Morphology of the Respiratory Trees in the Holothurians Apostichopus japonicus and Cucumaria japonica

The morphology of the respiratory trees in the holothurians Apostichopus japonicus and Cucumaria japonica was studied using histochemical and electron microscopic techniques. The epithelium of the respiratory tree cavity in A. japonicus consists of columnar cells about 17–20 m high. In C. japonica, this epithelium is composed of two cell types: bulbous cells embedded in the connective tissue layer and secretory cells; cells are 1–12 m high. A characteristic feature of cells of the respiratory tree cavity epithelium in these species is the presence of numerous phagosomes and coated vesicles in the apical cytoplasm. The cell surface has many microvilli and a single cilium. Cells of the coelomic epithelium contain vacuoles in the apical part and myofibrils in the basal region; the thickness of this epithelium in A. japonicus and C. japonica is 9–16 and 10–30 m, respectively. Based on the different structure of the respiratory trees and the absence of hemocytes in A. japonicus, it is suggested that the holothurian species studied have different routes of oxygen transport from the environment to the internal organs.     

Sea cucumbers of the Arabian Peninsula and Iran – A review of historical and current research trends

Sea cucumbers are benthic marine invertebrates with immense ecological and commercial value. Processed sea cucumbers known as “Beche-de-mer” are a delicacy in southeast Asian countries with an ever-increasing demand depleting wild stocks on a global scale. Aquaculture techniques are well developed for commercially important species (e.g. Holothuria scabra) to aid in conservation and trade. In the Arabian Peninsula and Iran, where the major land mass is surrounded by marginal seas (Arabian Gulf, Gulf of Oman, Arabian Sea, Gulf of Aden, and Red Sea), studies on sea cucumbers are rather limited and its economic value is underestimated. Historical and current research trends indicate impoverished diversity (82 species) due to environmental extremes. Artisanal fisheries exist for the sea cucumbers of Iran, Oman, and Saudi Arabia, with Yemen and United Arab Emirates (UAE) playing a key role in collection and export to Asian countries. Stock assessment and data on export indicates depletion of natural stocks in Saudi Arabia and Oman. Aquaculture trials of high value species (H. scabra) were successful in Saudi Arabia, Oman and Iran with prospects for further expansion. Research on ecotoxicological properties and bioactive substances conducted in Iran demonstrates an immense research potential. Molecular phylogeny, biology, use in bioremediation, and characterisation of bioactive compounds were identified as potential gaps in research. Expanding aquaculture operations could revive exports and recuperate damaged stocks through sea ranching. Furthermore, regional cooperation, networking, training, and capacity building could help fill the gaps in sea cucumber research, which will aid in its effective conservation and management.     

Muscle regeneration in the holothurian Stichopus japonicus

The regeneration of longitudinal muscle bands (LMBs) in the sea cucumber Stichopus japonicus was studied using light and electron microscopic and immunocytochemical methods. Previous investigations of holothurian organs showed the presence of some cytoskeletal proteins which were specific for LMBs only. One of them, the 98 KDa protein, was isolated by means of SDS-electrophoresis and used as an antigen to obtain polyclonal antibodies. When tested on paraffin sections of sea cucumber organs, the antibodies were shown to interact only with coelomic epithelial cells covering the LMBs. The antibodies were used to study LMB regeneration after transverse cutting. During regeneration no signs of myocyte dedifferentiation or mitotic division were observed. In the wound region, damaged myocytes degenerated and muscle bundles desintegrated. However, the coelomic epithelial cells dedifferentiated and began to invade the LMB. Just beneath the surface these cells formed clusters (muscle bundle rudiments). The number and size of the clusters gradually increased, the cells lengthened and developed contractile filaments. These observations suggest that new muscle bundles arise from coelomic epithelial cells covering the LMBs. The migration of coelomic epithelial cells into the damaged LMBs and their myogenic transformation are the basic mechanism of holothurian muscle regeneration.     

The family Myriotrochidae Théel (Echinodermata: Holothurioidea) in the deep northeast Atlantic Ocean

Recent sampling in the Rockall Trough, Porcupine Seabight and Porcupine Abyssal Plain, in the NE Atlantic, has yielded 200 specimens of apodous holothurians belonging to seven species of the family Myriotrochidae Théel from depths between 1000 and 4310 m. These include the type species of a new genus and two new species of existing genera. Parvotrochus belyaevi gen. et sp. nov . is described from some minute specimens from the Rockall Trough that possess both exceptionally small wheel-like deposits and numerous, large curved rods in the body wall and tentacles. Myriotrochus clarki sp. Nov . has affinities to M. vitreus (M. Sars) but shows differences in the shape of the plates of the calcareous ring and in having larger, frequently abnormally formed, wheels. Siniotrochus myriodontus sp. Nov . is similar to the type species of this genus, S. phoxus, Pawson, but differs in the arrangement of the teeth on the wheels. A single small specimen of Prototrochus Belyaev et Mironov from the Whittard Canyon, northern Bay of Biscay, is similar to P. minutus (Östergren), a species known only from the Sea of Japan, but differs in some characteristics of the wheels and tentacles. A new subspecies, P. zenkevitchi rockallensis subsp. nov. , is proposed for a form of P. zenkevitchi (Belyaev) that was the most common myriotrochid encountered. P. zenkevitchi was known previously only from a few localities in the Pacific and S Atlantic deep-sea trenches. Similarly, two species previously known only from the NE Pacific, Myriotrochus bathybius H. L. Clark and M. giganteus H. L. Clark, are also recorded from the N Atlantic for the first time. The synonymy of M. giganteus and M. sp. ex gr. macquariensis-giganteus Belyaev et Mironov is proposed. The greatest number both of specimens and species came from the areas most intensively sampled. The present records show that several species have world-wide distributions. The wide geographic separation of many records is the result of both poor sampling effort in the deep sea, particularly with fine-meshed gear, and the difficulties in sampling infaunal animals in the deep sea. Box core samples in the Rockall Trough suggest that the myriotrochids are more common in this area than would be supposed from epibenthic sledge data. Hence, myriotrochids may be more prevalent in the deep sea than previously thought.     

Effects of reef-top gathering and fishing on invertebrate abundance across take and no-take zones

Gathering of molluscs on the reef-top, largely by women, is part of the traditional fishery practised by Bedouin in South Sinai, Egypt. The catch is dominated by Tridacna spp. and Octopus spp. Within the Nabq Managed Resource Protected Area, on the southern Gulf of Aqaba coast, a network of no-take zones (NTZs) was established (in 1995) to promote sustainable management of finfish stocks. Since this zoning also applied to exploitation of invertebrates, surveys of large species of molluscs and echinoderms across selected NTZs and adjacent fished areas were conducted (over 2000-2002) to assess any effects of gathering. Pooled data from all three years showed significantly higher abundances of Tridacna and Tectus dentatus in the NTZs, with greater abundances occurring at the reef edge zone. Size-frequency distributions revealed both a greater size range of Tridacna and a greater mean size of both Tridacna and Te. dentatus, within the NTZs, as compared to the fished areas. The size-frequency distribution of gleaned Tridacna, determined from discarded shells, also showed a smaller size range than did live Tridacna within the NTZs. By contrast, holothurians, which are not currently exploited by the local Bedouin, showed greater abundance in fished areas than in NTZs. Large diadematid sea urchins, along with the non-commercial strombs, Strombus gibberulus and Strombus fasciatus, were also significantly more abundant within fished areas, an effect presumed due to reduced predation pressure from fish as a result of fishing. Within the fished areas, there was a positive relationship between local abundance of Tridacna and of diadematids, thought to be due to high densities of the urchins acting as a deterrent against gathering. The establishment of NTZs has led to significant differences in invertebrate populations between take zones (TZ) and no-take zones. However, since there can be little or no spillover of adults of less mobile or sedentary invertebrates from NTZs to fished areas, any benefit to the fishery will depend largely on the greater larval production and export from protected populations.