Ecological traits of sea cucumbers with commercial relevance from the north-eastern Atlantic coast
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1
Faculdade de Ciências, Universidade de Lisboa, MARE - Marine and Environmental Sciences Centre, Portugal
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2
ESTM, Polytechnic Institute of Leiria, Portugal, MARE – Marine and Environmental Sciences Centre, Portugal
Sea cucumbers (Class Holothuroidea) are echinoderms with an extremely important ecological role. They dwell on the benthic zone being either deposit or suspension feeders, feeding on tiny particles like algae, small aquatic animals, or organic matter. The holothurians reduce the organic load of the ecosystems while excreting inorganic nitrogen and phosphorus, playing major roles in nutrient recycling while enhancing the productivity of benthic biota. Apart from nutrients redistribution due to ingestion and release of fecal matter and by their locomotion across the sea bed, sea cucumbers also play an active role on ocean acidification buffering. Some species can increase water alkalinity and dissolved inorganic carbon through their digestive processes and release of ammonia, thereby facilitating calcification by organisms such as corals and increasing the seawater buffering capacity. Commercial exploitation of sea cucumbers provides sources of income to millions of people, mostly in Asian countries. Global assessments reveal that overfishing is a big concern and is leading to an accentuated decline of several sea cucumber populations, generating an increasing number of threatened species. Overfishing is also likely to cause a reduction in value and promote a change in the harvesting regions. The distribution of commercially exploited sea cucumbers is of special interest because their natural abundance can be greatly altered by fishing.
This study aims to understand how environmental variables and geomorphological characteristics may influence the distribution and abundance of three sympatric sea cucumbers species. While most of the ecology of sea cucumbers of the Holothuriida Order is well known, north-eastern Atlantic holothurian species lack information. Environmental variables were analyzed to see how they can affect the distribution of Holothuria forskali, Holothuria tubulosa and Holothuria arguinensis in the Sado estuary and its adjacent coastal area, three sea cucumber species of commercial relevance. The sampling campaign took place monthly, during the winter and spring seasons, and comprised a total of 16 sampling stations for this study of which, 10 were in the Sado estuary, west Portuguese coast, and 6 in its adjacent coastal area. Environmental biotic and abiotic parameters were collected using a multiparameter EXO2 sonde. Geomorphological features with potential influence over sea cucumbers’ distribution were also considered, such as local current exposure and presence of shelter. In addition, nutrients and phytoplankton pigments were quantified in the water column, through HPLC, as well as sediment total organic matter (TOM) and granulometry.
In each sampling station two habitats were defined, sand and rock, and three replicates were done in each, parallel to the coast, at the same depth stratum. Every transect was thirty (30) meters long and three (3) meters wide covering an area of about 90 square meters. Sampling was carried out by scuba diving and sea cucumbers were identified to the species level, counted and total length was measured in situ along each transect. Throughout the sampling period, a total of 1541 sea cucumbers were sampled of which 59 were H. arguinensis (3,8%), 545 H. tubulosa (35,4%) and 937 H. forskali (60,8%).
To test if there were differences, in relative abundances of sea cucumbers, between the sampled months, a two tailed Wilcoxon test was performed. Paired samples included same stations for each month. The Wilcoxon test was done for the total of the three species and for each one of them. To explore the differences of relative abundance of sea cucumbers between habitats (rock or sand bottom), distribution (estuary or coast) and sampling stations, analyses of variance (PERMANOVA) and ordination methods (PCO - Principal Coordinate Analysis) were conducted. All analyses were performed with a significance level of 0.05.
No temporal (monthly) variations were observed in relative abundances, either for the total of the three sea cucumber species or for each species. However, the spatial analysis, revealed that the abundance of each of the three sea cucumber species was higher in coastal stations, negatively correlated with turbidity, temperature and sediment grain size, and there was a preference for rocky habitats within the marine environment. Additional pair-wise tests and the PCO analysis suggested that the site’s exposure to ocean currents (site geomorphology) and the absence of shelter (rock crevices and depressions and closed angles between substrates) have a negative impact on the abundance of these sea cucumbers.
The results of this study show that these three species have a preference for coastal areas and rocky habitats providing shelter, as opposed to open areas or flat rocky substrates. Moreover, the spatial patterns of distribution and abundance appear to be relatively stable and none of the three species occurs under estuarine conditions. Apart from helping with fisheries strategic planning, these results highlight the importance of rocky reefs in the Atlantic distribution area of these, ecological and commercially valuable, sea cucumber species.
Acknowledgements
Acknowledgements
This work was financed by the Operational Program Mar2020. It received further financial support from Fundação para a Ciência e Tecnologia (project UID/MAR/04292/2013 and A.C. Brito with the Research Programme – IF/00331/2013).
Keywords:
Holothuroidea,
echinoderms,
rocky reefs,
marine resources,
invertebrate ecology,
Sado estuary
Conference:
IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018.
Presentation Type:
Poster Presentation
Topic:
Biodiversity, Conservation and Coastal Management
Citation:
Simões
TD,
Azevedo E Silva
FH,
Sousa
JN,
Brito
AC,
Pombo
A,
Venâncio
E and
Félix
PM
(2019). Ecological traits of sea cucumbers with commercial relevance from the north-eastern Atlantic coast.
Front. Mar. Sci.
Conference Abstract:
IMMR'18 | International Meeting on Marine Research 2018.
doi: 10.3389/conf.FMARS.2018.06.00147
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Received:
04 May 2018;
Published Online:
07 Jan 2019.
*
Correspondence:
Mr. Tomás D Simões, Faculdade de Ciências, Universidade de Lisboa, MARE - Marine and Environmental Sciences Centre, Lisbon, 1749-016, Portugal, tomas.simoes@gmail.com