Publication Date:
2012-07-06
Description:
Macroalgae face a high predation risk, since herbivores like fishes and other grazers can remove up to 90% of the daily produced biomass in tropical marine systems. Algae use a variety of defence strategies like spatial and temporal escapes, tolerance or defence against grazing attacks. Chemical compounds produced by secondary metabolism can make themselves e.g. distasteful, toxic or reduce their digestibility for herbivores. The cues which are necessary to initiate a constitutive or inductive defence are controversy discussed.
In my diploma thesis, I used different methods to remove biomass from Codium decorticatum (Chlorophyta). Afterwards, bioassays were used to observe if the algae induced a chemical defence. Until now this algae was not known to deter itself chemically. Under laboratory conditions the alga was exposed different time periods long to amphipods (Crustacea) and sea urchins (Echinodermata). Experiments in controlled aquaria systems allowed constant regulated conditions, weather and water quality wise. The effect of herbivory was observed via two‐choice feeding bioassays with fresh material or pellets produced by extracts and powder of the algae. By scissors, different amounts of biomass were removed to test for a reaction on simulated herbivory. Again, bioassays were used to determine if a deterrent effect was caused. To examine if the removed biomass or the amount of artificial wounding matters for the induction, the algae was clipped with different number of cuts. Calorimetric measurements were used to ensure that the observed defence was not due to nutritional differences between mechanically wounded and intact pieces. HPLC was used to determine if a difference of chemical compound content existed between damaged and intact algae. This experimental part was conducted in Brazil. In Germany I repeated parts of the approaches with Fucus vesiculosus (Phaeophyta). This brown alga is known to defend against Isopods (Crustacea). With the clipping approach the reaction to simulated herbivory was tested.
Codium decorticatum was until now not known to feature a chemical defence. This could be shown the first time by deterring sea urchins when the algae was previously consumed by them and when the algae was clipped by scissors. Amphipod grazing did not lead to a repellent answer. The HPLC fraction allows the assumption that for different cues (grazing / clipping) not the same compounds seam to repel the sea urchins. It could not be determined if either the amount of biomass removed or the number of wounding triggers for a defence. Fucus vesiculosus showed as well a repellent answer to clipping.
Type:
Thesis
,
NonPeerReviewed
Format:
text
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