Effects of Natural and Anthropogenic Stressors on Fucalean Brown Seaweeds Across Different Spatial Scales in the Mediterranean Sea

Abstract

Algal habitat-forming forests composed of fucalean brown seaweeds (Cystoseira, Ericaria, and Gongolaria) have severely declined along the Mediterranean coasts, endangering the maintenance of essential ecosystem services. Numerous factors determine the loss of these assemblages and operate at different spatial scales, which must be identified to plan conservation and restoration actions. To explore the critical stressors (natural and anthropogenic) that may cause habitat degradation, we investigated (a) the patterns of variability of fucalean forests in percentage cover (abundance) at three spatial scales (location, forest, transect) by visual estimates and or photographic sampling to identify relevant spatial scales of variation, (b) the correlation between semi-quantitative anthropogenic stressors, individually or cumulatively (MA-LUSI index), including natural stressors (confinement, sea urchin grazing), and percentage cover of functional groups (perennial, semi-perennial) at forest spatial scale. The results showed that impacts from mariculture and urbanization seem to be the main stressors affecting habitat-forming species. In particular, while mariculture, urbanization, and cumulative anthropogenic stress negatively correlated with the percentage cover of perennial fucalean species, the same stressors were positively correlated with the percentage cover of the semi-perennial Cystoseira compressa and C. compressa subsp. pustulata. Our results indicate that human impacts can determine spatial patterns in these fragmented and heterogeneous marine habitats, thus stressing the need of carefully considering scale-dependent ecological processes to support conservation and restoration.

Spring composition of the macroalgal vegetation of a small offshore island in the north-western Mediterranean (Gallinara Island, Ligurian Sea)

“…Differently from Bianchi et al (2018) we found that two other large brown seaweeds, Cystoseira compressa and Dictyopteris polypodioides, are still generally common on the island, although with distribution concentrated in certain habitats and certain parts of the shoreline (Table 1). These are two widespread Mediterranean phaeophytes that thrive in a wide range of environmental conditions and may also occur at sites moderately affected by anthropogenic disturbances (Mangialajo et al 2008;Mancuso et al 2018;Orfanidis et al 2021). We also confirm the presence of Gongolaria elegans in the rockpool on the SE shore, where this species was previously recorded by Mangialajo (2007).…”

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

“…As a result of multiple anthropogenic impacts (e.g., coastal urbanisation, eutrophication, sediment loading and overgrazing), Cystoseira stands have gradually disappeared in many Mediterranean coastal areas, often being replaced by filamentous or ephemeral taxa (e.g., Mangialajo et al, 2008;Falace et al, 2010;Vergeś et al, 2014;Thibaut et al, 2015;Rindi et al, 2017;Rindi et al, 2018;Catra et al, 2019;Mariani et al, 2019;Bernal-Ibañez et al, 2021;Orlando-Bonaca et al, 2021a;Orfanidis et al, 2021). In addition, human changes in the marine environment also affect connectivity, leading to habitat fragmentation and loss, and genetic disjunction even at small spatial scales (Alberto et al, 2010).…”

Assessing the expansion and success of a restored population of Gongolaria barbata (Stackhouse) Kuntze (Fucales, Phaeophyceae) using high-precision positioning tools and size distribution frequencies

“…Gongolaria barbata (Stackhouse) Kuntze [formerly known as Cystoseira barbata (Stackhouse) C. Agardh; Molinari-Novoa & Guiry, 2020], an engineering species growing in shallow and sheltered environments, has seen its already limited distribution in the Mediterranean reduced over time (Orfanidis et al, 2021). This macroalga is currently considered as threatened by the Barcelona Convention (Annex II; UNEP/MAP, 2013).…”