Benthic assemblages,biodiversity and invasiveness in marinas and commercial harbours: an investigation using a bioindicator group

Fouling communities on artificial marine structures are generally different from benthic communities in natural rocky habitats. However, they may also differ among different types of artificial structures. Two artificial structures in direct contact with arriving vessels were compared: floating pontoons within recreational marinas, and sea-walls within commercial harbours. Natural rocky habitats were used as a reference, and the genus Eudendrium (Cnidaria, Hydrozoa) was chosen as a bioindicator. The assemblages were different among the three types of habitat studied, with different species characterising each habitat. The probability of finding an invasive Eudendrium species was significantly higher on pontoons. Diversity was the lowest on pontoons, but it was not significantly different between sea-walls and natural rocks. In general, a barrier to the spread of exotic species exists between harbours and natural rocky habitats. Floating pontoons seem to be a less suitable habitat for native fauna and a key element in marine biological invasions.     

An ultrastructural study of the spermatozoon of Eudendrium ramosum

Summary Spermatozoa of the colonial marine hydroid, Eudendrium were examined with the electron microscope. The spermatozoa of this species were found to differ greatly in structure from previously described spermatozoa in the phylum. The mature sperm are acrosomeless and retain a considerable amount of perinuclear cytoplasm following their maturation. The perinuclear cytoplasm contains numerous organelles: Golgi apparatus, endoplasmic reticulum, multivesicular bodies, ribosomes and membranous vesicles. The nucleus is elongate and cylindrical, rather than conical, in shape. The four wedge-shaped mitochondria which lie posterior to the nucleus form a fossa which contains proximal and distal centrioles. Centriolar satellites are associated with the distal centriole. The relatively short (15 ) flagellum consists of two distinct segments: a proximal thick portion and a distal thin portion. The thick segment contains the typical 9+2 arrangement of tubules plus a variable number of peripheral, supernumerary tubules. The thin segment contains from one to eleven tubules.The morphological differences between the spermatozoa of Eudendrium and those of closely related species are discussed with particular reference to sexual life history.The author wishes to acknowledge the technical assistance of his wife, Robin, during the course of this study. The assistance of Dr. Julian Haynes and Mr. Richard Turner in the preparation of the drawings is greatly appreciated. This work was supported by NIH grants 5T1 HD 9703 and 5T1 GM 793 and by NSF grant GB 7582 and by grants-in-aid of research from Sigma Xi-RESA and the University of Maine. Bermuda Biological Station Contribution No. 549.