Demography and interannual variability of salp swarms (Thalia democratica)

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Journal Article
Marine Biology, 2014, 161 (1), pp. 149 - 163
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Swarms of the pelagic tunicate, Thalia democratica, form during spring, but the causes of the large interannual variability in the magnitude of salp swarms are unclear. Changes in asexual reproduction (buds per chain) of T. democratica populations in the coastal waters of south-east Australia (32-35°S) were observed in three austral springs (October 2008-2010). T. democratica abundance was significantly higher in 2008 (1,312 individuals m -3 ) than 2009 and 2010 (210 and 92 individuals m -3 , respectively). There was a significant negative relationship (linear regression, r 2 = 0.61, F 1,22 = 33.83, P < 0.001) between abundance and asexual reproduction. Similarly, relative growth rates declined with decreasing abundance. Generalised additive mixed modelling showed that T. democratica abundance was significantly positively related to preferred food >2 μm in size (P < 0.05) and negatively related to the proportion of non-salp zooplankton (P < 0.001). Salp swarm magnitude, growth, and asexual reproduction may depend on the abundance of larger phytoplankton (prymnesiophytes and diatoms) and competition with other zooplankton. © 2013 Springer-Verlag Berlin Heidelberg.
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