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.
Highlights
Predicting the effects of abiotic and biotic stressors on marine vegetation changes has been a central concern of marine science in the last decades world-wide (Lotze et al, 2006; Airoldi and Beck, 2007; Coleman et al, 2008), and in the Mediterranean sea (Viaroli et al, 2008; Macreadie et al, 2014; Papathanasiou et al, 2015; Tsioli et al, 2019)
Algal forests composed by the genera Cystoseira, Ericaria, and Gongolaria (Fucales), with the exception of C. compressa, likely represent the most endangered habitat in the Mediterranean Sea (Barcelona Convention-Annex II; United Nations Environment Programme/Mediterranean Action Plan-UNEP/MAP; Verlaque et al, 2019) and have undergone a major decline in the last decades (Thibaut et al, 2005; Blanfuné et al, 2016; Rindi et al, 2020)
We explored the potential correlation between stressors individually or cumulatively (MA-LUSI index), including natural stressors, and the functional groups percentage cover at forest spatial scale
Summary
Predicting the effects of abiotic and biotic stressors on marine vegetation changes has been a central concern of marine science in the last decades world-wide (Lotze et al, 2006; Airoldi and Beck, 2007; Coleman et al, 2008), and in the Mediterranean sea (Viaroli et al, 2008; Macreadie et al, 2014; Papathanasiou et al, 2015; Tsioli et al, 2019). The processes driving fucalean species diversity, abundance, and coexistence along environmental gradients are still unclear, the cumulative impacts of local anthropogenic stressors such as coastal development, habitat destruction, pollution, and fisheries along with climate change are considered the main causes (Sala et al, 2012; Gianni et al, 2013; Strain et al, 2014; Mineur et al, 2015; Bianchi et al, 2018; Fabbrizzi et al, 2020). Disruption of climatic patterns with more frequent and stronger storm events, as well as heat waves, which are becoming increasingly frequent during summer in the whole Mediterranean Sea (Darmaraki et al, 2019), are expected to have severe effects at local scales on fragmented populations of fucalean species (Verdura et al, 2021)
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