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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 wa- ters, 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.

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