Undaria pinnatifida : A case study to highlight challenges in marine invasion ecology and management

Marine invasion ecology and management have progressed significantly over the last 30 years although many knowledge gaps and challenges remain. The kelp Undaria pinnatifida, or “Wakame,” has a global non-native range and is considered one of the world's “worst” invasive species. Since its first recorded introduction in 1971, numerous studies have been conducted on its ecology, invasive characteristics, and impacts, yet a general consensus on the best approach to its management has not yet been reached. Here, we synthesize current understanding of this highly invasive species and adopt Undaria as a case study to highlight challenges in wider marine invasion ecology and management. Invasive species such as Undaria are likely to continue to spread and become conspicuous, prominent components of coastal marine communities. While in many cases, marine invasive species have detectable deleterious impacts on recipient communities, in many others their influence is often limited and location specific. Although not yet conclusive, Undaria may cause some ecological impact, but it does not appear to drive ecosystem change in most invaded regions. Targeted management actions have also had minimal success. Further research is needed before well-considered, evidence-based management decisions can be made. However, if Undaria was to become officially unmanaged in parts of its non-native range, the presence of a highly productive, habitat former with commercial value and a broad ecological niche, could have significant economic and even environmental benefit. How science and policy reacts to the continued invasion of Undaria may influence how similar marine invasive species are handled in the future

Morse homology for the heat flow

We use the heat flow on the loop space of a closed Riemannian manifold to construct an algebraic chain complex. The chain groups are generated by perturbed closed geodesics. The boundary operator is defined in the spirit of Floer theory by counting, modulo time shift, heat flow trajectories that converge asymptotically to nondegenerate closed geodesics of Morse index difference one.Comment: 89 pages, 3 figure

Removal treatments alter the recruitment dynamics of a global marine invader - Implications for management feasibility

Frameworks designed to prioritise the management of invasive non-native species (INNS) must consider many factors, including their impacts on native biodiversity, ecosystem services, and human health. Management feasibility should also be foremost in any prioritisation process, but is often overlooked, particularly in the marine environment. The Asian kelp, Undaria pinnatifida, is one of the most cosmopolitan marine INNS worldwide and recognised as a priority species for monitoring in the UK and elsewhere. Here, experimental monthly removals of Undaria (from 0.2 m2 patches of floating pontoon) were conducted at two marinas to investigate their influence on recruitment dynamics and the potential implications for management feasibility. Over the 18-month experiment there was no consistent reduction in Undaria recruitment following removals. Cleaning of pontoon surfaces (i.e. removal of all biota) led to significant short-term reductions in recruitment but caused a temporal shift in normal recruitment patterns. Non-selective removal (i.e. all macroalgae) generally promoted recruitment, while selective removal (i.e. Undaria only) had some limited success in reducing overall recruitment. The varied results indicate that the feasibility of limiting Undaria is likely to be very low at sites with established populations and high propagule pressure. However, where there are new incursions, a mixture of cleaning of invaded surfaces prior to normal periods of peak recruitment followed by selective removal may have some potential in limiting Undaria populations within these sites. Multi-factorial experimental manipulations such as this are useful tools for gathering quantitative evidence to support the prioritisation of management measures for marine INNS

Impacts of ocean warming on kelp forest ecosystems

Kelp forests represent some of the most diverse and productive habitats on Earth, and provide a range of ecosystem goods and services on which human populations depend. As the distribution and ecophysiology of kelp species is strongly influenced by temperature, recent warming trends in many regions have been linked with concurrent changes in kelp populations, communities and ecosystems. Over the past decade, the number of reports of ocean warming impacts on kelp forests has risen sharply. Here, I synthesise recent studies to highlight general patterns and trends. While kelp responses to climate change vary greatly between ocean basins, regions and species, there is compelling evidence to show that ocean warming poses an unequivocal threat to the persistence and integrity of kelp forest ecosystems in coming decades

The influence of native macroalgal canopies on the distribution and abundance of the non-native kelp Undaria pinnatifida in natural reef habitats

The Asian kelp Undaria pinnatifida (‘Wakame’) is one of the most widespread invasive non-native species in coastal marine habitats and is fast approaching cosmopolitan status, yet its interactions with native species are poorly understood. Within the Plymouth Sound (UK) Special Area of Conservation (SAC), Undaria has become a conspicuous and important component of assemblages in shallow rocky reef habitats, where it co-exists with native canopy-forming brown macroalgae. We examined the hypothesis that rocky reef habitats supporting dense macroalgal canopies will have more biotic resistance to the invasion of Undaria compared with reef habitats supporting disturbed or sparse native canopies. Field surveys were completed at two spatial scales and sampling resolutions, and a short-term field-based canopy removal experiment was conducted to examine the influence of native macroalgal assemblages on the abundance, cover, biomass and morphology of Undaria. Field surveys indicated that Undaria was negatively related to the cover of macroalgal ‘competitors’, particularly Laminaria spp. However, multiple, large Undaria sporophytes were observed within dense native canopies, suggesting that disturbance to, or the absence of, canopies is not a prerequisite for Undaria colonisation. The short-term canopy removal experiment indicated that Undaria functions primarily as a pioneer species in this system. Where native canopies were left intact, Undaria sporophytes were far less abundant and were generally smaller with lower biomass compared with those in disturbed patches. The spread of Undaria into natural habitats is inhibited by the presence of native competitors, particularly large perennial species such as Laminaria spp., although the persistence of intact dense canopies does not completely prevent assimilation of Undaria into native assemblages

Community responses to seawater warming are conserved across diverse biological groupings and taxonomic resolutions

Temperature variability is a major driver of ecological pattern, with recent changes in average and extreme temperatures having significant impacts on populations, communities and ecosystems. In the marine realm, very few experiments have manipulated temperature in situ, and current understanding of temperature effects on community dynamics is limited. We developed new technology for precise seawater temperature control to examine warming effects on communities of bacteria, microbial eukaryotes (protists) and metazoans. Despite highly contrasting phylogenies, size spectra and diversity levels, the three community types responded similarly to seawater warming treatments of +3°C and +5°C, highlighting the critical and overarching importance of temperature in structuring communities. Temperature effects were detectable at coarse taxonomic resolutions and many taxa responded positively to warming, leading to increased abundances at the community-level. Novel field-based experimental approaches are essential to improve mechanistic understanding of how ocean warming will alter the structure and functioning of diverse marine communities

Appreciating interconnectivity between habitats is key to Blue Carbon management

We welcome the recent synthesis by Howard et al. (2017), which drew attention to the role of marine systems and natural carbon sequestration in the oceans as a fundamental aspect of climate-change mitigation. The importance of long-term carbon storage in marine habitats (ie “blue carbon”) is rapidly gaining recognition and is increasingly a focus of national and international attempts to mitigate rising atmospheric emissions of carbon dioxide. However, effectively managing blue carbon requires an appreciation of the inherent connectivity between marine populations and habitats. More so than their terrestrial counterparts, marine ecosystems are “open”, with high rates of transfer of energy, matter, genetic material, and species across regional seascapes (Kinlan and Gaines 2003). We suggest that policy frameworks, and the science underpinning them, should focus not only on carbon sink habitats but also on carbon source habitats, which play critical roles in marine carbon cycling and natural carbon sequestration in the oceans

Spatial variability in the diversity and structure of faunal assemblages associated with kelp holdfasts (<i>Laminaria hyperborea</i>) in the northeast Atlantic

<p>Map indicating the locations of the four study regions in the UK, northeast Atlantic: (A) northern Scotland, (B) western Scotland, (C) southwest Wales and (D) southwest England. Smaller panels show the positions of the 3 study sites within each region.</p

Impacts of climate change on shallow and shelf subtidal habitats, relevant to the coastal and marine environment around the UK

A comprehensive review of the literature identified thirteen new relevant studies published since the MCCIP 2013 report on ‘what is already happening’, of which all but one were conducted in UK waters. A further four studies have been published since 2013 on ‘what is likely to happen in the future’. • North Sea infaunal (burrowing) species have shifted their distributions in response to changing sea temperature, however, most species have not been able to keep pace with shifting temperature, meaning that species are subjected to warmer conditions. Leading (expanding) edges are responding more quickly than trailing (retreating) edges, which has been observed elsewhere in the world. • Analysis of a 40-year data–series found that small, generally shorter lived, infauna experienced some changes in community structure related to changes in Sea-Surface Temperature (SST), but this affect was dampened because increased food availability meant that temperature induced rises in energy use were counteracted. This was not the case for large-bodied species that experienced increased competition leading to altered community structures. This highlights that changes in non-climate drivers may interact with climate change to mediate species – community level responses and that responses may depend on species life-history traits. • A number of UK kelp species have experienced changes in abundance linked to altered SST. In particular the warm-water species, Laminaria ochroleuca, has increased in abundance and expanded its distribution into more wave-exposed conditions. While superficially similar, there are differences between warm-water and cold-water species in terms of life history characteristics (e.g. cold-water species such as L. hyperborea and L. digitata are perennial, whereas the warm-water species Saccorhiza polyschides is a pseudo-annual), and habitat provision (e.g. L. hyperborea supports diverse epiphyte assemblages whereas L. ochroleuca does not)