Holothuria

Abstract: In aquarium experiments and during field observations, Holothuria (Halodeima) atra (Jaeger, 1883) and Stichopus chloronotus (Brandt, 1835) consumed an average of 67 and 59 g dry wt of sediment individual -1 d -1 , respectively. A model calculation showed that a mixed population of both species on a reef flat near Lizard Island GBR has the potential to rework about 4600 kg dry wt yr 1 1000 m 2 which is approximately the weight of the upper 5 mm of sediment in this area. Gut content analyses showed no significant decrease in phycopigments (chlorophylls a and c and fucoxanthin) during gut passage. In both species the oesophagus pigment content was similar to the concentration in sediments directly in front of the individuals. However, pigment content in front of S. chloronotus and in all gut segments of this species were significantly higher than the corresponding values in H. atra suggesting patch selectivity in the former species. Extremely low meiofauna contents in holothurian guts indicated that meiofauna play a negligible part in the nutrition of H. atra and S. chloronotus. In contrast, the ratio of living to dead diatoms was significantly lower in the guts of both holothurian species compared to the adjacent sediment, indicating digestion of the ingested diatoms. In aquarium experiments, feeding and bioturbation activity ofboth species significantly reduced microalgal biomass (measured as chlorophyll a concentrations) in sediments inoculated with diatoms or cyanobacterial mats.

Abstract: Echinoderms are the deuterostome group with the most striking capacity to regenerate lost body parts. In particular, members of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process. Such formation of new viscera in an adult organism provides a unique model to study the process of organogenesis. We have studied this process in the sea cucumber Holothuria glabberrima by describing the spatial and temporal pattern of cellular events that occur during intestine regeneration following chemically induced evisceration. Regeneration begins as a thickening of the mesenteries that supported the autotomized organs to the body wall. The mesenterial thickening consists of tissues where most of the cellular populations found in the normal intestine are already present. However, the cell numbers differ, particularly those of hemocytes and amoebocytes, suggesting that some of these cells play an important role in the formation of the solid rod of hypertrophic mesentery that characterizes the intestinal primordia. The appearance of the luminal epithelium, together with the formation of the lumen, occurs during the second week of regeneration by proliferation and extensive migration of cells from the esophagus and cloacal ends into the thickenings. At this stage all tissue layers are present, but it takes an additional week for them to exhibit the proportions typical of the normal organ. Cell division, as determined by BrdU labeling, mainly occurs in the coelomic epithelia of the hypertrophic mesentery and in the regenerating luminal epithelium. Our study provides evidence that the process of new organ formation in holothurians can be described as an intermediate process showing characteristics of both epimorphic and morphallactic phenomena.

Abstract: Samples of sea urchins ( Paracentrotus lividus ), holothurians ( Holothuria polii ), green algae ( Ulva lactuca , Codium vermilara and Enteromorpha prolifera ) and sediments were collected from different coastal zones of the South Adriatic Sea (Italy). The occurrence of metals in macroalgae is poor especially if compared with that reported in other coastal areas affected by human activities, with the exception of Fe that showed high mean values (405 μg g −1 dry wt.). Likewise, relationships between metal concentrations in holothurians and sediments were found, demonstrating that H. polii could serve as bioindicator for Hg and Cu.

Abstract: To investigate patch selectivity in aspidochirotide holothurians, individuals of five species (Holothuria (Halodeima) atra Jager, H. (H.) edulis Lesson, H. (Microthele) nobilis Selenka, Stichopus chloronotus Brandt and S. variegatus Semper) were subjected to multiple choice experiments. As a food source, sediments were pre-cultivated in petri dishes under different light and nutrient regimes. This resulted in four sediment treatments with different levels of microalgal biomass (measured as chlorophyll a and phaeophytin concentrations). Only two sediment treatments were used for experiments with H. nobilis and S. variegatus. The sediments were offered simultaneously to individual holothurians (six per experiment), and the weights of the sediment in each petri dish at the start and after 48 h were used to calculate a selection index together with confidence intervals for each food type. In experiments with H. atra and H. edulis, the animals exhibited no preference for any food type. In contrast, S. chloronotus significantly selected sediments with the highest contents of microalgae and avoided the sediment with the lowest pigment concentrations. These results were supported by field collections of sediments found directly underneath holothurians. Sediment underneath H. edulis did not differ from the average sediment of the habitat, while H. atra was found on sediments only slightly higher in chlorophyll a. Chlorophyll a concentrations underneath S. chloronotus were distinctly higher than in the adjacent sediment and that underneath H. atra. H. nobilis showed only a weak preference for sediments with higher pigment concentrations in aquarium experiments, and no patch selectivity in this species was found in the field. Stichopus variegatus exhibited a very distinct patch selectivity towards sediments with more nutritional value in both aquaria experiments and field measurements. Thus members of the genus Holothuria had no, or only a weak, tendency to select their food source, whereas both Stichopus species appeared to carefully select the sediment patch to feed on.

Abstract: Summary Proximate composition and fatty acid (FA) profile of three commercial sea cucumbers; Holothuria tubulosa, Holothuria polii and Holothuria mammata caught from Aegean Sea of Turkey were analysed. The effects of regional variation and drying process on FA composition were also investigated. Moisture, protein, fat and ash contents of the species ranged between 81.24% and 85.24%, 7.88% and 8.82%, 0.09% and 0.18%, and 5.13% and 7.85%, respectively, with a significant changes among species (P < 0.05) with some exceptions. Although FA values varied significantly (P < 0.05) among species and regions, the changes for most FA types representing the same region for different species were not significantly different. Total polyunsaturated fatty acids (PUFA) were found to be higher than total saturated (SFA) and monosaturated FAs (MUFA) accounting for 53.0–62.12% for P PUFA, 13.28–16.41% for P MUFA and 13.99–19.21% for P SFA. While some individual SFAs and PUFAs decreased after drying process, various individual FAs of MUFA increased in their amounts (P < 0.05). Among PUFAs, the highest mean value of eicosapentaenoic acid and docosahexaenoic acid for all regions were determined for H. polii as 7.25% and H. tubulosa as 12.37% in fresh samples, respectively. This study represents new information relating to FA contents and drying effect on FA profile for these species.