Dear Katrina,

algal bloom cannot be regulated by zooplankton. It is vise versa. Blooming is provide by extremely large amounts of bio-gens - esp N & P., and suitable hydrological conditions - like no turbidity, no turbulence and high tenperature (shallow water)! But should note that hypersaprobic conditions are mainly oligotrophic. 

As to Copepods, so what group you mean? Calanoids are algophagous,  Harpacticoids of freshwaters - detritophagous, marine - both, Cyclopoids - the very divers in feeding, some are raptors, some feed on algae, but mainly not at species that produce blooming...

Andrey

1) If the population increase consumes more than 30% of a phytoplankton species, then the latter would come under critical threat. If in the process the vegetative phase gets critically diminished, then the consumer will have to satisfy its self with the next best feed available, which in turn increases foraging competition with remaining zooplankton population.

2) Proliferation of a single species may lead to exclusion of others to a great extent, if conditions for proliferation of the former are conducive. In such a case there would be population imbalance of that of the affected ones.

3) If population bloom takes place especially during thermal stratification, then the epiliminion could come under anaerobic conditions or with low O2 levels, preventing fish from coming to surface waters.

The bacterial kinetics does matter which is controlled by the exopolysaccharide levels in the water body. What is the difference in temperature between pond surface and pond bottom ? How big is the pond ? To destabilise the pond ecological renewability, we need to know the fish biodiversity and fish biomass load in the pond. Is the pond water renewed with fresh water inputs? Planktonic vegetation along the pond mesocosm can steadily perform an oxygenation role. What is the zooplankton density per litre ? Surfacial fanning of the water body and wave action can also provide sustenance to the pond biome. Nature regulates itself through anoxic mortalities of zooplankton in high schooling pockets at the water/sediment interface. Dissolved organic carbon kinetics matters overall.

Thank you for your replies!

R.S. Daniel, the lake I was picturing is actually Taal lake, found in the Philippines. It's described to be a typical tropical lake (third largest in the country).

Andrey, 

Dear Katarina,

we actually work on copepods diversity and abundance in tropical waters and observed that microcopepods are more abundant that 30 years ago and this is true in coastal waters but also in lake. Abundance can easily reach 120.000 cop /m3.. All will depend or how rich in nutrients and phyoplankton is you lake? The most important parameter is to study the taxonomy and abundance in different monsoon period.. Probably, you will see succession of bloom, partially controled by grazing. Dont forget microzooplankton, one of the main grazers of phytoplankton!!

Best

Pascal

Strangely enough, no previous answers actually target the question - what negative consequences may arise with increase in copepod abundance?:) I would not seriously consider oxygen depletion in the epilimnion of the large lake....But this is a very good question. It is commonly assumed that the more zooplankton - the better (=higher trophic efficiency, etc.), but this is not just this simple...

What comes to my mind as a possible negative consequence of the situation that is described is:

- possible blooms of infectious deceases and pathogens that copepods may carry as primary or intermediate hosts;

- food web alterations for other primary consumers (competition) or secondary consumers (cascading effects);

- increased grazing of algae that are important food source for benthos relying on high sedimentation;

- transfer of algal toxins (if any) to higher trophic levels should the copepods bioaccumulate these toxins.

Thank you Katrina for this question and thank you Elena Gorokhova for an equally interesting answer.  I agree with you that if the zooplankton numbers are increased, it is not just the positive that can happen but also the negative. In every ecosystem, there are checks and balances that help to maintain the status quo but the status quo can change if the ecosystem is disturbed in one way or another.

And the points you have listed above hold to my view. The one I had in mind especially  is the issue of increased grazing on phytoplanktons. Becasue the zooplanktons feed on the phytoplanktons. This could lead to destabilization of the aquatic food chain and the other food webs in whole ecosystems. Like for example we know that the algae are the primary producers in these ecosystems..they are at the base of the food chain. If they are eliminated by the increased grazing by the zooplanktons, then what next? Where will the food and the energy in turn come from? It means the whole ecosystem is doomed! what do you think?

I am working with zooplankton, phytoplankton and periphyton communities in Arctic ponds and we are finding that we need to pay more attention on species level. In these ponds the main grazers and common zooplankton are Daphnia middendorffianna (key specie) and these can be highly grazed during their juvenile stage by a copepod Heterocope septentrionalis. Daphnia  can control algal blooms in these nutrient-poor freshwater bodies. But the copepod can easily erase Daphnia pulex which is smaller than D. middendorffianna. If these grazers disappear we can have algal blooms in our ponds or can alter dramatically the equilibrium of these sensitive environments. Interestingly, we find that nutrients can alter the species composition of algae. We know that Daphnia prefer some species (edible species), if we talk about  algal blooms we are talking about high growth rate of non edible species and these algal species can cause so many changes in algae including a release of harmful substances (toxins) and affect more organisms in the food web. If predator species (copepods) increase we might have a disequilibrium or cascading effects of so many things. If in this poor environments we have so many Daphnias at some point they will starve and if they eat a lot of edible species the cyanobacteria (mucilaginous colonies) will reproduce more and Daphnias have trouble swimming with high densities of these organisms, without mentioning the release of toxins and the less light penetration through the water column. Light penetration in these environments is very important because periphyton (algae attached to mud) is more abundant and is also the main food source for herbivores (Daphnia). Creating hypoxic conditions probably causing a decrease in algal production and cascading effects on the entire ecosystem. 

Thank you for such a thought provoking question. I think the answer depends on the traits of the zooplankton, as the above answers also highlight. We have increasing evidence that calanoid copepods may facilitate toxic cyanobacteria by grazing on their eukaryotic competitors (i.e., other phytoplankton). Increased grazers that avoid toxic algae could promote or stabilize harmful blooms - which means that the answer to your question also depends on the grazing behaviour (selectivity) of your zooplankton. 

Copepods do prevent algal blooms. Other than that, their fast growth rates (relatively faster than krill and other minute planktonic species) and easily even distribution across oceans make them contribute to probably the largest carbon sink in the world? (through biomass). But, copepods tend to be parasitic or at least most of them. One example would be the parasitism of Achantochondria cornuta on the European flounder (Platichthys flesus). I got this information from a study by Wouter Koch "The inventory of parasitic copepods and their hosts in the Western Wadden Sea in 1968 and 2010". Interestingly, copepods can also be parasitic hosts usually by dinoflagellates, Blastodinium sp., and even that dreaded Guinea worm (or Dracunculus medinensis - the one that comes out of a host's blister which causes a lot of disgusting pain). With this in hand, both features (being a parasite and being a host of a parasite) can be detrimental if their numbers are to increase highly in number since they can reduce the fitness of another species or they can be vectors for parasites to host on another different species decreasing its fitness. :) 

There is always the need the maintain and sustain an equilibrium in any ecosystem.The grazing relationship between zooplankton and phytoplankton will tilt heavily towards the zooplankton, thereby shifting the balance in the pyramid of biomass. So increasing the abundance of zooplankton is detrimental to the phytoplankton in particular and the ecosystem in general.  

The increasing of zooplankton its have negative effect on population dynamic and abundance also distribution of phytoplankton that effect food chain in the aquatic environment

The role of zooplankton is very important in natural waters. In addition to control algal communities, it serve as a food resource for many other aquatic animals especially young fish. However, overpopulation could have a negative effect on the primary productivity of the water body.

Regards

SM Najim

hi

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