Aspectos biológicos, ecología y dinámica de poblaciones de darina solenoides en el Golfo San Jorge.
Cargando...
Fecha
2023
Autores
Título de la revista
ISSN de la revista
Título del volumen
Editor
Universidad Nacional de la Patagonia San Juan Bosco. Facultad de Ciencias Naturales y Ciencias de la Salud.
Resumen
Darina solenoides (King, 1832) es una almeja que habita los intermareales arenosos del sur de Sudamérica. Es una especie con gran importancia ecológica, por su abundancia y porque es un recurso alimenticio de varios predadores marinos, incluyendo especies de aves playeras, tanto endémicas como migratorias, además de ser hospedador intermediario de parásitos. El objetivo principal de la presente tesis fue estudiar distintos aspectos de la biología y ecología de D. solenoides en la costa central del Golfo San Jorge (GSJ). Los objetivos particulares pretenden: (1) describir el ciclo reproductivo y analizar el patrón de reclutamiento de la especie y su relación potencial con variables ambientales (Capítulo II); (2) determinar la edad de los ejemplares, modelar el crecimiento individual además de examinar la relación entre variables morfométricas de la especie (Capítulo III); y (3) modelar la distribución espacial de la
abundancia de la especie, examinar las variables abióticas que puedan ser condicionantes de la misma, como así también describir la estructura de tamaños y la segregación espacial de los componentes de la población (Capítulo IV). Para cumplir todos los objetivos, se seleccionaron como sitios de estudio dos playas de arena: Playa Belvedere (PB) y Playa Acina (PA), las cuales presentan extensos intermareales con escasa influencia antrópica. Para la descripción del patrón reproductivo en relación con variables
ambientales, se examinaron mensualmente 60 ejemplares en cada playa durante 2016-2017 (n= 1.315). Se analizaron cortes histológicos de los diferentes estadios gonadales descriptos, e indicadores cualitativos. El rango de largos de las almejas examinadas
osciló entre 25,2 y 42,8 mm y la proporción de sexos no difirió significativamente de 1:1. Darina solenoides presenta un patrón reproductivo anual, caracterizado por una alta sincronía entre sexos, años y sitios de estudio. La proliferación de las ovogonias es
lenta y se extiende en los meses fríos, mientras que la vitelogénesis ocurre principalmente en primavera cuando la temperatura del agua empieza a aumentar y dos meses después del pico fitoplanctónico. La madurez total (diámetro ovocitario medio = 162,8 ± 47,1 ind.m-2) y evacuación de las gametas acontece en el verano y coincidió con el segundo bloom fitoplanctónico, lo que podría favorecer el desarrollo acelerado de las larvas y el subsecuente reclutamiento temprano durante la misma estación. Se hallaron ejemplares con trematodes digeneos ocupando la gónada de D. solenoides. La proporción de almejas que mostraban castración total o parcial fue baja (< 5%) y diferencial entre sitios de estudio. El estudio del crecimiento individual se realizó empleando dos metodologías
complementarias, una directa por medio de la validación de la periodicidad de formación de anillos de crecimiento y determinación de edades en valvas; y otra indirecta a través del análisis de progresión modal (APM). Para esta última, se colectaron mensualmente tres muestras de sedimento tamizado in situ en dos playas de arena del GSJ, y a los individuos recolectados (n= 12.200) se les registró el largo y alto total. Las valvas fueron incluidas en resina, cortadas transversalmente para obtener una sección delgada de la misma (n= 192). La especie forma dos anillos anuales, uno traslúcido entre primavera y principios del verano y otro opaco de crecimiento lento,
durante el resto del año. Las edades observadas en ambas playas fueron sutilmente diferentes, ya que en la PA (edades: 1 a 6 años) se registraron individuos un año más grande que en la PB (edades: 1 a 5 años). El crecimiento individual, ajustado a través de la ecuación de von Bertalanffy, resultó significativamente diferente entre sitios empleando el método directo (PA: L∞= 46,49 mm –
k= 0,48 años-1 – t0= -0,35 años; PB: L∞= 38,29 mm – k= 0,85 años-1 – t0= -0,12 años). A partir del APM, se observó que el reclutamiento de esta especie fue sostenido en los años estudiados, caracterizado por una elevada mortalidad de los juveniles luego del asentamiento. Se detectaron entre una y cuatro componentes modales en ambos sitios, pero, resultó dificultoso el seguimiento de las cohortes cuando las almejas alcanzan los 25 mm de largo total. Se 8 ajustaron curvas de crecimiento de von Bertalanffy para ambos sitios, sin embargo, empleando esta metodología, no se hallaron diferencias significativas entre playas (PA:L∞= 42,3 mm –
k= 0,79 años-1 – t0= -0,01 años; PB: L∞= 38,24 mm – k= 1,01 años-1 – t0= -0,04 años). La especie muestra un crecimiento alométrico negativo e isométrico entre el largo y el alto de la valva en PA y PB respectivamente. Por otro lado, la relación entre el peso y el largo de las almejas describe un crecimiento alométrico positivo, demostrando que las almejas crecerían mayormente en peso que en largo en ambos sitios analizados. Para el análisis de la distribución espacial de D. solenoides y las variables ambientales que podrían ser condicionantes de la misma, se realizó un muestreo sistemático (grillado) en ambos sitios de estudio, donde se relevaron 249 estaciones de muestreo y se recolectaron muestras biológicas y se registraron variables ambientales en cada uno de ellos. Los sitios de estudio (PA y PB) se describen como playas disipativas macromareales, con pendientes poco pronunciadas (< 2 %), que contienen mayor proporción de arenas finas (~2,2 Phi) con escasa materia orgánica (< 1,4 %) y baja humedad en su sedimento (< 24 %). El análisis de los patrones espaciales de D. solenoides en las costas del centro del GSJ evidenció que la población presenta una marcada agregación estructurada espacialmente en ambos sitios de estudio. Esto ocurre a pequeñas escalas que van desde 100 a 400 m. Las almejas se agrupan formando bancos o parches a lo largo de todo el intermareal, los cuales exhiben forma de elipses con el mayor eje paralelo a la línea de costa. Los bancos presentaron superficies similares entre playas (~20.250 m2) aunque exhibieron algunas diferencias entre sitios, siendo más largos y menos anchos en PB respecto de PA. Considerando la densidad como variable, los bancos tienden a ser más densos en el mesolitoral medio e inferior (2 - 2,5 m; 1.000 a 1.500 ind.m-2) y su abundancia disminuye en el supra (> 4 m; 50 a 500 ind.m-2) e infralitoral (< 1 m; 200 a 500 ind.m-2). La estructura demográfica de la población de D. solenoides del GSJ, se encuentra representada por individuos con longitudes comprendidas entre 2 y 45,3 mm. En PA, se observó una distribución polimodal siendo los juveniles los más representados (~50 %), y en menor medida los adultos (~30 %) y reclutas (~20 %), mientras que PB exhibió una distribución bimodal muy marcada, con mayores abundancias de adultos
(> 50 %) y en menor medida de juveniles (~25 %) y reclutas (~18 %). En PA, el conjunto de reclutas, juveniles y adultos se encontraron estructurados espacialmente, aunque se observó una variación notable en la abundancia, el tamaño y la ubicación
de los bancos. El reclutamiento se propició en casi la totalidad de la PA, pero el parche de reclutas se ubicó en una zona donde no había grandes concentraciones de juveniles y adultos. Los parches más extensos y abundantes son los de los juveniles (~29.900 m2;
~275 ind.m-2) y reclutas (~43.300 m2; ~176 ind.m-2 ubicados en el sector sur de la playa, mientras que los adultos (~14.900 m2; ~150 ind.m-2) se ubicaron al norte. Esta tesis resume el estudio de aspectos biológicos y ecología poblacional de la almeja D. solenoides en la costa central del GSJ, y presenta información útil para el entendimiento de los procesos y patrones, no solo inherentes a la población en cuestión, sino también posiblemente extrapolables a la especie en la región de la Patagonia central. Los resultados que se presentan permiten entender la dinámica de una especie clave de los ecosistemas costeros de la Patagonia Argentina.
Darina solenoides (King, 1832) is a marine clam that inhabits intertidal sandy shores of southern South America. It is an ecologically relevant species, mainly due to its high abundance and its role as food resource for several marine predators, including species of coastal fishes and shorebirds (endemic and migratory species) and is an intermediate host of parasites. The main objective of this thesis was to study different aspects of the biology and ecology of D. solenoides in the central coast of the San Jorge Gulf (SJG). The particular goals are: (1) to describe the reproductive cycle and to analyze the recruitment pattern of the species and its potential relationship with environmental and biotic variables (Chapter II); (2) to determine the age of the specimens, model individual growth as well as examine the relationship between some morphometric variables of the species (Chapter III); and (3) to model the spatial distribution of its abundance and biomass at sandy shores and to explore some abiotic variables that may be conditioning it, as well as to describe the size structure and spatial segregation of the population components (Chapter IV). Two sandy shores were selected like study sites: Belvedere Beach (BB) and Acina Beach (AB). For the description of the reproductive pattern in relation to environmental variables, 60 specimens were examined monthly during 2016-2017 (n= 1,315). Histological sections of the different gonadal stages were described, and qualitative indicators, were analyzed. The size range of the clams examined was between 25.2 and 42.8 mm and the sex ratio did not differ significantly from 1:1. Darina solenoides shows an annual reproductive pattern, characterized by a high synchrony between sexes, years and study sites. The proliferation of oogonia is slow and extends in the cold months, while vitellogenesis occurs mainly in spring when the water temperature begins to increase and two months after the phytoplankton peak. Ripe (mean oocyte diameter = 162.8 ± 47.1 ind.m-2) and spawning occurs in the summer and coincides with the second phytoplankton bloom, which could favor the accelerated development of the larvae and the subsequent early recruitment during the same season. Individuals of D. solenoides with parasites (tremates, Digenea) in the gonads were found. The proportion of clams that showed total or partial castration was low (< 5%) and differential between study sites. Individual growth was studied using two complementary methodologies, one direct approach through the analysis and interpretation of growth rings and age data, and an indirect method, through modal progression analysis (MPA). Sediment samples were collected monthly on two sandy beaches of the SJG, and the total length and height of the individuals collected (n= 12,200) were recorded. The shells were embedded in resin and cut transversely to obtain a thin section (n= 192). The species forms two annual rings, one translucent between spring and early summer and another opaque during the rest of the year. The age composition in both sandy beaches were different, being PA clams (ages: 1 to 6 years) one year older than in those from PB (ages: 1 to 5 years). Individual growth, adjusted through the von Bertalanffy equation, was significantly different between sites using the direct method (BB: L∞= 38.29 mm – k= 0.85 years-1 – t0= -0.12 years; AB: L∞= 46.49 mm – k= 0.48 years-1 – t0= -0.35 years). From the MPA, it was observed that the recruitment of this species was sustained in the years studied, characterized by a high mortality of juveniles, after settlement. Between one and four modal components were detected at both sites, but it was difficult to follow the cohorts when the clams reach 25 mm in total length. von Bertalanffy growth curves were fitted for both sites, however, using this methodology, no significant differences were found between beaches (BB: L∞= 38.24 mm – k= 1.01 years-1 – t0= -0.04 years; AB: L∞= 42.3 mm – k= 0.79 years-1 – t0= -0.01 years). The species shows a negative allometric growth and isometric growth between the length and the height of the valve in PA and PB, respectively. On the other hand, the relationship between the weight and the length of the clams describes a positive allometric growth, showing that the clams would grow more in weight than in length in both analyzed sites. For the analysis of the spatial distribution of D. solenoides and the environmental variables that could be conditioning it, a spatial systematic sampling (grid) was carried out in both study sites, where 249 sampling stations were surveyed, and biological samples were collected. Environmental variables were also recorded in each of them. The study sites (BB and AB) are described as dissipative macrotidal beaches, with shallow slopes (< 2 %), containing a higher proportion of fine sand (~2.2 Phi) with low organic matter (< 1.4 %) and low water in its sediment (< 24 %). The analysis of the spatial patterns of Darina solenoides on the coasts of the center of the SJG showed that the population presents a marked spatially structured aggregation in both study sites. This occurs at small scales ranging from 100 to 400 m. The clams are aggregated forming banks or patches throughout the intertidal and exhibit an ellipsoid shape with its main axis parallel to the coastline. The banks detected using density as a response variable, showed similar overall surfaces between beaches (~20,250 m2) although there are some differences between sites: PB has longer, and less wide patches compared to PA. The juveniles of D. solenoides in the SJG tend to be distribute more densely towards the mid and low littoral levels (2 - 2.5 m; 1,000 to 1,500 ind.m-2) and its abundance decreases toward the supralittoral (> 4 m; 50 a 500 ind.m-2) and the infralittoral (< 1 m; 200 a 500 ind.m-2). The demographic structure of the population of D. solenoides of the SJG is represented by individuals with lengths between 2 and 45.3 mm and varied between studied locations. Clams from PB exhibited a marked bimodal distribution, with higher abundances of adults (> 50%) and low abundances of juveniles (~25%) and recruits (~18%). In AB, a polymodal size structure distribution was observed, with juveniles being the most represented cohort (~50%), while adults and recently recruited clams contribute ~30% and ~20% respectively. In AB, the distribution of recruits, juveniles, and adults were found to be spatially structured, although a high variation in abundance, body size, and location was observed. Recruitment was observed throughout the intertidal in PA, but a higher concentration patch was usually seen in areas showing reduced density of juveniles or adults. The largest and most abundant patches of those juveniles (~29,900 m2; ~275 ind.m-2) and recruits (~43,300 m2; ~176 ind.m-2) were located in the southern sector of the beach, while adults (~14,900 m2; ~150 ind.m-2) were located to the north. This doctoral thesis summarizes the study of biological and population ecology of Darina solenoides on the central coast of the SJG and provide useful information for the understanding of the main processes and patterns that regulates the population dynamics of a key species from understudied coastal habitats of central Patagonia (Argentina).
Darina solenoides (King, 1832) is a marine clam that inhabits intertidal sandy shores of southern South America. It is an ecologically relevant species, mainly due to its high abundance and its role as food resource for several marine predators, including species of coastal fishes and shorebirds (endemic and migratory species) and is an intermediate host of parasites. The main objective of this thesis was to study different aspects of the biology and ecology of D. solenoides in the central coast of the San Jorge Gulf (SJG). The particular goals are: (1) to describe the reproductive cycle and to analyze the recruitment pattern of the species and its potential relationship with environmental and biotic variables (Chapter II); (2) to determine the age of the specimens, model individual growth as well as examine the relationship between some morphometric variables of the species (Chapter III); and (3) to model the spatial distribution of its abundance and biomass at sandy shores and to explore some abiotic variables that may be conditioning it, as well as to describe the size structure and spatial segregation of the population components (Chapter IV). Two sandy shores were selected like study sites: Belvedere Beach (BB) and Acina Beach (AB). For the description of the reproductive pattern in relation to environmental variables, 60 specimens were examined monthly during 2016-2017 (n= 1,315). Histological sections of the different gonadal stages were described, and qualitative indicators, were analyzed. The size range of the clams examined was between 25.2 and 42.8 mm and the sex ratio did not differ significantly from 1:1. Darina solenoides shows an annual reproductive pattern, characterized by a high synchrony between sexes, years and study sites. The proliferation of oogonia is slow and extends in the cold months, while vitellogenesis occurs mainly in spring when the water temperature begins to increase and two months after the phytoplankton peak. Ripe (mean oocyte diameter = 162.8 ± 47.1 ind.m-2) and spawning occurs in the summer and coincides with the second phytoplankton bloom, which could favor the accelerated development of the larvae and the subsequent early recruitment during the same season. Individuals of D. solenoides with parasites (tremates, Digenea) in the gonads were found. The proportion of clams that showed total or partial castration was low (< 5%) and differential between study sites. Individual growth was studied using two complementary methodologies, one direct approach through the analysis and interpretation of growth rings and age data, and an indirect method, through modal progression analysis (MPA). Sediment samples were collected monthly on two sandy beaches of the SJG, and the total length and height of the individuals collected (n= 12,200) were recorded. The shells were embedded in resin and cut transversely to obtain a thin section (n= 192). The species forms two annual rings, one translucent between spring and early summer and another opaque during the rest of the year. The age composition in both sandy beaches were different, being PA clams (ages: 1 to 6 years) one year older than in those from PB (ages: 1 to 5 years). Individual growth, adjusted through the von Bertalanffy equation, was significantly different between sites using the direct method (BB: L∞= 38.29 mm – k= 0.85 years-1 – t0= -0.12 years; AB: L∞= 46.49 mm – k= 0.48 years-1 – t0= -0.35 years). From the MPA, it was observed that the recruitment of this species was sustained in the years studied, characterized by a high mortality of juveniles, after settlement. Between one and four modal components were detected at both sites, but it was difficult to follow the cohorts when the clams reach 25 mm in total length. von Bertalanffy growth curves were fitted for both sites, however, using this methodology, no significant differences were found between beaches (BB: L∞= 38.24 mm – k= 1.01 years-1 – t0= -0.04 years; AB: L∞= 42.3 mm – k= 0.79 years-1 – t0= -0.01 years). The species shows a negative allometric growth and isometric growth between the length and the height of the valve in PA and PB, respectively. On the other hand, the relationship between the weight and the length of the clams describes a positive allometric growth, showing that the clams would grow more in weight than in length in both analyzed sites. For the analysis of the spatial distribution of D. solenoides and the environmental variables that could be conditioning it, a spatial systematic sampling (grid) was carried out in both study sites, where 249 sampling stations were surveyed, and biological samples were collected. Environmental variables were also recorded in each of them. The study sites (BB and AB) are described as dissipative macrotidal beaches, with shallow slopes (< 2 %), containing a higher proportion of fine sand (~2.2 Phi) with low organic matter (< 1.4 %) and low water in its sediment (< 24 %). The analysis of the spatial patterns of Darina solenoides on the coasts of the center of the SJG showed that the population presents a marked spatially structured aggregation in both study sites. This occurs at small scales ranging from 100 to 400 m. The clams are aggregated forming banks or patches throughout the intertidal and exhibit an ellipsoid shape with its main axis parallel to the coastline. The banks detected using density as a response variable, showed similar overall surfaces between beaches (~20,250 m2) although there are some differences between sites: PB has longer, and less wide patches compared to PA. The juveniles of D. solenoides in the SJG tend to be distribute more densely towards the mid and low littoral levels (2 - 2.5 m; 1,000 to 1,500 ind.m-2) and its abundance decreases toward the supralittoral (> 4 m; 50 a 500 ind.m-2) and the infralittoral (< 1 m; 200 a 500 ind.m-2). The demographic structure of the population of D. solenoides of the SJG is represented by individuals with lengths between 2 and 45.3 mm and varied between studied locations. Clams from PB exhibited a marked bimodal distribution, with higher abundances of adults (> 50%) and low abundances of juveniles (~25%) and recruits (~18%). In AB, a polymodal size structure distribution was observed, with juveniles being the most represented cohort (~50%), while adults and recently recruited clams contribute ~30% and ~20% respectively. In AB, the distribution of recruits, juveniles, and adults were found to be spatially structured, although a high variation in abundance, body size, and location was observed. Recruitment was observed throughout the intertidal in PA, but a higher concentration patch was usually seen in areas showing reduced density of juveniles or adults. The largest and most abundant patches of those juveniles (~29,900 m2; ~275 ind.m-2) and recruits (~43,300 m2; ~176 ind.m-2) were located in the southern sector of the beach, while adults (~14,900 m2; ~150 ind.m-2) were located to the north. This doctoral thesis summarizes the study of biological and population ecology of Darina solenoides on the central coast of the SJG and provide useful information for the understanding of the main processes and patterns that regulates the population dynamics of a key species from understudied coastal habitats of central Patagonia (Argentina).
Descripción
Palabras clave
ALMEJA, INFAUNAL, REPRODUCCION, CRECIMIENTO, DISTRIBUCION ESPACIAL, DARINA SOLENOIDES
Citación
López, María Eugenia. (2023). Aspectos biológicos, ecología y dinámica de poblaciones de darina solenoides en el Golfo San Jorge. Tesis doctoral. Unniversidad Nacional de la Patagonia San Juan Bosco.