A global assessment of species diversification in aquaculture

Aquaculture is a diverse food production system, and a high species diversity in aquaculture can make the global food system more resilient. Species diversification could facilitate aquaculture growth through multiple mechanisms and increase the sector's resilience and long-term sustainability. Facing increasing challenges from climate change, disease outbreaks, market fluctuations, and other disturbances, species diversification has become a widely recognized and endorsed development strategy in the policy and scientific communities for the growth and resilience of the aquaculture sector. However, many attempts to establish new species have yielded little long-term success, and the private sector often concentrates efforts on the most advantageous species for rapid growth. This paper presents a comprehensive assessment of aquaculture species diversification at the global, regional (more than 30 country groups), and national (nearly 200 countries) levels, covering the period 1950 to 2020 with a focus on 1990 to 2020. The assessment employs the concept of "effective number of species" as a measure of diversity and uses two sub-indicators to assess within-group versus between-group diversity. The indicator system reveals detailed patterns of species diversity and uncovers different driving forces of species diversification. Additionally, the study maps the status and trends of species diversity to offer a refined perspective on species diversity profiles and diversification patterns. The findings reveal that beneath high species diversity in world aquaculture lies generally low diversity at the national level; nearly half of national aquaculture has no within-group or between-group diversity. Furthermore, species diversification has been losing momentum in recent decades, and concentration has become a more prominent development pathway, with a tendency to drive aquaculture towards a low-diversity system similar to terrestrial farming. Public interventions are crucial to promote species diversification in aquaculture for the sector's resilience and long-term sustainability. It is important to not only reduce the cost of species diversification for the private sector but also to dedicate more public efforts towards increasing its benefits and viability. While diverse diversification patterns among national aquaculture indicate no one-style-fits-all species diversification pathway, a country may draw guidance from others' experiences, especially since countries with similar species diversity profiles or diversification patterns tend to cluster geographically. Evidence-based policymaking and sector management regarding species diversification entail collaborative efforts among policymakers, scientists, and the aquaculture community to expand and refine assessment frameworks, improve data availability and quality, and efficiently utilize information, knowledge, and insights generated by these assessments to inform decision making at various levels.