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Kelp forests occur on more than a quarter of the world's coastlines, serving as foundation species supporting high levels of biodiversity. They are also a major source of organic matter in coastal ecosystems, with the majority of primary production released and exported as detritus. Kelp detritus also provides food and shelter for macroinvertebrates, which comprise important components of inshore food-webs. Hitherto, research on kelp detritus-associated macroinvertebrate assemblages remains relatively limited. We quantified spatiotemporal variability in the structure of detritus-associated macroinvertebrate assemblages within Laminaria hyperborea forests and evaluated the influence of putative drivers of the observed variability in assemblages across eight study sites within four regions of the United Kingdom in May and September 2015. We documented 5167 individuals from 106 taxa with Malacostraca, Gastropoda, Isopoda and Bivalvia the most abundant groups sampled. Assemblage structure varied across months, sites, and regions, with highest richness in September compared to May. Many taxa were unique to individual regions, with few documented in all regions. Finally, key drivers of assemblage structure included detritus tissue nitrogen content, depth, sea surface temperature, light intensity, as well as L. hyperborea canopy density and canopy biomass. Despite their dynamic composition and transient existence, accumulations of L. hyperborea detritus represent valuable repositories of biodiversity and represent an additional kelp forest component which influences secondary productivity, and potentially kelp forest food-web dynamics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier Ltd. All rights reserved.)

We examined spatiotemporal variability in the structure of faunal assemblages associated with the warm-temperate pseudo-kelp Saccorhiza polyschides towards its range centre (Western English Channel, southwest UK), to better understand its role as a habitat-former in the northeast Atlantic. A total of 180 sporophytes and their associated fauna were sampled across three months, three sites, and two depths. Assemblage abundance and biomass varied markedly between three morpho-functional sporophyte components (i.e., holdfast, stipe, blade). We recorded rich and abundant macroinvertebrate assemblages, comprising nine phyla, 28 coarse taxonomic groups, and 57 species of molluscs, which consistently dominated assemblages. We observed pronounced seasonality in faunal assemblage structure, marked variability between sites and depths, and strong positive relationships between biogenic habitat availability and faunal abundance/biomass. S. polyschides sporophytes are short-lived and offer temporary, less-stable habitat compared with dominant perennial Laminaria species, so shifts in the relative abundances of habitat-formers will likely alter local biodiversity patterns., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Habitat heterogeneity is considered a primary causal driver underpinning patterns of diversity, yet the universal role of heterogeneity in structuring biodiversity is unclear due to a lack of coordinated experiments testing its effects across geographic scales and habitat types. Furthermore, key species interactions that can enhance heterogeneity, such as facilitation cascades of foundation species, have been largely overlooked in general biodiversity models. Here, we performed 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which variation in biodiversity is explained by three axes of habitat heterogeneity: the amount of habitat, its morphological complexity, and capacity to provide ecological resources (e.g. food) within and between co-occurring foundation species. We show that positive and additive effects across the three axes of heterogeneity are common, providing a compelling mechanistic insight into the universal importance of habitat heterogeneity in promoting biodiversity via cascades of facilitative interactions. Because many aspects of habitat heterogeneity can be controlled through restoration and management interventions, our findings are directly relevant to biodiversity conservation., (© 2022. The Author(s).)

Kelp species function as important foundation organisms in coastal marine ecosystems where they provide biogenic habitat and ameliorate environmental conditions, often facilitating the development of diverse understorey assemblages. The structure of kelp forests is influenced by a variety of environmental factors, changes in which can result in profound shifts in ecological structure and functioning. Intense storm-induced wave action in particular, can severely impact kelp forest ecosystems. Given that storms are anticipated to increase in frequency and intensity in response to anthropogenic climate change, it is critical to understand their potential impacts on kelp forest ecosystems. During the 2021/22 northeast Atlantic storm season, the United Kingdom (UK) was subject to several intense storms, of which the first and most severe was Storm Arwen. Due to the unusual northerly wind direction, the greatest impacts of Storm Arwen were felt along the northeast coast of the UK where wind gusts exceeded 90 km/h, and inshore significant wave heights of 7.2 m and wave periods of 9.3 s were recorded. Here, we investigated temporal and spatial variation in the structure of L. hyperborea forests and associated understorey assemblages along the northeast coast of the UK over the 2021/22 storm season. We found significant changes in the cover, density, length, biomass, and age structure of L. hyperborea populations and the composition of understorey assemblages following the storm season, particularly at our most north facing site. We suggest continuous monitoring of these systems to further our understanding of temporal variation and potential recovery trajectories, alongside enhanced management to promote resilience to future perturbations. • Spatio-temporal variation in the structure, abundance, and composition of L. hyperborea forests and their associated understorey macroalgae and macrofauna assemblages along the northeast coast of the UK was assessed between two timepoints spanning the 2021/22 northeast Atlantic storm season. • Storm Arwen, which was characterised by an unusual northerly wind direction, was one of the most impactful storms along the northeast coast with winds gusts exceeding 90 km/h and significant wave heights of over 7m. • We found significant variation in the cover, density, length, biomass, and age structure of L. hyperborea populations and the composition of understorey assemblages between pre and post storm timepoints. • Differences between timepoints were generally most pronounced at the most north facing site. • The results suggest that the storm season likely had an impact on the kelp forest ecosystem, but seasonal variation may also have contributed to observed differences between timepoints. [ABSTRACT FROM AUTHOR]

Kelp species function as foundation organisms along almost one third of the world's coastlines, where they underpin diverse and productive forest habitats. The three-dimensional structure of the forest modifies local environmental conditions, which in some regions allows rich understorey macroalgal and macrofaunal assemblages to develop. These understorey assemblages, however, represent somewhat overlooked components of kelp forest ecosystems, with fundamental information on their structure and the processes that shape them often lacking. Here, we used an underwater suction sampler to characterize understorey macroalgal and macrofaunal assemblages within Laminaria hyperborea forests across the mid northeast Atlantic (United Kingdom). Specifically, we investigated spatial and temporal variation in the structure, abundance, diversity, and evenness of assemblages at twelve sites nested in four regions of the UK distributed along a 9° latitudinal gradient that encompassed a ∼ 2.5 °C gradient in mean sea surface temperature. Collectively, the samples comprised of 2.4 kg of understorey macroalgae from five functional groups, and 65,323 macrofaunal individuals from 179 taxa, demonstrating that understorey assemblages represent important repositories of biodiversity within coastal marine systems. Univariate assemblage metrics exhibited significant site-level variation, while the multivariate structure of assemblages exhibited both site and regional-level variation, and all metrics exhibited significant temporal variation. The observed variation was attributed in part to complex interactions between sea surface temperature, wave exposure and habitat structure, while the high site-level variation suggests that unquantified local-scale processes are also important influencers of understorey assemblages. Given that kelp forests are becoming increasingly threatened by multiple stressors, our results provide important evidence to support enhanced management of kelp forests, as well as baseline information that can serve as a benchmark to monitor, restore, and ultimately conserve these forests and their associated ecosystem services. • Kelp understorey macroalgal and macrofaunal assemblages are abundant and diverse but exhibit spatiotemporal variation. • Sea surface temperature, wave exposure, and habitat structure are important drivers of macrofaunal assemblage structure. • Results provide a baseline upon which to detect change in understorey macroalgal and macrofaunal assemblages. [ABSTRACT FROM AUTHOR]

Enhanced persistence of stress sensitive species in harsh environments due to amelioration of physical stress by habitat‐forming species has been widely documented. By contrast, less attention has been given to positive species interactions that may enhance stress tolerance in habitat‐forming species, with positive cascading effects on biodiversity and ecosystem functioning.We used a combination of field surveys and experiments to assess the effects of the epiphyte Jania rubens, on its subtidal macroalgal host Halopithys incurva, and their cascading effects on the associated invertebrate community, along a depth gradient associated with increasing stress (i.e. light stress at shallower depths).Correlative studies showed that the biomass and photosynthetic efficiency of H. incurva increased with depth, along with a decrease of epiphyte biomass. The experimental manipulation of epiphytes (removal in shallow water and addition in deep water) revealed that their effects on H. incurva physiology varied from positive in shallow habitats to negative in deep habitats. These results suggest that reduction of light/UV stress by J. rubens allows H. incurva to persist in shallow‐water habitats that would be otherwise unsuitable. In addition, colonization by large clumps of J. rubens increased the abundance and diversity of associated invertebrates in shallow habitat, suggesting that positive feedbacks between H. incurva, acting as the primary habitat‐former, and J. rubens, acting as a secondary habitat‐former, generate a facilitation cascade.Synthesis. Our study suggests that the persistence of some habitat‐forming species and their ability to support biodiversity may rely upon physical stress reduction by other species (e.g. epiphytes in our case) that are generally neglected when planning conservation strategies. A deeper understanding of context dependency in positive species interactions is essential for predicting patterns of species distribution under increasingly stressful climate scenarios. [ABSTRACT FROM AUTHOR]

Aim: In marine ecosystems, habitat‐forming species (HFS) such as reef‐building corals and canopy‐forming macroalgae alter local environmental conditions and can promote biodiversity by providing biogenic living space for a vast array of associated organisms. We examined community‐level impacts of observed climate‐driven shifts in the relative abundances of two superficially similar HFS, the warm‐water kelp Laminaria ochroleuca and the cool‐water kelp Laminaria hyperborea. Location: Western English Channel, north‐east Atlantic Methods: We compared algal and invertebrate assemblages associated with kelp stipes and holdfasts, across multiple sites and sampling events. Significant differences were recorded in the structure of assemblages between the host kelp species at each site and event. Results: Assemblages associated with stipes of the cool‐water HFS were, on average, >12 times more diverse and supported >3600 times more biomass compared with the warm‐water HFS. Holdfast assemblages also differed significantly between species, although to a lesser extent than those associated with stipes. Overall, assemblages associated with the warm‐water HFS were markedly impoverished and comprised far fewer rare or unique taxa. Main conclusions: While previous research has shown how climate‐driven loss of HFS can cause biodiversity loss, our study demonstrates that climate‐driven substitutions of HFS can also lead to impoverished assemblages. The indirect effects of climate change remain poorly resolved, but shifts in the distributions and abundances of HFS may invoke widespread ecological change, especially in marine ecosystems where facilitative interactions are particularly strong. [ABSTRACT FROM AUTHOR]

Kelp species are ecologically-important habitat-formers in coastal marine ecosystems, where they alter environmental conditions and promote local biodiversity by providing complex biogenic habitat for an array of associated organisms. While it is widely accepted that kelps harbour significant biodiversity, our current understanding of spatiotemporal variability in kelp-associated assemblages and the key environmental drivers of variability patterns remains limited. Here we examined the influence of ocean temperature and wave exposure on the structure of faunal assemblages associated with the holdfasts of Laminaria hyperborea, the dominant habitat-forming kelp in the northeast Atlantic. We sampled holdfasts from 12 kelp-dominated open-coast sites nested within four regions across the UK, spanning ~9° in latitude and ~2.7° C in mean sea surface temperature. Overall, holdfast assemblages were highly diverse, with 261 taxa representing 11 phyla recorded across the study. We examined patterns of spatial variability for sessile and mobile taxa separately, and documented high variability between regions, between sites within regions, and between replicate holdfasts for both assemblage types. Mobile assemblage structure was more strongly linked to temperature variability than sessile assemblage structure, which was principally structured by site-level variability in factors such as wave exposure. Patterns in the structure of both biogenic habitat and associated assemblages did not vary predictably along a latitudinal gradient in temperature, indicating that other processes acting across multiple spatial and temporal scales are important drivers of assemblage structure. Overall, kelp holdfasts in the UK supported high levels of diversity, that were similar to other kelp-dominated systems globally and comparable to those recorded for other vegetated marine habitats (i.e. seagrass beds), which are perhaps more widely recognised for their high biodiversity value. [ABSTRACT FROM AUTHOR]

Significant warming has been observed in every ocean, yet our ability to predict the consequences of oceanic warming on marine biodiversity remains poor. Experiments have been severely limited because, until now, it has not been possible to manipulate seawater temperature in a consistent manner across a range of marine habitats. We constructed a "hot-plate" system to directly examine ecological responses to elevated seawater temperature in a subtidal marine system. The substratum available for colonisation and overlying seawater boundary layer were warmed for 36 days, which resulted in greater biomass of marine organisms and a doubling of space coverage by a dominant colonial ascidian. The "hot-plate" system will facilitate complex manipulations of temperature and multiple stressors in the field to provide valuable information on the response of individuals, populations and communities to environmental change in any aquatic habitat. [ABSTRACT FROM AUTHOR]

Abstract: Spatial variability in the structure of subtidal macroalgal assemblages in southwest Australia was examined at multiple spatial scales using a three-factor hierarchal design. Spatial extents ranged from metres (between quadrats) to many hundreds of kilometres (between regions), and the study encompassed >2000km of temperate coastline. In addition, the influence of taxonomic resolution, from species level data to class level, on spatial patterns was investigated to assess the potential evolutionary timescales of the pattern and for developing cost effective regionally applicable surrogates for biodiversity monitoring. Almost 300 species were identified from 14 sites, representing considerable biodiversity and a significant subset of the total benthic macroalgal diversity in the region (∼1000 species). Multivariate variability was significant at all spatial scales examined, but most prominent at smallest spatial scales, regardless of taxonomic resolution. Assemblage and species turnover was pronounced at scales of metres to hundreds of metres. Generally, small scale patchiness was a ubiquitous pattern for all individual taxa examined, regardless of taxonomic resolution, while variability at the scale of 10s of km was less important. Even so, differences in spatial variability between taxa were observed, and ecological and historical reasons for such differences are proposed. Taxonomic aggregation to family level had minimal effect on spatial patterns, but aggregation to order level led to changes in some aspects of patterns of assemblage structure. The unique and speciose macroalgal assemblages on subtidal reefs in southwest Australia are shaped by a complex array of historical and contemporary processes that act at multiple spatial (and temporal) scales. Understanding the relative importance of these processes requires that further manipulative and correlative work is conducted across a range of ecologically-important spatial scales. [Copyright &y& Elsevier]

The cover image, by Harry Teagle and Dan A. Smale et al., is based on the Biodiversity Research Climate‐driven substitution of habitat‐forming species leads to reduced biodiversity within a temperate marine community, https://doi.org/10.1111/ddi.12775. Photo Credit: Dan Smale. [ABSTRACT FROM AUTHOR]

Abstract 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 pinnatifid a, 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. Highlights • Undaria is a cosmopolitan marine invader but has had limited management success. • Experimental removals were conducted to examine recruitment dynamics and management feasibility. • Over the 18-month experiment there was no consistent reduction in recruitment. • Certain removal methods can promote recruitment and alter recruitment dynamics. • This study should allow better decisions to be made on future management attempts. [ABSTRACT FROM AUTHOR]

The article reports on the ice scour disturbance in Antarctic waters. It states that ice scour is a key structural force acting on benthic communities at high latitudes and affects one-third of the world's coastlines. Ice scouring may also cause high faunal mortality, angled population structures, and an ascendancy of mobile secondary consumers. According to the author, ice disturbance plays a major role in defining marine biodiversity at high latitudes. However, on longer time scales, a drastic reduction of ice disturbance is visualized, as glaciers of the Antarctic Peninsula withdraw past their grounding lines and the amount of free-floating sea ice reduces.

Kelps are ecologically important primary producers and ecosystem engineers, and play a central role in structuring nearshore temperate habitats. They play an important role in nutrient cycling, energy capture and transfer, and provide biogenic coastal defence. Kelps also provide extensive substrata for colonising organisms, ameliorate conditions for understorey assemblages, and provide three-dimensional habitat structure for a vast array of marine plants and animals, including a number of commercially important species. Here, we review and synthesize existing knowledge on the functioning of kelp species as biogenic habitat providers. We examine biodiversity patterns associated with kelp holdfasts, stipes and blades, as well as the wider understorey habitat, and search for generality between kelp species and biogeographic regions. Environmental factors influencing biogenic habitat provision and the structure of associated assemblages are considered, as are current threats to kelp-dominated ecosystems. Despite considerable variability between species and regions, kelps are key habitat-forming species that support elevated levels of biodiversity, diverse and abundant assemblages and facilitate trophic linkages. Enhanced appreciation and better management of kelp forests are vital for ensuring sustainability of ecological goods and services derived from temperate marine ecosystems. [ABSTRACT FROM AUTHOR]