Biophysical connectivity explains population genetic structure in a highly dispersive marine species

© 2016 Springer-Verlag Berlin Heidelberg Connectivity, the exchange of individuals among locations, is a fundamental ecological process that explains how otherwise disparate populations interact. For most marine organisms, dispersal occurs primarily during a pelagic larval phase that connects populations. We paired population structure from comprehensive genetic sampling and biophysical larval transport modeling to describe how spiny lobster (Panulirus argus) population differentiation is related to biological oceanography. A total of 581 lobsters were genotyped with 11 microsatellites from ten locations around the greater Caribbean. The overall FST of 0.0016 (P = 0.005) suggested low yet significant levels of structuring among sites. An isolation by geographic distance model did not explain spatial patterns of genetic differentiation in P. argus (P = 0.19; Mantel r = 0.18), whereas a biophysical connectivity model provided a significant explanation of population differentiation (P = 0.04; Mantel r = 0.47). Thus, even for a widely dispersing species, dispersal occurs over a continuum where basin-wide larval retention creates genetic structure. Our study provides a framework for future explorations of wide-scale larval dispersal and marine connectivity by integrating empirical genetic research and probabilistic modeling

Increasing the Depth of Current Understanding: Sensitivity Testing of Deep-Sea Larval Dispersal Models for Ecologists

Larval dispersal is an important ecological process of great interest to conservation and the establishment of marine protected areas. Increasing numbers of studies are turning to biophysical models to simulate dispersal patterns, including in the deep-sea, but for many ecologists unassisted by a physical oceanographer, a model can present as a black box. Sensitivity testing offers a means to test the models' abilities and limitations and is a starting point for all modelling efforts. The aim of this study is to illustrate a sensitivity testing process for the unassisted ecologist, through a deep-sea case study example, and demonstrate how sensitivity testing can be used to determine optimal model settings, assess model adequacy, and inform ecological interpretation of model outputs. Five input parameters are tested (timestep of particle simulator (TS), horizontal (HS) and vertical separation (VS) of release points, release frequency (RF), and temporal range (TR) of simulations) using a commonly employed pairing of models. The procedures used are relevant to all marine larval dispersal models. It is shown how the results of these tests can inform the future set up and interpretation of ecological studies in this area. For example, an optimal arrangement of release locations spanning a release area could be deduced; the increased depth range spanned in deep-sea studies may necessitate the stratification of dispersal simulations with different numbers of release locations at different depths; no fewer than 52 releases per year should be used unless biologically informed; three years of simulations chosen based on climatic extremes may provide results with 90% similarity to five years of simulation; and this model setup is not appropriate for simulating rare dispersal events. A step-by-step process, summarising advice on the sensitivity testing procedure, is provided to inform all future unassisted ecologists looking to run a larval dispersal simulation

Ocean sprawl facilitates dispersal and connectivity of protected species

Highly connected networks generally improve resilience in complex systems. We present a novel application of this paradigm and investigated the potential for anthropogenic structures in the ocean to enhance connectivity of a protected species threatened by human pressures and climate change. Biophysical dispersal models of a protected coral species simulated potential connectivity between oil and gas installations across the North Sea but also metapopulation outcomes for naturally occurring corals downstream. Network analyses illustrated how just a single generation of virtual larvae released from these installations could create a highly connected anthropogenic system, with larvae becoming competent to settle over a range of natural deep-sea, shelf and fjord coral ecosystems including a marine protected area. These results provide the first study showing that a system of anthropogenic structures can have international conservation significance by creating ecologically connected networks and by acting as stepping stones for cross-border interconnection to natural populations

Simulating Deep Oil Spills Beyond the Gulf of Mexico

As deep-sea oil exploitation increases worldwide, the probability of another Deepwater Horizon (DWH) blowout also increases. The DWH disaster directly impacted the coastal communities of the Gulf of Mexico (GoM) with 11 deaths and the release of 172.2 million gallons of gas-saturated oil, covering over 1000 miles of coastline and contaminating an estimated 300,000 million cubic meters of GoM water. In the aftermath of the DWH blowout, the question of what a similar event would look like outside the GoM is of fundamental importance. Anticipating the extent and potential environmental impact of major spills in other locations becomes important for effective oil preparedness and response, including coordination of emergency response between neighboring countries. Avoiding deep-sea drilling in environmentally sensitive and some of the world’s most biodiverse and productive fishing areas is also of upmost importance. The west coasts of Cuba and West Africa may be two of the most environmentally sensitive areas across the North Atlantic, yet exploitation of deepwater oil reservoirs has already started or is imminent. Northwest Cuba holds abundant coral reefs characterized by uniquely high diversity and fish biomass, and the region is also home of multi-species spawning aggregations, crucial for the persistence of fish populations. In addition, this area contains Cuba’s most important lobster fishery grounds. A major oil spill occurring in NW Cuba is thus likely to have deleterious impacts on the biodiversity and seafood resources of the region. The West African coastal upwelling system is an extremely productive area, harboring one of the world’s main “hot spots” in terms of fish abundance and biomass. This important system is most likely also a crucial mechanism regulating the climate, and an oil spill in this area could thus have severe local and global impacts. Here we simulate a DWH-like spill in two deepwater prospect blocks offshore Cuba and Senegal, West Africa, and evaluate their extent and impact against the DHW oil spill hindcast as a benchmark. These two hypothetical spills are not locally contained and are both severe, yet we find distinctive differences between their impact on the coastline, the seafloor, and the water column. Overall, the Senegal deep blowout scenario seems to be the most impactful with the highest sedimented and beached oil mass; the Cuba deep blowout scenario is the second worst, with the highest impact in terms of oiled area and volume. In this context, our study demonstrates that if another DWH occurred in a different region, poorly regulated emergency responses for international waters at the time of the spill could result in more detrimental impacts on marine ecosystems and coastal communities compared to the DWH. Here, we bring forward, quantify, and visualize the possible outcomes of another mega-spill similar to the DWH in two strategic locations to increase the awareness of decision-makers and the public to such implications. Since oil exploration is not expected to decrease in the near future, we urge governments to focus on establishing international agreements protecting sensitive marine resources and areas