Analyses of organic matter content, organic carbon, nitrogen, sulfur and granulometric variables were performed on 101 surface sediment samples from Ubatuba Bay in order to investigate the spatial distribution of organic matter, its origin and the relationships among its components. The samples were obtained with a manual corer, from water depths between 1 and 15m during 5 cruises of the R/V ''Veliger II'', two months apart. Pearson correlation, regression and Principal Component Analysis (PCA) statistical methods were used to analyze the data. Strong correlations between organic matter and fine sediment fractions were obtained. The PCA revealed at least two main sample groups that reflect the different environmental conditions prevalent in the bay. There is a simple linear relationship between organic carbon content and the organic matter content determined by the calcination technique. Taking into account that the analysis of organic matter content is less expensive and less time consuming than the analysis of organic carbon, the present method of estimation can be useful when fast evaluation of the organic carbon content is needed for samples from similar environments.

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Burrow morphology and mating behaviour of Upogebia noronhensis was studied using resin casting of burrows in the ¢eld and observation of laboratory maintained animals. Burrows of U. noronhensis showed a typical Y-shaped pattern in over 70% of the cases analysed. The remaining 30% comprised U-shaped burrows lacking the lower tunnel (shaft) and burrows with long additional branches projecting from the U portion. Results from animals left to construct burrows in the aquarium closely matched those found in nature. Field and laboratory burrows showed that di¡erent shapes are related to the collapse of the burrow walls, the burrowing activities of other individuals and species, and to the behaviour of the species itself. U-shaped burrows form as a result of the partial construction of the burrow (the U part is always built ¢rst) or owing to the collapse of the shaft. Burrows with additional branches always belonged to males and result from their search for a female with which to reproduce. This process also produced connected burrows. Mating occurs within the female burrow and this is the only time when two animals occupy the same burrow. After mating, the male returns to its burrow and immediately closes the connection. Larvae are planktonic and probably settle in adult areas, since the smallest juvenile burrows were always associated with adult burrows. This may contribute to the high population densities found in the ¢eld ($200 ind m 72 ), which in consequence facilitates fossorial encounters for reproduction. This is the ¢rst time fossorial encounters for reproduction are reported for an Upogebia species and probably for all Thalassinidea.