ABSTRACT As climate change accelerates, increasing ocean temperatures and altered herbivory pressure are reshaping temperate marine ecosystems dominated by macrophyte foundation species. Despite the importance of these processes, it remains unclear how herbivory affects the thermal performance of macrophytes. We simulated herbivory by clipping the leaf length of two temperate seagrass species, Posidonia australis and Heterozostera tasmanica, and grew them at temperatures extending below and above their current thermal range (6°C–32°C). We assessed the effects of reduced leaf size (i.e., simulated herbivory) on thermal performance by quantifying growth, photosynthetic rates, leaf nutrient content and pigment concentrations. Responses to clipping treatment and growing temperature were species‐specific. Highly clipped P. australis showed higher photosynthetic rates and nutrient concentrations at 32°C, relative to low‐clipped and control plants, while growth did not differ between clipping treatments, and survival was high across treatments. In H. tasmanica, clipping lowered optimal growth temperatures, and survival declined sharply at 32°C across treatments. Our results indicate that simulated herbivory can increase the thermal resilience of P. australis but decreases the performance of H. tasmanica under thermal stress. Increased herbivory pressure under climate change may therefore have positive implications for some seagrasses, highlighting the importance of considering species‐specific responses when predicting the future resilience of seagrass ecosystems.

Reliable predictions of species responses to intensifying temperature extremes are crucial for managing climate change impacts. However, limited data of species' responses to heat stress across their distribution restricts prediction accuracy. Here we analyse three-decades of kelp abundance observations in Australia, including cool to warm-edge populations, relative to marine heatwaves (MHWs). As MHWs intensified, changes in kelp abundances shifted from positive to negative. Warm-edge populations displayed steeper declines in abundance change than central and cool-edge populations under comparable MHWs. Our results support a hybrid thermal performance model, whereby thermal limits differ between populations, but performance volatility increases toward species' warm-edge, heightening vulnerability of warm-edge populations. Importantly, realised impacts of MHWs were evident at smaller thermal anomalies than predicted by experiments and distribution models, highlighting the importance of calibrating theoretical approaches with realised ecological change. By integrating a multi-faceted approach, our study is generalisable for improving predictions of species' population vulnerability.

BACKGROUND AND AIMS:Kelp forests provide myriad ecosystem services to human society, many of which are being eroded by climate-driven extreme events, before they have been measured. Here, we assess how dive tourism in giant kelp forests (Macrocystis pyrifera) has been impacted by marine heatwaves over three decades in southeast Tasmania. METHODS:Dive trip logs and business records were compiled from 1991-2021 from the Tasman Peninsula, Tasmania. Dives sites were georeferenced and matched to the dominant habitat (e.g. cave, wreck, sponge garden, kelp forest) for each dive site. The distribution and frequency of all dives conducted in giant kelp forests were analysed to determine changes in the gross margin of kelp forest dives over time. Dive patterns were compared to marine heatwave metrics and patterns in kelp forest cover from remote sensing data. KEY RESULTS:Giant kelp forest diving steadily increased in Tasmania between 1991-2010, before repeated marine heatwaves in 2010 and 2016 caused abrupt loss of kelp and eventual collapse of kelp forests diving by 2017. The sharp decline in dives in 2011 resulted in a 255% decrease to the gross margin for the local operator. Poleward retreat of giant kelp forests between 2001-2017 resulted in a ∼44 km increase in travel and 15% reduction in gross margin per trip, before their eventual loss from the region. CONCLUSION:Our results provide one of the first quantitative assessments of kelp forest dive tourism and highlights the fragility of these ecosystems to climate disruption. This study adds to the growing body of literature demonstrating social and economic impacts of climate extremes on kelp forest ecosystems and highlights the fundamental importance of healthy, functional kelp forests to support ecosystem services.

The interaction between herbivorous sea urchins and their macroalgal food source plays a fundamental role in regulating community structure on temperate reefs across the globe. Water temperature strongly influences the strength of this interaction, through its effects on the rate of metabolic processes. In southeastern Australia, warming temperature has also facilitated the range extension of some urchin species, which are now threatening macroalgal habitats across ∼ 2000 km of coastline. Despite the importance of temperature in this system, the impact of warming on the relative performance of macroalgae and urchins across their range is unknown. We measured the temperature dependence of respiration rates in two barren-forming sea urchin herbivores (Centrostephanus rodgersii and Heliocidaris erythrogramma), and of photosynthetic rates of their macroalgal food source (Ecklonia radiata). This was done at 6-9 temperatures ranging from 5°C-35°C at each of six sites in Australia. These sites span these species' latitudinal distributions, covering a latitudinal range of 12° and a temperature range of 8°C. We found clear differences across latitude in the performance of all three species. At warmer latitudes, E. radiata showed decreased maximum photosynthetic rates while respiration rates for C. rodgersii demonstrated increased sensitivity to acute temperature change. For H. erythrogramma, cool-edge populations showed a plateau in respiration rates at the highest temperature tested, while rates in central and warm-edge populations continued to increase. Overall these patterns indicate that temperatures at the warm range edge may be approaching upper thermal tolerance limits for all three species, although C. rodgersii may have a slightly higher thermal threshold compared to E. radiata , and may persist longer in a warming environment. This study provides novel insights into the comparative thermal performance of kelp and urchins across their entire latitudinal distribution and highlights the need to consider different populations of species to understand the impacts of warming on marine ecosystems.

• As climate change accelerates, increasing ocean temperatures and altered herbivory pressure are reshaping temperate marine ecosystems dominated by macrophyte foundation species. Despite the importance of these processes, it remains unclear how reduced above-ground biomass, due to anticipated in-creased herbivory, will affect the thermal performance of macrophytes. • We simulated herbivory by clipping the leaf length of two temperate seagrass species, Posidonia australis and Heterozostera tasmanica, and grew them at temperatures spanning their thermal range (6-32 °C). We assessed the effects of leaf size on thermal performance by quantifying growth, photosynthetic rates, leaf nutrient content and pigment concentrations. • Responses to clipping treatment and growing temperature were species-specific. Highly clipped P. australis showed higher photosynthetic rates and nutrient concentrations at 32 °C, relative to low-clipped and control plants, while growth did not differ between clipping treatments and survival was high across treatments. In H. tasmanica, clipping lowered optimal growth temperatures, and survival declined sharply at 32 °C across treatments. • Our results suggest that smaller leaf size can increase thermal resilience in P. australis, whereas high herbivory of H. tasmanica is likely to increase its sensitivity to thermal stress. Increased herbivory pressure under climate change may therefore have positive implications for some seagrasses, highlighting the importance of considering species-specific responses when predicting the future resilience of seagrass ecosystems.

BACKGROUND AND AIMS:Widespread shifts in seawater chemistry are occurring across spatial and temporal scales, with important consequences for coastal ecosystems. Giant kelp (Macrocystis pyrifera) forests elevate seawater pH and dissolved oxygen (DO) through photosynthesis, potentially providing short-term refugia from ocean acidification and deoxygenation. However, whether these effects persist across contrasting environmental settings remains unclear. Here, we assess how biological and oceanographic conditions regulate giant kelp-mediated modification of seawater chemistry across multiple sites. METHODOLOGY:Hourly measurements of seawater pH, DO, and temperature were collected during spring-summer 2022-2023 using paired deployments inside and outside giant kelp forests at one site in central Chile and four sites in Tasmania, Australia. The influence of giant kelp density was also evaluated at two sites in southern Chile and three sites in Tasmania. An upwelling index was calculated for the central Chile site to assess the influence of regional oceanographic forcing on kelp-associated seawater chemistry patterns. KEY FINDINGS:Hourly pH and DO were higher inside giant kelp forests than outside at the central Chile site and at one Tasmanian site. At these locations, stronger daytime pH-DO relationships indicated that photosynthetic carbon uptake exceeded nighttime respiration, generating a net positive metabolic signal. In Tasmania, giant kelp density was positively associated with hourly pH and DO, whereas no such relationship was detected in southern Chile. At the central Chile site, kelp-associated effects intensified during a strong upwelling event, reducing the severity of low pH and DO conditions. CONCLUSIONS:Giant kelp forests can locally buffer short-term fluctuations in seawater pH and DO, but this capacity is highly site dependent and influenced by giant kelp density and environmental conditions. Overall, our findings suggest that continued giant kelp forests loss of in Tasmania may reduce their potential to provide short-term refugia, while in Chile, the strength of kelp-mediated seawater chemistry modification is likely to remain strongly influenced by variability in upwelling and freshwater inputs.

Urchin herbivory is a key function in temperate reef ecosystems. Some urchin species overgraze macroalgal forests, leading to their collapse into barren states. In Australia, climate change is enabling the poleward range extension of urchin species, resulting in increased barrens formation at the cool-edge of their distribution. Despite their ecological importance and association with warming, broad-scale effects of temperature on sea-urchin feeding ecology remain unknown. We characterise in-situ feeding rates of two barrens-forming urchin species, one range-extender (Centrostephanus rodgersii), the other range-persistent (Heliocidaris erythrogramma), across a temperature range of 8 °C and 12 degrees of latitude, as well as over seasonal cycles. We assess the extent to which ecological drivers (temperature, macroalgal nutrition, urchin size/weight metrics) explain grazing patterns. We find contrasting patterns in, and drivers of, performance between urchin species. C. rodgersii shows a peak in grazing and abundance at its range-centre, and temperature is shown to be an important driver of grazing rates for this species. For H. erythrogramma, gonad index and macroalgal nutrition are key drivers of grazing rates, which display no significant change across latitude. These contrasting patterns suggest each species occupies different thermal niches, providing key insights into how their ecological impacts may change across their distribution and in response to ocean warming.

Habitat loss is a key threat to ecosystems and species that rely on them, with direct consequences for human well-being. Quantifying the degree to which species depend on specific habitats is critical for many fields of knowledge, such as conservation biology or economic valuations, yet poses a complex challenge. We introduce a new method to objectively quantify how much species depend on a habitat by integrating their life-cycle habitat associations. Through a comprehensive literature review focusing on 36 species associated with kelp forests, we demonstrate how this ‘Habitat Dependency Index’ (HDI) effectively discriminates between closely related species and captures differences in their reliance on kelp forests. We suggest this new HDI constitutes a powerful tool for understanding the role of marine habitats in supporting fisheries, biodiversity, and other ecosystem services. Moreover, the approach is broadly applicable and can provide essential information for managing both aquatic and terrestrial ecosystems.

Ecosystem restoration is gaining momentum as communities and policymakers increasingly appreciate the need to recover lost ecosystem services. However, more knowledge about the potential ecological outcomes of restoration for ecosystem services is needed to promote engagement of stakeholders with restoration targets. In Tasmania, the giant kelp, Macrocystis pyrifera, is a productive canopy species that has declined by 95%. We aimed to predict the effects of M. pyrifera restoration on food webs and fisheries production. The primary productivity ratio of M. pyrifera compared to the dominant understory species Ecklonia radiata was quantified and then incorporated into an Ecopath with Ecosim (EwE) model of Tasmanian waters. Predator/prey interactions were estimated using the EwE model framework, which fits the model to historical fisheries data. Several scenarios were then simulated, representing uncertainty in predator/prey interactions and different areas of M. pyrifera restoration. Restoration of degraded reefs with M. pyrifera was predicted to increase primary productivity by about 40 times per unit area compared to the existing habitat. We predicted that restoring 30% of the degraded M. pyrifera area would increase abalone and coastal demersal fish catches by similar to 2.7%. Rock lobster and reef-associated fisheries catches were predicted to increase by 0.4% and 1.4%, respectively. Future improvements could include downscaling the model to capture local increases in biomass and catch and refining predator/prey interactions through experimental studies. By modelling outcomes of ecological restoration, achievable targets can be set that are locally relevant and therefore more likely to attract support.

Temperate reef ecosystems are increasingly challenged by acute marine heatwaves and chronic overfishing which can lead to trophic cascades. While these disturbances differ in their impact and temporal expression, both can manifest as a collapse of kelp followed by proliferation of filamentous algal turfs. However, the importance of these disturbance types in turf proliferation remains unclear. Here, we investigate whether turf proliferation on Tasmanian reefs is driven primarily by acute kelp loss or chronic urchin grazing. Using standardised settlement tiles, we quantified short-term (2.5 mo) turf proliferation across 4 treatments: (1) intact kelp beds, (2) intact urchin barrens, (3) kelp beds with kelp removed, and (4) urchin barrens with urchins removed. Additionally, we tracked the longer-term (similar to 12 mo) fate of these experimental patches to assess either kelp recovery or turf persistence. Turf proliferated in all treatments where kelp was absent or removed, with approximately 50-fold higher turf cover in disturbed kelp beds. This suggests that acute kelp loss is the predominant mechanism that allows turf proliferation in this system. However, the capacity of turf to persist was dependent on chronic urchin grazing. After 12 mo, our results revealed that at a site with lower urchin densities, kelp recovered within the patches with an associated decline in turf cover. At a site with higher urchin densities, kelp failed to recover, and turf continued to proliferate. Overall, when kelps are lost, competitive release allow turfs to establish, but their persistence appears dependent on chronically elevated levels of herbivory preventing kelp re-establishment.

Introduction: Global degradation of natural ecosystems demands urgent action to stem losses and, where possible, identify opportunities for scalable restoration. Giant kelp forests, formed by Macrocystis pyrifera, have declined by similar to 95% along eastern Tasmania in recent decades, with limited propagule supply constraining recovery. Direct interventions to restore giant kelp have been attempted here since the 1990s, although attempts have been constrained by methodological and logistical limitations, underscoring the challenges of scaling restoration in subtidal marine environments. Objectives: This study details the methodological development of a rapid and forest-scale in situ approach to reseed threatened giant kelp forests that have declined. Methods: Here we provide an overview of the "holdfast-graft" method, as a forest-scale technique to reseed reefs with mass-produced hatchery-reared giant kelp sporophytes seeded to twine. Taking inspiration from true grafting of terrestrial vascular plants, we apply an analogous approach of effectively binding the equivalent of a "scion" (i.e., hatchery-reared giant kelp sporophytes) to a "root-stock" (i.e., holdfast stubs of other common seaweed species). By comparing rates of kelp sporophyte attachment between twine seeded to holdfast stubs and directly to boulders, as well as seeded gravel, we evaluate the effectiveness of this method. Results: We reveal a 40-fold higher rate of kelp sporophyte attachment to the reef when twine was wrapped around holdfast stubs compared to twine wrapped over boulders or deployments of hatchery seeded-gravel methods. Refinement of the "holdfast-graft" method led to targeted wrapping of short 60-cm seeded twine lengths directly to individual holdfast stubs, enabling rapid and forest-scalable deployment by divers. Conclusions: The "holdfast-graft" method represents an efficient and scalable method for out-planting giant kelp.

Kelps have a long history of human use and exploitation. Knowledge of past harvesting practices offers insights into environmental baselines and the contemporary management and conservation of these critically important ecosystems. In Tasmania, Australia, giant kelp ( Macrocystis pyrifera ) was commercially harvested for alginate production from 1964 to 1973, but those forests have since undergone precipitous declines due primarily to climate change. We reviewed a collection of archival data and sources to describe the history, methods, and scale of this understudied and largely forgotten industry. We calculated that >65,000 tonnes (wet weight) of Macrocystis were harvested from eastern Tasmania over a decade (mean annual harvest = 6531 t), making it one of the largest wild harvest industries to ever exist in the region. However, the industry had challenges finding sufficient biomass to sustain operations, ultimately driving its closure in less than a decade. Feasibility surveys prior to harvesting suggested much greater kelp availability than was ultimately realized, perhaps motivating overexpansion. Against a backdrop of climate change in this ocean warming hotspot, harvest efforts grew wider and more intensive, and during summer months when stocks were lowest, almost all exploitable biomass was harvested. It remains unclear whether harvesting contributed to the decline of Tasmanian Macrocystis forests, but it may have reduced their resilience and exacerbated other stressors, particularly in heavily harvested areas. This historical review provides a rare opportunity to examine the past scale and use of now-endangered Macrocystis forests and also to help inform the contemporary management and conservation of seaweed resources.

Kelp forests provide habitat for many species, but it remains uncertain whether specific kelp forest types support distinct biodiversity. Surface canopy-forming giant kelp (Macrocystis pyrifera) forests in Tasmania, Australia, have declined significantly due to climate change, and have been widely replaced by forests dominated by smaller stipitate kelps like Ecklonia radiata. However, there is limited knowledge of the community composition of Macrocystis forests and how this may differ from the stipitate kelp forest community. Underwater visual census surveys were conducted of the fishes and macroinvertebrates (> 2.5 cm length) in remnant Macrocystis forests in south-eastern Tasmania, and in adjacent stipitate kelp forests. 18 sites (9 of each forest type) were surveyed across two regions during the period of peak growth and canopy cover (i.e. winter-spring). Faunal community composition varied little between forest types, although Macrocystis forests supported more than double the abundance and biomass of mobile fishes, while cryptic fishes differed by forest type depending on region. Macroinvertebrate assemblages did not differ between forest types nor regions. Thus, for the taxa and time period examined, Tasmanian Macrocystis and stipitate kelp forests supported mostly similar faunal communities. Kelp forest communities showed spatial variation and were also likely influenced by a variety of other habitat characteristics, such as the relatively small patch sizes and/or ephemeral state of the remnant Macrocystis forests. Quantifying the community structure of these endangered communities informs the ecological changes that have occurred and will serve as an important reference for ongoing conservation and restoration activities.

Scientific working groups bring together experts from different disciplines and perspectives to tackle the "wicked problems" facing natural systems and society. Yet participants can feel overwhelmed or inadequate in groups within academic environments, which tends to be most acute at early career stages and in people from systematically marginalized backgrounds. Such feelings can block innovation that would otherwise arise from gaining the full spectrum of unique perspectives, knowledge and skills from a group. Drawing on personal experiences and relevant literature, we identify ten contribution strategies, ranging from generating ideas, analyzing data, and producing visuals to supporting facilitation. Next, we share approaches for an inclusive and supportive process, considering the roles of both participants and leads. Generating the most productive and relevant outcomes from working groups requires engaging the full team in a constructive and supportive environment. We advocate that adopting inclusive approaches that respect the diversity of personality types and perspectives will lead to more innovative solutions to achieve conservation and sustainability goals.

Marine kelp forests cover 1/3 of our world's coastlines, are heralded as a nature-based solution to address socio-environmental issues, connect hundreds of millions of people with the ocean, and support a rich web of biodiversity throughout our oceans. But they are increasingly threatened with some areas reporting over 90% declines in kelp forest cover in living memory. Despite their importance and the threats they face, kelp forests are entirely absent from the international conservation dialogue. No international laws, policies, or targets focus on kelp forests and very few countries consider them in their national policy. The Kelp Forest Challenge addresses that gap. Together with 252 kelp experts, professionals, and citizens from 25 countries, the Kelp Forest Challenge was developed as a grassroots vision of what the world can achieve for kelp forest conservation. It is a global call to restore 1 million and protect 3 million hectares of kelp forests by 2040. This is a monumental challenge, that will require coordination across multiple levels of society and the mobilization of immense resources. Pledges may therefore include area for protection or restoration, enabling pledges which assist in conservation (funding, equipment, professional expertise, capacity building), or awareness-based pledges which increase awareness or education about kelp forests. Correspondingly, participants may be from government, scientific institutions, private sector, NGOs, community groups, or individuals. This challenge is the beginning of a 17-year mission to save our kelp forests and anyone and any organisation is invited to participate.

Disentangling spatial variation in climate change impacts is a pressing challenge. Here we compared the performance of Posidonia oceanica seagrass populations to temperature, throughout a year-long translocation experiment across 2800 km in the Mediterranean Sea. Transplants in central and warm-edge locations experienced temperatures >29 ºC during summer, representing thermal anomalies >5ºC above long-term maxima for cool-edge populations, 1.5ºC for central and <1ºC for warm-edge populations. At the onset of the experiment, a highly selective herbivory event removed 75% of cool-to-warm transplant biomass but left adjacent central and warm-edge treatments intact. Despite big differences in thermal stress and acute herbivory, cool-edge populations recovered and matched warm-edge populations across all performance metrics. Central populations displayed significantly lower growth and survivorship in response to thermal stress. Our findings reveal that intraspecific variation in thermal performance does not necessarily reflect thermal geography and suggest greater resilience to warming for Posidonia oceanica than previously recognised.

The abundance of herbivorous fishes is known to vary strongly with latitude. However, our understanding of this pattern is largely based on the examination of nominally herbivorous fishes (i.e. both herbivores and detritivores) as a single group. Therefore, we do not know how this collective classification may have confounded our understanding of distribution patterns, nor how different trophic pathways function across latitudes and associated temperature gradients. This constrains our ability to predict how tropicalising reefs may function as oceans warm, especially following range extensions of tropical taxa. Here, we explored the productivity of seven groups of roving nominally herbivorous fishes across eastern (34° of latitude; 3800 km) and western (23°; 2600 km) Australia, with specific consideration of the herbivore versus detritivore dichotomy across key spatial and environmental gradients. In terms of the total nominally herbivorous fish community, we found near-continuous declines in species richness with increasing distance from the equator, while total biomass and productivity were maintained across nearly 30° of latitude in eastern Australia. However, when we separated herbivores and detritivores, we found detritivore productivity dominated the tropics but declined abruptly in temperate regions, with this decline closely correlated with decreasing temperature in a synchronous manner along both coastlines. No such synchronous relationship was observed between herbivore productivity and temperature. These results highlight the importance of the herbivore versus detritivore division in understanding reef trophodynamics across latitudes, and the importance of understanding fish-based detritivory when predicting how the trophodynamic functioning of reefs may change along warming coastlines.

Herbivorous fishes are a key functional group in coral reef ecosystems and have been the focus of a vast body of research. While substantial progress has been made in research, challenges persist, especially in respect to quantifying patterns versus processes. Despite this challenge being recognised over 40 years ago. To help clarify such challenges, and work towards solutions, in this perspective we explore how the definition of 'herbivorous reef fishes' precludes an easy translation between patterns of herbivore abundance and the process of herbivory. Indeed, if herbivorous fishes are defined as, a fish in which the diet is predominantly based on plant material, then this encompasses a diverse suite of fishes which all remove primary producers to varying extents and have markedly different impacts on reef functioning. Given this situation, we explore how our approaches to directly quantifying herbivory on reefs have progressed. We highlight how lessons learnt from macroalgal assays could be applied to the direct quantification of herbivory from algal turfs in the epilithic algal matrix (EAM); a community of primary producers that are invariably difficult to work with and quantify. Nevertheless, given the abundance of turfs on coral reefs, and their relative importance in herbivore dynamics, widespread process-based assessment of EAM herbivory represents an avenue for expanding future research. Recognising the difficulty of translating patterns in herbivore abundance to the process of herbivory, and an enhanced focus on EAM herbivory, will be necessary to comprehensively quantify the process of herbivory on Anthropocene coral reefs.

Abstract Tasmania is an island state in south-eastern Australia that has a long and rich history of seaweed use, research, and development. It is a cool-temperate system with 750 macroalgal species currently described. Tasmanian Aboriginal peoples have lived on this land for at least 40,000 years utilising seaweed as food, shelter, water carriers and medicine, as well as for ceremonial reasons. Modern taxonomic investigations began with French naturalist Jacques-Julien Houtou de La Billardière in 1791, and there are 184 type specimens of seaweeds originating from Tasmania. Ecological and physiological studies of seaweed in Tasmania have focussed on the dominant large brown seaweeds (Laminariales and Fucales) and have contributed significantly to the global understanding of these systems, particularly related to community resilience, seaweed-urchin interactions, their habitat-forming role for other species, responses to global change, and restoration of lost habitat. Ocean warming and changing oceanography have caused a 95% decline in surface canopy cover of Macrocystis pyrifera in eastern Tasmania since the 1950s and led to a focus on restoring these lost forests. Tasmanian seaweed communities have a uniquely high proportion (up to ∼90%) of seaweeds that rely solely on CO2 for photosynthesis, which has implications for responses to ocean acidification. Tasmania has industries that use brown seaweeds for fucoidan extraction and beach-cast harvest for alginates, fertilisers, and feeds for agriculture. New aquaculture initiatives include integrated multi-trophic aquaculture, offshore kelp mariculture and Asparagopsis cultivation for bioactive products to reduce methane emissions in ruminants, as and the development of unexploited species including Caulerpa spp. for food.