Shell morphometric relationships of the most common bivalve species (Mollusca : Bivalvia) of the Algarve coast (southern Portugal) (original) (raw)
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Scientia Marina, 2002
A study was undertaken to evaluate the existence of depth segregation between size classes of Donax trunculus populations that occur along the Algarve coast (southern Portugal). Five collecting areas were sampled in the Ria Formosa barrier islands, namely in the Culatra, Barreta and Armona Islands, between March and June 1998. The study was based on size frequency distribution analysis and shell biometric relationships. The size frequency distribution showed the predominance of smaller individuals (<25 mm) in the renewal area (0.5-1.0 m depth) and the prevalence of larger individuals (≥25 mm) at greater depths (4.0-6.0 m depth). The biometric study revealed the existence of significant differences in the type of growth between size classes in relation to depth distribution and burrowing activity. On the basis of these results, some specific management measures were proposed for this important bivalve fishery, taking into account the distinct fishing strategies and operations (manual and boat-operated dredging) performed at different depths.
The European Zoological Journal, 2019
Length-weight relationships of bivalve species collected during razor clam (Ensis minor) surveys along Italian coastal waters (Northern Adriatic and Tyrrhenian Sea) in the 3-year period 2016-2018 are reported. A total of 13,588 individuals, belonging to 12 bivalve species and 20 populations between the Adriatic and Tyrrhenian Seas, were sampled for this study. Analyzing growth parameters for each population, we found 11 allometries and nine isometries. About half of the species investigated showed different growth characteristics between the two areas.
Fisheries Research, 1999
The shell growth and reproductive cycle of Donax trunculus (Mollusca: Bivalvia) from southern Portugal were studied from December 1993 to November 1994. Both the acetate peel method and quanti®cation of surface growth rings were used to establish age and estimate growth rate. Widely spaced growth bands were formed in spring and summer whilst narrowly spaced bands were deposited in late summer and early autumn. No cessation of growth was observed during the winter. The von Bertalanffy growth curve estimated from the internal bands did not differ signi®cantly from that obtained from the surface rings. However, the age of clams can be determined more accurately from acetate peels than directly from surface rings. Laboratory experiments demonstrated that periodicity of the deposition of microgrowth bands was related to an innate rhythm. Gonadal development was monitored using standard histological methods. Both males and females showed synchronism in gonadal development. The gametogenic cycle began in late November and ended in late August. Spawning occurred between March and August with two major spawning phases: March and May±August. D. trunculus reached maturity during the ®rst year of life.
The present study aimed at estimating the age and growth in three populations of Dosinia exoleta from the Portuguese coast (Aveiro in the north, Setúbal in the southwest and Faro in the south). Two techniques were compared to ascertain the most suitable method for ageing D. exoleta. Growth marks on the shell surface and acetate peel replicas of sectioned shells were the techniques applied. Two hypotheses were tested: growth parameters present latitudinal variation along the Portuguese coast; growth parameters are influenced by the fishing exploitation. Shell surface rings proved inappropriate for ageing this species, whereas acetate peels provided realistic estimates of the von Bertalanffy growth parameters (K, L ? and t 0 ). A latitudinal gradient in growth rate was detected, with a clear southward increase in the growth coefficient (K) of D. exoleta (Faro [ Setúbal and Aveiro) indicating that warmer waters in southern Portugal provide optimal conditions for the growth of this species. Fishing exploitation in northern Portugal targets larger individuals and leaves behind a younger population of smaller individuals, decreasing the asymptotic shell length (L ? ) of D. exoleta from Aveiro. The overall growth performance was compared among populations of D. exoleta and with other venerid species worldwide.
Journal of Sea …, 2011
This study investigated the absolute and relative growth patterns of the fan mussel Pinna nobilis along the Tunisian coastline, taking into consideration both the variability among different areas and between the two shell forms "combed" and "straight and wide". Five subpopulations of the species were sampled, one from northern, two from eastern and two from southern Tunisia. Various assumptions on the growth patterns were tested based on an information theory approach and multi-model inference. For absolute growth, the assumption of different growth patterns between the two shell forms of P. nobilis and no difference among subpopulations was the most supported by the data. For the same age, "straight and wide" individuals gained on average greater lengths than the "combed" individuals. The absolute growth of the species was found to be asymptotic and the logistic model was the one most supported by the data. As for the relative growth, apart from the classical allometric model Y = aX b , more complicated models of the form lnY = f(lnX) that either assumed non-linearities or breakpoints were tested in combination with assumptions for possible differences between the two forms and among subpopulations. Among the eight studied relationships between morphometric characters, the classical allometric model was supported in only two cases, while in all other cases more complicated models were supported. Moreover, the assumption of different growth patterns between the two forms was supported in three cases and the assumption of different growth patterns among subpopulations in four cases. Although precise relationships between the morphometric plasticity of the fan mussel and environmental factors have not been proven in this paper, local small scale constraints might be responsible of the different growth patterns observed in the same locality. A possible co-action of genetic factors should be evaluated in the future.
Brazilian Journal of Oceanography, 1998
The spatial distribution of bivalve molluscs and its relation to granulometry and to the percentage of organic matter and silt-clay were studied in the Saco do Céu Inlet. Bivalves and samples of sediment were collected in 39 stations, in January and July 1992, using a 0.1 m2 Petersen grab. The type of sediment varied :&omvery fine to coarse sand. Nineteen species of bivalves were quantified, 14 of which were present in the two periods of the year. The highest diversity was found in medium and fine sand in summer and in coarse sand in winter. These bottoms presented a greater structural heterogeneity. A community dominated by Corbula caribaea was distinguished in fine bottoms with relative high content of organic matter, whereas another community dominated by Anomalocardia brasiliana occurred in coarser bottoms. Both communities were distributed in continuum a10nga sediment gradient.. Resumo: A distribuição espacial dos bivalves e sua relação com a granulometria e os teores de matéria orgânica e silte-argila foram estudados no Saco do Céu. Obteve-se amostras de fauna e sedimento em 39 estações nos meses de janeiro e julho de 1992, utilizando-se um busca-fundo de Petersen de 0,1 m2. O sedimento variou de areia fina a areia grossa. Foram quantificadas 19 espécies sendo que 14 ocorreram nos dois períodos do ano. Os fundos de areia média e [ma no verão e areia grossa no inverno apresentaram os maiores valores de diversidade e uma maior heterogeneidade estrutural. Evidenciou-se a existência de uma comunidade dominada por Anomalocardia brasiliana em fundos grossos e outra dominada por Corbula caribaea em fundos finos, ricos em matéria orgânica. Ambas distribuíram-se em contínuo, ao longo de um gradiente sedimentológico.
Regional and temporal changes in bivalve diversity off the south coast of Portugal
2008
From 2000 to 2006, a total of 75 bivalve species were identified, varying from 29 (spring 2001) to 54 species (spring 2005) per year. Seasonal tendencies in diversity varied according to year, thus the interpretation of long-term and regional scales is essential before drawing any conclusions in other studies. Richness and diversity consistently decreased with depth and increased with sediment grain size (from low in very coarse sand to high in coarse silt). Diversity decreased progressively from 3 to 16 m depth, thus the harsher shallower environments (due to waves and tidal air exposure) showed greater diversity than the most stable areas. Communities in finer sediments were more diverse than those in coarser sand. Evenness showed patterns opposite to diversity, overall. Diversity and evenness maps (produced with multivariate universal kriging), showed that most geographic areas with greater diversity were farther from river outflows and wastewater treatment plants. Two types of geographic pattern were observed: areas with persistently greater bivalve diversity through time and areas that changed locally from year to year. This spatial analysis can be used to establish priority conservation areas for management purposes, and to analyse the persistency of regional diversity patterns. The area with most habitat heterogeneity (Sotavento) corresponded to greatest diversity. There was a positive relationship between Spisula solida and Chamelea gallina landings and bivalve diversity two years and one year later, respectively. Possibly, local fisheries, by selectively withdrawing the commercial numerically dominant species from the ecosystem, increased diversity one to two years later, as the ecological niches of the dominants are quickly filled by several other species thereby creating a more even community. It was not found any significant impact of local fisheries, on regional scales long term bivalve diversity
2015
This paper is aimed at describing spatio-temporal variation in abundance, size structure and length-weight relationship of a Donax denticulatus population at Levisa Beach on the Southeastern coast of Cuba. From April to September 2008, monthly samples were collected from four stations located along the beach; three strata were established across the intertidal zone of each station. Three replicate sediment samples were collected from each stratum with a 0.025 m 2 PVC corer and sieved with a 1 mm mesh. Mean density ranged from 612.2 to 1366.7 ind. m-2 , and no differences were found among the sampled months but rather among strata. There is a relationship between the abundance of recruits, young and adults, and strata. The middle intertidal zone showed the highest proportion of individuals, mainly young and adults. Monthly length frequencies showed that recruits appeared in April and May. Length-weight relationship showed a significant correlation between these variables; however, the allometric coefficient value is different considering different life stages. This population shows potential to be exploited, but some management measures proposed in this paper must be taken into account to ensure sustainability.
Geographical variation in shell shape of the pod razor shell Ensis siliqua (Bivalvia: Pharidae)
Helgoland Marine Research, 2013
The present study assessed the existence of variation in the shell shape of the pod razor shell (Ensis siliqua) throughout its distributional range in the northeastern Atlantic. Shells of E. siliqua caught at seven collecting sites (three in Portugal, three in Spain and one in Ireland) were studied by geometric morphometric methods, using both landmark-and contour-based methods. Both approaches (landmarks inside the valves and shell outline) discriminated the shells from Aveiro (centre of Portugal) and Strangford Lough (Ireland) from those caught in the nearby localities (remaining Portuguese and Spanish sites, maximum distance of 550 km by sea). Landmark analysis revealed that shells from Aveiro were more similar to shells from Ireland (*1,500 km far away). Contour analysis revealed that shells from Aveiro had a shape with a comparatively larger height-to-width ratio, whereas shells from Ireland showed a slightly more curved outline than in the remaining sites. Landmark-and contour-based methods provided coherent complementary information, confirming the usefulness of geometric morphometric analyses for discerning differences in shell shape among populations of E. siliqua. A brief review of previous applications of geometric morphometric methods to modern bivalve species is also provided.