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Kelp species are found along ~ 25% of the world’s coastlines, where they provide myriad of ecological goods and services. However, compared with many other terrestrial and marine vegetated ecosystems, kelp forests have been critically understudied in many regions, leading to pressing knowledge gaps that hinder management and conservation efforts. We conducted a large-scale survey of understorey macroalgae within subtidal kelp forests dominated by Laminaria hyperborea at 12 sites, nested within 4 regions in the United Kingdom (UK). Regions spanned ~ 9° in latitude and encompassed a gradient in average sea surface temperature of ~ 2.5 °C. We employed a combination of traditional hand-harvesting of quadrat samples and a novel 3D photogrammetry technique to quantify crustose coralline algae. The structure of understorey macroalgal assemblages was highly variable but showed clear partitioning at the spatial scales of both regions and sites. At the regional-scale, we observed a general increase in richness, diversity and biomass from north to south, most likely due to biogeographical context, ocean climate and the structure and composition of overlying kelp canopies. Site level variation was most likely driven by concurrent variability in wave exposure and kelp canopy structure. Our study shows that understorey macroalgal assemblages represent a rich and abundant component of kelp forests in the northeast Atlantic, with high biodiversity value that warrant conservation measures. As these kelp forest ecosystems are structured by multiple physical and biological processes, current and predicted environmental change will likely alter the diversity and composition of understorey macroalgal assemblages.

Very little is known about the marine macroalgae of artificial reefs—especially in the North Atlantic—despite the growing number and extent of man-made structures in the sea, and even though seaweed communities have paramount importance as primary producers, but also as feeding, reproductive and nursery grounds in coastal ecosystems. This paper explores the macroalgal diversity of a large system of artificial reefs in Loch Linnhe, on the west coast of Scotland, in a quantitative and qualitative study based on diving surveys and correlates the observations with the prevalent abiotic factors. The study was conducted in order to test the hypothesis that artificial reefs can enhance seaweed habitats—in particular, for kelps—and that there is a clear correlation with substrate type. While the reef is home to a large range of biota and abundance of early-successional species of turf and bushy macroalgae, totalling 56 taxa and withDelesseria sanguineaas the dominant species, canopy-forming perennial kelp species are conspicuously relatively rare. Macroalgal vegetation is explored in correlation with reef geometry/geography and depth. Statistical analysis shows benthic communities were strongly affected by substrate type, with turf algae and invertebrates dominating the artificial reefs, while bushy algae dominate the natural ones. Common macroinvertebrates associated with the phytobenthic communities are assessed qualitatively.

Marine protected areas (MPAs) are widely used as management tools to conserve species and ecosystems at risk from human impact. Coastal managers often focus MPA designation on biogenic reef environments due to their value and sensitivity to damage. However, difficulties in enforcement and a lack of capacity to adequately monitor MPAs often make it hard for managers to assess the effectiveness of MPAs, particularly in under‐resourced, low‐income coastal countries. Reef community data were collected at three long‐term managed reserves within the Western Visayas region of the central Philippines in order to assess the state of reef community structure inside and outside of these small‐scale locally managed MPAs. In addition, 3D structural data were captured using recently developed 'Structure from Motion' photogrammetry techniques, demonstrating how multiple quantitative metrics of physical structural complexity and health can be recorded in such analyses. These community‐run MPAs were shown to be effective even when small (10–20 ha). Mean fish biomass density was five times greater within present‐day protected sites, alongside significantly increased levels of fish diversity, richness, and size. No significant structural differences were observed inside and outside of MPAs; however, average reef rugosity, height, and roughness were significantly higher in unfished reefs compared to blast‐fished reefs. Reef substrate complexity, coral composition, and level of management, were also shown to structure fish community assemblages, with the link between reef structure and fish richness/abundance disrupted outside of MPAs. The Structure from Motion technique allows a greater range of quantitative morphometrics to be assessed than traditional methods and at relatively low cost. The technique is rapid, non‐destructive and can be archived, increasing the value of data for managers wishing to quantify reef health and efficiently monitor benthic changes through time. We discuss both the limitations and benefits of this technology's future use.

Loch Creran on the west coast of Scotland supports the most expansive reefs of the serpulid (Serpula vermicularis) in the world. It also supports flame shell (Limaria hians) and horse mussel (Modiolus modiolus) reefs, thereby ensuring this loch received designation as a European Special Area of Conservation in 2005. In 2015, environmental DNA of the invasive, non-native colonial tunicate Didemnum vexillum, which has a worldwide distribution, was detected in Loch Creran. Didemnum vexillum was confirmed as being present at an oyster farm in the sea loch, using the cytochrome oxidase I gene (COI), following rapid intertidal and dive surveys in early September 2016. The abundance and distribution range assessment carried out at the farm indicated an early-stage D. vexillum invasion. The follow up dive surveys and wider loch intertidal surveys carried out in 2017 and 2018 confirmed that the D. vexillum presence continues to be associated exclusively with the oyster farm. This is the first time that such a highly invasive species has been found within a protected area of global significance and it has significant biosecurity and policy implications regarding how to manage such invasive species.

Given the recent trend towards establishing very large marine protected areas (MPAs) and the high potential of these to contribute to global conservation targets, we review outcomes of the last decade of marine conservation research in the British Indian Ocean Territory (BIOT), one of the largest MPAs in the world. The BIOT MPA consists of the atolls of the Chagos Archipelago, interspersed with and surrounded by deep oceanic waters. Islands around the atoll rims serve as nesting grounds for sea birds. Extensive and diverse shallow and mesophotic reef habitats provide essential habitat and feeding grounds for all marine life, and the absence of local human impacts may improve recovery after coral bleaching events. Census data have shown recent increases in the abundance of sea turtles, high numbers of nesting seabirds and high fish abundance, at least some of which is linked to the lack of recent harvesting. For example, across the archipelago the annual number of green turtle clutches (Chelonia mydas) is ~ 20,500 and increasing and the number of seabirds is ~ 1 million. Animal tracking studies have shown that some taxa breed and/or forage consistently within the MPA (e.g. some reef fishes, elasmobranchs and seabirds), suggesting the MPA has the potential to provide long-term protection. In contrast, post-nesting green turtles travel up to 4000 km to distant foraging sites, so the protected beaches in the Chagos Archipelago provide a nesting sanctuary for individuals that forage across an ocean basin and several geopolitical borders. Surveys using divers and underwater video systems show high habitat diversity and abundant marine life on all trophic levels. For example, coral cover can be as high as 40–50%. Ecological studies are shedding light on how remote ecosystems function, connect to each other and respond to climate-driven stressors compared to other locations that are more locally impacted. However, important threats to this MPA have been identified, particularly global heating events, and Illegal, Unreported and Unregulated (IUU) fishing activity, which considerably impact both reef and pelagic fishes.

Mytilid mussels form abundant, species-rich reefs on rocky substrates, but the role of this key habitat in carbon (C) cycling remains poorly understood. We performed a seasonal study on a 5 m deep photicMytilus trossulusreef in the Central Baltic Sea to investigate pathways and rates of organic C flow. Reef gross primary production (GPP) and respiration (R) were estimated seasonally using underwater O2eddy covariance on hourly and daily timescales. Photogrammetry and biotic sampling were used to quantify reef rugosity and mussel coverage, and to derive mussel filtration and biodeposition. Mussels were highly abundant, reaching ~50000 ind. m-2, and the reef structure increased the seabed surface area by 44%. GPPhourlywas up to 20 mmol O2m-2h-1and GPPdailywas up to 107 mmol O2m-2d-1, comparable to a nearby seagrass canopy. Hourly eddy fluxes responded linearly to light intensity and flow velocity, with higher velocities enhancing reef O2uptake at night. ReefRdailyexceeded GPPdailyon 12 of 13 measurement days, andRannual(29 mol O2m-2yr-1) was 3-fold larger than GPPannual. The reef sustained a productive community of microbes and fauna whose activities accounted for ~50% ofRannual. Horizontal water advection promoted food supply to the reef and likely facilitated substantial lateral C export of mussel biodeposits. Our analyses suggest that a reduction in mussel reef extent due to ongoing environmental change will have major implications for the transport and transformation of C and nutrients within the coastal Baltic Sea.

Microplastics are widespread in the natural environment and present numerous ecological threats. While the ultimate fate of marine microplastics are not well known, it is hypothesized that the deep sea is the final sink for this anthropogenic contaminant. This study provides a quantification and characterisation of microplastic pollution ingested by benthic macroinvertebrates with different feeding modes (Ophiomusium lymani, Hymenaster pellucidus and Colus jeffreysianus) and in adjacent deep water > 2200 m, in the Rockall Trough, Northeast Atlantic Ocean. Despite the remote location, microplastic fibres were identified in deep-sea water at a concentration of 70.8 particles m−3, comparable to that in surface waters. Of the invertebrates examined (n = 66), 48% ingested microplastics with quantities enumerated comparable to coastal species. The number of ingested microplastics differed significantly between species and generalized linear modelling identified that the number of microplastics ingested for a given tissue mass was related to species and not organism feeding mode or the length or overall weight of the individual. Deep-sea microplastics were visually highly degraded with surface areas more than double that of pristine particles. The identification of synthetic polymers with densities greater and less than seawater along with comparable quantities to the upper ocean indicates processes of vertical re-distribution. This study presents the first snapshot of deep ocean microplastics and the quantification of microplastic pollution in the Rockall Trough. Additional sampling throughout the deep-sea is required to assess levels of microplastic pollution, vertical transportation and sequestration, which have the potential to impact the largest global ecosystem.

The atolls and coral banks of the Chagos Archipelago (British Indian Ocean Territory) in the central Indian Ocean were badly affected by the warm water event that started in 2015 and lasted for nearly two years. On these reefs, coral mortality was very severe, reducing coral cover to

It is frequently assumed that taking samples of soft marine sediments using surface-based gravity coring equipment causes minimal disruption to their sedimentological, biogeochemical, and biological condition. This assumption was evaluated by examining the potential disturbances caused when obtaining soft-sediment samples either by SCUBA or Craib-coring, comparing sediment oxygen microprofiles, benthic oxygen flux rates and sediment solid phase analyses (chlorophyll a (Chl a), organic carbon, and porosity) between both methods and against reference values measured in situ by benthic lander. The two sampling methodologies were tested in shallow coastal environments on the west coast of Scotland and generally the results obtained from cores collected using SCUBA exhibited values closest to those observed in situ. Oxygen penetration depth was significantly shallower in cores obtained by Craib-corer compared with the SCUBA cores. Craib cores also produced higher oxygen uptake rates which could be caused by greater levels of sediment disturbance during sampling. In addition, more homogenous levels of Chl a in the top 1 cm of the Craib cores, compared with the SCUBA samples, may indicate either resuspension or compression during gravity coring. Using SCUBA for shallow-water soft-sediment sampling permits steady and controlled core-tube insertion and extraction, and more measured retrieval of the cores to the surface; this probably accounts for the observed differences. Whereas benthic lander-based in situ measurement would be the preferred method for analyzing sediment parameters in detail in this type of environment, SCUBA-based sampling offers a more accurate alternative to surface-based gravity coring.

The last few decades have seen dramatic increases in the abundance and variety of data that can be collected within benthic marine environments to monitor species and ecosystems. These developments are now allowing ecologists to view their study systems in ever greater detail and over scales ranging from microscopic to global. Here we give an overview of current widely used techniques, touch on a number of recent advances in both technologies and methodologies, and focus on photogrammetry. We recommend that greater synergies, standardization, and automation of a range of these methods could further improve many monitoring programs’ effectiveness.

Substratum collected during diving surveys of sublittoral communities off the Greek island of Rhodes (Dodecanese, South-East Aegean) in late 2015 was incubated in the laboratory. Among the emerging macroalgal germlings, there was the second-ever record and isolate of the small benthic multicellular alga Schizocladia ischiensis of the poorly known monotypic Schizocladiophyceae, the sister group of the brown algae (Phaeophyceae). Its nuclear ribosomal small subunit, Rubisco spacer (rbcL, psaA, and psbC sequences (in total 5237 bp)) were similar to those of the only previous isolate of the species from Ischia, western Mediterranean. Our new strain formed branched upright thalli attached to the substratum by an amorphous substance secreted at the bottom of the basal cell. It is possible that S. ischiensis is a common member of the infralittoral and circalittoral communities in the Mediterranean and generally overlooked because of its minute size. Germling emergence appears to represent the method of choice to reveal benthic algae of this small size.

Reef structural complexity provides important refuge habitat for a range of marine organisms, and is a useful indicator of the health and resilience of reefs as a whole. Marine scientists have recently begun to use ‘Structure from Motion’ (SfM) photogrammetry in order to accurately and repeatably capture the 3D structure of physical objects underwater, including reefs. There has however been limited research on the comparability of this new method with existing analogue methods already used widely for measuring and monitoring 3D structure, such as ‘tape and chain rugosity index (RI)’ and graded visual assessments. Our findings show that analogue and SfM RI can be reliably converted over a standard 10-m reef section (SfM RI = 1.348 × chain RI—0.359, r2 = 0.82; and Chain RI = 0.606 × SfM RI + 0.465) for RI values up to 2.0; however, SfM RI values above this number become increasingly divergent from traditional tape and chain measurements. Additionally, we found SfM RI correlates well with visual assessment grades of coral reefs over a 10 × 10 m area (SfM RI = 0.1461 × visual grade + 1.117; r2 = 0.83). The SfM method is shown to be affordable and non-destructive whilst also allowing the data collected to be archival, less biased by the observer, and broader in its scope of applications than standard methods. This work allows researchers to easily transition from analogue to digital structural assessment techniques, facilitating continued long-term monitoring, whilst also improving the quality and additional research value of the data collected.

Monitoring temperature of aquatic waters is of great importance, with modelled, satellite and in-situ data providing invaluable insights into long-term environmental change. However, there is often a lack of depth-resolved temperature measurements. Recreational dive computers routinely record temperature and depth, so could provide an alternate and highly novel source of oceanographic information to fill this data gap. In this study, a citizen science approach was used to obtain over 7,000 scuba diver temperature profiles. The accuracy, offset and lag of temperature records was assessed by comparing dive computers with scientific conductivity-temperature-depth instruments and existing surface temperature data. Our results show that, with processing, dive computers can provide a useful and novel tool with which to augment existing monitoring systems all over the globe, but especially in under-sampled or highly changeable coastal environments.

Bacterial species associated with the dimethylsulfoniopropionate (DMSP)-producing phytoplankton Scrippsiella trochoidea were cultured and identified, with the aim of establishing their ability to metabolise DMSP, dimethylsulfide (DMS) and dimethylsulfoxide (DMSO). Results demonstrate that of the cultivable bacteria only α-Proteobacteria were capable of producing DMS from DMSP. The concentration of DMSP was shown to affect the amount of DMS produced. Lower DMSP concentrations (1.5 μmol dm−3) were completely assimilated, whereas higher concentrations (10 μmol dm−3) resulted in increasing amounts of DMS being produced. By contrast to the restricted set of bacteria that metabolised DMSP, ~ 70% of the bacterial isolates were able to ‘consume’ DMS. However, 98-100% of the DMS removed was accounted for as DMSO. Notably, a number of these bacteria would only oxidise DMS in the presence of glucose, including members of the γ-Proteobacteria and Bacteroidetes. The observations from this study, coupled with published field data, identify DMS oxidation to DMSO as a major transformation pathway for DMS, and we speculate that the fate of DMS and DMSP in the field are tightly coupled to the available carbon produced by phytoplankton.