Science for Everyone

Aliens in the Ice Pond: What Macroinvertebrates Can Tell Us About Our Freshwater Environments

Guest blog post by Science Educator Isabelle Holt

  Students sort and identify their net contents using field guides and macro-lenses so they could gather count data for various freshwater macroinvertebrate families.

Students sort and identify their net contents using field guides and macro-lenses so they could gather count data for various freshwater macroinvertebrate families.

The word ecology comes from the Greek words oikos meaning “the family household” and logy meaning “study of.” This past week High School Island Ecology (HSIE) got to explore the world of freshwater macroinvertebrates.

Our ambitious high school students studied the households of our freshwater macroinvebrate communities by sampling in both the Ice Pond and one of the old foundation ponds and compared what they found in each.

Invertebrates are extremely important for all ecosystems and make up 96% of animal species. The freshwater macroinvertebrates, defined as spineless animals that can be seen with the naked eye, on Hurricane are responsible for the breakdown and cycling of nutrients within their ponds similarly to the ways in which earthworms allow for the cycling of nutrients in soil. The species we were studying feed on autochthonous detritus, decaying organic matter that has come from flowering plants, mosses, or algae and is typically high in its cellulous content.

  Dragonfly larvae will molt between 5 and 14 times before it is ready to emerge as an adult dragonfly  (Image from  Shropshire Dragonflies )

Dragonfly larvae will molt between 5 and 14 times before it is ready to emerge as an adult dragonfly (Image from Shropshire Dragonflies)

Many freshwater invertebrates act as indicator species of habitat health allowing for the process of biomonitoring. Dragonfly nymphs, for example are very sensitive to pollutants and their presence in a freshwater system indicates that that body of water is relatively clean and free of contaminates. Don’t let the adult dragonfly’s beauty bewitch you; they are fearsome predators who, in their larval form, look like the aliens of horror movie fame. Dragonfly larvae have extendable jaws called labium that they thrust out towards their prey. Equipped with sharp bristles and pincers, once a prey item is in the grasp of a dragonfly nymph it has little hope. These nymphs have even been known to hunt and capture freshwater fish 10x larger than they are. Upon careful study students noted that the most prevalent family of dragonfly in the Ice Pond were the Libellulidae or Skimmer dragonflies. One student even remarked that the nymphs he was finding appeared to be the inspiration behind Predator, the 1987 science fiction action horror film. Who says science can’t be cool?!  

  Fingernail clams are so small they are easy to misidentify as pieces of sediment, however, our observant HSIE students were able to sort through quite a few. (Image from the  Natural Environment Research Council )

Fingernail clams are so small they are easy to misidentify as pieces of sediment, however, our observant HSIE students were able to sort through quite a few. (Image from the Natural Environment Research Council)

Closely related to their marine bivalve cousins, the scallops, the freshwater environments on Hurricane are rife with Sphaeriidae otherwise known as fingernail or pea clams. The HSIE students pulled dozens of these tiny bivalves up in their nets from the soft substrate of the ice pond. When sorting through the muck in our nets the fingernail clams looked like little pearls that had burrowed into the surrounding leaf litter. Fingernail clams have a lifespan of 1-3 years but can reach maturity as rapidly as at one month old. One of the reason fingernail clams are so prevalent in freshwater environments is that they can burrow up to 25 cm into soft sediment and therefore are able to avoid desiccation (drying out) for several months at a time.

  Anybody home? A student holds a caddisfly larva case who's shy inhabitant hides inside its self constructed home.

Anybody home? A student holds a caddisfly larva case who's shy inhabitant hides inside its self constructed home.

The Humpless Case Maker Caddisflies (Brachycentridae) construct four sided tapering cases made of thinly stacked spruce needles gathered from the environment around them and cemented together with their own spit. These freshwater engineers use whatever is in the environment around them to construct a protective shell and feed by clinging to decaying logs in their environment and filtering small particles of organic matter from the surrounding water. Intriguingly we found more caddisfly larvae in the foundation pond than we did in the Ice Pond. Determining what factors lead to this difference in distribution could be a potentially fruitful area for inquiry by future program participants!  

HSIE returned to the Ice Pond later in the week for the raft challenge and as students constructed and tested their rafts they discussed the creatures they now knew lived beneath its murky waters. Their splashes and kicks in the pond, as they moved their rafts across, allowed these young ecologists to become part of the Ice Pond ecosystem by aerating the water, which in turn increased its dissolved oxygen content allowing the pond to hopefully support a greater diversity and abundance of macroinvertebrates. 

 

 

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