Abstract
This study analyzes the temporal variability/stability of the spatial distributions of key exploited species in the Gulf of Lions (Northwestern Mediterranean Sea). To do so, we analyzed data from the MEDITS bottom-trawl scientific surveys from 1994 to 2010 at 66 fixed stations and selected 12 key exploited species. We proposed a geostatistical approach to handle zero-inflated and non-stationary distributions and to test for the temporal stability of the spatial structures. Empirical Orthogonal Functions and other descriptors were then applied to investigate the temporal persistence and the characteristics of the spatial patterns. The spatial structure of the distribution (i.e. the pattern of spatial autocorrelation) of the 12 key species studied remained highly stable over the time period sampled. The spatial distributions of all species obtained through kriging also appeared to be stable over time, while each species displayed a specific spatial distribution. Furthermore, adults were generally more densely concentrated than juveniles and occupied areas included in the distribution of juveniles. Despite the strong persistence of spatial distributions, we also observed that the area occupied by each species was correlated to its abundance: the more abundant the species, the larger the occupation area. Such a result tends to support MacCall's basin theory, according to which density-dependence responses would drive the expansion of those 12 key species in the Gulf of Lions. Further analyses showed that these species never saturated their habitats, suggesting that they are below their carrying capacity; an assumption in agreement with the overexploitation of several of these species. Finally, the stability of their spatial distributions over time and their potential ability to diffuse outside their main habitats give support to Marine Protected Areas as a potential pertinent management tool.
Highlights
The Mediterranean Sea is a marine biodiversity hotspot [1,2,3] that is subject to growing anthropogenic pressures, such as fisheries, eutrophication [4] and climate change [5,6]
This study focuses on this second aspect and aims to describe and quantify the spatial dynamics of benthic-demersal marine resources in the Gulf of Lions (Northwestern Mediterranean Sea), using the 17 years of scientific time-series surveys carried out in this region
We examined if the annual empirical variograms of a given species were significantly different from year-to-year, in comparison with the sampling variance associated with the mean variogram
Summary
The Mediterranean Sea is a marine biodiversity hotspot [1,2,3] that is subject to growing anthropogenic pressures, such as fisheries, eutrophication [4] and climate change [5,6]. MPAs are designed without adequate information regarding the functioning of the local ecosystem, failing to meet the objectives for which they were implemented in the first place [13]. Modeling both fishing effort and spatial distributions of the exploited species can help stakeholders and managers in the decision of where to place the MPAs [14]. This study focuses on this second aspect and aims to describe and quantify the spatial dynamics of benthic-demersal marine resources in the Gulf of Lions (Northwestern Mediterranean Sea), using the 17 years of scientific time-series surveys carried out in this region. Our aim is to rigorously quantify the temporal stability/variability of the spatial distributions of key exploited species since 1994, which is of interest from a MPA perspective
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