Settlement dynamics and recruitment responses of Mediterranean gorgonians larvae to different crustose coralline algae species

Abstract

Sessile marine species such as Anthozoans act as ecosystem engineers due to their three-dimensional structure. Gorgonians, in particular, can form dense underwater forests that give shelter to other species increasing local biodiversity. In the last decades, several Mediterranean gorgonians populations have been affected by natural and anthropogenic impacts which drastically reduced their size. However, some species showed unexpected resilience, mainly due to the supply of new individuals. To understand the mechanisms underlying recovery processes, studies on the first life history stages (i.e. larval dispersal, settlement and recruitment) are needed. In tropical coral reefs, crustose coralline algae (CCA) are known to influence coral larvae habitat selection and settlement. This capacity however is not ubiquitous among CCA species and larvae of different coral species may have different preferences. The present work focuses on three Mediterranean gorgonians (Eunicella singularis, Paramuricea clavata and Corallium rubrum) with the objective of quantifying settlement and recruitment in presence of two common CCA species (Litophyllum styctaeforme and Litophyllum incrustans). Results showed that the presence of CCA activates earlier settlement in E. singularis and increase the density of recruits, with different trends for the three species. Our results suggest that CCA should be taken into account in the implementation of conservation strategies. Moreover, a deeper comprehension of settlement mechanisms could help improving restoration techniques based on sexual reproduction.

Survive or swim: different relationships between migration potential and larval size in three sympatric Mediterranean octocorals

“…A recent study indicated that metamorphosis happened even earlier in the larval stage for E. singularis (8 days) and P. clavata (11 days) 43 . However, in the same study 43 , metamorphosis of C. rubrum larvae was only observed after 27 days, a duration similar to their median longevity, suggesting that competence, and hence minimum PLD, might not be related to a brooding or spawning reproductive strategy. Nevertheless, in biophysical modeling, the minimum PLD defined by competency is related to the lower range of dispersal distances 17,21 .…”

“…In contrast, the migration potential of C. rubrum is less consistent with the genetic differentiation observed at a half-meter-square spatial scale 60 . A median larval longevity of 30 days, a precompetence period of 27 days 43 and the high swimming activity of C. rubrum conflict with such genetic population structure, as the transport of neutrally buoyant larvae after 15 days can reach 100 km 61 . Factors other than limited dispersal capabilities can reduce gene flow and could be invoked to explain such population genetic structuring of C. rubrum 62 .…”

Artificial reefs geographical location matters more than shape, age and depth for sessile invertebrate colonization in the Gulf of Lion (NorthWestern Mediterranean Sea)

“…Like most gorgonians, E. singularis releases lecithotrophic larvae in early summer (June to August). Even though larval competency period can reach up to 2 months (Guizien et al, 2020; Zelli et al, 2020), PLDs ranging from 7 to 14 days best explain gene flow among E. singularis natural populations dwelling in the fragmented rocky habitat of the GoL (Padron et al 2018). E. singularis life span can reach 25-30 years with sexual maturity before 6 years (Gori et al, 2007; Weinberg and Weinberg, 1979) (Weinberg and Weinberg 1979, Gori et al 2007).…”

First report of chimerism in the Mediterranean red coral (Corallium rubrum)

“…C. rubrum larvae were maintained in a closed circuit, oxygenated, and temperature-controlled aquaria (see Zelli et al, 2020 for details) and offered two marble tiles (10 x 10 cm) as a settlement substrate (Bramanti et al, 2003). In September 2019, once larvae settled and metamorphosed into polyps, the tiles were transferred to an open-circuit oxygenated, and temperature-controlled 3.5 L aquarium.…”

“…It is an internal brooding species that releases larvae once a year (Santangelo et al, 2003;Bramanti et al, 2003;2005). Low larval settlement rates and post-settlement survival represent a bottleneck in the population dynamics of this species (Zelli et al, 2020). In particular, slow growth rates result in prolonged vulnerability of young settlers that, due to their small size, are exposed to predation and affected by sedimentation (Cau et al, 2016).…”