Elminius

Abstract: Numerous studies have shown that only a small percentage of the organic carbon produced by photosynthesis in the upper layers of the oceans reaches the underlying sediments (see review by Angel, 1984). During intense phytoplankton blooms, plant cells could account for most of the organic carbon contributed to sediments in certain shallow inshore areas (Smetacek, 1980). Examination of the sediments from open ocean environments, however, indicates that the main contribution of organic carbon to these is in the form of faecal material released by zooplankton, for example salps (Iseki, 1981) and larger species of copepod (Schrader, 1971; Krause, 1981).

Abstract: The grey mangrove tree, Avicennia marina, forms a hard substratum in an area otherwise dominated by soft-sediment. Various intertidal organisms attach to and move about on the trees. The abundant barnacles Elminius covenus, Hexaminius popeiana and Hexaminius foliorum live on a variety of substrata in mangrove forests. Their patterns of distribution and abundance were recorded and models proposed to explain these patterns. Densities of barnacles on bark, leaves and twigs of A. marina were estimated in a locality near Sydney. Elminius covenus were more abundant on bark than on leaves or twigs of A. marina. Hexaminius popeiana, although less abundant on bark than E. covenus, were not found on twigs or leaves. In contrast, H. foliorum were more abundant on twigs than leaves and were not found on the bark of A. marina. Densities of barnacles were greater in the seaward than in landward parts of the forest. Elminius covenus were the most abundant barnacles, H. foliorum were less abundant and H. popeiana were virtually absent in the landward zone. Barnacles in the seaward zone were most abundant at mid-tidal levels, less at high and low tidal levels of trunks and more abundant on lower than upper surfaces of trunks and leaves. The densities of barnacles differed according to the orientation of the bark or leaf. Models are proposed to explain the patterns of distribution and abundance of these barnacles. Each involves larval supply, settlement and post-settlement mortality. It is concluded that similar processes determining patterns of distribution and abundance for sessile organisms living on rock platforms may be applicable to sessile organisms living in the very different habitats of mangrove forests.

Abstract: The larval stages of the acorn barnacles Chamaesipho columna, Chamaesipho brunnea, Elminius plicatus, Elminius modestus, Balanus trigonus, and Tetraclita purpurascens are described from larvae reared in the laboratory. A key and a table are included for separating larval stages and species. Skeletonema costatum appears to have a wide application as a food in the rearing of larvae of the Balanidae. The two Chamaesipho species show typical chthamalid characters of hispid antennal setae and unilobed labrum. The similarity between the larvae of Elminius plicatus and Tetraclita purpurascens supports the classification of E. plicatus as a tetraclitid.