Volume 64, Issue 5 - "Changes in Marine Botanical Biodiversity and Ecology under Global Climate Change"; Guest Editors: Put Ang, Jeong Ha Kim and Wendy Nelson

Since 2011 we have been documenting seaweed diversity and abundance along a poorly studied area of the central coast of British Columbia, Canada. This first installment focuses on the Chlorophyta. To date, 42 species have been recorded, and we have obtained DNA sequences for most. Although most of these species reportedly have wide distributions along the west coast of North America, others appear to represent new northern or southern records or possible introductions, and a number have yet to be described. New southern limits are recorded for Acrosiphonia sonderi , Acrosiphonia sp., Protomonostroma undulatum , and Ulva pouliotii sp. nov., and new northern records are documented for Ulva expansa , U. stenophylla , and another undescribed species of Ulva . Among species of Cladophoraceae, we obtained a sequence only for Cladophora opaca , a Japanese species not previously recorded from North America, and an undetermined species of Rhizoclonium . We sequenced three species of Derbesia , none of which is D. marina , the currently recognized species for this area; all three require taxonomic treatment. A sequence for a shell-boring species, which is tentatively identified as Eugomontia sacculata , was also obtained. These findings extend our understanding of the diversity and biogeography of green macroalgae in the northeast Pacific.

Partial rbc L sequences were obtained from the type specimens of Lithophyllum coarctatum and L. gardineri . Both species were variably assigned to either Hydrolithon or Porolithon during the last two centuries, with L. coarctatum , from the tropical eastern Indian Ocean currently considered a synonym of L. gardineri from the tropical western Indian Ocean. Phylogenetic analyses show that both belong in Porolithon and that they are distinct species despite their morpho-anatomical similarities, including a columnar morphology. Porolithon epiphyticum sp. nov ., from the same locality as P. coarctatum , Cocos-Keeling Islands, is the first reported epiphytic species in the genus. Eight of the currently recognized 15 species of Porolithon have had their type specimens sequenced to correctly apply names, including the generitype specimen. DNA sequencing provides independent confirmation that the morpho-anatomical character of the presence of horizontal fields of trichocytes without intervening vegetative cells is diagnostic for Porolithon . The generitypes of the four genera classified in the subfamily Metagoniolithoideae, Dawsoniolithon , Floiophycus , Harveylithon , and Metagoniolithon as well as Hydrolithon in the subfamily Hydrolithoideae, have not been sequenced. The taxonomic and nomenclatural uncertainties in each of these genera are discussed.

The recognition of non-indigenous marine macroalgae in New Zealand and the potential pathways and vectors contributing to their arrival were discussed by Nancy Adams in 1983 along with a list of 14 species she considered to be “possibly naturalised”. In the following 38 years many more species have been identified as non-indigenous, a few of which have become widespread and invasive around New Zealand. We present an updated list of 61 taxa that we consider to have been introduced to the archipelago, and highlight a range of issues associated with the recognition of non-indigenous species, particularly increased taxonomic knowledge, the impact of an expanded collection baseline, as well as targeted investigations in New Zealand, increasing data availability globally, and the role of molecular tools for confirming species identifications and distinguishing cryptic species.

Eisenia arborea has a disjunct distribution along the west coast of North America. We detail the current distribution of E. arborea and use long-term records to examine how present-day shifts in E. arborea prevalence and abundance in British Columbia (BC), relative to the dominant stipitate kelp Pterygophora californica , may be driven by interactions between changing grazing pressure and warming water. We further speculate on how the disjunction of E. arborea arose. The ancestor of E. arborea likely dispersed from Japan to North America where glaciation disrupted its distribution and speciation occurred . As glaciers retreated E. arborea likely dispersed into BC from warmer waters in the south and/or expanded from refugia off Vancouver Island and Haida Gwaii. While E. arborea is uncommon, our records extend its range into Alaska and Washington State. Along western Vancouver Island, BC, under warming conditions, E. arborea prevalence and abundance increased where once-extirpated sea otters ( Enhydra lutris ) removed urchins. Where otters were absent, however, reduced summer wave heights, associated with warming, apparently allowed urchins to graze shallow-water kelps, which declined. We suggest that under warming conditions, sea otters may increase kelp resilience, with E. arborea becoming more prevalent in NE Pacific kelp forests.

The distribution and ecology of the invasive brown alga Fucus serratus along the 500 km Atlantic coast of Nova Scotia, Canada, has been poorly explored. We observed significant intertidal penetration at four sites in the southwestern part of the province, and then examined numerous sites along the Atlantic coast of Nova Scotia. Surveys of attached algae in intertidal and shallow subtidal zones and wrack show that F. serratus has become a dominant plant in the low to mid-intertidal zone and can be expected on headlands along the South Shore of Nova Scotia where it can occupy up to 40% of the intertidal zone with cover >75% and mean densities of up to 10 kg m −1 . In this zone, F. serratus has replaced Chondrus crispus as the major canopy species, although C. crispus and Corallina officinalis remain primary understory species. At slightly higher elevations, F. serratus was common as an understory beneath Ascophyllum nodosum and Fucus vesiculosus . While geographic spread along the Atlantic coast might reflect the natural dispersal capacity of F. serratus , we hypothesize that the ecological extension into the intertidal zone may be facilitated by harvesting of A. nodosum and by climate change in an ocean-warming hotspot.

Species diversity in a habitat is often termed alpha diversity. As it influences various community properties, many studies have investigated its drivers. For instance, intertidal macroalgal canopies limit understory thermal stress during low tides and thus often increase alpha diversity. More recently, beta diversity has also become of interest. Beta diversity measures the change in species composition across space and is another important attribute of communities because it influences their multifunctionality, productivity, and resilience. Using data from a field experiment done in Atlantic Canada, we tested the hypothesis that fucoid macroalgal canopies limit beta diversity in intertidal communities. This prediction stems from previous evidence that such canopies limit thermal variation across the substrate during low tides, an important consideration because spatial thermal changes influence spatial variability in species composition. To test our hypothesis, we compared two treatments (full canopy cover and canopy removal) created the year before on intertidal areas that were originally all fully covered by canopies. Separately for each treatment, we calculated beta diversity as the Bray-Curtis dissimilarity between nearby quadrats using species abundance data. Overall, fucoid macroalgal canopies significantly reduced beta diversity, showing that these foundation species can have opposing effects on alpha and beta diversity.

This study aims to investigate the relative effects of urchin removal, non-urchin gastropod herbivores removal, and transplantation on macroalgal forest restoration using an additive manipulation design. A field experiment was conducted in subtidal urchin barren rocks in the eastern coast of South Korea from August 2017 to June 2020 with three experimental treatments: no urchins (NU), NU plus no herbivorous gastropods (NH), NH plus Ecklonia bicyclis transplant (NHT). Six months after experiment initiation, seaweed abundance rapidly increased in all three experimental treatments. The highest peak was found in the spring season of the first year (2018). The year-to-year variations became smaller throughout the survey period. The results of comparing NU and control site indicated that urchin removal had an exclusive effect on algal recovery while additional removal of herbivorous gastropods did not affect algal recovery quantitatively. With the successful establishment of E. bicyclis , the community assemblages of the three treatments became more distinct in the subsequent years, showing diverse dominance in NU, red algal dominance in NH, and dominance of E. bicyclis canopy and understory groups in NHT. This study provides evidence that urchin removal on its own from barren grounds can lead to rapid restoration of seaweed forest in subtidal habitats.

Seaweeds play essential ecological and biogeochemical roles and support important industrial applications. Sustaining natural populations of seaweeds under climate change while simultaneously putting seaweeds to use in climate solutions requires that we weave together disparate lines of inquiry—the ecological and the industrial—to create a more holistic perspective and integrated research agenda. Innovation in the use of seaweeds must be more than aspirational—it requires evidence of effectiveness in the short term, and a promise to sustain nature and people in the long term.