Shell Microgrowth Patterns Research Articles

The giant inoceramid Platyceramus platinus as a high-resolution paleoclimate archive for the Late Cretaceous of the Western Interior Seaway

Platyceramus platinus was a giant inoceramid bivalve that inhabited the outer shelf environments of the Western Interior Seaway (WIS) in North America. With axial heights typically exceeding 1 m, the shells of this species potentially serve as a unique high-resolution geochemical proxy archive for Late Cretaceous paleoclimate. Here we present the first sclerochronological investigation of P. platinus shells to evaluate the usefulness of this species as an archive of short-term (e.g., seasonal to inter-annual) paleoenvironmental variability. We analyzed the growth patterns, the stable oxygen (δ18O) and carbon (δ13C) isotope values of well-preserved P. platinus shell fragments from the Santonian Niobrara Formation at Monument Rocks (Kansas, USA), a National Natural Landmark. A series of diagenetic tests, including cathodoluminescence (CL), scanning electron microscopy (SEM), and geochemical (LA-ICP-MS) analysis, confirmed the good state of preservation of the material. Shell microgrowth patterns suggested lunar daily (circalunidian) growth and that P. platinus grew nearly uninterruptedly throughout the year. Assuming a δ18Ow value of −3.45 ± 0.26‰, reconstructions based on shell δ18O data suggest average seasonal temperature variations between 12.5 ± 3.0 and 25.5 ± 1.1 °C and a mean annual temperature of 17.0 ± 4.1 °C for the outer shelf environment of the WIS. Repeated sudden negative δ13C shifts of up to 2.00‰ and Mn-rich shell growth bands (Mn/Ca ratios up to 90.21 μmol/mol) suggest that P. platinus filter-fed on suspended organic detritus which sank from the upper water column during episodic events. The availability of large amounts of suspended food, however, slowed shell accretion rates of P. platinus. This shell growth behavior combined with the positive δ13C values (0.03–3.96‰) possibly indicate a chemosymbiotic lifestyle that allowed P. platinus to survive under oxygen-depleted conditions at the seafloor.

Assessing cockle shells (Anadara granosa) for reconstruction subdaily environmental parameters: Implication for paleoclimate studies

This study aims to investigate the potential of cockle shells as an environmental recorder, examining the environmental factors controlling the shell growth of the intertidal Anadara granosa from west coast of Malaysia. Subdaily environmental factors were recorded from December 2011 to November 2012. A total of 600 individuals were collected on a monthly basis and the shells sectioned from umbo to ventral margin, polished, etched and photographed under a light microscope to observe microgrowth bands and increments. Comparison of correlation matrix between mean increment width and each environmental factor indicated that shell growth had the highest positive correlation with seawater temperature (+0.72) and weak positive correlation with salinity (+0.53). Multiple regression analysis was used to assess independent associations between shell mean increment width and environmental parameters. Study model showed that 60.8% of the variation in shell growth could be explained by temperature, salinity, rainfall and tidal change. Individually, temperature and salinity made the greatest unique contribution to explain shell growth, respectively (p < 0.01). Laboratory results showed shell growth was in a linear trend to optimum temperature and salinity. These findings provide a basis for the interpretation of the temporal changes in shell microgrowth patterns in terms of environmental conditions of cockle shells.

Age and growth of the sword razor clam Ensis arcuatus in the Ría de Pontevedra (NW Spain): Influence of environmental parameters

The sword razor clam Ensis arcuatus is the most important commercial species of razor clam in Spain, and its fishery in the Ría de Pontevedra (Galicia, NW Spain) is the most productive. Despite the economic importance of this species, information on its biology is scarce. This study reports shell morphometric relationships, age, and growth rates of E. arcuatus in three fishing beds in the Ría de Pontevedra (Brensa, Bueu and Ons, located in respectively the inner, middle and outer zones of the ria), providing the first estimates of growth parameters for the species in the Iberian Peninsula. Growth was estimated by examination of surface growth rings and internal shell microgrowth patterns (acetate peel technique) that proved to be the most suitable method for growth estimate. Growth of E. arcuatus was slower in Bueu (L∞=140.4, k=0.40) followed by Brensa (L∞=151.91, k=0.40) and Ons (L∞=172.7, k=0.33), and the clams reached commercial size in 1.7, 2.3 and 2.8years in Ons, Brensa and Bueu, respectively. The differences in growth between sites in relation to environmental parameters are evaluated and the implications for the razor clam fishery are discussed.

Sclerochronology – a highly versatile tool for mariculture and reconstruction of life history traits of the queen conch,Strombus gigas(Gastropoda)

The queen conch, Strombus gigas, is an important fisheries resource in the Western Tropical Atlantic. In order to maintain harvesting success, improve fisheries management and contribute to mariculture pursuits, a detailed understanding of the life history traits of this species is required. Traditionally, this has been achieved by tedious and time-consuming long-term field observations. This study presents a highly versatile and rapid technique to estimate the timing and rate of shell growth based on sclerochronology. The Belizean S. gigas specimens (N = 2) from the offshore atoll, Glovers Reef, reached their final shell size (maximum shell height: 22.7 and 23.5 cm, respectively; completed formation of the flared lip) after only two years. However, seasonal growth rates varied considerably. Shells grew up to 6 mm d−1 during spring (April-June) and fall (September-November) but only 1 to 2 mm d−1d uring July and August. Furthermore, shell growth ceased between December and March. Fastest shell growth occurred nearly contemporaneously with times of maximum precipitation which probably resulted in increased food availability. Slowest shell growth however, occurred during times of reduced rainfall and reduced riverine runoff, i.e. during times of reduced food supply. Sea-water temperature apparently did not exert a major control on shell growth. Notably, the slow winter growth was marked by a distinct purple-colored growth line in the cross-sectioned flared lip. Formation of a second major growth line (brown) fell together with the main reproduction period (late October/early November). Shell microgrowth patterns potentially represent daily or semidiurnal periods but cannot be used to assign exact calendar dates to each shell portion, because they were not visible across the entire cross-section of the whorl. Also, the protruding spines developed on the outer shell surface do not function as time gauges. The time represented by the shell portion between consecutive spines varies greatly from 1 to 72 days. Sclerochronology can potentially facilitate maricultural strategies and aid in site pre-testing and selection to grow S. gigas.

Environmental and physiological controls on shell microgrowth pattern of Ruditapes philippinarum (Bivalvia: Veneridae) from Japan

The reproductive cycle and shell microgrowth patterns of the venerid bivalve Ruditapes philippinarum from Matsukawa-ura, a small inlet facing the Pacific Ocean, northeastern Japan were examined. Histological examination of the gonads revealed that spawning in this species occurred twice in 2005, once between late June and early August and the other between late September and early October. Comparison of the shell microgrowth patterns with the developmental stages of the gonad in each individual revealed that in spawning individuals (mature and spawning stages), the mean lunar-day growth rates were significantly smaller than those in individuals which were not in spawning condition (spent, recovery and growing stages). In non-spawning individuals, the mean lunar-day growth rates were positively correlated with seawater temperature up to 20°C. However, in spawning individuals, no correlation was observed between shell growth and seawater temperatures >16°C. These facts suggest that physiological stress during reproduction has a negative influence on shell growth and results in spawning breaks. The present study indicate that spawning breaks can be used to identify the timing of sexual maturity and to count the number of spawning events occurring per year in extant and fossil bivalves.

Environmental controls on daily shell growth of Phacosoma japonicum (Bivalvia: Veneridae) from Japan

This study examined the environmental factors controlling the daily shell deposition of the intertidal bivalve Phacosoma japonicum from Seto Inland Sea, west Japan, and Tokyo Bay, central Japan. Sclerochronological analyses of microgrowth patterns in marked-and-recovered specimens in- dicate that a pair of 2 etch-sensitive increments and 2 etch-resistant lines is formed every lunar day (duration 24.8 h). The accretionary pattern of the lunar day growth increments (LDGIs) reflects tidal cycles. Prominent growth lines were formed during spring tides, when the bivalves were subaerially exposed, and weak ones were deposited during neap tides, when they were continuously submerged. The bivalves stop secreting shell carbonate during winter and early spring. The time interval encom- passed by the winter break in the specimens from Tokyo Bay lengthened as the shells grew older. Although seawater temperature is the main controlling factor for shell growth, a number of mutually related environmental factors such as salinity and food availability also affect shell growth. In Tokyo Bay, the broadest LDGIs were deposited between temperatures of 21 and 24°C. Our findings provide a basis for the interpretation of the temporal changes in shell microgrowth patterns in terms of environmental conditions of extant and fossil P. japonicum specimens.

The direct and indirect effects of suction dredging on a razor clam (Ensis arcuatus) population

Surveys were conducted in two shallow bays in the Orkney Islands, UK; Orphir Bay, an unexploited (control) site, and Bay of Ireland, a fished site, to investigate the effects of suction dredging on the resident razor clam, Ensis arcuatus, populations. A lower density and significantly smaller mean length of razor clams were present at the dredged site compared with the control site. The age of individual razor clams was estimated using internal shell microgrowth patterns, visible in acetate peels of polished and etched shell cross-sections. Ensis arcuatus are relatively slow growing animals with the two study populations characterized by old individuals and an obvious lack of juveniles, indicating populations with little resilience to disturbance. An analysis of the shell sections of razor clams from the Bay of Ireland revealed the presence of shell margin breaks, consisting of deep clefts in which sand grains were embedded in the shell matrix, whilst those from Orphir Bay had fewer disturbances to shell growth. It is suggested the disturbances to shell growth are the result of repeated suction dredging operations in the Bay of Ireland. In situ reburrowing experiments were conducted to determine the survival rate of E. arcuatus (<160 mm shell length), returned to the sea after capture and to estimate the indirect effect of dredging on the razor clam population. These individuals displayed a slow initiation of “escape-digging” which rendered them vulnerable to attack from predatory crabs and fish, indicating that there is likely to be a low survival rate of any returned undersized clams or ones that are disturbed and escape from the suction dredge.

Shell microgrowth patterns of bivalves reflecting seasonal change of phytoplankton abundance

Shell microgrowth patterns of bivalves reflecting seasonal change of phytoplankton abundance

Records of Life-History Information Preserved in the Shell Microgrowth Patterns

Records of Life-History Information Preserved in the Shell Microgrowth Patterns

The effects of dredging on shell formation in the razor clamEnsis siliquafrom Barrinha, southern Portugal

Shell growth of the razor clamEnsis siliqua(Mollusca: Bivalvia) from southern Portugal has been analysed using both surface growth rings and internal shell microgrowth patterns. The growth rate estimated from an analysis of the growth rings is slower (von Bertalanffy growth, constant K=0·27) than that determined from the annual narrowing of the internal microgrowth patterns present in shell sections (K=0·65), although both methods predict a similar asymptotic length, L∞, of 144·8 and 139·6 mm, respectively.The Barrinha razor clam population occurs in a heavily dredged area and an analysis of shell sections reveals the presence of a series of shell margin breaks consisting of deep clefts in the outer shell layer in which sand grains are embedded. It is suggested that these disturbances to shell growth are the result of repeated dredge damage. The frequency of the clefts increases with the size and age of the razor clams, and thus the shells provide a record of the intensity and frequency of unsuccessful capture or retrieval attempts. Cleft formation also occurred seasonally with the deposition of a small cleft during June, but these annual clefts were much less pronounced than those caused by dredge damage.

Annual variation in the growth rate of Yoldia notabilis (Bivalvia: Nuculanidae) in Otsuchi Bay, northeastern Japan, analyzed using shell microgrowth patterns

Annual variation in the growth rate of the protobranch bivalve Yoldia notabilis (collected in Otsuchi Bay, northeastern Japan between 1989 and 1991) was determined by measuring shell length at successive growth lines. Factors affecting growth rates were assessed by examining long-term environmental data. Shell cross-sections of Y. notabilis showed a clear pattern of internal growth lines which formed simultaneously with the annual external lines on the outer shell surface. Hence, they were used as an age marker. A maximum lifespan of 17 yr was determined for this species, and a sigmoidal growth curve was obtained by the internal growth line analysis. Examination of the growth lines also revealed a large annual variation in growth rate, fluctuating as much as 32-fold during the past 9 yr. The variation correlated negatively with water temperature and positively with chlorophyll a content in the water column. It is suggested that the variation in annual growth rate is dependent on food supply during the spring phytoplankton bloom which varies from year to year according to the flow of the cold Oyashio current each spring.