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    Factors affecting monthly variation in population density of the capitellid polychaete Heteromastus filiformis in a hyperhaline Mediterranean coastal lagoon
    (2009) Can, E.; Kevrekidis, T.; Cihangir, B.
    1 - The aim of the study was to elucidate the population ecology of opportunistic species in the Mediterranean coastal lagoon environment by investigating the monthly variation in population density of the capitellid polychaete Heteromastus filiformis and the potential environmental factors affecting it in an eu- to hyperhaline (Homa lagoon, Eastern Aegean Sea). 2 - Monthly samplings were conducted from January 2006 to January 2007. 3 - A Principal Component Analysis (PCA) was conducted using the values of several abiotic variables of the water and sediments. A randomization procedure based on eigenvalues showed the presence of only one significant axis; according to the bootstrapped eigenvector method, salinity and dissolved oxygen were found to load significantly on the first axis, having negative and positive weights, respectively. 4 - Salinity, which exceeded 40 psu all year round except for February-March, peaked in July-September (59-61.5 psu), while dissolved oxygen concentrations were lowest from July to October (2.3-3.9 mg l-1). 5 - Population density of H. filiformis was low (21-58 individuals m-2) through most of the year; however, a recruitment was detected in spring (290 ind.m-2) followed by a significant decrease in density in summer. 6 - Density was significantly correlated with the first PCA component (positive correlation) and with salinity (negative correlation), particularly indicating that (a) relatively lower salinities (<50 psu) in early spring may favor reproductive activity and subsequent recruitment, while higher salinities (>50 psu) during summer may have negative effects on population density, and (b) salinity effects during summer may have been increased by other simultaneously effective environmental conditions (low oxygen concentrations). 7 - Our results indicate that opportunistic species experience extreme environmental conditions, particularly high salinities, during summer in eu- to hyperhaline Mediterranean coastal lagoons, which restrain them to develop highly abundant populations. © 2009 University of Salento - SIBA.