Increment Width Research Articles

Disentangling the effects of inherent otolith growth and model-simulated ecosystem parameters on the daily growth rate of young anchovies

Otolith increment widths have often been used to infer somatic growth history when studying the influence of temperature and food supply. However, there is no functional relation- ship between otolith accretion rate ('inherent otolith growth') and somatic growth rate; although both may be mediated by temperature and food, the uncoupling of these rates under changing environmental conditions or during ontogenetic transitions can undermine the sensitivity of incre- ment width analyses. We used otolith microstructure analysis to model the daily growth of anchovy Engraulis encrasicolus juveniles collected from the North Aegean Sea in July 2007, December 2007 and February 2009. To assess the environmental causes of seasonal variability in growth we used daily outputs of environmental variables from a coupled 3D hydrodynamic-bio- geochemical model (POM-ERSEM) as a proxy for the potential environment that fish experienced during their development. According to the simulation, juveniles that hatched in late autumn- winter developed in unfavorable conditions (low temperature, low productivity); however, they exhibited wider otolith increments before metamorphosis. To specifically study environmental influences on the daily growth rates, we used the simulated environmental variables in gener- alised additive model (GAM) analysis of otolith increment widths, while also taking into con - sideration inherent otolith growth, expressed by the explanatory variables 'previous increment width' and 'age'. The inclusion of the interaction term 'age' × 'sampling period', rather than 'age', accounted for the seasonal effects on ontogenetic changes (timing and duration of metamorphosis) and the differences in growth-selective mortality among samples. Results showed that the daily growth rate of anchovy is influenced by temperature, exhibiting an optimum at 24.5°C, and increases significantly with increased mesozooplankton concentration (i.e. food availability). The analysis highlights that, in order to infer the daily somatic growth from fish otolith increment data and understand the environmental influences, inherent otolith growth has to be disentangled and otolith width trajectories standardised for between-sample differences in ontogenetic changes and growth selective mortality.

Tree ring analysis as an indicator of environmental changes caused by tourist trampling — A potential method for the assessment of the impact of tourists

This paper shows that tree-ring trends might be used for the assessment of the intensity of trampling along touristic tracks in the forests. The study aims at determining the effects of trampling, on the dynamics of annual increments in trees subject to pressure from hiking tourism. The studies were conducted at a spruce stand in the Tatra Mts., on sections of different trails. Within each trail, four transects were determined. Transects include the zones with damage from trampling and the un-affected areas, treated as a reference zones. Selected trees growing in both zones were sampled by coring and the core samples were used to develop sequences of annual increment widths. Next, the dynamics of increments in trees growing in the tourist zone and the reference zone were compared. The decrease in the annual increments was significantly more rapid in trees growing directly along the trail that those in trees deep in the forest stand in one locality. This finding may testify the adverse effects of hiking along tourist routes on the radial increments in trees in the neighbourhood of the trails. The results of the study indicate that the impact of trampling in the form of soil compaction and mechanical damage to root systems of trees may, to some extent, be compensated by better light access and lessened competition experienced by trees growing along the edges of hiking trails. Tree-ring analyses might be an efficient alternative for assessment of tourism intensity conducted by the other methods.

Preboreal oscillations inferred from Arctica islandica sclerochronology

An increasingly important source of annually resolved palaeoenvironmental proxy data originates from cross-dated incremental chronologies summarizing the shell growth of several individuals. Here, we have analysed annual increment variations in a collection of radiocarbon-dated shells of ocean quahog (Arctica islandica) from early Holocene prodelta deposits in north Norway. Radiocarbon dating of the shell material showed that the increments were formed contemporaneously during Preboreal times. The biologically youngest shell contains 35 annual increments, whereas the oldest shell shows 169 increments. Time-series of annual increments demonstrated clear age trends with the widest increments during the very early years of bivalve life, followed by a notable decline in increment widths as the bivalves aged. Subsequent to removing these biological trends from the series, a sclerochronological cross-dating was carried out and resolved the temporal alignments of the shell growth increment records relative to each other. The resulting shell growth increment chronology evidences vigorous growth variations. Spectral analysis of the chronology revealed 3.7- and 4.3-year periodicities, indicative of Preboreal environmental oscillations. Periodicities of longer period were not detected. Our results prove the value of radiocarbon-dated shell assemblages to build “floating” geochronologies for periods and regions where dead shells from museum collections or seabed are not obtainable. Increasing constructions of such chronologies enhance the potential of sclerochronological cross-dating of annual shell growth increment chronologies to depict and detail annually-resolved climate variability not only for late Holocene, as previously illustrated, but also for early Holocene times, when large-scale oscillations punctuated the global climate dynamics. Development of longer chronologies with higher sample replication remains an attainable interdisciplinary target.

Does the structure of wood contribute to understanding the oaks decline phenomenon

Vascular cambium is a meristematic tissue which produces wood centriphugaly and phloem centripetaly. In the structure of wood and phloem, data concerning developmental processes taking place in the cambium is recorded. The history of the cambium is encoded in the dimensions, numbers and arrangements of the wood and phloem cells. For investigations, the wood is usually preferred because it is durable and such data could remain unchanged for centuries, whereas in the phloem due to distorted processes, it deranges after a few years. In broadleaves, the wood is composed of vessels, tracheids, fibers and parenchyma cells. The process of the wood formation consists of the cambial cell derivatives expansion, lignification of its walls and programmed cell death. Since the seventies of the nineteenth century, the process of declining oaks taking place in Europe on a regular basis has been observed. Oak decline is a complex process that involves interactions of both biotic and abiotic factors leading to increased trees mortality. The main goal of the studies is the examination of the structure of wood in declining oaks (Quercus robur L.) in respect to physiological (conductive) role of this tissue. It is known that on the level of the wood structure, water transport efficiency depends on the diameter of vessels - the main elements of the hydraulic conductivity system. Any reduction of the vessels lumen causes the reduction of the water transport to the organs of the trees body and, therefore, influences organisms survival rate. Anatomical analyses were carried out on wood samples (comprising all annual rings formed during the 30-40 years life of the analyzed trees) collected at breast height from the main stem of healthy, weakened and dead oaks. The anatomical traits of the wood like as the width of the annual increments, the diameter and density of early wood vessels were measured. The results which are described in the paper by Tulik (2014) revealed that anatomical traits of the wood changed both with the age of trees and in response to unfavorable factors. The largest early wood vessels were observed in healthy trees, which implied that they had the highest hydraulic conductivity, whereas trees considered being in decline produce smaller vessels and hence had reduced conductivity. Therefore, it seems that the size of vessel elements responsible for water transport in whole tree, is a crucial feature that should be taken into consideration in dendro-eco-physiological studies designed to unravel the issue of oak-tree decline.

Investigating the population structure of small yellow croaker (Larimichthys polyactis) using internal and external features of otoliths

In this study, we investigated the population structure and potential changes of the small yellow croaker from nine main spawning grounds covering most of the distributional range of the species in China. The geographic variability of otolith shape and increment growth were used as tools for stock separation. Otolith growth was based on the annual increment width estimated for the age 2 groups of the spawning stock. Otolith shape was described by the shape variables and Fourier coefficients, that were standardized to remove any size effects. Significant differences and gradual variation with latitude were observed in both the otolith growth and shape variables among stocks; these patterns were supported by discriminant analysis with correct classifications ranging from 26.1% to 82.3%. These results taken together show that the nine stocks could be divided into four subpopulations which were correctly classified by around 75.8–95.9%; the main difference of average otolith shapes for these subpopulations appeared on the ventral side. In contrast to previous population studies, the East China Sea group was further divided into the Southern and Northern two subpopulations and the Haizhou Bay stock appear to be more similar to the Lvsi stock. Moreover, considerable spatial variation in otolith shape and increment growth implied different environmental factors experienced by subpopulations and limited levels of inter-connection, and suggested that the small yellow croaker might be comprised of a metapopulation structure.

Can the structure of dormant cambium and the widths of phloem and xylem increments be used as indicators for tree vitality?

We investigated the structure and width of the dormant cambium and of the increments of phloem and xylem of Quercus robur to estimate their potential as indicators for tree vitality. The samples were taken from three woodlands, two in Slovenia [Krakovo forest (KRA) and Murska Suma (MUS)] and one in Croatia [Kobiljak (KOB)], with reported tree decline. The number of dormant cells seems to reflect the initial capacity of the cambium to accomplish cell division. With the exception of two trees at KRA, cell production was always higher on the xylem side than on the phloem side. The annual phloem increments were narrower, less variable among trees and with clear lower and upper limits. With increased cambial cell productivity, the share of the xylem in the total annual radial increment increased following a curvilinear function. In trees with an annual radial increment >3.5 mm, the xylem size represented more than 90 % of the total radial growth. The anatomical variables analyzed show that the most limiting environmental conditions seem to prevail at KRA, whereas the conditions at MUS seem to be most favorable in terms of radial growth. Analysis of the width and structure of xylem and phloem increments, the number of dormant cambial cells and their inter-relationships can provide additional information on the vitality of oaks.

Planktonic duration in fourteen species of intertidal rocky fishes from the south-eastern Pacific Ocean

The planktonic duration (PD) was determined in fourteen intertidal rocky fishes from the south-eastern Pacific Ocean by counting the otolith micro-increments from hatch check to a transition mark (TM). TMs were validated by comparing the PDs estimated from post-settlers with the total increment counts from otoliths of more recent (new) settlers. In 11 species (79%), the most common TM corresponded to a notable decrease in increment width after settlement. The PDs ranged from 45 days in the kyphosid Girella laevifrons to 135 days in the labrisomid Auchenionchus variolosus, and eight species (57%) had mean PDs of longer than three months. The mean observed size-at-settlement (SASM) values ranged from 17.5 ± 7.2 mm TL in Gobiesox marmoratus (Gobiesocidae) to 40 ± 5.5 mm TL in Calliclinus geniguttatus (Labrisomidae) and showed low variability within species of the same family. PDs were markedly longer in intertidal rocky fishes than in other littoral and reef fishes in tropical and temperate waters. A lengthy and variable duration of the pre-settlement phase, along with a relatively consistent size-at-competence within closely related species, are suggested as mechanisms through which these fishes may increase their probability to settle in the spatially restricted habitat of exposed rocky pools.

Do otolith increments allow correct inferences about age and growth of coral reef fishes?

Otolith increment structure is widely used to estimate age and growth of marine fishes. Here, I test the accuracy of the long-term otolith increment analysis of the lemon damselfish Pomacentrus moluccensis to describe age and growth characteristics. I compare the number of putative annual otolith increments (as a proxy for actual age) and widths of these increments (as proxies for somatic growth) with actual tagged fish-length data, based on a 6-year dataset, the longest time course for a coral reef fish. Estimated age from otoliths corresponded closely with actual age in all cases, confirming annual increment formation. However, otolith increment widths were poor proxies for actual growth in length [linear regression r 2 = 0.44–0.90, n = 6 fish] and were clearly of limited value in estimating annual growth. Up to 60 % of the annual growth variation was missed using otolith increments, suggesting the long-term back calculations of otolith growth characteristics of reef fish populations should be interpreted with caution.

Larval growth rates differ in response to seasonal temperature variations among clupeoid species inhabiting the Pacific coastal waters of Japan

Growth rates of round herring Etrumeus teres, Japanese anchovy Engraulis japonicus, and Japanese sardine Sardinops melanostictus larvae respond differently to seasonal temperature variations in Sagami Bay on the Pacific coast of central Japan. Larvae of these three clupeoid species were collected from small seine net catches between February 2008 and April 2009. Correlations between otolith growth increment widths and ambient temperatures were examined at five body sizes and indexed to otolith radii of 50–175 μm, which corresponded to notochord lengths of 15–24 mm. Round herring larvae showed positive correlations between growth rate and habitat temperature at all five body sizes. In contrast, Japanese sardine larvae did not show significant correlations between growth rate and ambient temperature at any of the five body sizes. Japanese anchovy larvae showed significant but weaker correlations between growth rate and temperature than round herring. Although these three species share habitats with some differences in seasonal occurrence in the bay, they showed different species-specific responses to seasonal habitat temperature variations. These differences in response to temperature variations may constitute an ecological basis for different migration patterns among the three species.

Oxygen isotopic distribution along the otolith growth axis by secondary ion mass spectrometry: Applications for studying ontogenetic change in the depth inhabited by deep-sea fishes

This study using tuna otoliths as working standards established a high lateral resolution and precision analysis to measure δ18Ootolith by secondary ion mass spectrometry. This analytical approach of the ion probe was applied to deep-sea fishes to reconstruct the likely depths inhabited by the fishes at different life history stages based on the measured δ18Ootolith values as a proxy of water temperature. Dramatic increases up to 5–6‰ in δ18Ootolith, representing a temperature decrease of approximately 20°C, were detected in a blind cusk eel (Barathronus maculatus) otolith and in the otoliths of Synaphobranchus kaupii during leptocephalus metamorphosis to glass eel, inferred from the drop of otolith Sr/Ca ratios and increase of otolith growth increment width. δ18Ootolith profiles clearly divided the fish's life history into a planktonic stage in the mixed layer of the ocean and a benthic stage on the deep-sea ocean bottom. The habitat shift signal was recorded within a 150µm width of otolith growth zone, which was too narrow to be clearly detected by mechanical drilling and conventional isotopic ratio mass spectrometry. However, variations down to −7‰ were found in δ18Ootolith profiles as the result of Cs2+ beam sputter in the core and larval portions of the otoliths. Carbon mapping by electron probe microanalyzer and staining by toluidine blue suggested abundant proteins existed in the areas with anomaly negative δ18Ootolith values, which cannot be interpreted as a habitat change but due to the isotopic fractionation by O emission from the proteins. These results implied that careful design and understanding of the chemical composition of the analytical areas or tracks on the heterogeneous otolith was essential for highly accurate and precise analysis.

Sclerochronological studies reveal that patterns of otolith growth of adults of two co-occurring species of Platycephalidae are synchronised by water temperature variations

Chronologies are developed from the otolith growth-increment widths of adult rock flathead (Platycephalus laevigatus) and longhead flathead (Leviprora inops) collected from three inter-connected embayments in temperate south-western Australia. Marginal increment trends on otoliths, in combination with the dendrochronological technique of crossdating, provide strong evidence that an opaque zone is formed annually in the otoliths of both species. Increment widths between opaque zones in the otoliths of individuals of P. laevigatus (maximum age 20 years) and L. inops (maximum age 21 years) were synchronised within and between species. The correlation between the two master otolith chronologies, i.e. mean standardised increment width for each year, was highly significant (P < 0.01). The master otolith chronology for each species was positively correlated with mean sea surface temperatures from 1 July to 30 June, which encompassed the austral summer when growth is typically greatest, and with mean monthly sea surface temperature between September and March. Leeuwin Current strength, which influences the biotic characteristics of some marine species on the south coast, has little influence on the pattern of otolith growth, presumably because the inter-connected embayments from which fish were obtained were partially enclosed. On the basis of the above data and the geographical distributions of P. laevigatus and L. inops, it is proposed that, while both species would grow faster with increasing temperature, the temperatures on the south coast are closer to the optimum for the former species.

Age validation of the growth lamellae in the cuttlebone from cultured Sepia pharaonis at different stages

Here we examine growth rates of lamellae in the cuttlebones of Sepia pharaonis reared at different stages and temperatures (20, 25 and 30°C). Juveniles showed a faster and more stable increase in the number of lamellae than hatchlings. Different temperatures affect the widths of increments; these decrease as the temperature increases from 20 to 30°C. Our results suggest that in S. pharaonis the pattern of growth of the cuttlebone's structure does not follow a ‘daily’ increment, and that increments of lamellae vary between life stages. The growth of the cuttlebone is therefore considered to be affected by a combination of physiological and environmental factors.

Temperature determines growth rates of larval round herring Etrumeus teres in the Pacific coastal waters off southern Japan

Seasonal variation in daily growth rates in the early and middle larval stages of round herring Etrumeus teres were largely determined by the sea temperatures experienced by hatch-date cohorts in the Pacific coastal waters off southern Japan. Round herring larvae were collected by purse seining in the coastal waters of central Tosa Bay. A total of 451 larvae were aged by reading daily rings in otoliths. Individuals within a range of 2–5 hatch dates were grouped as hatch-date cohorts. We selected 16 cohorts that hatched during September 2000 and March 2002 and calculated mean widths of otolith growth increments for each cohort during the first feeding stage (WFF, increments 1–5) and the maximum increment width in the middle larval stage (WMAX). Seasonal variation in mean WFF and WMAX among the 16 cohorts was largely (80–90 %) explained by the sea temperature in the bay. These results indicate that temperature was a predominant determinant of larval growth rates; other environmental factors, such as food availability, did not substantially affect growth rates of round herring larvae in coastal waters along the subtropical Kuroshio Current off southern Japan.

The effects of day length, hibernation, and ambient temperature on incisor dentin in the Turkish hamster (Mesocricetus brandti)

Dentin is deposited on a circadian basis, and daily layers manifest as bands on the medial surfaces of rodent incisors. Hibernation alters dentin deposition, and a distinct hibernation mark has been described on incisor surfaces of several rodent species; the factors that influence the morphology of this mark are poorly understood. We tested the effects of day length, torpor expression, and ambient temperature on incisor surface morphology in Turkish hamsters housed in one of four conditions: long days (LDs) at 22°C, short days (SDs) at 22°C, SDs at 5°C, and SDs at 13°C. Body temperature was monitored continuously with implanted radio transmitters, and teeth examined postmortem. Teeth of SD hamsters had narrower, less distinct circadian increments than those of LD hamsters, but the width of ultradian increments was similar in both photoperiods. Hibernation at both 5 and 13°C was associated in most specimens with very narrow, sharply defined dentin increments and increased tooth heterogeneity. Hamsters in SDs at 5°C that did not hibernate lacked characteristic hibernation increments. At 5°C, but not 13°C, the number and cumulative width of hibernation increments were related to number and cumulative duration of periodic arousals. Our results suggest that incremental deposition of dentin in rodent incisors may be a useful trait for characterizing hibernation behavior in both evolutionary and historical contexts.

A record of hibernation on the surface of incisor teeth in the hamster Mesocricetus raddei (Nehring, 1894)

The surface of the lower incisor teeth was studied in an adult male Mesocricetus raddei hamster with a temperature logger implanted into its peritoneal cavity in June 2010. From July 2010 to March 2011, the hamster lived under natural conditions in an enclosure and overwintered in a self-made burrow. Logger data showed that, beginning from mid-August, the animal body temperature periodically dropped and then returned to the norm, with the duration and depth of hypothermia (torpor bouts) increasing and those of nor-mothermia (arousals) decreasing with time. Growth increments on the incisor surface (presumably, daily increments) were unclear in the apical and middle tooth parts but very distinct in the basal part. The number and width of basal increments generally corresponded to the number and duration of arousals. The growth of the incisors apparently continued throughout the winter season, with every arousal after a torpor bout being marked by the formation of a distinct increment on the incisor surface. Thus, it appears that the pattern of increments on the incisor surface can be used to evaluate the course of wintering in hibernating hamsters. Experiments with vital markers are needed to confirm this assumption.

Incisor growth rate in rodents and the record of the entire annual cycle in the incisors of Marmota baibacina centralis

The lower incisors of 80 specimens of Marmota baibacina of 1–10 years old killed in spring in the highland of the Tien Shan Mountains were investigated. On the surface of all the incisors, regular daily increments and “hibernation zones” were revealed. The mean width of increments was used as an indicator of the incisor growth rate before hibernation. We found that the mean width did not depend on the sex of animals, locality, and incisor length, but depended on animal age. The increment width significantly decreased, and the number of the increments formed before hibernation significantly increased with age. This means that the growth rate of the incisors and the intensity of their attrition decrease with the animals’ age. The decrease in the incisor growth rate with age is a manifestation of the well-known decrease with age in the intensity of all growth processes in mammals. As a result of this decrease, in the majority of old marmots under study, zones of hibernation were revealed in the basal as well as in the apical parts of the incisor. The zone in the basal part formed during the latest hibernation and the zone in the apical part corresponded to the previous one. Thus, the incisor preserved the record of the entire year of animal life.

Temperature and Somatic Growth Effects on Otolith Growth of Larval Atlantic Menhaden, &lt;I&gt;Brevoortia Tyrannus&lt;/I&gt; (Actinopterygii: Clupeiformes: Clupeidae)

Background. If a link exists between somatic and otolith growth, otolith size and microstructure analysis can be a useful tool in studies of larval fish growth and condition&#8212;methods like growth back-calculation or marginal increment width analysis can be employed. Because significance of that link may vary among species and can be additionally modified by temperature, the aim of the present paper is to evaluate how sagittal otoliths of Atlantic menhaden responded to somatic growth and temperature. Materials and methods. Larval Atlantic menhaden, Brevoortia tyrannus (Latrobe, 1802) (age range: 20&#8211;120 days; length range: 14&#8211;35 mm SL), collected during 3 years were evaluated for length-at-age and groups of the shortest and longest-at-age individuals (8% of sampled population in each group) were used in the analyses. Similarly, otolith size-at-age estimated from sagittae length was evaluated and then compared with the earlier estimated growth indices of larvae. Results. Otolith growth rate (OGR) indicated growth differences among analysed larvae. Additionally, temperature effect on OGR independent of somatic growth was detected for larvae that were short-at-age (i.e., the slow growth group). For the fast grow group, temperature effect on OGR was insignificant. Conclusion. Back-calculation of growth from otoliths of larval and early juvenile Atlanticmenhaden is justified but less accurate estimates can be expected for the slowest growing individuals due to the independent temperature effect on otolith growth.

Bayesian hierarchical modeling of Pacific geoduck growth increment data and climate indices

Growth increment widths from hard structures of marine and freshwater fish and bivalve species are increasingly used to model growth and elucidate relationships with environmental variability. Fully characterizing the intrinsic age-related growth variation among individuals within and between populations, while estimating the extrinsic environmental effects simultaneously, can be challenging. Using the long-lived bivalve Pacific geoduck (Panopea generosa), we develop an integrated approach to analyze the relationship between growth increment data and climate indices using Bayesian hierarchical methods. Fitting models to growth increment data from multiple individuals over two sites, we examined different covariance structures related to random individual effects, long- and short-term environmental effects and unexplained errors. The best fitting hierarchical model accounted for a site-specific mean growth response, individual growth variability through random parameter effects, and site-specific error variances. Extrinsic environmental effects on growth were also significant and included a random year effect and the Pacific Decadal Oscillation (PDO) as a predictor of mean growth across both individuals and sites. Once intrinsic age-related growth was accounted for, PDO accounted for 18% to total variability in growth increment data; geoduck shell size was predicted to increase as a function of larger PDO anomalies. However, the greatest variability in growth increment data was explained by random year effects (∼60–70%), and while largely unexplained, sea surface temperature (SST) is a likely determinant on geoduck growth rates showing a positive growth–SST response.

Daily growth patterns of six species of young-of-the-year of Chilean intertidal fishes

Otolith microstructure analysis was used to reveal daily growth patterns of young-of-the year (YOY) of six species of perciform fishes,Bovichtus chilensis(Bovichtidae),Girella laevifronsandGraus nigra(Kyphosidae),Helcogrammoides chilensis(Tripterygiidae) andHypsoblennius sordidusandScartichthys viridis(Blenniidae). YOY collected in intertidal pools from June to December 2008 in Central Chile, ranged from 24 to 76 mm total length and from 25 to 390 days of age. In the six species, sagittal otoliths showed a slightly oval shape, symmetrical and laterally compressed and showed micro-increments distinguishable after a two-side polishing. Increment width of sagittae showed two patterns irrespective of hatch month and species: (i) a parabolic growth with wider increment widths (during the first 150 of YOY life, e.g.B. chilensis,G. nigraandG. laevifrons); and (ii) a more irregular pattern with lower increment widths during most of the seasons inH. chilensisandH. sordidus. Further results were: (i) a unique central primordium enclosed by two checks after which distinctive increments were deposited; (ii) low instantaneous growth rates estimated through the slope of the length-at-age relationship (range 0.1–0.21 mm d−1); and (iii) a linear fish size–otolith size relationship.

Testing stress responses of the bivalve Protothaca thaca to El Niño–La Niña thermal conditions

Protothaca thaca is an important bivalve species inhabiting the upwelling ecosystem of Chile and Peru. Temperature in this ecosystem changes dramatically during El Niño (EN) events, with P. thaca showing high tolerance to increased temperatures. To understand the metabolic processes behind this adaptation we studied the effects of temperature on standard metabolism, growth and body condition index of P. thaca from Northern Chile. Oxygen consumption, daily growth rate and body condition index of animals acclimated to 12, 16 and 20°C were measured using an intermittent flow-through system. Our results show that these processes are significantly lower at 12°C compared to 16 and 20°C. No differences are observed between the higher temperatures. The relative thermal independence of routine metabolism is suggested to conserve energy, which allows the species to be more tolerant to high temperatures. Overall, the physiological responses of P. thaca at whole-animal level largely confirm that this clam is well suited to tolerate positive thermal anomalies associated with strong EN in the study area. However, results at lower temperatures show contrasting responses, which emphasizes the need to be cautious in sclerochronological studies, which tend to assume direct relationships between single environmental factors and micro-growth increment width.