Combined biophysical and genetic modelling approaches reveal new insights into population connectivity of New Zealand green-lipped mussels

Abstract

Understanding how ocean currents affect larval transport is crucial for understanding population connectivity in sessile marine invertebrates whose primary dispersal opportunity occurs during the pelagic larval stage. This study used Lagrangian particle tracking experiments to examine population connectivity in New Zealand green-lipped mussels (Perna canaliculus) at the national scale. Predicted patterns of larval dispersal were compared to published multi-locus microsatellite data of observed population genetic structure. Estimates of oceanographic circulation correlated significantly with FST, and we conclude that hydrodynamic processes are important in driving genetic connectivity. However, no evidence was found for an oceanographic barrier to gene flow south of Cook Strait, an important feature of genetic structure observed across several marine invertebrate species. Discrepancies between genetic and biophysical data may be explained by several factors including the different timescales of connectivity described by the two methods and the impact of localised ecological conditions and corresponding adaptations in genetic structure not captured by the bipohysical model. Population genetic analyses provide empirical data on realised connectivity and Lagrangian particle tracking experiments reveal information about directionality and asymmetry of connections that often cannot be determined by molecular analyses alone, thus a multidisciplinary approach is recommended.

Spatial and temporal variation in the predicted dispersal of marine larvae around coastal Aotearoa New Zealand

“…We chose this model because it is the most recent, highest resolution (5 km) openly accessible model covering the entirety of Aotearoa New Zealand, a necessary condition for a study at the national scale. The 5 km resolution has been shown to be suitable in modeling larval dispersal along the Aotearoa New Zealand coastline (Quigley et al, 2022;Chaput et al, 2023). While higher resolution coastal models have been created for some Aotearoa New Zealand coastal regions, harbors and bays (e.g.…”

“…Chiswell (2009) MIKE 21 to model the hydrodynamics of the Whangarei Harbor to show which sites can recolonize the surrounding areas by cockle Austrovenus stuchburyi. Recent efforts in Aotearoa New Zealand (e.g., Quigley et al, 2022;Chaput et al, 2023) have used the recently developed Moana Project hydrodynamic model (de Souza et al, 2022) with the open-source Lagrangian trajectory software OpenDrift (Dagestad et al, 2018) to assess the dispersal of green-lipped mussels Perna canaliculus. Few studies (e.g., Cecino and Treml, 2021) have examined the larval dispersal of multiple species, and none have undertaken this around Aotearoa New Zealand.…”

“…Few studies (e.g., Cecino and Treml, 2021) have examined the larval dispersal of multiple species, and none have undertaken this around Aotearoa New Zealand. Most studies examine a single species and determine the patterns of larval dispersal and settlement for only that species (e.g., Viard et al, 2006;Domingues et al, 2012;Norrie et al, 2020;Quigley et al, 2022). This work uses a biophysical model to predict larval dispersal and settlement patterns for differing PLDs and spawning months from representative locations around the entirety of the coastline of the main islands of Aotearoa New Zealand.…”

I aha ki ngā toheroa nō Horowhenua, what happened to the toheroa of the Horowhenua?

“…As these northern populations have declined over time, this has meant that there is even more limited larval input to the more southern beaches, and therefore restoration should also focus on these two beaches. To increase the validity of the findings of the larval connectivity modelling, further investigation through tools such as shell microchemistry and/ or genetic analysis, as seen in the MOANA project, will be useful (e.g., Quigley et al, 2022).…”

“…Therefore, toheroa populations on the Horowhenua coast may have limited larval connectivity with Te Tai Tokerau populations, although there could be connectivity with other populations elsewhere. Biophysical models can be used to assess larval dispersal capability among populations (Quigley et al, 2022), which has been done for kūtai (Quigley et al, 2022;Chaput et al, 2023), tuangi (Lundquist et al, 2008), and snapper (Le Port, 2014) in Aotearoa, but not yet for toheroa.…”