Elevated micro-topography boosts growth rates in <i>Salicornia procumbens</i> by amplifying a tidally driven oxygen pump:Implications for natural recruitment and restoration

• Background and Aims: The growth rate of pioneer species is known to be a critical component determining recruitment success of marsh seedlings on tidal flats. By accelerating growth, recruits can reach a larger size at an earlier date, which reduces the length of the disturbance-free window required for successful establishment. Therefore, the pursuit of natural mechanisms that accelerate growth rates at a local scale may lead to a better understanding of the circumstances under which new establishment occurs, and may suggest new insights with which to perform restoration. This study explores how and why changes in local sediment elevation modify the growth rate of recruiting salt marsh pioneers. • Methods: A mesocosm experiment was designed in which the annual salt marsh pioneer Salicornia procumbens was grown over a series of raised, flat and lowered sediment surfaces, under a variety of tidal inundation regimes and in vertically draining or un-draining sediment. Additional physical tests quantified the effects of these treatments on sediment water-logging and oxygen dynamics, including the use of a planar optode experiment. • Key Results: In this study, the elevation of sediment micro-topography by 2 cm was the overwhelming driver of plant growth rates. Seedlings grew on average 25 % faster on raised surfaces, which represented a significant increase when compared to other groups. Changes in growth aligned well with the amplifying effect of raised sediment beds on a tidally episodic oxygenation process wherein sediment pore spaces were refreshed by oxygen-rich water at the onset of high tide. • Conclusions: Overall, the present study suggests this tidally driven oxygen pump as an explanation for commonly observed natural patterns in salt marsh recruitment near drainage channels and atop raised sediment mounds and reveals a promising way forward to promote the establishment of pioneers in the field

Thermal stress affects bioturbators' burrowing behavior:A mesocosm experiment on common cockles (<i>Cerastoderma edule</i>)

The intensity of marine heatwaves is increasing due to climate change. Heatwaves may affect macroinvertebrates' bioturbating behavior in intertidal areas, thereby altering the deposition-erosion balance at tidal flats. Moreover, small-scale topographic features on tidal flats can create tidal pools during the low tide, thus changing the heat capacity of tidal flats. These pools could then potentially operate as refuge environments during marine heatwaves. We studied behavior responses to heat waves using the well-known bioturbating cockle Cerastoderma edule as a model species. Different temperature regimes (i.e., fluctuating between 20 and 40 °C) and micro-topographies (i.e., presence vs. absence of tidal water pools) were mimicked in a mesocosm experiment with regular tidal regimes. Our results demonstrate that behavioral responses to heat stress strongly depend on the site-specific morphological features. Cockles covered by shallow water pools moved up when exposed to thermal stress, while burrowing deeper into the sediment in the absence of water pools. But in both cases, their migratory behavior increased under heat stress compared to regular ambient treatments. Moreover, long-term cumulative heat stress increased cockles' respiration rates and decreased their health conditions, causing mass mortality after four weeks of gradually increasing heat exposure. Overall, the present findings provide the first insights into how bioturbating behavior on tidal flats may change in response to global warming

The role of seasonality in reproduction of multiannual delayed gametophytes of <i>Saccharina latissima</i>

Delayed gametophytes are able to grow vegetatively for prolonged periods of time. As such, they are potentially very valuable for kelp aquaculture given their great promise in opening up novel opportunities for kelp breeding and farming. However, large-scale application would require more in-depth understanding of how to control reproduction in delayed gametophytes. For newly formed gametophytes, many environmental factors for reproduction have been identified, with key drivers being light intensity, temperature, and the initial gametophyte density. However, the question of whether delayed gametophytes react similarly to these life cycle controls remains open for exploration. In this study, we performed a full factorial experiment on the influences of light intensity, temperature, and density on the reproduction of multiannual delayed gametophytes of Saccharina latissima, during which the number of sporophytes formed was counted. We demonstrate that delayed gametophytes of S. latissima can reliably reproduce sexually after more than a year of vegetative growth, depending on the effects between light intensity and temperature. Under higher light intensities (≥29 µmol photons · m-2 · s-1 ), optimal reproduction was observed at lower temperatures (10.2°C), while at lower light intensities (≤15 µmol photons · m-2 · s-1 ), optimal reproduction was observed at higher temperatures (≥12.6°C). Given the seasonal lag between solar radiation and sea surface temperature in natural systems, these conditions resemble those found during spring (i.e., increasing light intensity with low temperatures) and autumn (i.e., decreasing light intensity with higher temperatures). Seasonality can be used as an aquaculture tool to better control the reproduction of delayed gametophytes

Growth forms and life-history strategies predict the occurrence of aquatic macrophytes in relation to environmental factors in a shallow peat lake complex

Aquatic ecosystems provide vital services, and macrophytes play a critical role in their functioning. Conceptual models indicate that in shallow lakes, plants with different growth strategies are expected to inhabit contrasting habitats. For shallow peat lakes, characterized by incohesive sediments, roles of growth forms, life-history strategies and environmental factors in determining the occurrence of aquatic vegetation remain unknown. In a field survey, we sampled 64 points in a peat lake complex and related macrophyte occurrence to growth forms (floating-leaved rooted and submerged), life-history strategies for overwintering (turions, seeds, rhizomes) and environmental factors (water depth, fetch, and porewater nutrients). Our survey showed that macrophyte occurrence relates to water depth, wind-fetch, and nutrients, and depends on growth form and life-history strategies. Specifically, rooted floating-leaved macrophytes occur at lower wind-fetch/shallower waters. Submerged macrophytes occur from low to greater wind-fetch/water depth, depending on life-history strategies; macrophytes with rhizomes occur at greater wind-fetch/depth relative to species that overwinter with seeds or turions. We conclude that growth form and life-history strategies for overwintering predict macrophytes occurrence regarding environmental factors in peat lakes. Therefore, we propose an adapted model for macrophyte occurrence for such lakes. Altogether, these results may aid in species-selection to revegetate peat lakes depending on its environment

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

Ecosystems are degrading world-wide, with severe ecological and economic consequences. Restoration is becoming an important tool to regain ecosystem services and preserve biodiversity. However, in harsh ecosystems dominated by habitat-modifying organisms, restoration is often expensive and failure prone. Establishment of such habitat modifiers often hinges on self-facilitation feedbacks generated by traits that emerge when individuals aggregate, causing density- or patch size-dependent establishment thresholds. To overcome these thresholds, adult or juvenile habitat-forming species are often transplanted in clumped designs, or stress-mitigating structures are deployed. However, current restoration approaches focus on introducing or facilitating a single life stage, while many habitat modifiers experience multiple bottlenecks throughout their life as they transition through sequential life stages. Here, we define and experimentally test ‘life cycle informed restoration’, a restoration concept that focuses on overcoming multiple bottlenecks throughout the target species’ lifetime. To provide proof of concept, and show its general applicability, we carried out complementary experiments in intertidal soft-sediment systems in Florida and the Netherlands where oysters and mussels act as reef-building habitat modifiers. We used biodegradable structures designed to facilitate bivalve reef recovery by both stimulating settlement with hard and fibrous substrates and post-settlement survival by reducing predation. Our trans-Atlantic experiments demonstrate that these structures enabled bivalve reef formation by: (a) facilitating larval recruitment via species-specific settlement substrates, and (b) enhancing post-settlement survival by lowering predation. In the Netherlands, structures with coir rope most strongly facilitated mussels by providing fibrous settlement substrate, and predation-lowering spatially complex hard attachment substrate. In Florida, oysters were greatly facilitated by hard substrates, while coir rope proved unbeneficial. Synthesis and applications. Our findings demonstrate that artificial biodegradable reefs can enhance bivalve reef restoration across the Atlantic by mimicking emergent traits that ameliorate multiple bottlenecks over the reef-forming organism’ life cycle. This highlights the potential of our approach as a cost-effective and practical tool for nature managers to restore systems dominated by habitat modifiers whose natural recovery is hampered by multiple life stage-dependent bottlenecks. Therefore, investment in understanding how to achieve life cycle informed restoration on larger scales and whether the method it is applicable to restore other ecosystems is now required

Initiating and upscaling mussel reef establishment with life cycle informed restoration:Successes and future challenges

Worldwide, coastal ecosystems are rapidly degrading in quality and extent. While novel restoration designs include facilitation to enhance restoration success in stressful environments, they typically focus on a single life-stage, even though many organisms go through multiple life-stages accompanied by different bottlenecks. A new approach – life cycle informed restoration – was designed to ameliorate multiple bottlenecks throughout an organism's life cycle. It has successfully been tested on a small scale to facilitate intertidal bivalve reef formation in the Netherlands and Florida. Yet, it remains unknown whether this approach can be scaled to ecosystem-relevant scales. To test whether life cycle informed restoration is upscalable, we conducted a large-scale restoration experiment using blue mussel reefs as a model system. In our experiment, we used biodegradable structures to temporarily facilitate mussel reef formation by providing early-life settlement substrates, and subsequently, reduce post-settlement predation on an intertidal flat in the Wadden Sea, the Netherlands. The structures were placed in 10 × 20 m plots, mimicking bands found in natural mussel beds, spread out across 650 m, and were followed for two years. Our results show that the structures enhance mussel biomass (0.7 ± 0.2 kg DW m−2), as mussels were absent in bare plots. However, biomass varied within plots; in intact structures it was 60 times higher (1.2 ± 0.2 kg DW m−2) than in those that became buried (0.02 ± 0.009 kg DW m−2). Next to burial, 18–46% of the structures were lost due to technical failure, especially during winters at this exposed site. We show that the life cycle informed restoration principle works, but we encountered technical challenges due to larger scale processes (e.g. sedimentation). Furthermore, environmental information is essential for site selection, and for restoration, the functioning of such structures should be tested under extreme conditions before upscaling

Mimicry of emergent traits amplifies coastal restoration success

Contains fulltext : 221224.pdf (publisher's version ) (Open Access

A probabilistic framework for windows of opportunity: the role of temporal variability in critical transitions

The establishment of young organisms in harsh environments often requires a window of opportunity (WoO). That is, a short time window in which environmental conditions drop long enough below the hostile average level, giving the organism time to develop tolerance and transition into stable existence. It has been suggested that this kind of establishment dynamics is a noise-induced transition between two alternate states. Understanding how temporal variability (i.e. noise) in environmental conditions affects establishment of organisms is therefore key, yet not well understood or included explicitly in the WoO framework. In this paper, we develop a coherent theoretical framework for understanding when the WoO open or close based on simple dichotomous environmental variation. We reveal that understanding of the intrinsic timescales of both the developing organism and the environment is fundamental to predict if organisms can or cannot establish. These insights have allowed us to develop statistical laws for predicting establishment probabilities based on the period and variance of the fluctuations in naturally variable environments. Based on this framework, we now get a clear understanding of how changes in the timing and magnitude of climate variability or management can mediate establishment chances

A probabilistic framework for windows of opportunity: the role of temporal variability in critical transitions

The establishment of young organisms in harsh environments often requires a window of opportunity (WoO). That is, a short time window in which environmental conditions drop long enough below the hostile average level, giving the organism time to develop tolerance and transition into stable existence. It has been suggested that this kind of establishment dynamics is a noise-induced transition between two alternate states. Understanding how temporal variability (i.e. noise) in environmental conditions affects establishment of organisms is therefore key, yet not well understood or included explicitly in the WoO framework. In this paper, we develop a coherent theoretical framework for understanding when the WoO open or close based on simple dichotomous environmental variation. We reveal that understanding of the intrinsic timescales of both the developing organism and the environment is fundamental to predict if organisms can or cannot establish. These insights have allowed us to develop statistical laws for predicting establishment probabilities based on the period and variance of the fluctuations in naturally variable environments. Based on this framework, we now get a clear understanding of how changes in the timing and magnitude of climate variability or management can mediate establishment chances.</p

The SeaCoRe system for large scale kelp aquaculture: a plug-and-play, compatible, open-source system for the propagation and transport of clonal gametophyte cultures

The future of large-scale kelp aquaculture is standing at a crossroad, with the diverging paths being characterized by two fundamentally different cultivation methods that differ on how well gametophyte reproduction can be controlled. The cultivation method that does not directly control gametophyte reproduction is more widely utilized at the moment, but interest in better controlling gametophyte reproduction is growing steadily. Here, we validate a bioreactor system that overcomes a number of implementation challenges for this controlled reproductive method, expanding the possibility of clonal gametophyte cultivation outside of expensive laboratory settings. The main goals of this system include (i) the maintenance of clean gametophyte clonal cultures in non-sterile environments over prolonged periods of time, (ii) the production of large numbers of juvenile sporophytes, and (iii) effective transportation of gametophytes and sporophytes. The “SeaCoRe system” consists out of three parts that correspond to these three challenges: (1) clone-reactors, (2) a clone-inducer, and (3) a transporter. The validation of the system showed that delayed Saccharina latissima and Alaria esculenta gametophytes can grow reliably for 75 days in the clone-reactors. Initial gametophyte densities of 0.4 mg DW and 0.6 mg DW gametophtyes mL−1 were optimal for S. latissima and A. esculenta, resulting in reproductive successes of 604 and 422 sporophytes mL−1, respectively. Lastly, gametophyte transport was simulated, with high reproductive success still achieved within 19 days in ~ 20 °C environments. The SeaCoRe system helps unlock the full potential of large-scale kelp cultivation using multiannual delayed clonal