Fauna
in the groundwater discharge area
Objective
Macrofauna and Meiofauna - abundance, taxonomical composition,
seasonal pattern
General description of the
data set
Results of the benthic fauna research in the shallow area of the Puck Bay (south Baltic), comparison of the two sites, first with direct and constant groundwater seepage, second without the disturbance. Field sampling was conducted between years 2009 and 2011 at Hel Peninsula during field sampling campaigns in different seasons:
á March 2009
á September 2009
á November 2009 (additional sampling)
á March 2010
á May 2010 (additional sampling)
á October 2010
Methodology
Samples were collected in two sites, first called "impacted" (with fresh groundwater outflow), second "non impacted" (without fresh water impact), according to the regimen set out below
Meiofauna:
Meiofauna is regarded as a group of benthic organisms
that are passing through a sieve with 0.5mm mesh size and are retained on
0.032mm sieve.
Plexiglass cores of 5cm diameter and 30cm length, equipped with
rubber stoppers are pressed into the sediment down to at least 20cm. After
applying the upper stopper the core is gently removed from the sediment and the
lower stopper is placed. The core is transported vertically to the surface and
placed into the stand. From each site 6 replicates are collected. The collected
cores are transported immediately to the lab, where the stand with the cores is
placed in a dark and cool place.
One by one each core is mounted onto the sediment
cutting device, where after gently pressing, the sediment is cut into 4 slices
(0-5, 5-10, 10-15, 15-20). Each slice is placed into the marked plastic
container and fixed with 4% formaldehyde solution with a Bengal Rose stain.
Each sediment slice (sample) after 24 hours of fixation is placed into the 2 liter cylinder and filled with 1 liter
of filtered freshwater. The cylinder is shaken vigorously to mix and move up
all the sand grains, and few seconds after the sand settles the supernatant
water is washed through the 0.032mm sieve. This procedure is repeated 9 times
(this allows some 90% of meiofauna to be washed out
from the sandy sediment). After washing the sample, meiofauna
that was retained on the sieve is gently washed to the 25ml, marked, plastic
container and fixed again with 4% formaldehyde.
Fixed sample of meiofauna is
washed from formaldehyde before the microscopic analyse, and first checked at
the low power stereomicroscope. Then the organisms are counted and separated to
the main taxonomic groups (Nematoda, Turbellaria, Oligochaeta, Harpacticoida, Tardigrada, Polychaeta, Gastrotricha, Rotatoria, etc). All organisms after counting and
identification for main taxa are fixed with 4%
formaldehyde again for further analysis.
The densities of all organisms are presented for the
10cm2 area of given sediment thickness.
Macrofauna:
Macrofauna is regarded as a group of benthic organisms
that are retained on 0.5mm sieve.
Plexiglass cores of 14 cm diameter and 30 cm length,
equipped with rubber stoppers are pressed into the sediment down to at least 20 cm.
After applying the upper stopper the core is gently removed from the sediment
and the lower stopper is placed. The core is transported vertically to the
surface and placed into the stand. From each site 6 replicates are collected.
The collected cores are transported immediately to the lab, where the stand
with the cores is placed in a dark and cool place.
One by one each core is is
gently washed on 0.5mm sieve, and all the organisms are removed with foreceps to the marked plastic container. After washing the sample, macrofauna is
fixed with 4% formaldehyde.
Fixed sample of macrofauna is washed from formaldehyde
before the microscopic analyse, and checked at the low power stereomicroscope.
The organisms are counted, measured
and identified to the species level. All organisms after counting and
identification are fixed with 4% formaldehyde again.
The densities of
all organisms are presented for the 1m2 area of given sediment
thickness
Results
á A total of 8 macrofaunal
taxa were identified in the material obtained, Bathyporeia pilosa, Hydrobia sp and Oligachaeta being the most frequent in the study area (>
92 %). Other taxa Marenzellaria viridis, Hediste diversicolor, Mya arenaria, Cerastoderma glaucum occured
in more than 36 % of samples. The three most frequent taxa
also dominated the community from the point of view of their average
contributions to the total abundances.
á A total of 12 higher meiofaunal taxa, including Copepoda nauplii were recorder in research area during all field campaigns: Turbellaria, Cnidaria, Nematoda, Gastrotricha, Rotifera, Oligochaeta, Polychaeta, Harpacticoida, Acari, Bivalvia and Gastropoda. Their abundances ranged between 53 and more than 1400 individuals per 10cm2 depending on the season and disturbance of fresh water discharging.
á
The vertical distribution of
organisms in the sediment core shows the highest density of meiofauna
between 1 and 5 cm of sediment depth.
á
According
to the classification done by Wieser (1953, 1960)
based on the buccal morphology, the 4 feeding groups
of nematodes can be distinguished:
selective deposit feeders (mainly bacterial feeders)
non-selective deposit feeders (grazing on bacteria, diatoms, algae,
macromolecules)
epistratum feeders (grazing on diatoms and algae)
omnivores/predators (variable feeding strategies including predation)
á
An early phytoplankton bloom in March
á
Low nutrient concentration in the water column from late March until late
October.
á
Increasing of permeability of the sediment in winter and early spring
compare to summer and autumn seasons without statistically significant changes
in the ganulometry of sediment
Additional observation showed that meiofaunal assemblages are affected by the small-scale topography caused by ripples in sediment Microtopography clearly inßuenced the distribution of the benthic meiofaunal assemblages in their distribution in troughs and crests of the ripple-beds. The results confirmed that benthic organisms may be affected also by hydrodynamic environments.