Biology and ecology of the family Eucalanidae in the North Western Indian Ocean.

摘要

Eight species of the subfamilies Eucalaninae (Eucalanus elongatus, Paraeucalanus sewelli and P. attenuatus) and Subeucalaninae (Subeucalanus crassus, S. mucronatus, S. subtenuis, S. subcrassus and S. pileatus) inhabit the North Western Indian Ocean (NWIO). The development of morphological characteristics in the six copepodid stages, the reproductive strategy and the morphology and elemental composition of the teeth on the pair of dentate mandibles was investigated in each species.; A key finding was that extra setae (one or more) on the coxa of the maxilliped of P. sewelli (mean TL = 5295 +/- 79 mum) distinguish all its six copepodid stages it from P. attenuatus (mean TL = 4450 +/- 71 mum). The present study agrees with Fleminger (1973), Geletin (1976) and the molecular phylogeny of the family Eucalanidae (Goetze, 2003) and finds no taxonomic basis for grouping any of the genera into an emergent taxon such as a subfamily as suggested by (Geletin, 1976) when additional criteria such as the ovary structure of adult females and tooth morphology of all copepodid stages are considered.; Three different species groups with distinct reproductive strategies were evident: (i) annual reproduction with diapause; Paraeucalanus sewelli and Subeucalanus crassus, (ii) biannual reproduction with quiescence; Eucalanus elongatus and S. mucronatus and (iii) continuous reproduction and active year-round; P. attenuatus, S. subtenuis, S. subcrassus and S. pileatus. Potential competitors used contrasting reproductive strategies consequently, the center of distribution and abundance of the developmental stages of a pair or group of potential competitors occurred at different times and habitats. The spatio-temporal separation enabled them to partition consumption in the epipelagic layer seasonally and/or horizontally and attain niche separation. For example, P. sewelli reproduced in the SWM season, was restricted to the coastal upwelling habitat and accumulated lipids at stage C5 for diapause. In contrast, P. attenuatus reproduced in the Northeast Monsoon (NEM) season, was widely dispersed extending offshore to the center of the NWIO, lacked arrested development and had minimal lipid storage.; The morphology of the teeth was influenced by phylogeny (distinct structure in each genus) and suitable for herbivory. The mineralized tooth cap in any species contained the organic elements (% weight); carbon (41% +/- 4, N=610), nitrogen (19% +/- 3, N=610) and oxygen (27% +/- 2, N=610) and various inorganic elements. However, fluorine (8% +/- 0.8, N=610) and silicon (2.82% +/- 1.74, N=610), probably bound up in a compound such as fluorosilicate, were the most important. The condition of the tooth cap (intact or abraded) consistently accounted for differences in the proportion of silicon among the teeth on a single mandible, or copepodid stage or the eight species. Teeth with an intact cap had a higher than average percentage of silicon (>2.82% +/- 1.74, N=610). Differential chemical composition of the teeth may be related to habitat partitioning. For example, species (P. sewelli and S. crassus) that reproduced in the SWM season and whose distribution was restricted to the coastal upwelling habitat dominated by diatoms had robust intact teeth with a higher than average content of silicon (>2.82% +/- 1.74, N=610). All the species with a widespread spatio-temporal distribution and most likely a diverse diet had abraded tooth caps depleted of silicon (2.82% Si +/- 1.74, N=610).