The relationship between mowing and large branchiopod presence in the Ciuc Basin, Eastern Carpathians

László Demeter 1, Anna-Mária Csergő 2, Gabriella Péter 3

1 Sapientia University, Libertăţii Str. 1, Miercurea-Ciuc, Romania.
domedve@gmail.com
2 Sapientia University, Sighişoarei Str. 1C, Corunca, Romania.
csergo.anna.maria@gmail.com
3 Sapientia University, Libertăţii Str. 1, Miercurea-Ciuc, Romania.
ptrgabriella@gmail.com

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KEYWORDS:

hydroperiod, large branchiopods, mowing, temporary ponds, traditional land use

ABSTRACT

Large branchiopods are a vulnerable crustacean group inhabiting temporary ponds. Their habitats are often found on agricultural land and are heavily influenced by agricultural practices. In this paper we examine the relationship between mowing, the presence of five large branchiopod species, and body size and fertility of one species in the Ciuc Basin, Romania. Our data suggest that small scale mowing as part of local traditional agriculture is beneficial to large branchiopods.

INTRODUCTION

Large branchiopods are an ancient group of crustaceans, inhabiting mainly temporary ponds and other extreme habitats, like salt lakes (Belk 1996). In addition to their conservation value, their relatively large body size, often colorful appearance and special life cycle make them suitable for environmental education (e.g. Belk 1998). Romania has the largest number of species in Europe for a country (Demeter and Stoicescu 2008). Eight species have been recorded in the Ciuc Basin, which is almost one third of the Romanian large branchiopod fauna, of which three are found only in the mountain basins of Southeastern Transylvania (Demeter 2005). All known large branchiopod habitats (approximately 80) are situated between 640 and 750 m a.s.l., in an open agricultural landscape. No large branchiopods have been identified in the Ciuc Mountains.

From a conservation point of view, it is of primary importance to understand habitat requirements and relationships between habitat parameters, human land use and large branchiopods. This paper examines (1) the relationship between vegetation, mowing and large branchiopod presence and (2) body size and fertility differences between populations in mown and unmown ponds in the Ciuc Basin.

MATERIAL AND METHODS

The Ciuc Basin (46o39'N, 25o29'E and 46o11'N, 25o59'E) is a roughly 1400 km2 tectonic mountain basin of the Eastern Carpathians, constituting the upper catchment area of the Olt river. Its altitude varies from 630 to 1800 m above sea level. It consists of a mountain region covered mainly by spruce forests, clearings and mountain pastures, and the river floodplain, terraces and sediment cones of the creeks, occupied mainly by agricultural areas and settlements.

Average total annual precipitation is 580 mm, while average annual mean temperature is 5.7oC (data of the Meteorological Office of Miercurea-Ciuc).

The spatial arrangement of agricultural land use is determined by topography, soil wetness and traditions. The general picture is that low altitude wet areas such as the floodplain of the river are used as hay meadows (winter fodder), while dryer areas like the terraces are used as arable land, and areas with steeper slopes on the hill foots are used as cattle pastures. Mountain pastures are mainly grazed by sheep.

We compared the frequency of appearance of active populations of five large branchiopod species (Chirocephalus shadini, Drepanosurus hankoi, Lepidurus apus, Eoleptestheria ticinensis and Lynceus brachyurus) (Fig. 1-4) in four types of temporary ponds (Fig. 5-8): ponds with non-tussock sedges (dominated by Carex vesicaria) (n=10), with tussock-sedges (C. elata, C. caespitosa, C. acutiformis) (n=10), with cattail (Typha latifolia) (n=10) and with peat moss (Sphagnum sp.) (n=7) (see Csergő and Demeter 2011 for a more detailed description of pond vegetation). We calculated an index of large branchiopod species occurrence (frequency of observed occurrence during five years of observations, with values from 0 to 1), an index of total large branchiopod species occurrence (the sum of average presence of the five species in a given pond type, with values between 0 to 5) and an index of mowing (the average mown area of a given pond type, with values from 0 to 1).

Fig. 1. Green fairy shrimp Chirocephalus shadini male

Fig. 2. Hankó’s fairy shrimp Drepanosurus hankoi females

Fig. 3. Tadpole shrimp Lepidurus apus and clam shrimps Eoleptestheria ticinensis

Fig. 4. Clam shrimp Lynceus brachyurus

Fig. 5. Pond with Typha latifolia, June aspect

Fig. 6. Mown pond with Carex vesicaria, June aspect

Fig. 7. Tussocky pond with Carex elata, late April aspect

Fig. 8. Pond with Sphagnum, Comarum palustre and Eriophorum latifolium

RESULTS

Non-tussock sedge ponds have the highest large branchiopod index and mowing index, followed by tussocky sedge ponds. Typha ponds have very low large branchiopod index and are not mown at all, while Sphagnum ponds are not inhabited by large branchiopods and not mown. Non-tussock sedge ponds have distinctly (four times) higher large branchiopod index than tussock sedge ponds and Typha ponds (ten times). On the species level, Chirocephalus shadini has the highest occurrence index, occuring sometimes even in ponds with Typha. At the other end, Eoleptestheria ticinensis only occurs in non-tussock ponds (Table 1).

The body size of female Chirocephalus shadini was 32-55% larger, while fertility was three to ten times larger in mown ponds than in unmown ponds (Table 2).

Table 1. Large branchiopod index (Ilb) and mowing index (IM) of four pond types. Cs – Chirocephalus shadini, Dh – Drepanosurus hankoi, Et – Eoleptestheria ticinensis, Lb – Lynceus brachyurus, La – Lepidurus apus.

Pond type Cs Dh Et Lb La Ilb IM N
Tussock sedge 0.69 0.2 0 0.17 0.05 1.11 0.13 10
Non-tussock sedge 1 0.4 0.9 1 0.9 4.2 0.85 10
Typha 0.11 0 0 0 0 0.11 0 10
Sphagnum 0 0 0 0 0 0 0 7

Table 2. Body length and fertility (mean ± standard deviation) of female Chirocephalus shadini in five ponds.

Habitat Body length (mm) Egg number N Mown
1 13.36±1.25 19.2±11.6 17 No
2 18.26±0.72 174.8±19.5 8 Yes
3 11.75±0.7 15.7±6 15 No
4 17.61±1.2 128.6±35 14 Yes
5 12.69±1.95 26.8±12.3 17 No

DISCUSSION

Most large branchiopod species are adapted to temporary ponds, i.e. shallow waters that dry out from time to time. The adaptation to the periodicity of the habitat resulted in the evolution of the capacity to predict hydroperiods long enough to allow successful breeding and egg production. This can last from days in deserts (e.g. Brendonck and Riddoch 2001) to several months in temperate climates (e.g. Eder et al. 1997). Most species inhabiting the Ciuc Basin have one generation per year in the spring. Resting eggs will not continue to hatch if the hydroperiod is longer than one generation and they will not hatch if after a dry period, a new hydroperiod starts later in the season. Although it is not demonstrated in experiments in the species present here, it is known from the literature that the resting eggs of some species need a dry phase and freezing, followed by flooding in order to hatch, although in many other species, a dry phase is not required (Brendonck 1996). This implies that the ideal habitats for the large branchiopod species of this area are temporary ponds that have at least two months hydroperiod followed by a dry period until winter. The need for a dry period in the case of species studied here may explain why no large branchiopods were observed in Sphagnum ponds.

The Ciuc Basin has relatively low annual average temperature (4-6oC) and precipitation (600 mm) but low evaporation and a dense hydrographic network with extensive fens (Nyárády 1929). Under natural circumstances, without human interference, natural vegetation (especially sedges and bushes) decreases evaporation and keeps temperatures low in early spring, as well as increases hydroperiod later in the season by shading. Traditional farming activities like mowing, removal of bushes, tussocks and moderate filling all result in the decrease of hydroperiod, which seems to be favorable to large branchiopods.

The other positive effect of removing vegetation is the change of light regimes. A higher exposure to sunlight is favorable to phytoplankton and so the food supplies available for larger sized filter feeders like large branchiopods. This effect seems to be reflected by the body size and fertility differences of the studied fairy shrimp species, which can be very spectacular, up to an order of magnitude difference in the case of fertility. A similar case of large differences between populations was attributed to Spirogyra blooms (Hössler et al. 1995).

A third effect of mowing may be the removal of vegetation which prevents the accumulation of detritus and improves the conditions for large branchiopods for example by allowing free swimming.

The mowing of shallow ponds is easier by hand scythe than by machinery. The trend of the past two decades in the studied area was a transition from hand mowing to machine mowing. This results in the abandonment of wet places, which seems to be unfavorable for large branchiopods.

A common practice in the studied area is the burning of dry vegetation in late autumn or early spring especially by herdsmen. It seems that this has a positive effect on the number of spawn laid in certain ponds by frogs (Demeter and Benkő 2007), but the effect on large branchiopods is not known. At least at the start of the season, better light conditions may be positive for plankton.

CONCLUSIONS

Our data indicate that mowing was favorable for large branchiopods in the Ciuc Basin by shortening hydroperiod and improving light conditions in some ponds which otherwise would be shaded and would have longer hydroperiod. Furthermore, our data suggest that removing vegetation increases body size and fertility of large branchiopods. Field and laboratory experiments should be conducted to better document these processes. We recommend the continuation of mowing (and removal of vegetation) to keep suitable conditions for large branchiopods.

The effect of vegetation burning on large branchiopods is not well documented, but mowing seems to be a better management option than burning because of potential harmful effects on wildlife and nutrient cycling of ponds.

AKNOWLEDGEMENTS

We thank Dr Barbara Knowles for financing this study.

REFERENCES

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