Excess salinity does have detrimental effect on marine organisms, but that is for an entirely different reason; it has nothing to do with the pH of the saline water. When the water is highly saline, then water from the cell cytoplasm tends to move out of the body by osmosis. Thus the cells are plasmolysed. Moreover, ions like $\ce{Na+}$, $\ce{Mg^{2+}}$, $\ce{Cl-}$ etc. which are present abundantly in the saline water, tends to diffuse into the body. For removing these ions, the kidney starts to produce more and more urine. The end result is that the organism cannot survive in saline water.
When the level of salinity is not high enough (like in oceans), then the aquatic plants and animals can use various physiological modifications or adaptations to stay alive in the salty water. In some fishes, the ions are pumped out of the cell cytoplasm and blood by active transport (ATP operated proteins). Many fishes also drink sea water to counteract the loss of water by osmosis. Some other fishes may also have dissolved compounds in blood to increase its concentration and prevent osmosis.
When the salinity is really high, then neither of these countermeasures become effective enough. So, marine organisms cannot survive. (Think about dead sea)
But to answer your original question, increasing the salinity does affect the pH of the water (see below), but the osmosis is more likely cause of death than change of pH.
The main ions in the sea water are $\ce{Na+}$, $\ce{Cl-}$, $\ce{SO4^{2-}}$, $\ce{Mg^2+}$, $\ce{Ca^2+}$ and $\ce{K+}$ [1]. As you can see, the acids and bases which produce these ions in solutions are: $\ce{NaOH}$, $\ce{HCl}$, $\ce{H2SO4}$, $\ce{Mg(OH)2}$, $\ce{Ca(OH)2}$, $\ce{KOH}$. Out of these, only $\ce{Mg(OH)2}$ is not a strong base. So, change in the concentration of $\ce{Mg^2+}$ will make the water more acidic[2]. Also, sea water contains an appreciable amount of $\ce{CO3^2-}$. Increase in concentration of this ion will make the water more alkaline. So, it all depends upon the specific salt which is the cause of excess salinity at the region.
Notes:
Britannica article
The conjugate acid of a strong base is a weak acid. The conjugate acid of a weak base is a strong acid. So, the other ions do not affect the pH. (Read the Wikipedia page and the Chemistry LibreTexts page for further information)