Abstract
In the present work we focus on the distribution of two species of sponges. One of these is Asconema setubalense, a sponge found in rocky substrate that was sampled with a photogrammetric vehicle through georeferenced images. The other is Pheronema carpenteri, which inhabits soft bottoms and was sampled by beam trawl. For the spatial distribution modeling of both sponges, the geomorphological variables of depth, slope, broad and fine scale bathymetric position index (BPI), aspect, and types of bottoms were used, all with a resolution of 32 m. Additionally, layers of silicates and currents near the bottom were extracted from Copernicus Marine Environment Monitoring Service (CMEMS), with a resolution of ∼4 and ∼9 km, respectively. Due to the low resolution of the layers, it was considered necessary to validate their use by model comparison, where those that included these variables turned out to be more explanatory than the others. The models were developed in a complex continental break of the Central Cantabrian Sea, which comprises several submarine canyons and a seamount (Le Danois Bank). On the one hand, a very high resolution (32 m) spatial distribution model based on A. setubalense presence was developed using the MaxEnt maximum entropy model. On the other, depending on the availability of density data, generalized additive models (GAMs) were developed for P. carpenteri distribution, although in this case the sampler only allowed a maximum resolution of almost 1 Km. For the A. setubalense, the variables that best explained their distribution were ground types and depth, and for P. carpenteri, silicates, slope, northness, and eastward seawater velocity. The final model scores obtained were an AUC of 0.98 for the MaxEnt model, and an R squared of 0.87 for the GAM model.
Highlights
The great majority of sponges are sessile filter feeders whose importance lies in that, along with corals, they are essential for characterizing a multitude of specific deep-sea habitats
The central Cantabrian Sea is an area of complex morphostructural characteristics dominated by an intricate canyon system and a seamount partially isolated from the continental shelf
The need of comprehensive knowledge of the seabed is increasingly urgent, especially in regard to vulnerable marine ecosystems (VME). This is difficult in the deep-sea, where, due to its remoteness, the sampling is too often very scarce, or focused on a particular aspect, or does not have the quality of data that would be desirable. This is why it is so necessary to optimize the data yield while achieving consistent spatial resolution that is in accordance with the objectives of the study
Summary
The great majority of sponges are sessile filter feeders whose importance lies in that, along with corals, they are essential for characterizing a multitude of specific deep-sea habitats. In many deep-sea areas, sponges may be the dominant organism, forming structurally complex and often highly diverse ecosystems known as sponge grounds (Hogg et al, 2010; Beazley et al, 2013; Maldonado et al, 2017). Due to their vulnerability, mainly to trawl fisheries, their need for protection has been the object of great concern since the beginning of the present century. Given that the preservation of VMEs will be the first step toward achieving a good environmental status (GES) of the marine environment, and that the preservation of sponges will be one of the main contributions to establish the necessary environmental objectives and associated indicators, their protection will be a good starting point for developing the maritime spatial planning (MSP) required in the Marine Strategy Framework Directive (MSFD) as it relates to MSP Community action (European Union, 2014)
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