Historical Zooplankton Composition Indicates Eutrophication Stages in a Neotropical Aquatic System: The Case of Lake Amatitlán, Central America

This paper presents a study of freshwater zooplankton biodiversity, deemed as a reliable indicator of water quality. The Guatemalan Lake Amatitlán, currently used as a water source, has shown signs of progressive eutrophication, with perceptible variations of the local zooplankton diversity. Biotic and abiotic parameters were determined at four sites of Lake Amatitlán (Este Centro, Oeste Centro, Bahía Playa de Oro, and Michatoya) in 2016 and 2017. The local composition, the species richness and abundance of zooplankton, and the system environmental parameters were analyzed during both years surveyed. Biological data suggesting eutrophication of this tropical system were obtained, including a high rotifer abundance (11 species: the rotifers Brachionushavanaensis (109 ind L−1) and Keratellaamericana (304 ind L−1) were the most abundant species in this lake). The presumably endemic diaptomid copepod species, Mastigodiaptomusamatitlanensis, was absent in our samples, but we report the unprecedented occurrence of two Asian cyclopoid copepods (i.e., Thermocyclopscrassus and Mesocyclops thermocyclopoides) for Lake Amatitlán and Guatemala. The presence of larger zooplankters like adults and immature copepods (i.e., Arctodiaptomusdorsalis) and cladocerans (Ceriodaphnia sp.) at site “Este Centro” indicates a relatively healthy zooplankton community and represents a focal point for managing the conservation of this lake.

Dispersal ability and niche breadth act synergistically to determine zooplankton but not phytoplankton metacommunity structure

It is well known that both niche requirements and dispersal act together to structure communities; however, it remains unclear how the underlying mechanisms create the observed patterns in nature. In plankton communities, traits related to dispersal ability (e.g. body and propagule sizes) and niche breadth (i.e. habitat generalists and habitat specialists) have recently shown promise in this regard. Here, we hypothesized that body size (a proxy for dispersal ability) and niche breadth act together to determine limnetic plankton metacommunity structure in a tropical system of natural landlocked lakes in Brazil. Our hypotheses were partially supported for zooplankton community. Copepoda showed no relation to environmental variables, and the larger-bodied Calanoida was structured only by space. The Cladocera showed the largest spatial and environmental limitation. Rotifers showed the lowest association with space; however, its pure environmental fraction was higher than expected. The phytoplankton community was largely structured by both environment and space. The spatial limitation of this group was a clear divergence from our expectations. Lastly, we revealed that intragroup variation (when species were evaluated individually) was equal or larger than between group variation, indicating that group-specific traits may play a more important role in determining metacommunity structure.

SUCCESSIONAL PATTERNS ON FOULING PLATES IN THE BAY OF SANTA MARTA, COLOMBIAN CARIBBEAN

Successional progress was followed in fouling communities, developing under tropical conditions. Primary succession was simulated by immersing asbestos plates. The plates represent small, discrete, isolated parts of habitat. According with expectations, a trend of increasing space dominancy by colonial forms was detected as succession progressed. High within-habitat diversity but global persistency was confirmed for this tropical system. Several mechanisms of succession were found to operate simultaneously. In this Caribbean fouling system thestrong self-replacement tendencies of solitary forms and the low recruitment and growth rates of the potential space dominants (colonial forms) were mostly responsible for the successional patterns observed

Climatology of Tropical System Rainfall in the Eastern Corn Belt

This study examines the frequency of daily rainfall totals greater than 2.54 cm (1 in.) averaged within a climate division (CD) associated with tropical systems that moved through the U.S. eastern Corn Belt region during the growing season. These occurrences are defined as “events.” From 1913 to 2012, the tracks of 60 tropical systems moved over a study area that included 24 CDs—9 in Illinois, 9 in Indiana, and 6 in western Ohio. Of those 60 tropical systems, 37 were associated with events. Event risk varied through the growing season ranging from 3 events in June to 21 events in September. Decadal analysis showed an increase in the frequency of tropical systems and events during the last decade of the study (2003–12). Tropical systems were infrequent, and the timing of rainfall associated with the majority of events (i.e., September) was too late to impact corn and soybean development or yield in this region. Events had some impact on current and subsequent CD average soil moisture conditions; however, only 8 of the 37 events produced dramatic improvements in Palmer drought severity index (PDSI) values from categorical moderate to severe drought levels to near-normal conditions in the eastern Corn Belt. Those CDs that experienced a September or October event were associated with significantly higher PDSI values (+1.34) prior to the following summer than those that did not experience an event (+0.54).