The aquaculture industry as a global network of perturbation experiments

The industrial production of finfish (e.g., salmon, tilapia, and carp) has well documented ecological consequences (Ottinger et al. 2016; Carballeira Braña et al. 2021). Negative impacts of the aquaculture industry include excessive nutrient loading (Islam 2005) and subsequent eutrophication, disease introduction (Kennedy et al. 2016), heavy metals pollution (Emenike et al. 2022), and the assimilation of escapee fish into wild populations (Toledo-Guedes et al. 2014). Despite ecological concerns, the aquaculture industry has continued to grow in recent decades (Naylor et al. 2021, FAO 2022), driven by increasing market demands and rapidly declining wild fisheries. The continued pursuit of a sustainable future for aquaculture is critical not only to meet global food demands, but also to support local economies and communities. Though by no means a silver bullet for solving systematic inequities, aquaculture can play a critical role in improving public health and well-being by increasing access to nutrition (Gephart et al. 2021), providing employment opportunities, especially for women (Gopal et al. 2020), and contributing to sustainable development overall (Subasinghe et al. 2009). In terms of the United Nation's Sustainable Development Goals (SDGs), truly sustainable aquaculture (i.e., continued production in farms that do not adversely alter the ecosystem they inhabit) is well suited to tackling several of the 17 goals, including Zero Hunger (SDG 2) (Stead 2019) and those related to economic opportunities, particularly zero poverty, and good jobs and economic growth (SDGs 1 and 8, respectively), as well as many of the targets and related indicators associated with the SDGs (Griffin et al. 2019).

In addition to the above costs and benefits, we posit that global-scale aquaculture operations constitute an untapped research opportunity that goes beyond the study of environmental impacts of aquaculture and the development of more sustainable methods. We propose that aquaculture operations, in particular cage culture farms, act as perturbation experiments and are therefore well suited for fundamental research in ecology, biogeochemistry, limnology, and oceanography (among other fields). In the following sections we explore this “aquaculture as perturbation experiments” framework. We first identify the elements of cage culture farms that make them good candidates for replicable, global-scale perturbation experiment-based research. We then explore potential research opportunities enabled by the framework to advance our understanding of ecosystem and community ecology, global biogeochemical cycling, and carbon sequestration.

Mechanisms of eutrophication as well as the eutrophying effects of aquaculture have been well documented (Gowen 1994; Smith and Schindler 2009, among others), even where top sustainability certifications have been achieved (Amundsen et al. 2019; Fadum and Hall 2022). Eutrophication is driven by the increased nutrient loading (carbon, phosphorus, nitrogen, and micronutrients) from mineralized constituents of organic matter (i.e., uneaten feed pellets and fecal matter) as well as N-rich gill excretion. Operations supporting year-round, multi-year production effectively act as a press experiment (rather than the alternative “pulse” method of nutrient enrichment experiments). This press experiment gradually applies both organic matter (OM) and nutrient loading stress which potentially drives an ecosystem closer to a regime shift. The causal relationship between increased nutrient availability and/or the alleviation of nutrient limitation and accelerated primary productivity has been well established. However, with the exception of large-scale experiments such as those done in the Experimental Lakes Area (Emmerton 2015), opportunities to assess such regime shift thresholds and the cascading effects of eutrophication in situ and at an ecosystem scale are rare. This is partially due to a paucity of eutrophic systems with continuous datasets, which span the years of nutrient additions. Furthermore, considering aquaculture as a global perturbation experiment provides a unique opportunity to understand the impacts and implications of ecosystem disturbance at a scale, which would be otherwise unfeasible (given the quantity of additions needed to achieve a given threshold) or environmentally irresponsible or unethical (such as induced eutrophication). The proposed “aquaculture as perturbation experiments” framework applies the concept of learning from ecosystem manipulation and broadens the scale at which we can pursue fundamental ecological questions. Below, we identify three research opportunities aimed at developing a deeper mechanistic understanding of ecosystem response to anthropogenic OM and nutrient loading stress more broadly.

Interdisciplinary collaboration between the aquaculture industry, researchers studying the impacts of aquaculture, and scientists pursuing fundamental research in fields such as biogeochemistry and ecology will help to illuminate how anthropogenic disturbance interfaces with the varied and pressing impacts of global change. In addition to OM and nutrient loading, other inputs from aquaculture farms such as heavy metals which are introduced through antifouling agents and formulated feed (Emenike et al. 2022), microplastics from farming equipment (Chen et al. 2021), antibiotics (Pepi and Focardi 2021; Adenaya et al. 2023), pathogens (Ahne et al. 1989), and contaminants of emerging concern (Ahmad et al. 2022) could similarly be used to investigate other types of anthropogenic disturbance in aquatic ecosystems. In recommending such research, we acknowledge two simultaneous positions: that the aquaculture industry, even within highly accredited operations, is often unsustainable and that it provides a research opportunity. Aquaculture is an environmental sustainability challenge, a means of meeting sustainable development goals, and also a research platform. The proposed “aquaculture as perturbation experiments” framework has the potential to dramatically improve our understanding of OM and nutrient enrichment in aquatic ecosystems at the global scale.

None declared.