Whether mesophotic reefs will behave as refugia for corals threatened by global climate change and coastal development depends on vertical exchange of larvae between diverse habitats. Here we use a biophysical model of larval dispersal to estimate vertical connectivity of a broadcasting (Orbicella faveolata) and a brooding (Porites astreoides) species of coral in the US Virgin Islands. Modeling predicts subsidy to shallow areas by mesophotic larvae of both species based on local hydrology, adult reproductive characteristics, larval traits, and a wide range of scenarios developed to test depth-sensitive factors, such as fertilization rates and post-settlement survivorship. In extreme model scenarios of reduced fertilization and post-settlement survivorship of mesophotic larvae, 1-10 % local mesophotic subsidy to shallow recruitment is predicted for both species, which are demographically significant. Although direct vertical connectivity is higher for the broadcaster, the brooder demonstrates higher local multigenerational vertical connectivity, which suggests that local P. astreoides populations are more resilient than those of O. faveolata, and corroborates field studies. As shallow habitat degrades, mesophotic-shallow subsidy is predicted to increase for both species. This study is the first of its kind to simulate larval dispersal and settlement between habitats of different depths, and these findings have local, regional, and global implications for predicting and managing coral reef persistence in a changing climate.

The Patos Lagoon estuary is an important environment for the life cycle of many species, including the pink shrimp Farfantepenaeus paulensis. This area acts as a nursery ground for the shrimp larvae, which are spawned in a coastal area and transported into the lagoon during spring and early summer (September to December). Harvesting of shrimp occurs from January to May, and yields have varied from around 1,000 to 8,000 tons year −1 . This study is based on analysis of river discharge, pink shrimp catches, and wind velocity time series from 1964 to 2004. Negative correlation between pink shrimp catches and river runoff reflects the influence of discharge on the lagoon circulation and, consequently, on the intrusion of salt water and larvae. When river discharge is below average, landward currents forced by SW winds can enhance larval transport into the estuarine area, leading to an increase in pink shrimp captures. Above average river input would force a seaward flow that works as a barrier to ingress of larvae. This is unusual when compared to many other estuarine systems, and the main factor that accounts for this behavior is the morphology (choking) of Patos Lagoon. Interannual variability related to El Niño/Southern Oscillation events also influence pink shrimp production in this area. Low/high shrimp catches are related to El Niño (flood)/La Niña (drought) events. Wind can also impact production through its effect on the southward displacement of larvae from the spawning area. Long-term trends indicate an increase in river discharge around 20 m 3 s −1 year −1 and a decrease in shrimp catches on the order of 57 tons year −1 .

There is growing awareness that fluctuations in larval flux (connectivity) depress the long-run growth of marine metapopulations, but by how much is unclear. Here, we explore how reproductive schedule and larval behavior affect how much connectivity fluctuations depress growth. We combine larval dispersal simulations from the Florida Keys with theoretical results to calculate the effect of fluctuations on bicolor damselfish (Stegastes partitus). We find that fluctuations depress growth only slightly (∼2%), but the effect would be much stronger for an organism that spawned only part of the year. Larval behavior can also matter, as vertical migration allows larvae to become entrained in eddies. Eddies synchronize connectivity fluctuations, further decreasing growth. However, here, they also divide the Keys into largely independently fluctuating regions, mitigating the effects of local synchrony. Therefore, in situations where connectivity fluctuations matter, the presence of independently fluctuating regions due to larval behavior may be important.

[1] Understanding population connectivity is a contemporary challenge in marine ecology. Connectivity results from a combination of biological traits and physical mechanisms, at different life stages. We focus on the transport of particles around an oceanic island, simulating transport at early life stages of marine organisms. We aim to investigate through case studies how mesoscale features influence particle transport, recruitment, and connectivity. We determine particle dispersion by using an individual-based model and the flow fields derived from a regional implementation of an ocean circulation model. To understand the underlying physical processes of transport, we locate coherent structures in the flow field, identify recurrent physical features, and observe how particle transport is related to them. Our results show that the varying eddying flow increases connectivity among populations located on different sides of the island. Both the flow field and dispersal patterns are highly variable. In this scenario, eddy events influence transport in distinct ways, and the timing of release plays an important role in dispersal. Our results highlight the need for modeling studies to use hydrodynamical model flows that represent the scales of variability affecting transport and dispersion.

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