Kelp forests are being degraded and/or lost in many regions, and as such, interest in active kelp restoration approaches to reinstate forests is growing. ‘Green gravel’ is a promising new kelp restoration technique that involves seeding small rocks with kelp zoospores, rearing the gametophyte and juvenile sporophyte stages in aquaria before outplanting them at restoration sites. However, to be considered a viable approach to kelp forest restoration, the efficacy of this technique needs to be assessed across a range of environmental contexts and kelp species. Here, we aimed to understand the utility of green gravel as a kelp restoration technique for wave-exposed intertidal shores. Two substrate types – gravel and cobbles – were seeded with Saccharina latissima, reared in the aquarium and outplanted at two sites along the northeast coast of England. Outplanted rocks were monitored for retention, and the density and length of S. latissima. Juvenile sporophytes persisted on both rock types, although declines in density and variations in length were observed over time. Substrate retention was low, with gravel more likely to be removed from restoration sites compared to cobbles, and all outplanted rocks were lost after eight months. While our initial testing of the green gravel restoration technique on wave-exposed shores was not successful, our results provide important insights for developing/refining the technique and a baseline for comparison for future efforts. However, prior to commencing large-scale kelp restoration in wave-exposed areas using green gravel, further testing of the technique and comparisons with other restoration approaches are needed.

Recently, there has been emphasis on the need to shift away from the use of synthetic chemical herbicides to low-risk alternatives derived from natural sources. This is aimed at lowering or averting the negative impact synthetic herbicides have on the environment and dealing with the emergence of weed species resistant to these chemicals. As a result, more stringent measures or outright bans on the use of most synthetic herbicides have been put in place by regulatory bodies. As seaweeds are abundant resources in the marine environment that have the capacity to produce diverse bioactive compounds, they could serve as sustainably viable, natural, and low-risk alternatives/sources to explore for potential phytotoxic capabilities. This could in turn help to enhance or boost the availability of effective solutions in the global bioherbicide market. This review highlights the prospects of using seaweeds as novel biopesticides for the control and management of various plant pests, including weed species, and for the development of sustainable agriculture/forestry practices. More specifically, it focuses on their use as a rich natural source for novel bioherbicide development, a potential that has remained underexplored for many years. However, to unlock the full potential of seaweed-derived bioherbicides and to create a potential path toward their development, increased research and development efforts are urgently needed to tackle and overcome possible constraints posed in this novel area, such as variability in seaweed chemical composition, formulation technologies, stability and efficacy of seaweed bioactive compounds, cost and scalability, and environmental considerations.

The spread of the brown seaweed Sargassum muticum is one of the best documented invasions of a non-native marine species. Observation of a potentially established population of S. muticum in the Orkney Islands archipelago, located off the northern coast of Scotland, was reported by recreational snorkellers in 2019 and 2020. The present study summarises a focussed investigation to confirm its presence and current local distribution, using data from 46 survey sites monitored as a part of the Orkney Islands Council Harbour Authority monitoring programme. Findings in this study represent the most northerly record of an established population of S. muticum in the United Kingdom, extending the latitudinal range in this country by 1.44° (159 km) northwards, and indicate only localised presence of this species. Analysis of a partial cytochrome oxidase I gene sequence confirmed the visual species identification. Possible vectors of introduction, gaps in the geographic range, local ecological and economic impacts, and the potential ameliorating factor of deep rockpools on wave exposed shores for S. muticum are discussed.

Management efforts to control starry stonewort [Nitellopsis obtusa (Desvaux in Loiseleur) J. Groves] have been limited to stressing the thalli and have not been able to directly target the reproductive bulbils. Smaller-scale efforts such as the use of hand pulling can be employed, but hand pulling is not realistic for larger infestations. This research was conducted to test the effects of clipping stress on N. obtusa to provide a baseline for the effect of stress on the production of bulbils and the regrowth of thalli. Mesocosms were set up under greenhouse conditions to test the effects on N. obtusa of simulated mechanical harvesting once, twice, and four times per growing season. Different seasonal timing and frequency of clipping treatments will remove different amounts of thalli biomass. The four-clipping treatment always reduced thalli biomass in this study at both 16 and 52 wk after treatment (WAT) compared with the nontreated reference, but there was no difference among clipping treatments at 52 WAT. At 16 WAT, one clipping reduced bulbil density by 44% (Trial 1) to 50% (Trial 2), two clippings reduced bulbil density by 28% (Trial 2) to 52% (Trial 1), and four clippings reduced bulbil density by 22% (Trial 2) to 88% (Trial 1). At 52 WAT, bulbil densities were 69% and 93% lower than those of the nontreated reference Trials 2 and 1, respectively. Results from this study indicate that clipping may be effective for N. obtusa control and could impact bulbil production.

Metal concentrations in coastal zones are a critical study subject since anthropogenic activities surrounding these zones are increasing and affecting environmental concentrations of metals. Macroalgae have been used as biomonitors since they can act as indicators of metal concentrations in the water column. Tissue samples of three abundant macroalgae species (Spyridia filamentosa, Padina mexicana and Ulva ohnoi) were collected from three sites with different anthropogenic impacts at La Paz Bay and Guaymas Bay, Mexico, during three contrasting seasons (dry, rainy and cold) in the year 2016. Tissue concentrations of iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), cadmium (Cd) and lead (Pb) were determined by atomic absorption spectrophotometry. The highest concentrations were found in S. filamentosa inhabiting both bays. The highest Cd and Mn concentrations were recorded in algae from La Paz Bay, while the highest concentrations of Cu, Zn, Pb and Fe were recorded in algae from Guaymas Bay. Metal concentrations varied seasonally; the highest Fe, Cu, Zn, Ni and Pb levels were recorded in the cold season in algae from both bays. S. filamentosa concentrated more Fe, Ni, Cu, Zn and Pb, while P. mexicana and U. ohnoi showed higher Mn and Cd. Therefore, S. filamentosa proved to be the most suitable indicator of metal concentrations, followed by P. mexicana and U. ohnoi. The high metal concentrations recorded in algae from San Juan de la Costa, La Paz Bay, are related to mining activities, whereas those in algae from Guaymas Bay are related to canneries, maritime traffic and others.

We report on the relationships between some conspicuous Mediterranean photophilous sponge species and Caulerpa cylindracea, a non-indigenous species. A diversification of defence strategies and behaviour is highlighted in target species belonging to different orders of Demospongiae from a western Mediterranean Marine Protected Area (NW Sardinian Sea). Caulerpa cylindracea displays a strongly invasive behaviour during body colonization of the Irciniidae Sarcotragus spinosulus and Ircinia retidermata (order Dictyoceratida). These sponges possess pre-adaptive defensive morpho-functional and physiological traits enabling them to partly withstand algal invasion. Also Aplysina aerophoba (order Verongiida) seems to be able to control colonization. Successful anti-Caulerpa strategies characterize the rarely affected Crambe crambe (order Poecilosclerida). Species-specific competitive strategies are displayed at different levels of body architecture, behaviour and physiology by native sponge species. The invasion patterns on sponges, the invasion dynamics in 2016–2017 and topographic distribution of C. cylindracea on S. spinosulus confirm this algal species as a threat, with potential long-term effects on sponge assemblages. Data suggest other kinds of poorly investigated synergic stressors affecting these habitat-forming species. Defence strategies of sponge species take the form of: (1) passive deterrence by morpho-functional pre-adaptive traits as growth form, biomass amount, surface traits, and microhabitat within the sponges' aquiferous system; (2) active physiological defence, whereby the morphology/anatomy of the sponge body is adapted to control invaders, by body remodelling and regenerative processes within the aquiferous system and at the sponge surface; (3) presumed active chemical defence by exudation processes of bioactive compounds.

The use of medicinal zinc oxide (ZnO) must be phased out by 2022, thus prompting an urgent need for alternative strategies to prevent diarrhoea in weaner piglets. The objectives of this study were to assess the impact on weaner piglet performance, diarrhoea incidence and gut development, when (1) dietary ZnO supplementation was substituted by alternative commercial products based on macroalgae, specific probiotics or synbiotics, or (2) dietary ZnO inclusion was reduced from 2500 to 1500 ppm. A total of 4680 DLY piglets (DanBred, Herlev, Denmark), weaned around 35 days of age, were randomly assigned according to sex and BW to six different dietary treatment groups. A basal diet was supplemented with no ZnO (NC = negative control), 2500 ppm ZnO (PC = positive control), 1500 ppm ZnO (RDZ = reduced dose of ZnO) or commercial macroalgae (OceanFeed™ Swine = OFS), probiotic Miya-Gold or synbiotic GærPlus products. The piglets entered and exited the weaner unit at ~7.0 and 30 kg BW, respectively. In-feed ZnO was provided the first 10 days post-weaning, while the alternative supplements were fed throughout the weaner period. As expected, the average daily feed intake, average daily weight gain (ADG), feed conversion ratio (FCR) and diarrhoea incidence were improved in the PC compared to NC group (P < 0.05) during phase 1 consistent with improved indices of villi development observed in subgroups of piglets sacrificed 11 days post-weaning. Reduction of ZnO to 1500 ppm lowered ADG (P < 0.05) and slightly increased incidence of diarrhoea during the first 10 days after weaning (but not later) without affecting FCR. None of the three alternative dietary additives, including a 10-fold increased dose of GærPlus than recommended, improved piglet performance, gut health and gut development above that of NC piglets. The OFS piglets sacrificed 11 days after weaning had significantly lower weights of hindgut tissue and contents compared to the PC group, consistent with antimicrobial activity of the product, which was detected from anaerobic in vitro fermentation. In conclusion, dietary ZnO supplementation during the first 10 days post-weaning may be reduced from 2500 to 1500 ppm without major negative implications for weaner piglet performance and health in herds under a high management level. However, none of the alternative dietary supplements were able to improve piglet performance or gut health, when ZnO was omitted from the diet.

Macrophytes provide a habitat for many species of marine invertebrates, the gastropods being one of the main components. This study provides new information about Sargassum-associated gastropod biodiversity, through characterization of the fauna from a highly impacted area of Brazil, investigating its variation at a small spatial scale and between two main seasons of the year, as well as its relationship with macroalgae parameters. Density of gastropods was higher during the warmest season and varied throughout sampling sites. A significant and positive, however weak, relationship between gastropod density and Sargassum dry weight was found in all localities. For all sites, a marked and unusual dominance of Bittiolum varium was observed. The high dominance of this species seems to be related to the impacts caused by shipping activities and highway construction in the 1970s and 1980s, which caused a decline in local species diversity that seems to have continued until now. Many species, both typical of these habitats and characteristic of other, nearby habitats, benefit from Sargassum sp. These macrophytes allow gastropods to establish and grow during their most vulnerable stages, as shown by the growth series and juvenile forms found for most species of gastropods. The present data highlight the importance of macrophyte habitats for gastropod biodiversity in coastal areas and call attention to the importance of raising knowledge on this fauna, especially in impacted areas, thus contributing to the conservation of these highly diverse and ecologically important macrophyte–gastropod systems.

The continued development of the aquaculture industry is contributing to the proliferation of artificial structures in the marine environment. Observations of seaweed farms (infrastructure and biomass) suggest they act as a habitat for associated species. Seaweed farms differ from other forms of artificial infrastructure as the material deployed already has marine organisms (i.e. culture species) growing on it. This ‘priming’ of ropes with juvenile sporophytes may affect future development of communities by facilitating colonizing species or suppressing competitors. We call this process ‘ecological priming’: the provision of a biological platform that influences the successional development of specific communities. The communities that developed on ropes primed with Alaria esculenta individuals were compared with unprimed ropes to assess the ecological priming effect, at a commercial kelp farm in south-west Ireland. Species richness increased over two cultivation seasons and species composition was consistent between years, with distinct communities developing on primed and unprimed treatments. Timing of species occurrence on primed ropes was predictable with no predictable pattern occurring on unprimed ropes. Multivariate tests indicated distinct communities between treatments, with suppression of other algal species and potential facilitation of some species that have a particular association with A. esculenta on primed ropes. Communities from primed holdfasts contained a lower diversity of algal species compared with unprimed communities. Cultivated kelp holdfasts represent a habitat for distinct assemblages that reflect ecological priming of the substratum.

Macroscopic algae can be found in large open ponds or harvested from the sea. Macro algae includes three distinct groups based on colour: green, brown and red. They are unique in containing secondary metabolites that can be extracted and used for various purposes. This review examines the antimicrobial properties (bacteria, viruses and fungi) of macro algae and its extracts to improve poultry health and performance. This includes body weight gain, feed conversion efficiency and carcass yield improvements in broilers and egg weight and shell quality in layers. As an example, in one study, 35-day body weight of broilers was increased 7.6% with the inclusion of 0.5% Undaria pinnatifida (brown macroalgae) to the diet. The investigations discussed show the diversity of the species available and broad scope where research has been done and the potential for the future.

Animals develop behavioural strategies throughout life to improve their survival in nature. Juvenile activity and behaviour of the commercial tropical sea cucumber Stichopus cf. horrens were examined considering factors that may influence survival at this critical developmental stage. Wild juveniles were observed in situ to describe diel activity and movement. Wild and hatchery-reared juveniles were observed in the laboratory to evaluate the influence of different light-dark cycles and microhabitats on feeding and sheltering behaviour. All juveniles (4–54 g) displayed a distinct nocturnal activity pattern both in the field and laboratory. Nocturnal activity was strongly associated with feeding and locomotion. Wild and hatchery-reared juveniles were most active at night, displayed intermediate activity during twilight, and minimal to no activity during daytime. Movement rates of wild juveniles in situ were significantly influenced by time and size to a lesser extent. Under constant light and constant dark for 48 h, juvenile feeding rhythm was endogenously controlled and strongly entrained to natural light-dark cycles. Sheltering was directly affected by light and linked to strong phototactic and thigmotactic reflexes. Juveniles preferred vegetation as shelter compared to coral, sand or open space, and showed equal preference for seagrass and macroalgae. Deviations in behaviour of hatchery-reared juveniles under laboratory conditions indicate some degree of acclimation to an artificial environment with minimal threats and a decreased sensitivity to light. The implications of nocturnal feeding, light-induced sheltering, shelter preferences and acclimation to artificial conditions are discussed in relation to juvenile survival in nature and potential restocking of the species.

Canopy-forming fucoid algae have an important role as ecosystem engineers on rocky intertidal shores, where they increase the abundance of species otherwise limited by exposure during low tide. The facilitative relationship between Ascophyllum nodosum and associated organisms was explored using a frond breakage experiment (100%, 50%, 25%, 0% intact-frond treatments) in southern England, to assess the consequences of disturbance. Understorey substratum temperature was on average 3°C higher in 0% and 25% intact-frond treatments than in plots with 50% and 100% intact fronds. Light (as PAR during low tide) doubled in 0% intact-frond treatments in comparison to other treatments (which had similar light levels). Mobile invertebrate species richness declined by on average 1 species per m2 in the treatments with only 25% and 0% intact fronds, and the abundance of Littorina obtusata declined by 2.4–4.2 individuals per m2 in the treatments with 25 and 0% intact fronds. Sessile taxa, including Osmundea pinnatifida and encrusting coralline algae, declined by half on average in the 0% intact-frond treatment. These results suggest that the ability of Ascophyllum to mediate environmental conditions to the understorey is the mechanism responsible for species distributed in the understorey (autogenic ecosystem engineering). The results of this study imply that a pulse disturbance resulting in a 50% breakage of Ascophyllum fronds significantly increases temperature and decreases the abundance of mobile invertebrates usually associated with Ascophyllum. Sessile taxa associated with Ascophyllum can, however, withstand disturbances down to 25% intact Ascophyllum fronds.

Coastal ecosystems are highly complex and driven by multiple environmental factors. To date we lack scientific evidence for the relative contribution of natural and anthropogenic drivers for the majority of marine habitats in order to adequately assess the role of different stressors across the European seas. Such relationship can be investigated by analysing the correlation between environmental variables and biotic patterns in multivariate space and taking into account non-linearities. Within the framework of the EMBOS (European Marine Biodiversity Observatory System) programme, hard bottom intertidal communities were sampled in a standardized way across European seas. Links between key natural and anthropogenic drivers and hard bottom communities were analysed using Boosted Regression Trees modelling. The study identified strong interregional variability and showed that patterns of hard bottom macroalgal and invertebrate communities were primarily a function of tidal regime, nutrient loading and water temperature (anomalies). The strength and shape of functional form relationships varied widely however among types of organisms (understorey algae composing mostly filamentous species, canopy-forming algae or sessile invertebrates) and aggregated community variables (cover or richness). Tidal regime significantly modulated the effect of nutrient load on the cover and richness of understorey algae and sessile invertebrates. In contrast, hydroclimate was more important for canopy algae and temperature anomalies and hydroclimate separately or interactively contributed to the observed patterns. The analyses also suggested that climate-induced shifts in weather patterns may result in the loss of algal richness and thereby in the loss of functional diversity in European hard bottom intertidal areas.

Despite the ecological relevance of tropical reefs, information on species composition and coverage on sandstone reefs is very scarce. Most studies on reef systems have been conducted for true coral reefs, ecosystems that show calcareous formations with extensive coral cover and diversity. The aim of this study was to analyse the coverage of benthic assemblages in a submerged sandstone reef (22–24 m) in a relatively non-explored region (Tropical South-western Atlantic). In this area, filamentous algae (43.6%) and sponges (19.6%) are the main components of the benthic reef assemblages. Other benthic reef fauna (ascidians, corals and zoanthids) showed lower coverage, although their importance may vary depending on the area. A negative correlation between filamentous algae and slow-growing reef-building organisms (calcareous algae) was observed. High sand coverage (19.6%) over the reef revealed a high rate of silting. A low coral diversity (only two resilient species) was quantified, and most of the coral colonies were small-sized. The results provide a baseline assessment for a poorly known ecosystem with turbid-water benthic communities and higher sea-surface temperatures near the Earth's equator.

Understanding the variables (biotic or abiotic) controlling coastal communities is the main goal of ecology research and it is crucial to predict how communities will evolve under the increasing pressure on coastal systems by human activities. The general aims of this study were to assess the variables affecting the distribution of the fast-growing sponge Hymeniacidon cf. perlevis, and to evaluate if physical stressful conditions have an influence in the relationship between Hymeniacidon and the sea lettuce Ulva lactuca. Specifically, the aims were to evaluate the abundance patterns of Hymeniacidon and Ulva and to assess the relationship of Ulva and physical variables on the abundance of Hymeniacidon at both intertidal and subtidal. Hymeniacidon and Ulva showed opposite abundance patterns. Hymeniacidon was more abundant in sites without Ulva, and negatively correlated with Ulva abundance at both heights. Intertidal Hymeniacidon abundance was not correlated with physical variables, but subtidal Hymeniacidon was.

Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two sites on rocky walls in New Zealand and monitored for approximately 1.5 years. We hypothesized that the removal of the E. radiata canopy would affect the structure of subcanopy assemblages, such that there would be a reduction in sponge species richness and abundance. Furthermore, we investigated the biological and physical (predictor) variables that best explained variability in sponge assemblages after canopy removal. Canopy removal led to a community dominated by turf algae, which corresponded with a decrease in sponge abundance and richness. Our results suggest that the Ecklonia canopy may positively influence the presence of sponge species such as Crella incrustans; we propose that the canopy may allow its coexistence with turf algae underneath the canopy by altering the light regime and other environmental factors, which may be detrimental for some species. Our results highlight how any loss of canopy-forming species might have negative effects on sponge assemblages, which could affect the energy flow and the overall biodiversity found in these habitats.

Kelps, fucoids and other large brown seaweeds are common and important features of temperate coastal zones. The British Isles is a centre for seaweed diversity in the NE Atlantic, but, despite numerous surveys, an incomplete picture of the distribution remains. Survey data and herbarium specimens were used to examine the environmental preference of 15 species of large brown seaweeds, covering the orders Laminariales (kelps), Fucales (wracks) and one species of Tilopteridales. Habitat suitability models were developed to estimate broad-scale distribution and area of habitat created by these species around the British Isles. Topographic parameters were important factors limiting distributions. Generally, temperature did not appear to be a limiting factor, probably because the British Isles lies in the centre of the NE Atlantic distribution for most species, and not at climatic tolerance limits. However, for the recent migrant Laminaria ochroleuca, temperature was found to be important for the model, thus range expansion could continue northwards provided dispersal is possible. In contrast, the widespread Alaria esculenta showed a negative association with warmer summer temperatures. The total potential habitat around the British and Irish coastline is more than 19,000 km2 for kelps and 11,000 km2 for wracks, which represents a significant habitat area similar in scale to British broadleaf forest. We conclude that large brown algal species need to be managed and conserved in a manner that reflects their scale and importance.

Sanya Bay lies at the southern part of Hainan Island, 18°15′N 109°28′E. The seawater in the bay has been catastrophically polluted during the past two decades with urban sewage from the rapidly developing Sanya City. The marine flora research in Sanya Bay was started at the beginning of the 1930s and the most detailed studies were performed by two German-Chinese expeditions in 1990 (October–December) and in 1992 (March–April). In April, October, November and December 2008–2010 the marine flora of Sanya Bay was studied by the authors at three localities: Luhuitou Peninsula, Xiaodong Hai and Dadong Hai. Marine algae were sampled in the intertidal and upper subtidal zones (to 4–5 m depth). The list of species (including varieties and forms) of the marine algae for Sanya Bay sampled during the period from 2008 to 2010 is compared with those collected at the same localities in 1990/1992. Comparative analysis of the floristic composition of the marine red, brown and green algae (found during different time periods) revealed that considerable changes have taken place between 1990/1992 and 2008–2010 at Sanya Bay. There was an increase in filamentous, tubular and fine blade-like green and red algae (mainly epiphytes with a high surface to volume ratio) and a displacement of upright-growing fleshy, foliose and other large green, brown and red algae with a low surface to volume ratio. It is assumed that the changes reflect mainly increased pollution by urban sewage and mariculture pond wastes and probably by coral bleaching events of 1998.

Concentrations of cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn) and iron (Fe) were measured in three macroalgal species, Codium simulans, Sargassum sinicola and Gracilaria pachydermatica, and in the sea slug Elysia diomedea, living in marine ecosystems dominated by Sargassum species and located near exploited phosphorite deposits. Metal concentrations in macroalgae and sea slugs were significantly different among sites. The highest concentrations of Cd recorded in C. simulans and S. sinicola, as well as in E. diomedea were recorded at the site closest to the phosphorite deposit. In general, Cd and Zn concentrations in E. diomedea were higher than those recorded in specimens of C. simulans, S. sinicola and G. pachydermatica. In contrast, Pb, Cu, and Fe concentrations in E. diomedea were lower than or similar to those in macroalgae from all sampled sites. The information generated contributes to the knowledge about potential mobility and metal bioaccumulation at lower trophic levels in marine eco systems.

A floristic study of the marine plants and algae at Luhuitou reef, Sanya Bay, Hainan Island, China, was conducted during the rainy (October 2008 and November 2010) and dry seasons (April 2009 and February 2012). Specimens were collected in the upper subtidal zone (from 0.5 to 3 m depth at low tide). A total of 156 taxa were collected, including 143 macrophyte species (90%), 12 blue–green algal species (10%), and the seagrass, Thalassia hemprichii. The most diverse group was the Rhodophyta (79 taxa or 55%), followed by the Chlorophyta (38 taxa or 25%) and then the Phaeophyceae (26 taxa or 20%). In the upper subtidal zone, macroalgae formed two types of communities: polydominant communities of turf-forming algae and monodominant and bidominant communities of foliose or fleshy algae. Seasonal changes occurred in the dominant species, which appear to be caused by periodic annual events of thalli detachment and subsequent community succession. In spite of heavy pollution from dissolved inorganic nitrogen and phosphorus in Sanya Bay, the subtidal flora has not undergone any dramatic changes in species numbers or composition and is similar to that of unpolluted regions in the Indo-Pacific.