Abalones are the one of the most important mollusks fished in many coastal regions of the world, such as Australia, New Zealand, South Africa, Chile and California. In recent years, the different countries have implemented a variety of regulations on the fishery to avoid overfishing. However, an unresolved question is whether regulations such as these need to be implemented over large scales over thousands of miles of coast, or whether small scale regulations at the level of individual fishing towns can be successful? It has recently been shown that the populations of the various Abalone species can be genetically quite different from one another over small spatial scales, implying that these populations do not exchange dispersing larvae and that small scale fishery regulation is reasonable. On the Northern California coastline, state regulators are poised to set up a new series of abalone fishery regions with little guidance about how populations disperse. This project is a transcriptome-wide survey of the genetic variation in California from around Cape Mendocino to Monterey Bay. The aim is to identify regions in the genome that are differentiatied at a local population level. Differences in these regions could then be correlated with environmental variables to identify the factors affecting the genetic structure of Abalones within this region. This knowledge will shed light on the structuring processes, which will be invaluable information for management efforts of Abalone fisheries not only in California, but worldwide.
The Abalone fishery is one of the world’s most economically important gastropod fisheries (Leiva and Castilla, 2001). Unfortunately, due to increasing fishing effort, the stocks of gastropods have steadily decreased in the last 40 years (Leiva and Castilla, 2001). Most notably, the Californian Abalone fishery, which was peaking in landing size at around 1970 ended in the crash of stocks of all four commercially fished species, to the point where it had to be closed down completely in 1997 (Leiva and Castilla, 2001); the white Abalone, Haliotis sorenseni being the first marine invertebrate protected under the Endangered Species Act of 2001 (Micheli et al., 2008). Disappointingly, despite efforts to the contrary, the stocks of Abalone have not increased since the closure of the fishery, and all species along the California coast except the Red Abalone are currently under concern (Gruenthal and Burton, 2005; Kashiwada and Taniguchi, 2007; Micheli et al., 2008).
Recent genetic studies on various species of Abalone in California indicate that the populations differ genetically from each other, even along the same coastline (Chambers et al., 2006; Gruenthal et al., 2007; Gruenthal and Burton, 2008; Gutierrez-Gonzalez et al., 2007). This indicates that there are barriers to dispersal along the coastline, dividing the Abalones into separated populations. This is a very important realization for the management of the fishery, as one cannot expect the recovery of isolated populations without larval influx, the lack of which often is the result in a collapsed population (Miller et al., 2009). In other parts of the world such as Australia, Tasmania, China and Japan, genetic structure of Abalone populations have also been reported (Li and Kijima, 2006; Li et al., 2006; Maynard et al., 2004; Tang et al., 2004; Temby et al., 2007; Zhang et al., 2006).
In particular, a recent study on Red Abalone (Haliotis rufescens) showed that the population along the California coastline is structured geographically (Gruenthal et al., 2007). In this case, there seems to be a shift in population structure around the Cape Mendocino region. This region has also been shown to be a breakpoint in the distributions of many other species, such as mussels (Braby and Somero, 2006) and a variety of fishes (Hyde and Vetter, 2009; Tolimieri and Levin, 2006). Recently, Kelly and Palumbi (2010) showed strong population genetic structure in six species of invertebrates across the Mendocino region. This is attributed to several physical factors, especially a strong jet of upwelling water at the Cape as well as temperature gradients.
Currently, this project investigates the genetic population structure of Red Abalone (Haliotis rufescens) along the coastline of California. Abalone populations from northern California (Crescent City) down to Monterey Bay are being sampled. To study genetic differences on this scale, microsatellite DNA data (“DNA finger-printing”), or sequences from the control region of mitochondrial DNA are regularly used, both rather simple and cost-effective methods. Unfortunately, this kind of data has not always given good results in the past (e.g. Gruenthal et al., 2007). Therefore, the genome of the Abalone is now being studied in further detail, by extracting total RNA from select individuals and using the Illumina Hi-Seq platform to assemble a reference transcriptome.
The reference transcriptome can then be used for multiple tasks. Candidate genes can be identified which could elucidate the population structure of H. rufescens as well as other Abalone species along the coast, which in turn could be correlated with dispersal patterns as well as local environmental conditions. Outlier tests could also identify genes under selection and perhaps help us understand how upwelling conditions with cold, low-pH water could locally affect the genetic makeup of populations along the coast.
Knowledge of how Abalones are structured geographically and what processes regulate their recruitment is crucial for management and for the task of rebuilding the stocks of these seriously overfished species. This study will help us gain an understanding of the small-scale variability which could then be extrapolated to study large scale variation, not only in California, but all over the world. As many other benthic invertebrates and fish show similar patterns, these results will hopefully also be applicable to the management of a wide variety of organisms.
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