PhD Code: MARES_11_20:
- Host institute 1: P13 - University of Aveiro
- Host institute 2: P12 - Pavia University
- T1 - Future Oceans: temperature changes - hypoxia - acidifation
- T2 - Understanding biodiversity effects on the functioning of marine ecosystems
- Henrique Queiroga
- Dario Savini
- Roberta Cupido (email@example.com)
In the last decades, a higher frequency and shorter return time of extreme events such as thermal anomalies have been recorded with diseases and mass mortalities affecting an increasing number of marine species and ecosystems worldwide (Harvell et al. 1999). In particular, populations of the Mediterranean purple sea-fan Paramuricea clavata (Risso 1826), one of the main components of the coralligenous communities of circalittoral rocky bottoms (Ballesteros 2006), faced the highest mortality reported ranging from 60 to 90% (Linares et al. 2005, Cupido et al. 2008). Despite this species is considered an essential part of the Mediterranean natural heritage, because it plays a key ecological role in habitat structure and functioning, knowledge about its recover ability has been only recently attained and major information is still lacking before we can assess with precision the resilience of populations affected by such extreme climate events.
After disturbance, population recovery largely depends on supply of recruits (Linares and Doak 2010). Reduction of colony density and change in the size structure following mortalities, causing a reduction in population reproductive output, may in turn affect sexual recruitment. Consequently, in self-seeding populations, in which local gamete production contributes to the majority of recruitment, recover is expected to be slow. On the contrary, in open systems population resilience will be foster by the supply of larvae from undisturbed area. For species whose life histories include a pelagic larval phase, the assessment of the spatial scale and pattern of connection among populations is crucial for the development of realistic population models useful for understanding population resilience following disturbance (Palumbi 2003).
While the life history characteristics of P. clavata suggest that the majority of dispersal should be local (Coma et al. 1995), in laboratory experiments the time required for the metamorphosis of the larvae into primary polyps (minimum 10 days) suggests rather high dispersal potential (Linares et al. 2008, Cupido unpublished). Genetic markers are effective tools to obtain indirect information on larval dispersal and demographic relatedness over a given spatial scale (Underwood et al. 2007). Since information about gene flow among Mediterranean gorgonian populations is scarce, the aim of this study will be to assess the genetic structure of the Mediterranean gorgonian Paramuricea clavata in an area strongly affected by repeated mass mortalities related to climate change. Using molecular techniques, we will assess the potential for dispersal as well as the level of connectivity between populations. The genetic structure in P. clavata populations along a depth gradient will also be analysed. During termal anomalies, deeper populations (down to 40 m depth) may be less affected so representing key areas for the recovery of affected populations. By comparing the genetic structure of different populations, we will infer populations interdependence or connectivity. This is particularly important for small populations in which loss of genetic diversity could lead to a reduction in fitness and to an increase in risk of extinction.
In some coral species, sexual and asexual reproduction contribute equally to population maintenance, growth and resilience after disturbances while in several others one mode of reproduction clearly dominates over another (Foster et al. 2007). Differently than other gorgonians (Lasker 1983), P. clavata is an external brooder, in which sexual reproduction is dominant and abundant, while asexual reproduction mode has been rarely described (Coma et al. 1995).
Asexual reproduction is considered to be an adaptation to both stable and unfavorable local environmental conditions (Coffroth and Lasker 1998). Following disturbance, corals should have the priority to allocate energy to recovery of dead tissue rather than to reproduction (Oren et al. 2001), thus the contribution of sexual reproduction to recruitment could be dramatically reduced (Michalek-Wagner and Willis 2001). Under stress conditions, organisms that have multiple reproductive options may be favored by alternative asexual means of propagation to ensure population maintenance and resilience.
In this project we will aim to assess the level of clonal propagation in damaged P. clavata populations by comparing the genetic structure of adults, juveniles and recruits. Utilizing highly variable DNA markers such as microsatellites, we will able to shift the units of analysis from population to individual, allowing more detailed and direct estimates of gene flow. Levels of asexual recruitment in healthy and damaged populations of P. clavata across the western Mediterranean and Atlantic will be estimated using polymorphic microsatellite loci. Results will allow to understand the role of asexual reproduction on P. clavata populations’ dynamics across gradients of environmental disturbance.
Ballesteros E (2006) Mediterranean coralligenous assemblages: a synthesis of present knowledge. Oceanography and Marine Biology: An Annual Review 44: 123-195.
Coma R, Ribes M, Zabala M, Gili JM (1995a) Reproduction and cycle of gonadal development in the Mediterranean gorgonian Paramuricea clavata. Mar Ecol Prog Ser 117: 173–183
Coffroth MA, Lasker HR (1998) Population structure of a clonal gorgonian coral: the interplay between clonal reproduction and disturbante. Evolution 52 (2): 379-393
Cupido R, Cocito S, Sgorbini S, Bordone A, Santangelo G (2008) Response of a gorgonian (Paramuricea clavata) population to mortality events: recovery or loss? Aquat Conserv: Mar Freshw Ecosyst 18 (6): 984-992
Harvell CD, Kim K, Burkholder JM, Colwell RR, Epstein PR, Grimes DJ, Hofmann EE, Lipp EK, Osterhaus ADME, Overstreet RM, Porter JW, Smith GW, Vasta GR (1999) Emerging marine diseases: Climate links and anthropogenic factors. Science 285: 1505–1510
Foster NL, Baums IB, Munby PJ (2007) Sexual vs asexual re production in an eco system engineer: the massive coral Montastraea annularis. Journal of Animal Ecology 76: 384–391
Lasker HR (1983) Asexual reproduction, fragmentation and skeletal morphology of a plexaurid gorgonian. Mar Ecol Prog Ser 19: 261-268
Linares C, Coma L, Diaz D, Zabala M, Hereu B, Dantart L (2005) Immediate and delayed effects of a mass mortality event on gorgonian population dynamics and benthic community structure in the NW Mediterranean Sea. Mar Ecol Prog Ser 305: 127-137
Linares C, Coma R, Mariani S, Díaz D, Hereu B, Zabala M (2008b) Early life history of the Mediterrenean gorgonian Paramuricea clavata: implications for population dynamics. Invert Biol 127: 1-11
Linares C, Doak DF (2010) Forcasting the combined effects of disparate disturbances on the persistence of long-lived gorgonians: a case study of Paramuricea clavata. Mar Ecol Prog Ser 402: 59-68
Palumbi SR (2003) Population genetics, demographic connectivity and the design of marine reserves. Ecological Applications 13(1): 146–158
Michalek-Wagner K, Willis BL (2001) Impacts of bleaching on the soft coral Lobophytum compactum. I. Fecundity, fertilisation and offspring viability. Coral Reefs 19: 231-239
Oren U, Benayahu Y, Lubinevsky H, Loya Y (2001) Colony integration during regeneration in the stony coral Flavia favus. Ecology 82 (3): 802–813
Underwood JN, Smith LD, Van Oppen MJH, Gilmour JP (2007) Multiple scales of genetic connectivity in a brooding coral on isolated reefs following catastrophic bleaching. Molecular Ecology 16: 771–784
Forecasting the ecological effects of climate change is critical for developing conservation strategies that increase population resilience under changing climate conditions. Ecology can actually give a real contribution to biodiversity conservation by means of methods and models suitable for this target. Conservation of long-lived, slow growing, low turnover species is one of the most difficult task for ecologists. These organisms deserve protection not only because they can be rare, endemic or endangered by human impacts, but also because they play a key ecological role in the habitat structure and functioning. Understanding patterns of connectivity among populations will allow to get insight on population maintenance, growth and resilience after disturbance throughout the development of realistic population models. The results of the proposed PhD project will be published in international scientific journals and presented at international conferences. Moreover, since the target species is one of the most common gorgonian along the Mediterranean coast, well known to the diving community, the results will be disseminate to the broad public via the local and international media.