Patrick Gillet

Polychaetes from the Atlantic seamounts of the southern Azores : biogeographical distribution and reproductive patterns

A study of the polychaetes living on isolated seamounts was undertaken to give data on marine biogeography and the dispersal of marine invertebrates. The data from the Meteor and Josephine seamounts came from Hartmann-Schroder and Rosenfeldts work in the 1980s. Data from Hyeres came from Bellans work in the 1960s, and data from the Atlantis and Hyeres seamounts were obtained during the Seamount 2 French expedition on board the ‘Suroit’ in 1993. Thirty-five sites from 280 to 2205 m were sampled: 16 on Atlantis (13 with polychaetes), and 19 on Hyeres (16 with polychaetes). In all 84 polychaete taxa from four seamounts were studied: Atlantis, 36; Hyeres, 33; Josephine, 34; and Meteor 50, but data analysis was based on the following number of taxa: Atlantis, 31; Hyeres, 29; Josephine, 34, and Meteor 48. Two groups of sites were identified by cluster analysis: I, Atlantis and Hyeres; and II, Josephine and Meteor. Only seven species were present at all sites. Nine families were present only in group I and six other families only in group II. Hesionidae (three species) occurred in group I, conversely Syllidae (16 species) were sampled only in group II. Some of the species were cosmopolitan (31%), 49% had a large distribution in the Atlantic, 11% were lusitano–mauretanian species, and only 6% were endemic; 51% of the species have direct development against 46% of the species which had a planktotrophic development and 3% a lecithotrophic development. Results of the biogeographical distribution and reproductive patterns of the polychaetes collected on these four sites were compared.

Revision of Chauvinelia , redescriptions of Flabelliseta incrusta , and Helmetophorus rankini , and their recognition as acrocirrids (Polychaeta: Acrocirridae)

Chauvinelia contains two abyssal species, C. biscayensis, and C. arctica. Because of the lack of some relevant details in the original descriptions, they are redescribed, the generic diagnosis is emended, and a key to separate them is included. Flabelliseta incrusta and Helmetophorus rankini, the type and only species for these genera are redescribed; they lack annulated or mold-articulated capillaries, their chaetae have a detachable cortex carrying successive rows of tiny spines, and they share several features with Chauvinelia. Therefore Flabelliseta, and Helmetophorus, currently regarded as members of Flabelligeridae de Saint-Joseph, 1894, are transferred to the Acrocirridae Banse, 1969. Consequently the family diagnosis is emended to include simple capillary neurochaetae, and a key for all acrocirrid genera is also included.

Population structure and secondary production of Heteromastus filiformis (Polychaeta: Capitellidae) in the Loire estuary, France

A survey was carried out from April 1998 to June 2000 to study the structure and the secondary production of the population of Heteromastus filiformis in the Loire estuary. Each month, samples were collected in the intertidal zone of Mindin harbour. The length of the thorax (L12) was correlated with the fresh weight (FW) with the relation FW=1.49848 L12-3.62804 (r=0.92). In 1999, the mean density was 2184 ind m -2 with a minimum of 1104 ind m -2 in December and a maximum of 3328 ind m -2 in March. The mean annual biomass was 15.4 g m -2 with a minimum of 2.6 g m -2 in December and a maximum of 28.2 g m -2 in March. Most of the histograms of size--frequency are unimodal and could be considered a single cohort except in May and November/ December 1999. The abundance and biomass of the population of H. filiformis decreased during summer and winter which are mortality periods and increase during spring and autumn which are recruitment periods for the population. The life time for a cohort was from six to nine months depending on the recruitment period and on the inter-annual variations. The secondary production was estimated by the method of Crisp (1971). The annual secondary production in 1999 was P=104.3 g m -2 with B=15.4 g m -2 and P:B=6.8. The quantity of sediment reworked by H. filiformis is about 1161 m -2 y -1 or 65 kg m -2 y -1 which is approximately a deep-sediment layer of 12 cm transported to the surface annually.

Preliminary Data on the Bioturbation Activity of Hediste Diversicolor (Polychaeta, Nereididae) from the Loire Estuary, France

The ragworm Hediste diversicolor (O. F. Muller, 1776) plays a key role in the estuarine water-sediment interface. This scientific project comes under the framework of the International network Nereis Park Experiment gathering 27 laboratories from all over the world. The experiments were carried out concurrently in spring 2007 using a common protocol. In the Loire estuary, the samples were collected in the intertidal zone of the Saint-Nazaire Bridge. During the field experiment, we estimated the surface area of the burrow walls (Sb) value varied from Sb = 0.26 m2.m-2 to 2.18 m2.m-2 (mean Sb = 0.75 m2.m-2), and the pumping rate (Pr) value from Pr = 0.9 l.d-1m-2 to 7.7 l.d-1 m-2 (mean value Pr = 2.7 l.d-1m-2). The density and the biomass of H. diversicolor populations largely controlled the amount of reworked sediment. In the laboratory, we estimated the pseudo-diffusive mixing, Db value varied from Db = 1.2 to 1.6 (mean Db = 1.5). The non-local transport (r) from the upper layers to the bottom of the tubes varied from r = 1 to 7.2 (mean r = 4.3). A positive relationship could be established between Db and the temperature while on the contrary a negative relationship could be established between the Db and biomass. It seems that small individuals are more efficient reworkers than big ones.