Articles

Published journal articles by MLML faculty, staff and students. Full text is included when copyright allows.


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Variability in per capita oogonia and sporophyte production from giant kelp gametophytes (Macrocystis pyrifera, Phaeophyceae)
Variability in per capita oogonia and sporophyte production from giant kelp gametophytes (Macrocystis pyrifera, Phaeophyceae)
Vegetative growth and fertility of kelp gametophytes are thought to be antagonistic, such that most successful kelp recruitment is assumed to result from fertilization of single oogonia released from unicellular female gametophytes. We used laboratory culture experiments to study the effect of temperature and nutrient addition on the per capita production of oogonia and sporophytes from Macrocystis pyrifera female gametophytes. Our results indicate that individual multicellular female gametophytes can give rise to more than one oogonium and that per capita oogonia production significantly increases with the enhancement of culture conditions (i.e., decreased temperature and increased nutrient concentration). Furthermore, the production of multiple oogonia per female often led to the production of multiple sporophytes per female. We discuss the importance of these results relative to variability in M. pyrifera life histories (e.g., annual vs. perennial) and their likely ecological and evolutionary consequences., Cited By (since 1996):11, Seaweeds
Variability in reactions of Pacific harbor seals, Phoca vitulina richardsi, to disturbance
Variability in reactions of Pacific harbor seals, Phoca vitulina richardsi, to disturbance
Disturbances to harbor seals, Phoca vitulina richardsi, during 1991 and 1992 pupping seasons were observed at Puffin Island, Clements Reef, and Skipjack Island in Washington state. Harassment (≥ one seal entering the water) of seals ashore was common (≥71% of survey days) and primarily caused by powerboat operators approaching to observe seals. Recovery (number of seals on a haul-out site returned to preharassment levels) following a harassment was less at Puffin Island (19%) than at Clements Reef (54%) and Skipjack Island (45%). Additionally, seals were more vigilant (P<0.003) at Puffin Island than at the other two locations. These results indicated that seals at Puffin Island were less tolerant of disturbance than seals at other sites. This could possibly be attributed to a greater (P<0.05) percentage of pups ashore (17%) than at Clements Reef (3%) and Skipjack Island (3%). Because of this, we expected that powerboats would disturb seals from greater distances at Puffin Island. To test this, we used a theodolite to determine distance between seals and an approaching vessel at Puffin Island and Clements Reef. There was, however, no significant (P>0.05) difference in distances at which disturbances occurred. The most notable difference in distance of disturbance was between initial and subsequent harassments during a haul-out period. Those seals remaining or returning to shore after a harassment were more tolerant of powerboats, allowing significantly (P<0.05) closer approaches than those initially harassed. Seals detected (head raised and oriented toward the potential disturbance) a powerboat at a mean distance of 264 m, and harassments occurred when boats approached, on average, to within 144 m. Results of this study exemplify the variability in reaction to disturbance and the necessity for considering these differences for minimizing disturbance., Cited By (since 1996):29, CODEN: FSYBA, Marine Mammals, Birds & Turtles Harbor Seals
Variability of Euphausia superba populations near Elephant Island and the South Shetlands: 1981 vs. 1984
Variability of Euphausia superba populations near Elephant Island and the South Shetlands: 1981 vs. 1984
March 1981 and 1984 Euphausia superba populations were compared using acoustics and net catches near Elephant Island, the South Shetlands, and in the Bransfield Strait. In 1981, krill tended to form large, thick swarms and in 1984, smaller, more dispersed, shallower patches. March body lengths of juvenile-adult krill were 22-59 mm in 1981 and 13-59 mm in 1984. Near Elephant I. in 1981, krill >45 mm were most numerous; in 1984 sizes <45 mm were dominant. In March 1984, the larger (>45 mm) body-size group was prereproductive and occurred from just west of Elephant I. westward into waters north of the South Shetlands; in 1981 the larger krill were postreproductive and more widely distributed in the Elephant I. area. Overall, netted postlarval krill, 1981 vs. 1984, averaged 73 vs. 48 individuals/m2, or 54 vs. 16 g/m2; acoustic biomass estimates were 229 vs. 134-201 g/m2. Larvae near Elephant I. averaged >2000/m2 in 1981 vs. <1/m2 in 1984-compatible with respective March reproductive states. Net-type comparisons revealed short-term (15 min to 6h) variability of a similar scale in both MOCNESS and bongo net catches, but bongo abundances averaged greater. Variation in maturity composition across 1981 swarms, patches, and random transects was like variation among the random 1984 tows; spatial distributions were more heterogeneous in 1984. The March 1984 krill of 20-44 mm (Year-2, mode 34 mm) relate to November 1983 krill of 9-30 mm (mode 21 mm), indicating growth averaging 12 mm during the season. Body-lengths and size-frequency modes of Year-2 and combined Years-3,3+ krill from comparable Feb-Mar data collected since 1968 suggest trends between times when (1) Year-2 krill average small and peak reproduction seems to be late in the season and/or weak (1979, 1982-1984), and (2) Year-2 krill are larger, and reproduction is possibly earlier and more successful (1976, 1980, 1981). © 1987 Springer-Verlag., Cited By (since 1996):9, CODEN: POBID
Variability of upper ocean thermohaline structure during a MJO event from DYNAMO aircraft observations
Variability of upper ocean thermohaline structure during a MJO event from DYNAMO aircraft observations
This paper reports upper ocean thermohaline structure and variability observed during the life cycle of an intense Madden Julian Oscillation (MJO) event occurred in the southern tropical Indian Ocean (14°S-Eq, 70°E-81°E). Water column measurements for this study were collected using airborne expendable probes deployed from NOAA's WP-3D Orion aircraft operated as a part of Dynamics of MJO field experiment conducted during November-December, 2011. Purpose of the study is twofold; (1) to provide a statistical analysis of the upper ocean properties observed during different phases of MJO and, (2) to investigate how the upper ocean thermohaline structure evolved in the study region in response to the MJO induced perturbation. During the active phase of MJO, mixed layer depth (MLD) had a characteristic bimodal distribution. Primary and secondary modes were at ∼ 34 m and ∼ 65 m respectively. Spatial heterogeneity of the upper ocean response to the MJO forcing was the plausible reason for bimodal distribution. Thermocline and isothermal layer depth deepened respectively by 13 m and 19 m from the suppressed through the restoring phase of MJO. Thicker (> 30 m) barrier layers were found to occur more frequently in the active phase of MJO, associated with convective rainfalls. Additionally, the water mass analysis indicated that, in the active phase of this MJO event the sub-surface was dominated by Indonesian throughflow, nonetheless intrusion of Arabian Sea high saline water was also noted near the equator.
Variable effects of a kelp foundation species on rocky intertidal diversity and species interactions in central California
Variable effects of a kelp foundation species on rocky intertidal diversity and species interactions in central California
The effect of foundation species on community assemblages in physically stressful environments has received much recent attention because of the importance of foundation species in ameliorating environmental stress. Many studies have described variable effects of foundation species on community diversity at small scales, but net positive effects over large scales. Egregia menziesii (Turner) J.E. Areschoug is a large and robust perennial kelp that creates a structurally complex habitat on rocky shores of the Northeast Pacific. This study investigated the effects of Egregia sporophytes on benthic assemblages of the rocky intertidal along the central California coast. Egregia sporophytes strongly impacted the structure of associated communities, due to wave-driven whiplash of fronds, shading, or habitat provision. A survey of Egregia populations at 10 stations along 200. km of the central California coast found effects of Egregia density on the intertidal to be consistent among sites. Increased Egregia sporophyte density negatively affected algal species richness, total algal cover, and cover of the most conspicuous species of algae. However, there was a positive relationship with algal crusts, geniculate coralline algae, and sessile invertebrates. Egregia removal experiments at two sites within the study area experimentally tested for the effects of Egregia on intertidal communities. Results from Soberanes Pt. were consistent with survey results because of the negative effect of Egregia on algal species diversity, subcanopy layering, and cover of abundant algal species. However, removal experiments at Pigeon Pt. resulted in a positive Egregia effect on algal diversity and cover of abundant algal species possibly due to lower Egregia densities, lower wave exposure than Soberanes Pt., and stress amelioration. In the lower energy environment, Egregia acted as a sand trap, yet sand accumulation did not negatively impact algal diversity. Negative effects of large brown algae on benthic assemblages have been observed in temperate waters around the world for certain intertidal or subtidal kelp in wave-swept environments allowing for scouring and substrate shading. This study shows that Egregia and morphologically similar brown algal species can have both negative and positive effects on community diversity depending on variation in density and local environmental conditions. Egregia has the opposite effect on community diversity than what has been previously reported for foundation species because it negatively affects biodiversity in stressful environments, but has a positive effect in less stressful environments. © 2010 Elsevier B.V., Cited By (since 1996):3, CODEN: JEMBA, Seaweeds
Variable responses of temperate calcified and fleshy macroalgae to elevated pCO2 and warming
Variable responses of temperate calcified and fleshy macroalgae to elevated pCO2 and warming
Anthropogenic carbon dioxide (CO2) emissions simultaneously increase ocean temperatures and reduce ocean surface pH, a process termed ocean acidification (OA). OA is expected to negatively affect the growth and physiology of many calcified organisms, but the response of non-calcified (fleshy) organisms is less well understood. Rising temperatures and pCO2 can enhance photosynthetic rates (within tolerance limits). Therefore, warming may interact with OA to alter biological responses of macroalgae in complicated ways. Beyond thresholds of physiological tolerance, however, rising temperatures could further exacerbate negative responses to OA. Many studies have investigated the effects of OA or warming independently of each other, but few studies have quantified the interactive effects of OA and warming on marine organisms. We conducted four short-term independent factorial CO2 enrichment and warming experiments on six common species of calcified and fleshy macroalgae from southern California to investigate the independent and interactive effects of CO2 and warming on growth, carbonic anhydrase (CA) enzyme activity, pigment concentrations, and photosynthetic efficiency. There was no effect of elevated pCO2 on CA activity, pigment concentration, and photosynthetic efficiency in the macroalgal species studies.However,we found that calcareous algae suffered reduced growth rates under high pCO2 conditions alone, although the magnitude of the effect varied by species. Fleshy algae had mixed responses of growth rates to high pCO2, indicating that the effects of pCO2 enrichment are inconsistent across species. The combined effects of elevated pCO2 and warming had a significantly negative impact on growth for both fleshy and calcareous algae; calcareous algae experienced five times more weight loss than specimens in ambient control conditions and fleshy growth was reduced by 76%. Our results demonstrate the need to study the interactive effects of multiple stressors associated with global change on marine communities., http://icesjms.oxfordjournals.org/content/early/2015/09/25/icesjms.fsv168.abstract, Advanced view
Variation in Responses of Fishes across Multiple Reserves within a Network of Marine Protected Areas in Temperate Waters
Variation in Responses of Fishes across Multiple Reserves within a Network of Marine Protected Areas in Temperate Waters
Meta-analyses of field studies have shown that biomass, density, species richness, and size of organisms protected by no-take marine reserves generally increase over time. The magnitude and timing of changes in these response variables, however, vary greatly and depend upon the taxonomic groups protected, size and type of reserve, oceanographic regime, and time since the reserve was implemented. We conducted collaborative, fishery-independent surveys of fishes for seven years in and near newly created marine protected areas (MPAs) in central California, USA. Results showed that initially most MPAs contained more and larger fishes than associated reference sites, likely due to differences in habitat quality. The differences between MPAs and reference sites did not greatly change over the seven years of our study, indicating that reserve benefits will be slow to accumulate in California's temperate eastern boundary current. Fishes in an older reserve that has been closed to fishing since 1973, however, were significantly more abundant and larger than those in associated reference sites. This indicates that reserve benefits are likely to accrue in the California Current ecosystem, but that 20 years or more may be needed to detect significant changes in response variables that are due to MPA implementation. Because of the high spatial and temporal variability of fish recruitment patterns, long-term monitoring is needed to identify positive responses of fishes to protection in the diverse set of habitats in a dynamic eastern boundary current. Qualitative estimates of response variables, such as would be obtained from an expert opinion process, are unlikely to provide an accurate description of MPA performance. Similarly, using one species or one MPA as an indicator is unlikely to provide sufficient resolution to accurately describe the performance of multiple MPAs.
Variation in marine benthic community composition allows discrimination of multiple stressors
Variation in marine benthic community composition allows discrimination of multiple stressors
Predicting how communities respond to multiple, potentially interacting chemical stressors is inherently difficult because community structure and dynamics, the chemical properties of contaminants, and biological-chemical interactions vary with environmental conditions. Using a field experiment conducted in Antarctica, we tested whether 3 phyla of benthic soft-sediment marine invertebrates - annelids, arthropods, and echinoderms - respond differently to 2 common forms of contamination, organic enrichment and toxic contamination. Based on life history strategies and physiological tolerances to contaminants, we hypothesized that the principal responses of the 3 phyla would be: (1) enhanced abundance of annelids in organically enrichment sediments and (2) decreased abundance of arthropods and echinoderms in toxic metal contamination. Sediment treatments were established in the field experiment with an orthogonal combination of 3 levels of total organic carbon (TOC; 0, 1, and 2% by weight) and copper (Cu; 0, 100, and 500 μg Cu g-1 sediment), and colonization patterns were observed after 1 yr. Densities of annelids (mainly polychaetes) increased with TOC across all levels of Cu. Arthropods and echinoderms decreased with Cu, but responded variably to TOC, based largely on differences in habitat preferences exhibited by epifaunal and infaunal species. Small subsurface arthropod species (amphipods, isopods, cumaceans, and ostracods) decreased in high organic loading, due to induction of and exposure to hypoxia and hydrogen sulfide, but large surface deposit-feeding echinoderms (asteroids and echinoids) responded positively to increased carbon food supply. We present a predictive model based on assessment of benthic community structure conducted at the taxonomic level of phyla that could be used to link cause and effect for multiple chemical stressors in marine ecosystems., Cited By (since 1996):36, CODEN: MESED, Antarctica
Variation in the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands during the 1999/2000 austral summer
Variation in the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands during the 1999/2000 austral summer
Vessels from Japan, Peru, and the USA conducted four sequential surveys designed to estimate the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands between late December 1999 and early March 2000. The surveys were conducted during the same austral summer as the CCAMLR 2000 Survey in the Scotia Sea (Watkins et al., Deep-Sea Research, II, this issue [doi: 10.1016/j.dsr2.2004.06.010]), and the data were analyzed in a similar manner. Biomass densities were not significantly different between the surveys and averaged 49 g m -2. Maps of krill biomass indicate three areas of consistently high density: one near the eastern end of Elephant Island, one mid-way between Elephant Island and King George Island, and one near Cape Shirreff on the north side of Livingston Island. The areas of highest krill density appeared to move closer to the shelf break as the season progressed. This apparent movement was accompanied by a change in the demographic structure of the population, with smaller krill absent and a larger proportion of sexually mature animals present in late summer., Cited By (since 1996):8, CODEN: DSROE, Antarctica
Variations in the biomass of Antarctic krill (Euphausia superba) around the South Shetland Islands, 1996-2006
Variations in the biomass of Antarctic krill (Euphausia superba) around the South Shetland Islands, 1996-2006
The time-series of acoustically surveyed Antarctic krill (Euphausia superba) biomass near the South Shetland Islands (SSI) between 1996 and 2006 is re-estimated using a validated physics-based model of target strength (TS), and a species-discrimination algorithm based on the length-range of krill in plankton samples to identify krill acoustically, derived from TS-model predictions. The SSI area is surveyed each austral summer by the US Antarctic Marine Living Resources Program, and the acoustic data are used to examine trends in krill biomass and to assess the potential impact of fishing to the reproductive success of land-based predators (seals and penguins). The time-series of recomputed biomass densities varies greatly from that computed using an empirical log-linear TS-model and fixed-ranges of differences in volume-backscattering strengths (ΔS v), conventionally used to identify krill acoustically. The new acoustic estimates of biomass are significantly correlated with both proportional recruitment and krill abundance estimated from zooplankton samples. Two distinct peaks in biomass (1996 and 2003) are in accord with recruitment events shown by net-based krill time-series. The foundation for the new TS-model and the associated krill-discrimination algorithm, coupled with the agreement between acoustic- and net-survey results, provides strong support for the use of the new analytical technique. Variable biases in the re-estimated krill biomass have been greatly reduced. However, survey variability increased as a result of the increased rejection of acoustic backscatter previously attributed to krill. Management of Southern Ocean krill stocks based on a precautionary approach may therefore result in decreased allocations of krill, given its dependence on the variability of survey estimates. © 2008 US Government and the Department of Commerce/National Oceanic and Atmospheric Administration/National Marine Fisheries Service/Southwest Fisheries Science Center., Cited By (since 1996):41, CODEN: ICESE, Antartica
Vector-sensor beamforming for autonomous glider networks
Vector-sensor beamforming for autonomous glider networks
Detection and localization of sound sources in an ocean environment can be achieved with a distributed array of passive acoustic sensors. Utilizing an array of autonomous littoral gliders, which offer long-term and quiet operation, and vector sensors, which measure both acoustic pressure and particle velocity, the array's localization performance can be improved. However, vector sensors are susceptible to errors induced by acoustic noise, and autonomous gliders as a sensor platform introduce positional errors. Through both simulations and at-sea data, the localization performance of four processing methods are evaluated under various noisy conditions. In both simulated and at-sea data results, a new cross-coherent method outperforms traditional methods by mitigating the effects of acoustic noise, provided sufficient positional accuracy of the array elements.
Vent fluid chemistry in Bahía Concepción coastal submarine hydrothermal system, Baja California Sur, Mexico
Vent fluid chemistry in Bahía Concepción coastal submarine hydrothermal system, Baja California Sur, Mexico
Shallow submarine hydrothermal activity has been observed in the Bahía Concepción bay, located at the Gulf coast of the Baja California Peninsula, along faults probably related to the extensional tectonics of the Gulf of California region. Diffuse and focused venting of hydrothermal water and gas occurs in the intertidal and shallow subtidal areas down to 15 m along a NW-SE-trending onshore-offshore fault. Temperatures in the fluid discharge area vary from 50 °C at the sea bottom up to 87 °C at a depth of 10 cm in the sediments. Chemical analyses revealed that thermal water is enriche d in Ca, As, Hg, Mn, Ba, HCO3, Li, Sr, B, I, Cs, Fe and Si, and it has lower concentrations of Cl, Na, SO4 and Br than seawater. The chemical characteristics of the water samples indicate the occurrence of mixing between seawater and a thermal end-member. Stable isotopic oxygen and hydrogen composition of thermal samples plot close to the Local Meteoric Water Line on a mixing trend between a thermal end-member and seawater. The composition of the thermal end-member was calculated from the chemistry of the submarine samples data by assuming a negligible amount of Mg for the thermal end-member. The results of the mixing model based on the chemical and isotopic composition indicate a maximum of 40% of the thermal end-member in the submarine vent fluid. Chemical geothermometers (Na/Li, Na-K-Ca and Si) were applied to the thermal end-member concentration and indicate a reservoir temperature of approximately 200 °C. The application of K-Mg and Na/Li geothermometers for vent fluids points to a shallow equilibrium temperature of about 120 °C. Results were integrated in a hydrogeol ogical conceptual model that describes formation of thermal fluids by infiltration and subsequent heating of meteoric water. Vent fluid is generated by further mixing with seawater. © 2004 Elsevier B.V. All rights reserved., Cited By (since 1996):39
Vertex: Phytoplankton/iron studies in the Gulf of Alaska
Vertex: Phytoplankton/iron studies in the Gulf of Alaska
VERTEX studies were performed in the Gulf of Alaska in order to test the hypothesis that iron deficiency was responsible for the phytoplankton's failure to remove major plant nutrients from these waters. In view of the observed Fe distributions and the results of phytoplankton Fe enrichment experiments, it was concluded that Gulf of Alaska atmospheric Fe input rates are sufficient to support moderately high rates of primary productivity; however, not enough Fe is available to support the high growth rates that would lead to normal major nutrient depletion. Enhanced Fe input does occur along the Alaska continental margin, where normal NO 3 surface depletion is observed. Coccolithophorids appear to be best able to cope with low Fe conditions; however, they cannot compete with diatoms when Fe is readily available. Iron may be more important than available N in determining global rates of phytoplankton new production. Offshore Pacific Ocean water, replete with major nutrients, appears to be infertile without supplemental iron from the atmosphere or continental margin. © 1989., Cited By (since 1996):399
Vertical concentration profiles of lead in the Central Pacific at 15°N and 20°S
Vertical concentration profiles of lead in the Central Pacific at 15°N and 20°S
Concentrations of lead were measured in a surface transect and at two vertical profile stations (15°N and 20°S) in the Central Pacific. These measurements complement similar measurements made earlier in the North Pacific at 33°N and in the Northwest Atlantic at 34°N [1,2], as well as recent measurements of eolian lead input fluxes near each of these locations [3]. The new transect of surface water concentrations of lead corroborates previous measurements, which decrease from 13 ng/kg at 30°N to 4 ng/kg at 17°S in the Central Pacific [4]. This transect gradient is shown to overlie a similar geographic gradient of subsurface maximum concentrations of lead in the three Pacific vertical profile stations, decreasing from 14 ng/kg at 33°N to 11 ng/kg at 14°N to 2.5 ng/kg at 20°S. Lead concentrations at each of those locations exhibit maxima at 400 m, decreasing concentrations to 2500 m and approximately concentrations of 0.8-1.1 ng/kg below that depth. The subsurface maximum at the northwest Atlantic profile station (36 ng/kg at 34°N) is also congruent with surface water lead concentrations which decrease from 806 ng/kg to 32 ng/kg in an offshore transect from Rhode Island to 34°N, 66°W [5], and the shape of the Atlantic profile is congruent with those in the Pacific. There is a positive correlation between the magnitudes of eolian lead input fluxes and the magnitudes of the upper water maxima in lead concentration profiles at corresponding locations as follows: South Pacific easterlies 3 ng/cm2 yr vs. 2.5 ng/kg; North Pacific easterlies 6 ng/cm2 yr vs. 11 ng/kg; North Pacific westerlies 50 ng/cm2 yr vs. 14 ng/kg; and North Atlantic westerlies 170 ng/cm2 yr vs. 36 ng/kg. This relationship enables one to view the anthropogenic perturbations of the marine lead cycle on a global scale, since the industrial origin of eolian and seawater lead has been established by correlations between geographic patterns of industrial lead emissions to the atmosphere and isotopic ratios of industrial leads [3] and by geographic patterns of Pb/silicate-dust ratios and lead isotopic ratios in ocean surface waters [3-5]. These new data coupled with earlier biogeochemical data indicate that surface water concentrations of lead in the North Pacific and North Atlantic are now conservatively estimated to be 8 to 20-fold greater and those in the South Pacific are 2-fold greater than natural concentrations because of industrial emissions of lead to the atmosphere. © 1983., Cited By (since 1996):49
Vertical distribution, transport, and exchange of carbon in the northeast Pacific Ocean: Evidence for multiple zones of biological activity
Vertical distribution, transport, and exchange of carbon in the northeast Pacific Ocean: Evidence for multiple zones of biological activity
A sediment trap experiment was conducted to investigate the production, decomposition, and transport of organic matter from 0 to 2000 m at a station 100 km northeast of Point Sur, California. Parameters measured included (1) rates of autotrophic production of carbon, (2) vertical depth distributions of total carbon, nitrogen, and living biomass, and (3) downward flux of organic carbon, nitrogen, ATP, RNA, and fecal pellets. Metabolic activity and microbial growth rates (RNA and DNA synthesis) were also estimated in situ, for both the 'suspended' (i.e., samples captured in standard water bottles) and 'sinking' (i.e., samples captured in sediment traps) particles. Daily depth-integrated rates of primary production averaged 564 mg C m-2, of which 10 to 15% was removed from the euphotic zone by sinking, assuming steady-state conditions. The profiles of suspended carbon, nitrogen, C:N ratios, and ATP conformed to previously published concentration-depth profiles from the region. The vertical flux profiles of organic matter, however, revealed two important features that were not evident in the suspended particulate matter profiles. First, there was an obvious mid-water depth increase (i.e., an increase in organic carbon and nitrogen flux with increasing depth) between 700 and 900 m, suggesting horizontal advection or in situ production. Similar flux profiles were also observed for ATP, RNA, and total fecal pellets. Second, the C:N ratios for the sediment trap materials collected at mid-ocean depths (600 to 1200 m) were low compared to values measured for 'suspended' particulate organic materials collected from comparable depths, supporting the in situ production hypothesis. An observed maximum in the rate of RNA and DNA synthesis for microorganisms associated with particles collected at 700 m confirmed that the flux anomalies were the result of in situ microbiological processes rather than horizontal advection. We hypothesize that the in situ activity measured at 700 m is the result of a chemolithotrophic-based carbon production system supported by the presence of reduced inorganic compounds (e.g., NH4+, HS-) found in association with the sinking particles. "New carbon production" (a value equivalent to the increased downward flux of carbon) between 700 and 900m was 15 mg C m-2 d-1, or 2 to 1% of the daily integrated primary production. These regions of intense biological metabolic activity, growth, and organic matter diagenesis may have a profound influence on the oceanic carbon cycle and on the observed steady-state distributions of various non-conservative properties of seawater. © 1984., Cited By (since 1996):51
Vertical distributions and relations of euphausiid populations off Elephant Island, March 1984
Vertical distributions and relations of euphausiid populations off Elephant Island, March 1984
Distributional relationships are described for post-larval and larval Euphausia superba and Thysanoessa sp. (probably macrura) and post-larval Euphausia frigida collected in 0-70/80 m and 0-175/200 m depth ranges with a MOCNESS sampler north of Elephant Island (61°S, 55°W) during 17-23 March 1984. Larval E. superba (predominantly calyptopes stage 2 and 3) were rare shallower than 80 m at night. Day catches of post-larval E. suberba were small and night catches were primarily near the top of the thermocline above 50 m depth. Thysanoessa sp. occurred throughout the 0-200 m depth range and was abundant in the upper 80 m both night and day. E. frigida migrated to the upper 80 m at night from deeper day depths. Larval stages of E. superba and bost-larval stages of all three species demonstrated independent and variable vertical distribution patterns both night and day. Changes in E. superba abundance and distributional patterns could to a certain extent be associated with observed environmental changes. An increase in larval and decrease in post-larval E. superba abundances between 0-80 m was associated with an intrusion of cold water at depth. At night, vertically restricted concentrations of post-larval E. superba were associated with shallow mixed layer depths, and a significant vertical separation of developmental stages and size categories was observed only during periods of stratification in the upper 80 m. Fluctuations in the distribution and abundance of Thysanoessa sp. and distribution of E. frigida did not appear to be influenced by physical parameters within the upper 80 m. Within the 0-80 m depth range, the distributions of these two species differed from each other and from E. superba and showed large tow to tow variability that could not be related to physical parameters in the upper water column. © 1987 Springer-Verlag., Cited By (since 1996):8, CODEN: POBID
Vital stain in bait as a tag
Vital stain in bait as a tag
This study evaluated the use of various vital stains and tetracycline placed in bait to mark fish in situ. The procion dye, reactive red 8, was the only stain detectable after 11 weeks; tetracycline was not detected in the otoliths.
Walkers Cay Fault, Bahamas: Evidence for Cenozoic faulting
Walkers Cay Fault, Bahamas: Evidence for Cenozoic faulting
Interpretation of seismic reflection data reveal evidence of a Cenozoic fault (Walkers Cay Fault) north of Little Bahama Bank. This fault strikes N15-30°E, perpendicular to the adjacent bank margin and offsets a late Oligocene reflector by as much as 100 m. The origin of this near-surface fault is uncertain, but its location and strike are nearly coincident with an independently mapped basement fault. Walkers Cay Fault may be the result of recurrent faulting, implying intermittent basement fault movement during the post-rift history of the northern Bahamian continental margin. © 1981 A.M. Dowden, Inc., Cited By (since 1996):2, CODEN: GMLED
Walrus feeding disturbance: Scavenging habits and recolonization of the Bering Sea benthos
Walrus feeding disturbance: Scavenging habits and recolonization of the Bering Sea benthos
Walruses (Odobenus rosmarus Illiger) influenced the structure of macrobenthic assemblages in a variety of ways as they excavated their major bivalve prey from soft sediments. Benthic animals were attracted to discarded bivalve shells and they colonized pits and furrows made during prey excavation. Discarded shells contained soft tissues that were eaten by several invertebrate scavengers. The most abundant and widespread scavenger was the sea star, Asterias amurensis Lutken. Sea stars out-competed brittle stars (Amphiodia craterodmeta Clark) for fresh scavenging events. They also attacked brittle stars under shells in the laboratory, and thus may have obtained two meals from discarded shells by eating remnant tissue and by consuming animals that used the shell as a habitat. In nature, brittle stars were abundant under discarded shells. In experiments, brittle stars invaded shells with soft tissue in the absence of sea stars, but not in their presence. In other experiments, brittle stars were most abundant under shells with soft tissue, but were also attracted to shells without organic matter. Large brittle stars were more abundant under shells than in the surrounding bottom, and the reverse was true of small individuals. Bottom communities recovered gradually inside experimental feeding excavations, which were not invaded by large numbers of opportunistic infaunal or epifaunal invertebrates. This is in contrast to gray whale feeding excavations, which are colonized by a large number of opportunistic peracarid crustaceans. © 1985., Cited By (since 1996):32, CODEN: JEMBA
Warmer temperatures reduce the influence of an important keystone predator
Warmer temperatures reduce the influence of an important keystone predator
Predator-prey interactions may be strongly influenced by temperature variations in marine ecosystems. Consequently, climate change may alter the importance of predators with repercussions for ecosystem functioning and structure. In North-eastern Pacific kelp forests, the starfish Pycnopodia helianthoides is known to be an important predator of the purple sea urchin Strongylocentrotus purpuratus. Here we investigated the influence of water temperature on this predator-prey interaction by: (1) assessing the spatial distribution and temporal dynamics of both species across a temperature gradient in the northern Channel Islands, California, and (2) investigating how the feeding rate of P. helianthoides on S. purpuratus is affected by temperature in laboratory tests. On average, at sites where mean annual temperatures were <14°C, P. helianthoides were common, S. purpuratus was rare and kelp was persistent, whereas where mean annual temperatures exceeded 14°C, P. helianthoides and kelp were rare and S. purpuratus abundant. Temperature was found to be the primary environmental factor influencing P. helianthoides abundance, and in turn P. helianthoides was the primary determinant of S. purpuratus abundance. In the laboratory, temperatures >16°C (equivalent to summer temperatures at sites where P. helianthoides were rare) reduced predation rates regardless of predator and prey sizes, although larger sea urchins were consumed only by large starfishes. These results clearly demonstrate that the effect of P. helianthoides on S. purpuratus is strongly mediated by temperature, and that the local abundance and predation rate of P. helianthoides on sea urchins will likely decrease with future warming. A reduction in top-down control on sea urchins, combined with other expected impacts of climate change on kelp, poses significant risks for the persistence of kelp forests in the future.
Water quality assessment in the Mexican Caribbean: Impacts on the coastal ecosystem
Water quality assessment in the Mexican Caribbean: Impacts on the coastal ecosystem
Coastal zones are dominated by economically important ecosystems, and excessive urban, industrial, agricultural, and tourism activities can lead to rapid degradation of those habitats and resources. Groundwater in the Eastern Yucatan Peninsula coastal aquifer discharges directly into the coastal ocean affecting the coral reefs, which are part of the Mesoamerican Coral Reef System. The composition and impacts of groundwater were studied at different coastal environments around Akumal (SE Yucatan Peninsula). Radium isotopes and salinity were used to quantify fresh groundwater and recirculated seawater contributions to the coastal zone. Excess Ra distribution suggests spatially variable discharge rates of submarine groundwater. High NO3- levels and high coliform bacteria densities indicate that groundwater is polluted at some sites. Dissolved phosphorous content is elevated in the winter and during the high tourism season, likely released from untreated sewage discharge and from aquifer sediments under reducing conditions.
What are algal turfs?: Towards a better description of turfs
What are algal turfs?: Towards a better description of turfs
The use of standardised classifications, or operational definitions, is essential if different researchers are to measure and compare similar entities. In the marine realm, algal 'turfs' are increasingly reported to be globally expanding at the expense of kelps and canopy-forming algae. However, ecological research about the underlying drivers of this shift is limited by a vague and inconsistent definition of what exactly a turf is. In order to stimulate more effective descriptions of 'turfs' and facilitate communication of research outcomes and comparisons across studies, we reviewed the use of the term turf in ecological studies of temperate coasts and coral reefs and (1) identified the main types and distribution of algal assemblages known as 'turfs', (2) examined the descriptions of turfs so that we may recognise some general characteristics, including those contingent on environmental conditions; and (3) offered character descriptions that could improve communication and comparisons. These descriptors centre on reporting information on the morphology, height, density of thalli, the amount of sediment trapped in turfs and a description of the area covered by turfs, including their patchiness and persistence. Our review recognised these as common attributes that could be usefully described across a wide range of circumstances and provide insights into the ecology of turfs and their interactions with other assemblages in a community. The use of common descriptors would provide the term 'turf' with greater scientific value. © Inter-Research 2014., Seaweeds
What controls dissolved iron concentrations in the world ocean?
What controls dissolved iron concentrations in the world ocean?
Dissolved (<0.4 μm) iron has been measured in 354 samples at 30 stations in the North and South Pacific, Southern Ocean and North Atlantic by the Trace Metals Laboratory at Moss Landing Marine Laboratories. These stations are all more than 50 km from a continental margin. The global distribution of dissolved iron, which is derived from these profiles, is remarkable for several reasons. The dissolved iron profiles have a uniform shape with a nutrient-like profile at each station. Concentrations at the surface are all <0.2 nmol kg-1 and average 0.07 nmol kg-1. Below 500 m, the average concentration is 0.76 nmol kg-1. The largest value in the data set is 1.38 nmol kg-1. There is no inter-ocean fractionation, which is unique for an element with a nutrient-like profile. Published estimates of the iron residence time are on the order of 100 to 200 yr, indicative of rapid removal. Other elements with such short residence times are characterized by vertical profiles that decrease with depth and deep concentrations that decrease with age as water passes from the Atlantic to the Pacific. This is not the case for iron. The largest horizontal changes in dissolved iron are observed in gradients from the continental margin. There is only a factor of three difference between the minimum (0.4 nmol kg-1) and maximum (1.3 nmol kg-1) value in the data set at a depth near 750 m, where variability is at a maximum. The minimum concentrations are found at stations in the remote central Pacific and the maximum values occur at stations adjacent to the continental margin. The major source of iron in the deep sea is generally aeolian deposition. Integrated (surface to 500 m) concentrations of iron at each station are only weakly correlated with the aeolian iron deposition flux, however. This contrasts with other elements such as lead that also have strong atmospheric sources. These observations lead us to conclude that the nutrient-like profile is maintained by a mechanism that reduces the scavenging rate of dissolved iron at concentrations less than 0.6 nmol kg-1. This mechanism may be complexation by strong iron binding ligands, which have been found in both the Atlantic and Pacific at concentrations near 0.6 nM. This apparent solubility would act to diminish inter-ocean fractionation. It would allow a nutrient-like profile to develop before scavenging began to remove iron. In order to test the concept, we developed a numerical model to make quantitative predictions of dissolved iron concentrations from place to place. The dissolved iron source in the ocean interior is remineralization from sinking particulate organic matter. Scavenging removes dissolved iron only at concentrations greater than the apparent solubility. The only geographically variable parameter in the model is the export flux of carbon from the surface layer, which carries iron with it. The model generated dissolved iron profiles, based on measured or estimated values of the carbon export flux, are in remarkable agreement with the observed profiles at all stations from the North Atlantic through the Southern Ocean to the North Pacific., Cited By (since 1996):386, CODEN: MRCHB, Oceanography

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