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Foraging plays a crucial role in influencing the growth and stability of sea turtles and their populations (Bjorndal 1997). It helps in their somatic growth which consequently affects their rate of maturity and reproductive ability (Arthur & Balazs 2008). A delay in the maturity of individuals could have adverse effects on their survival until adulthood (Balazs & Chaloupka 2004). In addition, the quality and quantity of their foraging resources are also known to impact the inter-annual variability in nesting (Arthur & Balazs 2008). Therefore, availability and quality of resources determine the diet and consequently, the health of a population.

In the Indian subcontinent, the Lakshadweep islands, located between 8° to 12° N and 71° to 74° E (Fig. 1), serve as foraging and nesting grounds for adult and juvenile green turtles in the northwestern Indian Ocean (Tripathy et al. 2002, 2006). The low- lying lagoons of the islands support thriving populations of various seagrasses and algae which, in turn, provide suitable feeding sites for the herbivorous green turtles. It has been observed that of the seven seagrass species found in the Lakshadweep islands, green turtles tend to feed specifically on Thalassia hemprichii and Cymodocea rotundata, of which Thalassia sp. is preferred (Kelkar et al. 2013).

Figure 1. Map of the Lakshadweep islands and the two islands - Agatti and Kalpeni - from where the fecal samples were collected.

Apart from the consumption of these two seagrass species, there is little known about the remainder of green turtle diets in the Lakshadweep islands. Moreover, the green turtle population may have increased in the last 15 years leading to overgrazing of Thalassia and Cymodocea communities resulting in a shift in species composition in the lagoons (Kelkar et al. 2013). This could induce a change in their diets or a change in their foraging grounds. Hence, it is important to determine diet preferences, which will assist in devising a management plan for green turtles as well as conservation strategies for seagrass communities. Therefore, a fecal analysis was conducted to identify components that constitute green turtle diet in the Lakshadweep islands.

A total of 39 fecal samples were collected opportunistically from the islands of Agatti (n = 18) and Kalpeni (n = 21) over 2 field seasons (2018-2019). The availability of fecal samples corresponded with the presence of turtles in the lagoons of these two islands. The feces were mainly collected when washed up on
the beaches or when floating on water. Upon collection, all samples were sun-dried for 24 hours to prevent fungal formation. The feces were then brought to the lab to separate and identify individual components. In order to separate the fecal matter, the samples were immersed in water overnight to loosen the contents. To ensure uniformity in the size of the samples, bigger samples were cut into smaller parts of which one part was used for identification (approx. 8 g). From each of the samples, macroscopic parts were separated and stored in individual jars for identification. Identification was done using a Leica© microscope (Model No: DM 1000) under 10X and 40X magnification for smaller components. Each component was identified and its occurrence in the samples was recorded.

Table 1. Frequency of occurrence (%FO) for items - food and non-food - in green turtle feces from 39 samples.

Figure 2. Constituents of green turtle feces show a clear preference toward seagrass than towards algae in Agatti Island (left side) and Kalpeni Island (right side).

Based on these data, the frequency of occurrence of each component was calculated for different years (Table 1). Coral fragments, animal tissue and seagrass blades were more frequently observed in Agatti, but sample sizes were too small to make inferences on food choice between sites. Seagrass stem and blades formed the bulk of identified components (85-88%) of the total in both islands (Fig. 2). From the seagrass components, only the blades were useful in species identification. The species of seagrass blades found in the feces comprised Thalassia hemprichii (Fig. 3), Cymodocea rotundata and Halodule uninervis (Fig. 4). Species- level identification could not be conducted using the stem epidermis or rhizomes. Coir or coconut husk was another commonly found component in the fecal matter. In addition, smaller percentages of cloth pieces, bits of plastic and small fragments of dead corals were found in some of the samples. We also found evidence of sponges in the form of spicules in 2018 and algae in 2019; however, these remain unidentified.

Figure 3. Thalassia hemprichii leaf blade found in some samples in 2018. Bar = 0.4mm.

Figure 4. Halodule uninervis leaf blade found in two samples from Agatti. Bar = 0.4mm.

Figure 5. Filamentous green algae samples found in feces collected in Kalpeni. Bar = 0.4mm.

Our results support previous findings that the seagrass species preferred by green turtles in the Lakshadweep islands are Thalassia hemprichii and Cymodocea rotundata. In addition to these two species, undigested bits of Halodule uninervis (Fig. 3) blades in fecal samples were also detected. However, it is not clear if Halodule was ingested accidentally as it closely resembles blades of two preferred species or if the blades were consumed as an alternative food source. Despite the reduction in the density of Thalassia and Cymodocea, there is no clear indication that green turtles are altering their diet to compensate for the lack of resources. In addition, there was evidence of seagrass rhizomes from the samples, which shows that green turtles resort to the uprooting of rhizomes for consumption. This could prove detrimental to the recovery of seagrass if there are no remnants of the plant from which the shoots can regrow (Christianen et al. 2014).

Coir was also found in the turtle feces. This conforms to local observations of green turtles eating coconuts that get washed into the lagoon (Kale pers. obs. 2018). In addition, cloth pieces and plastic strands were also found in the feces. Cloth pieces are an indication of poor waste management as a lot of household waste gets thrown onto the beach, which then enters the lagoon. The presence of plastic probably indicates accidental ingestion by green turtles in the Lakshadweep islands; this coincides with global observations of increased plastic presence in sea turtle guts, even from remote oceanic islands (McCauley & Bjorndal 1999; Parker et al. 2011; Ng et al. 2016). In the Lakshadweep islands, this could be due to plastic getting trapped in seagrasses and algae or direct consumption of plastics.

Filamentous green algae were also observed in the feces from one of the two islands that were sampled, potentially belonging to Cladophora spp (Fig. 5). Previous studies in these islands suggest that green turtle herbivory results in a drastic reduction in densities of Thalassia hemprichii and Cymodocea rotundata (Lal et al. 2010; Kelkar et al. 2013). This study provides the first observation that green turtles may also consume algae with seagrass. This could potentially mean that, in cases of low availability of seagrass, some individuals could shift their diet toward algae. Components such as traces of sponge spicules, other animal tissue, and algal matter were observed in the fecal samples for the first time, which could suggest that adult green turtles might have a broader diet spectrum.

Fecal analysis is not the most effective method to determine diet components at a species level as completely digested material will not be identifiable in the feces. Moreover, microscopic components such as algae, seagrass seeds, etc. cannot be easily detected using this method. Techniques such as stable isotope analysis or gastric lavage will improve our understanding of green turtle diets in this region. Broadly though, the results suggest that green turtles in the Lakshadweep lagoons are maintaining their preferred diet of seagrass species and are perhaps compensating for the lack of it by eating other seagrass species and algae. While the presence of Halodule sp. and algae was in very small quantities, it could indicate the onset of diet change, given the declines in overall seagrass cover and density. Further information on their diets will be useful in informing management plans for green turtles as well
as for the conservation of their foraging habitats.

Acknowledgments. The authors thank the Departments of Science & Technology (DST) and Environment & Forests (DEF) of the Lakshadweep Administration for granting the research and entry permits to conduct work in the Lakshadweep islands. The authors also thank the Rufford Small Grants Foundation and the Marine Turtle Conservation Act Fund for their financial support that enabled this study.

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