the OLiVA Vol.1, n.4 October 8, 2011

List and iconography of the Oliva species found at low tide on some beaches of and Gili Trawangan island (). Shelling trip report.

Gilberto Centomo

Via Forte Campolongo,15 – 36015 Schio (VI) – ITALY e-mail: [email protected]

Key-words

Mollusca, Gastropoda, Olividae, Oliva bulbiformis, Oliva reticulata, Oliva caerulea, Oliva irisans , Oliva tigridella , Oliva elegans , Oliva oliva , Bali, Gili, Indonesia.

Introduction

During recent years the idea that the species belonging to the Genus Oliva mainly live in the intertidal zone has been definitively rejected. Nowdays we know that each species shows different behaviours chosing to live at different depth. In my last trip to Bali and Gili Trawangan islands in September 2011, I have checked what Oliva species were present in the intertidal zone and if the specimens found in those beaches were adult, juvenile or both. Moreover, each species found was photographed in its habitat and some specimens were collected. The olives were found both by following their tracks and by baits (small pieces of squid).

Bali island

Fig.1. Bali Island. “A” Pegametan (8°12’20’’S, 116°61’86’’E). “B” Lovina (8°16’33’’S, 115°02’18’’E). “C” (from 8°69’60’’S, 115°16’00’’E to 8°72’27’’S, 115°16’92’’E) and “ D” (8°81’38’’S, 115°22’90’’E)

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As you can see on the fig.1 and 2, on this island four beaches were investigated: Lovina and Pegametan in the North, Nusa Dua and Kuta in the South. In these places the habitat and the color of the sand are quite different. A recent grassland of seagrass has growth at Nusa Dua. Kuta have a tide with great waves and the sand has a beige color. In the North, Lovina beach has a very dark volcanic sand while at Pegametan the sand is more muddy. I made the researches along the day time while the low tide was present.

Fig.2 Bali island. In these pictures you can see the four explored beaches.

At Lovina I was not able to find any live oliva. I only found some beached specimens of Oliva bulbiformis Duclos, 1840 and Oliva oliva (Linnaeus, 1758) forma “ coke ” - so called by Perini in the card on olives n°5 in its website. At Pegametan Bay in the North I found only one live species: Oliva tigridella Duclos, 1835, but I found other two beached olives: Oliva reticulata (Röding, 1798) and Oliva dactyliola Duclos, 1840. At Nusa Dua there is a wide beach divided into bays by short artificial and natural headlands. Here is a meadow of seagrass as well as stationary nets to catch fish or pick up algae (see photo above). In these places I found Oliva reticulata (Röding, 1798) to be syntopic with Oliva elegans Lamarck, 1811 while in a second bay, at sunset, I found Oliva irisans Lamarck, 1811. Kuta is a very long beach, often windswept, where the sea is always rough. Here I've done the research for a stretch about two and a half kilometers finding olny juvenile specimens of Oliva oliva (Linnaeus, 1758). The olives were hidden under a few millimeters of sand . The tiny mollusks were identified thanks to small bumps which appeared when the waves retreated. Local people informed me that in this period there were no adults.

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Plate 1 . Oliva bulbiformis Duclos 1840. Beached specimens found at Lovina (8°16’33’’S, 115°02’18’’E). Size 28.25mm and 28.80mm.

Plate 2. Oliva oliva (Linnaeus, 1758). Beached specimen found at Lovina. (8°16’33’’S, 115°02’18’’E). Size 32.15mm Note: this is the form who Perini calls “ coke ”.

Plate 3 . Oliva elegans Lamarck, 1811 found alive at Nusa Dua (8°80’43’’S, 115°23’60’’E) Size 36.95mm. This species was found to be syntopic with Oliva reticulata (Röding, 1798).

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Plate 4 . Oliva irisans Lamarck, 1811 found at sunset on Nusa Dua beach (8°81’38’’S, 115°22’90’’E). Size 51.00mm.

Plate 5. Dark specimen of Oliva reticulata (Röding, 1798) at Nusa Dua.

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Plate 6. Oliva reticulata (Röding, 1798) From Nusa Dusa (8°81’65’’S, 115°22’58’’E) “A” and ”B” are adults with size 40.20mm and 41.85mm. “C” Two subadult specimens with size 38.35mm and 37.60mm. In this colony the specimens showed two different colorations, some of them were reddish while others were dark brown. As you clearly see in the above plate, also the animals had two different intensity of color. I found both male and female but I can not say if we are at the presence of a sexual dimorfism or if this is only the intraspecific variability of this species.

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Plate 7. Oliva tigridella Duclos, 1835. Specimens found at Pegametan Bay (8°12’20’’S, 116°61’86’’E) at low tide in muddy sand. Average size 19.30mm.

In the following three plates, n.8, 9 and 10, you can see a selection of very juvenile specimens of Oliva oliva (Linnaeus, 1758) which I picked up on Kuta beach.

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Plate 8. Oliva oliva (Linnaeus, 1758) found on Kuta beach. Average size 14,50mm. This is the form who Perini calls “ beehive ”.

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Plate 9. Oliva oliva (Linnaeus, 1758) found on Kuta beach. Average size 13,50mm. This is the form who Perini calls “ beehive ”.

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Plate 10. Oliva oliva (Linnaeus, 1758) found on Kuta beach. “A” is the form who Perini calls “ coke” (size from 18.50mm to 22.15mm) while “B” is the form he calls “ sleek ” (size 20.65mm).

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Gili islands

The Gili are three small islands just off the northwest coast of Lombok Is., Indonesia. The largest of them is called Trawangan. These islands are a paradise for divers who can enjoy a beautiful reef. Here the sand is of coral origin. Consequently, the olives on the Gili island have the shell lighter than those living on the beaches of Bali. As you can see in the fig.3, a large portion of the coast of Trawangan is strewn with stones and rocks (B), making it poorly suited to olives. I was able to find three Oliva species in a short stretch of coast (A: 8°33’92’’S, 116°03’37’’E) where there was only sand.

Fig.3

The picture “A” shows the place where three Oliva species were found:

- Oliva bulbiformis Duclos, 1840 - Oliva reticulata (Röding, 1798) - Oliva caerulea (Röding, 1798)

( 8°33’92’’S, 116°03’37’’E )

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Plate 11. Olive found at Gili Trawangan Island in coral sand. “A” Oliva bulbiformis Duclos, 1840 size 34.20mm. “B” Oliva caerulea (Röding, 1798) size 39.00mm.

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Plate 12. Oliva reticulata (Röding, 1798) found at Gili Trawangan in coral sand. Size 45.60mm.

Conclusions

From this research at least three facts are relevant: A) The presence of Oliva reticulata in different habitats indicates that this species is very adaptable. B) The Oliva species present in Bali are all of small size. This is probably due to harsh environmental conditions. C) The temporary lack of adult Oliva oliva on the beach of Kuta is likely to indicate that this species make regular migrations from deeper waters.

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