Annual Growth Bands Research Articles

Trophic interaction between striped marlin and swordfish using different timescales in waters around Baja California Sur, Mexico

ABSTRACTIsotopic niche and resource partitioning were examined between striped marlin (Kajikia audax) and swordfish (Xiphias gladius) using stable isotope ratios from spine bone and muscle samples. The δ13C (13C/12C) and δ15N (15N/14N) values were measured in annual growth bands from fin spines and muscle collected from striped marlin and swordfish off Baja California Sur to evaluate the trophic interaction between these two species, the relative contribution of the main prey and the isotopic niche within two different timescales. Mean trophic level (TL) values were different when tissues were compared with the highest value found in muscle samples from K. audax. When TL was analysed in all growth bands for both species, no changes were detected throughout time, suggesting only minor differences in feeding habits between these species. We determined that Dosidicus gigas, Sthenoteuthis oualaniensis, and Ancistrocheirus lesueurii were the most important prey for both species, but the relative contribution of each of them to the diet differed. There is likely no trophic overlap between K. audax and X. gladius off Baja California Sur, as K. audax occupied a larger isotopic niche with more diverse prey than X. gladius.

Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain)

Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain)

Age estimation of striped marlin (Kajikia audax) in the eastern North Pacific using otolith microincrements and fin spine sections

The age of striped marlin (Kajikia audax) in days and years (daily and yearly ages) were estimated by counts of otolith microincrements (n=25) and dorsal fin spine annuli (n=175) using specimens caught in the tropical eastern North Pacific between September and November 2004. Daily ages of small striped marlin (87.0–145.5cm lower jaw–fork length) were estimated to range from 81 to 239 days, which indicates that the species in the area grow, on average, to over 100cm within 4 months. Back-calculated hatch dates were estimated to be from March to July; this period is earlier than the known spawning season in a slightly more northern area. Approximately 20% of these year-0 striped marlin had one or more growth bands in the sectioned spine. They were thought to be false annual growth bands and excluded from yearly age estimation. The estimated yearly age of 175 individuals (87.0–228.4cm) ranged from 0 to 5 and was dominated by ages-0 to 3 (>90%). Age composition was different among three subregions in the eastern North Pacific.

Variation in skeletal extension, density and calcification of the Scleractinian coral Porites lobate across the northern Persian Gulf

In chronological and geochemical studies of coral reefs, the annual coral growth bands function as an indicator for monitoring environmental change. In this study, the annual linear growth rates were measured in two core samples of Scleractinian coral Porites lobate collected from two geographically distinct islands across the northern Persian Gulf Using CoralXDS, the linear extension rates, densities, and calcification rates for each x-rayed samples were evaluated The mean (±SE) for extension (cm.yr−1), density (g.cm−3), and calcification (g.cm−2.yr−1) rates in Kharg Island within the period of 1985 to 2015 were 1.04 ± 0.05, 2.09 ± 0.01 and 2.17 ± 0.1, respectively and in Hendourabi Island within the period of 1999 to 2016 were 1.09 ± 0.07, 2.02 ± 0.02 and 2.19 ± 0.14, respectively The mean for a linear extension, skeletal density, and calcification rates were nearly 10% lower, 60% higher and close to the global average rates, respectively. No association was found between SST as independent variable and extension, skeletal density and calcification rates as dependent variables in both islands at this study. This suggests that the high inter-annual variability of growth parameters in this region might be the underlying reason for the poor association among these parameters with SST. The difference in the results of this study with others elsewhere in the world might be linked to the severe environmental stress under which reef-building corals occur in the Persian Gulf.

The crustacean cuticle does not record chronological age: New evidence from the gastric mill ossicles

A proposed method to determine chronological age of crustaceans uses putative annual bands in the gastric mill ossicles of the foregut. The interpretation of cuticle bands as growth rings is based on the idea that ossicles are retained through the moult and could accumulate a continuous record of age. However, recent studies presented conflicting findings on the dynamics of gastric mill ossicles during ecdysis. We herein study cuticle bands in ossicles in four species of commercially important decapod crustaceans (Homarus gammarus, Nephrops norvegicus, Cancer pagurus and Necora puber) in different phases of the moult cycle using dissections, light microscopy, micro-computed tomography and cryo-scanning electron microscopy. Our results demonstrate that the gastric mill is moulted and ossicles are not retained but replaced during ecdysis. It is therefore not plausible to conclude that ossicles register a lifetime growth record as annual bands and thereby provide age information. Other mechanisms for the formation of cuticle bands and their correlation to size-based age estimates need to be considered and the effect of moulting on other cuticle structures where ‘annual growth bands’ have been reported should be investigated urgently. Based on our results, there is no evidence for a causative link between cuticle bands and chronological age, meaning it is unreliable for determining crustacean age.

Microatolls document the 1762 and prior earthquakes along the southeast coast of Bangladesh

In order to understand the seismic hazard associated with the Sunda megathrust along SE Bangladesh, it is necessary to document geologic evidence for the 1762 Arakan earthquake (M8.5–8.8) and prior events. Historical records indicated that the 1762 earthquake caused extensive damage along the Arakan segment of the Sunda subduction system, but geologic evidence for the earthquake farther north is necessary to better understand its associated seismic hazard to the heavily populated nation of Bangladesh. To document the paleoseismic history and understand ongoing tectonic deformation, we conducted detailed analyses of corals and microatolls in Saint Martin's Island, SE Bangladesh. The coral growth bands were studied, dated using U/Th systematics and their elevation was measured using high-precision GPS with RTX™ capability. The U/Th dating and >2 m of elevation differences between dead and living corals provide strong evidence of the coseismic uplift of 1762 Arakan earthquake. Based on annual banding patterns and reconstruction of the highest level of survival, coral microatolls indicate a tectonic subsidence rate of 2.2 ± 0.8 mm/yr prior to their uplift, consistent with elastic strain accumulation before the earthquake. In contrast, annual growth bands of a living coral microatoll indicate that Saint Martin's Island is presently experiencing uplift, at a rate of 1.8 ± 0.1 mm/yr. This suggests that the anticline underlying Saint Martin's Island is actively deforming following the earthquake. Our study also provides evidence for two additional earthquakes taking place in ~700 and ~1140 CE. These findings suggest a preliminary earthquake recurrence interval of ~500 years. Based on our results, the 1762 rupture can be extended from Faul Island (18°N) to Saint Martin's Island in SE Bangladesh (20.6°N). The motions documented from the corals suggest that this segment of the Arakan collision zone is storing sufficient energy to cause a future earthquake of M > 8.

Implications for measuring seasonality in the marine bivalve, Saxidomus gigantea

Sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites afford the opportunity to understand environmental change and its impacts on human populations through time. During the Late Holocene in the Gulf of Alaska (GOA), the paleoenvironmental record reflects fluctuating marine conditions throughout the region. In the Kodiak archipelago in the Gulf of Alaska, changing environmental conditions, population growth, technological transitions, and contact with other communities likely promoted the transition from needs-based maritime hunting and gathering to surplus-based, semi-permanent villages. The precise role of climate in this transition is understudied. Few paleoclimate reconstructions are available for the Kodiak archipelago and climate reconstructions for the GOA are often insufficient for archaeological research because they lack sub-annual resolution and cannot produce a detailed understanding of seasonal behaviors in human populations.Analysis of shellfish remains from archaeological sites in the archipelago may provide additional paleoenvironmental information for the Gulf of Alaska. Measuring and comparing the length of seasonal shell growth in select species of bivalves may complement stable oxygen isotope analysis, together providing a more precise paleoclimate reconstruction. This research utilizes the growth of Saxidomus gigantea (also known as S. giganteus), abundant both on modern and ancient coastlines to provide information about the length of its growing seasons. To measure seasonality, a total of 25 modern samples were collected from Alaska and British Columbia and the number of lunar-daily growth increments (LDGI) was counted between annual winter growth bands confirmed by δ18O maxima measured in sinusoidal time series. Clams collected from Alaska grew a total of 143 ± 34 days while British Columbian clams grew 273 ± 14 days. δ18O values and the number of LDGI per year were then compared to previous studies along the Pacific Northwest coast. δ18O values were more positive from annual winter growth bands from Alaskan samples (average value of 1.0‰) than British Columbian samples (average value of −0.2‰). Maximum δ18O values from winter growth generally increased with latitude (R2 = 0.67), as did the number of LDGI per year (R2 = 0.74). Minimum δ18O values did not appear to be significantly related to latitude (R2 = 0.42).This method was then applied to three archaeological samples collected from the Rice Ridge site (KOD-363), the Uyak site (KOD-145), and the Settlement Point site (AFG-105) from the Kodiak archipelago, Alaska, which grew an average of 166 ± 22 days, to confirm that these methods can be applied to archaeological samples through time to detect spatial and temporal changes in seasonality. These results suggest that changes in sea surface conditions and seasonality are detectable both spatially and temporally through detailed sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites and offer the potential to reconstruct marine environmental conditions throughout the Holocene.

Reservoir Ages in the Western Tropical North Atlantic from One Coral off Martinique Island (Lesser Antilles)

AbstractSea surface reservoir ages (R) are reported from radiocarbon (14C) measurements of the annual growth bands of coral Siderastrea siderea collected on the Atlantic coast off Martinique Island, in the Lesser Antilles volcanic arc. Mean values of R are similar between 1835 and 1845 during pre-anthropogenic times at 385±30 yr and between 1895 and 1905 at 382±20 yr when there was a huge eruption from the Montagne Pelée volcano in 1902–1903. Limited 14C aging of sea surface (~40 yr) may be due to enhanced volcanic activity. Variability of R is slightly greater during 1835–1845 than during 1895–1905. It is linked to a moderate increase of ∆14C of 5‰, strengthened by a clear increase of δ18O of 0.4‰. This is attributed to a decrease of the northward advection of the South Atlantic Waters into the western tropical North Atlantic and Caribbean Sea and relative enhanced westward flux of the tropical North Atlantic surface waters, the southern waters having lower values of 14C and δ18O than the North Atlantic ones. From 1835 to 1845, the fraction of the South Atlantic Waters transported up to Martinique Island was reduced from 25% to 15%.

Uptake and distribution of organo-iodine in deep-sea corals

Understanding iodine concentration, transport, and bioavailability is essential in evaluating iodine's impact to the environment and its effectiveness as an environmental biogeotracer. While iodine and its radionuclides have proven to be important tracers in geologic and biologic studies, little is known about transport of this element to the deep sea and subsequent uptake in deep-sea coral habitats. Results presented here on deep-sea black coral iodine speciation and iodine isotope variability provides key information on iodine behavior in natural and anthropogenic environments, and its geochemical pathway in the Gulf of Mexico. Organo-iodine is the dominant iodine species in the black corals, demonstrating that binding of iodine to organic matter plays an important role in the transport and transfer of iodine to the deep-sea corals. The identification of growth bands captured in high-resolution scanning electron images (SEM) with synchronous peaks in iodine variability suggest that riverine delivery of terrestrial-derived organo-iodine is the most plausible explanation to account for annual periodicity in the deep-sea coral geochemistry. Whereas previous studies have suggested the presence of annual growth rings in deep-sea corals, this present study provides a mechanism to explain the formation of annual growth bands. Furthermore, deep-sea coral ages based on iodine peak counts agree well with those ages derived from radiocarbon (14C) measurements. These results hold promise for developing chronologies independent of 14C dating, which is an essential component in constraining reservoir ages and using radiocarbon as a tracer of ocean circulation. Furthermore, the presence of enriched 129I/127I ratios during the most recent period of skeleton growth is linked to nuclear weapons testing during the 1960s. The sensitivity of the coral skeleton to record changes in surface water 129I composition provides further evidence that iodine composition and isotope variability captured in proteinaceous deep-sea corals is a promising geochronometer as well as an emerging tracer for continental material flux.

Localized zinc distribution in shark vertebrae suggests differential deposition during ontogeny and across vertebral structures.

The development of shark vertebrae and the possible drivers of inter- and intra-specific differences in vertebral structure are poorly understood. Shark vertebrae are used to examine life-history traits related to trophic ecology, movement patterns, and the management of fisheries; a better understanding of their development would be beneficial to many fields of research that rely on these calcified structures. This study used Scanning X-ray Fluorescence Microscopy to observe zinc distribution within vertebrae of ten shark species from five different orders. Zinc was mostly localised within the intermedialis and was generally detected at levels an order of magnitude lower in the corpus calcareum. In most species, zinc concentrations were higher pre-birth mark, indicating a high rate of pre-natal zinc deposition. These results suggest there are inter-specific differences in elemental deposition within vertebrae. Since the deposition of zinc is physiologically-driven, these differences suggest that the processes of growth and deposition are potentially different in the intermedialis and corpus calcareum, and that caution should be taken when extrapolating information such as annual growth bands from one structure to the other. Together these results suggest that the high inter-specific variation in vertebral zinc deposition and associated physiologies may explain the varying effectiveness of ageing methodologies applied to elasmobranch vertebrae.

Skeletal growth controls on Mg/Ca and P/Ca ratios in tropical Eastern Pacific rhodoliths (coralline red algae)

The Mg/Ca ratios of non-geniculate coralline red algae (CA) are often assumed to be solely dependent on the sea surface temperature (SST) in which they grow, suggesting that they are ideal proxies for SST reconstruction. Mg/Ca ratio cyclicity is also commonly used as a marker for annual growth band identification in many CA species. However, other controls on elemental uptake such as light, calcification mechanisms, and vital effects may control elemental ratios (e.g. Mg/Ca and P/Ca) in certain genera or species of CA, thus complicating the use of Mg/Ca and P/Ca ratios as a proxy source for SST and paleo-environmental reconstructions. Here we present evidence showing that the Mg/Ca and P/Ca ratio cyclicity in unattached living tropical Lithothamnion sp. (n=8) rhodoliths correlate >90% to the number of sub-annual growth bands (n=1 to 20) formed during a 172-day controlled growth experiment and not to temperature or other environmental conditions (e.g. salinity, pH, etc.). This pattern is also observed in the wild, pre-experimental growth further supporting that the bands are not annual. The Mg/Caalga (R2=0.67; p-value=0.013; n=8) and P/Caalga (R2=0.64; p-value=0.018; n=8) significantly correlate to skeletal extension during the experiment. This work has implications for trace elemental proxy development using CA as well as the influence of skeletal extension on elemental incorporation in biogenic carbonates, particularly rhodoliths of Lithothamnion sp. from the Gulf of Panama, Panama.

Assessing multi-site δ18O-climate calibrations of the coralline alga Clathromorphum across the high-latitude Northern Hemisphere

An increased number of climate proxy records and more refined interpretation of proxy data are crucial to improve projections of future climate at high latitudes, where internal feedbacks amplify warming and established high-resolution climate archives are especially sparse. Encrusting coralline algae are being developed as a mid- to high-latitude marine climate archive. These long-lived algae form a solid high-Mg calcite skeleton with annual growth bands similar to those of trees and tropical corals. The oxygen isotope ratio of the algal skeleton (δ18Oalg) records local environmental and climatic factors, notably sea surface temperature and seawater δ18O.Here we assess the δ18Oalg–climate relationship in diverse environments across the algal habitat range utilizing two species of coralline algae from the genus Clathromorphum. Clathromorphum is widely distributed from the cold-temperate North Atlantic and Pacific to the Arctic Ocean and has recently yielded numerous climate reconstructions of up to 650years in length. In this study, we calibrate δ18Oalg of four specimens to gridded temperature and salinity data, the latter a proxy for seawater δ18O. These specimens were collected from a variety of algal growth environments across the high-latitude Northern Hemisphere: two specimens from the Aleutian Archipelago, one from the Canadian Arctic, and one from the Gulf of Maine. Low winter temperatures and insolation restrict the months when algae record local climate in the δ18O of their skeletons; we therefore determine these response seasons by correlating monthly temperature and salinity anomalies with annual δ18Oalg anomalies at each site. We then average gridded data over months that correlate significantly (95% confidence interval) for regression with δ18Oalg. While the timing and nature of the climate signal vary across sites, we find significant relationships between δ18Oalg and either temperature or salinity averaged over the response season at three sites. Variation in local climatology among the four sites provides a physical explanation for calibration differences, compounded by uncertainties stemming from the proxy chronology, biological variability, temporal coverage, and sparse historical climate data. This work takes an essential step toward reconstructing high-latitude marine climate patterns with coralline algal δ18O and developing algae proxy system models.

Low Florida coral calcification rates in the Plio-Pleistocene

Abstract. In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands often allow for reconstructions of annual extension ( = growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. This report presents the bulk density, extension rates and calcification rates of fossil reef corals which underwent minor diagenetic alteration only. The corals derive from unlithified shallow water carbonates of the Florida platform (south-eastern USA), which formed during four interglacial sea level highstands dated approximately 3.2, 2.9, 1.8, and 1.2 Ma in the mid-Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, voids are commonly present along centres of calcification which lack secondary cements. Mean extension rates were 0.44 ± 0.19 cm yr−1 (range 0.16 to 0.86 cm yr−1), mean bulk density was 0.96 ± 0.36 g cm−3 (range 0.55 to 1.83 g cm−3) and calcification rates ranged from 0.18 to 0.82 g cm−2 yr−1 (mean 0.38 ± 0.16 g cm−2 yr−1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification rates with those of modern zooxanthellate corals (z corals) from the Western Atlantic (WA) and Indo-Pacific calibrated against sea surface temperature (SST). In the fossil data, we found a widely analogous relationship with SST in z corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localised to account also for low extension rates of Pliocene z corals throughout the tropical WA region. Low aragonite saturation on a more global scale in response to rapid glacial–interglacial CO2 cyclicity is also a potential factor, but Plio-Pleistocene atmospheric pCO2 is generally believed to have been broadly similar to the present day. Heat stress related to globally high interglacial SST only episodically moderated by intermittent upwelling affecting the Florida platform seems to be another likely reason for low calcification rates. From these observations we suggest some present coral reef systems to be endangered from future ocean warming.

CRECIMIENTO DEL CORAL ACROPORA PALMATA (LAMARCK, 1886) EN EL PARQUE NACIONAL NATURAL CORALES DEL ROSARIO, CARIBE COLOMBIANO.

The growth rate in ten months (September 1992 - july 1993) for 30 colonies of Acropora palmata along the northern zone of the Corales del Rosario national natural park, Colombian Caribbean, was determined. Three measuring techniques were used: by hand, by staining with alizarin red, and from growth bands by X ray photography. The annual growth estimate for the species in the Park was 5.2 ± 1.3 cm and was found inversely correlated to the size of the colony (lenght, width and height). The growth presented a spatial variation. The smallest growth was found at Caleta Island and the largest at Caribaru Island. The maximum growth rate was observed in the dry season (December-February). No significant differences were found between measurement by hand and by alizarin red. The X-ray technique showed that Acropora palmata does not present discernible annual growth bands.

Reconstruction of seasonal precipitation in Hawai'i using high-resolution carbon isotope measurements across tree rings

Determination of carbon isotope (δ13C) values of tree-ring tissue is a well-established method to reconstruct past climate variability at annual resolution, but such records are limited in tropical latitudes due to the lack of well-defined annual growth bands. Recent work has demonstrated the potential for high-resolution, intra-ring δ13C records to help define ring boundaries in tropical environments and provide additional climate information at sub-annual resolution. Here we present a high-resolution, intra-ring carbon isotope (δ13C) record of the Hawaiian endemic species Sophora chrysophylla (also known as “māmane”) in order to assess the ability to extract seasonal climate information from these drought tolerant trees. Tree cores were sampled from high-elevation māmane trees growing on the west side of Mauna Kea, Big Island. Across our entire dataset (1986–2008), we identified a notable decreasing linear trend in the δ13C record of 0.061‰/year that can be attributed to changes in the δ13C value of atmospheric CO2 and pCO2 concentration associated with fossil fuel burning. Correcting for these affects yields a nearly flat δ13C record with a slope of −0.0075‰/year, suggesting no long-term trends in climate across the study period. We observe a quasi-periodic change in the δ13C values [Δ(δ13C)] measured within each ring that averages 1.09±0.50‰ (±1σ, n=23) in amplitude. These variations are interpreted as the intra-annual isotopic signal in tree photosynthesis. The δ13C variability correlates with the visible ring structure of the sample, suggesting the presence of annual growth rings at this tropical high elevation site.We applied these data to a model that relates the Δ(δ13C) value to seasonal changes in precipitation in order to reconstruct annual changes in total summer (May through October) and winter (November through April) precipitation at the site. Across the 23-year record (1986–2008; n=579 δ13C measurements), reconstructed values for the ratio of summer to winter precipitation, total summer precipitation, and total winter precipitation correlate well with rainfall data collected from a nearby weather station (r=0.65, 0.36, and 0.70, respectively). These results support application of this model to reconstruct inter-annual changes in seasonal precipitation from long-term tree-ring chronologies. They also demonstrate the potential of using māmane δ13C for future long-term climate reconstructions.

Stable carbon and nitrogen isotope values of dorsal spine age rings indicate temporal variation in the diet of striped marlin (Kajikia audax) in waters around Cabo San Lucas, Mexico.

Billfishes, such as marlin, are top pelagic predators that play an important role in maintaining the stability of marine food webs. Notwithstanding the importance of these species, there remain gaps in our knowledge on their movements, foraging, and trophic status in the early stage of life. We measured the δ(13)C and δ(15)N values in each annual growth band deposited in the dorsal spine from striped marlin caught off Cabo San Lucas, Mexico, to produce retrospective isotopic profiles that would enable us to detect any significant isotopic changes across development. The samples were analyzed using an elemental analyzer coupled to an isotope ratio mass spectrometer. There was no relationship between the size of striped marlin and the δ(15) N values. Differences in δ(15)N mean values across different age classes were not significant and the variation in δ(15)N values through the marlins' life cycle was less than 2‰. However, the mean δ(15)N values between individuals varied by up to 6‰. The δ(13)C values increased as a function of age, and the mean δ(13)C values varied significantly between age classes. Fin spines can be used to construct retrospective isotopic histories for the investigation of trophic dynamics and migratory histories in billfishes, for which population dynamics are often poorly known.

Feasibility of using growth band counts in age determination of four crustacean species in the Northern Atlantic

The age information of commercially important species is crucial in fisheries management. Age of various fish and molluscan species has routinely been determined by counting annual growth bands deposited within the hard structures. In crustaceans such structures were previously believed to be lost and replaced due to molting. However, a technique was recently developed to use growth bands deposited in hard structure retained through molting as an age indicator. In the present study, the applicability of the novel technique is investigated for four crustacean species collected from Northern Atlantic for the first time: European lobster, Homarus gammarus (Linnaeus, 1758); Norway lobster, Nephrops norvegicus (Linnaeus, 1758); Atlantic rock crab, Cancer irroratus Say, 1817; and northern shrimp, Pandalus borealis (Kroyer, 1838). The gastric mill ossicles in the first three species were processed to show the growth bands while the eyestalk was used in the shrimp species. Four growth bands were visible in European lobster hatched in a Norwegian hatchery and maintained alive for four years before prior processing. Band counts in the other three species were identical to size-at-age interpretation determined from length-frequency analysis. Validation of the periodicity of annual deposition of growth bands is essential before applying the technique on a wider scale.

Climatic and environmental changes during the middle to late Holocene in southern South America: A sclerochronological approach using the bivalve Retrotapes exalbidus (Dillwyn) from the Beagle Channel

Little is known about the effects of Holocene climate variability on marine environments and their biota in southern South America. Fossil shells of the aragonitic bivalve Retrotapes exalbidus (Dillwyn) offer the possibility of investigating climate variability and particularly the seasonal dynamics of sea-water temperature in the Beagle Channel during different parts of the middle to late-Holocene. We compared three specimens of different geological age (determined by 14C), i.e. 5190 BP, 3839 BP, and 431 BP. These shells, respectively, refer to a cooling period at ca. 5000 BP, a climate optimum at ca. 4000 BP, and a further cooling at ca. 500 BP. All three shells showed clear annual growth bands, with a distinct intra-annual δ18O cycle. δ18O ranges clearly indicate higher summer temperatures in the 3839 BP shell (1.53‰–−1.16‰) compared with the 5190 BP shell (1.29‰–0.72‰) and the 431 BP shell (1.55‰–0.44‰), which correspond to maximum SSTs of 17.73 °C, 9.61 °C and 10.81 °C, respectively. Apparently, R. exalbidus shells are suitable bioarchives that allow comparing seasonal patterns through the Holocene, thus constituting another proxy for evaluating paleoclimatic and paleoenvironmental changes in this region.

Age determination and growth estimation from otolith micro-increments and fin spine sections of blue marlin (Makaira nigricans) in the western North Pacific

Age determination and growth estimation of blue marlin (Makaira nigricans) were performed by combining method of otolith micro-increment counts of 27 young (17–185-cm lower jaw–fork length, LJFL) and sectioned dorsal fin spines of 571 adult individuals (155–352cm). Otolith micro-increments were counted with ages of 26–338 days old. The estimated mean length (185cm) at Year 1 and growth rate were used to predict the position of the first annual growth band in sectioned fin spines. Distinct growth bands were formed in fin spines annually between September and October. Indistinct growth bands were considered false-annual growth bands. The observed and back-calculated LJFLs at each age were highly variable for both sexes. Von Bertalanffy growth parameters were estimated using mean back-calculated LJFL data as: L∞=295cm, k=0.23, t0=–3.31 years for females and 212cm, 0.29, –4.49 years for males. Females grew to >200cm in 2 years and to >250cm in 5 years on average, whereas the growth of males slowed appreciably after they reached the age of 1 year. This is the first study of blue marlin growth for entire life stages.

Late Holocene coral reef environment recorded in Tridacnidae shells from archaeological sites in Okinawa‐jima, subtropical southwestern Japan

AbstractSeasonally resolved records of carbon and oxygen isotopic composition (δ18O) in fossil shells of giant clams (Tridacnidae) recovered from the Kogachibaru Shell Mound (26°26′N, 127°49′E) and the Second Aragusuku‐Shichabaru Ruin (26°18′N, 127°46′E) in Okinawa‐jima, southwestern Japan, were investigated to reconstruct subtropical coral reef environments of the past. The samples, mainly composed of aragonite shells with limited amounts of diagenetically‐altered calcite cements, were selected for geochemical analyses. The radiocarbon dating of the samples for stable isotope analyses yields about 4000 yr cal. BP for the Kogachibaru Shell Mound and about 1900–1700 yr cal. BP for the Second Aragusuku‐Shichabaru Ruin, respectively, that correspond to the early and middle Shell Mound periods in Okinawa‐jima. These show good agreement with the respective ages inferred from excavation. The shell δ18O values roughly show seasonal variations, coincident with the occurrence of annual growth bands. Applying corrections for the effect of diagenetic alteration, the averages of annual, summer, and winter δ18O values of fossil shells were significantly lower (by 0.1–0.7‰) than those of aragonite theoretically precipitated in present‐day coral reef water of Okinawa‐jima. These results demonstrate that annual mean seawater temperature and salinity at the sites where the Tridacnida spp. lived were about 1–3°C higher and/or about 1–2 lower than at present. This variation cannot be fully explained by global climate change, sea level change, and topographic growth of coral reef. Therefore, it is likely that the giant clams lived in extremely small and/or closed coral‐reef lagoons with less water circulation where seawater is highly susceptible to insolation‐induced temperature increase and input of fresh water; the effect could be enhanced by the fisheries lifestyle that stonewalling would be constructed at shallow waters through the use of tidal variation during the early and middle Shell Mound period in Okinawa‐jima.