Dietary analysis of two sympatric marine turtle species in the eastern Mediterranean

Abstract

Dietary studies provide key insights into threats and changes within ecosystems and subsequent impacts on focal species. Diet is particularly challenging to study within marine environments and therefore is often poorly understood. Here, we examined the diet of stranded and bycaught loggerhead (Caretta caretta) and green turtles (Chelonia mydas) in North Cyprus (35.33° N, 33.47° E) between 2011 and 2019. A total of 129 taxa were recorded in the diet of loggerhead turtles (n = 45), which were predominantly carnivorous (on average 72.1% of dietary biomass), foraging on a large variety of invertebrates, macroalgae, seagrasses and bony fish in low frequencies. Despite this opportunistic foraging strategy, one species was particularly dominant, the sponge Chondrosia reniformis (21.5%). Consumption of this sponge decreased with increasing turtle size. A greater degree of herbivory was found in green turtles (n = 40) which predominantly consumed seagrasses and macroalgae (88.8%) with a total of 101 taxa recorded. The most dominant species was a Lessepsian invasive seagrass, Halophila stipulacea (31.1%). This is the highest percentage recorded for this species in green turtle diet in the Mediterranean thus far. With increasing turtle size, the percentage of seagrass consumed increased with a concomitant decrease in macroalgae. Seagrass was consumed year-round. Omnivory occurred in all green turtle size classes but reduced in larger turtles (> 75 cm CCL) suggesting a slow ontogenetic dietary shift. Macroplastic ingestion was more common in green (31.6% of individuals) than loggerhead turtles (5.7%). This study provides the most complete dietary list for marine turtles in the eastern Mediterranean.

Underreported in-water behaviours of the loggerhead sea turtle:Foraging on sea cucumbers

“…Similar frequencies for Holothuroidea (3.3%) were found by Karaa et al ., 2018, after performing necropsies on 132 loggerheads from the Gulf of Gabes, Tunisia. Further reports can be also found in Palmer et al ., 2021, where also a photograph of a possibly intact sea cucumber recovered from a turtle’s ingestive tract is provided.…”

“…Similar frequencies for Holothuroidea (3.3%) were found by Karaa et al, 2018, after performing necropsies on 132 loggerheads from the Gulf of Gabes, Tunisia. Further reports can be also found in Palmer et al, 2021, where also a photograph of a possibly intact sea cucumber recovered from a turtle's ingestive tract is provided. This relatively low frequency of consumption of sea cucumbers reported in the above studies, reflects the rarity of observations of this consumption in our study site.…”

Huge spring migrations of insects from the Middle East to Europe: quantifying the migratory assemblage and ecosystem services

“…6E, F; Forster unpubl. ; Palmer 2021). These observations highlight the extent of nutrient transfer and food web structuring by migratory insects and hint at the importance of these transient events for linking geographically separated ecosystems.…”

High mortality of beetle migrants along the Eastern Mediterranean Flyway

“…The stranding events recorded in the current study likely represent a small percentage of the number of beetles migrating, suggesting that large quantities of nutrients from the beetles' bodies could end up in the sea and, therefore, be available for the marine ecosystem. For example, autopsies performed on loggerhead and green turtles during spring 2019 revealed that migratory invertebrates, such as painted lady butterflies ( Vanessa cardui ) and migratory Orthoptera, had been ingested (Palmer et al, 2021). Other marine residents, such as fish and marine invertebrates, no doubt also feed on the migrant insects falling into the ocean.…”