Tolerance of two size classes of Bivalve Donax trunculus (Linnaeus, 1758) to salinity changes, a laboratory assay
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1
University Pablo de Olavide, Spain
Estuaries and coastal areas close to river mouths and fluvial discharges are strongly influenced by flooding, temperature and salinity. Climate changes may induce alterations in these factors (salinity reduction, ocean surface temperature increase and sea level rise) and consequently may induce alterations on benthic communities that inhabit these ecosystems. In the last decades, the Iberian Peninsula climate has undergone significant changes translated in the occurrence of extreme weather events, altering precipitation patterns and seasonal temperature. Because of this, the intertidal species are affected by abrupt changes in salinity.
Bivalves of genus Donax are important components of the macrofauna in shallow areas of sandy beaches. They feed by filtering phytoplankton and organic matter particles in suspension. D. trunculus (L., 1758) is considered in many localities as a resource species with high contribution rates. It is distributed along the Atlantic and Mediterranean by the French coast, the Iberian Peninsula and North Africa. Wedge clams live buried in sandy bottoms. D. trunculus is distributed between 0-6 m of depth. The spatial distribution of wedge clams shows an intraspecific segregation between young and adult specimens; the smaller individuals are commonly located in shallower depths, while the largest specimens occur at greater depths.
Temperature and salinity changes are more remarkable in the intertidal zone than in deeper waters. Due towedge clam cohorts are distributed in depth according to the sizes of animals, young specimens are more exposed to abrupt changes of salinity, which could determine a higher mortality among juveniles. This could affect future cohorts of adults and therefore the reproductive capacity of populations.
This study aims to evaluate the responses of juveniles and adults of D.trunculus submitted to salinity changes. Four essays of 504 h for each cohort (juveniles <20 mm; adults> 20 mm) were performed using tanks with 15 L of filtered seawater and diluted to different salinity (1.7, 6.7; 11.7; 16 7; 21.7; 26.7; 31.7; 36.7). The water was continuously aerated and maintained at a constant temperature (20.3 ° C) in a germination chamber. In each tank, five juveniles and five adults were introduced into perforated cups to allow water flow, and provided with sediment. Wedge clams were fed every 2 days using a mixture of algae Isochrysis galbana and Chaetocerops gracilis diluted in water with the same salinity than the treatments. Mortality was registered every 12h.
For data analysis, median lethal salinity to 504 h (LC50504 h) and median lethal time for each salinity in which there were not 100% survival or 100% mortality (LT50), were determined from Probit analysis. The differences between essays with juveniles and adults were explored by a two-way ANOVA. For these statistical analyzes the software IBM SPSS Statistic 22.was used
Considering the results of juvenile wedge clams, throughout all the time of the experiments it was observed that: in salinities of 1.7 and 6.7 100% mortality was achieved within 36 hours starting the experiments; for treatments with salinity 11.7, 100% mortality was reached at 156 hours and at salinity 14.2 to 396 hours. With salinities of 16.7, 19.2 and 21.7 at the end of the experiments the mortalities were 40, 30 and 30%, respectively. In salinities ranged between 26.7-36.7 survival was 100%.
Regarding the adults, it shows that: in salinities of 1.7 and 6.7 100% mortality was achieved at 36 and 48 hours starting the experiments, respectively; in animals subjected to salinity 11.7 100% mortality was reached at 108 hours and at salinity 14.2 at 420 hours. With salinities of 16.7, 19.2 and 21.7 at the end the experiments the mortality was 95, 60 and 35%, respectively. In salinities 26.7-36.7 survival was 100%.
Median lethal salinity values for a 504h exposure (LC50504 h) were 18.15 and 20.71 for juveniles and adults, respectively. The estimates of the median lethal time showed that for salinities 21.7, 14.2 and 11.7 LT50 was similar for juveniles and adults. However, for salinities of 16.7 and 19.2 the differences were remarkable (23.9, 24.17 days in juvenile; 8.76, 18.2 days in adults). The two-way ANOVA tests revealed significant statistical differences between juveniles and adults in LC50 and LT50.
In conclusion, D. trunculus is a euryhaline species whose tolerance to low salinities varies between juvenile and adult specimens. Juveniles are able to resist lower salinities than adults and withstand sudden changes in salinity over a longer period. This may be related to the differential distribution of space existing in this species, with a tendency to locate the smaller cohorts in intertidal and shallow areas than adults.
Keywords:
Bivalvia,
Donacidae,
Donax trunculus,
salinity tolerance,
Median lethal salinity,
Median lethal time,
intertidal
Conference:
XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016.
Presentation Type:
Poster Presentation
Topic:
1. ECOLOGY, BIODIVERSITY AND VULNERABLE ECOSYSTEMS
Citation:
Reyes Martinez
MJ,
Soler Navarro
D,
Martinez Pita
I and
García-García
FJ
(2016). Tolerance of two size classes of Bivalve Donax trunculus (Linnaeus, 1758) to salinity changes, a laboratory assay.
Front. Mar. Sci.
Conference Abstract:
XIX Iberian Symposium on Marine Biology Studies.
doi: 10.3389/conf.FMARS.2016.05.00152
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Received:
29 Apr 2016;
Published Online:
03 Sep 2016.
*
Correspondence:
Dr. Francisco J García-García, University Pablo de Olavide, Seville, 41013, Spain, fjgargar@upo.es