Population ecology and secondary production of the polychaete Loimia medusa (Terebellidae)

In soft-sediment marine and estuarine habitats, population dynamics of resident species are an important aspect of commnity structure and function, yet the population dynamics of many members of these communities remain poorly studied. The population dynamics and secondary production of the infaunal terebellid polychaete Loimia medusa (Savigny) were investigated in a shallow sand habitat of the York River, Chesapeake Bay, Virginia, between June 1989 and December 1990. Monthly sampling throughout 1 yr revealed that individuals were present year-round with maximum densities of 60 ind m^-2 and a life span of 1 yr. Abundances were highest from August through September when two cohorts recruited to the population. Mean individual growth was highest in summer, and appeared to be a function of temperature rather than food limitation. Adults were reproductive from May through October and exhibited high fecundity; the number of oocytes segment^-1 ranged from 201 to 15840 among worms. Larvae initially appeared approximately 1 mo after gametes were first observed in adult L. medusa, and these larvae appeared to spend less than 1 mo in the plankton. Abundances of larvae in the water column were significantly higher around new moon, suggesting lunar spawning periodicity. New recruits attained sexual maturity within 2 mo of settlement. Secondary production was 3.3 g ash-free dry wt m^-2 yr^-1 and the P/B (production/biomass) ratio was 3.0. Despite equilibrium species characteristics such as large size, high fecundity, and planktonic larvae, L. medusa exhibits some characteristics typically ascribed to opportunistic species, namely, the capacity for rapid growth and maturation, a short life span and a relatively high P/B ratio. This mixture of life history characteristics emphasizes that there is no simple dichotomy between opportunistic and equilibrium species. We caution that the dominance of large infaunal polychaetes in soft-bottom estuarine and marine environments may not be a useful indicator of undisturbed habitats.     

Impact of land use on soluble organic nitrogen in soil

Although it has been hypothesized that soluble organic nitrogen (SON) plays a central role in regulating productivity in some terrestrial ecosystems, the factors controlling the size of the SON pool in soil remain poorly understood. Therefore our principal aim in this work was to assess the impact of seven different land use systems (rough and managed grassland, deciduous and coniferous woodland, heathland, wetland and tilled land) on the size of the SON and inorganic N (NO^? ₃, NH⁺ ₄) pools in the surface soil layer (0–15 cm). After extraction with deionised water, we found that in most cases the size of the water extractable organic N (WEON) pool was similar in size to the inorganic N pool. In contrast, the KCl extractable organic N (KClEON) pool constituted the dominant form of soluble N in soils under all land uses, perhaps indicating that significant amounts were held on the soil exchange phase. In contrast to inorganic N, which varied significantly with land use, the size of the KClEON and WEON pool was similar for all land uses with the exception of KClEON in tilled land, where significantly lower amounts were observed. We conclude that SON constitutes an important soil N pool in a broad range of land uses, and that its role in microbial N assimilation, plant nutrition and ecosystem responses to atmospheric N deposition warrants further attention.     

Distribution Pattern of Benthic Invertebrate Communities in Traunsee (Austria) in Relation to Industrial Tailings and Trophy

Traunsee, an oligotrophic Alpine lake, has suffered from inputsof industrial tailings (soda- and salt-mining industries) forseveral decades. The effects of the industrial sludges on thespatial distribution of the littoral and profundal invertebratefauna was investigated along three transects at five dates. Inthe littoral zone, no negative impacts were found. A distinctgradient in faunal composition and diversity was, however,observed along a profundal transect relative to the distance fromthe waste emission. Near the industrial input, the enhanced pH,the substrate instability, and the poor sediment quality forsubstrate- and deposit-feeders were the main factors that loweror prohibit colonization of the industrial sludges. Along atransitional zone between the waste emission and the deepestbasin, recolonization was delayed, but did occur as soon aslayers of a few mm natural sediment seal the sludge. Mobile,epibenthic organisms are the first to settle these areas, whereasrecolonization by tube-building oligochaetes and chironomidsrequires thicker sealings of the industrial sludges. Differencesin the abundance of benthic invertebrates at different profundalsites were not only related to the waste emission, but also tothe influence of the main tributary, the River Traun. Theenhanced availability of allochthonous organic matter wasprobably responsible for high densities of tubificids near theinlet in the South of Traunsee. Moreover, a higher proportion oftolerant oligochaete and ostracod species in the lower profundaloutside the influence of the industrial tailings was interpretedas reflecting the increased trophy of Traunsee in the 1970s,which forced sensitive species to shift to the upper profundalwhen the oxygen climate deteriorated.     

Nachweis von Lichtsinnesorganen bei Seeigeln durch deren Bedeckungsreaktion

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