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MEPS prepress abstract   -  DOI:

Food web constraints on larval growth in subtropical coral reef and pelagic fishes

Miram R Gleiber*, Su Sponaugle, Kelly L Robinson, Robert K Cowen

*Corresponding author:

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 (10’s m) 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 three ecologically important fishes: two coral reef labrids (Thalassoma bifasciatum and Xyrichtys novacula) and one tuna (Katsuwanus 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 (>2SD 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.