Local improvements to species diversity through the creation of microhabitat features have been adopted as an approach for "Greening Grey Infrastructure" (GGI) in urbanised coastal ecosystems. To confidently implement these enhancements asset managers and engineers need quantitative information on the value of different feature types, densities, and configurations. We compared the biodiversity benefits of horizontal arrays of semi- contiguous 3 and 5 artificial rockpools with single isolated rockpool units and unenhanced sections of seawall. Rockpools were fixed within seawall sections 2 m wide at Mean High Water Neap Tide Level. At low tide, biota was monitored inside the pools, on the side of the pool units, the sea wall adjacent to the rockpools and in sea wall zones above and below the pools. After 36 months, species richness (all zones combined) of seawall sections with five rockpools was up to four times greater than controls and included protected and non- indigenous species. Increased richness was attributable to a higher density of rockpools and not rockpool contiguity. Grazers attracted to areas between and above rockpools modified assemblages that may limit persistence of algae. At one site, recovery of brown algae following disturbance during rockpool installation remained incomplete after 36 months. Benefits of arrays of semi-contiguous pools remain unclear, and deployment of individual rockpools (or similar enhancements) over a larger habitat area, that experience a wider range of conditions, may be at least as valuable. Quantifying species richness per unit size/ area of structure should assist managers and the development of metrics designed to measure ecological benefits in GGI.

Rockpools are fundamental habitats on natural rocky shores that provide refugia for marine life at low and high tide. Yet, artificial coastal structures lack the topographical complexity seen in these natural habitats. Eco-engineering, that may include the deployment of artificial rockpools, attempts to address the lack of suitable habitat on coastal infrastructure but most studies focus on species abundance metrics at low tide. It is important to understand how eco-engineering interventions may provide habitat at high tide compared to the surrounding artificial substrate.In this study, we demonstrate how groups of rockpools (1, 3 or 5 rockpools) add habitat complexity at high tide to a concrete seawall in Poole Harbour, UK. Between April and October 2022, eighteen GoPro cameras were deployed to record species richness and abundance in artificial rockpools and the adjacent concrete sea wall. Additionally, the length of time the most abundant fauna (the shanny fish Lipophrys pholis and the European shore crab Carcinus maenas) spent engaging in different behaviour (resting, feeding, moving) was recorded.Overall, there was no significant difference in the abundance and species richness of mobile fauna using the artificial rockpools versus the seawall. However, both the shanny and shore crab generally spent more time in the rockpools than on the seawall. Both crabs and shanny preferentially engaged in feeding behaviours on the seawall, which has been attributed to the high percentage cover of barnacle prey. Crabs and shanny spent more time resting in the rockpools than the seawall and the only reproductive behaviour observed occurred within the rockpools. Our work suggests that artificial rockpools support the habitat needs and multiple life history requirements of these species at high tide. Both the seawall and rockpools provide valuable resources, which further emphasises the need for variety in eco-engineering feature designs.

Eco-engineering of coastal infrastructure aims to address the insufficient intertidal habitat provided by coastal development and flood defence. There are numerous ways to enhance coastal infrastructure with habitat features, but a common method involves retrofitting artificial rockpools. Often these are 'bolt-on' units that are fixed to existing coastal infrastructure but there is a paucity of literature on how to optimise their arrangement for biodiversity. In this study, 24 artificial rockpools were installed at three levels between High Water Neaps and Mean Tide Level on a vertical concrete seawall on the south coast of the UK. The species abundance of the rockpools and adjacent seawall were surveyed at low tide for 2 years following rockpool installation and compared. Over the course of the study, sediment had begun to accumulate in some of the rockpools. At the 2-year mark, the sediment was removed and assessed for macrofauna. Algal biomass of the seawall and rockpools was estimated using previously obtained dry weight values for the dominant algae taxa. After 2 years, it was determined that artificial rockpools successfully increase species richness of seawalls, particularly at higher tidal levels where water-retaining refugia are crucial for many species. The rockpools hosted 37 sessile taxa and 9 sessile taxa were recorded on the seawall. Rockpools increased the vertical elevation for brown canopy-forming seaweeds by providing better attachment surfaces. Although the retained sediment only hosted 3 infaunal species, it was observed to provide shelter for shore crabs during surveys. As sea levels and ocean and air temperatures continue to rise, vertical eco-engineering arrangements will play a crucial role in allowing species to migrate up the tidal zone, negating habitat loss and localised extinction.

In the marine environment, greening of grey infrastructure (GGI) is a rapidly growing field that attempts to encourage native marine life to colonize marine artificial structures to enhance biodiversity, thereby promoting ecosystem functioning and hence service provision. By designing multifunctional sea defences, breakwaters, port complexes and off-shore renewable energy installations, these structures can yield myriad environmental benefits, in particular, addressing UN SDG 14: Life below water. Whilst GGI has shown great promise and there is a growing evidence base, there remain many criticisms and knowledge gaps, and some feel that there is scope for GGI to be abused by developers to facilitate harmful development. Given the surge of research in this field in recent years, it is timely to review the literature to provide an update update on the state-of-the-art of the field in relation to the many criticisms and identify remaining knowledge gaps. Despite the rapid and significant advances made in this field, there is currently a lack of science and practice outside of academic sectors in the developed world, and there is a collective need for schemes that encourage intersectoral and transsectoral research, knowledge exchange, and capacity building to optimize GGI in the pursuit of contributing to sustainable development.

Concrete is extensively used in coastal engineering and development which, in addition to its high carbon footprint, threatens intertidal habitats and ecosystems. Eco-engineering addresses this by designing habitat features into coastal infrastructure. The chemical bioreceptivity of cement has been shown to vary, but ordinary Portland cement is generally considered to be the least bioreceptive. In this study, we compare two low carbon mortars (a natural, single source cement (VP), and an ordinary Portland cement/ ground granulated blast furnace slag blend (GGBS)) with an ordinary Portland cement-based control mix (OPC). The three mortars were made into smooth blocks which were secured to crates and deployed subtidally in two estuary sites on the south UK coast for 1 year. At 3-, 6- and 12-months intervals a crate was recovered from each site and species abundance, biomass and assemblage composition were determined. After 12 months, the VP mortar was significantly more species rich than both the OPC control and GGBS mortar, and organisms were significantly more abundant (numeric counts only), though this varied by mortar and site. However, OPC controls showed significantly higher percentage cover of biota than both low carbon mixes in both harbours. Overall, the GGBS mortar showed the least bioreceptivity of all three mortars. It is evident that the primary chemical bioreceptivity of OPC, GGBS and VP is inconsistent between ecological metrics and study sites and that using lower carbon cements does not necessarily enhance colonisation. The primary chemical bioreceptivity of these mortars may therefore perform inconsistently and other intrinsic factors that impact bioreceptivity and primary succession, such as rugosity, should be prioritised when designing ecological enhancements. Sustainability of materials, such as opting for low carbon cements, should also be a priority.

Artificial coastal structures (ACSs) are primarily designed to provide services for human use, such as flood defence or shipping, and are generally poor for marine biodiversity. Consequently, there has been significant research effort to enhance these hard structures to increase biodiversity and habitat availability via eco-engineering. On seawalls and breakwaters, this has included the creation of habitats for benthic species found on natural rocky shores, including the provision of cracks, crevices and water retaining features, such as artificial rockpools. When sediment retention in these features has occurred, it has often been deemed detrimental to the overarching aim of the intervention. Yet, it is soft sediment habitat that is impacted the most through coastal construction. As ecological enhancement of a flood defence scheme, nine concrete retrofit rockpools were installed at three different tidal elevations between mean high water neap tide and mean tide level on steel sheet piling on the Arun Estuary in Littlehampton Harbour, United Kingdom, which naturally filled with mud 1 year after installation. To explore how analogous the faunal assemblages and sediment profile of rockpool mud were to two local mudflats, core samples were taken and analysed for species richness, abundance, biomass, assemblage structure, median grain size, and organic matter content. More benthic species were observed in the artificial rockpool than in the local mudflats. Although the rockpools were placed at higher tidal levels than the lower shore mudflat, their assemblage structure and species richness were more similar to the lower shore mudflat at the base of the sheet piling than the upper shore mudflat. This study demonstrates that retained sediment within eco-engineered features on hard ACSs can create habitat for benthic assemblages. Providing sediment-retentive features on ACSs has the potential to provide a novel eco-engineering option that may be appropriate for some heavily modified waterbodies on sheltered, depositional coasts.

Poole Harbour is protected and recognised, both nationally and internationally, for its ecological importance. However, it has also been classified as polluted and ‘eutrophic’. These twin designations – protected yet polluted – exemplify the condition of many English estuaries, making Poole Harbour a useful case study for elucidating the circumstances behind this apparent paradox.The outcome of a conference entitled ‘Spotlight on Poole Harbour: Environment & Economics’ organised by the Poole Harbour Study Group, this book consists of four main parts. After a short preamble, Part I, ‘Background’, provides a broad introduction to the harbour in terms of its pre-historical and historical significance for human communities and a conceptual overview of its modern character and uses. Part II, ‘Ecology’, contains chapters on subjects ranging from plankton to mammals. Insofar as they also consider anthropogenic aspects of the ecology, these contributions anticipate the remaining sections of the book, which deal specifically with aspects of the ecological service industries supported by Poole Harbour. Part III, ‘Fisheries’, covers recreational and commercial fishing and aquaculture, examining economic value and key shellfish species. Part IV, ‘Water Quality’, addresses those industries for which the harbour’s chemical and biological processes remediate various effluents, as well as some of the environmental consequences and noteworthy efforts to reduce such impacts. Part V, ‘Conclusion’, by the editors looks at certain general shortcomings of environmental legislation and regulation in the case of Poole Harbour. A central concern throughout is the question of sustainable development in coastal estuarine and marine contexts, making this far-reaching study relevant well beyond the bounds of its primary geographical focus. DOI: 10.53061/LGUG2858

The proliferation of artificial concrete structures (ACSs) in the marine environment causes intertidal habitat loss and is a poor surrogate for natural rocky shores in terms of species richness, abundance, and community composition. As hard engineered coastlines increase, there is growing interest in how new concrete structures can facilitate improved habitat and biodiversity compared to existing concrete structures. Experiments that have substituted cement binder and aggregates in varying proportions and combinations have demonstrated that it is possible to enhance the primary bioreceptivity of concrete, either chemically or via microtopographical texture. This review synthesises key literature and identifies which concrete formulas prove most effective at enhancing bioreceptivity and those that have limited value, providing recommendations for coastal practitioners and for formulas that warrant further study. It is evident that the efficacy of chemical bioreceptivity of concrete is likely to be spatio-temporally limited (months) and enhancing surface roughness should be prioritised as a way to enhance colonisation. However, both chemical and physical methods require further investigation in within in situ marine settings for longer durations (>12 months).

The deleterious effects (biodeterioration) and the protective benefits (bioprotection) of biological colonisation on manmade structures have long been debated. Lichens, biofilms, algae, bivalves and gastropods contribute both directly and indirectly to damaging substrata in the coastal zone which can enhance abiotic erosive forces that exploit biologically induced superficial damage. There is mounting evidence that these same species may also provide protective benefits. This debate often impacts approaches to managing fouling on concrete assets in the coastal environment. The net benefit or detriment a species or assemblage has on a structure is spatially and temporally dynamic and subject to the influence of various abiotic and biotic factors at different scales. However, the net outcome may be more pronounced under different contexts, particularly under warming and ocean acidifying climate change scenarios which is where further research should focus. Additionally, as bioprotection represents a potentially valuable ecosystem service, it supports the argument for increasing and improving habitat availability and biodiversity on artificial coastal structures via ecological enhancement. Quantifying bioprotection in useful metrics, such as monetary value or time added to serviceable life, would help demonstrate the benefits of bioprotective species in a meaningful way. Outline:

To ensure ecological resilience to environmental change, Marine Protected Area networks will require a proactive response to new conditions that will maintain ecosystem functionality, connectivity and adaptive capacity. Coastal lagoons are a Priority Habitat for conservation in Europe and protected in many regions, yet they are especially vulnerable to the potential impacts of climate change and specifically rising sea levels. As relatively small and closed environments, the risk of extinction of specialised benthic invertebrates and algal species is high and the rate of recolonisation of biota following disturbances may be low. Here we report on a variety of approaches and cases studies aimed at maintaining ecosystem resilience in Poole Harbour Special Protection Area (SPA) on the south coast of England by (i) creating new lagoon habitats (ii) restoring undesignated, degraded and polluted lagoons (iii) identifying and survey new coastal lagoon habitats. Although sea level rise presents considerable challenges for the conservation of these habitats, new managed realignment projects and set-back schemes offer significant opportunities for the creation of lagoons. A principle of continual review, monitoring and pro-active spatial planning needs to be extended to the design of other regional and national coastal MPA networks to maintain ecosystem integrity and resilience.

To ensure ecological resilience to environmental change, Marine Protected Area networks will require a proactive response to new conditions that will maintain ecosystem functionality, connectivity and adaptive capacity. Coastal lagoons are a Priority Habitat for conservation in Europe and protected in many regions, yet they are especially vulnerable to the potential impacts of climate change and specifically rising sea levels. As relatively small and closed environments, the risk of extinction of specialised benthic invertebrates and algal species is high and the rate of recolonisation of biota following disturbances may be low. Here we report on a variety of approaches and cases studies aimed at maintaining ecosystem resilience in Poole Harbour Special Protection Area (SPA) on the south coast of England by (i) creating new lagoon habitats (ii) restoring undesignated, degraded and polluted lagoons (iii) identifying and survey new coastal lagoon habitats. Although sea level rise presents considerable challenges for the conservation of these habitats, new managed realignment projects and set-back schemes offer significant opportunities for the creation of lagoons. A principle of continual review, monitoring and pro-active spatial planning needs to be extended to the design of other regional and national coastal MPA networks to maintain ecosystem integrity and resilience.