Incremental Growth Layers Research Articles

Ocean acidification stunts molluscan growth at CO2 seeps

Ocean acidification can severely affect bivalve molluscs, especially their shell calcification. Assessing the fate of this vulnerable group in a rapidly acidifying ocean is therefore a pressing challenge. Volcanic CO2 seeps are natural analogues of future ocean conditions that offer unique insights into the scope of marine bivalves to cope with acidification. Here, we used a 2-month reciprocal transplantation of the coastal mussel Septifer bilocularis collected from reference and elevated pCO2 habitats to explore how they calcify and grow at CO2 seeps on the Pacific coast of Japan. We found significant decreases in condition index (an indication of tissue energy reserves) and shell growth of mussels living under elevated pCO2 conditions. These negative responses in their physiological performance under acidified conditions were closely associated with changes in their food sources (shown by changes to the soft tissue δ13C and δ15N ratios) and changes in their calcifying fluid carbonate chemistry (based on shell carbonate isotopic and elemental signatures). The reduced shell growth rate during the transplantation experiment was further supported by shell δ13C records along their incremental growth layers, as well as their smaller shell size despite being of comparable ontogenetic ages (5–7 years old, based on shell δ18O records). Taken together, these findings demonstrate how ocean acidification at CO2 seeps affects mussel growth and reveal that lowered shell growth helps them survive stressful conditions.

Reconstructing skeletal fiber arrangement and growth mode in the coral <i>Porites lutea</i> (Cnidaria, Scleractinia): a confocal Raman microscopy study

Abstract. Confocal Raman microscopy (CRM) mapping was used to investigate the microstructural arrangement and organic matrix distribution within the skeleton of the coral Porites lutea. Relative changes in the crystallographic orientation of crystals within the fibrous fan-system could be mapped, without the need to prepare thin sections, as required if this information is obtained by polarized light microscopy. Simultaneously, incremental growth lines can be visualized without the necessity of etching and hence alteration of sample surface. Using these methods two types of growth lines could be identified: one corresponds to the well-known incremental growth layers, whereas the second type of growth lines resemble denticle finger-like structures (most likely traces of former spines or skeletal surfaces). We hypothesize that these lines represent the outer skeletal surface before another growth cycle of elongation, infilling and thickening of skeletal areas continues. We show that CRM mapping with high spatial resolution can significantly improve our understanding of the micro-structural arrangement and growth patterns in coral skeletons.

Environmental controls on the stable isotopic composition of Mercenaria mercenaria: Potential application to paleoenvironmental studies

We have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern Mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of North America. Seasonal profiles of δ18O and δ13C obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity. We show that M. mercenaria δ18O profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell δ18O values. Growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10°C, implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations. Although further measurements of water δ18O and a better understanding of seasonal variations of the water δ18O‐salinity relationships are necessary, Mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium. Whereas the amplitude of the seasonal profiles of δ18O reflects variations in water temperature, the annual average δ18O decreases with latitude, reflecting the trend of rainfall and riverwater δ18O with latitude over the Northern American continent.

Age determination in jackals (Canis adustus Sundevall, 1846, andCanis mesomelas Schreber, 1778; Carnivora: Canidae) with reference to the age structure and breeding patterns of jackal populations in Zimbabwe

Methods for determining the age of individual jackals using canine teeth were assessed as part of a study of the population structure of jackal species (side striped jackal, Canis adustus, and black backed jackal, Canis mesomelas), the main wildlife species maintaining rabies in Zimbabwe. Specimens of both species of jackal were obtained from rabies submissions and culling operations, although the major part of the study involved C. adustus. A method of ageing based on relative pulp cavity width of canine teeth differentiated young adults (one year old) from mature adults, but was of no value in determining the age after one year. A method based on cementum incremental growth layers was of no value as the layers were irregular and did not correspond with pulp cavity width. Canis adustus will breed in their first year but no evidence was found to show that C. mesomelas will normally breed at this age. Up to 60 % of C. adustus were young of year jackals, indicating high population turn over and the potential for rapid population recovery following population crashes.

Seasonality in the early Holocene climate of Northwest Sudan: interpretation of Etheria elliptica shell isotopic data

The oxygen isotope ratios in the incremental growth layers in the shells of Etheria elliptica constitute a proxy record of rainfall patterns, and thus a record of seasonality. Analyses of shells of early Holocene age (6800 14C years BP or 5600 BC) collected from the lower reaches of Wadi Howar, near the confluence of that now-extinct river with the Nile, show an annual pattern of two rainy seasons in the present-day hyperarid southeastern Sahara, similar to that which prevails today in much of East Africa.

Aging Bison by the Incremental Cementum Growth Layers in Teeth

Aging mammals by the cementum-annuli method to count incremental growth layers in the roots of teeth is a technique that many wildlife managers use to monitor the demographic structure of populations. However, managers of bison (Bison bison) herds have not been able to use this aging technique, because a correlation between the cementum age and the known age of an animal has never been established. This paper presents the results of a study designed to fill that void and establish whether bison can be aged accurately by the number of incremental growth bands present in the roots of their teeth. The results indicate bison do produce regular cementum annuli in the roots of teeth that correspond accurately with age.

A First Eastern Canadian Stranding Record for Risso's Dolphin, Grampus griseus

We discovered a dead male Risso's dolphin, Grampus griseus, on Sable Island, Nova Scotia, Canada on January 7 1994. The 277 cm long corpse was unmarked by net entanglement or propeller scarring. Transverse sections of fusiform teeth exhibited 13 incremental growth layers in the dentine, in addition to a neonatal line. No other specimens of this species have been reported on the island. Risso's dolphins are not sighted commonly in Canadian waters and we are aware of no other published sightings or stranding records for this species within 100 km of the island. The pristine condition of this corpse, and the fact that it was not seen during regular beach surveys prior to discovery, indicates that it was a recent stranding. If this dolphin had died at sea, it did so close enough to Sable Island as to preclude scavenging by aerial or marine organisms before washing ashore.

Laser ablation ICP-MS analysis of incremental biological structures: archives of trace-element accumulation

Incremental growth layers occur in the hard structures of many types of organisms (tree xylem, mollusc shells, vertebrate teeth, otoliths, scales, etc.). Microprobes have previously shown that these layers contain archival information about an organism's chemical environment. However, trace elements, including metals, are generally undetectable with these instruments. A relatively new technique, laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) promises multielement analytical capability with extremely low detection limits (conservatively, <1 ppm), combined with very fine spatial resolution (down to 30–100 μm beam diameter). Fish otoliths and vertebrate tooth cement and dentin offer the greatest potential for retrieving element archival information, because they are not subject to resorption, and reflect the organism's exposure to or accumulation of trace elements from the ambient environment. Other structures are less promising, because they exhibit element mobility between growth layers (tree rings), or are subject to metabolic turnover and resorption (scales, bones, shells). While the LA-ICP-MS technique is novel in the biological sciences, the few studies available indicate that reproducible, year-by-year data on metal accumulation or exposure will probably be retrievable from many types of incremental structures. The main problem currently is the lack of solid standard reference materials which match the physicochemical properties of hard biological tissues.Key words: laser ablation, mass spectrometry, trace metals, environmental pollution, calcified tissues.

GROWTH LAYER GROUPS (GLGs) IN THE TEETH OF AN ADULT BELUKHA WHALE (DELPHINAPTERUS LEUCAS) OF KNOWN AGE: EVIDENCE FOR TWO ANNUAL LAYERS

AbstractGrowth layer groups (GLGs) were counted in teeth from an adult male belukha whale (Delphinapterus leucas) that had lived for 23 yr in captivity and was estimated to have been 14 mo at capture. As defined here, GLGs are repeating areas of alternating opaque (denser) and translucent (less dense) dentin or cementurn, or nodes at the dentin‐cementum interface. A GLG involves at least one change from opaque to translucent, dense to less dense or ridge to groove, but may be further subdivided by incremental growth layers or laminations. Teeth were prepared by two techniques. Thick sections (longitudinal half sections) were examined with a dissecting microscope under reflected light. Thinner cross and longitudinal sections were x‐rayed and the plates scanned with a microdensitometer. Scanning electron photomicrographs were prepared from thick sections, but SEM proved to be the least useful technique. Counts of GLGs were variable because the laminations were numerous and some surface layers had been lost from wear. Thick‐ and thinner‐section techniques gave comparable results, and approximately 40 GLGs were counted consistently. Although captive environments are less variable than natural ones, our findings are further evidence that belukhas in the wild deposit more than one—and probably two—GLGs per year.

Validation of Age Estimation in the Harp Seal, Phoca groenlandica, Using Dentinal Annuli

We investigated the validity and accuracy of age estimation in harp seals, Phoca groenlandica, using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG), representing Ist-year growth, consists of two IGLs: an outer layer of opaque dentine, bounded by the neonatal line, and an inner layer of translucent dentine. Subsequent GLGs, each representing 1 yr of growth, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May–June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4% of estimates of 0-group seals were correct using only transverse sections. These errors were virtually eliminated (99.0% correct age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages 1, 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, being 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.

Incremental growth layers in the dentine of dugong incisors (Dugong dugon (Müller)) and their application to age determination

An attempt has been made to determine the absoulte age, in terms of incremental growth layers in the dentine of unworn incisors, of dugong skulls already relatively aged by Mitchell (1973). About 60 loose incisors were also included in the study. Layer numbers were found to range from zeros to 57 1/2. Upper jaw tooth succession was related to layer number, tooth 5 coming into wear at 2 1/2 to 3 layers and tooth 6 between 5 1/2 and 8 1/2 layers. The date of death of the animals from which 11 of the skulls came was known with certainty and a twelfth possibly, and this information indicated that the layers are either annual or biannual but are unlikely to be laid down more frequently than this. It is suggested that sexual maturity is reached at approximately 10 layers (i.e. 10 or 5 years of age).