Joint Excursion WANats and WAISS, 9-11 June 2023

The WA Naturalists’ Club has its very own field station situated on Cooleenup Island in the Murray River Delta of the Peel Inlet, one of the few Deltas Western Australia calls its own. The Yunderup Nature Observatory was built in 1985 by Club members and has since hosted many excursions. The latest survey of the island was on June 10th-12th, a joint excursion alongside members of the WA Insect Study Society led by Daniel Heald and attended by four other members who stayed for the weekend. Accompanied by the group were the Observatory’s caretakers, Lucy and Roman Mandyczewsky, who also provided transport to and from the island in their boat.

The trip had been postponed from last September due to bad weather, so everyone was keen to get out there and explore what the island had to offer. Unfortunately, the weather had other ideas in mind, but armed with wellies and raincoats, we persisted through the continual on-and-off showers. We conducted opportunistic surveys from the Observatory to Coopers Mill to the west and east ends of the island and invertebrate light trappings on both nights. Upon arrival to the island, Daniel closely examined the path between the jetty and the field station staircase, finding as many as six different species of invertebrate, plant, and lichen off one brick alone! We also found seven other species of ant just between the kitchen of the field station and the jetty.

On Friday evening, we set up three light traps, with one of the lights inside a small mesh pop-up tent and the other two in front of vertical white sheets. Strong winds on Saturday night did not bode well for the sheets, so we gathered all three lights inside the tent to create a brighter beacon. Many moths were drawn in during the night, alongside a few grasshoppers and even a Western Dung Beetle (Onthophagus ferox). Species observed on the traps were much the same across the two nights.

Image by Daniel Heald

Daniel’s keen eye spotted a Jumping Peacock Spider just inland of a small sand patch not far west of the station on the afternoon of the second day. It was an exquisite male Maratus spicatus; not long after, a female M. spicatus also made her presence known.

Image by Patrick Wake

We reported the total invertebrate tally observed over the weekend, many of which have been identified down to species. Ranging from a very soggy Feather-horned Beetle (Rhipicera sp.), Iridomyrmex purpureus & discors, to camouflaged Squathoppers and even a Melobasis Jewel Beetle carapace.

The night stalks proved just as fruitful, with a wide variety of spider species such as the Leishmann’s Huntsman (Isopeda leishmanni) and a surprise visit from an Australian House Centipede (Allothereua maculate). Seventeen different species of Fungi & Slime Moulds were observed. These include a relatively large Brown Oyster Mushroom (Pleurotus australis), scatterings of Scotsman’s Beard (Calocera guepinioides), plenty of Lavender-pored Bracket Fungus (Phaeotrametes decipiens) and a considerably deteriorated Ghost Mushroom specimen (Omphalotus nidiformis).

Lavender-pored Bracket Fungus (Phaeotrametes decipiens) – Image by Jasper Dean

Thirty-five different birds were seen. A charming Sacred Kingfisher hovered close to the Mill on the final morning, and an unusually large gathering of Cormorants was spotted across the shore. There was some concerning erosion at the island’s western end, along the beaten pedestrian path leading to Cooper’s Mill. The mudbanks along the shoreline are riddled with holes making the trek somewhat tedious to navigate during a downpour. The likely culprit is Leptograpsodes octodentatus, the Burrowing Shore Crab. However, we don’t know if the increased salinity in the Peel Inlet, since the Dawesville Cut was opened, has made it more hospitable to the crab. Haswell’s Crab Helograpsus haswellianus was also present, an east coast species only recently found in WA. Unfortunately, Watsonia, an invasive weed, appears to have started reclaiming the island again. Despite prior extermination efforts, their numbers have sprung back with vigour. Very few flowering plants were in bloom or with fruit at the time, which would have limited bird and insect variety. A return trip during the warmer months would likely see an abundance of Melobasis Jewel Beetles and most other insects.

A complete species list will be available as an estimate by the end of next week. Photographs of the species observed during the excursion have been uploaded to iNaturalist and can be viewed under the ‘Cooleenup Island Biodiversity’ https://www.inaturalist.org/observations?project_id=106997. Despite the rather dreadful weather, it was an enjoyable weekend out on the island, and we’re all very keen to return to the field station for future survey opportunities.

Jasper Dean
Western Australian Insect Study Society