Is the local extinction of Pinna nobilis facilitating Pinna rudis recruitment?

Abstract

Until the late 2010s the spiny fan-mussel Pinna rudis shared habitat in many Mediterranean sites with Mediterranean endemic Pinna nobilis, which dominated in abundance but that has gone locally extinct in most of its distribution area due to a recent widespread disease outbreak. In the Columbretes Islands Marine Reserve (NW Mediterranean) both species coexisted until 2017, when P. nobilis populations completely disappeared. In spring 2021 we revisited 7 permanent plots covering 1,485 m2 that had been previously monitored during the period from 2005 to 2009. We found that although previous studies described P. rudis populations as stable with low recruitment rates, recruitment after 2017 increased in comparison to 2005-2009. At least two cohorts of recruits (~3 and ~1 year in age) were to be found both within the plots as well as in other areas throughout the Columbretes archipelago, colonizing areas previously occupied by P. nobilis. We hypothesize that P. rudis has been benefited by the local extinction of the sibling species P. nobilis, most probably as a result of reduced interspecific competition. The ecological role once played mainly by P. nobilis as the dominant species, might now be taken over by P. rudis, whose populations could grow during the oncoming years.

Reconstructing the Evolutionary History of Pinna nobilis: New Genetic Signals from the Past of a Species on the Brink of Extinction

“…In the present scenario, it is interesting to observe that some ecological niches left vacant by P. nobilis following mass mortality are now being partially occupied by P. rudis . Kersting and Ballesteros [ 101 ] documented a behavioural shift in P. rudis populations in the Columbretes Islands Marine Reserve off the Iberian Mediterranean coast. Their study revealed a significant increase in the recruitment rates for P. rudis after the mass mortality event of P. nobilis in 2017.…”

Population status, distribution and trophic implications of Pinna nobilis along the South-eastern Italian coast

“…Kersting and Ballesteros 30 have suggested that other species, such as P. rudis, could benefit from the collapse of the P. nobilis population. During our surveys, only 5 specimens of P. rudis were found, located in 2 sites, but it must be considered that the survey was carried out only a short time after the MME of P. nobilis.…”

A Tale of Two Sisters: The Southerner Pinna rudis Is Getting North after the Regional Extinction of the Congeneric P. nobilis (Mollusca: Bivalvia)

“…Outside the Mediterranean, where P. nobilis does not occur, P. rudis can live indifferently on sandy, rocky and muddy substrata [8]. In the Mediterranean, the two species have different habitat preferences: P. nobilis inhabits sandy bottoms and seagrass meadows [9], P. rudis rocky bottoms [10], which may indicate the outcome of interspecific competition [11]. Occasionally, the two species have been seen to coexist, resulting in mixed populations normally dominated by P. nobilis [10].…”

“…P. rudis has received less attention than its endemic sister species: the few studies available describe its Mediterranean populations as stable despite being characterised by low densities [10]. However, as its more iconic sister [12,13], P. rudis has been listed in Annex II of the Bern Convention as strictly protected species and in the Barcelona Convention as threatened or endangered marine species [14].…”

“…As a superior competitor, it is reasonable to assume that the presence of P. nobilis was limiting P. rudis to some extent. The reasons may be competition for food, which is one of the main factors limiting growth in bivalves [30], and capture of larvae by the filtration activity of P. nobilis itself [10].…”