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Individual study: Nest monitoring highlights the extent of a previously little-known marine turtle egg predator, the click beetle Lanelater sallei, at Cape Florida State Park, Florida, USA

Published source details

Donlan E.M., Townsend J.H. & Golden E.A. (2004) Predation of Caretta caretta (Testudines: Cheloniidae) eggs by larvae of Lanelater sallei (Coleoptera: Elateridae) on Key Biscayne, Florida. Caribbean Journal of Science, 40, 415-420

Summary

Marine turtle (Cheloniidae, Dermochelyidae) nests are subject to predation by a variety of animals. During loggerhead Caretta caretta nest evaluations in 2001 at Cape Florida State Park, USA, coleopteran larvae were observed in many nests, apparently feeding on eggs. As well as directly observing larvae, their presence was indicated by small holes in the egg shell, and in some cases larvae were observed inside desiccated eggs.

The larvae were reared and identified as the click beetle Lanelater sallei. In 2003, the impact of these beetle larvae on turtle eggs at CFSP was assessed, prior to this egg loss had been thought primarily due to predation by raccoons Procyon lotor and to a lessr extent, ghost crabs Ocypode spp.

Study site: The turtle nest observations were undertaken at the Bill Baggs Cape Florida State Park (CFSP). The Park covers 174 ha and is situated at the southern end of Key Biscayne (Miami-Dade County), on the east coast of Florida. The beach at CFSP is 1.9 km long and incubating loggerhead eggs may be present from mid-April to early October. Occasionally, leatherback turtles Dermochelys coriacea also nest.

Turtle nest monitoring: Between April and October of 2001, 2002 and 2003, the beach was patrolled daily by staff and volunteers in order to mark and cage (with a wire mesh cage to exclude mammal predators) all new turtle nests and check for emergence of hatchlings. Nests were typically evaluated three days after hatchling emergence. Some that had apparently been completely predated by raccoons Procyon lotor or flooded by high tides were not carefully examined. If no emergence was observed after 70 days, nests were excavated to determine the status and assess possible causes of failure. In some cases, nest remains were badly deteriorated and so attributing a cause of failure was not straightforward.

During the 2001 and 2002 turtle nesting seasons the presence of beetle larvae in some nests was noted, with some eggs having small ragged holes in their shells. Typically, the contents of damaged eggs were not examined, but they often appeared desiccated. In most cases beetle larvae were not removed and were placed back in with the contents of the nest when reburied. Due to inconsistencies in data collection regarding such damaged eggs in 2001 and 2002, additional larvae-related egg damage may have been overlooked and the primary cause of damage may have been attributed to predation by crabs or raccoons, or other factors. In 2003 the presence of larvae in the nests was carefully documented, and an expanded data collection sheet, as well as additional training, was provided to volunteer nest evaluators.

Data collection was extended to record:

1) number of eggs with holes equal to or greater than 1/8” (approx. 4 mm)
2) number of beetle larvae observed
3) plant cover within a 2 m radius

Evaluators were encouraged to collect larvae and also recorded evidence of raccoon or crab predation, flooding, nest depth, hatchling mortality, as well as other aspects of nest condition.

In 2001 and 2002 L.sallei larvae were observed in 23% and 18% of loggerhead nests, respectively. In 2003, when data collection more specifically focused on detecting and counting L. sallei larvae, the percentage increased to 48% of nests. As survey effort was more concentrated in 2003, no fair comparison can be made between these three years. The number of nests present and evaluated also decreased in each of the three years (to a low of 59 in 2003).

The beetle larvae collected from loggerhead nests in 2003 ranged in size from 10.9 to 53.3 mm in length (average = 24.2, n = 30). In 2003, of the 59 loggerhead nests evaluated, 46 (78%) contained L. sallei larvae and/or turtle eggs with damage consistent with that observed in eggs of an experimental iguana Iguana iguana nest (see original paper), typically with ragged holes 3-5 mm in diameter with desiccated contents.

Extent of beetle damage to turtle eggs: L.sallei larvae damaged more eggs at CFSP than any other egg predators (see Table 1, attached), with three times as many eggs damaged by beetles compared to raccoons, the only other major egg predator. Some nests contained as many as 22 L.sallei damaged eggs. At least 18 nests were found to have eggs with small holes but no L.sallei larvae were visible. In such cases in earlier years, this may at times have gone unrecorded. The difference between the level of L.sallei predation and predation by larger animals may be somewhat misleading, as raccoons (and other mammals) were prevented from extensive predation due to placement of cages over the nests, as well as removal of raccoons from the nesting beaches during previous seasons. It should be borne in mind that many other insects and insect larvae have also been reported to prey on sea turtle eggs.

Plants recorded by nests: In 2003, at least 27 plant species were recorded within 2 to 50 m of the 59 nests observed. Only four nests that contained beetle larvae did not have vegetation within 2 m. It is not known if close proximity of plants is a true indicator of likelihood of turtle egg infestation by L.sallei larvae.

Conclusions: In 2003 predation by L.sallei larvae was unequivocally the largest cause of loss of loggerhead eggs at CFSP. L.sallei occurs on the Gulf and Atlantic coasts of the USA from Louisiana north to New York. It is typically known from near coastal beaches and sandy inland habitats. Given that all nesting localities for loggerhead turtles in the eastern United States fall within the range of L.sallei and that L.sallei inhabits sandy coastal areas, it is conceivable that predation by L.sallei larvae may have a major impact on US nesting marine turtle populations.

Interestingly, loggerhead nest surveys at nearby Crandon Park, also on Key Biscayne, failed to find any evidence of beetle larvae egg predation in 2001 or 2002. Infestation by L.sallei may therefore be local and/or sporadic. The extent of egg predation needs be examined further to determine what, if any, management practices may reduce the impact of the coleopteran larvae predation on turtle nest success.


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