Balgzand macrozoobenthos database 1967 - 2019

The Balgzand macrozoobenthos programme was set up initially to study the secondary production of the macrobenthic invertebrates of the Wadden Sea. This happened within the framework of the International Biological Programme (IBP) (1967), an initiative to study the biological productivity of various ecosystems worldwide. The programma was initially meant to study the productivity of biomass of larger macrozoobenthic invertebrate in- and epifauna. The focus was on species that easily could be separated into cohorts (year classes). This meant that bivalve molluscs that deposit clear growth marks in their shells had priority. Small items, e.g. small polychaetes, were ignored as contributing very little to the total invertebrate benthic biomass. To study the annual variability in benthic biomass, a frequent year-around sampling programme on 3 permanent quadrats was developed and started in 1967. These quadrats were selected based on sediment composition and tidal elevation, to cover a variety of sediments within Balgzand. Station Dk was nearshore with sandy mud, around mean tide level, station Sl was relatively near by Dk but closer to a tidal gully, on a sandy sediment and a tidal elevation of ± 10 cm above mean tide level, station Mz was on the northern tip of Balgzand, around mean low tide level with relatively course sand. On these quadrats, sampled roughly once per month, boxes of ± 0.1 m² were dug out, and additionally round cores of 0.009 m² were taken. Based on the results of these frequent samplings an additional series of 12 transects, scattered over intertidal Balgzand, was chosen to cover the variability of the study area. These 12 transects were sampled twice a year, in late winter to estimate the benthic biomass at the lowest level during the year, and in late summer at the moment of maximal benthic biomass values and to estimate the recruitment of the benthic invertebrates in the previous spring and early summer. The transects were explored first in summer 1968, the results are not incorporated in the database. The results from late winter 1969 onwards are included in the database. From summer 1969 onwards the frequency of sampling of the the 3 permanent quadrats was reduced to 4 times per year, from 1988 onwards to twice per year.