MEPS 650:19-36 (2020)  -  DOI: https://doi.org/10.3354/meps13217

ABSTRACT: Prey availability and predation pressure are thought to be key constraints on larval growth, especially in low-productivity, subtropical environments. Yet, measuring their effects on larval fishes has been challenging, given the dynamic biophysical drivers of plankton distributions and small scales of interactions. We integrated fine-scale net tows (10s of meters) with in situ imaging to explore how predator-prey interactions influence larval fish growth in the Straits of Florida. Otolith-derived recent growth was analyzed for 3 ecologically important fishes: 2 coral reef labrids (Thalassoma bifasciatum and Xyrichtys novacula) and 1 tuna (Katsuwonus pelamis), with differing mean growth rates (labrids 0.25 mm d^-1, K. pelamis 0.44 mm d^-1) and prey (labrids-copepods; tuna-appendicularians). We used generalized additive models to examine the interactive effect of background density and frequency of elevated (>2 SD above background) prey and predators on recent (last 3 d) larval growth. For all taxa, recent growth increased with prey background density. Recent growth of labrids was also higher when copepod densities were more often elevated (14% of transect >20 ind. m^-3) above otherwise low background densities (2 ind. m^-3). Predators (chaetognaths and hydromedusae) had a growth-selective effect: stronger selection in transects with high-density predator patches, although the direction of the effect was species-specific. The effect of temperature was taxa-specific: growth increased with temperature for the labrids and peaked at an optimum (28°C) for the rapidly growing tuna. Integration of these fine-scale sampling methods improves our understanding of the variable influence of prey and predators on larval growth and, consequently, larval survival.

KEY WORDS: Larval fish · Growth · Patchiness · Prey · Predators · Fine-scale · Tuna · Wrasse