Abstract
There is an increasing demand for sea cucumbers, for human consumption, mainly from Asian markets and, as a consequence, NE-Atlantic species are now new targets for exploitation and exportation. Holothuria mammata is one of the most valuable species in Europe. However, the lack of historical economic interest in this species in most European countries has also led to a lack of studies concerning biological and ecological aspects on wild populations and this is a major issue for stock management. This study aims to determine the temporal and spatial patterns of distribution of H. mammata, considering its abundance and demographic structure in a NE-Atlantic area, SW Portugal, as a function of environmental conditions. For that, a population from a marine protected area was followed for 1 year at 1.5-month intervals. Throughout the coastal area, six sites were selected and at each sampling campaign three random transects per site and substrate (rock and sand) in which all H. mammata individuals were counted and measured. For each site and survey several environmental parameters of interest, from the water column, the sediment and substrate cover, were also measured. Generalized Linear Models were used to model the spatial and temporal distribution of the species according to environmental conditions, to determine the species’ habitat preferences. The distribution models indicate that abiotic and biotic parameters of the water column are not the main drivers shaping the distribution of H. mammata. The species has a patchy distribution, and its habitat preferences depend on environmental stability, the presence of shelter and habitat complexity, which is more important for smaller, more vulnerable, individuals, while bigger size classes tend to venture more into less stable environments in an opportunistic fashion. The knowledge of these population traits is determinant to develop stock management measures, which are now urgent to prevent the depletion of commercial sea cucumber populations in the NE-Atlantic. Sustainable fisheries policies should be developed and start by considering to delimit fishing areas and periods, considering the species spatial and temporal distribution patterns.
Highlights
Sea cucumbers are a group of echinoderms with important ecological functions
Densities found in the present study were the highest, compared to a maximum density of 55 ind/10 m2 found in the Mediterranean, Aegean Sea (Aydin, 2019a), 16 ind/10 m2 reported in the Canary Islands (Navarro et al, 2013), and particular low densities observed at Ria Formosa of 1.2 ind/10 m2 (Siegenthaler et al, 2017)
H. mammata prefers a more stable environment, which is more important for smaller individuals, while bigger size classes tend to move to less stable environments, probably in an opportunistic fashion due to their size related resilience
Summary
Sea cucumbers are a group of echinoderms with important ecological functions. Deposit-feeders compose a large group of these holothurians, which play a critical role in habitat structuring through bioturbation, recycling and redistributing nutrients (e.g., MacTavish et al, 2012; Purcell et al, 2016). The majority of exploited sea cucumber species are, deposit-feeders (most of the formerly known aspidochirotids) (Purcell et al, 2016), and several of these are currently overexploited or depleted (Purcell et al, 2013) This can create a set of inevitable ecological consequences that can result in a curtailment in primary productivity, decrease in benthic diversity and biomass, decrease of buffering capacity of surrounding seawater acidity, preclude symbiotic associations, impair trophic relationships, etc. Considering the ecosystem services provided by these species, the overexploitation of multiple populations has the potential to create severe cascading effects in the ecosystems
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