Point Lobos Nudibranch Survey ProjectSeptember 19th 2007
The BAUE Point Lobos Nudibranch Survey is an ongoing effort to quantify opisthobranch mollusc populations inside the diving areas at Point Lobos State Reserve. Four transects have been established on the Middle Reef in Whaler's cove where a representative set of opisthobranch species are surveyed periodically. Further, study participants are recording all species of opisthobranchs seen on dives in the park in order to build a comprehensive list of all species present inside the park.
The primary focus of the study is our set of four transects on the Middle Reef where we sample fourteen species of opisthobranch. These were selected based upon abundance at Point Lobos, ease of identification and diversity of diet and life habits. It is hoped that these are representative of the opisthobranchs in the park and that their relative abundance will track that of similar species not in the study and also the health and diversity of prey items in each transect. The species included in the study are shown below.
Note that the transects are numbered 1, 2, 4 and 5. Originally there were five transects but number 3 was removed due to difficulty sampling it during the summer in heavy kelp growth.
Transect One is a west facing wall on the north end of the Middle Reef. The southern boundary is the crack which extends through the reef to the east side. The crack itself is not part of the transect. The northern boundary is the northern tip of the reef which features a knob shaped overhang. The transect starts at the sand at a depth of about 60 feet and extends up from there 10 feet from the bottom. The total length of the transect is roughly 20 feet.
Transect Two is an east facing wall with significant overhang on the north end of the Middle Reef. The southern boundary is the crack mentioned in Transect One. Again, the crack itself is not part of the transect. The northern limit is again the northern tip of the reef. Vertically the transect starts at the sand at about 60 feet and extends up from there 10 feet.
Transect Four is a notch in the west wall of the middle reef, about 100 feet south of Transect One. The left side of the notch is a south facing vertical wall shaped something like a keystone. It is only a foot or two wide at it's base and about 12 feet wide at the top which is about 15 feet from the bottom. The right side of the transect is a square wall about 8 feet wide and 10 feet high measuring from the sand.
Transect Five is a west facing reef with significant overhang about 100 feet south of Transect Four. Its main feature is a cave which narrows to about a 2 foot diameter hole extending to the other side of the middle reef. In most places the overhang/cave is extends about 3 feet into the reef. The northern and southern boundaries of the transect are the edges of this cave. The transect extends from the sand at a depth of about 40 feet up 10 feet. The top of the reef above the cave is somewhat indistinct.
There is an ongoing mapping project on the Middle Reef which we hope to use to provide more exact descriptions of the four transects. For now participants are taught the boundaries of the transects by the project leaders.
Transects are sampled at a quarterly frequency at a minimum with additional surveys done based on availability of the team members. Surveyors record a count of the number of each species in the study seen in the transect, the start and stop time of their survey for each transect, water temperature and estimates for surge and visibility. The intent is for each transect survey to be completed in about 20 minutes to maintain consistency from survey to survey.
Additionally on all project dives at Point Lobos team members will record the presence of all species of opisthobranchs seen on their dives. In this way we hope to make a complete list of opisthobranchs in the park. These surveys are not limited to the Middle Reef but are conducted in the entirety of the diving area of the park.
A spreadsheet with our current transect data to date can be found here.
Below is our complete list of all opisthobranchs seen in the diving area of the park.
Cadlina modesta/Cadlina sparsa
While the real value of this study may only become apparent over time as we build up body of data there are a few items of particular interest. First, there are several of our chosen species which have thus far been either absent or very rare from our transects. These are Dendronotus albus, Doris odhneri, Flabellina trilineata and Phidiana hiltoni. These species were included on our list since we have regularly observed them in the past at Point Lobos. It isn't clear why we haven't seen them yet on the transects. We have seen all of them with some frequency outside the transects in similar looking areas.
Also missing from our transects and our complete species list are a number of fairly common species. As with our study list most of these missing animals are aeolids or denronotids. For instance we have not found few examples of Cuthona, Doto or Eubranchus which are common in other areas of Monterey or Carmel Bay.
We have also been surprised to find several species in relative abundance in our transects which we had previously considered to be relatively rare. This include Aegiris albopunctatus and Diaphorodoris lirulaticuada. These two species are very small, usually less than 5 mm, which may account for our having missed them previously. Other species which are proving to be common but which are not included in the study are Cadlina flavomaculata, Cadlina modesta/sparsa (these two are hard to distinguish underwater) and Geitodoris heathi.
Update on 10-Oct-2007: John and I found Doto columbiana in a shallow area of the middle reef so that genus has now been seen. Also we finally found Flabellina trilineata in one of our transects (transect 4). Also Corambe pacifica was observed for the first time just outside transect 2.
Update on 20-April-2008: Allison, Rob and John found an mysterious white dorid near Twin peaks, which was subsequently ID'd as Aldisa albomarginata. We also found a yellow slug on Transect 1 which was later ID'd as Hallaxa chani. Two new (to us and the park) species in one day; not bad :-).
Update on 04-May-2008: Allison and Rob spotted Cuthona fulgens near Twin Peaks, adding another Cuthona species to the list.
Update on 11-May-2008: Allison and Rob found a mystery slug near Twin Peaks tentatively thought to be an unknown/undescribed species of Okenia.
Update on 12-Oct-2008: Allison and Rob spotted Cuthona divae and Doto amyra at Twin Peaks, adding 2 more species to the list.
Update on 2-July-2010: (DCB) Added Conualevia alba, Aldisa cooperi, Okenia sp., Dendronotus subramosus and Trapania velox based on recent observations. Updated the text a bit.
The Sea Slug Forum
The Slug Site
Eastern Pacific Nudibranchs by David W. Behrens and Alicia Hermosillo
Point Lobos State Reserve
Kickoff Meeting Slides (A bit out of date now)
Nudibranch Survey Video by Roberto Chavez Arce taken during Alicia Hermosillo's visit.