What are the effects of macroalgal blooms on the structure and functioning of marine ecosystems? A systematic review protocol

Abstract Background Anthropogenic activities are believed to have caused an increase in the magnitude, frequency, and extent of macroalgal blooms in marine and estuarine environments. These blooms may contribute to declines in seagrasses and non-blooming macroalgal beds, increasing hypoxia, and reductions in the diversity of benthic invertebrates. However, they may also provide other marine organisms with food and habitat, increase secondary production, and reduce eutrophication. The objective of this systematic review will be to quantify the positive and negative impacts of anthropogenically induced macroalgal blooms in order to determine their effects on ecosystem structure and functioning, and to identify factors that cause their effects to vary. Methods We will search a number of online databases to gather empirical evidence from the literature on the impacts of macroalgal blooms on: (1) species richness and other univariate measures of biodiversity; (2) productivity and abundance of algae, plants, and animals; and (3) biogeochemical cycling and other flows of energy and materials, including trophic interactions and cross-ecosystem subsidies. Data from relevant studies will be extracted and used in a random effects meta-analysis in order to estimate the average effect of macroalgal blooms on each response of interest. Where possible, sub-group analyses will be conducted in order to evaluate how the effects of macroalgal blooms vary according to: (1) which part of the ecosystem is being studied (e.g. which habitat type, taxonomic group, or trophic level); (2) the size of blooms; (3) the region in which blooms occurred; (4) background levels of ecosystem productivity; (5) physical and chemical conditions; (6) aspects of study design and quality (e.g. lab vs. field, experimental vs. observational, degree of replication); and (7) whether the blooms are believed to be anthropogenically induced or not

The effects of exotic seaweeds on native benthic assemblages: variability between trophic levels and influence of background environmental and biological conditions

Abstract Background Biological invasions are among the most severe threats to marine biodiversity. The impacts of introduced seaweeds on native macroalgal assemblages have been thoroughly reviewed. In contrast, no attempt has been made to synthesize the available information on the effects of exotic seaweeds on other trophic levels. In addition, it has not been clarified whether the effects of introduced seaweeds on native assemblages vary according to background physical and biological conditions. Methods This protocol provides details of our proposed method to carry out a systematic review aiming to identify and synthesize existing knowledge to answer the following primary questions: a) how does the impact of the presence of exotic seaweeds on native primary consumers (across trophic levels) compare in magnitude and extent to that observed on native primary producers (same trophic level)?; b) does the intensity of the effects of the presence of exotic seaweeds on native benthic ecosystems vary along a gradient of human disturbance (i.e. from urban/industrial areas to extra-urban areas to pristine areas)

A response-surface approach into the interactive effects of multiple stressors reveals new insights into complex responses

Understanding the difficult to predict interactive effects of anthropogenic stressors is recognized as one of the major challenges facing environmental scientists and ecosystem managers. Despite burgeoning research, predicting stressor interactions is still difficult, in part because the same two stressors can interact, or not, depending on their intensities. While laboratory experiments have provided useful insights about how organisms respond to serial doses of single stressors, we lack ‘response-surface’ field experiments in which naturally occurring assemblages are exposed to multiple types and concentrations of stressors. Here we used a field-based dosing system combined with a ‘response-surface’ design to test the individual and combined effects of two stressors (copper and chlorpyrifos) at five concentrations of each, for a total of 25 replicated treatments (n=4). After six weeks of dosing, chemical uptake and impacts at several levels of biological organization in mussel assemblages were measured. Stressor combinations produced interactive effects that would not have been revealed without using this replicated ‘response-surface approach’. Results show that non-additive effects of multiple stressors may be more complex and more common than previously thought. Additionally, our findings suggest that interactive effects of multiple stressors vary across levels of organization which has implications for monitoring and managing the chemical, biological and ecological impacts of priority pollutants in the real world

Replicating natural topography on marine artificial structures:A novel approach to eco-engineering

Ocean sprawl is a growing threat to marine and coastal ecosystems globally, with wide-ranging consequences for natural habitats and species. Artificial structures built in the marine environment often support less diverse communities than natural rocky marine habitats because of low topographic complexity. Some structures can be eco-engineered to increase their complexity and promote biodiversity. Tried-and-tested eco-engineering approaches include building-in habitat designs to mimic features of natural reef topography that are important for biodiversity. Most designs mimic discrete microhabitat features like crevices or holes and are geometrically-simplified. Here we propose that directly replicating the full fingerprint of natural reef topography in habitat designs makes a novel addition to the growing toolkit of eco-engineering options. We developed a five-step process for designing natural topography-based eco-engineering interventions for marine artificial structures. Given that topography is highly spatially variable in rocky reef habitats, our targeted approach seeks to identify and replicate the ‘best’ types of reef topography to satisfy specific eco-engineering objectives. We demonstrate and evaluate the process by designing three natural topography-based habitat units for intertidal structures, each targeting one of three hypothetical eco-engineering objectives. The process described can be adapted and applied according to user-specific priorities. Expanding the toolkit for eco-engineering marine structures is crucial to enable ecologically-informed designs that maximise biodiversity benefits from burgeoning ocean sprawl

Artificial shorelines lack natural structural complexity across scales

From microbes to humans, habitat structural complexity plays a direct role in the provision of physical living space and increased complexity supports higher biodiversity and ecosystem functioning across biomes. Natural coastlines are structurally complex transition zones between land and sea that support diverse ecological communities but are under increasing pressure from human activity. Coastal development and the construction of artificial shorelines are changing our landscape and altering biodiversity patterns as humans seek both socio-economic benefits and protection from coastal storms, flooding, and erosion. In this study, we evaluate how much structural complexity is missing, and at which scales, with the creation of artificial structures compared to naturally occurring rocky shores. We quantified the structural complexity of both artificial and natural shores at resolutions from 1 mm through to 10s of m using three remote sensing platforms (handheld camera, terrestrial laser scanner and uncrewed aerial vehicles) across both artificial and natural shorelines. Natural shorelines were approximately 20-50 % more structurally complex and offered greater structural variation between locations. In contrast, artificial shorelines were more structurally homogenous and typically deficient in structural complexity across scales. Our findings reinforce concerns that replacing natural rocky shorelines with artificial structures simplifies coastlines at organism-relevant scales. Furthermore, we offer much-needed insight into how structures might be modified to more closely capture the complexity of natural shorelines that support biodiversity

Habitat structure shapes temperate reef assemblages across regional environmental gradients

Intertidal artificial habitats are proliferating, but are generally simpler in structure and host lower biodiversity than natural rocky reefs. Eco-engineering aims to enhance the biodiversity of coastal infrastructure, often through physical structural modifications that mimic topographic properties of natural shores. Relationships between biotic assemblages and structural properties of natural and artificial reefs have been extensively studied at sampling scales of up to 1 m2. But evidence that quantified local structural variation has an appreciable influence on biotic assemblages, at a shore-wide scale across regional environmental gradients, is lacking. Here we addressed this knowledge gap with an observational study at 32 natural and artificial intertidal reef sites in Wales, UK. We used multivariate community analysis and permutation tests to examine associations between local physical structure, regional environmental variables and sessile biotic assemblages. A potential influence of local habitat structure on assemblage composition was evident across regional-scale environmental gradients. Compared to natural sites, artificial reefs had lower taxonomic richness, distinct and more variable assemblage composition, and different physical structure. After removing the effect of habitat (natural or artificial), canonical correspondence analysis showed that environmental variables (wave exposure, sea surface temperature and salinity variation), along with two metrics of physical structure (standard deviation in log-transformed detrended roughness and skewness of surface verticality, both at 0.5 m scale), explained 40 % of the variation in assemblage composition among sites. The two structural metrics independently explained 14.5 % of the variation. Associations identified between individual taxa and environmental variables indicated that sites with a higher proportion of horizontal surfaces hosted more canopy macroalgae, which in turn support other algae and invertebrates. Our findings provide evidence to inform scaling-up of structural eco-engineering interventions from experimental contexts to enhance the biodiversity of coastal infrastructure across regional extents

Harnessing positive species interactions as a tool against climate-driven loss of coastal biodiversity

Habitat-forming species sustain biodiversity and ecosystem functioning in harsh environments through the amelioration of physical stress. Nonetheless, their role in shaping patterns of species distribution under future climate scenarios is generally overlooked. Focusing on coastal systems, we assess how habitat-forming species can influence the ability of stress-sensitive species to exhibit plastic responses, adapt to novel environmental conditions, or track suitable climates. Here, we argue that habitat-former populations could be managed as a nature-based solution against climate-driven loss of biodiversity. Drawing from different ecological and biological disciplines, we identify a series of actions to sustain the resilience of marine habitat-forming species to climate change, as well as their effectiveness and reliability in rescuing stress-sensitive species from increasingly adverse environmental conditions.EuroMarine - European Marine Research Networ