marsh creeks in the southeastern United States. We video-recorded responses of naturally foraging crabs to odor plumes of varying composition and odor release rate (characteristic of clams of differing size). During each trial we presented crabs with an experimental plume that was a mixture of fluorescein-dyed seawater and clam mantle fluid, oyster mantle fluid, or a suite of amino acids, and a control plume which consisted of dyed seawater only. In addition to manipulating the chemical composition and odor release rate of the plume, we allowed flow speed to vary naturally with the tide. We tested for effects of odor composition, odor release rate, and flow speed on the success (i.e., finding the target) and efficiency (i.e., search path direction) of blue crab foraging. Mantle fluid solutions and wounded prey items elicited active search and upstream walking, while control and amino acid solutions had no effect on crab behavior. Odors released at a low rate (either low volume flow or low concentration) elicited fewer responses from crabs, and the resulting search was less efficient and less successful than responses to odors released at higher rates. Ambient current speed also affected both search success and efficiency. There was a decline in search success when current speed in the tidal channel was below 1 cm/s; search success remained constantly high, however, when current speed was above this threshold. Search efficiency was directly proportional to ambient current speeds. Such relationships between hydrodynamic and chemical properties of the environment and foraging success and efficiency suggest that variation in the physicochemical environment can influence the detectability of prey and strategies employed by foragers. These results extend beyond the foraging of marine crustaceans into other olfactorymediated interactions and habitats.
The ECOSTRESS multi-channel thermal radiometer on the Space Station has an unprecedented spatial ... more 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.
Ocean warming and acidification affect species populations, but how interactions within communiti... more Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remains poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioral plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam's feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most likely due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioral changes of key species.
Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to... more Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to the cooler sea temperatures associated with them. It has been suggested that global warming could lead to enhanced sea surface cooling in EBUS via the intensification of upwelling-favorable winds. Conversely, increased stratification and the widespread warming of the world's oceans could drive these systems in the opposite direction. These competing mechanisms hold the potential for driving the thermal envelopes of EBUS toward -or away from -the thermal envelopes found outside EBUS, with likely contrasting implications for biodiversity conservation in each scenario. Here we characterize the patterns of net sea surface warming rates over more than three decades throughout the global ocean to evaluate if waters inside EBUS are changing differently from those outside EBUS. Results point to a trend of reduced warming inside EBUS, especially along the nearshore. We found that reduced net warming was prevalent in Pacific EBUS but restricted in Atlantic EBUS. In contrast, net warming in the coastal ocean outside EBUS was pervasive and generally associated with proximity to land. Our results suggest that EBUS have been responding to climate change differently from the rest of the global ocean, potentially buffering coastal biomes from decades of global warming.
Intertidal organisms are often assumed to live close to their thermal limits, and have emerged as... more Intertidal organisms are often assumed to live close to their thermal limits, and have emerged as potential early indicators of the effects of climate change. We compared our survey of the 2004-2006 geographic distribution of the barnacle Semibalanus
Journal of Experimental Marine Biology and Ecology, Mar 1, 2000
This study investigates how the presence of symbiotic crabs (Pinnixa chaetopterana or Polyonyx gi... more This study investigates how the presence of symbiotic crabs (Pinnixa chaetopterana or Polyonyx gibbesi) in the tubes of the polychaete Chaetopterus variopedatus affects the worms' pumping activity and growth rates under laboratory and field conditions. In the field, worms whose tubes are inhabited by Pinnixa beat their fan segments significantly more frequently than do worms hosting Polyonyx, but other measures of pumping activity do not differ according to symbiont species. In the lab, worms tend to move water through their tubes at higher rates when crabs are present. In 7-month laboratory experiments, growth rates of worms hosting either species of crab did not differ from growth rates of worms without crab symbionts. Although worms hosting Polyonyx are, on average, significantly larger than worms hosting Pinnixa, this appears to be due to competition between the crab species for hosts and not due to differential effects on host growth. Unlike the crabs in this study, pea crab species inhabiting bivalves are known to have strong deleterious effects on host growth and reproduction, suggesting that the evolution of virulence in symbiotic interactions is dependent upon specific ecological context.
Aim Ecosystem engineering polychaetes in the genus Diopatra are undergoing range shifts in wester... more Aim Ecosystem engineering polychaetes in the genus Diopatra are undergoing range shifts in western Europe. Here we: (1) assess the species diversity underlying these shifts; (2) link biogeographic patterns to sea surface temperature patterns; and (3) predict possible ecosystem-level outcomes of Diopatra's northward expansion. Methods We use molecular phylogenetic and morphological evidence to assess species diversity and biogeographic ranges. Using regression tree analyses, we assess thermal limits for two Diopatra species. We compare biogeographic patterns with historical sea surface temperature patterns to draw links between range shifts and climate change. Finally, we review published data to predict potential ecological changes as Diopatra invades new habitats. The native Diopatra neapolitana range has contracted 130 km to the south. A cryptogenic species, Diopatra sp. A, has extended the northern limit of the genus 350 km to the southern Brittany Peninsula. Both shifts can be explained by historical sea surface temperature anomalies. The Diopatra sp. A expansion is predicted to continue into the English Channel and the North Sea, introducing large tube structures to sheltered sedimentary habitats that currently lack such structures. As climate change intensifies, the sediment-stabilizing Diopatra sp. A will invade habitats dominated by the bioturbating lugworm Arenicola marina. The resulting interaction between functionally different ecosystem engineers will probably cause ecological changes in northern European coastal waters. Existing data for Diopatra species and arenicolids suggest that the diversity and biomass of macroalgae, vascular plants, infauna and epibenthic fauna may increase, while microbial activity may decrease. Net changes in productivity will depend on the relative rates of these changes.
The interactions between the intertidal barnacles Semibalanus (Balanus) balanoides and Chthamalus... more The interactions between the intertidal barnacles Semibalanus (Balanus) balanoides and Chthamalus fragilis were examined in order to determine whether the factors which influence local zonation in the intertidal also contribute to the establishment of geographic limits. Both physical and biotic factors influence intertidal zonation at the northern limit of Chthamalus in New England. On sloping surfaces Semibalanus died at all shore levels higher than mid tide level, apparently as a result of desiccation associated with high summer temperatures. Chthamalus settlement occurred at all shore levels above mean tide level, and postsettlement mortality apparently restricts Chthamalus to high shore locations where Semibalanus growth and survival is inhibited. North of the northern limit of Chthamalus, Semibalanus does not suffer summer heat death, so it occupies the zone where Chthamalus would have a refuge from competition further south. The northern limit of Chthamalus is set not by factors directly related to cold acting on Chthamalus. Rather the northern limit appears to be set by cold which allows the dominant competitor to exclude Chthamalus from its refuge zone. South of the northern limit the competitor, Semibalanus, is excluded from the high shore by high summer temperatures.
In the following decade(s), a set of satellite missions carrying thermal infrared (TIR) imagers w... more In the following decade(s), a set of satellite missions carrying thermal infrared (TIR) imagers with a relatively high noise equivalent differential temperature (NEdT) are expected, e.g., the high resolution TIR imagers flying on the future Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment (TRISHNA), Land Surface Temperature Monitoring (LSTM) and NASA-JPL/ASI Surface Biology and Geology Thermal (SBG) missions or the secondary payload on board the ESA Earth Explorer 10 Harmony. The instruments on board these missions are expected to be characterized by an NEdT of 0.1 K. In order to reduce the impact of radiometric noise on the retrieved sea surface temperature (SST), this study investigates the possibility of applying a multi-pixel atmospheric correction based on the hypotheses that (i) the spatial variability scales of radiatively active atmospheric variables are, on average, larger than those of the SST and (ii) the effect of atmosphere is accounted for via the split window (SW) difference. Based on 32 Sentinel 3 SLSTR case studies selected in oceanic regions where SST features are mainly driven by meso to sub-mesoscale turbulence (e.g., corresponding to major western boundary currents), this study documents that the local spatial variability of the SW difference term on the scale of 3 × 3 km 2 is comparable with the noise associated with the SW difference. Similarly, the power spectra of the SW term are shown to have, for small scales, the behavior of white noise spectra. On this basis, we suggest to average the SW term and to use it for the atmospheric correction procedure to reduce the impact of radiometric noise. In principle, this methodology can be applied on proper scales that can be dynamically defined for each pixel. The applicability of our findings to high-resolution TIR missions is discussed and an example of an application to ECOSTRESS data is reported.
Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We exp... more Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We expected these activities to generate low-frequency pressure waves that would propagate through sediments and be detectable at some distance from the source. Pressure sensors in intertidal sediments recorded large-amplitude porewater pressure signals. Laboratory recordings of single individuals allowed us to identify characteristic signals of arenicolid and nereidid polychaetes and tellinid bivalves. In the bivalve Macoma nasuta, these high-amplitude signals were associated with burrowing, expulsion of pseudofeces, and siphon relocation. In the polychaetes Neanthes brandti and Abarenicola pacifica, the high-amplitude pressure signals were associated with burrowing, burrow construction, burrow ventilation, and defecation. These signals were detectable in the field at distances of at least 20 cm. Since the waveforms are species-specific as well as activity-specific, they may provide a mechanism for prey detection, for predator avoidance, for competitor detection, and perhaps even for mate detection.
In marine sediments, many of the processes associated with high post-settlement mortality of infa... more In marine sediments, many of the processes associated with high post-settlement mortality of infauna have similar effects on the sediment surface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments reported here tested the ability of new juvenile infauna to discriminate between undisturbed and recently disturbed sediment surfaces (i.e.. subsurface sediment exposed). Recently settled juveniles of two polychaete species (Nereis vexillosa and Arenicola cristata) and one bivalve species (Alercenaria mercenaria) were exposed to simulated erosional and mixing events as well as to fresh feces. burrow tailings, and feeding tracks. Where the disturbance buried or removed several millimeters of the sediment surface, the time to initiate burrowing or the percentage of individuals failing to burrow increased significantly over times and percentages for juveniles on undisturbed surfaces. In all cases the results were consistent with the hypothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old. For example. 51% of nereid juveniles did not burrow when placed on subsurface sediments, whereas 100% burrowed into surface sediments; their average burrowing time on surface sediments was 29.3s compared with 109.7s on fecal mounds of arenicolid polychaetes or 106.1 s on burrow tailings ofthalassinid crustaceans. Individuals that did not indicate acceptance of a sediment surface by burrowing were all rapidly eroded from the surface in the presence of flow. Erosion of nonburrowing individuals occurred within 90 s of initiation of flow. Burrowing individuals were not eroded. The decision as to the acceptability of a sediment was made within 30 s. These data imply that
Synopsis Biogenic forces alter sediment characteristics along several axes with important consequ... more Synopsis Biogenic forces alter sediment characteristics along several axes with important consequences for structure of benthic communities. The usual axes discussed are those of sediment stabilization versus resuspension and mobile versus temporally persistent organisms. A third axis of bioadvection is typically subsumed within the others. Here we argue that given the complex fluid dynamics resulting from the bidirectional forces that organisms exert on porewater, bioadvection needs to be examined separately. The probable major players in generation of bioadvection are described with impacts on transport both of materials and heat. Illustrations are given of the bidirectionality of bioadvection and the resultant changes in oxygenation either surficially or at depth, as well as of heat transport both laterally within the sediment and vertically.
The symbiosis with zooxanthellae among tridacnid bivalve molluscs has been examined in order to a... more The symbiosis with zooxanthellae among tridacnid bivalve molluscs has been examined in order to assess the morphological relation of the algae to the hosts' tissues and the dynamics of the interactions between the algae and the clams. Light and electron microscopic evidence indicates that the zooxanthellae located in the haemal sinuses of the hypertrophied siphon are intercellular in all six tridacnid species studied. The algae pass from the siphonal tissues to the alimentary tract from which they are voided as feces. Many of the defecated symbionts are morphologically intact and photosynthetically functional. The concretions in the kidneys of tridacnids, previously thought to be the indigestible remains of zooxanthellae, are identified as phosphorite deposits, which are not unique to tridacnids. Analyses of photosynthesis-radiant flux relations in Tridacna maxima indicate that over 24 h the algae produce more oxygen than is consumed by the association, and estimates suggest that the algae may contribute more than 50% of the animals' metabolic carbon requirements.
Catastrophe, Extinction, and Species Diversity: A Rocky Intertidal Example
Ecology, Apr 1, 1985
Geographically widespread episodes of catastrophic mortality affect local species di- versity. Se... more Geographically widespread episodes of catastrophic mortality affect local species di- versity. Sea ice has been a frequent catastrophic mortality agent on rocky shores in New England during the historical past. Empirical demographic data and the historical record of winters with sea ice were used in a population projection model of intertidal barnacles. Projections indicate that animals that live exclusively in the zone affected by ice would have become extinct under the conditions of sea ice disturbance that have existed in New England during the past 300 yr. This may explain the absence from New England of abundant, large, long-lived species with delayed reproduction that are restricted to the mid to low intertidal zone. Such species are common elsewhere in the world on shores unaffected by ice. Given the cyclic nature of the postglacial climate, global patterns of species richness may be influenced by climatically induced extinction pressures of this kind.
The physicochemical environment can strongly constrain the outcome of ecological interactions suc... more The physicochemical environment can strongly constrain the outcome of ecological interactions such as predation, mating, and competition. This is especially true of processes mediated by the sense of olfaction, because wind and water currents control the dispersal of odor signals and act as ancillary cues during odor plume following. In the field, we examined how variations in the physical and chemical properties of odor plumes would alter the foraging behavior of the blue crab Callinectes sapidus, a common predator/ scavenger in tidal marsh creeks in the southeastern United States. We video-recorded responses of naturally foraging crabs to odor plumes of varying composition and odor release rate (characteristic of clams of differing size). During each trial we presented crabs with an experimental plume that was a mixture of fluorescein-dyed seawater and clam mantle fluid, oyster mantle fluid, or a suite of amino acids, and a control plume which consisted of dyed seawater only. In addition to manipulating the chemical composition and odor release rate of the plume, we allowed flow speed to vary naturally with the tide. We tested for effects of odor composition, odor release rate, and flow speed on the success (i.e., finding the target) and efficiency (i.e., search path direction) of blue crab foraging. Mantle fluid solutions and wounded prey items elicited active search and upstream walking, while control and amino acid solutions had no effect on crab behavior. Odors released at a low rate (either low volume flow or low concentration) elicited fewer responses from crabs, and the resulting search was less efficient and less successful than responses to odors released at higher rates. Ambient current speed also affected both search success and efficiency. There was a decline in search success when current speed in the tidal channel was below 1 cm/s; search success remained constantly high, however, when current speed was above this threshold. Search efficiency was directly proportional to ambient current speeds. Such relationships between hydrodynamic and chemical properties of the environment and foraging success and efficiency suggest that variation in the physicochemical environment can influence the detectability of prey and strategies employed by foragers. These results extend beyond the foraging of marine crustaceans into other olfactorymediated interactions and habitats.
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