Low reproductive success for copepods during a bloom of the non‐aldehyde‐producing diatom Cerataulina pelagica in the North Adriatic Sea

Abstract

Egg production rates and/or hatching success in the copepods Acartia clausi, Calanus helgolandicus and Temora longicornis were negatively affected by a late spring (May–June 2003) phytoplankton bloom in the North Adriatic Sea, dominated mainly by the large diatom Cerataulina pelagica. Highest total concentrations of 3.3·104 cells·ml−1 were located in the vicinity of the Po River, which also corresponded to the area where the highest numbers of phaeophorbides were measured (0.779, 0.528 and 0.419 μg·l−1, respectively, compared to an average of the remaining stations of 0.183 ± 0.049 SD), suggesting some grazing on the bloom. Phytoplankton biomass in terms of carbon was dominated by diatoms, representing on average 42% of total phytoplankton carbon and more than 80% at several stations. Cerataulina pelagica, Cyclotella spp., Chaetoceros spp. and small unidentified centric diatoms dominated the diatom community numerically but C. pelagica was by far the dominant diatom in terms of carbon due to its large cell size. This species represented more than 60% of the diatom biomass at nine of the 14 stations sampled, and was absent only at one station, which was the most offshore station sampled during the cruise. Although polyunsaturated aldehydes (PUAs) were not detected, other oxylipins which are hydroxy and keto derivatives of eicosapentaenoic and docosahexaenoic acids that affect copepod reproduction were found in these samples. Hence, we can attribute the negative impact of diatoms not only to PUAs, as previously believed, but also to these compounds. This is the first direct evidence of the presence of oxylipins other than PUAs in marine blooms dominated by diatoms.

Non-volatile oxylipins can render some diatom blooms more toxic for copepod reproduction

“…Also egg viability of C. helgolandicus was higher during the winter bloom of 2004 (76%) compared to 2005 (59.2%), and much higher than in February 1998 (6.5%) (Miralto et al, 2003) and May-June 2003 (30.7%). During this latter period the large, oxylipin-producing diatom Cerataulina pelagica was blooming in the northern Adriatic Sea (Ianora et al, 2008).…”

“…Similar compounds are also produced by benthic diatoms, where these compounds have been suggested to play a role as foraging kairomones, indicating the presence of abundant food (Jü ttner et al, 2010). NVOs were first reported at sea during a late-spring bloom of the non-PUAproducing diatom Cerataulina pelagica, the likely cause for reduced copepod egg production and hatching success at the time (Ianora et al, 2008).…”

“…The discovery of an enzyme cascade leading to the production of volatile and non-volatile biologically active oxylipins in marine phytoplankton is rather new (Miralto et al, 1999) even though the oxidative cleavage of fatty acids to form similar defensive compounds is well known in higher terrestrial plants (Farré -Armengola et al, 2013) and freshwater microalgae (Farré -Armengola et al, 2013;Fink, 2007;Ianora et al, 2008;Jü ttner et al, 2010). Oxylipins are believed to play a pivotal role in plant survival because they act as chemical attractors (e.g.…”

Impact of the diatom oxylipin 15S-HEPE on the reproductive success of the copepod Temora stylifera

“…Briefly, it has been shown that when copepods are fed with certain diatom diets, the eggs produced either fail to develop to hatching or hatch into malformed nauplii that die soon after birth (Ianora et al, 2004). These observations have also been confirmed in the field, with low hatching success of copepod eggs during periods of intense diatom blooms (Miralto et al, 1999;Halsband-Lenk et al, 2005;Vargas et al, 2006;Ianora et al, 2008). The causes for induced reproductive failure and the ecological relevance of these findings are currently fervidly disputed in the biological oceanography community (e.g., Flynn & Irigoien, 2009 and references therein).…”

Induced defences in marine and freshwater phytoplankton: a review

“…For instance, the bloom-forming diatom Cerataulina pelagica released oxylipins that affect copepod reproduction, but not PUAs (Ianora et al, 2008). Oxylipin-associated reproductive failure and poor recruitment are called 'insidious effects', because there is no or little direct effect on adult zooplankter mortality or on their grazing rate.…”