Introduction New Zealand’s coastal environments –including beaches, harbours, estuaries, and rocky shores – support over 17,000 marine species and hold significant cultural and economic value (Department of Conservation, 2023). These dynamic systems are subject to multiple pressures, necessitating robust ecological impact assessments (EcIAs) under the Resource Management Act 1991 (RMA). Despite signalled legislative changes with anticipated simplification of the consenting process, a future system is likely to still require robust assessments of the coastal environment in the foreseeable future. Assessment processes, however, are complicated by challenges in adequately characterising these complex habitats at different scales and in detecting both near and far field cumulative effects. This is particularly apparent when working within the constraints of significant data gaps, restricted budgets and tight timeframes.
Complexity of Coastal Environments Coastal habitats are characterised by their heterogeneity, with ecological processes driven by tides, currents, weather, sediment dynamics and nutrient cycling. Spanning over 15,000 km, New Zealand’s coastline includes over 50 recognised habitat types, from subtropical reefs to subantarctic kelp forests, supporting interconnected species like shellfish, fish, marine mammals and seabirds (NIWA, 2023a). The overlap of terrestrial and marine influences, direct and indirect effects, combined with legislative complexities, creates a system where small changes can have wide-ranging and cascading effects, making assessing cumulative impact, and appropriately managing those effects, acutely challenging.
Pressures on Coastal Environments Coastal ecosystems face pressures from a variety of stressors including our changing climate, urbanisation, coastal development, resource extraction (such as fishing pressures and sand mining), aquaculture, shipping, as well as recreation and tourism. Around 70% of New Zealanders live within 5 km of the coast and, while improvements have been made, many of our treated wastewater systems, industrial and stormwater discharges, together with sedimentation and nutrients from our land use practices, end up in the coastal environment; the very places where we choose to live, work and play. These pressures interact, with the potential for amplifying impacts in synergistic fashion. This necessitates a consideration of cumulative effects across habitats and multiple spatial and temporal scales in coastal EcIAs.
Challenges in Characterising Habitats at Varying Scales Characterising coastal habitats at different spatial (local to regional) and temporal (daily to decadal) scales is complex. For instance, de Luca (2019) argues that a coastal development might have minimal impact at a “harbour scale”, but significant effects at an “embayment scale.” Temporally, assessments must account for short-term disturbances and perturbations, while also attempting to account for long-term trends like habitat loss that may be driven by pressures from overlapping usage, and radically different activities (e.g. structures, point source discharges and diffuse run off discharges), or from sea level fluctuations and changing climate.
In general, there is a lack of standardised guidance, high field survey costs, and the need for engagement with iwi partners and other stakeholders—factors which influence the cost-effectiveness and timeframe requirements for assessments. An explicit focus on the elements that govern the rates of change in ecological status (both positive and negative) provide opportunities to assess impacts and the most appropriate management actions even when data quantity and quality are low (Gladstone-Gallagher et al, 2024).
Challenges in Detecting and Quantifying Cumulative Effects in EcIAs Cumulative effects come from incremental, accumulating, and/or interacting stressors from human activities and natural events. These events can overlap in space and time (Rojas-Nazar et al., 2023). Detecting and quantifying these cumulative effects over multiple time scales of past, present, and reasonably foreseeable future actions, is one of the most significant challenges in coastal EcIAs. Several specific challenges emerge:
Data Limitations and Baseline Uncertainty: Cumulative effects require a clear understanding of baseline conditions, but historical data for coastal ecosystems is often sparse or inconsistent. In addition, large bodies of potentially useful and relevant information are often locked within “grey literature” as part of resource consent application or consent monitoring reports. For example, long-term trends in sediment quality or species abundance may be unknown, making it difficult to isolate the incremental contribution of a new project. Despite the efforts of Regional Councils in national State of Environment (SoE) reporting, the lack of widespread comprehensive monitoring programs for coastal areas exacerbates this issue.
Spatial and Temporal Scale Mismatches: Cumulative effects often manifest at scales larger or longer than individual project assessments or SoE monitoring programs. A single development might have negligible local impact, but when combined with regional developments or indirect stressors, the cumulative effect on water quality or habitat fragmentation can be severe. Temporally, short-term assessments may miss slow-onset impacts, such as gradual species decline due to cumulative pollution or habitat loss (Smith et al., 2023).
Interconnectedness and Indirect Effects: Coastal ecosystems are highly interconnected, with land-based activities (including point source discharges and diffuse effects like agriculture runoff) affecting marine habitats. Indirect effects, such as changes in predator-prey dynamics due to fishing pressure combined with changing climate, are hard to predict and quantify and the component pressures are difficult to reliably isolate. For instance, the combined effect of sediment runoff from multiple catchments and coastal engineering projects can alter tidal flows, impacting estuarine biodiversity in ways that are difficult to model (NIWA, 2023). Historically, the tendency to compartmentalise environments and potential impacts presents challenges for an integrated approach to the impact assessment.
Regulatory and Methodological Gaps: Legislation provides limited guidance on assessing cumulative effects, leading to inconsistent approaches. Practitioners often rely on qualitative judgments rather than quantitative models, which can risk underestimating impacts. Recent efforts by EIANZ are noted as a start in providing guidance and consistency in assessing coastal environments.
Stakeholder and Cumulative Pressure Attribution: It is crucial to engage partners and stakeholders, including iwi and local communities. Yet attributing cumulative effects to specific actions is challenging. For example, a community might experience declining fish stocks due to a combination of factors like overfishing, pollution, and climate change, but isolating each contributor’s role is complex and contentious, potentially leading to legal challenges and disputes over responsibility and mitigation.
Despite these challenges, addressing cumulative effects is essential for sustainable coastal management. Tools like cumulative effects frameworks, which map past and future projects, and scenario modelling can help, but they require significant investment in robust data collection and analysis. The lack of cost-effective methods means that cumulative effects are often underrepresented in impact assessments, risking long-term ecological degradation. Gladstone-Gallagher et al (2024) advocate a principles-based risk framework to select priority habitats and location attributes and to enhance cost-effective management for environmental improvement through reduced need for assisted recovery. Looking ahead, the proposed Natural Environment Act may include provisions setting out national goals for environmental indicators and many of these goals are derived from sections 5 and 6 of the RMA but could provide greater clarity of what is to be achieved.
Developing Technologies May Assist Emerging technologies offer some potential to overcome some of these challenges, including in detecting and quantifying cumulative effects. eDNA can provide baseline biodiversity data and track changes over time, helping identify cumulative species impacts without extensive fieldwork (NIWA, 2023b). There remain limitations in the information that can be extracted from this data. Machine learning can analyse large datasets, such as satellite imagery and acoustic surveys, to model cumulative landcover changes and predict indirect effects, achieving over 85% accuracy in coastal mapping (Smith et al., 2023). Remote sensing, using LiDAR and multispectral data, can be used to monitor habitat changes at regional scales, reducing costs while providing temporal data to assess cumulative trends (NIWA, 2023c). Integrating these technologies within a systems-based approach can enhance cumulative effects analysis, but factors such as data integration, training, and cost management are lingering challenges. Many of these tools are beyond the scope of individual practitioners or individual projects and the data collection and analysis may require investment by a central agency or collective with access provided to practitioners and interested parties.
Conclusion New Zealand’s coastal environments are under significant and growing pressure. Their complexity, combined with challenges in characterising habitats and addressing cumulative effects, complicates accurate, robust and timely impact assessments. Detecting and quantifying cumulative impacts is particularly difficult due to data limitations, compartmentalisation of ecosystems and analyses, scale mismatches, and regulatory gaps, yet it is critical for sustainable management. Technologies like eDNA, machine learning, and remote sensing offer tools to improve assessment accuracy and efficiency, but their success depends on integrated application, effective stakeholder collaboration, and investment in capacity building. Even so, there are limitations with these technologies and the ability for individual projects to utilise them effectively. As NZAIA and others continue to guide impact assessment practices against the background of changing environmental legislation, technological innovations may provide practitioners with some assistance for appropriate management actions, with the ultimate goal of ensuring coastal resilience for future generations.
References
De Luca, S. (2019). Issues for Ecological Impact Assessment in the Marine Environment in New Zealand. NZAIA Impact Connector, 7.
Rojas-Nazar, U.; Hewitt, J.; Pilditch, C. & Cornelisen, C. (2023). Managing Cumulative Effects in the Marine Environment – Research Roundup. Sustainable Seas National Science Challenge.
Smith, J., Brown, T., & Lee, R. (2023). A Methodology for National-Scale Coastal Landcover Mapping in New Zealand Using Machine Learning. Remote Sensing 14(19), 4827. doi:10.3390/rs14194827