Highly restricted dispersal in habitat-forming seaweed may impede natural recovery of disturbed populations

Abstract

Cystoseira sensu lato (Class Phaeophyceae, Order Fucales, Family Sargassaceae) forests play a central role in marine Mediterranean ecosystems. Over the last decades, Cystoseira s.l. suffered from a severe loss as a result of multiple anthropogenic stressors. In particular, Gongolaria barbata has faced multiple human-induced threats, and, despite its ecological importance in structuring rocky communities and hosting a large number of species, the natural recovery of G. barbata depleted populations is uncertain. Here, we used nine microsatellite loci specifically developed for G. barbata to assess the genetic diversity of this species and its genetic connectivity among fifteen sites located in the Ionian, the Adriatic and the Black Seas. In line with strong and significant heterozygosity deficiencies across loci, likely explained by Wahlund effect, high genetic structure was observed among the three seas (ENA corrected FST = 0.355, IC = [0.283, 0.440]), with an estimated dispersal distance per generation smaller than 600 m, both in the Adriatic and Black Sea. This strong genetic structure likely results from restricted gene flow driven by geographic distances and limited dispersal abilities, along with genetic drift within isolated populations. The presence of genetically disconnected populations at small spatial scales (< 10 km) has important implications for the identification of relevant conservation and management measures for G. barbata: each population should be considered as separated evolutionary units with dedicated conservation efforts.

Stranded seaweeds (Gongolaria barbata): an opportunity for macroalgal forest restoration

“…In turn, this has important implications for the identification of relevant conservation and management measures: each population, indeed, should be considered as separated units with dedicated conservation and restoration efforts (Riquet et al 2021). On the other hand, dispersal of these species could be facilitated by rafting (Riquet et al 2021). Moreover, detachment, rafting, and stranding of adults may be the effect of extreme events, such as heatwaves or storms, which are predicted to be more and more frequent in the future, due to climate change (Blanfuné et al 2019).…”

“…populations are often fragmented and genetically disconnected also at small spatial scales, and connected by very low migration rates, along Mediterranean coasts (Buonomo et al 2016;Verdura et al 2023). In turn, this has important implications for the identification of relevant conservation and management measures: each population, indeed, should be considered as separated units with dedicated conservation and restoration efforts (Riquet et al 2021). On the other hand, dispersal of these species could be facilitated by rafting (Riquet et al 2021).…”

Distribution of sea urchin barrens in shallow algal communities along the eastern Adriatic coast

“…The impoverishment of shallow-water algal communities, especially those with canopy-forming algae, in the central part of the eastern Adriatic Sea, must be seriously considered. Following degradation, natural recovery can take decades due to low dispersal capacity (Riquet et al, 2021).…”

Limited Stress Response to Transplantation in the Mediterranean Macroalga Ericaria amentacea, a Key Species for Marine Forest Restoration

“…Despite substantial conservation efforts (most of these species are protected by the Barcelona Convention, 1972, and the Bern Convention, 1976), many of the depleted populations have not been able to recover naturally due to very limited dispersal ability [12], highlighting the need for active intervention measures. For this reason, restoration of several macroalgal forests has recently been attempted using different approaches including transplanting of adults taken from healthy forests and ex situ or in situ recruitment enhancement (i.e., germling outplanting), recently reviewed by Cebrian et al [13].…”