**5. Food sources: how to survive?**

How can so many arthropod species—even predators—thrive on bare ground, before higher plants have established, or are very few? Based on analyses of the gut contents in springtails, beetles, harvestmen and chironomid midge larvae, we found that there were three 'invisible' food sources on newly deglaciated ground: biofilm with diatom algae, tiny pioneer mosses and ancient carbon delivered by the glacier.

## **5.1. Terrestrial biofilm as food**

The springtail *A. bidenticulata* (**Figure 12**) was a 'super-pioneer', following the retreating glacier edge closely. Their guts contained a rather compact material dominated by tiny mineral particles, but diatom algae could often be seen [29, 31] (**Figure 13**). We assume that mineral Animal Successional Pathways for about 200 Years Near a Melting Glacier: A Norwegian Case Study http://dx.doi.org/10.5772/intechopen.68192 163

**Figure 12.** Some pioneer invertebrates. A = the biofilm-eating springtail *Agrenia bidenticulata*. B = the moss-eating springtail *Bourletiella hortensis*, together with four bulbils (dispersal units) of the moss *Pohlia* sp. C = newly hatched adult and a larva of the moss-eating beetle *Simplocaria metallica*. From Ref. [31].

particles were ingested accidentally when 'grazing' on biofilm. Terrestrial diatoms have the ability to establish a slimy, nutrient-rich biofilm on open ground by producing large quantities of extracellular polymeric substances [41, 42]. Diatom algae were also found in some guts of two other pioneer springtails: *D. olivacea* and *I. viridis* [31]. The early presence of terrestrial diatom algae shows that chlorophyll-based food chains start almost immediately after deglaciation.

#### **5.2. Pioneer mosses as food**

be able both to arrive, to tolerate the harsh environmental conditions, to manage competition, to find food and to reproduce. In other words, pioneers must pass two 'filters': a 'dispersion

**Figure 11.** Invertebrates taken in sticky traps, proving airborne transport. A = the springtail *Bourletiella hortensis*. B = the

How can so many arthropod species—even predators—thrive on bare ground, before higher plants have established, or are very few? Based on analyses of the gut contents in springtails, beetles, harvestmen and chironomid midge larvae, we found that there were three 'invisible' food sources on newly deglaciated ground: biofilm with diatom algae, tiny pioneer mosses

The springtail *A. bidenticulata* (**Figure 12**) was a 'super-pioneer', following the retreating glacier edge closely. Their guts contained a rather compact material dominated by tiny mineral particles, but diatom algae could often be seen [29, 31] (**Figure 13**). We assume that mineral

filter' to arrive and an 'ecological filter' to establish a population.

mite *Bryobia* sp. C = the mite *Tectocepheus velatus*. D = the spider *Erigone arctica*. From Ref. [28].

**5. Food sources: how to survive?**

162 Glacier Evolution in a Changing World

and ancient carbon delivered by the glacier.

**5.1. Terrestrial biofilm as food**

Already on a four-year-old ground, five mosses were observed: *Ceratodon purpureus, Bryum arcticum, Pohlia filum, Racomitrium canescens* and *Funaria hygrometrica* [31]. On nunataks of

**Figure 13.** Hind part of the springtail *Agrenia bidenticulata* showing diatom algae in the gut. Most diatoms are densely packed, but a single one is easily seen to the left. From Ref. [31].

Omnsbreen glacier, about 10 km further North, a similar pioneer moss community has been found [40].

Due to characteristic cell structure in each moss species or genus, it was possible to identify small moss fragments in arthropod guts. On a 3-year-old ground, the relatively large and spherical springtail *B. hortensis* (**Figure 12**) had eaten leaves of *C. purpureus, Bryum* sp. and *Pohlia* sp., as well as nutrient-rich dispersal units (bulbils) of *P. filum* [31]. Among beetles, the family Byrrhidae is known to have moss-feeders, and on a six-year-old ground, guts of *S. metallica* (**Figure 12**) contained three different mosses (**Figure 14**). Two carabid beetles on three–six-year-old ground were omnivores, as their guts contained both invertebrates and moss fragments: *A. alpina* and *A. quenseli*. Conclusively, as much as four pioneer arthropods grazed on pioneer mosses [31].

#### **5.3. Ancient carbon as food**

The identification of this food resource was gradual, and surprising. A publication from a glacier foreland in the Austrian Alps showed that heterotrophic microbial communities used ancient carbon released by the glacier [43]. We wondered whether ancient carbon was released also by our glacier, and if so, whether it could be used as a nutrient source for pioneer arthropods. In September 2010, samples of surface soil (sand and silt) were taken 20 m from the glacier edge. During that summer, the glacier had retreated as much as 34 m. Analyses by Beta Analytic in Florida concluded that the samples contained material which was in average 21,000 years old. Furthermore, radiocarbon dating of chironomid midges and four predators, which were pitfall trapped on a 6–7-year-old ground showed that they all contained ancient carbon. The wolf spider *P. trailli*, had a radiocarbon age of 340 years, the harvestman *M. morio* 570 years, the carabid beetle *N. nivalis* 690 years, the carabid beetle *B. hastii* 1100 years and chironomid midges 1040 years [29]. Even larvae and adults of predatory diving beetles collected in young ponds had a radiocarbon age of 1100–1200 years. Springtails, however, did not contain ancient carbon.

New samples of surface soil taken close to the ice edge 4 years later corrected the age of released organic material to about 5160 years [30]. In the latter analysis, samples were pretreated at a lower temperature so that possible graphite particles from the phyllite-containing bedrock were not combusted and included in the analysis.

We found that chironomid larvae living in the sediment of young ponds assimilated the ancient carbon, and achieved a radiocarbon age up to 3270 years. We assumed that these larvae were eaten by diving beetles (**Figure 15**), and that adult midges ending on the soil

**Figure 14.** Moss fragments recorded in the gut of the beetle *Simplocaria metallica*. A = cross sections of a moss stem. B = leaf of *Pohlia* sp. C = leaf of *Ceratodon purpureus*. D = typical cell structure of a *Bryum* leaf. From Ref. [31].

surface after swarming fed terrestrial predators. Studies of the gut contents of the carabid beetles *N. nivalis* and *B. hastii*, and the harvestman *M. morio* confirmed that adult chironomid midges were an important part of their diet.

To be sure that ancient carbon was assimilated into the body tissue, measurements were also made on the larvae of Tipulidae (another Diptera group) in the same pond sediment, being careful to remove the gut contents before analysis. The actual body tissue from Tipulidae larvae had a radiocarbon age of 1610 years [30]. Moreover, chironomid larvae collected in the glacier river, and freed from their gut contents, had radiocarbon ages up to 1260 years.

We concluded that ancient organic material released by the glacier was assimilated by chironomid larvae, and transported further to aquatic and terrestrial predators. Chironomid midges thus supported early succession, and bound aquatic and terrestrial food webs together [29, 30].

The remaining question was: What is the source of the ancient carbon that had been stored in the glacier? We gradually abandoned the possibility that it came from old forest, bogs or soils from earlier periods where the glacier had been periodically absent. One reason was that the actual organic particles were probably extremely small. A purely chemical process, where carbon from non-biological bicarbonate served as a CO2 source for aquatic algae, was also abandoned, since gut contents of chironomid larvae were practically free from algae [30]. Instead, our suspicion was led towards long-transported aerosols, originating from the incomplete combustion of fossil fuels. Such aerosols make up a part of the organic matter that glaciers collect by surface accumulation [30]. These aerosols are C14 depleted, and radiocarbon dating will reveal that they are very old [44, 45]. In fact, heavily glaciated watersheds may transport ancient, bioavailable carbon all the way to oceans, where marine microorganisms can assimilate the old carbon [46]. The aerosol hypothesis would fit with all our results [30].

## **5.4. A pioneer food web**

**Figure 14.** Moss fragments recorded in the gut of the beetle *Simplocaria metallica*. A = cross sections of a moss stem. B = leaf

Omnsbreen glacier, about 10 km further North, a similar pioneer moss community has been

Due to characteristic cell structure in each moss species or genus, it was possible to identify small moss fragments in arthropod guts. On a 3-year-old ground, the relatively large and spherical springtail *B. hortensis* (**Figure 12**) had eaten leaves of *C. purpureus, Bryum* sp. and *Pohlia* sp., as well as nutrient-rich dispersal units (bulbils) of *P. filum* [31]. Among beetles, the family Byrrhidae is known to have moss-feeders, and on a six-year-old ground, guts of *S. metallica* (**Figure 12**) contained three different mosses (**Figure 14**). Two carabid beetles on three–six-year-old ground were omnivores, as their guts contained both invertebrates and moss fragments: *A. alpina* and *A. quenseli*. Conclusively, as much as four pioneer arthropods

The identification of this food resource was gradual, and surprising. A publication from a glacier foreland in the Austrian Alps showed that heterotrophic microbial communities used ancient carbon released by the glacier [43]. We wondered whether ancient carbon was released also by our glacier, and if so, whether it could be used as a nutrient source for pioneer arthropods. In September 2010, samples of surface soil (sand and silt) were taken 20 m from the glacier edge. During that summer, the glacier had retreated as much as 34 m. Analyses by Beta Analytic in Florida concluded that the samples contained material which was in average 21,000 years old. Furthermore, radiocarbon dating of chironomid midges and four predators, which were pitfall trapped on a 6–7-year-old ground showed that they all contained ancient carbon. The wolf spider *P. trailli*, had a radiocarbon age of 340 years, the harvestman *M. morio* 570 years, the carabid beetle *N. nivalis* 690 years, the carabid beetle *B. hastii* 1100 years and chironomid midges 1040 years [29]. Even larvae and adults of predatory diving beetles collected in young ponds had a radiocarbon age of 1100–1200 years. Springtails, however, did not contain ancient carbon.

New samples of surface soil taken close to the ice edge 4 years later corrected the age of released organic material to about 5160 years [30]. In the latter analysis, samples were pretreated at a lower temperature so that possible graphite particles from the phyllite-containing

We found that chironomid larvae living in the sediment of young ponds assimilated the ancient carbon, and achieved a radiocarbon age up to 3270 years. We assumed that these larvae were eaten by diving beetles (**Figure 15**), and that adult midges ending on the soil

found [40].

164 Glacier Evolution in a Changing World

grazed on pioneer mosses [31].

**5.3. Ancient carbon as food**

of *Pohlia* sp. C = leaf of *Ceratodon purpureus*. D = typical cell structure of a *Bryum* leaf. From Ref. [31].

bedrock were not combusted and included in the analysis.

Pioneer ground of 3–7 years of age contained a surprisingly diversity of food sources for pioneer arthropods (**Table 3**). Primary production was represented by invisible biofilm with

**Figure 15.** These pond-living invertebrates contained ancient carbon supplied by the melting glacier. A = sediment with chironomid larvae in tubes. B = chironomid larvae which have been partly freed from their tubes. C = two predacious larvae of the diving beetle *Agabus bipustulatus*, and three saprophagous, cylindrical larvae of Tipulidae (crane flies). D = adult predacious diving beetle, *Agabus bipustulatus*. From Ref. [30].


**Table 3.** Food sources of terrestrial invertebrates on 3–6-year-old ground, based on gut content analyses. From Ref. [31].

diatom algae, tiny bryophytes and scattered vascular plants. Fungal hyphae found in some springtail guts were early terrestrial decomposers, and chironomids eaten by several predators were (as larvae) detritus feeders on ancient organic material. In addition, some inblown insects certainly contributed as prey. Two 'super-pioneers' followed the ice edge most closely: the biofilm-feeding springtails *A. bidenticulata* and *D. olivacea*.

To understand the food web on pioneer ground, we must combine aquatic and terrestrial food chains, and distinguish between chlorophyll-produced carbon, inblown carbon and ancient carbon released by the glacier. **Figure 16** summarises these relationships, and distinguishes between autotrophs, herbivores, predators and decomposers.

A pioneer food web can probably be of local character. In the present case, chironomid midges hatching from young ponds fed several terrestrial predators. In the Rotmoos foreland in Austria, however, springtails were found to be the main prey, and intraguild predation was demonstrated [47, 48].

#### **5.5. Feeding categories during succession**

**Figure 17** shows that throughout the 200-year-old succession, the great majority of trapped macroarthropods were predators. While all spiders are predators, beetles contained a mixture of feeding categories. Pure herbivores were always represented by few species, even in the oldest sites.

Animal Successional Pathways for about 200 Years Near a Melting Glacier: A Norwegian Case Study http://dx.doi.org/10.5772/intechopen.68192 167

**Figure 16.** This food web from pioneer ground combines aquatic and terrestrial habitats. Shaded boxes illustrate the flow of ancient carbon, lower boxes with a grey frame show the flow of chlorophyll-produced carbon and the two upper boxes with a black frame show the use of carbon from inblown organic material. It is distinguished between autotrophs, herbivores, predators and decomposers. From Ref. [29].

diatom algae, tiny bryophytes and scattered vascular plants. Fungal hyphae found in some springtail guts were early terrestrial decomposers, and chironomids eaten by several predators were (as larvae) detritus feeders on ancient organic material. In addition, some inblown insects certainly contributed as prey. Two 'super-pioneers' followed the ice edge most closely:

**Table 3.** Food sources of terrestrial invertebrates on 3–6-year-old ground, based on gut content analyses. From Ref. [31].

Coleoptera x x

To understand the food web on pioneer ground, we must combine aquatic and terrestrial food chains, and distinguish between chlorophyll-produced carbon, inblown carbon and ancient carbon released by the glacier. **Figure 16** summarises these relationships, and distinguishes

A pioneer food web can probably be of local character. In the present case, chironomid midges hatching from young ponds fed several terrestrial predators. In the Rotmoos foreland in Austria, however, springtails were found to be the main prey, and intraguild predation was

**Figure 17** shows that throughout the 200-year-old succession, the great majority of trapped macroarthropods were predators. While all spiders are predators, beetles contained a mixture of feeding categories. Pure herbivores were always represented by few species, even in the

the biofilm-feeding springtails *A. bidenticulata* and *D. olivacea*.

between autotrophs, herbivores, predators and decomposers.

demonstrated [47, 48].

oldest sites.

**5.5. Feeding categories during succession**

**Species Group Biofilm Fungal** 

Collembola x

Collembola x

Collembola x x

Coleoptera x

*Amara alpina* Coleoptera x x x *Amara quenseli* Coleoptera x x

*Nebria nivalis* Coleoptera x x

*Mitopus morio* Opiliones x x

*Isotoma viridis* Collembola x x

*Desoria olivacea* Collembola x

166 Glacier Evolution in a Changing World

*Agrenia bidenticulata*

*Lepidocyrtus lignorum*

*Bourletiella hortensis*

*Simplocaria metallica*

*Bembidion hastii*

**hyphae**

**Bryophytes Vascular** 

**plants**

**Invertebrates Ancient carbon via** 

**Chironomidae**

**Figure 17.** Feeding categories among pitfall-trapped macroarthropods at different ages of the ground. All spiders are predators, while beetles contained various feeding groups. Pure herbivores were rare throughout the gradient. From Ref. [26].
