Explanation:
In many cases, DNA viruses utilize cellular enzymes for synthesis of their DNA genomes and mRNAs; all viruses utilize normal cellular ribosomes, tRNAs, and translation factors for synthesis of their proteins.
When a population of any species decreases, it leads to a decrease in populations of species that feed on them, as there is less food available and they may die of starvation or competing against each other for food. Crabs are eaten by big marine animals, such as otters and terrapins. Algae and snails does not feed on crabs. Therefore, the correct answer are the options B. Otter and D. Terrapin.