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Parasites of sea turtles: Variety of parasites and impact on turtles.

David BlairSchool of Marine and Tropical Biology,

James Cook University, TownsvilleOutline of talk;• Survey of the parasite groups (especially trematodes) and theirtransmission to turtles.• What is known about the effects on the hosts?

Green, hawksbill and loggerhead turtles.

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Most parasites are acquired by their host via the food chain.

• Green turtles, as juveniles in the open ocean, have a mixed diet which includes a range of invertebrates etc. As sub-adults they return to near-shore habitats and become herbivorous (seagrassesand algae).

• Hawksbills feed on sponges, algae, seagrasses and invertebrates.

• Loggerheads feed on a wide range of benthic invertebrates.

• Sea turtles have lots of parasites, mostly trematodes, but some nematodes and a few protists.

• Taxonomy of turtle parasites still in poor shape. Huge numbersof trematode species have been named, but many of these will prove to be synonyms.

Parasite fauna of green turtles is best known.Few researchers have noted whether parasites from green turtles were from adult or juvenile animals.My own poorly documented observation has been that a much wider range of trematodes occurs in juvenile greens: ontogenetic shift in diet leads to a change in parasite fauna. +Aspidogastrea

++Brachycoeliidae+++Pachypsolidae+++Gorgoderidae

+++Paramphistomidae+Hemiuridae++Plagiorchiidae+Calycodidae+++Rhytidodidae++++Spirorchiidae++++Pronocephalidae

+++Microscaphidiidae

Loggerhead

Haw

ksbill

Juvenile Green

Adult G

reen

Trematode

Family

Trematode families known from sea turtles.

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Some trematodesof sea turtles

Left: a pronocephalid and right, a microscaphidiid.Members of these families are termed “monostomes” because of the lack of a ventral sucker.

Most of these trematodes live in the gut or its associated organs. Most cause little overt pathology…

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… but spirorchiidtrematodes are real villains. These live in the circulatory system. Their eggs accumulate throughout organs all over the body.

Above: from Werneck et al 2006; appearance of serosal surface of gut of green turtle infected with blood flukes.

Right: A common spirorchiid –Learedius learedi.

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Spirochiids are very important parasites of turtles. All sea turtles around here have spirorchiids in them, and these commonly debilitate or kill the turtles.

Spirorchiideggs in turtle brain

Packet of eggs on edge of spinal cord

Above: these spirorchiideggs were thought to be schistosome eggs when they were found in the faeces of aborigines in northern Australia. Probably, hunters had caught a turtle and had eaten the gut lining, containing many eggs. These eggs could not pose a threat to humans.Blair & Miller 1992

Below: spirorchiid eggs come in a range of shapes and sizes.Work et al 2005

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Adult flukes in heart – Mark Flint.

Blocked aorta in turtle – Mark Flint.

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Fluke eggs in brain and salt glands – Mark Flint.

Spirorchiid eggs are very common in fibropapillomalesions, but are probably not a direct cause of them.

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What do we know about the life-cycles of any of these trematodes?

Nothing!

Spirorchiids are likely to have fork-tailed cercariae and penetrate the skin of the host directly.

The “monostomes”are likely to have metacercariae sitting on seagrasses and algae.

Nematodes. The few species in sea turtles are most likely to beencountered in loggerheads. Sulcascaris sulcata (below) has a larval stage in bivalve molluscs such as scallops.

Lester et al image of Sulcascaris sulcata