Many animals have specialized feeding structures for consuming specific prey types.  In contrast, coral reef mantis shrimp (Stomatopoda) may be generalist predators, even though they have raptorial appendages specialized to produce fast, powerful strikes for smashing hard-shelled prey. My objective was to determine the diet breadth of Neogonodactylus bredini, a species that lives in different habitats with varied prey availability, but is thought to specialize on hard-shelled molluscs. Although diet breadth is notoriously difficult to quantify, stable isotope analysis (SIA) has potential to circumvent the problems associated with traditional measures of diet breadth.  Here, I use SIA to determine the diet breadth of N. bredini from two habitats.

Thirty individuals N. bredini individuals, along with their potential prey (clams, crabs, hermit crabs, fish, and snails), were collected from a seagrass and coral rubble habitat. δ¹³C and δ¹⁵N isotope ratios were measured and mixing model analyses were conducted for the two habitats. Results from the seagrass habitat suggested that not all potential prey were included in this analysis. Thus, I used behavioral experiments to determine the potential diet range of N. bredini from seagrass. N. bredini was presented with 9 different, live prey types (algae, alpheid shrimp, bivalves, brittle stars, crabs, gastropods, hermit crabs, sardines, and worms).  Feeding trials for each prey type were replicated ten times with a different N. bredini individual for each trial and prey consumption was documented.

Results/Conclusions

The mixing model analysis of N. bredini from rubble revealed mean (±SD) percentages of 65±2% fish, 13±8% clams, 12±8% crabs, 5±4% hermit crabs, and 4±3% snails, while the analysis of N. bredini from seagrass failed to yield percentages, because the predator isotope values were too different from those of the prey to reconstruct diet. The behavior experiment revealed that N. bredini consumed every prey item except for algae.  In fact, it consumed soft-bodied, evasive prey more often than hard-shelled prey. For example, fish were consumed in 10/10 trials, whereas marine snails were consumed in 6/10 trials. The results of these studies show that SIA has the potential to reveal intraspecific habitat differences in stomatopod diet and that, while N. bredini appears to be specialized for breaking hard-shelled molluscs, it actually consumes a wider diversity of prey than what is currently documented in the literature.  Thus, N. bredini’s broad diet of hard and soft-bodied prey indicates that specialized morphology does not limit stomatopods to a narrow diet.