**4. Global distribution of microalgae and macroalgae**

In the marine coastal area, green algae are the major contributor to photosynthesis, especially microalgae from the Mamiellophyceae class are abundant in number while Chlorophyceae are the least. Microalgae from Pyramimonadales and Chlorodendrophyceae are ubiquitous in marine coastal regions [22]. In desert soil, cyanobacterial species are mostly found than other microalgae species because of their greater desiccation tolerating capacity [23]. In the alpine region of New Zealand, microalgae from Chrysophyceae, Xanthophyceae, Chlorophyceae, Trebouxiophyceae, and Charophyceae are more prevalent [24]. A study on the southeast coast of India showed that *Isochrysis galbana* was the dominant species in that area, while *Nannochloropsis oculata* was the less common species observed. The dominance of other species found were *Chlorella marina* > *Chromulina freibergensis* > *Dicrateria inornata* > *Chaetoceros calcitrans* [25]. On the other hand, the coastal region of Indonesia is dominated by diatoms, especially *Rhizosolenia* spp., *Chaetoceros* spp. and *Coscinodiscus* spp. [26]. In the case of benthic harmful algal bloom species (BHABs), two main species, *Gambierdiscu* and *Fukuyoa,* are widespread in the Caribbean Sea, the South Pacific, Indian Oceans, North Atlantic Ocean and the Canary Islands. Additionally, they are also reported from the coastal area of Japan, Korea, New Zealand and Australia. On the other hand, *Ostreopsis* spp. is common in the Mediterranean Sea [27].

A wide variety of seaweed species are distributed on the coasts, and their similarity is dependent on climatic zones. Most of the Rhodophyta belongs to warm temperate Pacific flora. The number of Rhodophyta is more than double in these Pacific florae compared to the cold temperate floras [28]. Seaweed species are vastly available in 30–50° latitude, which covers southern Australia, Japan and the Mediterranean as well as in the Philippines [29]. In recent studies, the distribution of invasive seaweeds has been documented. The highest invasion cases belong to the Mediterranean region (132), followed by the NE Atlantic region, covering the North and Baltic Sea and the eastern Atlantic Islands. Among the Rhodophytes, the Rhodomelaceae and the Ceramiaceae accommodate more invaders, while Chlorophyta, *Caulerpa* spp. and *Codium* spp. are recorded as the most successful invader species [30].
