MEPS 614:209-214 (2019)  -  DOI: https://doi.org/10.3354/meps12916

ABSTRACT: The degree to which marine fish larvae aggregate (i.e. patchiness) is predominantly determined by the physical oceanographic environment. Biological traits, however, can also influence spatial distributions and have adaptive value for larvae (e.g. favorable transport or reducing predation mortality). Although several fish families are known to release eggs within a gelatinous matrix, hatched larvae have not been found inside this type of structure. We present observations of hatched, preflexion yolk-sac larvae encased within a pelagic gelatinous matrix (mass). Two different masses (40-60 mm in length) containing free swimming, elongate larvae were imaged in the northern Gulf of Mexico (nGOM) near the pycnocline (~12-17 m depth) during spring 2016. The first mass contained 67 larvae ranging from 2.4-3.2 mm notochord length (NL), while the second mass contained 119 larvae between 3.4-4.5 mm NL. One gelatinous matrix contained an oil globule that may have aided in buoyancy. The larvae were identified as Ophidiiformes based on morphological characteristics. Both the size and developmental stage of the larvae suggested that these masses had persisted for several days. The larval fish mass life history strategy may have survival benefits in predator-rich shelf environments such as the nGOM. These observations raise new questions about how the masses influence larval fish interactions with their environment, both through physical transport and encounters with potential predators.

KEY WORDS: Larval fish · Imaging · Life history traits · Survival · Reproductive strategy · Zooplankton · Gulf of Mexico