We found zooplankton species richness increasing whereas abundance and biomass were decreasing. Have you seen something similar and what could be the reason?
Any references and explanation would be helpful. The research area is very shallow water in brackish-water Baltic Sea.
I studied zooplankton in the Lagoon of Venice for some years and typically species richness was highest when biomass and abundance were lowest: frequently, in winter-spring, just before the start of the reproductive peak of dominant species like Oithona nana and Acartia tonsa. Resource limitation could be a possible explanation? I am not totally convinced because it is difficult to imagine that such limitation can occur in brackish shallow waters. However, resource monopolization is likely to occur when one or few species are rapidly becoming dominant. Which is your opinion?
Our situation could be vice versa to yours. Our research area environment is often resource eutrophicated which gives big boost for some less sensitive species whereas those who need cleaner water will not survive. But in the big picture it is the same - the situation where few species are rapidly becoming dominant.
Hi Lennart, inverse relationship between these metrics is well documented, particularly for zooplankton inhabiting brackish water, or, water of varying salinity (in time) such as in classic estuaries. Before adding my 2 cents worth, can you tell me more about what is meant by "increasing"? I take it you mean diversity has changed over time yes? What time scales, hours/days/weeks or by season/ year-to-year? Have you noticed a concomitant change in any environmental variables?
The study was carried out in the northeastern part of the Baltic Sea. The three selected shallow water areas present different sets of abiotic (upwelling, exposure, nutrition, light) and biotic (community structure, biomass) conditions. The measurements were carried out in summer and autumn 2010 and in spring 2011. In each season, experiments were replicated in space and time i.e. three separate experiments were run at three sites within area in three consecutive days.
We calculated the means for each site and each season: richness as H´ index according to biomass and abundance separately (Shannon, Wiever 1949), and abundance (is. m3) and biomass (mg m3) were calculated as means+-SE.
Look at the figures. Sorry these are right now in Estonian language but you can get the idea. Each season has its color and the names below are the names of the test-sites.
First two from left: abundance and biomass
and below H´(abundance) and H´(biomass)
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