Effective dispersal and density-dependence in mesophotic macroalgal forests: Insights from the Mediterranean species Cystoseira zosteroides

Abstract

Dispersal and recruitment are fundamental processes for population recovery following disturbances in sessile species. While both processes are well understood for many terrestrial species, they still remain poorly resolved for some macroalgal species. Here we experimentally investigated the effective dispersal and recruit survival of a mesophotic Mediterranean fucoid, Cystoseira zosteroides. In three isolated populations, four sets of settlement collectors were placed at increasing distances (from 0 to 10 m) and different orientations (North, South, East and West). We observed that effective dispersal was restricted to populations’ vicinity, with an average of 6.43 m and not further than 13.33 m, following a Weibull distribution. During their first year of life, survival was up to 50%, but it was lower underneath the adult canopy, suggesting a negative density-dependence. To put our results in a broader context we compared the effective dispersal of other fucoid and kelp species reported in the literature, which confirmed the low dispersal ability of brown algae, in particular for fucoids, with an effective dispersal of few meters. Given the importance of recruitment for the persistence and recovery of populations after disturbances, these results underline the vulnerability of C. zosteroides and other fucoid species to escalating threats.

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

“…As in other Cystoseira sensu lato species, our results may suggest a common ancestral gene pool but loosely connected populations 22,26,41 . This is supported by the patchy distribution of T. elegans, a pattern likely due to the scattered presence of rocky and suitable habitats in the area and the limited dispersal range of gametes in fucoids 19,20,21,42 . Unfortunately, our data are not sufficient to detect a clear correlation between distance and genetic differentiation within populations.…”

Are we ready for scaling up restoration actions? An insight from Mediterranean macroalgal canopies

“…In the literature, high mortality rates are normally encountered by macroalgal recruits [61, 62], and low survival rates in the first year have been reported also for Cystoseira sp. [63, 64]. Schiel et al [41] estimated survival rates from embryos to visible recruits variable from 0.001% to 3.8%.…”

“…compressa , [25–27, 77]; C . zosteroides , [63, 64, 68, 87]) out of 45 Cystoseira species existing in the Mediterranean Sea [88], limiting the potential of selecting suitable species in a restoration framework. Although the Mediterranean Action Plan, adopted within the framework of the Barcelona Convention (1976), identifies, in an amendment of 2009 (Annex IV, SPA/BD Protocol—United Nations Environment Programme [UNEP]), the conservation of all but one Mediterranean Cystoseira species ( C .…”

The ups and downs of a canopy-forming seaweed over a span of more than one century

“…The rapidity of the 2012 natural recovery, just 5 years after the previous minimum, was unexpected. Long-lived seaweeds, especially fucoids, are often K strategists, with heavy eggs disseminated at short distances and a low rate of recruitment 59–63 . This dynamic, with decline and recovery trajectories, has been previously observed for kelp forest (Laminariales such as Laminaria and Macrocystis ) around worldwide 2,14,64 , in contrast to the sharp decline observed for fucoids in the Mediterranea Sea.…”