From marine deserts to algal beds: Treptacantha elegans revegetation to reverse stable degraded ecosystems inside and outside a No‐Take marine reserve

Abstract

Canopy-forming algae play a key role in temperate coastal ecosystems sustaining complex habitats that provide food and refuge for rich associated biotic communities. These macroalgae are in decline in many coastal areas, where overgrazing by herbivores can lead to the loss of these highly structured and diverse habitats toward less complex sea urchin barren grounds. Once established, low productive barren grounds are considered stable states maintained by several positive feedback mechanisms that prevent the recovery of marine forests. To revert this global decline, restoration efforts and measures are being encouraged by EU regulations and local actions. Here, we tested the success of active revegetation techniques as a tool to promote functional and productive Treptacantha elegans forests in sea urchin barren grounds under different restoration strategies (active, and combined active with passive strategies). Active revegetation was performed in 6 barren grounds, 3 located inside a Mediterranean No-Take marine reserve (active and passive strategy) and 3 outside (active strategy alone), following a three-step protocol: (1) sea urchin population eradication, (2) seeding with Treptacantha elegans, and (3) enhancement of T. elegans recruitment. Revegetation success was assessed 1 year later in the six barren grounds, but was only achieved after combining active with passive restoration strategies. Our results encourage revegetation of barren grounds to shift from less productive habitats to complex T. elegans forests, highlight the potential of the combined passive and active restoration strategies, as well as the important role of marine reserves not only in conservation but also in ecological restoration.

Ecological traits, genetic diversity and regional distribution of the macroalga Treptacantha elegans along the Catalan coast (NW Mediterranean Sea)

“…While the dispersal distance of early life stages is less than 10 m from source populations in T. elegans 43 , here we show the existence of two populations 30 km away from the Medes Islands NTZ. This may be explained by the fact that this species, as other fucoids, is capable to disperse through detached or drifting fertile parts of mature individuals 21,27,44 or by animals 18 .…”

“…For this to happen, however, it is important to improve the water quality and to protect population sources that ensure dispersal like those found in the Medes Islands NTZ, especially in organisms with short-dispersing propagules. Finally, given its fast and stable population dynamics (early fertile maturity and high turnover rate), we highlight that T. elegans represent an ideal organism to conduct habitat restoration actions in previously degraded systems such as sea urchin barrens or turfdominated habitats 43 .…”

First Restoration Experiment for Gongolaria barbata in Slovenian Coastal Waters. What Can Go Wrong?

“…The first technique provides the transplantation of adult thalli onto artificial modules, by fixing the holdfasts using arched hooks or by covering the basal part of the plant with polyurethane foam [48], and by fixing the thalli with epoxy glue [49]. For the second technique, bags containing fertile receptacles were tied to a pick and directly fixed near the sea bottom (in situ) at selected restoration sites [44,50]. The third technique provides the outplanting of juveniles cultured ex situ under laboratory conditions [43][44][45]51,52].…”

Depth distribution of canopy‐forming algae of the order Fucales is related to their photosynthetic features

“…Bianchi et al, 2014;Catra et al, 2019;Cormaci & Furnari, 1999;Mariani et al, 2019;Thibaut et al, 2005Thibaut et al, , 2015, their vulnerability to pollution (e.g. Arévalo et al, 2007;Ivesa et al, 2016;Munda, 1993;Pinedo et al, 2013;Sales et al, 2011;Soltan et al, 2001), grazing (Agnetta et al, 2015;Bonaviri et al, 2011;Sala et al, 2011;Vergés et al, 2009Vergés et al, , 2014 or warming (Capdevila et al, 2019;Celis-Plá et al, 2017a), as well as on information about measures to improve their conservation (De la Fuente et al, 2019;Medrano et al, 2020;Verdura et al, 2018), very few studies have been devoted to their photosynthetic features (Celis-Plá et al, 2017b;Coudret & Jupin, 1985;Delgado et al, 1995;Tremblin et al, 1986) and none has addressed the light-related ecophysiological features that explain their bathymetric distribution.…”