Final answer:
A 75% reduction in the sardine population due to disease would decrease their predators' carrying capacity and population, causing a cascade of effects throughout the marine ecosystem.
Step-by-step explanation:
If the sardines in a given ecosystem experienced a disease that caused their population to shrink by 75%, it would likely have cascading effects throughout the food web. Since sardines are often a primary food source for various predators, including seals, a significant reduction in their population could lead to a decrease in the carrying capacity of their predators due to a lack of available food. As a result, the population of predators, such as seals, would also likely decrease. The imbalance can further affect other species interconnected through the food web, both predators and competitors of sardines, leading to shifts in species composition and abundance. Additionally, other marine animals and plants indirectly connected to sardines through the food web could be impacted, altering the overall marine ecosystems. It is important to consider that the carrying capacity is not just about space but the availability of resources needed to sustain a population.