Colloquium on diatom-copepod interactions

Abstract

From 3 to 6 November 2002, a colloquium was convened at the Benthos Laboratory of the Stazione Zoologica Anton Dohrn on Ischia, Italy, with the goal of evaluating the present status of the effects of diatoms on their main consumers, planktonic copepods, and to develop future research strategies to enhance our understanding of such interactions. These included (1) toxic effects of diatom metabolites on copepods, particularly reproduction, and (2) nutritional effects of diatoms on juvenile to adult copepods. Key issues involved in the impact of diatoms on the dynamics of natural plankton communities in situ were also addressed. During the plenary session, the most recent advances on this topic were presented. The plenary session was followed by 3 working groups on (1) production of aldehydes by phytoplankton, (2) toxic and nutritional effects of diatoms on zooplankton, and (3) the chemistry of diatom defense, as well as of their nutritional quality. These working groups focused on suggesting future research needs for the different topics. As a result, several recommendations were outlined, including experimental studies. It became evident that interdisciplinary efforts are needed, involving chemists, oceanographers and experimentalists, since many of the biological observations under controlled conditions and in situ require an integrated approach, including chemical causation. Extensive field observations based on common protocols are also recommended for investigation of the intrinsic variability of such effects and their environmental controls. Laboratory experiments are seen to be essential for the full understanding of environmentally occurring processes.

Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms

“…(2) The isolation and identiWcation of an unsaturated aldehyde from P. pouchetii (Hansen et al 2004) may indicate a line of defence that was recently revealed for diatoms (PaVenhöfer et al 2005, and references therein). Membrane lipids are converted into mildly toxic polyunsaturated fatty acids (PUFAs) by a grazing-activated enzymatic conversion.…”

Metabolic profiling reveals growth stage variability in diatom exudates

“…Accordingly, these studies are limited by problems arising from the extraction and identification of chemicals, as well as from the lack of realistic bioassays (Paffenhofer et al 2005;Van Holthoon et al 2003;Von Elert and Pohnert 2000). Matrix complexity, high dilution, and limited stability represent major challenges that have to be overcome during the identification of infochemicals from plankton.…”

Effect of food concentration and type of diet on Acartia survival and naupliar development

“…T. weissflogii was second best, leading also to high naupliar survival rates and fast development, but to slower copepodite development. The successful use of T. weissflogii as a food organism is in contrast with the experimentally based view that diatoms in general are bad diet for raising copepods (Ianora et al 1995(Ianora et al , 2003Miralto 1999;Paffenhöfer et al 2005), while it agrees to field studies supporting a positive nutritional role of diatoms (Irigoien et al 2002). It is now well illustrated that not all diatom species per se are toxic, but even taxa lacking toxic metabolites can be insufficient to support copepod recruitment and development in mono-diet (Jones and Flynn 2005).…”