Seamount Area Research Articles

Biological and ecological aspects of the deep‐water red crab populations inhabiting isolated seamounts to the west of the Azores (Mid‐Atlantic Ridge)

AbstractSeamounts are common topographic features in the Mid‐Atlantic Ridge (MAR) including the Azores. However, the knowledge on the ecology of seamounts in this region remains scarce despite needs for assessment and management of seamount resources such as the developing fisheries for deep‐water crabs. We described here for the first time the biological characteristics of an unexploited virgin deep‐water red crab Chaceon affinis population on seamount areas of the MAR to test the hypothesis that its general life history characteristics are similar in different ecosystem types (coastal areas and seamounts) across Macaronesia. We used a randomly stratified design to prospect a layer between 600 and 900 m depth around the summit of two isolated seamounts off the Azores. Results were consistent with the literature information in relation to the patterns of depth distribution, size and sex structure, and reproductive aspects. On the other hand, seamounts showed higher abundances when compared to previously studied coastal areas. Abundance may be also different between seamount areas as a function of the suitable bottom type available and presence of hydrothermal vents. We recommend that the essential habitat of the species should be better mapped identifying vulnerable areas before the development of any fishery.

Psychropotes verrucicaudatus, a new species of deep-sea holothurian (Echinodermata: Holothuroidea: Elasipodida: Psychropotidae) from a seamount in the South China Sea

A new species of psychropotid holothurian, Psychropotes verrucicaudatus sp. nov., is described from Jiaolong Seamount in the South China Sea. A single specimen was taken by a manned submersible from soft bottom at a depth of 3615 m. Psychropotes verrucicaudatus has a violet body surrounded by a brim of fused tube feet, an unpaired dorsal appendage, 16 tentacles, and two rows of midventral tube feet. Both the dorsal skin and unpaired dorsal appendage are covered with conspicuous warts. The body-wall ossicles are crosses with three or four arms, and a short, central apophysis; in addition, a giant cross is present in each wart of the dorsal skin; the tentacles ossicles are rods with spines. The new species differs from its congeners in having a very short and warty dorsal appendage. We also provide the Genbank accession numbers of partial sequences of 16S rRNA and mitochondrial cytochrome oxidase subunit I gene. This is the first report of an elasipodid holothurian from the Jiaolong Seamount area.

Environmental characteristics in three seamount areas of the Tropical Western Pacific Ocean: Focusing on nutrients

Nutrients distribution and influencing factors in three seamount areas named Y3, M2 and C4 of the Tropical Western Pacific Ocean (TWPO) were investigated. Nutrients showed obvious uplifts around the three seamounts, consistent with the uplifts of isotherms and isohalines, indicating the existence of a bottom-up process of nutrients. Meanwhile, compared with the stations away from seamount and the reference stations in the TWPO, nutrients concentrations around seamount were much higher. Among the three seamounts, the average nutrients concentrations were highest in Y3, while they were lowest in C4. Moreover, compared with the obvious nitrogen limitation in Y3 and M2, the N:P (13.5:1) and Si:N (6.1:1) were closed to the Redfield ratio. The current-seamount interaction was the determining influencing factor on nutrients distribution, causing the hydrology dynamic changes such as uplifts and Taylor column. Meanwhile, T and S also affected nutrients distribution, especially nutrients and T showed significant negative correlations.

Archaeal community structure in sediments from a seamount in the Mariana Volcanic Arc

Seamounts are subsurface mountains in the ocean. Examination of the abundance and distribution of Archaea in seamount ecosystems may provide a better understanding of their ecological functions. Most studies of marine archaeal assemblages in seamount area have focused on hydrothermal vents or ferromanganese crusts. We investigated the archaeal communities from a seamount of the Mariana Volcanic Arc, in the tropical western Pacific Ocean by using high-throughput sequencing. Thaumarchaeota was dominant in the sediments of all sample stations. Community diversity and species richness were greatest at stations near the top of the seamount, and lowest at the deepest station. One sample station on the steep southeast slope that faced the Yap-Mariana trench had a unique composition of Archaea. In summary, depth has an important influence on archaeal community structure, and the geographic properties and sediment characteristics may explain the unique distribution patterns of Archaea in this seamount. This study provides a foundation for future research on Archaea in seamounts.

Concentrations and distribution of phthalate esters in the seamount area of the Tropical Western Pacific Ocean

A total of 14 phthalate esters (PAEs) were analysed by gas chromatography–mass spectrometry (GC–MS) to better understand its occurrence and distribution in seawater samples of M2 seamount in the Tropical Western Pacific Ocean (TWPO). The concentrations of ΣPAEs in the seawater ranged from 12.13 ng L−1 to 60.69 ng L−1 (av. 28.86 ng L−1), dominated by dibutyl phthalate (DBP), di(2‑ethylhexyl) phthalate (DEHP) and diisobutyl phthalate (DiBP). ΣPAEs concentrations in the southwest of the seamount were lower than those in the northeast, with the minima appearing above the seamount summit. Current-seamount interaction was reckoned to be the principal driving factors in the distribution of PAEs. DEHP posed a medium risk in seawater, suggesting that marine plastic pollution has become an urgent environmental issue that calls for more attention and actions. Microplastics leaching and atmospheric deposition might be the potential sources of PAEs.

Metal flux as an alternative parameter in evaluating the resource potential for co-rich ferromanganese crusts

ABSTRACTWe propose a geochemical parameter, “metal flux” in evaluating hydrogenetic Co-rich ferromanganese crust deposits in the Pacific seamount area, that is based on physical, chemical, and geological characterization of the integrated growth piles of crusts. We calculated the metal flux for fifteen sites from different depths ranging between 900-6000m from different seamounts. The secular and areal variations of metal flux indicate a strong geological controls, and also can be a reliable tool for estimating an economic potential of the crusts. The Co flux decreases with increasing water depth, followed by almost constant flux of Ni and Mn. The Al and Fe fluxes vary with regions, indicating higher values in the western regions near the island arc probably related to a supply from the Asian continents. The results imply that Co, a redox sensitive metal element, is controlled by redox conditions of seawater, while Fe and Al are by terrigenous input. The metal flux reflects global and regional conditions and controls the compositional diversity of metals, thus consequently, the parameter can be a reliable powerful tool to estimate or single out more potential areas.

Tectono-stratigraphic evolution of the western margin of the Levant Basin (offshore Cyprus)

Abstract Stratigraphic interpretation of twenty-four 2D seismic reflection profiles coupled with available well data from the Ocean Drilling Program (ODP) offshore Cyprus enabled identification of the main unconformities and the seismic packages in the western part of the Levant Basin and their correlation with major geodynamic events. The basic concepts of seismic stratigraphy were applied to improve our understanding of the tectonostratigraphy and the sedimentary architecture of Eratosthenes isolated carbonate platform. This platform is composed of dominant retrograding and aggrading Mesozoic carbonate build-ups and its evolution partly resembles that of the Egyptian margin. Deep-water mixed carbonates and siliciclastics probably prevailed in the basin during the Early Cretaceous. During the Late Cretaceous, these platforms were drowned. Following the convergence of the two plates, both the Eratosthenes Seamount (ESM) area and the Levant Basin progressively became part of a foreland basin along the Cyprus Arc. Different units in the Eratosthenes carbonate platforms (ECPs) and the transition to the deep Levant Basin are detailed here for the first time. We present a 3D conceptual model for the evolution of the western margin of the Levant Basin. We discuss the effect of the Miocene collision between the Cyprus Arc and Eratosthenes to understand the presence of upper Miocene Mass transport complexes (MTCs) in the deep basin and the tilting of the top of the adjacent ECPs. We briefly examine the deformation mechanisms of the Messinian salt near the paleo-shelves of the ECPs.

Application of association analysis for identifing indicator taxa of vulnerable marine ecosystems in the Emperor Seamounts area, North Pacific Ocean

Reflecting the growing interest in ecosystem-based fishery management, deep sea bottom fisheries are being called upon to minimize adverse impacts on vulnerable marine ecosystems (VMEs), communities of marine organisms susceptible to anthropogenic disturbance. Many fishery management organizations have introduced indicator-based management measures for VME conservation, such as encounter protocols, in which VME indicator species and bycatch weight thresholds are assigned. If the bycatch amount of the indicator species in a fishing operation exceeds the predetermined threshold, the fishing vessel halts the fishing operation and moves a certain distance away from the encounter point. However, the representativeness of VME indicator taxa has not been evaluated quantitatively. In this study, we analyzed the co-occurrence of benthic animals collected by scientific bottom tow-net surveys in the Emperor Seamounts area, North Pacific Ocean, to characterize benthic communities in the area and to examine the ability of six candidate indicator taxa (gorgonians, Alcyonacea excluding gorgonians, Antipatharia, Scleractinia, Stylasterina, and Porifera) to represent the local benthic communities. Cluster analysis revealed four clusters of benthic communities, each of which includes both sessile and mobile benthos: (1) gorgonians-Scleractinia community with many mobile benthic taxa and Pisces; (2) Porifera-Stylasterina community with Polychaeta and Bivalvia; (3) Antipatharia-Alcyonacea (excluding gorgonians) community with Cephalopoda; and (4) Zoanthidea-Pennatulacea community with Crinoidae and Holothuroidea. The first cluster included the largest number of taxa and showed strong tendencies of co-occurrence, possibly reflecting the habitat-providing function of gorgonians and Scleractinia as well as the common environmental preferences of filter feeders, which constitute major components of the cluster. We used association analysis to identify VME indicator species in the study area. Association analysis reveals relationships between items in the form of association rules, where the occurrence of an “antecedent” {A} implies the co-occurrence of a “consequent” {B}; {A} and {B} contain items, in this case, taxa. Association analysis applied to the co-occurrence data extracted many effective association rules that include gorgonians or Scleractinia as the consequent and many benthic taxa as antecedents. These results demonstrate that gorgonians and Scleractinia are effective VME indicators in the study area because they co-occur with many other benthic animals and represent VME characteristics such as functional significance as habitat and structural complexity as well as fragility and slow recovery from physical damage.

Megafaunal composition of cold-water corals and other deep-sea benthos in the southern Emperor Seamounts area, North Pacific Ocean

Megafaunal composition of cold-water corals and other deep-sea benthos in the southern Emperor Seamounts area, North Pacific Ocean

A study of sea level variability and its long-term trend in the South China Sea

On the basis of the satellite maps of sea level anomaly (MSLA) data and in situ tidal gauge sea level data, correlation analysis and empirical mode decomposition (EMD) are employed to investigate the applicability of MSLA data, sea level correlation, long-term sea level variability (SLV) trend, sea level rise (SLR) rate and its geographic distribution in the South China Sea (SCS). The findings show that for Dongfang Station, Haikou Station, Shanwei Station and Zhapo Station, the minimum correlation coefficient between the closest MSLA grid point and tidal station is 0.61. This suggests that the satellite altimeter MSLA data are effective to observe the coastal SLV in the SCS. On the monthly scale, coastal SLV in the western and northern part of SCS are highly associated with coastal currents. On the seasonal scale, SLV of the coastal area in the western part of the SCS is still strongly influenced by the coastal current system in summer and winter. The Pacific change can affect the SCS mainly in winter rather than summer and the affected area mostly concentrated in the northeastern and eastern parts of the SCS. Overall, the average SLR in the SCS is 90.8 mm with a rising rate of (5.0±0.4) mm/a during 1993–2010. The SLR rate from the southern Luzon Strait through the Huangyan Seamount area to the Xisha Islands area is higher than that of other areas of the SCS.

Buried ferromanganese nodules of the Magellan Seamounts

Buried ferromanganese nodules and their stratiform accumulations (nodule horizons), which are widespread in sedimentary sequences of the Magellan Seamounts, have been studied in core obtained by shallow drilling on its guyots in the course of expeditions of the R/V Gelendzhik in 2001–2010. The study included description of morphological features, structure, and composition of buried nodules, the assessment of their geological age, and the analysis of host geological environments. It was revealed that nodule horizons are developed in areas with unstable hydroand lithodynamic conditions. The frequent changes of these conditions were responsible for the formation of such nodule horizons and overlying ferromanganese crusts. It is shown that the crusts and nodules developed at the surface of bottom sediments and nodules buried within them are characterized by the similar structure and composition, which indicates their belonging to the same ore formation, i.e., ferromanganese ores of seamounts. The age of buried nodule horizons is correlated with that of layers in ferromanganese crusts, on the one hand, and with the age of host sedimentary complexes defined in the Magellan Seamounts area. The buried nodules include both Cenozoic and Late Cretaceous varieties. The finds of Cenomanian nodule horizons provide grounds for the assumption that the formation of ferromanganese ores on gyuots of the Magellan Seamounts could start prior to the Senonian.

서태평양 해저산 해역에서 수괴와 무기영양염 거동에 기초한 동적 수층환경 특성

서태평양 해저산 해역에서 수괴와 무기영양염 거동에 기초한 동적 수층환경 특성

Linking environmental forcing and trophic supply to benthic communities in the Vercelli Seamount area (Tyrrhenian Sea).

Seamounts and their influence on the surrounding environment are currently being extensively debated but, surprisingly, scant information is available for the Mediterranean area. Furthermore, although the deep Tyrrhenian Sea is characterised by a complex bottom morphology and peculiar hydrodynamic features, which would suggest a variable influence on the benthic domain, few studies have been carried out there, especially for soft-bottom macrofaunal assemblages. In order to fill this gap, the structure of the meio-and macrofaunal assemblages of the Vercelli Seamount and the surrounding deep area (northern Tyrrhenian Sea – western Mediterranean) were studied in relation to environmental features. Sediment was collected with a box-corer from the seamount summit and flanks and at two far-field sites in spring 2009, in order to analyse the metazoan communities, the sediment texture and the sedimentary organic matter. At the summit station, the heterogeneity of the habitat, the shallowness of the site and the higher trophic supply (water column phytopigments and macroalgal detritus, for instance) supported a very rich macrofaunal community, with high abundance, biomass and diversity. In fact, its trophic features resembled those observed in coastal environments next to seagrass meadows. At the flank and far-field stations, sediment heterogeneity and depth especially influenced the meiofaunal distribution. From a trophic point of view, the low content of the valuable sedimentary proteins that was found confirmed the general oligotrophy of the Tyrrhenian Sea, and exerted a limiting influence on the abundance and biomass of the assemblages. In this scenario, the rather refractory sedimentary carbohydrates became a food source for metazoans, which increased their abundance and biomass at the stations where the hydrolytic-enzyme-mediated turnover of carbohydrates was faster, highlighting high lability.

Variability of zooplankton communities at Condor seamount and surrounding areas, Azores (NE Atlantic)

Seamounts are common topographic features around the Azores archipelago (NE Atlantic). Recently there has been increasing research effort devoted to the ecology of these ecosystems. In the Azores, the mesozooplankon is poorly studied, particularly in relation to these seafloor elevations. In this study, zooplankton communities in the Condor seamount area (Azores) were investigated during March, July and September 2010. Samples were taken during both day and night with a Bongo net of 200µm mesh that towed obliquely within the first 100m of the water column. Total abundance, biomass and chlorophyll a concentrations did not vary with sampling site or within the diel cycle but significant seasonal variation was observed. Moreover, zooplankton community composition showed the same strong seasonal pattern regardless of spatial or daily variability. Despite seasonal differences, the zooplankton community structure remained similar for the duration of this study. Seasonal variability better explained our results than mesoscale spatial variability. Spatial homogeneity is probably related with island proximity and local dynamics over Condor seamount. Zooplankton literature for the region is sparse, therefore a short review of the most important zooplankton studies from the Azores is also presented.

Tidal and residual currents over abrupt deep-sea topography based on shipboard ADCP data and tidal model solutions for three popular bathymetry grids

The response of tidal and residual currents to small-scale morphological differences over abrupt deep-sea topography (Seine Seamount) was estimated for bathymetry grids of different spatial resolution. Local barotropic tidal model solutions were obtained for three popular and publicly available bathymetry grids (Smith and Sandwell TOPO8.2, ETOPO1, and GEBCO08) to calculate residual currents from vessel-mounted acoustic Doppler current profiler (VM-ADCP) measurements. Currents from each tidal solution were interpolated to match the VM-ADCP ensemble times and locations. Root mean square (RMS) differences of tidal and residual current speeds largely follow topographic deviations and were largest for TOPO8.2-based solutions (up to 2.8 cm s−1) in seamount areas shallower than 1,000 m. Maximum RMS differences of currents obtained from higher resolution bathymetry did not exceed 1.7 cm s−1. Single depth-dependent maximum residual flow speed differences were up to 8 cm s−1 in all cases. Seine Seamount is located within a strong mean flow environment, and RMS residual current speed differences varied between 5 % and 20 % of observed peak velocities of the ambient flow. Residual flow estimates from shipboard ADCP data might be even more sensitive to the choice of bathymetry grids if barotropic tidal models are used to remove tides over deep oceanic topographic features where the mean flow is weak compared to the magnitude of barotropic tidal, or baroclinic currents. Realistic topography and associated flow complexity are also important factors for understanding sedimentary and ecological processes driven and maintained by flow–topography interaction.

An ecosystem evaluation framework for global seamount conservation and management.

In the last twenty years, several global targets for protection of marine biodiversity have been adopted but have failed. The Convention on Biological Diversity (CBD) aims at preserving 10% of all the marine biomes by 2020. For achieving this goal, ecologically or biologically significant areas (EBSA) have to be identified in all biogeographic regions. However, the methodologies for identifying the best suitable areas are still to be agreed. Here, we propose a framework for applying the CBD criteria to locate potential ecologically or biologically significant seamount areas based on the best information currently available. The framework combines the likelihood of a seamount constituting an EBSA and its level of human impact and can be used at global, regional and local scales. This methodology allows the classification of individual seamounts into four major portfolio conservation categories which can help optimize management efforts toward the protection of the most suitable areas. The framework was tested against 1000 dummy seamounts and satisfactorily assigned seamounts to proper EBSA and threats categories. Additionally, the framework was applied to eight case study seamounts that were included in three out of four portfolio categories: areas highly likely to be identified as EBSA with high degree of threat; areas highly likely to be EBSA with low degree of threat; and areas with a low likelihood of being EBSA with high degree of threat. This framework will allow managers to identify seamount EBSAs and to prioritize their policies in terms of protecting undisturbed areas, disturbed areas for recovery of habitats and species, or both based on their management objectives. It also identifies seamount EBSAs and threats considering different ecological groups in both pelagic and benthic communities. Therefore, this framework may represent an important tool to mitigate seamount biodiversity loss and to achieve the 2020 CBD goals.

Is there a seamount effect on microbial community structure and biomass? The case study of Seine and Sedlo seamounts (northeast Atlantic).

Seamounts are considered to be “hotspots” of marine life but, their role in oceans primary productivity is still under discussion. We have studied the microbial community structure and biomass of the epipelagic zone (0–150 m) at two northeast Atlantic seamounts (Seine and Sedlo) and compared those with the surrounding ocean. Results from two cruises to Sedlo and three to Seine are presented. Main results show large temporal and spatial microbial community variability on both seamounts. Both Seine and Sedlo heterotrophic community (abundance and biomass) dominate during winter and summer months, representing 75% (Sedlo, July) to 86% (Seine, November) of the total plankton biomass. In Seine, during springtime the contribution to total plankton biomass is similar (47% autotrophic and 53% heterotrophic). Both seamounts present an autotrophic community structure dominated by small cells (nano and picophytoplankton). It is also during spring that a relatively important contribution (26%) of large cells to total autotrophic biomass is found. In some cases, a “seamount effect” is observed on Seine and Sedlo microbial community structure and biomass. In Seine this is only observed during spring through enhancement of large autotrophic cells at the summit and seamount stations. In Sedlo, and despite the observed low biomasses, some clear peaks of picoplankton at the summit or at stations within the seamount area are also observed during summer. Our results suggest that the dominance of heterotrophs is presumably related to the trapping effect of organic matter by seamounts. Nevertheless, the complex circulation around both seamounts with the presence of different sources of mesoscale variability (e.g. presence of meddies, intrusion of African upwelling water) may have contributed to the different patterns of distribution, abundances and also changes observed in the microbial community.

Foraging ecology of Cory’s shearwaters in different oceanic environments of the North Atlantic

The use of stable isotopes of animal tissues to infer diet and habitat selection has emerged as a powerful tool, particularly when combined with conventional dietary analysis to pro- vide an integrated view of the assimilated diet. We used 3 techniques during 3 yr (2006 to 2008) on 6 different populations of Cory's shearwaters Calonectris diomedea), ranging from neritic (Berlengas archipelago) to oceanic areas (Azores, Desertas and Selvagens archipelagos), to evaluate the trophic and foraging ecology of this species over the North Atlantic. We deployed data loggers to track for- aging movements and feeding locations, and collected blood and diet samples from each individual after each foraging excursion. We also measured the isotopic signatures of the main prey species for each population. Analysis of stomach regurgitations showed that Trachurus picturatus was the main prey for populations exploiting oceanic environments (Azores and Desertas); Sardina pilchardus and Belone belone dominated the diet of birds feeding in neritic areas (Berlengas); and Trachurus trachu- rus, Scomber sp. and Exocoetus volitans were important for birds exploiting both neritic and oceanic areas (Selvagens). Cephalopods (squid) were important for all populations. The birds' blood δ 13 C sig- natures matched those of their main prey items. The blood δ 13 C signature was negatively correlated with the latitude of the main feeding locations of individuals and segregated populations exploiting neritic and shelf systems from those feeding in oceanic and seamount areas. Even the signatures of geographically different populations that fed in the same oceanic regions were similar. The δ 15 N sig- nature was negatively correlated with the abundance of cephalopods in the diet. Results from a sta- ble isotopic mixing model estimated higher proportions of cephalopods in the birds' diet than propor- tions obtained by direct diet inferences, presumably due to the advanced digestion stage of cephalopods in the regurgitations. Our findings should have broader relevance to the study of forag- ing ecology of other top marine predators in the north Atlantic region.

Seamount Ecosystem Evaluation Framework (SEEF): A Tool for Global Seamount Research and Data Synthesis

The Seamount Ecosystem Evaluation Framework (SEEF) is an innovative multidisciplinary tool developed to standardize the parameters by which seamounts are characterized, to report the extent of knowledge about individual seamounts, and to identify and assess threats to them, and to address other issues. Initially developed by Pitcher and Bulman (2007) and Pitcher et al. (2007), SEEF identifies critical gaps in knowledge and may be used as a guide to develop future research plans for a specific seamount. By systematizing sets of seamount data, it can also promote and assist consistent seamount ecosystem modeling, meta-analysis, and, for management, development of ecosystem-based plans. SEEF is available to the scientific community and general public through the SEEF web site (http://www. seamounteef.org), and through the Seamounts Online initiative (http://seamounts.sdsc.edu; Stocks, 2009). using this interface, individuals can update the existing knowledge of a specific seamount, thus contributing to an improved framework. The SEEF version presented here incorporates revisions to the original schema made by a group of participants at the March 2009 Seamount Biogeosciences network workshop held at Scripps Institution of Oceanography (http://earthref.org/ events/SBn/2009/). SEEF incorporates three different parts. The first part (Part A in Figure 1) scores the extent of our knowledge about individual seamounts by listing their most important attributes, including geological, oceanographic, and ecological features that are found on seamounts that may contribute to their role in enhancing local biomass and biodiversity. The second part of SEEF (Part B in Figure 1) scores the relative severity of threats posed by human activities to the abundance and diversity of seamount resources, principally fishing and other extractive exploitation. Effectively, it identifies seamounts in different conservation states. Parts A and B are scored by experts in the field; scoring disagreements can lead to productive research and useful expressions of uncertainty. The left-hand side of Figure 1 lists attributes and issues. A full description is available on the SEEF web site. The third part of SEEF (C), currently under development, aims to quantify each attribute and threat using actual values, or categories of values, in a fuzzy logic system. In doing so, SEEF will determine the extent of local enhancements in the food web, biodiversity, or biomass, and at the same time will quantify the different threats posed to seamount ecosystems. Scores can be color coded, so that scanning or mapping a set of SEEFs immediately reveals the extent of our ecological ignorance as well as the location of threatened seamount areas. At the same time, it highlights gaps in understanding of general seamount ecosystems, promotes seamount data synthesis, and thus uses and contributes to existing online data sets such as Seamounts Online.

Heavy metals in the benthic animals from hydrothermal vents: Results of neutron activation analysis

A series of samples of inhabitants of hydrothermal vents were collected during the 12th cruise of R/V Akademik Mstislav Keldysh in Guaymas Basin (the Gulf of California) and the Axial Seamount area (Juan de Fuca Ridge). The concentrations of trace and heavy metals in the tissues of Ridgeia piscesae, Riftia pachyptila, and Paralvinella palmiformis were analyzed. The neutron-activation analysis revealed significantly higher concentrations of uranium in the tissues of Paralvinella palmiformis as compared to the ambient seawater. The possible reasons for such phenomenon are discussed. The data obtained by the neutron-activation method are compared with those obtained by the atomic-absorption method for the same tissues analyzed.