Juvenile fish assemblages in temperate rocky reefs are shaped by the presence of macro-algae canopy and its three-dimensional structure

Abstract

Arborescent macro-algae forests covering temperate rocky reefs are a known habitat for juvenile fishes. However, in the Mediterranean, these forests are undergoing severe transformations due to pressures from global change. In our study, juvenile fish assemblages differed between pristine arborescent forests (Cystoseira brachycarpa var. balearica) versus an alternate state: bushland (Dictyotales – Sphacelariales). Forests hosted richer and three-fold more abundant juvenile assemblages. This was consistent through space, whatever the local environmental conditions, along 40 km of NW Mediterranean subtidal rocky shores (Corsica, France). Among Cystoseira forests, juvenile assemblages varied through space (i.e. between localities, zones or sites) in terms of total abundance, composition, richness and taxa-specific patterns. More than half of this variability was explained by forest descriptors, namely small variations in canopy structure and/or depth. Our results provide essential cues for understanding and managing coastal habitats and fish populations. Further studies are needed to explain the residual part of the spatial variability of juvenile fish assemblages and to help focus conservation efforts.

Can ecosystem functioning be maintained despite climate‐driven shifts in species composition? Insights from novel marine forests

“…Both species are also morphologically similar and form canopies of similar heights and plant densities Supporting Information replaced by low-lying, architecturally poor habitats dominated by turf-forming algal species in several regions across the globe (Filbee-Dexter & Wernberg, 2018). Since the ecological characteristics of algal turfs differ markedly from those of larger canopy-forming seaweeds, such replacements can lead to substantial reductions in associated biodiversity (Cheminée et al, 2017;Smale & Wernberg, 2013) and alterations to key functions such as net primary productivity (Copertino, Connell, & Cheshire, 2005). Similarly, the introduction of nonnative seaweeds with traits differing from those of kelps modified the trophic dynamics and the circulation of organic matter within recipient marine ecosystems (Dijkstra et al, 2017;Pedersen et al, 2005).…”

Mapping and Classification of Ecologically Sensitive Marine Habitats Using Unmanned Aerial Vehicle (UAV) Imagery and Object-Based Image Analysis (OBIA)

“…For instance, we reported the presence of brown macroalgae (especially Cystoseira spp., Figure 8b-d). This species is very important along rocky coasts because well-developed Cystoseira belt communities indicate good water quality [67] and, in general, arborescent macro-algae forests covering temperate rocky reefs are a known habitat for juvenile fish [68]. On the other hand, the southern part of the P. oceanica meadow presented an impacted area (represented by dead "matte", Figure 8e-g) near to the port, probably due to the works for the expansion of the breakwater.…”

Impact of structural habitat modifications in coastal temperate systems on fish recruitment: a systematic review

“…It has become apparent that identifying and quantifying impacts on fish recruitment of native coastal habitat loss and the nursery value of a variety of coastal and estuarine habitats are needed [17,[109][110][111][112]. In this context habitat structure and complexity are emerging as critical factors influencing nursery values of coastal habitats [16,113,114]. Human-induced changes in habitat structure are one of the main pressures affecting estuarine and coastal systems worldwide [10,12], yet our review clearly shows that the degree and rate of these changes and their impact on fish recruitment are rarely studied and poorly understood.…”