Temporal variation of the family Spionidae (Annelida: Polychaeta) in two subtidal muddy bottoms of the Ría de Aldán (Galicia, NW Iberian Peninsula)
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1
Universidade de Vigo, Departamento de Ecoloxía e Bioloxía Animal, Spain
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2
Universidade de Vigo, Estación de Ciencias Mariñas de Toralla (ECIMAT), Spain
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3
Universidad Autónoma de Madrid, Departamento de Biología (Zoología), Spain
Introduction
Spionids are relatively small- to medium-sized polychaetes that can be found in different kinds of both sedimentary and hard substrata. Although they differ in life cycle features and biological traits, most of them are usually sedentary, burrowers or tube-dwellers and selective deposit-feeders. Some small-sized species can reach very high densities in sedimentary bottoms and even dominate numerically the macrofaunal assemblages in certain types of sediments. Despite of that, their temporal variation in these bottoms remains a poorly studied issue. The Ría de Aldán is a small estuarine-like embayment; it is about 7-km long by its main axis and has a maximum width of 3.5 km by its opening, with depths of up to 45 m. It is at the SW of the Ría de Pontevedra and is part of the Galician Rías Baixas, a group of tectonically-formed bays located in the NW of the Iberian Peninsula. The influence of the eastern boundary upwelling system of the North Atlantic subjects the Rías to both seasonal and event-scale variability.
Material and methods
Two areas were studied for this work: an 18m-depth muddy sand bottom in the westerly part of the ría (Site 1), and a 17m-depth organically enriched muddy bottom in its innermost part (Site 2). Five replicate samples were taken monthly at each site from May 1998 to May 1999 by means of a Van-Veen grab with an operating surface of 0.056m2. Samples were sieved through a 0.5-mm mesh, and then fixed in 10% buffered formalin. An additional sample was taken to determine sediment characteristics (granulometric composition, carbonate content and total organic matter content). Spionids present in the samples were sorted, identified and counted in the laboratory using a stereo microscope. The following univariate measures were calculated for each sampling date: total abundance (N), number of species (S), Shannon-Wiener diversity index (H’, log2) and Pielou’s evenness (J’). Non-metric multidimensional scaling (nMDS) analysis was used to obtain a visual representation of the similarities among samples. The correlation between sediment features and species abundances or assemblage variables was evaluated by means of the Spearman’s correlation coefficient. The relationship between environmental variables and the assemblages at multivariate level was evaluated using BIO-ENV procedure and Distance-Based Linear Model (DistLM). PRIMER 6 & PERMANOVA+ software package was used for all mentioned analysis.
Results
Along the study, 11882 individuals belonging to 16 different species were collected. Abundance was remarkably higher at Site 1, both overall and considering the monthly results (except for June), which were more variable than those at Site 2. From the 16 species identified, 2 were exclusive of Site 1, 4 were only present at Site 2 and the remaining 10 species were found at both sites. The value of S was rather stable and broadly similar at both sites during the whole study period. Results for H’ and J’ indexes were more variable and they showed higher values at Site 2, both on average and on most of the months. Spio decoratus Bobretzky, 1870 was the most abundant species both at Site 1 and overall, and the second most abundant at Site 2. Prionospio fallax Söderström, 1920 and Prionospio pulchra Imajima, 1990 were the second and third most abundant species at Site 1, respectively, and the latter was also the most abundant species at Site 2 and the second most abundant overall. Ordination of the samples through the nMDS analysis showed a weak but still defined separation between sites. It did not show defined groups of months within each site, but a rather continuous temporal variation. Relationships between sediment characteristics and spionid assemblages were stronger at Site 1 according to all the analyses carried out. The abundances of numerically dominant species did not show significant correlations (P < 0.05) with sediment features at any of the sites. Regarding the univariate measures of the assemblages, none of them at Site 2 and only H’ at Site 1 showed significant correlations with sediment variables. BIO-ENV and DistLM provided the combinations of sediment features that showed the best correlation with the structure of the assemblages and both of them found substantially higher correlation values at Site 1.
Discussion
Spionid polychaetes have been found to be relatively abundant at both studied sites, especially at Site 1. If the whole polychaete assemblages are considered, Spionidae is the dominant family at that site, while it is second to Paraonidae both at Site 2 and overall. Both families have been reported as abundant and even dominant in sedimentary bottoms similar to the ones studied here. In this particular case, the higher organic matter content in sediment at Site 2 is likely to be an important advantage for non-selective deposit-feeders as paraonids over selective deposit-feeders like spionids. Focusing on the latter, the assemblage at Site 2 was more diverse and stable than that at Site 1 and, strikingly, it seems to be barely linked to the variations in sediment features. One possible explanation for this is that this assemblage is more influenced by either biotic factors or abiotic factors other than the sediment features studied here. Contrarily, the assemblage at Site 1 was considerably more variable; this is partly due to the seasonal variation pattern of the highly dominant species S. decoratus, and probably also to the higher hydrodynamism and subsequent instability at this site. Such instability showed up in June and November, when sediment characteristics were substantially different from the rest of the study period at Site 1. The effect of those changes on spionid assemblage become apparent in the results of the nMDS analysis. That influence explains the closer relationship between spionid assemblage and sediment features at Site 1.
Acknowledgements
F. Aneiros was funded by FPU program (Spanish Education Ministry, AP2010-2010). Partial funding for this study was obtained from FEDER GRC2013-004 project (Xunta de Galicia).
Keywords:
temporal variation,
Polychaeta,
Benthic macrofauna,
muddy sediments,
Galician Rías
Conference:
XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016.
Presentation Type:
Oral Presentation
Topic:
1. ECOLOGY, BIODIVERSITY AND VULNERABLE ECOSYSTEMS
Citation:
Aneiros
F,
Moreira
J and
Troncoso
JS
(2016). Temporal variation of the family Spionidae (Annelida: Polychaeta) in two subtidal muddy bottoms of the Ría de Aldán (Galicia, NW Iberian Peninsula).
Front. Mar. Sci.
Conference Abstract:
XIX Iberian Symposium on Marine Biology Studies.
doi: 10.3389/conf.FMARS.2016.05.00058
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Received:
15 Apr 2016;
Published Online:
02 Sep 2016.
*
Correspondence:
Mr. Fernando Aneiros, Universidade de Vigo, Departamento de Ecoloxía e Bioloxía Animal, Vigo, Pontevedra, 36310, Spain, f.aneiros@uvigo.es