Autor(es):
Lillebø, Ana Isabel 
; Pardal, Miguel Ângelo ; Marques, João Carlos
Data: 1999
Identificador Persistente: http://hdl.handle.net/10316/13091
Origem: Estudo Geral - Universidade de Coimbra
Assunto(s): Eutrophication; Hydrobia ulvae; Life cycle; Population dynamics; Productivity
Descrição
Eutrophication in the Mondego estuary gave rise to qualitative changes in the benthic community, involving the replacement of
eelgrass, Zostera noltii, by green algae such as Enteromorpha spp. and Ulva sp. It seems reasonable to assume that, through time, such changes
may determine a selected new trophic structure. Hydrobia ulvae, a dominant species in terms of abundance and biomass, was studied with regard
to life history, population dynamics and productivity in relation to changing environmental conditions along the eutrophication gradient. The
purpose was to examine to what extent this species may adapt to the new emergent conditions. During the study period, H. ulvae population
exhibited both temporal and spatial density variations. The settlement pattern did not change along the eutrophication gradient, and took place
in March, June, July and September. However, the population was denser in the less eutrophied areas, corresponding to Z. noltii meadows, when
compared to the eutrophied ones, where Enteromorpha spp. blooms are usually observed. Growth was continuous through life but growth rates
were higher during spring, decreased from early summer to mid fall and practically ceased during winter, and then gradually increased again
up to spring. Life span was estimated as 21 ± 3 months. Growth productivity (P) was estimated as 93.7 g AFDW⋅m–2⋅year–1 in the Z. noltii
meadows, 15.2 g AFDW⋅m–2⋅year–1 in the eutrophied area, and 30.3 g AFDW⋅m–2⋅year–1 in the strongly eutrophied area. Elimination
productivity (E) was estimated as 30.0 g AFDW⋅m–2⋅year–1 in the Z. noltii meadows, 51.8 g AFDW⋅m–2⋅year–1 in the eutrophied area, and
97.5 g AFDW⋅m–2⋅year–1 in the strongly eutrophied area. The average annual biomass (B) (standing stock) of the population was estimated as
√
70.2 g AFDW⋅m–2 in the Z. noltii meadows, 5.5 g AFDW⋅m–2 in the eutrophied area, and 7.4 g AFDW⋅m–2 in the strongly eutrophied area.
√ √
P/B and E/B ratios were estimated as 1.3 and 4.8 in the Z. noltii meadows, 2.8 and 9.5 in the eutrophied area, and 4.5 and 13.2 in the strongly
√ √
eutrophied area, respectively. As a pattern, the standing stock decreased as a function of increasing eutrophication, while P/B and E/B ratios
increased following the same gradient. There is evidence that H. ulvae population structure and annual production are seriously affected by
eutrophication, namely by macroalgal bloom dynamics. Moreover, results suggest that H. ulvae might be suffering a change in its adaptive
strategy along the eutrophication gradient, becoming closer to a typical ‘r’ strategist in the strongly eutrophied areas http://dx.doi.org/10.1016/S1146-609X(99)00137-X
