Fleshy red algae mats act as temporary reservoirs for sessile invertebrate biodiversity

Abstract

Many coastal ecosystems, such as coral reefs and seagrass meadows, currently experience overgrowth by fleshy algae due to the interplay of local and global stressors. This is usually accompanied by strong decreases in habitat complexity and biodiversity. Recently, persistent, mat-forming fleshy red algae, previously described for the Black Sea and several Atlantic locations, have also been observed in the Mediterranean. These several centimetre high mats may displace seagrass meadows and invertebrate communities, potentially causing a substantial loss of associated biodiversity. We show that the sessile invertebrate biodiversity in these red algae mats is high and exceeds that of neighbouring seagrass meadows. Comparative biodiversity indices were similar to or higher than those recently described for calcifying green algae habitats and biodiversity hotspots like coral reefs or mangrove forests. Our findings suggest that fleshy red algae mats can act as alternative habitats and temporary sessile invertebrate biodiversity reservoirs in times of environmental change.

Macroalgal features and their influence on associated biodiversity: implications for conservation and restoration

“…From a conservation and restoration point of view, such features gain relevance in coastal areas where seaweeds and seaweed habitats are in decline, or otherwise where lasting populations of rare, threatened, or endangered species of seaweeds can be found. Given the importance of these species, some of them coined foundation species (sensu Wikström and Kautsky, 2007;Dijkstra et al, 2017;El-Khaled et al, 2022) or ecosystem engineers (Schmidt and Scheibling, 2006;Schaal et al, 2016;Shelamoff et al, 2020), their loss likely entails escalating changes on associated communities. Based on most of the evidence reviewed here, such changes are most likely detrimental to diversity or abundance metrics (Ellison et al, 2005;Norderhaug et al, 2005;Marzinelli et al, 2016).…”

“…However, there is a need for these studies given ongoing climate events and anthropogenic disturbances, which are resulting in accelerated loss of species across coastal habitats worldwide (Bates and DeWreede, 2007). In this changing scenario, quantifying the contribution of macroalgae to biodiversity, both as individual algae or as clumps, beds, or populations, is undeniably important (Bates and DeWreede, 2007;El-Khaled et al, 2022).…”

“…It may also help conservation efforts, particularly in the case of macroalgal species that are threatened or are experiencing long-term declines (Lilley and Schiel, 2006;Marzinelli et al, 2014;Tummon Flynn et al, 2019). For those species, evidence showing their contribution to biodiversity and the features that enhance biodiversity levels, can support claims calling for their further protection and restoration (Marzinelli et al, 2014;Bursǐćet al, 2019;El-Khaled et al, 2022). Therefore, the goal of this minireview was to examine whether macroalgae influence biodiversity, and to identify the characteristics of individual seaweeds, or seaweed populations, that have an influence on any aspect of biodiversity.…”

Different approaches to estimate benthic metazoan diversity associated with free-living macroalgae (Fucus vesiculosus) on shallow soft sediments

“…Thus freeliving Fucus likely provide high complexity habitats alongside also influencing the normally associated fauna of soft sediment habitats. In fact algal mats are often associated with high biodiversity (El-Khaled et al 2022;Rossbach et al 2022Rossbach et al , 2021. As Baltic Sea benthic habitats are characterised by exceptionally low species diversity (Kotta and Orav 2001) the addition of algal cover may provide several conditions, including increasing food resources (Arroyo et al 2006;Norkko et al 2000) and providing protection from predation (Aarnio and Mattila 2000;Norkko et al 2000), which may in turn boost biodiversity.…”