The budding process in Tethya citrina Sarà & Melone (Porifera, Demospongiae) and the incidence of post-buds in sponge population maintenance

The relevance of the budding process in a population of Tethya citrina inhabiting an unpredictable environment subjected to frequent anoxic crisis (Mar Piccolo di Taranto) is described, and new data about the fate of the buds after their release are provided. At the individual level, for the first time in natural conditions, it has been demonstrated that several budding events follow each other, alternating with short periods (1–2 months) of rest. At the population level, budding proved to be a continuous process, being detected throughout the 13 months of study, with a short summer decrease both in the frequency of budding specimens and bud density. This trend was markedly different from that reported for conspecific populations inhabiting stable environments, in which budding is a seasonal process. It is hypothesized that the sudden and unpredictable variations of the ecological conditions could be responsible for the onset of repeated budding events, thus stressing the role of environmental factors in affecting the asexual reproductive pattern. T. citrina buds, here investigated, tend to detach from the adult sponge within 7/15 days of their differentiation, a feature coherent with experimental data carried out under laboratory conditions. A significant relationship between the size/age of the post-buds and the onset of the asexual reproduction has been proved: in particular, the first budding event was observed in nine-month-old sponges, measuring about 7 mm in diameter. As reported for other demosponges, in T. citrina post-buds the growth rate was positively related to the water temperature, with a significant increase during the summer. In addition, a negative effect of the budding process on the sponge growth, is hypothesized for a post-bud subjected to repeated budding events. Growth rate, however, proved highly variable.