Abstract
Schooling is very common in adult and juvenile fish, but has been rarely studied during the larval stage. Recent otolith micro-chemistry studies of coral reef fish have demonstrated that cohorts of larvae can move through similar paths and settle within a few meters one from another. However, little is known about the processes involved in the formation and maintenance of these cohorts. Here we use a biophysical modeling approach to examine whether local hydrodynamics, various individual behaviors, or larval schooling can explain cohesive patterns observed for Neopomacentrus miryae in the Gulf of Aqaba/Eilat (Red Sea), and whether schooling is feasible in terms of initial encounter probability and cohesiveness maintenance. We then examine the consequences of schooling behavior on larval settlement success and connectivity. Our results indicate that: (1) Schooling behavior is necessary for generating cohesive dispersal patterns, (2) Initial larval encounter of newly-hatched larvae is plausible, depending mainly on initial larval densities, and patchiness, And (3) schooling behavior increases the rate of larval settlement while decreasing the percentage of realized connections. Together with mounting evidence of cohesive dispersal, this numerical study demonstrates that larval schooling throughout the pelagic phase is realistic, and has a significant effect on settlement success and connectivity patterns. Future research is needed to understand the mechanisms of fission-fusion dynamics of larval cohorts and their effect on dispersal. Our findings should be considered in future efforts of larval dispersal models, specifically in the context of marine connectivity and the planning of marine protected area networks.
Highlights
Adult and juvenile fish often swim in groups
We examined the plausibility of larval encounter during the early pelagic phase; their capacity to overcome turbulent velocities and remain grouped; and we quantified the relative changes in settlementsuccess and connectivity in schooling vs. non-schooling dispersal
The grouping tendency of N. miryae and Chromis viridis was assessed using the sampling data from Kimmerling et al (2017). We focused on these two species as they were the species examined in Ben-Tzvi et al (2012), with N. miryae demonstrating cohesive dispersal pattern, while C. viridis did not
Summary
Adult and juvenile fish often swim in groups. Such schooling behavior can help reduce drag and conserve energy (Weihs, 1975), improve orientation (Codling et al, 2007), reduce the risk of predation (Shaw, 1978), and enhance the detection of food and mates (Shaw, 1978). The advantages of schooling may benefit the pelagic larval phase that characterizes the life-cycle of most coral reef fishes (Leis, 2006) These larvae are thought to actively group, mainly during late larval stages, once their sensory and movement capacities have matured enough to support this behavior (Shaw, 1978; Arvedlund and Kavanagh, 2009). The relative contribution of biological, physical, and bio-physical processes to the generation and maintenance of such cohesive dispersal pattern, i.e., shared dispersal paths among individuals within the same cohort, is largely unexplored This gap of knowledge is critical, given the demographic and ecological ramifications of the dispersive fate of marine larvae (Levin, 2006). We examined the plausibility of larval encounter during the early pelagic phase; their capacity to overcome turbulent velocities and remain grouped; and we quantified the relative changes in settlementsuccess and connectivity in schooling vs. non-schooling dispersal
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