Abstract:
The alveolate protist Perkinsus olseni infections impose
considerable stresses on the host Manila clam Ruditapes
philippinarum, often reducing their tissue weight due to the drain
on energy resources. However, the relationship between condition
factors and P. olseni infection exhibits inconsistency in different
scenarios, as it is influenced by various factors such as
environmental conditions, food availability, and reproductive
conditions. To gain deeper insights, we surveyed Manila clams
occurring on tidal flats in Anmyeondo Island, Cheonsu Bay to
assess P. olseni intensity and its effects on the fitness of Manila
clams. The Ray’s fluid thioglycollate medium assay revealed
that P. olseni infection in clams from inner Cheonsu Bay had
considerably greater P. olseni intensities in May and September
2021 than those from outer Cheonsu Bay and reference sites
(P < 0.05). Despite the high level of P. olseni infection, condition
index (CI), a ratio of the flesh weight to the shell weight, in clams
from inner Cheonsu Bay was also significantly higher than in
clams from outer Cheonsu Bay and reference sites (P < 0.05). A
noteworthy finding of this study was the positive association
between P. olseni infection intensity and CI in clams, which
suggests that despite the high parasite load, clams were able to
maintain a higher CI, possibly due to the abundance of nutrients
and organic matter present in the inner bay. The P.
olseni infection intensities measured in September were significantly higher at most of the sampling sites in the inner and
outer bay, which could be associated with the poor health
condition of clams during a post-spawning period. These results
highlight the complexity of bivalves’ ecological relationships in
Cheonsu Bay and offer new insights into their adaptability
accompanied by other factors to parasite stressors.
