Question

Which of the following would be helpful in forming algal blooms by the members of cyanobacteria?
1. Formation of zoospores
2. Ability to move to the desire position in the water column
3. Development of gas vacuoles
4. Formation of biconcave separation discs
Select the correct answer using the codes given
A. $1$,$2$ and $3$
B. $1$ and $4$
C. $2$ and $3$
D. $3$ and $4$

Answer 1

“In aquatic ecology, an algal bloom is described as a rapid rise in the population of algae”. Algal blooms can occur in both marine and freshwater environments. The discoloration on the water's surface is a clear indicator of the phenomena. It usually happens when a nutrient (such as nitrogen or phosphorus) is introduced into an aquatic habitat. The most prevalent cause of algal blooms is an abrupt increase of nutrients that algae require for growth. Agricultural runoffs, sewage runoffs, and other anthropogenic sources are the most common sources of these nutrients in aquatic ecosystems.

Complete answer:
Option A: Algae renew through sexual reproduction, which involves both male and female gametes (sex cells), or asexual reproduction, which involves both male and female gametes (sex cells). Many small algae reproduce asexually through cell division or fragmentation, but larger algae reproduce sexually through spores.
So, option A is correct.
Option B: Gas vacuoles are most typically found in true planktonic cyanobacteria that grow freely suspended in lakes. All water bloom-forming cyanobacteria have gas vacuoles, which are responsible for buoying them to the water surface.
So, option B is not correct.
Option C: Because of the combined impacts of water column structure, temperature, coastal development, and eutrophication, some dangerous algal blooms are expected to grow with continuous climate change. Increased $C{O_2}$ levels in marine and freshwater have been shown to worsen blooms and increase the toxicity of several HAB species, especially when accompanied with nutrient availability changes.
So, option C is not correct.
Option D: With further climate change, some severe algal blooms are projected to rise due to the combined effects of water column structure, temperature, coastal development, and eutrophication. Increased $C{O_2}$ levels in marine and freshwater have been proven to exacerbate blooms and increase the toxicity of some HAB species, particularly when combined with changes in nutrient availability.
So, option D is incorrect.

Hence, Option A is the correct answer.

Additional information:
In both marine and freshwater settings, cyanobacteria are one of the most abundant groups of phototrophic prokaryotes. Cyanobacteria has both advantages and disadvantages. They are important primary producers as well as a large source of secondary products, including cyanotoxins, a group of hazardous substances.
Increased anthropogenic eutrophication and global climate change have resulted in abundant proliferation of cyanobacteria in freshwater, estuarine, and coastal ecosystems, raising severe concerns about dangerous bloom formation and surface water contamination all over the world.

Note:
Cyanobacteria blooms occur when cyanobacteria, which are commonly found in water, multiply rapidly. Blooms can grow in warm, slow-moving waters that are high in nutrients from fertiliser runoff or septic tank overflows, for example. Blooms of cyanobacteria require nutrients to live.
Algae flourishes as a result of this process. Early blue–green algal blooms are most common in the spring, when the water temperature is warmer and more light is available. During the warmer months of the year, the growth continues. The growth of Cyanobacteria is best at temperatures over $25^\circ C$.