Heal the Bay Blog

Today’s blogger is Katherine Pease, Heal the Bay’s Watershed Scientist 

At Heal the Bay, May and June mean that it’s time for the Stream Team to conduct our yearly biological assessments of streams in the Malibu Creek Watershed.

Every month, the Stream Team tests water chemistry at 20 sites in the watershed and then once a year in May and June, we assess the biology of 11 sites. Biological testing indicates the water quality over a longer period of time since the biological organisms live in direct contact with the water. Thus, the organisms in a stream serve as a continuous indicator of water quality. Using an integrated approach of biological and chemical testing results in a comprehensive understanding of the overall health of a stream and can alert us to any potential problems or threats.

To conduct a bioassessment, we assemble a team of 4-5 adventurous and enthusiastic staff members, interns, and volunteers. We spend almost all day at one site and collect a large amount of data (26 pages!).

We study bugs — or aquatic benthic macroinvertebrates – for the biology component of the bioassessments. Benthic macroinverebrates are organisms with no backbone that live on the bottom (benthos) of the stream and are big enough to be seen with the unaided eye. They include such organisms as snails, worms, crayfish, and insects. Many of the insects found are larval stages of dragonflies, damselflies, black flies, and mayflies.

We sample benthic macroinvertebrates because they are largely immobile, spend most or all of their life in water, and are very good indicators of water quality. We know that certain species of bugs are sensitive to pollution while some are tolerant to pollution. By examining the types of bugs that we find in a stream, we can make conclusions about the water quality.

We sample a 150-meter stretch of a stream and take samples of the benthic macroinvertebrates as well as information on the physical habitat of the stream. Through this process we get to see Southern California streams up close and personal, which is something that most people never get to do. We have seen many interesting bugs and other species. For instance, we find caddisfly larvae, which are underwater architects; they construct cases around their bodies made up of items in the stream such as rocks, twigs, and sand. If you see a neatly organized pile of twigs moving slowly along a rock, you will likely find a caddisfly inside that construction.

Another cool bug that we find is the toe-biter or giant water bug. This is a large bug with big pincers that it uses to catch and feed on tadpoles and other insects. And just in time for Father’s Day, male toe-biters are excellent fathers. A female toe-biter lays her eggs on the male’s back and he then takes care of the eggs until they hatch, making sure they are protected and well oxygenated. We frequently find adult toe-biters as well as discarded egg cases after the eggs have hatched and fallen off the father’s back.

In Arroyo Sequit stream (near Leo Carrillo beach), we saw a very large black and yellow female dragonfly laying her eggs by dipping her tail in the water repeatedly. Additionally, we see many amphibians in the streams including California newts, Pacific tree frogs, and California tree frogs. The California newt is a poisonous species, with a potent neurotoxin in its skin. Due to non-native predators, habitat loss, and pollution, California newts are experiencing population declines and are considered a species of special concern. We are lucky enough to see newts in some of our more pristine streams — we have seen adults, larvae, as well as newt egg masses attached to a stick, getting ready to hatch.

By collecting data on the biological health of streams, we hope to both protect and improve the water quality of our local streams, making them habitable and enjoyable by organisms of all kinds, including us humans (a.k.a. terrestrial macrovertebrates).

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