Observed and modeled larval settlement of a reef fish to the Florida Keys

The bipartite life history of most marine organisms leads to complex patterns of replenishment in benthic populations. High variation in adult spawning, dynamic oceanographic currents, and often unknown larval behaviors create challenges in accurately predicting spatial and temporal patterns in the supply and settlement of pelagic larvae to nearshore juvenile habitats. Yet, understanding and predicting larval exchange underlies population dynamics, ecological interactions, and conservation practices. We compared observed patterns of larval settlement of the bicolor damselfish Stegastes partitus (Pomacentridae) along the Florida Keys, USA, to those obtained through model simulations using a high-resolution biophysical model parameterized with species-specific early life-history information. Light traps intercepted settlement-stage larvae, and divers censused new recruits at 2 replicate reefs in each of the upper (eastern) (UK) and lower (western) Keys (LK) during 6 peak settlement periods. Damselfish settlement and recruitment to the LK consistently exceeded that to the UK. Remarkably, model simulations successfully explained 70% of temporal variation in settlement within each region. However, the model did not capture the relative magnitude of observed settlement between the regions: settlement was either overestimated in the UK or underestimated in the LK. Potential causes include weak larval settlement cues or larval ability to navigate and swim to settlement habitat in the UK, higher larval condition and survival in the more productive waters of the LK, or substantial spatial variation in reproductive output. Connectivity matrices indicate that a majority of S. partitus settlement to the Florida Keys is sourced from Keys populations.