Age and growth of the naticid gastropod <Emphasis Type="Italic">Polinices pulchellus</Emphasis> (Gastropoda: Naticidae) based on length frequency analysis and statolith growth rings

In Red Wharf Bay, UK the naticid gastropod, Polinices pulchellus, was more abundant and more highly aggregated during the summer months (June–August 2001) than during the winter (December 2000). Whilst small numbers of juvenile P. pulchellus (4–6 mm shell length) were present throughout the year the population consisted mainly of individuals of 12–14 mm shell length. Juvenile snails grew rapidly in size during the winter and early spring; growth then virtually ceased between May and June, following which there was a further period of rapid growth between August and February. Densities ranged between 57 and 4,073 ha⁻¹ and the largest individual collected during this investigation measured 16.2 mm in shell length. Statoliths from adult P. pulchellus revealed the presence of a settlement ring and two prominent growth rings (rings 1 and 2). A curvilinear relationship exists between statolith diameter and shell length in snails up to 16 mm in length. Settlement rings ranged in diameter from 19.7 to 45.2 μm (mean 29.8 μm; SE=0.41) giving an estimated shell length of the settled juvenile of 1.1 mm. The diameter of ring 1 and ring 2 were significantly correlated indicating that rapid growth during the first year is maintained during year 2. Shell lengths estimated from the diameters of the prominent statolith rings and those obtained from length frequency data analysis (LFDA), were broadly congruent strongly suggesting an annual periodicity to the statolith rings. The largest snails (>15 mm) present within this population were estimated to be between 2 and 3 years old. Von Bertallanfy seasonal growth curves obtained from the LFDA predicted values of L∞, K and t ₀ of 14.32 mm, 1.54 and −0.14 years, respectively, suggesting that P. pulchellus rapidly attains its maximum asymptotic size.     

Observations on the biology of Donax trunculus and D. vittatus at Ile d'Oléron (French Atlantic coast)

Observations have been made on the biology of two species of the bivalve genus Donax, on two beaches, Vertbois and St. Trojan, on the Ile d'Oléron, French Atlantic coast. The two species displayed different vertical distribution: D. trunculus Linné in the intertidal; and D. vittatus (da Costa) between low-water spring tide (LWST) and 5 to 6m depth, with only the fringe of the population extending to the shore. D. trunculus also showed differential distribution by size or age, the youngest individuals being highest on the shore, and the oldest near LWST. The two species exhibited a similar pattern of seasonal recruitment and growth, but in both there were differences in growth characteristics between the two beaches, individuals at St. Trojan growing to a larger size than those at Vertbois. The mean pattern of mortality in the two areas was similar, and productivity per 100 recruits surviving to the first winter following settlement was greater at St. Trojan than at Vertbois. For D. trunculus the mean population density at Vertbois was higher and the production per unit area on the two beaches was similar. Production to biomass (B) and elimination to biomass (B) ratios were similar for the two beaches for both species, and while production was greater for D. trunculus at both beaches, the B and B ratios were higher for D. vittatus. Comparisons with other published data reveal that the rate of growth of D. trunculus is similar throughout its range from Brittany to the Mediterranean Sea, while that of D. vittatus shows more variation. In both species, there is a trend of increasing P/B and E/B ratios from north to south throughout the geographical range.     

Age and growth of the fan mussel Pinna nobilis from south-east Spanish Mediterranean seagrass (Posidonia oceanica) meadows

The calcitic and aragonitic shell of the fan mussel Pinna nobilis L. contains a record of the environmental changes experienced during its growth. Stable-isotope analyses of oxygen (¹⁸O:¹⁶O) in shell carbonate from the calcitic outer shell-layer have been used to validate the periodicity of clearly defined concentric rings on the aragonitic posterior adductor-muscle scar and to estimate the age and growth of fan mussels growing in Posidonia oceanica (L.) meadows at four locations on the south-east Spanish Mediterranean coast. The stable oxygen-isotope records obtained at intervals along a profile across the shell surface enabled seasonal changes in water temperature to be established, and hence seasonal patterns of shell growth to be inferred. Muscle-scar rings were found to be deposited annually in the shell in the spring and early summer (a period of increasing water temperatures), and represent an interruption in the migration of the posterior adductor muscle along the inner surface of the shell. In small pinnids (<25 cm) accretion of the shell is rapid during the first year, but in the second year it is distinctly slower than at the same time the previous year. This slowing down in growth during the second year coincides with the appearance of the “first” distinct muscle-scar ring, indicating that Pinna nobilis does not form a muscle-scar ring during its first year of shell growth. Maximum growth rates were recorded amongst pinnids from Carboneras, where they achieved a length of 59 cm in 8 yr, whilst those from Aguamarga were estimated to be the oldest (attaining a length of 45 cm in 13 yr). Received: 26 January 1998 / Accepted: 8 October 1998     

Age,growth and population structure of <Emphasis Type="Italic">Modiolus barbatus</Emphasis> from the Adriatic

Age, growth and population structure of Modiolus barbatus from Mali Ston Bay, Croatia were determined using modal size (age) classes in length frequency distributions, annual pallial line scars on the inner shell surface, internal annual growth lines in shell sections of the middle nacreous layer and Calcein marked and transplanted mussels. The length frequency distributions indicated that M. barbatus attain a length of ∼40 mm in 5–6 years indicating that a large proportion of the population in Mali Ston Bay is <5 years old. Some mussels of ∼60 mm were predicted to be 14 years old using the Von Bertalanffy growth (VBG) equation. Up to the first 6 pallial line scars were visible in young (<6 years) mussels but in older shells the first scars became obscured by nacre deposition as the mussel increased in length and age. The age of the older shells (>6 years) was determined from the middle nacreous lines in shell section, which formed annually in winter between February and March; the wider dark increments forming during summer (June to September). The oldest mussel, determined from the middle nacreous lines, was >12 years, with the majority of mussels aged between 3 and 6 years of age. The ages of mussels ascertained using the growth lines were not dissimilar to the ages predicted from the length frequency distributions. Age at length curves produced using modal size class data were not different from the data obtained using the pallial scar rings and internal growth lines. Taken together these data suggest that M. barbatus attains a length of 40 and 50 mm within 5 and 8 years, respectively. Eighty one percent of individual M. barbatus injected with a Calcein seawater solution (300 mg Calcein l⁻¹), into their mantle cavity successfully deposited a fluorescent line, which was visible in suitably prepared shell sections under ultra violet light. Incorporation of Calcein into the mussel shells was seasonally variable with the lowest frequency of incorporation in mussels marked in February and recovered in May. Seasonal shell growth was observed with significantly higher growth rates in mussels marked in May and removed in August (ANCOVA, F _3,149 = 23.11, P < 0.001). Mussels (∼18 to 22 mm) marked in May and recovered in August displayed maximal growth rates of >2.5 mm month⁻¹ compared with a mean mussel growth rate of 1.2 ± 0.6 mm month⁻¹. At other times of the year mussel shell growth ranged from immeasurable to 1.48 mm month⁻¹.     

Experimental prey species preferences of Hexaplex trunculus (Gastropoda: Muricidae) and predator–prey interactions with the Black mussel Mytilus galloprovincialis (Bivalvia: Mytilidae)

Hexaplex trunculus is one of the most widespread Mediterranean species of muricid gastropod and lives on rocky, sandy-mud and mud substrata. Although common in the Adriatic Sea, relatively little is known about its ecology especially feeding behaviour. The aim of this study was to explore the aspects of the feeding behaviour of H. trunculus using Arca noae, Modiolus barbatus and Mytilus galloprovincialis as experimental prey. Prey species preference, predator size, prey size choice, feeding rates, handling times and mode and place of attack were analysed. Typically, only M. galloprovincialis was attacked: A. noae rarely at the byssal gape and M. barbatus never. Small (40 mm) H. trunculus could not easily attack large M. galloprovincialis (65 mm) and preferred small (20 mm) and medium (35 mm) sized prey. Conversely, medium (55 mm) and large (70 mm) H. trunculus fed randomly on M. galloprovincialis of all three sizes. The feeding strategy adopted by H. trunculus individuals varied with respect to size. A tendency to drill the prey shell was recorded for small predators, whereas marginal chipping was adopted more frequently by large individuals. On average small, medium and large H. trunculus consumed 2.4±1.6 (range 0–4), 1.2±1.6 (range 0–4) and 2.0±2.1 (range 0–6) M. galloprovincialis, respectively. There was a statistically significant difference in prey-handling time with respect to the method of access adopted, predator and prey sizes. The time required to access a M. galloprovincialis individual by marginal chipping was considerably less than that required for drilling. H. trunculus consumed an average of 0.60±0.80 g M. galloprovincialis tissue dry weight over a 5-week period, that is, ~40% of its own tissue body weight. This translates to an average-sized (55 mm shell height) H. trunculus consuming ~18 M. galloprovincialis of 50 mm shell length (minimum marketable size) per year. H. trunculus showed no preference to drill either the left or right valves of M. galloprovincialis but generally attacked the posterior shell margin.     

Short-term shell growth in bivalves: Individual,regional, and age-related variations in the rhythym of deposition ofCerastoderma (=Cardium) edule

The influence of potential sources of variations (age, site, region) on the production of shell microgrowth increments was studied in the cockleCerastoderma edule (L.) from the shores of Denmark, Jersey Island and South Wales between 1978 and 1986. Microgrowth increments in the shell of the cockle were counted between annual growth marks corresponding to the second, third, and fourth yearly growth period of the cockle. The number of microgrowth increments per year showed a decrease with increasing age. Increments formed after deposition of the last annual mark in cockles sampled at different dates indicate that the rate of increment formation differed between age classes and populations. Furthermore, we observed pronounced intrapopulation differences in the number of increments for specimens of the same age, and differences in both number and clarity of increments in subtidal and intertidal populations. Our results do not support the hypothesis of a general endogenous rhythm of microgrowth that closely corresponds to tidal rhythms inCerastoderma edule. Instead, they emphasize the plasticity of deposition according to the origin and age of the experimental specimens.     

Environmental controls on shell growth rates and δ<Superscript>18</Superscript>O of the shallow-marine bivalve mollusk <Emphasis Type="Italic">Phacosoma</Emphasis><Emphasis Type="Italic">japonicum</Emphasis> in Japan

Microgrowth patterns and the oxygen isotope composition of juvenile, shallow-marine bivalve mollusk shells of Phacosoma japonicum (Reeve) in Japan were analyzed and cross-calibrated with environmental parameters. Mark-and-recovery experiments indicate that a pair of two microgrowth lines and two microgrowth increments is produced every lunar day. This finding makes it possible to assign exact calendar dates to each portion of the shell. Average daily growth rates decrease by 61% from age two to three and 55% from age three to four. The length of the growing season and the growth rate are mainly controlled by temperature: shell growth ceases below 14.2°C (age two) and 16.8°C (age four) and is most rapid between 24.6°C and 27.2°C. Based on local temperature cycles, the growing season is longest in Seto Inland Sea, central Honshu (from May to November) and shortest at Hakodate Bay, North Japan (from June to October). The annual oxygen isotope profiles of the shells reflect the temperature cycle and the varying amounts of freshwater added to the seawater by precipitation. The most negative '¹⁸O values of -3.15‰ occur during the rainy season, i.e. during the monsoon and typhoon seasons. Growth rates are only slightly affected by salinity changes. Strongly reduced growth rates during the second half of the year at Seto Inland Sea and to a lesser extent at Tokyo Bay are explained by nutrient deprivation. Our study provides the basis for the use of P. japonicum in high-resolution ecological studies and environmental reconstructions.     

Donax trunculus and Venus verrucosa as bioindicators of trace metal concentrations in Mauritanian coastal waters

Trace-metal concentrations (Cd, Cu, Fe, Mn and Zn) were investigated in two species of abundant filter-feeding molluscs from Mauritania, the wedge shell Donax trunculus L. and the clam Venus verrucosa L. D. trunculus were collected on the beach of Nouakchott at low tide and V. verrucosa were sampled at the Banc d'Arguin at depths varying from 10 to 20 m, in mid-February 1987. D. trunculus contains significantly higher Fe and Zn concentrations than the clam. Total trace-metal content per individual (Y) in D. trunculus could be related to body weight (W) as the power function Y=aW ^b . The subsequent regression coefficient b was >1 for Cu, Fe, Mn and Zn and >1 for Cd. Metal concentrations in both species decreased in the order: Fe>Zn>Mn>Cu>Cd. Comparison of trace-metal concentrations in the small D. trunculus and the large V. verrucosa revealed lower contents in V. verrucosa, except for Cd. The trace-metal distribution in the various organs of V. verrucosa indicates that gills seem to concentrate metals, except Cu, to a greater degree than the other organs (visceral mass and remainder). The relatively elevated content of Fe in D. trunculus and of Cd, Fe and Zn in the gills of V. verrucosa seem to be of natural origin. In view of the scarcity of Mytilus sp. along the Mauritania coast, the molluscs D. trunculus and V. verrucosa are proposed as useful bioindicators of trace-metal concentrations.     

Analysis of growth rate in Mya arenaria using the Von Bertalanffy equation

Field studies were conducted in Gloucester, Massachusetts, USA, to determine linear shell growth rates for Mya arenaria. These rates were then compared with those reported for the same species from other locations. Most shell deposition occurred from March through November of each year. Winter interruptions in growth were not as marked in the small clams as in the larger ones (>60.0 mm). Annual variations in growth were slight during the period 1973–1974. Growth of mature clams (>35.0 mm) slowed during the spawning season. No significant sexual dimorphism in mean annual growth rates was detected. Winter rings were shown to be a reliable method for determining age in clams from Gloucester. Age-size relationships, based on two independent measures of annual growth, winter rings and tagging experiments, were computed using the Von Bertalanffy growth equation. No well-defined latitudinal patcerns in growth could be established for M. arenaria.     

Age and growth of the alfonsino Beryx splendens over the seamounts off New Caledonia

Age and growth of the alfonsino Beryx splendens from New Caledonia seamounts were determined by examination of whole and sectioned otoliths. One growth-ring (annulus) in the otoliths appears to be laid down each year. It consists of one opaque (summer, fast-growing) zone and one hyaline (winter, slowgrowing) zone. Thin-sections of otoliths revealed daily rings which allowed us to estimate that the formation of the nucleus takes 10 mo. The first annulus following the nucleus is incomplete. Females have a higher growth rate than males. Sexual maturity is reached at the age of 7 to 8 yr for males and 6 yr for females. Maximum age attained would be 20 yr for alfonsino >50 cm in fork length. the results are compared with those from the few other studies on the growth of alfonsino.     

Growth,survivorship, life-span,and sex change in the hermaphroditic shrimp<Emphasis Type="Italic"> Lysmata wurdemanni</Emphasis> (Decapoda: Caridea: Hippolytidae)

Lysmata wurdemanni (Gibbes) is a protandric simultaneous hermaphrodite. All individuals first mature as a male-phase individual (MP) and then later change to a female-phase individual (FP) that spawns and broods embryos but can also mate as a male. A Gulf of Mexico population was sampled monthly for 1 year and bimonthly the next. Estimates of basic population parameters were obtained from cohort analysis to reveal possible factors explaining the unusual sexual biology of L. wurdemanni as well as the broad variation in the size (age) of change from MP to FP. Growth rates of individuals from cohorts varied from 4–7 mm carapace length year ^-1. Growth of small MPs in the laboratory was somewhat faster but concordant with growth rates estimated from field samples. The period from recruitment to >50% sex change in cohorts varied from 3 months to 1 year. In the laboratory, the size and interval to sex change was similar to that of the most rapidly changing cohort observed. Survivorship of cohorts was high until later in life; life-span was estimated to be 12–18 months. Rates of sex change were highest from late winter through spring, in time for the spring–summer breeding season. The size and age of sex change in cohorts were related to the season of recruitment. MPs recruited from late winter to mid-spring rapidly changed to FPs at a relatively small size. A majority of MPs recruited in the summer and autumn did not change to FPs until the following late winter to spring, and they did so at a larger size. Rates of sex change were not correlated with the sexual composition of the population. We conclude that seasonal factors related to female breeding greatly influence sex change in L. wurdemanni. We found no evidence to support demographically influenced and socially mediated environmental sex determination, which has been suggested for L. wurdemanni and other sex-changing caridean shrimps.     

Growth and spawning of Urechis caupo (Echiura) in Bodega Harbor,California

Growth and spawning of the large, infaunal echiuran worm Urechis caupo Fisher and MacGinitie were studied at Bodega Harbor on the coast of central California, USA, from 1978 through 1981. In situ growth rates of marked worms were negatively related to initial size. Short-term, summer growth rates (volmo^–1) of small worms (<80 ml) were greater than longer-term growth rates measured over several seasons (asesonal). Size-frequency distributions of worms sampled from two sites also suggested a seasonal growth pattern with relatively fast spring-summer growth and slower winter growth. However, larger worms sometimes lost volume during in situ growth experiments, and the loss was most pronounced during short-term, summer growth periods. It is suggested that energy used in burrow construction may have contributed to volume loss during short-term growth experiments. In contrast, longer-term, aseasonal growth rates were nearly always positive, and indicated that reproductive size (about 56 ml) could be reached within about 1.5 yr of recruitment, and a large size (about 158 ml) could be reached within about 6 yr. A seasonal pattern of spawning was observed during three consecutive years, as indicated by ripeness indices (storage organ dry weight ÷ body wall dry weight). At least two spawning episodes occurred annually: ripe gametes that accumulated in the storage organs during the summer and fall were spawned during the winter; gametes that accumulated during late winter and early spring were spawned during the spring or early summer. Worms were spawned-out by mid-summer.     

Temporal population dynamics in arrow squid<Emphasis Type="Italic"> Nototodarus gouldi</Emphasis> in southern Australian waters

Nine monthly samples of arrow squid Nototodarus gouldi were obtained off Portland, Australia, during 2001. Statolith age analysis was used to determine growth rates and cohort structure during the study period. The results of statolith increment periodicity experiments were inconclusive due to difficulties in discerning increments in the cultured squids, although the region of the statolith in the maintained squids did increase over time. The maximum age obtained was 360 days, which is consistent with a 1-year life cycle in this species. Squid obtained were >150 days old and usually >200 mm mantle length. While there was often a mix of maturity stages for females, the majority of males were mature. Monthly length frequency distributions suggested that there was a complex mixture of cohorts in the samples obtained. Fitting a Normal mixture model to the age frequency distribution suggested that at least four cohorts were present during the period of the study. Growth was modelled with an exponential function with individuals grouped according to hatch season. The rate of growth for seasonal groups of squid was considerably different between males and females. There was no evidence of seasonal differences in growth rates of males. In contrast, the summer hatched females had significantly greater growth rates than winter and spring at P=0.05, and the growth rates of autumn hatched females were found to be significantly different to the winter hatched females at the 0.1 level.Communicated by M.S. Johnson, Crawley     

Phosphorus- and nitrogen-limited photosynthesis and growth of Gracilaria tikvahiae (Rhodophyceae) in the Florida Keys: an experimental field study

The relative effects of NH ₄ ⁺ (N) and PO ₄ ^3- (P) on growth rate, photosynthetic capacity (P_max), and levels of chemical constituents of the red macroalga Gracilaria tikvahiae McLachlan were assayed during winter and summer, 1983 in inshore waters of the Florida Keys by using in-situ cage cultures. During winter, both N and P enrichment enhanced growth over that of ambient seawater; however, P rather than N accounted for more (60%) of the increased winter growth. During summer, P, but not N, enhanced growth over ambient seawater and accounted for 80% of increased growth. Similarly, P_max was enhanced by both P and N during winter (but mostly by P) and only by P during summer. Elevated C:P, C:N and N:P ratios of G. tikvahiae tissue during winter, but only C:P and N:P ratios during summer, support the pattern of winter N and P limitation and summer P-limitation. This seasonal pattern of N vs P limited growth of G. tikvahiae appears to be a response to seasonally variable dissolved inorganic N (twofold greater concentrations of NH ₄ ⁺ and NO ₃ ^- during summer compared to winter) and constantly low to undetectable concentrations of PO ₄ ^3- . Mean C:P and N:P ratios of G. tikvahiae tissue during the study were 1 818 and 124, respectively, values among the highest reported for macroalgae.     

Life history and production of the mysid <Emphasis Type="Italic">Orientomysis robusta</Emphasis>: high <Emphasis Type="Italic">P/B</Emphasis> ratio in a shallow warm-temperate habitat of the Sea of Japan

Although mysids play important roles in marine food chains, studies on their production are scarce, especially for warm-water species. We investigated life history and production of Orientomysis robusta in a shallow warm-temperate habitat of the Sea of Japan. Its spawning and recruitment occurred throughout the year; 19 overlapping cohorts were recognizable over an annual cycle. The summer cohorts recruited in July–September exhibited rapid growth, early maturity, small brood size, and small body size. A converse set of life history traits characterized the autumn–winter cohorts recruited in October–March. The spring cohorts recruited in April–June had intermediate characteristics of both cohorts. Life spans were 19–33, 21–48, and 69–138 days for summer, spring, and autumn–winter cohorts, respectively, and mortality rates were high for spring and summer cohorts, especially during June–August but were low for autumn–winter cohorts. Production calculated from the summation of growth increments was 488.8 mg DW m⁻² year⁻¹ with an annual P/B ratio of 21.26. The short life span seems to be responsible for such an extremely high P/B ratio. A method not requiring recognition and tracking cohorts gave similar values (534.0 mg DW m⁻² year⁻¹ and 20.49). The close agreement in production values between the two methods indicates our estimates are valid.     

Prevalence, patterns, and effects of shell damage on Geukensia demissa in South Carolina estuarine habitats

Shelled molluscs frequently exhibit a record of damage on exterior surfaces that can evidence past predation attempts and may affect survival and growth. In South Carolina populations of the ribbed marsh mussel, Geukensia demissa, >90% of the individuals and up to 60% of the total shell area are damaged. A trend toward greater amounts of damage occurred on mid-marsh compared to oyster reef mussels from the barrier beach side of inlets. Shell damage effects on survivorship and shell and tissue growth were assessed seasonally during multi- and single-season field experiments. Mussels from a common mid-marsh site were divided into size classes (~50 or 70 mm), treated to create two damage levels (undamaged and damaged), and replaced within mid-marsh exclusion cages to minimize additional shell damage. In both multi- and single-season experiments increased shell damage resulted in significantly greater mortality. Linear shell growth was unaffected by increased damage, but 50 mm mussels grew twice as fast. Shell mass increased 16–50% in the multi-season and single-season winter period, but decreased 7–12% during the single-season summer period. Tissue mass significantly decreased 31–43% in 50 mm damaged mussels, but increased by 33% for 70 mm mussels in both multi-season and the single-season winter period experiments. Shell damage did reduce tissue mass 43% in 70 mm single-season summer mussels. Experimental results indicate shell damage from a simulated increase in predation can affect negatively both survival and growth of marsh mussels. Seasonal timing of shell damage and initial mussel size also influenced the effects of sublethal predation on shell and tissue growth. The previously unrecognized importance of sublethal predation and the resultant significant negative effects of shell damage on survival and growth will affect the distribution and population dynamics of G. demissa in coastal marshes and will influence the overall contribution of ribbed mussels to estuarine ecosystems.     

Reproductive habits and life cycle of the small clam Kingiella chilenica (Bivalvia: Cyamiidae) in an estuarine sand flat from the south of Chile

A population of the small clam Kingiella chilenica Soot Ryen 1959 was studied from March 1986 to December 1988 in an intertidal flat at Queule River, in the south of Chile. The life cycle and life history pattern of the bivalve were established contrasting population structure and dynamics to its reproductive habits. Individuals are gonochoristic and semelparous, presenting a typical annual life cycle. The species is a sequential brooder whose embryos undergo direct development. After the brooding season (summer through autumn), the adults disappear gradually (autumn through winter). Recruited juveniles overwinter during a relatively long period, undergoing rapid growth during the spring to attain the adult stage during the summer. The number of brooded embryos increases in proportion to adult length cubed. Life history traits of this bivalve are compared to those reported for other small brooder clams. Some basic tendencies become apparent when traits for semelparous versus iteroparous species are contrasted. As in other semelparous sequential brooders (Transennella tantilla, Gaimardia bahamondei), the relationship between brood size and shell length obseved in K. chilenica does not fit the allometry hypothesis for marine brooding invertebrtes that allometric constraints on the brooding space limit the fecundity of larger individuals. Also contrary to theoretical predictions, small body size does not limit the diversity of a clam's developmental patterns. Possible explanations for this finding are discussed.     

Population dynamics and growth of <Emphasis Type="Italic">Nassarius reticulatus </Emphasis>(Gastropoda: Nassariidae) in Rhosneigr (Anglesey,UK)

Seasonal changes in catch rate, growth and mortality of Nassarius reticulatus from an intertidal lagoon and a wave-exposed beach at Rhosneigr (Anglesey, North Wales, UK) are described. The number of N. reticulatus caught in baited traps from the lagoon was significantly higher (>125 individuals trap⁻¹) during the summer (>18°C), than at <12°C (<65 individuals trap⁻¹), and the numbers caught in the lagoon were an order of magnitude greater than on the beach, >13 individuals trap⁻¹ in July (>16°C), and <5 individuals trap⁻¹ between December and April (<9.5°C). Predictions of shell growth attained by N. reticulatus annually in the lagoon using graphical modal progression analysis (MPA) of length frequency data, were similar to the growth of marked and recaptured lagoon N. reticulatus. Predictions of shell growth using computerised length frequency distribution analysis (LFDA), however, did not reflect the growth as accurately as MPA. Modal progression analysis demonstrated that N. reticulatus from the lagoon achieved a higher asymptotic maximum shell length (L _∞) and a lower growth constant (K) than animals from the beach. Shell growth was seasonal with growth of the lagoon individuals slowing down towards the end of September and resuming in early April, about a month later than the beach individuals. Mortality of N. reticulatus was greater during the summer, and survival was lower in the lagoon than on the beach. Recruitment patterns were similar in the lagoon and on the beach, and MPA and LFDA predicted that larval N. reticulatus settled between late summer and early autumn, with juveniles (7–8.9 mm) appearing in the population the following year, between February and April. Growth of male and female N. reticulatus in the laboratory was similar and was temperature and size dependent. The different growth patterns between N. reticulatus from the two habitats, predicted using MPA, were maintained when individuals were reared under laboratory conditions for ∼6 months; N. reticulatus <21 mm from the beach grew faster than individuals from the lagoon, although N. reticulatus >21 mm from the lagoon grew faster and attained a larger length (26 mm) than individuals from the beach (24 mm). Low food availability did not affect N. reticulatus survival in the laboratory but significantly suppressed shell growth.     

Age determination of the soft-shell clam Mya arenaria using shell internal growth lines

Shells of known-age Mya arenaria have revealed an internal annual growth pattern in this bivalve. The number of external growth rings on the shell exterior does not correspond to the age of the clams. This study provides an alternative method to using external annual rings for age determination. The internal growth lines are visible in thin sections when the shells are cut from the umbo to the ventral margin. The lines are formed by late spring of each year prior to spawning and are probably in response to decreased winter growth. When the 7 year olds were examined it was difficult to distinguish the most recent growth line and the inner shell layer. This could result in ages being underestimated. This annual pattern of internal growth lines could be useful to biologists and paleoecologists engaged in population studies.     

Spatial and temporal variation in distribution and protein ubiquitination for <Emphasis Type="Italic">Mytilus</Emphasis> congeners in the California hybrid zone

Along the west coast of North America, the invasive mussel Mytilus galloprovincialis and a native congener M. trossulus overlap in range and compete for habitat in an extensive hybrid zone along central California. The two species have been shown to exhibit differential abiotic tolerances in laboratory studies, yet little is known about how such tolerances affect spatial and temporal patterns of geographic distribution, particularly in areas of competition. We examined distributions of the two congeners and their hybrids in neighboring intertidal and subtidal habitats in Bodega Bay, CA over 2 years, and compared shell length and seasonal ubiquitin (Ub) conjugates to estimate protein turnover and physiological stress for the species at each site. The two species were spatially segregated, with M. galloprovincialis dominating the subtidal habitat, and M. trossulus constituting a majority of the intertidal mussel population. Hybrid individuals appeared in low numbers at both sites. For each habitat, there was no statistical difference between shell lengths of M. galloprovincialis and hybrids but M. trossulus mussels were statistically smaller than the other two. In regards to physiological performance, ubiquitin conjugate values showed different seasonal cycles for the two species, suggesting different periods of peak environmental stress. The highest levels of Ub-conjugated proteins were observed in winter for M. galloprovincialis and in summer for M. trossulus, consistent with the respective range edges for their distributions since Bodega Bay is near the northern range edge of the invader and the southern edge of the native species. These findings suggest that future assessments of Mytilus populations along the California coast may need to consider vertical distributions and seasonal cycles as part of monitoring and research activities.