No abstract

Ulva compressa is one of the causal green macroalgae in many countries. In this study, complete chloroplast genome sequence of U. compressa was reported, and the total length of this species was 94,226 bp (GenBank accession number MT916929). The overall base composition of chloroplast genome was A (37.2%), T (37.0%), C (12.7%) and G (13.1%), and the percentage of A þ T (74.2%) was higher than C þ G (25.8%). U. compressa chloroplast genome encoded 90 genes, including 63 protein-coding genes, 23 transfer RNAs genes, and 4 ribosomal RNAs genes. The maximum likelihood phylogenetic analysis showed that U. compressa is the closest sister species of U. linza. This study will be helpful to understand the genetic diversity of Ulva species.

With global warming, in recent years, golden tides have frequently occurred off the coasts of China. Sargassum horneri, which attach to aquaculture rafts, can float and form small-scale golden tides after falling off. Temperature will affect the growth and reproduction of algae. In order to explore whether the temperature is the potential influence factor of the golden tide outbreak, in this study, the effects of global warming on the growth and proliferation of S. horneri in the mussel aquaculture area of Gouqi Island will be discussed. Samples of the macroalgae were collected monthly from August 2021 to July 2022 at various stages of its life cycle, and the relationship between algal growth and temperature was analyzed based on the concept of effective accumulated temperature, combined with the parameters of sea surface temperature, photosynthetic rate, growth rate, and growth cycle. Based on the continuous temperature variation observed, the growth cycle could be divided into five stages: the decreasing temperature period (October to November), the low-temperature adaptation period (December), the second suitable low-temperature period (January to February), and the high-temperature decay period (February to May). The effective accumulated temperature stored by S. horneri from 2021 to 2022 was 2772.4 °C·d; compared with previous studies, it decreased by about 800 °C·d. The winter temperature in 2022 was higher than the average temperature in the previous 5 years, allowing the macroalgae to enter the reproductive period in advance. This had a significant impact on the blooming time of golden tides and led to an earlier outbreak and extinction. Therefore, in the future, we can set up a monitoring system for the early warning of golden tides according to the change of SST in winter.

The green tide in the Southern Yellow Sea which has been erupting continuously for 14 years. Dominant species of the free-floating Ulva in the early stage of macroalgae bloom were Ulva compressa, Ulva flexuosa, Ulva prolifera, and Ulva linza along the coast of Jiangsu Province. In the present study, we carried out comparative studies on complete mitochondrion genomes of four kinds of bloom-forming green algae, and provided standard morphological characteristic pictures of these Ulva species. The maximum likelihood phylogenetic analysis showed that U. linza is the closest sister species of U. prolifera. This study will be helpful in studying the genetic diversity and identification of Ulva species.