Size distribution, density and disturbance in two Mediterranean gorgonians: Paramuricea clavata and Eunicella singularis

Abstract

Summary 1.Gorgonians are long-lived engineering species and their conservation is crucial to maintaining the biodiversity of marine communities. The slow dynamics displayed by these species make them especially vulnerable when faced with increasing disturbances. 2. The sessile nature and structural role of gorgonians provide several ecological similarities with trees, allowing the application of different approaches developed by forest ecology studies to overcome the constraint of long time-scales to collect valuable dynamic data. Using these approaches, we examined the distribution and demography of two representative Mediterranean gorgonian species, Paramuricea clavata and Eunicella singularis , along a regional spatial scale as well as their response to disturbances. 3. The regular spatial distribution and the upper distribution limit of E. singularis suggest that this species is more tolerant to a wide range of environmental conditions than P. clavata , which exhibited a more asymmetrical spatial distribution and variation in the upper distribution limit on the latitudinal scale. 4. Size distributions of both species showed contrasting population dynamics. The size distribution of E. singularis was characterized by initial stages of populations (0-10 cm) in contrast to the scarcity of this stage displayed by P. clavata . This suggests differences in recruitment between species. Furthermore, only P. clavata populations displayed a strong negative correlation between density and biomass with a slope close to -3/2, indicating a self-thinning mechanism and therefore the existence of a carrying capacity. This result and the trajectories of disturbed populations below the self-thinning line revealed this approach as a useful method to identify the effects of biological or physical disturbance. 5. Synthesis and applications . The approaches used in this study provide insights into management needs in face of the difficulty of having to deal with the population dynamics of very slow-growing threatened species. In particular, gorgonian populations can be used as an indicator of the effects of climatic anomalies on the coralligenous community.

Anthropogenic effects on reproductive effort and allocation of energy reserves in the Mediterranean octocoral Paramuricea clavata

“…Specifically, as tissue regeneration comes at an energetic cost, it affects the balance and quantity of energy reserves, thus resources normally used for reproduction may be allocated to regeneration (Silveira & Van't Hoff 1977, Rinkevich 1996, Henry & Hart 2005. This is in fact consistent with a recently observed reduction of fecundity in a population recovering from mass mortality (Linares et al 2008a). However, unexpected rates of tissue regeneration and growth of new branches have been documented in Paramuricea clavata (Cupido 2009), raising the question whether an overcompensation response exists as it does in some tropical gorgonian corals (Sánchez & Lasker 2004).…”

Forecasting the combined effects of disparate disturbances on the persistence of long-lived gorgonians: a case study of Paramuricea clavata

“…This species displays slow growth rates, low recruitment rates, and low natural mortality rates (Coma et al 1998, Linares et al 2007). Furthermore, the size distributions of P. clavata populations show that most local populations are long-established, indicating that recruitment failures or increased mortality due to disturbances in existing populations could lead to region-wide declines (Linares et al 2008a).…”

“…This species displays slow growth rates, low recruitment rates, and low natural mortality rates (Coma et al 1998, Linares et al 2007). Furthermore, the size distributions of P. clavata populations show that most local populations are long-established, indicating that recruitment failures or increased mortality due to disturbances in existing populations could lead to region-wide declines (Linares et al 2008a).The red gorgonian Paramuricea clavata has also been one of the species most severely affected during region-wide 'mass mortality' events (Cerrano et al 2000, Perez et al 2000, Garrabou et al 2009). During 1999 and 2003, high-diversity Mediterranean marine benthic communities dominated by suspension feeders were affected by 2 unusual, regional-scale (spanning several 100s of km) climatic anomalies, with warmer water temperatures resulting in a pulse of increased mortality for multiple species across the region (Romano et al 2000, Garrabou et al 2009).…”

Sexual structure of a highly reproductive, recovering gorgonian population: quantifying reproductive output

“…Changes in gorgonian population structure could lead to profound changes in the entire community. A better know ledge of gorgonian demographic structure and dynamics before and after such anomalous mortality events can shed some much needed light on the response of marine populations and communities to global climate change-induced changes (Linares et al 2007b(Linares et al , 2008a.…”