Free-floating Plants Research Articles

Survey and Review

From five thousand miles above Tahiti, the Earth appears to be all water. Almost all the land is hidden away on the back side of the globe---and even that side is half water, too. Earth is an ocean planet. Look inside any drop of that water with a microscope and you'll find it teeming with life. Thousands of species of free-floating plant and animal organisms, known as plankton, fill our oceans. They drive the aquatic food chain and generate most of the Earth's oxygen. Scientists have been studying plankton since van Leeuwenhoek (1700), and mathematicians have been modeling them since Volterra and Lotka (1925). More recently our knowledge of biology, the state of the oceans, and the relevant mathematics have all exploded. Plankton populations bloom and decay sometimes wildly in space and time, with consequences for fish and humans, and much of the irregularity can be modeled by reaction-diffusion partial differential equations. Part of the challenge of this field is to recognize when a reaction-diffusion model may capture the main phenomena, and when instead one must take into account that the spatial domain such a model depends upon will be torn apart by oceanic fluid motions. The following article by Medvinsky et al. introduces us to this beautiful subject. Like all good scientists, the authors show a recognition of the complexity of the real world they are trying to model; nearly 300 references attest that plankton and fish dynamics are not simple. Like all good mathematicians, they also show an ability to isolate, and enjoy, the simple mechanisms that play a crucial role. Take a look at Figure 10 to see how reaction-diffusion dynamics alone can lead to complex regular structures that then break down to irregular ones. To an unbiased observer of life on Earth, this turbulent teeming of the oceans is as big a story as the adventures of a few two-legged animals scuttling about on land.

Limnological changes in a sub‐tropical shallow hypertrophic lake during its restoration: two years of a whole‐lake experiment

Abstract1. Lake Rodó is a turbid system, a condition attributed to algal biomass. The proximal source of the eutrophication was stormwater discharges from an ill‐defined urban area. This paper describes an attempt to restore the water quality of Lake Rodó, the first time this has been done in Uruguay. In spring 1996 it was drained, sediments were removed and stream inputs were diverted. Groundwater was used to re‐fill the lake. Due to its high nutrient concentration a re‐circulation system was designed, pumping water from associated pools covered with free‐floating plants.2. After the lake was refilled, the system was characterized by oxygen saturation or over‐saturation, neutral to basic pH, and high phosphorus, nitrogen and silicate concentrations. Ratios of total nitrogen (TN):total phosphorus (TP) and chlorophyll a (Chl a):TP indicated that phosphorus was the primary limiting nutrient during the period of groundwater supply. Once groundwater pumping had ceased, there was a decrease in TN:TP and Chl a:TP ratios, suggesting N‐limiting conditions prevailed in some periods.3. Before restoration, the phytoplankton community was dominated year‐round by Planktothrix agardhii; since restoration the community has been more diverse. This change has favoured grazing by mesozooplankton, and the onset of clear‐water phases in spring.4. Abundant populations of small omnivorous fish maintained a high predation pressure on zooplankton, restricting the abundance of large‐bodied herbivores, which, in turn, allowed an increase in phytoplanton biomass and a decrease in water transparency. Based on this observation, together with the phosphorus concentration and the low abundance of filamentous cyanobacteria compared with previous studies, we suggest that top‐down control has played a key role in increasing transparency in Lake Rodó.5. A nutrient reduction programme, by the mechanical harvest of floating plants, and a removal of small omnivorous fishes and stocking strictly with piscivores, could be key factors in the achievement of a stable clear‐water phase. However, if blooms of Microcystis or other similar genera occur in summer, additional measures (e.g. reduction of the hydraulic residence time) will be needed to improve water transparency.Copyright © 2001 John Wiley & Sons, Ltd.

Winds subsurface pelagic Sargassum and Langmuir circulations

The long survival of the free-floating plant Sargassum in the wind-mixed surface waters of the oceans is poorly understood. Evidence is presented here that the amounts of Sargassum collected by net tows at the sea surface decrease with increased wind speed. From this new finding and additional evidence in the marine literature, it is hypothesized that the plant is adapted to a cyclic submergence in the wind-induced vortical currents of these waters, returning to the surface only when the currents are less than the plant's rise rate. Such adaptation, readily testable, indicates the plant's capacity to maintain its density and rise rate independent of depth, thus adding to our understanding of its survival at sea.

Carbonic anhydrase levels and internal lacunar CO2 concentrations in aquatic macrophytes

Carbonic anhydrase levels were examined in a variety of aquatic macrophytes from different habitats. Carbonic anhydrase levels increased across the habitat gradient, from low activity in submersed aquatic macrophytes, intermediate in floating-leaved and free-floating plants to high activity in emergent macrophytes. Internal CO2 concentrations ranged from low to high in submersed macrophytes, but were low in floating-leaved and emergent macrophytes. No correlation was found between internal lacunar CO2 concentrations and carbonic anhydrase activities.

The effect of Amazon water type on acetate metabolism by species of Salvinia and Limnobium

The uptake and incorporation of [1-14C]acetate was studied in two species of free-floating aquatic plants incubated in three different Amazon water types. Waters from the Rio Negro, the Rio Solimoes, and a local lake were used. The plants, species of Salvinia and Limnobium, were collected from the local lake. The results demonstrate that in September, the water of the Rio Negro and Rio Solimoes have similar effects on acetate metabolism by the lake plants and markedly different effects from those of the plants' home waters. Although the Rio Negro and Rio Solimoes are considered to be totally different water types, this study indicates they may cause similar biochemical responses in aquatic plants.

Marine Phytoplankton of the Welsh Coasts, With Special Reference to the Vicinity of Aberystwyth

IN the course of work done on the marine phytoplankton of the Welsh coasts, attention was paid more especially to the area in the vicinity of Aberystwyth. For purposes of comparison, visits were also made to, and samples obtained from, other parts of the Welsh coasts. As the work done was carried on from a land station, it was found that a study of the free-floating plant organisms as such tended to include also those forms which are not, strictly speaking, planktonic, but which occur as regular components of the plankton flora wherever coastal influences are in evidence. As compared with the open ocean, the distinguishing feature of such offshore or neritic areas is the considerably greater variation in hydrographic conditions, this in turn making for a correspondingly wider range of variation in the plankton organisms themselves. For such a specialised coastal community various terms have been proposed; Haeckel names it the meroplankton as distinct from the holoplanktonic or holopelagic ecological unit of the open sea'. Schimper's term hemiplankton connotes much the same plankton-association of the coast-line. Kolkwitz2 advocates the use of the term seston, but, including