Settlement and primary succession in a shallow submarine cave: the spatial and temporal benthic assemblage distinctness

Several studies have described patterns of distribution and species composition of sessile assemblages from marine caves but few have examined the processes of recruitment and larval settlement in the earlier stages of substrate colonisation. The present study evaluated (i) the distinctness of newly recruited assemblages on the local spatial scale, (ii) how this assemblage distinctness changes over time and (iii) how the recruitment patterns are affected by a different start-time in different positions in the cave. Two sets of 90 baked-clay panels (15 x 15 x 1 cm) were deployed in March (E1) and October 2002 (E2) at three positions in the shallow submarine cave 'Grotta di Ciolo' (South-East Italy, Central Mediterranean Sea): entrance (P1) and at 20 m (P2) and 80 m (P3) from the entrance, respectively. Each position was represented by two areas (1.5 x 1.5 m), and three panels from each area were randomly removed after 1, 3, 6, 12 and 24 months. The assemblages of the settled organisms comprised a total of 63 taxa. Different succession patterns were highlighted among assemblages across positions. A recruitment period of 2 years allowed a complete colonisation of panels at P1, where both encrusting algae dominated rocky walls and panels. In contrast, recruitment was very slow at P2 and P3, where the mature benthic community was not replicated on the 2-year panels. Finally, there was a partial convergence towards a common ecological succession in series started at different times