Macroalgal blooms have increased in frequency worldwide due to anthropogenic activities. Algal blooms can disrupt recreational activities, interfere with fisheries, and deplete oxygen during decomposition. Narragansett Bay has experienced macroalgal blooms dominated by blade-forming Ulva for over a century. Evidence from other systems has suggested that Ulva can negatively impact other organisms. The first objective of this study was to determine whether bloom-forming Ulva compressa and U. rigida inhibit the growth of co-occurring macroalgae, Gracilaria vermiculophylla, Cystoclonium purpureum, and Chondrus crispus, during co-culture via laboratory-based assays. We found that U. compressa and U. rigida significantly inhibited the growth of all three macroalgae. We were able to verify the negative effects of Ulva compressa, but not U. rigida on the growth of G. vermiculophylla in flow-through seawater tanks. Our second objective was to determine if Ulva exudate decreased the survival of eastern oyster larvae in laboratory challenge experiments. We documented a significant negative effect of Ulva exudate on oyster survival, which depended on both the Ulva species and the nutrient condition. The strongest effect on oyster larval survival was seen in larvae exposed to nutrient replete Ulva compressa exudate, which had less than 30% relative survival after one week. Our results indicate that bloom-forming Ulva has the potential to inhibit co-occurring macroalgae and cause oyster larval mortality.
The red alga Porphyra umbilicalis Kützing has a broad distribution within the North Atlantic. In the Northeast Atlantic, P. umbilicalis is dioecious and reproduces both sexually and asexually, while in the Northwest Atlantic, only asexual reproduction has been observed. In this study, transcriptomes were mined to identify putative single nucleotide polymorphisms (SNP) markers. A computational pipeline was developed that accounts for the specific characteristics of transcriptome dataset, filtered against the available red alga Chondrus genome and P. umbilicalis EST library to eliminate microbial contamination. Five hundred fortynine putative SNPs were detected within a single population (Schoodic Point, ME, USA). Five of the validated SNP markers were applied in a pilot study of genetic diversity and population structure of seven P. umbilicalis populations within the Gulf of Maine. Results of this study revealed the genetic diversity and structure of P. umbilicalis populations in the Gulf of Maine. Novel genotypes were found in the open coastal populations at Reid State Park, Schoodic Point, and the estuarine tidal rapid population at Wiscasset. Our study represents the first attempt to develop suitable bioinformatic pipeline for RNA-seq to detect SNP markers for red alga Porphyra umbilicalis and successfully used these SNP markers for population study.
Editorial on the Research Topic Macroalgal blooms in a global change contextFollowing the Second World War, the development of industrial agriculture and medical advances allowed for an exponential increase in the human population. During this period, the concept of mass consumption society was also encouraged in developed and developing countries, increasing the demand for resources (Cherubini et al., 2018;Gaulin and Le Billon, 2020;Elmqvist et al., 2021). The associated expansion and intensification of human activities necessary to cover the needs of a larger and more demanding population led to important changes in the earth system, making humankind one of the most important drivers of global change (e.g., ocean acidification, climate change, eutrophication, biological invasions). All of these human-induced changes in environmental conditions have produced important alterations and imbalances in the structure and functioning of ecosystems, especially in aquatic systems (Lotze et al., 2006;James et al., 2023).In coastal and estuarine waters, one of the most evident signs of the impact of human activities is the development of macroalgal blooms. Macroalgal blooms are accumulations of fast-growing opportunistic species, which can lead to anoxic events and release nuisance or toxic compounds during the degradation of the biomass (Fletcher, 1996;Valiela et al., 1997; Green-Gavrielidis et al., 2018). These blooms alter ecosystem functioning of nearshore environments and limit the services these areas provide (Fletcher, 1996; Gonzales et al., 2013). Macroalgal blooms became more frequent and larger in the 1970s, especially in industrialized countries. Since then, the number of reports from new locations and the magnitude of these blooms have continued to increase (Smetacek and Zingone, 2013). Important research efforts have been developed in order to understand the causes and mechanisms underlying these phenomena, which have demonstrated the key role nutrient over-enrichment and reduced herbivory play in explaining the occurrence of macroalgal blooms (
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