Impact of elevated temperature on the physiological and biochemical responses of Kappaphycus alvarezii (Rhodophyta)

Abstract

The eucheumatoids Kappaphycus and Eucheuma are cultivated in tropical or subtropical regions for the production of carrageenan, a hydrocolloid widely used in the food and cosmetic industries. Kappaphycus alvarezii is a highly valued economic crop in the Coral Triangle, with the Philippines, Indonesia and Malaysia ranked among the largest producers. In the absence of measures to mitigate climate change, extreme events including heatwaves, typhoons, severe El Niño and La Niña, are expected to increase in frequency and magnitude. This inadvertently brings adverse effects to the seaweed cultivation industry, especially in the tropics. Temperatures are rapidly reaching the upper limit of biologically tolerable levels and an increase in reports of ice-ice and pest outbreaks is attributable to these shifts of environmental parameters. Nevertheless, few reports on the response of eucheumatoids to a changing environment, in particular global warming, are available. Understanding the responses and possible mechanisms for acclimation to warming is crucial for a sustainable seaweed cultivation industry. Here, the physiological and biochemical responses of K . alvarezii to acute warming indicated that the strain used in the current study is unlikely to survive sudden increases in temperature above 36°C. As temperature increased, the growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment content (chlorophyll- a , carotenoid and phycobiliproteins) were reduced while the production of reactive oxygen species increased indicating the occurrence of stress in the seaweeds. This study provides a basis for future work on long term acclimation to elevated temperature and mesocosm-based multivariate studies to identify heat-tolerant strains for sustainable cultivation.

Seaweed Aquaculture in Indonesia Contributes to Social and Economic Aspects of Livelihoods and Community Wellbeing

“…This may already be contributing to the long-term decline in carrageenan yields discussed above [23]. Increasing water temperature reduces growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment (chlorophyll-a, carotenoid and phycobiliproteins) content of Kappaphycus [95]. Stress associated with cultivation in conditions approaching the upper thermal tolerance of seaweed will likely result in increased prevalence of disease outbreaks, including 'ice-ice' [23,95].…”

“…Increasing water temperature reduces growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment (chlorophyll-a, carotenoid and phycobiliproteins) content of Kappaphycus [95]. Stress associated with cultivation in conditions approaching the upper thermal tolerance of seaweed will likely result in increased prevalence of disease outbreaks, including 'ice-ice' [23,95]. The increasing prevalence of typhoons and extreme storm events, arising from more severe El Niño and La Niña weather patterns, is likely to contribute to destruction of seaweed farms [23,95].…”

“…Stress associated with cultivation in conditions approaching the upper thermal tolerance of seaweed will likely result in increased prevalence of disease outbreaks, including 'ice-ice' [23,95]. The increasing prevalence of typhoons and extreme storm events, arising from more severe El Niño and La Niña weather patterns, is likely to contribute to destruction of seaweed farms [23,95].…”

Exploring, harnessing and conserving marine genetic resources towards a sustainable seaweed aquaculture

“…Physiological responses of tropical seaweeds to warming and ecological responses to climate change are only starting to be understood (Kumar et al, 2020). Monitoring change and diversity loss in the marine environments continues to be a challenge, leading to the concern that vanishing tropical seaweed populations remain largely unnoticed.…”

Assessment of genetic diversity within eucheumatoid cultivars in east Sabah, Malaysia

“…This is partly because the local farmers still rely on conventional farming techniques, including the use of the probably original K. alvarezii cultivar which has been vegetatively propagated for the past 50 years. The decline in production has probably also been affected by difficulties in generating healthy and vigorous seed stock, disease problems, and climate change (FAO 2018;Kumar et al 2020;Ward et al 2021). It is therefore crucial that Malaysia focus on the selection of good quality cultivars as a replacement for the declining strains.…”