Vernal Rock Pools Nature’S Own Nano Aquaria Pedersen, Ole; Pulido Pérez, Cristina; Nicol, Dion; Winkel, Anders; Tuckett, Renee

Vernal Rock Pools nature’s own nano aquaria Pedersen, Ole; Pulido Pérez, Cristina; Nicol, Dion; Winkel, Anders; Tuckett, Renee

Published in: Aquatic Gardener

Publication date: 2009

Document version Publisher's PDF, also known as Version of record

Citation for published version (APA): Pedersen, O., Pulido Pérez, C., Nicol, D., Winkel, A., & Tuckett, R. (2009). Vernal Rock Pools: nature’s own nano aquaria. Aquatic Gardener, 22(4), 34-43.

Download date: 29. sep.. 2021 Vernal Rock Pools nature’s own nano aquaria Ole Pedersen1, 2, Cristina Pulido1, 2, Dion Nicol2 Anders Winkel1 & Renee Tuckett2, 3 Photos by Ole Pedersen.

Vernal rock pools host some of the South Africa and Australia) with the smallest and prettiest aquatic plants. Californian vernal pools being the most These rock pools may contain as little as well-described of them all (Keeley & 40 l (11 gal.) of water and yet host up to Zedler 1998). five or more species of aquatic plants. Vernal pools fill during periods The plants typically have to complete when precipitation exceeds evapora- their entire life cycle in four months as tion. In Western Australia, this typically the pools dry out and turn into a desert happens from May to August. The long until the winter rain fills them again. term average annual rainfall in the area These vernal pools also host a unique around Mukinbudin (300 km north east fauna that need similar adaptations to of Perth) is about 286 mm (12"), though periods of complete desiccation (drying this is highly variable. This will fill out) and high temperatures. Here we the vernal pools found on the granite Vernal pools on granite outcrops near Mukinbudin, Western Australia. The pools are shallow show examples of submerged plants outcrops. For a few months, these pools and most are water-filled for less than 6 months. At first glance, they seem devoid of plants from pools on granite outcrops in West- flourish and maintain a unique aquatic and animals but a closer look reveals a stunning aquascape in nature’s own nano aquaria. ern Australia, some of which display habitat with flora and fauna not found the most stunning aquascapes. elsewhere in the world. These vernal up in the water column. In Californian leaved and emergent species all being pools are shallow, often less than 10 cm vernal pools, pH decreased to 7 while represented in the flora. The flora is The physical environment deep, and experience dramatic diurnal CO rose to 200 µmol/L (9 mg/L). In comprised of no less than 22 specialist Rivers and lakes are usually con- changes water temperature, pH and 2 contrast, the plants consume all CO species growing in no other form of nected to the regional groundwater CO (Keeley & Zedler 1998). 2 2 during the day so that the CO concen- temporary wetland (such as peat-lands reservoir. Percolating rainwater fills The granite rock pools are nature’s 2 tration drops to almost zero while pH and sump-lands) in Western Austra- these reservoirs eventually resulting in nano aquaria. Some pools are less than may rise to 10 (Keeley & Zedler, 1998). lia, along with many cosmopolitan runoff via streams, rivers and some- 1 meter in diameter and perhaps only 5 The dramatic changes in pH is caused species. Examples of the cosmopolitan times lakes. However, some vernal cm deep and yet, such pools may host primarily by CO that acts as a weak flora include species from Aponogeton, pools found directly on the bedrock 2 – 3 species of aquatic plants along 2 acid but since the water consists of Isoëtes, Marsilea, Myriophyllum, Pilularia rely solely on rainfall to fill. The aquatic with highly specialized invertebrates poorly buffered rainwater, the change and non-native Callitriche and Cras- habitats found here fit Keeley and that keep the aquascape almost free in pH is enormous. When we visited Zedler’s (1998) definition of the vernal from algae. Other pools are much the vernal pools around Mukinbudin in pool habitat as “precipitation-filled larger, up to 20 m in diameter, but on August 2009, the pools had experienced seasonal wetlands inundated during the granite outcrops the depth rarely frost the previous night but the late periods when temperature is suffi- exceeds 10 cm. afternoon temperature of the shallow cient for plant growth, followed by a The small volume of water relative water was nevertheless 25°C (77°F). brief waterlogged-terrestrial stage and to the high plant biomass also results Consequently, the aquatic plants found culminating in extreme desiccating in huge diurnal fluctuations in pH and in this extreme physical environment soil conditions of extended duration”. CO . At night, when respiration pro- 2 display a suite of special adaptations to Vernal pool wetlands are found in cesses produce large amounts of CO , 2 cope with the physical challenges. many places in the world (USA, Chile, pH decreases and dissolved CO2 builds The plants of vernal rock pools Flora occupying a 5 cm deep rock pool. Vernal rock pools in Western Aus- 1Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, 3400 Hillerød, Denmark A small patch of Glossostigma sp. grows tralia host a diverse array of aquatic 2School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, 6009 WA, Australia in between several individuals of Isoëtes 3Kings Park and Botanic Garden, Fraser Avenue, West Perth, 6005 WA, Australia plants with submerged, floating- australis.

34 The Aquatic Gardener Volume 22 Number 4 35 Left: Two common genera in the vernal rock pools: Isoëtes (left) and Glossostigma trichodes (right; with the long slender peduncle). The plants are tiny and highly specialized to life in these shallow waters, where huge diurnal fluctuations in temperature, pH and CO2 dominate the physical envrionment. Above: Flower of Glossostigma drum- mondii (2 mm in diameter) side-by-side with terrestrial leaves of one the Isoëtes species that also occurs in the vernal rock pools. See Beardsley and Barker (2005) for a key to the Australian Glossostigma. Colony-forming blue-green algae (Nostoc sp.) are found scattered among numerous sula. Endemic species include members seedlings of Crassula natans. Species of Nostoc has devised another strategy than the of the dicots such as Glossostigma and evaporation highly exceeds precipita- annual plants. Nostoc is most commonly found in ephemeral ponds. Instead of trying to Hydrocotyle, and the monocots such as tion and the pools start drying out. accomplish its entire life cycle in one short growth season, it is able to survive extreme Amphibromus, Ottelia, Schoenus, Trithuria Some plants flower during this period, desiccation. It survives in periods where the ponds dry out completely and even a light and Wurmbea. whereas others have already done drizzle of rain is enough to activate the dry colony. After a few minutes of soaking, it is For the aquatic vegetation, perhaps so, but eventually the pools dry out capable of photosynthesizing. Herbarium specimens of Nostoc commune, which had the most important challenge is the completely and spores and seeds are been dried out for almost 100 years, were able to photosynthesize following rehydra- short duration of complete inunda- dormant waiting for the next rainy tion. This remarkable adaptation makes Nostoc extremely hardy and capable of surviving tion. In late fall, it starts raining and season. None of the higher plants found in arid locations where water is only periodically available. the dry substrate quells and promotes in the granite rock pools are perennials; the germination of many seeds and they are all annual plants and able to spores. Other seeds and spores do not complete their entire life cycle within germinate until they are waterlogged or the few months of inundation. There is or aerial leaves possessing stomata; or dissolves in the water column so there completely submerged. Then, a period one exception; Amphibromus nervosus, iii) sediment-derived CO2 taken up is definitely a source of inorganic of total inundation follows and growth a perennial grass, lives in some of the by the roots followed by molecular carbon to tap into during the early of seedlings begins and eventually the pools and resprouts every winter. diffusion up into the leaves. All plants morning hours. But what happens shallow rock pools are covered in adult During the period of complete in the vernal rock pools probably use when this pool of inorganic carbon has plants. It follows from the shallowness inundation, the submerged plants face dissolved CO2 from the water column been used? of the water that these plants are tiny; other challenges such as how to get to some extent but because of the huge Perhaps the most conspicuous ad- but also the substrate is shallow (often CO2 for underwater photosynthesis. biomass relative to the shallow water aptation to low CO2 availability during less than 2 cm deep) and offers little Basically, there are three sources of column, this source of CO2 only lasts the day is the evolution of CAM pho- support for anchoring the plants. The inorganic carbon that aquatic plants can for a limited time early in the morning, tosynthesis in some of the submerged shallow water and substrate together tap into: i) CO2 dissolved in the water after which CO2 drops to almost zero plants occupying the vernal rock pools. promote bonsai versions of plants column, which is then taken up by the (Keeley & Zedler 1998). On the other CAM was first described in the family found elsewhere—just much smaller. submerged leaves; ii) CO2 from the hand, the high biomass also produce of Crassulaceae and since it involves After a few months of inundation, atmosphere taken up by floating leaves respiratory CO2 during the night that organic acids as storage for CO2 it was

36 The Aquatic Gardener Volume 22 Number 4 37 termed Crassulacean Acid Metabolism and amino acids) for the fungus while a gently sloping or virtually level plain; or CAM. Terrestrial CAM plants often the fungus via its hyphae explores large also called a monadnock). These particu- inhabit dry habitats where lack of water volumes of soil, taking up inorganic lar pools are inundated for longer peri- severely limits plants growth. However, phosphorus, which is then given to the ods of the year (up to 10 months in 2008) CAM plants open their stomata primar- plant in return for the organic carbon. and have deeper soils that may be some ily during the night when the tempera- We hypothesize that mycorrhiza plays of the physical properties restricting this ture is lower and the relative humidity an important role in the nutrient uptake species to such few locations, although higher. CO2 can then be taken up from in these super nutrient-poor environ- no study has yet confirmed this. the atmosphere without causing much ments and thus, we are going to screen water loss. But since it is dark, photo- species of Isoëtes, Glossostigma and Cras- Invertebrates of vernal rock pools synthesis cannot fix CO2 into sugars sula for mycorrhizal symbiosis. Aquatic animals occupying vernal and CO2 must be temporarily stored Western Australian vernal pools are pools are met with the same major chal- in organic acids for use during the day. host to a number of rare and threatened lenges as the plants: the short duration Malate is the most abundant organic species including Myriophyllum lapidi- of inundation after which follows a acid in CAM plants (diurnal fluctua- Isoëtes australis has an odd morphology. cola recorded on just a few rocks in the long period of desiccation (Bayly 1997). tions in malate is used an indicator of It looks like a Chinese fan with its leaves northern wheatbelt of Western Austra- Probably one of the best adapted ani- CAM photosynthesis). But submerged arrange in a 2D fashion. The relative large lia. This particular species is morpho- mals to cope with this challenge is the plants in vernal rock pools do not root system forms symbiosis with fungi logically very different to the typical seed shrimp (Ostracoda). Seed shrimps suffer from lack of water and here, the in order to extract the nutrients from the Myriophyllum with round floating are laterally flattened crustaceans evolution of CAM photosynthesis is not nutrient-poor sediment. leaves compared to the dissected fila- protected by a two valves hinged on considered an adaption to conserving mentous seen in most common Myrio- the back of the animal. They are among water but rather an adaption to take up photosynthesis remains to be tested. phyllum species. Further, this particular the first animals to appear when setting CO2 when it is present in high concen- However, its morphology and anatomy species is restricted to a specific rare up a new aquarium and their eggs are trations during the night. do not suggest that sediment-derived type of vernal rock pool. While most extremely desiccation tolerant and We found at least two species in CO2 should not play an important role pools are flat and shallowM. lapidicola present almost everywhere. In vernal the vernal rock pools that are known and this makes Isoëtes australis one of only occurs deeper pools that form on pools, giant species of seed shrimps to exhibit CAM photosynthesis. One, the most specialized aquatic plants we the steep slopes of granite inselburgs sometimes appear as there are no fish Crassula natans, even belongs to the have ever come across. The next four (an isolated rock hill, knob, ridge, or or other predators to prey on them. The Crassulaceae whereas the other, Isoëtes months of research here at the Univer- small mountain that rises abruptly from vernal rock pools of Mukinbudin are no australis, is an aquatic fern. Crassula sity of Western Australia will show if natans is not native to Western Australia we are right in this assumption. but was brought in from South Africa. A final challenge that the aquatic The Crassula genus is also represented vegetation has to cope with is the in the well-studied Californian vernal nutrient-poor environment. To the best pools by Crassula aquatica. Apart from of our knowledge, no one has stud- CAM photosynthesis, Crassula natans ied nutrient availability in the vernal also forms floating leaves. The floating rock pools of Western Australia. Since leaves enable the plant to tap into the the pools are precipitation-fed, the rich CO2 pool of the atmosphere and water does not carry high amounts of it also presents a nice support of the nutrients. Consequently, the sediment aerial flower, which is formed on the must provide almost all nutrients to floating rosette. the plants but the sediment primarily In contrast, Isoëtes australis is only consists of coarse gravel produced by found in vernal pools in Australia. It weathering processes in the granite. In A tadpole of the burrowing frog rests Giant forms of seed shrimps (Ostracoda) exhibits CAM photosynthesis (Keeley this kind of nutrient-poor environment among the Isoëtes australis. The tadpoles filter the tiny water column and graze on 1983) and is annual. Species of Isoëtes mycorrhiza fungi could potentially play sometimes appear in large number and sediment and plant surfaces. These seed are also known to use sediment-derived an important role in nutrient uptake. then, they are able to graze down all shrimps are almost 2 cm in diameter and CO2 for photosynthesis but whether Mycorrhiza are symbiotic associations aquatic vegetation. In this pool, however, they occur only in waters without fish as Isoëtes australis also relies on sediment- between fungi and plants, where the the tadpoles can feed on algae and bio- they are easy prey. derived CO2 in addition to CAM plant provide organic carbon (sugars films without grazing on Isoëtes australis.

38 The Aquatic Gardener Volume 22 Number 4 39 Fairy shrimps (Anostraca) are also common in the vernal rock pools. Eggs of both seed shrimps and fairy shrimps are highly tolerant to desiccation enabling them to colonize the vernal rock pools year after year. exception; virtually all pools hold a de- and they grow in shallow nutrient- cent population of giant seed shrimps poor substrates. However, their natural feeding primarily on algae and ciliates. habitat is a high-light habitat with Another common invertebrate in direct sunlight in a really shallow water A dense carpet of Isoëtes australis. Some pools host almost a monoculture of Isoëtes vernal pools is the fairy shrimp (Anos- column that does not dampen light australis whereas others allow coexistence of the most common plants found in the vernal traca). The fairy shrimp swims around very much and so, they are all adapted rock pools. upside-down while filtering the water to high light levels. Whether they also used in planted aquaria but it is known water (www.tropica.com). The pools we for smaller zooplankton and phyto- require high light to grow is not really as a difficult plant. It requires high to visited were also characterized by hav- plankton, although a few of the giant known but they certainly do not mind very high light and only thrives in soft ing extremely soft water (from 10 – 90 forms are predators feeding on other direct sunlight. fairy shrimps. The eggs of the fairy In terms of providing a completely shrimps are also extremely tolerant to different architecture, Isoëtes australis desiccation but some species will hatch is perhaps the plant with the greatest only 24 hours after the eggs are exposed potential for planted tanks. The genus to water. Just like seeds of aquatic of Isoëtes has many species that thrive plants, some eggs must go through sev- under very modest light conditions— eral cycles of wetting and desiccation almost as modest as some of the aquatic before they hatch in order to guarantee mosses. For example, Isoëtes lacustris survival of the shrimps also when the grows primarily in the deeper water period of inundation is too short for the of lobelia lakes found in the northern shrimp to complete its entire life cycle. hemisphere; not because it does not like We observed two different color vari- high light but merely because it is such ants of fairy shrimps in the vernal rock a weak competitor so it is restricted pools around Mukinbudin but we do to depths of low light where no other not know if they are different species or plants are able to compete. Isoëtes aus- just variants (for example females and tralis, however, is found in direct sun- males) of the same species. light in shallow water so it may have intrinsic high light requirement. On the Potential use of plants from other hand, it often forms monocultures vernal pools in nano aquaria in the vernal pools so competition with The plants occupying the vernal other plants is absent. Time will tell if rocks pools in Western Australia are re- this unique little plant finds its way into ally pretty but whether they all are suit- the planted aquarium hobby. able for nano aquaria is uncertain. Their Glossostigma elatinoides, which also This pool is less than 10 cm deep and yet, the scattered rocks and the tiny Isoëtes australis bonsai stature is ideal for nano aquaria comes from Australia, is already being form a beautiful aquascape.

40 The Aquatic Gardener Volume 22 Number 4 41 Literature cited Keeley JE & Zedler PH (1998) Bayly IAE (1997) Invertebrates Characterization and global distribu- of temporary waters in gnammas on tion of vernal pools. pp. 1 – 14. In C.W. granite outcrops in western Australia. Witham, E.T. Bauder, D. Belk, W.R. Fer- Journal of the Royal Society of Western ren, Jr., and R. Ornduff (eds), Conserva- Australia 80: 167 – 172 tion and Management of Vernal Pool Beardsley PM & Barker WR (2005) Ecosystems—Proceedings from a 1996 Patterns of evolution in Australian Conference. California Native Plant Mimulus and related genera (Phry- Society, Sacramento. maceae ≈ Scrophulariaceae): a mo- Les DH, Capers RS & Tippery AP lecular phylogeny using chloroplast (2006) Introduction of Glossostigma and nuclear sequence data. Australian (Phrymaceae) to North America: a Systematic Journal 18: 61 – 73 taxonomic and ecological overview. Keeley JE (1983) Report of diurnal American Journal of Botany 93: 927 – 939 acid metabolism in two aquatic Austra- lian species of Isoëtes. Australian Journal of Ecology 8: 203 – 204

—”Fishkeeping & Aquascaping” con- patches of fairly intense red, distinct tinued from page 33. vertical marks; a preference for actively swimming in the open but near the ref- TetrasAndBarbs.com.) Most obvious uge of plants; and “pack” behavior (a group of fish that drift about the tank as This 8 cm deep pool reveals a spectacular aquascape showing natural bubble formation on is appearance: like plants, fish vary in a pack with ongoing interaction that is species of mosses and Crassula natans following intense photosynthesis. color, size and shape. But fish contrib- ute what plants and hardscape fairly intense—in contrast to the unison cannot—behavior. The common of tight schooling). Its bold markings µS/cm) since they are 100% rain-fed However, Glossostigma cleistanthum perception recites that these fishes are contrast both with horizontally-lined and sit on granite with no alkalinity at (previously thought to be Glossostigma “mid-water schooling” fishes. That per- species (such as Rasbora borapetensis) all. But we do not know if the species diandrum) has been shown to spread ception is overly simplistic and generic. and the green plants behind them. This found here are as demanding as Glos- and overgrow natural vegetation in Variations of behavior can be grouped species also contributes as a natural sostigma elatinoides. North American pristine waters (Les three ways: addition to a soft-water habitat and to Finally, Crassula natans is a pretty lit- et al. 2006); one of the few known the Malaysian biotope, should either tle stem plant that also forms beautiful examples where an invasive species • fish-to-fish (schooling, pack, shoal- of these be a theme of the composition. gas bubbles during periods of intensive require oligotrophic conditions in order ing, loaners, territorial, predators) The contribution of these roles should photosynthesis. Even under high light, to present any danger to the native • as a social catalyst within the com- be evaluated when composing for Crassula natans possesses relatively long vegetation. So, as always one should be munity (dither, target) theme, variation, contrast and balance. internodes making it somewhat less cautious upon disposal of these plants • niches (strata, proximity to various Much more easily said than done. attractive as an ornamental plant but in in non-native environments. aquascaping elements, water cur- Aquariums are about the satisfac- combination with low carpet-forming In conclusion, the vernal rock pools rent, nocturnal and contributing to tion that its keeper gets from keeping plants such as species of Glossostigma of Western Australia support stunning biotope/habitats themes) it. That satisfaction may come from it should make a nice morphological aquascapes formed by plants that have plants or it may come from fish. As a contrast in the tank. adapted well to the physical challenges Ultimately, the weight of both ap- result, the practices of aquarists can Being so small and inconspicuous of the changing environment. Some pearance and behavior can classify fish range from high-tech aquascaping to as most of the plants in the vernal rock of the plants described here may hold into compositional roles (showcase breeding fish in bare tanks. Aquariums pools, one could possibly come to the a potential for use in nano aquaria specimens, background fish, accent/ are also about the visual beauty of the wrong conclusion that these plants are and planted tanks although they are contrasting and novelty). As a quick whole. If this truly is the goal of an competitively inferior and do not pres- expected to have high light requirement example, let’s look at the five-banded aquarist, he or she should leverage ent much danger as invasive species. as judged from their natural habitats. barb (Barbus pentazona). It contributes both plants and fish.

42 The Aquatic Gardener Volume 22 Number 4 43