I've been spending time on Maui with classes since 1978--first as a student with Jerry Flora, then as staff with Jerry and others. Since the classes have stayed at Camp Pecusa/Olowalu at Hekili Point, it's been my home base and a focus for informal research. Keeping a qualitative list of species found at the site was always "part of the job." Starting in 1988, I added a quantitative component for sea slugs in the form of a running log of everything found. During the first three years, the counts were pooled for each trip. Then, from 1991 onward, the counts were recorded per session/activity. However, the project "just grew" rather than being designed as a formal survey. So, no attempt was made to sample the reef in a consistent pattern, sample habitats proportionately, standardize the length of sessions, standardize the number of sessions per trip, etc. Therefore, the results should be viewed with some caution. Nevertheless, the sheer number of samples over a 20+ year period presumably somewhat compensates for such deficiencies.

The following table is a preliminary tally extracted from my database and is subject to revision (currently updated through spring, 2009). The area sampled includes about 1 km of coastline extending from the large tide pool west of the sugar mill pier to the culvert a hundred meters or so east of the camp (see photo). Most sampling was done inshore of the surf break at depths less than 1 m although some material originated at depths up to 3 m. A small amount of data came from depths over 3 m but no species were added to the table due to live collecting at such depths. The following provides some details on methods linked to the columns in the table:

AW refers to "algae washes". An algae wash amounts to shaking algae-covered cobbles and/or sweeping algae-covered surfaces with a soft brush and collecting the resultant "plankton" in a fine mesh net (see photo of net and "brush glove"). All washes were done during the day due to the difficulty of handling lights and washing gear at night. The general approach was to brush a large area lightly rather than a small area intensively in order to minimize impact. During washes, all cobbles were restored to their original positions after shaking and there was no visible damage to the bottom after brushing an area. Collected material (typically amounting to a handful or two of algal fragments plus associated animals) was sorted in the lab, then released, usually near its source or in a similar habitat. Most opisthobranchs were also released after a period of observation. The table presents totals from over 318 washes. Most were done inside the surf break between the "point, proper" and the sugar mill pier but a moderate number were done in front of the camp and a few outside the surf break. (see photo). Species with a "+" are under counted slightly in the totals due to the use of "several" or "many" in recording the results of a few early washes. This was partially off-set during tabulation by assigning a value of 3 to "several" and a value of 9 to "many". However, the number of such washes was small so the effect on the totals is minimal. The method is particularly good for sampling small, cryptic species with patchy distributions but there are probably a few biases. It undoubtedly under counts some nocturnal species (most noticeably Phanerophthalmus cylindricus) that apparently conceal themselves deeply within the substrate during the day and species that are difficult to shake loose. Sand dwelling species that don't rest near the edges of sand patches (such as Pupa tessellata) are undoubtedly under counted since I did little sampling of sandy areas. Also, I avoided sweeping patches of a couple species of algae that are loosely attached in order to prevent damage to the substrate. That means one or two species (such as Hermaea sp. #1) that I know to be common in those patches are probably under counted.

DF refers to "daytime float/snorkel." Many snorkeling sessions with students involved other activities besides opisthobranch hunting. So, I only recorded those on which opisthobranchs were noticed. That portion amounted to over 416 sessions. With an average length of 1.5 to 2 hours, a reasonable estimate would be around 600-800 hours of "dedicated" daytime hunting. The sessions were split about evenly between the area in front of the camp and the area between the "point, proper" and the sugar mill pier. (see photo) Common species were often recorded as "several" or "many" resulting in substantial under counts in the totals. This was partially off-set during tabulation by assigning a value of 3 to "several" and a value of 9 to "many" with the affected species indicated by a "+". The true numbers of these species were undoubtedly much higher since some observations involved blooms running into the hundreds or thousands. Sampling included both scanning the bottom and rock turning so the list doesn't distinguish between diurnal and nocturnal species (though rock turning contributed a minority of the data). All rocks were returned to their original positions.

NF refers to "night float/snorkel". Unlike the day floats, all of the sessions were recorded and devoted mostly to opisthobranch hunting. With over 385 sessions and an average length of 1-1.5 hours, they represent 400 to 600 hours of searching. Almost all night work was done inside the surf break between the "point, proper" and the sugar mill pier with only a handful of sessions in front of the camp. (see photo) There was no rock turning so the results are limited to nocturnal species and those diurnal species that rest in the open at night. Common species were often recorded as "several" or "many" resulting in substantial under counts in the totals. This was partially off-set during tabulation by assigning a value of 3 to "several" and a value of 9 to "many" with the affected species indicated by a "+". The true numbers of these species were undoubtedly much higher since many observations involved blooms running into the hundreds or thousands (most notably for Stylocheilus striatus for which "many" could often be accurately translated as "uncountable thousands").

Int refers to intertidal rock turning. With over 166 sessions, it probably represents about 150 to 200 hours of searching split about evenly between day and night. Most intertidal work was done on the cobble beaches located a couple hundred meters east of the sugar mill pier and around the "point, proper". But, a small amount was done on the cobble bench west of the pier and around the culvert east of the camp. (see photo) For the common rock-dwellers, there doesn't seem to be any difference in efficiency between night and day sampling (nearly all are nocturnal species that hide under the rocks by day but are readily seen when the rocks are turned). So, the day and night sessions were pooled in the table. However, there are a couple exceptions--most notably, Hydatina amplustre which was recorded only during night sessions and, presumably, is burying itself in the sand under the cobbles during the day. Also, Smaragdinella calyculata is under counted since it is common in a narrow zone much higher in the intertidal than my usual sampling area. Species with a "+" are under counted slightly in the totals due to the use of "several" or "many" in recording the results of a few early sessions. This was partially off-set during tabulation by assigning a value of 3 to "several" and a value of 9 to "many." However, the number of such cases was small so the effect on the totals is minimal. All rocks were restored to their original positions. During interpretation, some caution should be used in labeling species as "intertidal" due to the fuzziness of the boundary between the low intertidal and shallow subtidal cobble habitats.

The "sand" column presents a list of species found in samples of dead shells extracted from sand. The typical approach was to skim shell material from the bottom in areas where it was concentrated by waves/currents with each sample containing 1-2 liters of material. The sand was then screened into convenient fractions and sorted under a microscope. At the moment, only the qualitative results have been tabulated. At some point, I'll have a quantitative list to add (the total sample probably included a couple thousand opisthobranch shells). Most of the samples were taken during an informal transect in 1991 that ran from the beach to the outer slope. Therefore, some of them came from deeper water than the roughly 3 m boundary of significant live collecting.

The "plank" column records species added from a single plankton tow taken during a class and is by no means comprehensive. One or two other minimal tows were taken by classes over the years without yielding opisthobranchs. It also includes Fiona pinnata and Doto sp. #1 taken from beached debris.

* Found by Mike Severns during a visit to the old pier on the property.
** Includes Gymnodoris sp. #7.

A total of 167 species have been recorded from Hekili Point. Seven species were added by sand samples extending from the beach to the outer slope (one planktonic, four generally found at over 3 m, two typically found in shallower water). Three species were added by plankton tows. Nine species were found only in the intertidal. Two species (Fiona pinnata & Doto sp. #1) were found only on beached debris. So, 148 species were found in shallow benthic habitats (including the two shallow water ones from sand samples). Of those: 114 were found in algae washes, 51 were found on day floats, 80 were found on night floats, 98 were found in combined visual searches, 49 were found only in algae washes, 21 were found only on night floats, 3 were found only on day floats and 32 were found only in combined visual searches. The algae washes picked up 77% of the fauna, the day floats 34%, the night floats 54% and the combined visual searches 66%. Or, in other words, 33% of the fauna would have been missed without algae washes, 22% would have been missed without visual searches, 14% would have been missed without night floats, and 2% would have been missed without day floats. Checking dead material from sand samples added an additional 1%. Of the species that were noted during day floats, only 24 are usually seen crawling about or resting in the open by day. The other 27 are typically nocturnal species that were found largely by rock turning. So, only about 16% of the fauna would be visible to casual daytime snorkelers. And, that estimate is probably high since several of the diurnal species are too small and cryptic to be easily seen in the field.

The breakdown by species for the site is:  4 acteonoideans, 40 cephalaspideans, 3 thecosomata, 8 anaspideans, 41 sacoglossans, 1 tylodinoidean, 5 pleurobranchomorphans, 41 dorids (29 cryptobranch, 12 phanerobranch), 4 dendronotids and 19 aeolids.

The breakdown by species for the shallow water benthic community is: 4 acteonoideans, 37 cephalaspideans, 8 anaspideans, 40 sacoglossans, 1 tylodinoidean, 3 pleurobranchomorphans, 34 dorids (22 cryptobranch, 12 phanerobranch), 3 dendronotids and 18 aeolids. One species, Stylocheilus striatus, contributed about 53% of the animals found in the algae washes with the second place species contributing only about 4%. However 30 species from the washes (or 26% of those found) were recorded from only one specimen. By number, the composition of the algae washes is: Acteonoidea--0.0%, Cephalaspidea--19.9%, Anaspidea--55.1%, Sacoglossa--18.4%, Pleurobranchomorpha--0.1%, Doridacea--3.1%, Dendronotacea--0.1% and Aeolidacea--3.2%. So, the shallow benthic community is dominated by cephalaspideans and sacoglossans although anaspideans contribute the greatest number of animals due to the prominence of S. striatus.

The breakdown by species for the intertidal community is: 2 acteonoideans, 4 cephalaspideans, 5 anaspideans, 4 sacoglossans, 3 pleurobranchomorphans, 22 dorids (20 cryptobranch, 2 phanerobranch), and 5 aeolids. By number, the composition of the intertidal community is: Acteonoidea--1.9%, Cephalaspidea--3.8%, Anaspidea--21.5%, Sacoglossa--1.9%, Pleurobranchomorpha--1.1%, Doridacea--67.6%, and Aeolidacea--2.3%. So, the intertidal community is dominated by dorids both in terms of species and numbers.

The sand samples yielded shells of about 35 species (with some uncertainty on three due to condition). As mentioned, above, these include four benthic species typically found in water deeper than the 3 m boundary of significant live sampling as well as three planktonic species leaving 28 species from the shallow benthic community. Two or them were collected only in the sand samples. So, shells of 26 (or 45%) of the 58 live-collected species that have internal or external shells were also found in a moderately extensive series of sand samples. More sampling would almost certainly increase that number but many of the species that are nominally shell-bearing have very fragile shells that presumably break up rapidly and are unlikely to be found. As would be expected, cephalaspideans dominated the sample.

What all this suggests is that (even with very intensive sampling) daytime and visual searches are insufficient for compiling a complete or nearly complete survey of an opisthobranch fauna. Rather, a variety of methods need to be used, particularly sweeping surfaces for small and cryptic species. So, a more rigorous application of the latter technique could provide an important complement to more widely used methods in baseline studies and other surveys.