Jonah Angelidis-Nordlund
Abstract
The taxonomic composition of the littoral zone of three ponds throughout coastal southwestern British Columbia has been analyzed. Surveys of aquatic communities occur, as a general rule, in summer, and so there is a lack of data on the taxonomic composition in winter. Samples were collected with a plankton net and preserved in alcohol, and then analyzed with a dissecting microscope. The crustacean subclass Copepoda was most ubiquitous, closely followed by the insects, including aquatic beetles, mosquito and mayfly larvae. The aquatic springtails and the Cladocerans were the least ubiquitous taxa, occurring in only one of the ponds sampled. The molluscs, represented solely by two individual snails in the genus Lymnaea, were found in one of the ponds sampled. Gastropod molluscs are limited by calcium levels in the pond, and so it is possible that the ponds lacking gastropod representatives had lower calcium levels. The cladocerans are known to reproduce principly via parthenogenesis, and so display denser populations when conditions are favourable.
Introduction
Ponds are diverse and dynamic organismal communities, filled with vibrant populations of microorganisms, plants, algae, vertebrates and invertebrates (Beat Oertli et al, 2002). However, most zoological surveys of ponds focus on the vertebrate and macro invertebrate communities, with few surveys searching specifically for microinvertebrates. Furthermore, few surveys are done in the winter, and so we have very little data on the taxonomic composition in the colder months. The littoral zone is occupied by a wide range of planktonic microcrustaceans, including the Cladocerans and Copepoda (Hann and Zrum, 1997). In fact, the Copepoda are known to be widespread across the ocean (Gonzáles and Smetacek, 1994), freshwater Lakes (Ferrante, and Parker, 1977) and brackish estuaries (Heinle et al, 1977). The cladocera are widespread across freshwater ponds, (Kwik and Carter, 1975). As many organisms, even invertebrates, display distinct seasonality (Frith and Frith,1990), with copepods having highest abundance in summer and fall (Uye and Sano,1995), Cladocerans having highest numbers when temperatures range between 15 and 20 degrees Celsius (Gillooly and Dodson, 2000), but little data in winter, there is a need to bolster the data collected on ponds during the colder months. The purpose of this survey is to provide insights into the macro and microinvertebrate communities living suspended in the littoral zone of ponds in winter.
Materials and Methods
Pre sampling organization
Diefenbaker park pond, which was eutrophic, and the mesotrophic North Creek duck pond and Boundary park pond was sampled on February the eighth of 2020. The NHBS 250 mm wide with a 100 micrometer mesh plankton net was held by the ring and was rinsed with water at the sampling location. Three meso habitats have been chosen at each pond.
Sampling Method
A Bernardin Mason jar was opened. The plankton net was cast into the water with a total of thirty seconds of net-in-water time. The bottom of the plankton net was emptied into the snap top container. Approx. 100 ml of equate brand 91% isopropyl alcohol was measured in a 100 ml beaker and poured into the container. The preserved sample was emptied into one of the mason jars, and labelled. After approx. 24 hours, the alcohol was replaced with 20 ml of fresh alcohol.
Data Analysis
A plastic pipette has had the tip cut off, and around three pipette full of the sample was added to a Petri dish. Starting at one end of the Petri dish, moving in a systematic up and down fashion, each organism was identified and counted using a Hudson optical limited dissecting microscope.
Results
The major taxa present in the littoral zone of ponds in winter includes arthropods and molluscs. Insects included representatives from the order Coleoptera, of which a single individual was found, one larval mosquito was found and one larval Ephemeroptera. Crustaceans included twenty-eight Copepods, and six Cladocerans. Two aquatic snails of the genus Lymnaea were found. Finally, around twenty-three aquatic springtails were found of the order Collembola. See Fig. 1
Diefenbaker park pond had a total of twenty-seven individuals, with representatives from the Arthropods and Molluscs. Two insects were found, one of which was an aquatic beetle, and the other a larval mosquito. The molluscs were Lymnaeans, and two individuals were found. Copepods formed the broad majority of the sample, with twenty-three being found. See Fig. 2
North Creek Duck Pond had a total of eight individuals, of which all were Arthropods. One larval mayfly was found. As well, a single copepod was found, and Six Cladocerans. See fig 3.
The Boundary Park sample had a total of twenty-seven individuals, composed entirely of Arthropods with representatives from two subphyla: the hexapods and crustaceans, with hexapods being solely represented by the order collembola, or the springtails, with twenty-three individuals being found. The crustaceans were solely represented by the Copepods, of which four were found. See fig. 4.
Figure 1: All Ponds
Figure 2: Diefenbaker Park Pond
Figure 3: North Creek Duck Pond
Figure 4: Boundary Park Pond
Discussion
Of the taxa present, Arthropods comprise the broad majority, 97%, and include representatives from two of its three major subphyla, the crustaceans and the hexapods across the three ponds.
Subclass Copepoda was the most ubiquitous taxa, closely followed by insects, which show a diversity of orders. Molluscs and springtails are the least ubiquitous taxa. Copepods are widespread across freshwater (Ferrante,and Parker, 1977, and Vinebrooke and Leavitt, 1999), brackish water (Heinle et al, 1977) and saltwater (Gonzáles and Smetacek, 1994), and these findings provide more support that Copepods are some of the most ubiquitous of aquatic microcrustaceans. Copepods were present in Diefenbaker pond, which contained the highest biodiversity and biological productivity; however, Copepods were present in the other ponds, including North Creek Duck pond which had the lowest productivity and boundary park pond which had the lowest biodiversity.
Cladocerans were present in one of the ponds sampled but were limited in number. Cladocerans are common in standing water (Sychra and Adamek, 2011), and so their numbers in Mesotrophic and eutrophic ponds seem relatively low. The limited presence of cladocera could be explained by their reproductive strategy of parthenogenesis. Thus, Cladocerans tend to fluctuate widely in populations, having higher concentrations when conditions are favourable (Smirnov, 2017), and so the unfavourable cold conditions of the pond in winter could explain their low numbers.
Insects were relatively well dispersed, being present in two of the three ponds. Ephemeroptera, or mayflies, are known to be present in their larval state in freshwater (Sychra and Adámek 2009), and were present in one of the ponds present in their larval stage, which provides evidence that mayflies are present in ponds in British Columbia. Mayflies are highly sensitive to pollution (Alhejoj et al, 2014), and denote a low level of pollutants in North Creek Duck pond. The number and biodiversity of Beetles, as well as insects in general, is highly dependent upon the presence of predatory vertebrates, such as fish (Fairchild et al, 2008). Boundary park has fish, and that could explain the absence of insects.
Boundary park pond, however, was not devoid of Hexapods, and there was a high presence of Collembolans populating the water’s surface.
The phylum mollusca was represented solely by the gastropoda genus Lymnaea. Molluscs are limited by levels of calcium in the water, as their shells are composed of calcium carbonate (Thomas, et al, 1974). Thus, it could be possible that North Creek Duck pond and Boundary Park Pond lack calcium.
Limitations of this study include random chance resulting in missing a taxon or finding a single unique taxon in the sample, and consequently inflating its numbers. The preservation method of isopropyl also does not preserve soft bodied animals, so groups such as the nematodes and rotifers, which may or may not be present, have not been observed. Furthermore, the method of transfer from net to temporary storage container to jar, as well as the process of changing the alcohol after 24 hours could lead to loss of organisms, and deflate their numbers, or even lose entire taxa. This paper barely scratches the surface of the taxonomic composition of ponds. Further research should focus on re-sampling in order to overcome many of the difficulties of this survey, as well as using genetic techniques in order to identify species. Furthermore, studies should compare and contrast the taxonomic composition of the same ponds in summer, as well as spring and autumn.
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