**1. Introduction**

Microalgae are unicellular photosynthetic organisms that can be eukaryotic or prokaryotic (cyanobacteria) and are ubiquitous; they can be found in fresh or marine water, soil and even extreme habitats [1]. Microalgae can transform atmospheric inorganic carbon into organic carbon biomass, and it has been estimated that half of their biomass comprises carbon (w/w) [2]. In addition, they contain approximately 50 % (w/w) carbon in their biomass, which helps them grow better [3]. Surprisingly, some species of marine microalgae can grow at high CO2 (40 %) concentrations, which is known to help curb greenhouse gases that ultimately have a positive effect on Blue Economy [4]. One of the main benefits of using microalgae in mitigating CO2 is that they can fix this gas up to 50 times more than terrestrial plants [5].

On the other hand, macroalgae or seaweeds are multicellular and macroscopic algae that contribute as huge biomass producers in the benthic region. Besides their consumption as nutritious food and feed, they are frequently used as fertiliser [6]. Like microalgae, seaweeds also contribute to mitigating climate change through the Blue Carbon strategy. Seaweed can sequester a large amount of CO2 from the environment that has been predicted that ongoing seaweed farming can capture more than 6 % of CO2 globally by 2050 [7]. Seaweed aquaculture benefits coastal habitats in different ways. For instance, a study showed that Chinese seaweed farming upgrades the coastal water quality by eliminating nitrogen and phosphate as well as by sequestering carbon, which in turn also helps in decreasing eutrophication. Interestingly, this kind of farming needs no chemical fertiliser pesticides as well saves cultivable lands [8].

Currently, changes in climate patterns give rise to several environmental hazards and the most drastic effect is evident in the marine ecosystem. Consequently, marine microalgae and seaweeds are also experiencing the negative impact of climate change. Studies revealed that changes in habitat conditions make the species migrate or to extinction [9]. Therefore, migration in seaweed species is becoming common. Range shifts in seaweed communities disturb the local distribution pattern and species richness, reported globally [10].
