Life cycle informed restoration: Engineering settlement substrate material characteristics and structural complexity for reef formation

A global synthesis of predation on bivalves

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer-reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non-native bivalves and non-native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions.

Using waste biomass to produce 3D-printed artificial biodegradable structures for coastal ecosystem restoration

The loss of ecosystem functions and services caused by rapidly declining coastal marine ecosystems, including corals and bivalve reefs and wetlands, around the world has sparked significant interest in interdisciplinary methods to restore these ecologically and socially important ecosystems. In recent years, 3D-printed artificial biodegradable structures that mimic natural life stages or habitat have emerged as a promising method for coastal marine restoration. The effectiveness of this method relies on the availability of low-cost biodegradable printing polymers and the development of 3D-printed biomimetic structures that efficiently support the growth of plant and sessile animal species without harming the surrounding ecosystem. In this context, we present the potential and pathway for utilizing low-cost biodegradable biopolymers from waste biomass as printing materials to fabricate 3D-printed biodegradable artificial structures for restoring coastal marine ecosystems. Various waste biomass sources can be used to produce inexpensive biopolymers, particularly those with the higher mechanical rigidity required for 3D-printed artificial structures intended to restore marine ecosystems. Advancements in 3D printing methods, as well as biopolymer modifications and blending to address challenges like biopolymer solubility, rheology, chemical composition, crystallinity, plasticity, and heat stability, have enabled the fabrication of robust structures. The ability of 3D-printed structures to support species colonization and protection was found to be greatly influenced by their biopolymer type, surface topography, structure design, and complexity. Considering limited studies on biodegradability and the effect of biodegradation products on marine ecosystems, we highlight the need for investigating the biodegradability of biopolymers in marine conditions as well as the ecotoxicity of the degraded products. Finally, we present the challenges, considerations, and future perspectives for designing tunable biomimetic 3D-printed artificial biodegradable structures from waste biomass biopolymers for large-scale coastal marine restoration.

Restoration ecology meets design-engineering: Mimicking emergent traits to restore feedback-driven ecosystems

Ecosystems shaped by habitat-modifying organisms such as reefs, vegetated coastal systems and peatlands, provide valuable ecosystem services, such as carbon storage and coastal protection. However, they are declining worldwide. Ecosystem restoration is a key tool for mitigating these losses but has proven failure-prone, because ecosystem stability often hinges on self-facilitation generated by emergent traits from habitat modifiers. Emergent traits are not expressed by the single individual, but emerge at the level of an aggregation: a minimum patch-size or density-threshold must be exceeded to generate self-facilitation. Self-facilitation has been successfully harnessed for restoration by clumping transplanted organisms, but requires large amounts of often-limiting and costly donor material. Recent advancements highlight that kickstarting self-facilitation by mimicking emergent traits can similarly increase restoration success. Here, we provide a framework for combining expertise from ecologists, engineers and industrial product designers to transition from trial-and-error to emergent trait design-based, cost-efficient approaches to support large-scale restoration.

Exposure to Alexandrium spp. impairs the development of Green-lipped mussel (Perna canaliculus) embryos and larvae

The green-lipped mussel (GLM) Perna canaliculus is an economically, ecologically, and culturally important species in Aotearoa New Zealand. Since 2011, harmful algal blooms (HABs) of Alexandrium spp. have occurred annually in the Marlborough Sounds, the largest GLM aquaculture region in New Zealand. Across a similar timeframe, there has been a severe reduction in wild spat (juvenile mussel) catch. This research investigated the effects of Alexandrium pacificum (which produces paralytic shellfish toxins; PSTs) and A. minutum (a non-producer of PSTs) on the development of four GLM larval life stages (gametes, embryos, D-stage and settlement). Early life stages of GLM were exposed to environmentally relevant concentrations of Alexandrium spp. as whole cell, lysate and filtrate treatments. A 48-h exposure of embryos to whole A. pacificum cells at 500 cells mL-1 caused lysis of embryos, severe abnormalities, and reduced development through to veliger (D-stage) larvae by 85%. GLM growth was impaired at cell concentrations as low as 250 cells mL-1 during a 4-day exposure of D-stage larvae to both Alexandrium spp. Exposure of GLM to both whole and lysed treatments of Alexandrium spp. at 500 cells mL-1 resulted in halved larval growth rates (2.00 µm day-1 vs 4.48 µm day-1 in the control) and growth remained impeded during a 4-day recovery period. Both A. pacificum and A. minutum were found to negatively impact D-larvae. Both whole-cell and lysed-cell treatments of A. pacificum had similar negative effects, suggesting that Alexandrium spp. toxicity to D-larvae is independent of PSTs. Additionally, cell membrane-free treatments of A. pacificum had no negative effects on embryo development, indicating that cell surface-associated bioactive compounds may be responsible for the observed negative effects during this early life stage. Conversely, non-PST-producing A. minutum was toxic to D-stage larvae but not to embryos; larval growth was reduced following a brief 1 h exposure of sperm to cell membrane-free treatments of A. pacificum. No effects were recorded in GLM larvae exposed during settlement, highlighting the potential for differences in susceptibility of early life stages to Alexandrium spp. exposure and the influence of exposure durations. In the wild, blooms of Alexandrium spp. can persist for several months, reaching cell densities higher than those investigated in the present study, and as such may be detrimental to the vulnerable early life stages of GLM.

Unraveling the wheel of recruitment for salt-marsh seedlings: Resistance to and recovery after dislodgement

Elucidating bottlenecks at critical life stages and quantifying associated resilience (including resistance and recovery) to physical processes are central in inform restoration and attain sustainable development of coastal biogeomorphic ecosystems. Seedling establishment is a key life stage determines saltmarsh restoration potentials. However, the resilience of these recruits, especially through recovery, remains poorly understood. Here, two contrasting globally occurring saltmarsh species, namely Salicornia europaea and Spartina anglica, were employed to generate insights in i) seedling resistance against dislodgement, and ii) seedling recovery potential after dislodgement. Regarding resistance, we found that 1) root-shoot antagonism characterizes the growth rate of seedling resistance to dislodgement through hydraulic disturbance, 2) the root length determines seedling resistance to dislodgement through sheet erosion; 3) a 5 mm sedimentary setting amplifies seedling resistance without inhibiting their morphological evolution. Regarding recovery, we found that 4) dislodged seedlings have a high probability for achieving long-distance dispersal; 5) seedling age and the inundation-free period regulate the re-establishment potential of dislodged seedlings. Overall, S. anglica showed stronger resilience than S. europaea, characterized by stronger seedling resistance against dislodgement and higher re-establishment potential. Our results on seedling resilience suggest that seedling dislodgement is not an end-of-life cycle but a new spin on the "Wheel of Recruitment", a proposed short-term cyclic behavior with alternating phases of seedling dislodgement, dispersal, and (re-)establishment. The Wheel of Recruitment concept is important for forecasting resilience and persistence of biogeomorphic systems such as salt marshes under global change and for guiding life cycle informed restoration.