We studied the effect of carbonate depositions covering stone surfaces on the growth of larvae and the biomass of subsequent adults of the grazing limnephilid caddisfly Melampophylax mucoreus (HAGEN, 1861) in a laboratory rearing experiment. M. mucoreus is mainly distributed in karst streams characterized by calcium carbonate precipitations (tufa). We reared larvae of M. mucoreus on stones covered by calcareous tufa crusts as well as on stones from which these crusts were experimentally removed to assess the influence on larval growth and the subsequent adult biomass. The rough surface of the covered stones provided a higher complexity of micro-habitats and supported algal growth compared to the smooth surface of stones without crusts. Larvae of M. mucoreus profited from the enhanced algal biofilm growth on the calcium carbonate precipitation indicated by faster larval growth and higher subsequent adult biomass. Biomass increase of larvae reared on stones covered by tufa crusts exhibited a faster biomass development (0.09 ± 0.015 mg/d) compared to the larvae reared on stones without crusts (0.06 ± 0.002 mg/d). Adult males (5.13 ± 0.25 mg) and females (7.64 ± 0.63 mg) were significantly heavier in the treatment with stones covered by tufa than their conspecifics from the treatment with uncovered stones (males: 4.26 ± 0.25 mg, p = 0.047; females: 4.96 ± 0.47 mg, p = 0.001). Additionally, males from the treatment with crust covered stones emerged significantly earlier (p = 0.003) than the males from the other treatment, whereas no significant difference was found for females. IntroductionCalcareous deposition on surfaces of submerged substrates is a typical phenomenon in spring-fed and groundwater dominated karst streams (DRYSDALE, 2001). The precipitation of calcium carbonate can build up considerable tufa crusts of several centimetres covering all present substrates, sometimes even leaves, caddisflies cases and mussel shells. Carbonate tufa streams, particularly small spring brooks are a characteristic type of karstic stream systems, often characterised by a temporary discharge regime (MEYER et al., 2003). The precipitation of calcium carbonate can be increased in carbonate-rich streams during periods of low flow (SZRAMEK and WALTER, 2004).Few effects of tufa crusts on the benthos in streams have been described, such as reduction of gammarid mortality caused by fish predators due to protective tufa deposits on the gammarid body surface (RUFF and MAIER, 2000) or increasing ciliate species diversity and higher periphyton biomass associated to increasing rate of tufa precipitation (PRIMC-HABDI- JA et al., 2001). On the other hand, animal activities can also promote tufa development in Internat. Rev. Hydrobiol.
Abstract. The behaviour of larvae of Melampophylax mucoreus (Limnephilidae; Trichoptera) is studied to test their capacity for food detection over long distances by olfaction. In aquaria experiments with stagnant water, the larvae rapidly accumulate on a biofilm‐covered stone (offered food patch) but not on control stones without biofilm‐cover. Larvae in an artificial flow channel (flume), with uni‐directional flow between an arrangement of stones covered with biofilm and stones without biofilm, can find food patches upstream from their location more rapidly than downstream. Stimuli transported towards the larvae by the water current might assist food location. However, no significant differences could be found in the movement of larvae with intact antennae compared with larvae without antennae. The results lead to the conclusion that the larvae of M. mucoreus find food patches mainly by random movement, which is assisted by their high mobility. Long‐distance olfactory orientation towards food patches, mediated by antennae, can be precluded. Gustatory stimuli appear to play an important role in contact‐chemoreception to identify biofilm patches on stone surfaces. Scanning electron microscopy studies of the larval head reveal that the antennae of M. mucoreus are small pegs (50 µm in length) with an apical plate (15 µm in diameter). The mouthparts of the larvae, especially the maxillary palps, show a variety of different sensilla types that are possibly used for contact‐chemoreception. These sensilla also could be responsible for the orientation towards a food resource upstream of the larvae.
Abstract. 1. Larvae of the grazing caddis‐fly Melampophylax mucoreus were reared in a laboratory experiment investigating the effect of food availability on different substrates and cannibalism on the size and biomass of emergent adults. All experiments were performed in stream‐water filled, aerated aquaria under controlled temperature and light conditions. Larvae (fourth and fifth instar) were reared in aquaria (50 larvae in each) with three substrate scenarios: (i) limestone (LS), (ii) limestone and leaf litter (LS + L), and (iii) silicate stone (SS).2. Cannibalism among the larvae in the LS scenario led to the highest adult dry masses (male = 5.13 ± 0.25 mg, female = 7.64 ± 0.63 mg) and to the highest mortality rate (88.7%). The SS scenario displayed the most unfavourable condition for larval growth indicated by the lowest adult dry masses (males = 3.12 ± 0.15 mg, females = 4.69 ± 0.25 mg) and a high mortality rate (81.7%). The limestone supplemented with leaf litter (ii) offered the most balanced nutrients to complete larval development and enough shelter to avoid excessive encounter rates of larvae within the aquaria, indicated by the lowest mortality rate (43.6%). Adults from the LS + L scenario showed biomasses (male = 3.94 ± 0.12 mg, female = 6.48 ± 0.24 mg) intermediate between the two other scenarios.3. The results implied that cannibalism among larvae can lead to higher adult biomasses and therefore to increased fitness, if cannibalism supplements larval feeding requirements. Larvae developing under insufficient food availability can not compensate for this by cannibalism. Additionally, leaf litter not only provided a complementary food source for developing larvae, but also provided shelter, which reduced encounter rates.4. Increased stress induced by high larval encounter rates (resulting in enhanced cannibalism) in the LS scenario and low food availability in the SS scenario could be indicated by premature emergence times compared with the LS + L scenario.
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