Cumulative biomass curves describe past and present conditions of Large Marine Ecosystems

Abstract

Implementing the Ecosystem Approach in marine ecosystems is moving from preliminary steps—dedicated to defining the optimal features for indicators and developing efficient indicator frameworks—towards an operational phase where multisector marine management decisions are executed using this information. Within this operational context, emergent ecosystem properties are becoming quite promising as they have been demonstrated to be globally widespread and repeatable, and to be quite effective in detecting significant state variations of complex systems. Biomass accumulation across TLs (CumB‐TL) combines two important emergent properties of an ecosystem (energy flow, in terms of transfer efficiency, and storage, expressed as biomass), both amenable to detecting rapid ecosystem change. However, for further application, it is crucial to understand which types of drivers an indicator is sensitive to and how robust it is in relation to modifications of the external conditions and/or the system state. Here we address some outstanding questions of these CumB‐TL curves related to their sensitivity to various drivers by carrying out a global scale assessment (using data from 62 LMEs) over six decades (1950–2010). We confirm the consistency of the S‐pattern across all the LMEs, independent from latitude, ecosystem, environmental conditions, and stress level. The dynamics of the curve shape showed a tendency to stretch (i.e. decrease of steepness), in the presence of external disturbance and conversely to increase in steepness and shift towards higher TL in the case of recovery from stressed conditions. Our results suggest the presence of three main types of ecosystem dynamics, those showing an almost continuous increase in ecological state over time, those showing a continuous decrease in ecological state over time, and finally those showing a mixed behaviour flipping between recovering and degrading phases. These robust patterns suggest that the CumB‐TL curve approach has some useful properties for use in further advancing the implementation of the Ecosystem Approach, allowing us to detect the state of a given marine ecosystem based on the dynamics of its curve shape, by using readily available time series data. The value of being able to identify conditions that might require management actions is quite high and, in many respects, represents the main objective in the context of an Ecosystem Approach, with large applications for detecting and responding to global changes in marine ecosystems.

Ecosystem‐level reference points: Moving toward ecosystem‐based fisheries management

“…Ecosystemlevel reference points could also be an early warning of changes that would not be apparent in single-species reference points for many years, allowing for management prevention of changes to come or social preparation and adaptation (Link 2021). The ELRPs that track higher-level ecosystem functions can provide information on ecosystem conditions without needing to understand individual ecological processes (Link et al 2015;Link 2018;Schlenger et al 2018;Pranovi et al 2019). Ecosystem-level reference points can help managers balance competing objectives in management decisions by improving the ability to identify and understand potential adverse impacts on other parts of the system (Fulton et al 2022).…”

“…Testing the theory with commercial marine fisheries capture or landings data as a proxy for biomass found that most marine systems exhibited the expected patterns (Libralato et al 2019;Pranovi et al 2019;Link 2021). Further, derived curve parameters (e.g., values of x and y at inflection points and slope; see Figure 4) for a single system tracked over time show patterns of perturbation and recovery.…”

“…Some ELRPs use widely available data and simple analyses that make them implementable in data-rich and datapoor systems. Often ELRPs include both direct and indirect indicators of change in an ecosystem (Pranovi et al 2019). To date, most research has been devoted to the identification of appropriate ecosystem indicators for marine systems (e.g., Shin et al 2012;Boldt et al 2014), including the physical, biological, and human dimensions.…”

“…Ecosystem-level reference points can help to improve our understanding of changes that are happening in the ecosystem, including biological marine communities and fisheries. The ELRPs can be used to monitor how an ecosystem functions at a higher level without needing to understand individual ecological processes (Link et al 2015;Link 2018;Schlenger et al 2018;Pranovi et al 2019). Ecosystem-level reference points can also be used to provide early warning of ecosystem changes (Link 2018(Link , 2021, allowing for management interventions to slow or stop the change or prepare users to adapt to the change.…”

“…Negative perturbations to the ecosystem, such as ecosystem overfishing, result in flattening of the curves relative to a normal stable state (i.e., removal of biomass at higher trophic levels reduces the magnitude of the asymptote; see Figure 4), while ecosystem recovery exhibits steepening of the curves relative to the perturbed state (Link et al 2015;Pranovi et al 2019). Theory suggests that perturbed ecosystems should have reduced cumulative production and biomass accumulation (e.g., stored energy spread across trophic levels) as biomass is shifted toward lower trophic levels.…”