Sampling protocol for the study of population dynamics of abundant littoral arthropod populations
- To carry out quantitative sampling on the studied populations (the samples must be expressed as a function of the sampled area)
- To collect, at each sampling date, 150 specimens of the key amphipod species Talitrus saltator (This is the suitable number for modal analysis studies addressing growth and biological features of the population)
- To merge results regarding variation of population dynamics among different sites, based on an integrated sampling programme.
From the shoreline to land, we may distinguish in the beach the intertidal and the supratidal areas, followed by the primary dunes. Talitrus saltator will be more abundant around the high tide level (see figure) and in the supratidal area. Nevertheless, the zonation of the age and sex classes of T. saltator may vary with climatic conditions (storms) and with the season.
a) Take the samples at regular intervals along transept guide lines, from the shoreline to the base of the dune, as indicated in figure 1. At least one replicate of the transept must be done. Additionally, at the level where the populations were found more abundant, take more samples randomly, to the left and to the right of the transepts (see figure). This sampling strategy will simultaneously allow to account for differential vertical distribution and to collect the minimum of individuals necessary for statistical analysis.
b) Sampling periodicity should be 15 days, following a sequence of neap tides. Rainy days must be avoided, which may cause animals dispersion. The total sampling period will last 18 months to perform cohort analysis.
c) Use a metal or wood square of 0.25 m2 to bound the sampling area. Next, using a small scoop, remove the first 10 cm of the sand surface layer, where the organisms will most probably be present. Sieve the sand through a 2 mm mesh size, throwing it into a rectangular plastic container with high walls and about 5 cm of sea water add to it. The largest animals will be retained in the sieve. Make sure to avoid animals from escaping, collecting them immediately into a plastic bottle (with some water in). The water in the plastic will prevent animals that passed through the sieve (juveniles) from escaping. At this point animals will most probably start swimming and may be caught using small hand nets or scoops. The container may also be slightly inclined to make the animals crawl out of the water and these could be captured with aspirators or with the hand net. Collect all the animals.
Figure : Sampling design.
d) Collocate all the organisms captured in a plastic bottle or bag and preserve it in 70% alcohol. Please do not use formaldehyde. Each time a minimum of 10 replicates (0.25 m2 each) should be sampled.
e) For each replicate, before doing point c) collect all superficial debris and sieve it through a 2 mm mesh size and preserve it in a plastic bag. In the laboratory freeze it at –18° C for a period no longer than 2 months. This sample is intended for laboratory determination of the organic matter (potential food) available in the sampled area (mg•m-2).
f) Using a mercury thermometer, take the temperature of the sediment, at 2 cm deep, and the air temperature close to the sediment surface.
g) Obtain data on maximum and minimum daily temperatures during the study period from the closest meteorological station.
The above protocol was applied at the same time at following study sites: Zouarâa beach by FST team - Tunis, the Maremma Natural Park by CONISMA team - Florence and an Atlantic beach of Portugal by IMAR team – Coimbra, for comparison. The organisms samples were sent to IMAR partner for processing. The statistical analysis of data, namely Modal Analysis, were performed by IMAR partner.