Changes In Plankton Dynamics Research Articles

Climate change in tropical fresh waters (comment on the paper ‘Plankton dynamics under different climatic conditions in space and time’ by de Senerpont Domis et al., )

Summary de Senerpont Domis et al. (2013, Freshwater Biology, 58, 463–482) forecasted changes in plankton dynamics in temperate, polar and tropical regions resulting from climate change. For tropical regions, they predicted an increase in precipitation intensity that would increase nutrient loading, increasing phytoplankton biomass and select for plankton adapted to flushing. We do not agree with these predictions, as regional projections from the IPCC did not forecast a major increase in precipitation in tropical regions. The only regions where a slight increase in precipitation was projected were eastern Africa and South‐East Asia. In eastern Africa, the major freshwater bodies are large, deep lakes that have very long residence times and are unlikely to be affected by flushing. Moreover, nutrient inputs from their catchment represent a small fraction of their total nutrient loading. Several independent studies carried out in this region have provided evidence of a decrease in primary productivity in some of these large tropical lakes due to climate change. The major process providing nutrients to the euphotic layer is internal loading, which has been reduced as warming of the surface waters has increased the temperature gradient and the water column stability. Moreover, reduced velocity of trade winds during the dry season has affected the mixed layer depth and decreased internal nutrient fluxes. Therefore, the trend for large tropical lakes in a warming climate is oligotrophication, not eutrophication. In tropical South America, the rainfall increase is not the dominant scenario; thus, the predicted changes in plankton dynamics do not stand. Therefore, we believe that the predictions presented in the paper for tropical systems under a changing climate are invalid for most tropical systems.

Predictability of plankton communities in an unpredictable world

Summary1. Plankton ecology contributes significantly to ecological theory building, because plankton organisms are relatively easy to manipulate and have short generation times and a relatively small set of traits making them an ideal experimental model system for addressing both general ecological questions as well more system‐specific questions.2. Since the environment is changing at an unprecedented rate, there is an ongoing demand for predictions from plankton ecology on the consequences of global change.3. In 2010, a colloquium was held on three subjects: chaos versus predictability in plankton dynamics, global patterns versus regional differences in plankton dynamics and climate‐induced changes in plankton dynamics.4. Papers in this Special Issue propose a new model of plankton dynamics under climate change in different climate zones; offer increased attention to the role of winters in resetting population dynamics; discuss the effects of climate change on ecological stoichiometry and efficiency of trophic transfer; describe the relative and interacting effects of changes in temperature and hydrology on plankton; and analyse the effects of climate change on host–parasite dynamics.5. Important research gaps include increased monitoring of understudied climatic zones, adaptation of plankton organisms to altered environmental conditions, interactions of climate change with legacy nutrients, interactions with other anthropogenic pressures and interactions with the infochemical network.

Impact of Farakka Barrage on the Hydrology and Fishery of Hooghly Estuary

Construction of the Farakka barrage on the Ganga River in April 1975 to augment water supply to the Calcutta port has brought about a significant increase in freshwater discharge in its distributary, the Hooghly estuary. This has naturally resulted in major changes in the ecology of this estuary, causing modifications in the structure of its fishery resources, fishing pattern, and fish production. This paper presents observations on salinity, plankton, bottom biota, fishery resource, and fish production of different zones of the Hooghly estuary during the period 1982-1992. Comparison with similar studies made before and immediately after commissioning of the Farakka barrage (1975-1977) has revealed that the increased freshwater discharge has resulted in considerable decrease in salinity throughout the estuary. The freshwater zone now extends toward the mouth of the estuary. The true estuarine zone has moved seaward and the marine zone has been restricted to the area near the mouth of the estuary. This has effected major changes in plankton dynamics, sharp decline in the fishery of marine and neritic species in the upper estuary, caused a significant increase in catch of Tenualosa ilisha and an over twofold increase in the average annual fish landings from the estuary as a whole. New zonations have been proposed based on the presently observed salinity values, which are the most significant factor in determining the fishery of any estuary. An interdisciplinary study of the ecology of the new zones is needed to establish their correct biological characteristics.