Early signs of recovery suggested by changes in the structure and function of deep-sea megabenthic communities on a seamount 19 years after fishing

\ua9 2025 The AuthorsBottom trawling is the most widespread and severe human disturbance affecting deep-seafloor environments. Seafloor communities inhabiting seamounts (undersea hills or mountains) are especially vulnerable to trawling impacts as they are often dominated by long-lived, sessile epifauna (e.g., cold-water corals) that are easily damaged and/or removed by fishing gear. Trawling on seamounts is spatially concentrated, compounding effects on the benthos. However, the extent to which communities on seamounts that are closed to fishing can recover from earlier trawling impacts is uncertain. Previous studies have hypothesised that any post-trawling recovery of benthic communities on seamounts will probably be initially patchy, recolonised by surviving remnant populations, and may take several decades or more to occur. A fine-scale approach is thus needed to understand and determine the spatio-temporal dynamics of recovery. To address this need, we studied a New Zealand seamount located on Chatham Rise, Morgue, that was heavily trawled in the 1990s before being closed to fishing in 2001. We analysed seafloor imagery collected with a towed camera during repeat surveys in 2001, 2005, 2009, 2015, and 2020 to examine potential changes in benthic community structure and function after trawling ceased. A temporal shift in community structure driven by changes in the abundances of several taxa (mainly bryozoans, stylasterid hydrocorals, and comatulid crinoids) was observed over the study timescale, indicating the communities may have been in the early stages of post-trawling recovery. However, structural variation between different seamount sides and the summit (i.e., spatial variation) was still more pronounced than temporal variation and reflected the trawl fishing footprint. Community function showed little sign of ongoing recovery overall, though some change (driven by colonisation by stylasterid hydrocorals and bryozoans) indicative of early recovery was observed for communities on the seamount summit. Juvenile colonies of the reef-forming stony coral Solenosmilia variabilis were also observed between 8 and 19 years after the closure, demonstrating that the fisheries closure may have facilitated the early recovery process of this species and its associates. Overall, this work has important implications for the spatial management of seamounts vulnerable to bottom-contact fishing operations

Evaluation of the full set of habitat suitability models for vulnerable marine ecosystem indicator taxa in the South Pacific high seas

\ua9 2024 The Authors. Fisheries Management and Ecology published by John Wiley & Sons Ltd. In the high seas, regional fishery management organisations are required to implement measures to prevent significant adverse impacts on vulnerable marine ecosystems (VMEs). Our objectives were to develop habitat suitability models for use in the spatial management of bottom fisheries in the South Pacific and to evaluate these and existing models using independent data from high-quality seafloor imagery. Presence-only models for seven VME indictor taxa were developed to complement previous modelling. Evaluation of habitat suitability models using withheld data indicated high mean True Skill Statistic scores of 0.44–0.64. Most habitat suitability models performed adequately when assessed with independent data on taxon presence and absence but were poor surrogates for abundance. We therefore advocate caution when using presence-only models for spatial management and call for more systematically collected data to develop abundance models

Species replacement dominates megabenthos beta diversity in a remote seamount setting

Seamounts are proposed to be hotspots of deep-sea biodiversity, a pattern potentially arising from increased productivity in a heterogeneous landscape leading to either high species co-existence or species turnover (beta diversity). However, studies on individual seamounts remain rare, hindering our understanding of the underlying causes of local changes in beta diversity. Here, we investigated processes behind beta diversity using ROV video, coupled with oceanographic and quantitative terrain parameters, over a depth gradient in Annan Seamount, Equatorial Atlantic. By applying recently developed beta diversity analyses, we identified ecologically unique sites and distinguished between two beta diversity processes: species replacement and changes in species richness. The total beta diversity was high with an index of 0.92 out of 1 and was dominated by species replacement (68%). Species replacement was affected by depth-related variables, including temperature and water mass in addition to the aspect and local elevation of the seabed. In contrast, changes in species richness component were affected only by the water mass. Water mass, along with substrate also affected differences in species abundance. This study identified, for the first time on seamount megabenthos, the different beta diversity components and drivers, which can contribute towards understanding and protecting regional deep-sea biodiversity

Independent statistical validation of the New Zealand Seafloor Community Classification

\ua9 2024 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons Ltd. The New Zealand Seafloor Community Classification (NZSCC) is a national-scale numerical community classification which depicts compositional turnover of 1716 taxa (demersal fish, reef fish, benthic invertebrates and macroalgae) classified into 75 groups representing seafloor communities. To ensure the continual use of the NZSCC for spatial planning and reporting, a robust maintenance framework must be set in place; key to this is being able to assess the ability of the classification to represent (discriminate between) different seafloor communities. Here we describe an approach for validating the NZSCC using temporally independent evaluation data for demersal fish and benthic invertebrates (the latter sampled via a different method), which identifies whether the NZSCC represents different seafloor communities (i.e., assesses classification strength), evaluates the underlying statistical model, and considers heterogeneity in environmental coverage and statistical uncertainty. Additionally, the availability of abundance estimates for these evaluation datasets provides an opportunity to test whether the NZSCC—which was developed using presence-absence data—can reflect abundance-weighted seafloor communities. The ANOSIM global R values (measuring classification strength) were 0.53 and 0.46 (and significant at the 1% level) for demersal fish and benthic invertebrates, respectively, indicating that the NZSCC groups define biologically distinctive environments. The proportion of significant inter-group differences were very high (95% and 97% for demersal fish and benthic invertebrates, respectively) suggesting NZSCC groups were distinct from each other in their taxonomic composition. There were positive relationships between the evaluation datasets and the underlying statistical model. There was no evidence of these relationships being affected by the statistical uncertainty of the NZSCC. NZSCC model validation metrics using abundance evaluation data were also moderately high (albeit lower than for presence-absence for invertebrates) suggesting that the NZSCC, can at least in part, represent variation in abundance-weighted communities. Results presented here suggest that the existing NZSCC is currently fit-for-purpose for informing management decisions

Bottom-trawling affects the viability of climate refugia for vulnerable marine ecosystem indicator taxa

\ua9 2025 The Author(s)Bottom trawling significantly impacts benthic ecosystems, including deep-sea habitats. International guidelines recognize Vulnerable Marine Ecosystems (VMEs) as ecologically critical ecosystems at risk from fishing. In New Zealand, spatial protection measures aim to mitigate some effects of bottom trawling but remain insufficient to preserve essential habitats of VME indicator taxa under current and future climatic conditions. Using the dynamic Relative Benthic Status (dRBS) approach and density predictions for 10 VME indicator taxa, we evaluated the historical impacts of bottom trawling across New Zealand\u27s seas, focusing on primary habitats and climate refugia predicted under future scenarios (SSP2-4.5, SSP3-7.0). Our results show that bottom trawling is expected to have impacted all assessed taxa across the study region, albeit with different intensities. Areas identified as climate refugia were particularly affected, showing the greatest reductions in both taxon density and habitat extent. Overall density losses were similar among taxa within internal climate refugia (i.e., current high-density areas predicted to maintain high densities in the future) at approximately 7–8 % and external refugia (i.e., new areas where certain taxa were predicted to expand into in the future) at approximately 9–10 % under both climate scenarios. Nevertheless, the predicted reduction in current-day density was higher in internal refugia (on average 4000 individuals per km2) compared to external refugia (on average 500 individuals per km2). Habitat extent reductions were also greater in internal refugia (∼10 %) than in external refugia (∼4 %). Identifying and protecting climate refugia must be a conservation priority, as they represent areas where taxa may persist or expand under future climates. Careful consideration of these areas is required to reduce extinction risk and ensure the long-term conservation of ecosystem services