Population dynamics and ecology of the surf clam Donax serra (Bivalvia, Donacidae) inhabiting beaches of the Benguela upwelling system
The surf clam Donax serra (Röding, 1798) dominates macrobenthic communities of extended and exposed sandy beaches of those southern African biogeographical regions where phytoplankton production is high: the cold Benguela upwelling system and areas of the warm Agulhas current system, which experienc...
| Main Author: | |
|---|---|
| Format: | Book |
| Language: | unknown |
| Published: |
2002
|
| Subjects: | |
| Online Access: | https://epic.awi.de/id/eprint/5726/ https://hdl.handle.net/10013/epic.16289 |
| Summary: | The surf clam Donax serra (Röding, 1798) dominates macrobenthic communities of extended and exposed sandy beaches of those southern African biogeographical regions where phytoplankton production is high: the cold Benguela upwelling system and areas of the warm Agulhas current system, which experience occasional upwelling and estuarine input. It feeds on phytoplankton and detritus, serves as food item for marine and terrestrial predators and is exploited by recreational anglers. The overall aim of this study was to investigate the population dynamics and ecology of Namibian D. serra in order to contribute essential knowledge for the understanding of its role in the Benguela upwelling ecosystem as well as for its potential use in aquaculture and exploitation activities. In particular two populations of the central Namibian coast were studied during November 1997 and December 1999.Histological examinations of D. serra gonads and the condition index indicated a seasonal reproductive cycle, coupled to the annual mean sea surface temperature cycle. Spawning started in August/September and lasted until February. Recruits, however, were present for only three months in the intertidal zone. The period when these juveniles are abundant is decoupled from the spawning period and therefore cannot be predicted. Starvation, hydrodynamic processes, chemical parameters and different release times during the spawning period are likely to cause spatial and temporal differ-ences in settlement time and recruitment strength.Individual growth is best described by a Von Bertalanffy growth function with an asymptotic length (L*) of 82 mm and a growth constant (K) of 0.274 y-1 in both intertidal populations. Growth performance of D. serra agrees with values of cold-temperate and upwelling donacids while temperate Donax-species have intermittent and tropical/subtropical congeners show lowest values. The intertidal biomass of the studied populations ranged between 141 g ash free dry mass (AFDM) m-2 and 546 g AFDM m-2, which is much higher ... |
|---|