Food web structure and ecosystem multifunctionality in a subsidized coastal ecosystem – Nature

Report on the Role of Marine Subsidies in Coastal Ecosystem Function and Structure

Executive Summary

This report examines the critical role of cross-ecosystem resource subsidies in supporting coastal biodiversity and functionality, with a direct focus on achieving the United Nations Sustainable Development Goals (SDGs). The study reveals that marine macrophyte wrack, originating from productive kelp forests, is a fundamental driver of community structure and ecosystem multifunctionality in sandy beach ecosystems. These findings highlight the profound interconnectedness of marine environments and underscore the vulnerability of recipient ecosystems to threats impacting donor ecosystems, such as climate change. The strong positive relationship between resource availability, biodiversity, and ecosystem health has significant implications for policies aimed at achieving SDG 14 (Life Below Water), SDG 13 (Climate Action), and SDG 15 (Life on Land). Protecting donor foundation species and maintaining ecological connectivity are paramount for the resilience of coastal zones and the sustainable services they provide.

Introduction: Coastal Ecosystems and the Sustainable Development Goals

Global ecosystems face unprecedented threats from anthropogenic pressures, including climate change and local development, jeopardizing biodiversity and the essential functions that support human well-being. This challenge is central to the 2030 Agenda for Sustainable Development. This report analyzes the dynamics of subsidized coastal ecosystems—specifically sandy beaches—which rely on external resources for primary production. The investigation aligns with the urgent need to understand the drivers of ecosystem health to better inform conservation strategies that support global sustainability targets.

The Challenge: Threats to Marine and Coastal Biodiversity (SDG 14 & SDG 15)

The degradation of coastal habitats directly threatens the achievement of multiple SDGs. Key challenges include:

• Biodiversity Loss: Climate-driven changes and habitat destruction are reducing biodiversity in both marine and terrestrial environments, undermining the targets of SDG 14 (Life Below Water) and SDG 15 (Life on Land).
• Ecosystem Function Collapse: The loss of species and altered community structures disrupt critical ecosystem functions such as nutrient cycling, secondary production, and the stability of food webs.
• Disrupted Connectivity: Many ecosystems, particularly those with low internal production like sandy beaches, depend on resource subsidies from adjacent, more productive ecosystems. Threats to these “donor” systems can trigger cascading failures in “recipient” systems.

The Role of Ecosystem Connectivity in Sustainable Development

This study hypothesized that marine macrophyte wrack, a subsidy from productive nearshore kelp forests, is a primary driver of the structure and function of sandy beach ecosystems. Understanding this linkage is crucial, as climate change is projected to alter the productivity and distribution of foundation species like giant kelp, thereby affecting the stability of the entire coastal seascape. This analysis provides a framework for evaluating how protecting one ecosystem can generate co-benefits for another, a vital consideration for integrated coastal zone management.

Study Findings: The Critical Role of Marine Subsidies

The study, conducted across 24 sandy beach sites, confirmed that the abundance of marine wrack subsidies is a powerful predictor of biodiversity and ecosystem health. The findings demonstrate a clear bottom-up control mechanism where resources from a donor ecosystem dictate the vitality of a recipient ecosystem.

Impact on Biodiversity and Food Web Structure (SDG 14 & SDG 15)

The availability of wrack as a basal resource directly supported a complex, multi-trophic food web, contributing directly to the conservation targets of SDG 14 and SDG 15.

1. Macroinvertebrate Communities: Wrack abundance had a strong positive effect on the diversity and biomass of both detritivorous (resource-consuming) and predatory macroinvertebrates. This demonstrates that the subsidy supports multiple levels of the food web.
2. Top Predators (Shorebirds): The diversity and abundance of shorebirds, key predators in the beach ecosystem, were significantly correlated with the availability of wrack and their macroinvertebrate prey. This finding links the health of subtidal kelp forests directly to the viability of avian populations, which are an integral part of coastal biodiversity under SDG 15.
3. Trophic Linkages: Structural equation modeling revealed that wrack abundance directly enhanced detritivore diversity and the biomass of both detritivores and predators. This confirms that the resource subsidy underpins the entire food web structure.

Enhancement of Ecosystem Multifunctionality

Ecosystem multifunctionality, an integrated measure of overall ecosystem health, was strongly influenced by wrack subsidies. This metric combines several key processes vital for a resilient and sustainable environment.

• Measured Functions: The study assessed five critical ecosystem functions:
  • Nutrient cycling (dissolved inorganic nitrogen)
  • Community respiration (sediment CO2 flux)
  • Secondary production (talitrid amphipods)
  • Food availability for predators (flying insect abundance)
  • Energy flow to top predators (shorebird energy requirements)
• Key Finding: Both resource inputs (wrack) and biodiversity were significant predictors of ecosystem multifunctionality. However, the role of biodiversity was itself strongly underpinned by the availability of wrack. This indicates that maintaining the flow of resources is a prerequisite for a high-functioning, biodiverse ecosystem capable of delivering services aligned with the SDGs.

Implications for Sustainable Development and Climate Action

The findings of this report carry significant weight for conservation policy and management, particularly in the context of global environmental change. The high degree of coupling between coastal ecosystems means that management actions must be integrated across ecosystem boundaries.

Cascading Effects of Climate Change (SDG 13)

The dependence of sandy beaches on kelp forest subsidies makes them highly vulnerable to the impacts of climate change, a core concern of SDG 13 (Climate Action).

• Threats to Donor Ecosystems: Warming ocean temperatures and increased storm frequency are projected to reduce the extent and productivity of giant kelp forests.
• Cascading Impacts: A decline in kelp will lead to a reduction in wrack subsidies, which this study shows would severely degrade the biodiversity and functionality of adjacent sandy beaches. This cascading effect could lead to wildlife declines and the loss of critical ecosystem services.
• Compounding Pressures: These climate impacts are compounded by sea-level rise and coastal development, which reduce the available habitat for beach ecosystems to exist, further threatening their long-term viability.

Policy and Management Recommendations for Achieving SDG 14 and SDG 15

To safeguard coastal ecosystems and make progress on SDG 14 and SDG 15, management strategies must recognize and protect cross-ecosystem connectivity.

1. Adopt an Ecosystem-Based Approach: Conservation efforts for coastal species and habitats must consider the linkages between different ecosystems. Protecting sandy beach biodiversity requires the simultaneous protection of nearshore kelp forests.
2. Prioritize Foundation Species: Marine foundation species, such as giant kelp, provide benefits that extend far beyond their immediate habitat. Their role as a source of detrital subsidies makes their conservation a high-leverage action for regional coastal health.
3. Integrate Climate Resilience: Coastal management plans must account for the cascading impacts of climate change. This includes actions to mitigate climate change and strategies to enhance the resilience of both donor and recipient ecosystems.

Conclusion

This report provides compelling evidence that the structure and function of subsidized coastal ecosystems are fundamentally driven by resource inputs from adjacent marine foundation species. The health of sandy beaches is inextricably linked to the vitality of nearshore kelp forests. This interconnectedness highlights a critical vulnerability in the face of climate change but also presents an opportunity for more effective, integrated conservation. Achieving the Sustainable Development Goals, particularly SDG 14 (Life Below Water) and SDG 13 (Climate Action), requires a holistic understanding of ecological connectivity and management actions that protect the vital flows of resources across ecosystem boundaries.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 14: Life Below Water

   This goal is central to the article, which focuses on the health and functioning of coastal and marine ecosystems. The study examines how marine foundation species, specifically “giant kelp (Macrocystis pyrifera) and surfgrass (Phyllospadix spp.)” from nearshore kelp forests, are fundamentally linked to the health of adjacent sandy beach ecosystems. The article highlights the “highly coupled nature of these coastal ecosystems,” demonstrating how impacts on the marine “donor ecosystems” (kelp forests) directly affect the recipient coastal ecosystems.

2. SDG 15: Life on Land

   The article directly addresses this goal by studying the “recipient beach ecosystem structure and function.” Sandy beaches are terrestrial ecosystems at the land-sea interface. The research quantifies the biodiversity (“detritivorous and predatory macroinvertebrates,” “shorebirds”), food web structure, and overall ecosystem health on land, showing how these are dependent on marine inputs. It warns that threats could lead to “wildlife declines and species extinctions” in these terrestrial coastal habitats.

3. SDG 13: Climate Action

   This goal is addressed through the article’s discussion of threats to coastal ecosystems. It explicitly states that these systems face growing threats from “global climate change.” It details how “climate change is projected to reduce the subsidy supply in many areas as macrophyte productivity declines due to warming and increased storm disturbance” and how “sea level rise” contributes to habitat loss. This frames the entire ecological study within the context of climate change impacts and the need to understand ecosystem resilience.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Under SDG 14: Life Below Water

   • Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.
     
     Explanation: The article’s entire premise is to understand the functioning of coupled marine (kelp forest) and coastal (sandy beach) ecosystems. It concludes that “As impacts to donor ecosystems can cascade to recipient ecosystems, predicted declines of giant kelp carry significant implications not only for subtidal reefs, but also for kelp subsidy-dependent intertidal systems.” This knowledge is essential for managing and protecting these ecosystems to avoid adverse impacts.

2. Under SDG 15: Life on Land

   • Target 15.1: By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains and drylands, in line with obligations under international agreements.
     
     Explanation: The study focuses on the conservation of sandy beaches, which are terrestrial coastal ecosystems. By quantifying how “wrack abundance had a strong positive effect on beach food web diversity and biomass,” the article provides a scientific basis for conservation strategies that must account for the cross-ecosystem connections that sustain these environments.
   • Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species.
     
     Explanation: The article directly addresses biodiversity loss by measuring species richness, abundance, and biomass of macroinvertebrates and shorebirds. It warns that the “loss of kelp subsidies could result in fundamental ecosystem changes including wildlife declines and species extinctions,” highlighting the urgency of action to protect these habitats and their biodiversity.

3. Under SDG 13: Climate Action

   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.
     
     Explanation: The article identifies climate-related hazards such as “warming,” “increased storm disturbance,” and “sea level rise” as major threats. By demonstrating the critical role of kelp subsidies, the research provides crucial insights for developing strategies to strengthen the resilience of coastal ecosystems, which are vulnerable to these climate impacts.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article explicitly measures and discusses several quantitative indicators that can be used to assess ecosystem health, biodiversity, and functioning, which are crucial for tracking progress towards the identified targets.

1. Indicators for Biodiversity (Targets 14.2, 15.5)

   • Species Richness: The study measured “species richness of macroinvertebrates” (ranging from 4 to 15 species) and “shorebird richness” (ranging from 0.7 to 8.2 species km⁻¹). This is a direct measure of biodiversity.
   • Species Abundance: The article quantified the abundance of key trophic groups, including “macroinvertebrate…abundance” (ranging from 1,057 to 53,720 individuals m⁻¹) and “shorebird abundance” (ranging from 1 to 172.4 individuals km⁻¹).
   • Biomass: The study measured the “biomass of the invertebrate community,” which is an indicator of the ecosystem’s productivity and ability to support a food web.

2. Indicators for Ecosystem Functioning and Health (Targets 14.2, 15.1)

   • Ecosystem Multifunctionality Index: The researchers created a composite index to “provide a more integrated index of functioning.” They calculated that “Ecosystem multifunctionality…ranged from 0.1 to 0.77 (on a scale of 0–1) among beaches,” providing a holistic indicator of ecosystem health.
   • Nutrient Cycling: Measured as “Nutrient concentrations (total dissolved inorganic nitrogen or DIN) in beach pore water,” this indicates the ecosystem’s capacity to process organic matter.
   • Community Respiration: Measured as the “flux of CO₂ from intertidal sediment,” this reflects the metabolic activity of the beach community, including decomposition.
   • Secondary Production: The study estimated the “secondary production of talitrid amphipods,” a key measure of energy transfer from basal resources (wrack) to higher trophic levels.

3. Indicators of Ecosystem Connectivity and Resilience (Targets 13.1, 14.2)

   • Abundance of Marine Wrack Subsidy: The primary independent variable, “wrack abundance, measured as percent cover,” serves as a direct indicator of the connectivity between the marine donor ecosystem and the terrestrial recipient ecosystem. Its decline, as projected by climate change models, would indicate a loss of resilience.

4. Table of SDGs, Targets, and Indicators

Source: nature.com