Final answer:
The primary stages of the C. vulgaris life cycle are most affected by increased salinity as it disrupts osmoregulation, inhibiting growth and cell division.
Step-by-step explanation:
The stages of the life cycle most directly affected by increased salinity exposure for C. vulgaris (Chlamydomonas vulgaris) would likely be the primary stages that involve cell division and growth, such as the germination, cell division, and potentially the growing stages.
In organisms such as Dunaliella spp., Halobacterium spp., and other halotolerant organisms, an increase in salinity affects their osmoregulation—their ability to control the water and ionic balance within their cells. When exposed to increased salinity, C. vulgaris must adapt by either accumulating compatible solutes (like glycerol) to balance osmotic pressure or by adjusting its metabolism to cope with the ionic changes and potential dehydration.
Failure to successfully osmoregulate would impact the ability of the cells to grow and divide properly, hence why the primary and early stages are most vulnerable. As the cells are actively dividing and growing, they are more sensitive to changes in osmotic pressure, which can disrupt normal cellular function, and impair growth and division—the quintessential processes of the primary stages of the cycle.
Final answer in 20 words: Increased salinity affects primary stages of C. vulgaris' life cycle, disturbing osmoregulation, growth, and cell division.