Where and how - new insight for brown algal forest restoration in the Adriatic

Abstract

Several anthropogenic factors are responsible for the decline of Cystoseira sensu lato (hereafter Cystoseira) forests along Mediterranean coasts. Some Cystoseira species are already regionally extinct, and their decline has been widely recorded. Sustainable and efficient techniques for the restoration of Cystoseira are needed. In this context, the objectives of this study were i) to analyse the reproductive traits of three populations of Gongolaria barbata from three nearby donor sites in the northern Adriatic Sea, assessing the differences in their reproductive potential and reproductive success; and ii) to evaluate the outplanting success in terms of the effectiveness of G. barbata restoration, in relation to the different donor and receiving sites (Miramare MPA and in front of the Marine Biology Station Piran - MBSP) and implemented methods (ex situ and hybrid method combining a mesocosm cultivation and a suspended culture in the field). After 2 weeks of cultivation in mesocosms, half of the tiles with germlings were transported to the receiving sites and placed on suspended lantern nets (hybrid method), which were later (after 3 months) transferred to the seabed on concrete plates with protective cages. The remaining tiles were placed on the seabed on concrete plates with protective cages after a 4-week culture (ex situ method). At both sites, lantern nets and plates were randomly placed at 3 m depth. Thallus length was measured monthly in each treatment. Seedlings in suspended culture showed lower performance at the Miramare MPA, most likely due to the unfavourable environmental conditions. The satisfactory results obtained at MBSP demonstrate the efficiency of the hybrid method and confirm its potential to reduce the cost and time required for cultivation. Since unpredictable climatic events pose the greatest threat to restoration performance, these challenges must be considered when establishing new restoration practices. Moreover, herbivore regulation is extremely urgent and should be planned and implemented on a larger regional scale.

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

“…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). The observed variability among G. barbata stands is consistent with previous studies, which reported two main morphologies: (1) long, sickle-shaped receptacles with numerous chained aerocysts, and (2) small, oval or spindle-shaped receptacles with no or few aerocysts (Orlando-Bonaca et al 2022). Different morphologies and reproductive success suggest the presence of a morphological plasticity of G. barbata, possibly driven by different ecological conditions (Orlando-Bonaca et al 2022).…”

“…in situ or their ex situ reproduction (or a combination of both). The recruits growth rates (on average 0.2–0.7 mm/week) and densities (up to 7 recruits 10/cm 2 ) reported here from the stranded seaweed G. barbata are similar to those previously reported in the Adriatic Sea and in other Mediterranean regions using the standard approaches (Verdura et al 2018; Savonitto et al 2021; Orlando‐Bonaca et al 2022). The same applies when we compare the data presented here with previous studies conducted in the same area, that is the Conero Riviera (Central‐eastern Adriatic Sea; Bianchelli et al 2023 a ).…”

“…In the last years, the possibility of restoring these macroalgal forests (e.g. G. barbata) was explored in the Adriatic Sea (Savonitto et al 2021;Orlando-Bonaca et al 2022). The restoration of fucalean forests is carried out either using in situ and ex situ (cultivated in mesocosms) recruitment approaches or using hybrid methods (combining cultivation in mesocosm and culture in the natural environment), also coupled with passive restoration measures (Verdura et al 2018;Orlando-Bonaca et al 2022;Bianchelli et al 2023aBianchelli et al , 2023b.…”

“…The main driver of this forest loss is the human impact on coastlines, increasing sediment resuspension, high nutrient concentrations, and loads (Rindi et al 2020). As a result, only C. compressa and Gongolaria barbata are still present, even though the latter species is in regression, due to their greater tolerance to environmental stress (Orlando‐Bonaca et al 2022).…”

The Lush Fucales Underwater Forests off the Cilento Coast: An Overlooked Mediterranean Biodiversity Hotspot

“…Although there has been a dramatic loss of these ecosystems in many regions [ 31 , 39 , 40 , 41 ], in other regions losses have been limited to the most affected areas and some populations have surprisingly maintained a relatively healthy state [ 42 , 43 ]. Moreover, restoration actions have been taken recently to return to a pristine state and restore the “ecological status” of these ecosystems [ 11 , 28 , 44 , 45 , 46 , 47 , 48 , 49 ].…”