Biota of Tropical Aquatic Environments An Overview

Taxonomic Classification ProkaryotesProkaryotes - Bacteria - Archaea EukaryotesEukaryotes - Protista - Fungi - Plantae - Animalia

Functional Classification Energy Source PhototrophsPhototrophs ChemotrophsChemotrophs Carbon Source AutotrophsAutotrophs HeterotrophsHeterotrophs

Herbivores Decomposers 1st Carnivores 1st Carnivores Top Carnivores Producers Ecological Classification

Producer Efficiency Gross 1 o Production (GPP) –GPP/Solar flux 0.5 – 4.0 % efficiency. Net 1 o Production (NPP) –GPP - Respiration –NPP/GPP % efficiency. 10,000 cal 9,500 cal 500 cal 150 cal

Consumer Efficiency 100 cal 200 cal 100 cal 50 cal Heat 10 cal Growth/ Reproduction 40 cal Waste Not Eaten

Classification According to Life Form Phytoplankton Zooplankton Benthic invertebrates Nekton

Plankton Small organisms suspended in the water column, with no or limited powers of locomotion. Plankton ranges in size from 20 µm (microplankton).Small organisms suspended in the water column, with no or limited powers of locomotion. Plankton ranges in size from 20 µm (microplankton). Phytoplankton refers to small plant plankton.Phytoplankton refers to small plant plankton. Zooplankton refers to small animal plankton.Zooplankton refers to small animal plankton.

Periphyton Community of algae growing attached to substrates (rock, plant, animal, sand).Community of algae growing attached to substrates (rock, plant, animal, sand). The entire community of microscopic organisms (bacteria, algae, protozoa, small metazoa) is referred to as biofilm (‘aufwuchs’)The entire community of microscopic organisms (bacteria, algae, protozoa, small metazoa) is referred to as biofilm (‘aufwuchs’)

Benthic Invertebrates Non-planktonic animals associated with substrate at the sediment-water.Non-planktonic animals associated with substrate at the sediment-water. –Epibenthos live and move about on the lake bottom. –Infauna are organisms that burrow beneath the mud surface.

Nekton Actively swimming organismsActively swimming organisms

Neuston (‘Pleuston’) Organisms (plant or animal) resting or swimming on the surface.Organisms (plant or animal) resting or swimming on the surface.

Osborne 2000

Prokaryotes Archaebacteria (archaea)Archaebacteria (archaea) Eubacteria (bacteria)Eubacteria (bacteria) DensityDensity 1,000,000,000 / g sediment (less in water)1,000,000,000 / g sediment (less in water) Diversity: c a. 5,000 species known (millions may exist)Diversity: c a. 5,000 species known (millions may exist) Surface area : volume ratio highSurface area : volume ratio high

High bacterial density ( /L vs /L in temperate systems) High bacterial activity Rapid decomposition and re-use of inorganic compounds (4-9 x faster than in the temperate zone) Numbers, biomass and productivity of bacterio- plankton generally increase with increasing trophic state and temperature. Tropical aquatic systems

Bacteria Autotrophs (examples)Autotrophs (examples) * Purple sulfur bacteria * Purple sulfur bacteria (anaerobic:CO 2 + H 2 S  CH 2 O + S) * Green sulfur bacteria * Green sulfur bacteria (anaerobic: ditto but different light wavelength) * Cyanobacteria * Cyanobacteria (‘blue-green algae’) Heterotrophs. Decomposition of particulate and dissolved organic matter.Heterotrophs. Decomposition of particulate and dissolved organic matter. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.)Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.)

Cyanobacteria Bloom Microcystis Anabaena

Bacteria AutotrophsAutotrophs * Purple sulfur bacteria * Purple sulfur bacteria (anaerobic:CO 2 + H 2 S  CH 2 O + S) * Green sulfur bacteria * Green sulfur bacteria (anaerobic: ditto but different light wavelength) * Cyanobacteria * Cyanobacteria (‘blue-green algae’) Heterotrophs. Decomposition of particulate and dissolved organic matter.Heterotrophs. Decomposition of particulate and dissolved organic matter. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.)Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.)

Surface Area to Volume Ratios Surface area (s) = 4(pi) r 2 Volume (V) = 4/3(pi) r 3 r = 1 µm r = 20µm s = 12.6 µm 2 V = 4.2 µm 3 = 3.0 s = 5028 µm 2 V = µm 3 = 0.15

Protozoa (1-2 days) Rotifera (3-5 days) Cladocera (7-14 days) Copepoda (3-5 weeks) Nutrient Release (per unit body weight) Body Size smalllarge low high Turnover Rate Surface Area Volume high low Rotifers and protozoans are often “co-blooming” with cyanobacteria in tropical waters

For a given nutrient status, primary production in the (sub)tropics is higher because Efficient nutrient cycling –High density/activity of bacterial decomposers –Importance of smaller organisms Greater stability in solar radiation Higher temperatures –Lowland tropics

Phyto- plankton Bacteria Crustaceans A B Rotifers and Protozoans Temperate lakes B A Fish Phyto- plankton Bacteria Tropical lakes Source: Nilssen 1984 B A

Importance of grazing Body size of grazer low high smalllarge bacteria algae Systems dominated by bacteria  abundant small grazers Systems dominated by algae (not blue-greens)  abundance of larger grazers

Role of Heterotrophic Bacteria in Food Webs Bacterial Decomposition Protozoa (Ciliates, Flagellates) Particulate organic matter AlgaeZooplanktonFish Nutrients Energy Soluble organic matter ‘Microbial loop’

Consequences: Protozoa may also consume cyanobacteria Ciliates, Flagellates (Protozoa) Algae Bacteria MacrozooplanktonFish DOM, POM DOM, POM Cyano bacteria (1) Toxins become concentrated in aquatic invertebrates and passed up the food chain (2) Added steps in food chain decrease food transfer efficiency to higher trophic levels (3) Exceptions to this decrease food transfer efficiency occur when cyanobacteria are directly consumed by higher trophic levels such as some cichlids, birds, humans (largely restricted to tropics).

Bacteria AutotrophsAutotrophs * Purple sulfur bacteria * Purple sulfur bacteria (anaerobic:CO 2 + H 2 S  CH 2 O + S) * Green sulfur bacteria * Green sulfur bacteria (anaerobic: ditto but different light wavelength) * Cyanobacteria * Cyanobacteria (‘blue-green algae’) Heterotrophs. Decomposition of particulate and dissolved organic matter.Heterotrophs. Decomposition of particulate and dissolved organic matter. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Rates of decomposition determined by chemical composition of organic matter, pH, temperature, availability of electron acceptors. Heterotroph Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.)Heterotroph Parasitic. Significant role in the spread of water-borne diseases (cholera, dysentery, salmonella, etc.) Vibrio cholerae

Tropics and the Transmission of Infectious Diseases Cultural factorsCultural factors –Lower standards of hygiene and health care –Lower standard of living (e.g., refrigeration, water supply & wastewater treatment) –Higher incidence of nutritional deficiencies (lower resistance) –Active control of vectors in non-tropical regions (spraying, draining of wetlands, etc.) Ecological factorsEcological factors –High temperatures, high humidity: Disease vectors (e.g., mosquitos, flies) are more abundant (particularly during the wet season) –Increased exposure to contaminated water and soil (particularly during the wet season) –Vectors survive year round Source: Sattenspiel 2000

Bacterial Waterborne Diseases Clinical FeaturesClinical Features –Acute dehydrating diarrhea (cholera), prolonged febrile illness with abdominal symptoms and malaise (typhoid fever), acute bloody diarrhea (dysentery), etc. Common agentsCommon agents –Vibrio cholerae, Campylobacter spp., Salmonella typhi, Shigella spp., and the diarrheogenic Escherichia coli. IncidenceIncidence –Each year, an estimated 3 million deaths (mostly among children) result from diarrhea. Waterborne bacterial infections may account for as many as half of these deaths. [More information: Centers for Disease Control, World Health Organization]

Bacterial Waterborne Diseases SequelaeSequelae –Many deaths among infants and young children are due to dehydration, malnutrition, or other complications. TransmissionTransmission –Contaminated surface water and poorly-functioning water distribution systems contribute to transmission of waterborne bacterial diseases. Chlorination, safe water handling, and water treatment can reduce the risks of transmission. TrendsTrends –Improvements in water and sanitation infrastructure have barely kept pace with population increases and migrations in the developing world. [More information: Centers for Disease Control, World Health Organization]

Source: WHO

Cases of cholera reported to WHO by continent and by year, Source: WHO 2010