The one-day hybrid workshop was structured around a combination of presentations and open discussions designed to provide scientific context, share practical experiences and generate a collective research agenda.

Presentations:

Introduction and background — Terri Souster (UiT);

Open discussions:

Opportunities for student involvement, including the integration of MSc projects into ongoing HSPl studies;

Lloyd Peck & Terri Souster

The concept of heated settlement plates (HSPl) was first developed at the British Antarctic Survey (BAS) between 2006–2008 by Lloyd Peck and engineer Mark Preston (Antarctic and Marine Engineering, AME). The aim was to design a system to heat artificial units of habitat (AUHs) in situ to simulate projected seabed warming. Initial calculations suggested that a power input of 50.75 W (watts) produced a 4.6℃ increase in plate surface temperature (equivalent to 11.25 W per 1℃). These calculations provided information for subsequent prototype development, although recalibration was required to account for voltage losses across cable lengths.

The first prototypes were deployed in Ryder Bay near Rothera Research Station (67°S, Western Antarctic Peninsula). Early iterations faced significant engineering challenges such as pressure seal failures, cable malfunctions and damage by icebergs. Between 2014 and 2016, a fourth set of HSPl, incorporating improved electrical configurations and robust physical protections, was deployed and successfully recovered (Fig. 1). This configuration tested two heated treatments (+1℃ and +2℃ above ambient), alongside unheated controls, generating a unique dataset on benthic community responses to in situ warming (Ashton et al. 2017, Clark et al. 2019, Barnes et al. 2021). An accessible narrative of the deployment challenges has been published in Warming up the Antarctic: Harder than you think (Clark 2019).

Terri Souster

The first Arctic HSPl deployment was initiated in September 2024 at Andersdalen, Tromsø Municipality, northern Norway (69°N). The array consists of three heated treatments (+1℃, +2℃, +3℃) and unheated controls, replicated four times (16 plates in total). Power is supplied via a 150 m cable from a nearby farm, with an electrical control panel housed in a protective Zarges box (Fig. 2a). The site offers several advantages: ease of access (~ 70 minutes by car and 45 minutes by RIB from Tromsø), suitable seabed topography at 10 m depth and absence of icebergs or significant winter snow or ice. However, challenges included regulatory restrictions on scuba diving (necessitating intertidal handling for photosampling), shallow-water turbulence during tidal change and freshwater input from the Andersdalelva River (Fig. 2b, Moreno and Souster (2025)).

Photosampling attempts in April 2025 produced poor image quality, prompting a series of trials in July and August 2025 to refine imaging protocols (Fig. 3a). These trials highlighted difficulties caused by water mixing in the shallow intertidal, but also led to practical guidelines for optimal photographic acquisition, documented in Suppl. material 1. Preliminary identifications from photomosaics included Heteranomia squamula and Circeis armoricana, with bryozoan taxa (Cellerporella, Diplosolen, Disporella) remaining tentative identifications pending further verification (Fig. 3b).

Note: For clarity, standardisation in the context of HSPl refers to general workflows — such as imaging, metadata documentation and data archiving — that allow comparability across studies. It does not imply rigid uniformity in ecological timelines or deployment logistics, which necessarily vary with latitude, seasonality and site-specific constraints (e.g. intertidal vs. subtidal operations, equipment availability). This distinction is important to ensure that future cross-site syntheses remain feasible while preserving the flexibility required by local conditions.

Workshop participants also contributed experience from a wide range of unheated AUH experiments.

David Barnes reported settlement plate deployments in Antarctica (Signy Island, 60°S; Rothera, 67°S) (Barnes 1996, Bowden et al. 2006, Barnes et al. 2025), Spitsbergen (78°N) (Sowa et al. 2023, Sowa 2025), Loch Hyne (51°N) and multiple lower-latitude sites (Barnes 2015). These experiments provide valuable baselines for interpreting HSPl results and have been central to studying settlement, recruitment, growth and competition across latitudinal and habitat gradients (Barnes and Neutel 2016).

Melody Clark described the deployment of eight Artificial Reef Monitoring Structures (ARMS) at Rothera since 2019 (Obst et al. 2020). Harsh Antarctic conditions, particularly iceberg activity, severely limited recovery: only three deployments yielded usable data, while others were damaged or lost entirely. These experiences underline both the logistical challenges of polar seawork.

Lloyd Peck

The development of heated settlement plate (HSPl) experiments is strongly shaped by latitude and local conditions, making a rigid standard protocol for deployment undesirable. Instead, comparability across sites may be best achieved by focusing on mechanisms of assemblage development, for example, by aligning comparisons to similar successional stages or equivalent area coverage, rather than fixed deployment durations. The starting point of an experiment is also critical, as assemblage development varies depending on the season of deployment and the prevailing local thermal regime.

The growing research focus on marine heatwaves (MHWs) underscores that warming has context-dependent effects: its biological meaning differs not only across regions, but also across seasons within the same location. For instance, in temperate regions, such as New Zealand, warm years are associated with stronger organismal responses during summer months. Experimental configuration also matters. Vertical arrangements of HSPl in flow-through environments have shown considerable algal growth on upper sections, most likely due to shielding effects of canopy algae.

Past deployments and research collaborations

Bangor, North Wales (53°N): shallow subtidal deployment; data unfortunately lost;

Planned and potential future deployments

King Sejong Korean Antarctic Station (62°S): deployment planned for 2025;

Melody Clark

Only one set of heated settlement plates (HSPl) has so far been subjected to molecular ecological analysis (Clark et al. 2019). In this Antarctic study, spirorbid worms colonising the plates were investigated using transcriptomics to assess how experimental warming affected their cellular physiology. Comparisons between controls and animals exposed to +1℃ and +2℃ revealed pronounced sensitivity: even +1℃ of warming induced significant stress responses, while individuals at +2℃ exhibited metabolic shutdown consistent with terminal senescence. These findings highlight how subtle temperature increases can critically affect early colonisers at the cellular level.

Technical challenges remain in applying molecular methods to HSPl samples. Animals inhabiting the thin warmed boundary layer above the plates (2 mm above +1℃ plates in Antarctica, Barnes et al. (2021)) are typically very small, yielding insufficient DNA or RNA for sequencing from individuals alone. Pooling multiple specimens is therefore required, which limits analyses such as population genetics. For microbial biofilms, Antarctic deployments showed no detectable changes in bacterial diversity between treatments. However, this absence of taxonomic shifts does not equate to functional stability; transcriptomic approaches are necessary to reveal how microbial metabolic pathways respond to warming.

Lessons learnt from this work:

Transcriptomes provide a more sensitive and informative measure of organismal health than candidate-gene approaches;

This pioneering study demonstrates the potential of combining HSPl deployments with molecular ecology to detect early-warning signals of stress that precede visible ecological changes. Despite current logistical and methodological challenges, molecular tools represent a powerful complement to ecological observations and hold promise for future cross-site HSPl–networks.

Bernabé Moreno

Research context and objectives

High-Arctic hard-bottom subtidal habitats provide natural laboratories for studying long-term ecological succession under rapid environmental variability. To explore these dynamics, lithophilic assemblages were studied using (non-heated) artificial settlement plates (Kuklinski et al. 2022) deployed in the shallow subtidal of northern (N) and southern (S1, S2) Isfjorden proper, West Spitsbergen (78°N) (Moreno et al. 2024). Site selection was guided by ecological and logistical criteria: the presence of habitat-forming brown macroalgae, environmental drivers such as seawater circulation and glacial influence, underlying geology and accessibility by rigid inflatable boat from Longyearbyen (Moreno et al. submitted to Polar Research).

Experimental design and methodology

Long-term successional experiments were initiated in 2009 and 2013 at the southern sites, with 10-year submersion intervals culminating in recoveries in 2019 and 2023. Yearly in situ photosampling was performed (except during recovery years) by an IOPAN scientific diver using a high-resolution macrophotography camera-system (Nikon D810, 60 mm macro lens, dual INON Z-240 strobes, SOLA-1200 focus light) (Fig. 4).

Multiple overlapping images (4–9 per plate) were taken with manual zenithal (orthogonal) control, for both upward- and downward-facing plates (Moreno 2024). Downward-facing plates consistently supported higher abundance, richness and structural complexity, particularly during late successional stages, where assemblages reached up to 30 mm in relief. Recovered plates were preserved in ethanol, then processed under laboratory conditions using the zenithal control of a stereomicroscope (Leica DFC450) and LED video-lighting (40W) for detailed imaging. The Leica Application Suite X (LASX) software was used for previewing, re-labelling and saving the images. Despite improved taxonomic resolution, this set-up introduced challenges, including artefacts from the air–water interface and overheating of underwater-designed lighting. Workflow for digital archiving and analysis of lithophilic assemblage succession are illustrated in Moreno and Souster (2025) or via YouTube (CC BY).

The subsequent DARKLITH camera-system, developed during Moreno’s doctoral project, resolved these issues by integrating full xyz-axes zenithal control, submerged optics (removing air–water interface distortions), tethered camera operation and advanced imaging protocols (e.g. exposure and HDR-bracketing). This approach significantly expanded the quality and reproducibility of benthic imagery, while also enabling broader applications in macrophotography of marine organisms.

Lessons learnt from the European high-Arctic experience:

Zenithal control is essential: avoiding perspective distortion and error/distortion accumulation in time-series analyses;

Bernabé Moreno

Marine imagery datasets are rapidly growing in size, scope and relevance, yet they are often fragmented, inconsistently documented or poorly accessible. Following the FAIR principles (Schoening et al. 2022) is therefore critical to maximise their scientific value. In practice, this means:

Findable: using persistent identifiers and standardised metadata frameworks (e.g. via iFDO – image FAIR Digital Object) to ensure datasets can be located by both humans and machines;

Applying FAIR practices into HSPl experiments from the outset — through standardised imaging, consistent labelling, structured metadata, open repositories and development of frameworks like iFDO — will transform local datasets into global assets, enabling comparative analyses, machine-learning training and ecosystem-scale syntheses.

FAIR note: Researchers can identify appropriate repositories via the Registry of Research Data Repositories, which catalogues trusted archives across disciplines. For example, DataverseNO is a curated, FAIR-aligned Norwegian repository that ensures long-term accessibility and reusability of datasets and organises them into institutional and special collections. While primarily serving Norwegian research institutions, it offers a model for how HSPl datasets could be curated in a sustainable and interoperable manner.

Proposed research directions

Building on the high-Arctic experience, the following areas are proposed for HSPl research development:

Standardisation of image workflows: testing and refining protocols (e.g. zenithal control, high dynamic range, metadata capture) across sites to ensure comparability. Standardisation here refers to reproducible imaging and metadata procedures that ensure comparability across deployments, without constraining site-specific adaptations in sampling or monitoring;

Markus Molis

Heated settlement plate (HSPl) deployments in northern Norway provide opportunities to test hypotheses about how temperature influences early benthic community assembly. Barnacles and their cyprid larvae can serve as a focal taxon for conceptual development, but the framework can be extended to a wide range of sessile invertebrates. Fig. 5 illustrates hypotheses concerning richness and diversity (a–d), larval settlement (e–f), performance (g), competitive interactions (h) and growth under variable food availability (i–j).

Hypotheses:

Assemblage richness and diversity

If food is abundant and elevated temperatures enhance settlement across multiple taxa, species richness and diversity will increase in heated treatments (Fig. 5a);

Under food limitation, growth responses to warming may be reduced and species-specific feeding preferences (beyond bulk chlorophyll or fluorescence proxies) must be considered. A targeted model-species approach is recommended. Plates may be retrieved for controlled laboratory assays (e.g. filtration, respiration) to quantify performance.

Scales of response. Response variables should be assessed across levels of biological organisation:

Ecological: growth, survival, fecundity, biomass (individual level); settlement and recruitment (population level);

Together, these hypotheses establish a research agenda linking temperature-driven shifts in settlement and recruitment to broader community dynamics, while emphasising the interplay of facilitation, competition and resource availability.

Kathy Dunlop, Amanda Ziegler and Èric Jordà Molina

Coastal benthic habitats worldwide are experiencing significant impacts from both human activities and warming waters with the most rapid changes occurring in polar regions. Human impacts beyond climate change affecting the coastal zone include bottom trawling, organic enrichment from aquaculture and human settlement, contaminants, non-indigenous/invasive species and more. Sessile benthic fauna are a key element of coastal ecosystems and impacts on their settlement and establishment from rising seawater temperatures and other human activities can have far reaching impacts on benthic coastal ecosystems. Disruptions at these stages can cascade through entire assemblages, altering ecosystem functioning, resilience and services provision. Understanding the vulnerability of benthic communities and the changes that may occur to their distribution and function under climate change scenarios is a necessary step to achieve effective ecosystem-based management, a goal of many nations.

Heated settlement plate (HSPl) experiments provide a powerful targeted approach for examining how climate-driven warming modulates these processes and for addressing questions directly relevant to ecosystem-based management and industry. By coupling controlled, in situ manipulations with long-term monitoring of benthic assemblage development, HSPl studies can reveal whether rising temperatures amplify or mitigate vulnerabilities to other stressors. For example: will benthic communities be more susceptible to organic enrichment or pollution under warmer regimes and should management strategies prioritise interventions accordingly? Such insights are vital to guide adaptive policies and practices in aquaculture, offshore infrastructure and shipping, where biofouling, invasive species risks and ecosystem degradation are pressing challenges.

Priority research areas:

Cumulative impacts in the coastal zone: disentangling the combined effects of warming, organic enrichment, sedimentation, pollutants, non-indigenous/invasive species and marine biofouling;

Illustrative proposal ideas:

Aquaculture stressors: pilot deployments of HSPl plates beneath aquaculture facilities to test interactive effects of warming, organic enrichment, sedimentation and pollutants;

Funding pathways and collaboration mechanisms

Although success rates for large-scale international funding remain low, a cohesive HSPl–network could enhance competitiveness and efficiency by pooling expertise and infrastructure. Key funding opportunities include:

Norwegian Seafood Research Fund (FHF): industry-financed, supporting R&D with direct application to seafood production;

Together, these pathways highlight the translational value of HSPl research, bridging fundamental ecological insight with applied management needs in the coastal zone.