Abstract
Despite their abundance in benthic ecosystems, life cycles and reproductive features of most sponge species remain unknown. We have studied the main reproductive features of two demosponges, Dysidea avara and Phorbas tenacior, belonging to phylogenetically distant groups: Orders Dictyoceratida and Poecilosclerida, respectively. Both sponges are abundant and share habitat in the Mediterranean rocky sublittoral. They brood parenchymella larvae with different morphology and behaviour. Sampling was conducted monthly over a two-year period in a locality where both species coexist. The two species reproduced in spring-summer, and presented species-specific reproductive features despite being subject to the same environmental conditions. D. avara has a shorter reproductive period than P. tenacior, ending before the peak of temperature in summer, while the reproductive period of P. tenacior lasts until beginning of autumn. Brooding larvae were present in June-July in D. avara, and in August-October in P. tenacior. Larval size, reproductive effort and number of larvae produced (measured the month with the maximum production) were significantly higher in D. avara than in P. tenacior. A higher reproductive effort and larval traits point to a more opportunistic life strategy in D. avara than in P. tenacior. A lack of overlap in the timing of larval release, as well as different reproductive traits, may reduce competition and facilitate the coexistence of these two sympatric and abundant sponges.
Highlights
Sponges are key structural elements in marine rocky bottoms (Vacelet, 1979; Uriz, Rosell & Martin, 1992) from sublittoral habitats to the deeper continental shelf (Boury-Esnault, Pansini & Uriz, 1994), where they play a paramount role in energy transfer processes (e.g., Gili & Coma, 1998; Ribes et al, 2005; De Goeij et al, 2013)
Clonal reproduction is frequent in sponges (e.g., Maldonado & Uriz, 1999; Calderón et al, 2007), it is usually combined with the release of sexually produced propagules, which accounts for the genetic variability reported for sponge populations
The percentage of individuals in reproduction was significantly higher in D. avara than in P. tenacior, while the effect of year or the interaction between year and species were not significant
Summary
Sponges are key structural elements in marine rocky bottoms (Vacelet, 1979; Uriz, Rosell & Martin, 1992) from sublittoral habitats to the deeper continental shelf (Boury-Esnault, Pansini & Uriz, 1994), where they play a paramount role in energy transfer processes (e.g., Gili & Coma, 1998; Ribes et al, 2005; De Goeij et al, 2013). Sponges present a large variety of larval types (e.g., Boury-Esnault & Rützler, 1997; Maldonado & Bergquist, 2002) with diverse swimming abilities (e.g., Mariani et al, 2006; Uriz, Turon & Mariani, 2008) that likely translate into contrasting dispersal capacities in the field and may determine genetic diversity and viability of sponge populations. Clonal reproduction is frequent in sponges (e.g., Maldonado & Uriz, 1999; Calderón et al, 2007), it is usually combined with the release of sexually produced propagules, which accounts for the genetic variability reported for sponge populations (reviewed in Uriz & Turon, 2012; Pérez-Portela & Riesgo, 2018). The reproductive traits of the species, such as larval characteristics, fecundity, and timing of larval release are crucial factors in controlling the connectivity between sponge populations
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