This study investigated biodiversity changes in host-virus coevolution, focusing on a system incorporating a resistance-growth trade-off. We derived the basic reproduction number for the host system and identified conditions for host-virus coexistence. Numerical simulations revealed that the resistance-growth trade-off may influence diversity patterns, leading to both monotonic and unimodal dynamics. Additionally, the resistance-growth trade-off may drive transitions between stable equilibria and periodic solutions under specific mutation rates, cause shifts in dominant species in both algal and viral communities, and trigger a hydra effect under specific dilution rates. Our results offer insights into the mechanisms driving biodiversity fluctuations in host-virus coevolutionary dynamics.