An assessment of environmental and ecological drivers of salp blooms in the world’s ocean

• Published in: Regional studies in marine science 2024-12, Vol.77, p.103718, Article 103718
• Main Authors: Ariffian, Nur Nabilah Ahmad, Swadling, Kerrie M., Moteki, Masato, Ishak, Nurul Huda Ahmad
• Format: Article
• Language: English
• Subjects: Biogeochemical cycle; Climate change; Microplastics; Salp bloom
• ISSN: 2352-4855; 2352-4855
• DOI: 10.1016/j.rsma.2024.103718

Salps provide an important mechanism for energy transfer from primary producers to higher-order consumers and they can also make a significant contribution to biogeochemical cycling in the ocean. Their reproductive strategy, alternation of generations between solitary asexual stages and colonial sexual stages, can result in large blooms (> 1000 ind m−3). Despite growing interest and understanding of salps, the factors influencing the formation of blooms remain understudied. Sampling and preservation of salps can be challenging due to their fragility and unpredictable occurrence. As a result, their abundance, biomass, distribution, and trophic positions may be under-recorded, especially for remote and poorly sampled regions of the ocean. Special attention is given to three species, Thalia democratica, Salpa fusiformis, and Salpa thompsoni, recognized for their capacity to form blooms and for their frequent observations. We review known information about the drivers of these species’ blooms, elucidating the factors contributing to their ecological success. Important criteria for defining salp blooms are provided to address the confusion around bloom definitions used in past literature reviews. Subsequently, we explore the significant contribution of salps to biogeochemical cycling in the ocean, noting that carbon sequestration may be impeded by microplastics, which could reduce the sinking rate, affect the physiology of salps, impede microbial regeneration, and diminish food sources for the benthic community. However, certain gaps persist in our understanding of salp ecology, particularly regarding the true extent of the effects of blooms on biogeochemical cycling in the face of on-going climate change and anthropogenic activities. Future research endeavours should aim to address these gaps by employing comprehensive sampling strategies at salp hot spots and integrating multidisciplinary approaches to better understand salp populations in marine ecosystems.