Genetic differentiation between estuarine and open coast ecotypes of a dominant ecosystem engineer

Abstract

Temperate intertidal shores globally are often dominated by habitat-forming seaweeds, but our knowledge of these systems is heavily biased towards northern hemisphere species. Rocky intertidal shores throughout Australia and New Zealand are dominated by a single monotypic species, Hormosira banksii. This species plays a key role in facilitating biodiversity on both rocky shores and estuarine habitats, yet we know little about the processes that structure populations. Herein we characterise the genetic diversity and structure of Hormosira and demonstrate strong restrictions to gene flow over small spatial scales, as well as between estuarine and open coast populations. Estuarine ecotypes were often genetically unique from nearby open coast populations, possibly due to extant reduced gene flow between habitats, founder effects and coastal geomorphology. Deviations from random mating in many locations suggest complex demographic processes are at play within shores, including clonality in estuarine populations. Strong isolation by distance in Hormosira suggests that spatial management of intertidal habitats will necessitate a network of broad-scale protection. Understanding patterns of genetic diversity and gene flow in this important ecosystem engineer will enhance the ability to manage, conserve and restore this key species into the future.

Local thermal adaptation and limited gene flow constrain future climate responses of a marine ecosystem engineer

“…Within this context, our study on the dominant intertidal macrophyte in Australasia, H. banksii, indicates highly restricted gene flow across much of its contemporary distribution with evidence of strong genetic structuring on all spatial scales examined. These findings are consistent with those reported previously for H. banksii over smaller geographic ranges (Bellgrove et al, 2017;Coleman et al, 2011Coleman et al, , 2019 and reports of finescale genetic structuring in other marine macrophytes including fucoids (Coleman & Brawley, 2005;Williams & Difiori, 1996) (Marzinelli, Leong, Campbell, Steinberg, & Verges, 2016;Wood et al, 2019).…”

Local Coastal Configuration Rather Than Latitudinal Gradient Shape Clonal Diversity and Genetic Structure of Phymatolithon calcareum Maerl Beds in North European Atlantic

“…In the region of Rías Baixas, connectivity along the coast was reduced between populations located in the inner zone compared to those of the outer-zone. Strikingly similar results have been reported in a brown alga living both inside and outside estuaries along the Australian coast (Hormosira banksii, Coleman et al, 2018). In H. banksii, patterns of connectivity were linked to coastal topography and water exchange between estuaries and the open coast, where populations inside estuaries acted as sinks of migrants.…”

“…Once trapped in the estuaries inner-zones, rhodoliths seem to mostly reproduce asexually. Similarly, a higher rate of asexual reproduction of H. banksia has been measured within estuaries when compared to areas along the open coast (Coleman et al, 2018). Authors further proposed that estuarine populations could have originated from floating thalli, teared off from neighboring open coast populations after large-scale storms.…”

“…In particular, knowledge on the impact of clonal propagation, scales of dispersal, and gene flow on spatial genetic diversity of these habitat-forming algae is required to develop relevant management strategies. Moreover, habitat differences such as those found between estuarine and open sea habitats may also be important features shaping the pattern of genetic differentiation at a local scale (as for example in a fucoid alga: Coleman et al, 2018).…”

The Influence of Canopy Cover on the Ecological Function of A Key Autogenic Ecosystem Engineer

“…Canopy-forming seaweeds can function as autogenic ecosystem engineers on rocky seashores, providing a suitable habitat for species that would otherwise be excluded or only occur in low abundance [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Many studies referring to species as autogenic ecosystem engineers [16,17] (or similar theoretical terms such as dominant species [18], facilitators, habitat-forming species [9] and biogenic habitat) have investigated the associated loss of species when this one species is lost through a major disturbance. What hasn't been examined in full is whether the fucoid intertidal alga Hormosira banksii functions as an ecosystem engineer under varying densities in the absence of disturbance.…”