Polhawn One Survey

This was our third trip to conduct surveys at The Rockpool Project’s Polhawn One survey site; the first of the year. The wind dropped and the rain stopped so we had a fairly decent time, although a large swell from the previous storm meant we could not get out to the far edge of the reef safely. Nor was it warm enough to want to get much more than ankles wet.

Tides and weather

Although a spring tide, it was not a particularly low one and the recent storm and southerly winds meant that the lowest reaches of the reef stayed beyond our reach.

Low tide02.031.1m
High tide08.005.4m
Low tide14.231.1m
High tide20.175.1m

The weather was pleasant by recent standards but still not a day for an extended visit.

Temperature (Celsius) and rainWind
06:00 - 12:009°, 0.0mm3 m/s from SW
12:00 - 18:0011°, 0.0mm5 m/s from SW
18:00 - 23:5910°, 2.9mm6 m/s from SSE

Crustacean survey

The main objective of the day was to complete a 45 minute crustacean survey for The Rockpool Project. This would be our third at the Polhawn One survey site and would allow for better comparison over the whole season.

For a long while we found no crabs at all and were unable to catch any prawns for identification purposes. That left us with a few pictures of barnacles. As the end of the survey approached we moved offf the main rib of rock that we usually found productive and followed a gully along to some flat rocks. Here we found the usual species: Brown crab (Cancer pagurus), Velvet swimming crab (Necora puber), Montagu’s crab (Xantho hydrophilus) and Shore crab (Carcinus maenas).

juvenile velvet swimming crab
Juvenile velvet swimming crab
Necora puber

Biodiversity survey

There is no time limit for a biodiversity survey and so we continued in the new area for a while after the crustacean survey. The highlight was a pair of grey sea slugs, presumably mating for the coming season. Both were returned to the same spot after we got photos and a bit of video of the one.

Common Grey Sea Slug

common grey sea slug
Common grey sea slug
Aeolidia papillosa

Grey sea slug on video

This sea slug kindly unwound his/herself once placed back in the water, showing the cerata properly and looking less like a jelly blob.

Other notable finds included:

breadcrumb sponge
Breadcrumb sponge
Halichondria panicea
dahlia anenome
Dahlia anenome
Urticina felina
site of barnacle volcano
Site of a Volcano barnacle, presumably knocked off in a recent storm
Perforatus perforatus
Lipophrys pholis
mason worm
Sand mason worm
Lanice conchilega

We also saw a number of small jelly balls, about the size of a glass marble and figured these to be small anenomes. We hope to have confirmation of the species at some point.

juvenile anenomes
Juvenile anenomes (awaiting confirmation)

This individual chose a bit of plastic to settle on. Perhaps not a permanent choice but the first hard surface after being bashed about in the recent storms.

juvenile anenome
Juvenile anenome (again, awaiting confirmation)