Seasonal exploitation of the seacucumber Stichopus hermanni (Semper) at Tuticorin

Stichopus hermanni earlier known as S. variegates is a widely distributed commercial species of Sea cucumber, popularly called 'pura attai' or 'pavaikya attai' in Tamil. In many of the western countries, apart from its food value as a rich protein diet (55% of dry weight) low in fat, sea cucumbers are valued for its medicinal properties. In India few works have been conducted on the biomedical aspects of sea cucumbers. Though this species have already been recorded from Gulf of mannar, the exploitation in huge quantities were never reported before. The recent development of the fishery of this species along Gulf of Mannar indicated its export potentiality as new resource. At Tuticorin along the Kalavasal area, huge quantities of this species have been processed since 2004

Nonlinear optical properties of molecular twins

Three different series of twin nonlinear optic (NLO) molecules were studied, in which the two NLO chromophores are linked by a central flexible polymethylene spacer. The first series, which had two azobenzene chromophores (Azo-twins), was designed to also exhibit liquid crystallinity. Most of the members of this series exhibited a nematic mesophase. The second series had two 4-nitrophenol units as chromphores (PNP-twins), while the third one was based on 4-alkylsulfonyl-4'-alkoxy azobenzene chromophores (Sulfazo-twins). These twin NLO systems exhibited interesting odd-even oscillations in their second harmonic generation (SHG) efficiencies in the powder form. When the spacer had an odd number of methylene groups, they exhibited significantly higher powder SHG efficiency than their even counterparts, with the even ones most often exhibiting no detectable SH signal. Preliminary single crystal X-ray diffraction studies performed on the PNP-twin series showed that while the even members possess a molecular center of symmetry and pack centro-symmetrically, the odd ones do not, leading to the observed alternation. The orientational-disordering dynamics of two of the twin series - the PNP and the Sulfazo-twin series, doped in a poly(methyl methacrylate) matrix, was also studied by monitoring the SH-signal decay in electric field poled samples. Interestingly, the maximum attainable SH signal, χ(2), in the poled samples also showed an odd-even oscillation with the odd ones again exhibiting a higher value of χ(2). The temporal stability of the SHG intensity at 70°C, after the removal of the applied corona, was also studied and the relaxation of the chromophores was found to follow a biexponential decay. The slower relaxation component exhibits a spacer length dependence, which suggests the interplay of two factors in governing the temporal stability in such polymer doped twin systems, one is the conformational discomfort experienced by the spacer in adopting a U-shaped geometry, and the other the electrostatic repulsion when two aligned dipoles lie very close to each other

Observation on juvenile sea cucumber occurrence in the shallow waters of Hare Island (erstwhile Pandian Island), Tuticorin

Understanding juvenile sea cucumber habitat preferences is very much essential for determining the carrying capacity of a given habitat which enables the successful release of sea cucumber juveniles for restocking purpose. Holothurians occupy different habitats such as rocky shores, sandy beaches, muddy flats, coral reefs and mangrove swamps at different depths. In general, the juvenile sea cucumbers exist in the habitat occupied by the adult but are obscured from view within the sediment or crevices or beneath obscuring objects such as corals and rocks. Juveniles of 21 species of holothurians have already been reported from Indian waters, of which 17 were observed in the same habitat as adults and 4 in the absence of adult

Environment degradation by chemical effluents along the Kayalpatinam coast of Gulf of Mannar with special reference to mercury

Studies were carried out on the level of mercury and other water quality parameters in the effluent lagoon of Dharangadhara Chemical Works, Tuticorin and the adjacent open sea over a period of three years and the impact of effluent discharge in bulk quantity into the coastal marine environment, over a distance of 18 km. The present study indicated that the presence of mercury, acidity and low oxygen concentration are the major impacts of effluent discharge. The mean concentration of mercury in the open sea during 1999 – 2002, was 4.7 μg. l-1 which got reduced to 1.68 μg. l-1 after five years, indicating the improvement of effluent treatment measures. However the mercury levels are still higher compared to those reported elsewhere. Except for salinity and pH, no statistically significant difference was observed in the variation of other parameters between stations during 1999-2002, but highly significant differences were observed in the variation of dissolved oxygen, chlorophyll, pH and salinity between stations during 2007-2008

Influence of salinity on hatching rate, larval and early juvenile rearing of sea cucumber Holothuria scabra Jaeger

The fertilized eggs, auricularia larvae and one month old juveniles of Holothuria scabra, obtained from induced spawning were used for various experiments to assess the effect of salinity on hatching rate and larval and early juvenile growth. The experiments were conducted for two days on hatching rate of fertilized eggs, for ten days on larval survival, growth and development and for 30 days on juvenile’s growth rate. The maximum hatching of 39% at 35 ppt, followed by 32% at 33 ppt indicated the suitability of an ambient salinity of 33 to 35 ppt for effective hatching of fertilized eggs. High survival, growth rate and fastest development of auricularia were obtained at salinity between 33 and 35 ppt. The maximum growth rate in length and weight, was at 30 ppt, which may be the optimum for juvenile rearing. The one way ANOVA on differences in the hatching rate, larval growth and survival rate and juvenile growth rate at different salinities indicated high level of significance (p<0.001 )

Stock enhancement of seacucumbers - a solution for the depletion of natural stocks of Holothuria scabra along Gulf of Mannar

Sea cucumbers form a valuable source of income for the poor fisherfolk along Gulf of Mannar and Palk Bay areas of South-east-coast of India. Owing to the high demand in international market and inadequate fishery management practice, the commercial sea cucumber species have been over-exploited leading to the extinction of sea cucumber populations in several habitats. The "Convention on International Trade in Endangered species of Wild Fauna and Flora" (CITES) has recommended inclusion of sea cucumbers in the list of endangered animals and cited the reasons as limited mobility, late sexual maturity, density depended reproduction, low rates of recruitment and ease of collections for their overexploitation and subsequent resource depletion. The releasing of hatchery produced juveniles of commercial sea cucumber species to their natural habitat, a process called restoration, restocking or reseeding is gaining momentum world wide, as the only way for replenishing the depleted stock of sea cucumbers

The effect of substituted benzene dicarboxylic acid linkers on the optical band gap energy and magnetic coupling in manganese trimer metal organic frameworks

We have systematically studied a series of eight metal-organic frameworks (MOFs) in which the secondary building unit is a manganese trimer cluster, and the linkers are differently substituted benzene dicarboxylic acids (BDC). The optical band gap energy of the compounds vary from 2.62 eV to 3.57 eV, and theoretical studies find that different functional groups result in new states in the conduction band, which lie in the gap and lower the optical band gap energy. The optical absorption between the filled Mn 3d states and the ligands is weak due to minimal overlap of the states, and the measured optical band gap energy is due to transitions on the BDC linker. The Mn atoms in the MOFs have local moments of 5 mu B, and selected MOFs are found to be antiferromagnetic, with weak coupling between the cluster units, and paramagnetic above 10 K

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