Trematode Ecology and Host-Parasite Dynamics in Marine Ecosystems

Marine trematodes are parasitic flatworms that undergo complex life cycles involving multiple hosts and free-living stages, playing critical roles in coastal food webs and ecosystem processes. Larval stages emerge from molluscan first intermediate hosts and infect secondary hosts—such as bivalves, fish or crustaceans—before reaching avian or mammalian definitive hosts. Transmission rates and host susceptibility are governed by a combination of abiotic factors (temperature, salinity, substrate composition) and biotic interactions (host density, immune responses). Trematode infections can regulate host populations, alter grazing patterns and modify nutrient cycling. They also serve as sensitive bioindicators of environmental change, reflecting habitat transformations and climatic fluctuations over both short and long temporal scales. Recent advances have elucidated the thermal tolerances of cercarial emergence, stage-specific vulnerabilities of hosts under warming scenarios and the cascading impacts of parasitism on community structure. In a warming and changing ocean, shifts in transmission dynamics may influence benthic community resilience, shellfish health and ecosystem services, with implications for conservation, fisheries management and disease forecasting on a global scale.

Research from Nature Portfolio

Recent studies have pinpointed the temperature sensitivity of cercarial emergence and transmission across climatic gradients. Investigations in the Persian Gulf identified unprecedented thermal optima for cercarial release, demonstrating that some trematode species thrive at temperatures exceeding 30 °C but experience sharply reduced emergence beyond upper limits. Complementary work in the Baltic Sea has mapped the thermal performance of both infected snails and free-swimming cercariae, revealing that warming events may narrow the window for successful host contact by shortening cercarial longevity and increasing host mortality. Palaeontological analyses of Holocene bivalve assemblages have further shown that centennial-scale flooding events correlate with historical surges in trematode prevalence, suggesting that sea-level rise and associated habitat shifts could intensify parasitism in future marine systems.

Trematode Ecology and Host-Parasite Dynamics in Marine Ecosystems publication trend

The graph below shows the total number of articles in trematode ecology and host-parasite dynamics in marine ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Cercariae: Free-swimming larval stage of trematodes that emerges from first intermediate hosts to seek subsequent hosts.

Intermediate host: Organism harbouring larval stages of a parasite before transmission to the definitive host.

Metacercariae: Encysted larval stage within the second intermediate host, poised for infection of the definitive host upon ingestion.

Mesocosm: Controlled experimental system replicating natural conditions to study ecological interactions.

Thermal optimum: Temperature at which a biological process, such as larval emergence, operates at maximum efficiency.

References

1. Thermal optima of cercarial emergence in trematodes from a marine high-temperature ecosystem, the Persian Gulf. Scientific Reports (2023).
2. Warming and parasitism impair the performance of Baltic native and invasive macroalgae and their associated fauna. Limnology and Oceanography (2023).
3. Marine trematode parasites as indicators of environmental changes. Ecological Indicators (2022).
4. Heat sensitivity of first host and cercariae may restrict parasite transmission in a warming sea. Scientific Reports (2022).
5. Surges in trematode prevalence linked to centennial-scale flooding events in the Adriatic. Scientific Reports (2017).
6. Freshening rather than warming drives trematode transmission from periwinkles to mussels. Marine Biology (2020).