Abstract
Numerous diatom taxa, including six endemic genera, have been reported to
live on the skin of cetaceans, none of which appear to be host specific. Presence of such epizoic
diatoms becomes obvious if macroscopic patches of different coloring develop.
Reports of diatom infestations of cetaceans most commonly involve Mysticetes
harvested during whaling activities. Diatoms are apparently not uncommon in skin films of, Blue
(Balenoptera musculus), Fin (B. physalus), Sei (B. borealis), Humpback
(Megaptera novaengliae), and Minke (B. acutorostrata) whales. The infestations are
reported to be most prevalent in whales with blubber thickness' indicating they have been in cold
water climates for some time. Whales described as "lean," presumably recent arrivals
from warmer waters, were noted to be free from diatom films. Nemoto et. al., (1980) report diatom
skin films to be more common in colder waters and less common in temperate waters. Thus diatom
films have been used to indicate movement patterns of the large cetaceans. Diatom skin films are
reportedly responsible for the description of Blue whales as "sulfur bottom"
whales.
While less common, descriptions of skin film diatoms have been found for the
following odontocetes- Dall's Porpoise (Phocoenoides dalli), Sperm Whale (Physeter
catodon), Bottlenose Whale (Hyperoodon rostratus), Killer Whale (Orcinus orca),
Franciscana Dolphin (Pontoporia blainvillei), Harbor Porpoise (Phocoena phocoena),
Pacific white-sided Dolphin (Lagenorhynchus obliquidens), Cuvier's Beaked Whale (Ziphus
cavirostis), Strap Toothed Whale (Mesoplodon layardii), and Baird's Beaked Whale
(Berardius bairdii). "Springer Dolphins" (Lagenorhynchus cruciger and
Cephalorhynchus commersoni) are also suspected of being infested. Apparently, diatom skin
films on Atlantic Bottlenose dolphins have not been reported in the literature, although there
are unconfirmed anecdotal reports of such films from Tursiops in Hawaii; the diatom taxon
involved was not described, however.
Two geriatric (>30 year) Atlantic Bottlenose dolphins, Tursiops
truncatus, one male and one female, housed at the same open ocean enclosure complex in San
Diego Bay, but not in-contact, developed "coffee-colored" skin films in January of
1997. Skin film samples were collected with a 4mm bone curette into sea water and 1% neutral
buffered formalin. Light microscopy (LM) revealed numerous diatom cells. Subsequently a diatom
skin film has been noted on a juvenile, incontact, male, however, the surface film is much
smaller and much more difficult to observe grossly. No clinical signs have been attributed to the
skin films.
The skin films were essentially monospecific (a single valve of the sessile
Fragilaria investiens (W. Smith) Cleve-Euler was observed in addition). LM and Scanning
Electron Microscopy (SEM) of material treated with hydrogen peroxide was performed to elucidate
the valve structure of the diatom involved. This allowed it to be identified as Epipellis
oiketis Holmes, the single representative of this monoraphid genus known so far, and reported
previously only from Killer Whale and Dall's Porpoise at latitudes north of Monterey Bay (Holmes,
1985). Although agreeing completely with this species in ultrastructural architecture, the valves
collected from Bottlenose dolphin revealed a significantly denser ornamentation pattern of
striae, areolae and marginal alveolae, which could possibly relate to intra specific
variation.
It is interesting to note both original animals noted with infestations
(which persist at time of abstract preparation) are geriatric and housed at the same location. No
other animals in our population, spread throughout San Diego Bay, have developed skin films. It
is also interesting that water temperatures in San Diego Bay are consistently the coldest in
January and February.
References
1. Denys, L. 1996. Morphology and taxonomy of epizoic diatoms
(Epiphalaina and Tursiocola) on a Sperm whale (Physeter macrocephalus)
stranded on the coast of Belgium in 1994. Manuscript submitted to Diat. Res.
2. Hart, T.J. 1935. On the diatoms of the skin film of whales, and
their possible bearing on problems of whale movements. Discovery Reports. Vol. Y., pp.
247-282.
3. Holmes, R.W. 1985. The morphology of diatoms epizoic on
cetaceans and their transfer from Cocconeis to two new genera, Bennettella and
Epipellis. British Phycology Journal 20: 43-57.
4. Holmes, R.W., S. Nagasawa, and H. Takano. 1993. A re-examination
of diatom samples obtained from cetaceans collected off South Africa. Bulletin of the National
Science Museum, Tokyo, Ser. B, 19(4):127-135.
5. Holmes, R.W., S. Nagasawa, and H. Takano. 1993. The morphology
and geographic distribution of epidermal diatoms of the Dall's porpoise (Phocoenoides dalli
True) in the northern Pacific ocean. Bulletin of the National Science Museum Tokyo, Ser. B,
19(l):1-18.
6. Morejohn, G.V. 1980. Dall's porpoise: Epizoic commensals.
In: Winn, H.E. and B.L. Ollas (eds.). Behavior of Marine Animals, Vol. 3: Cetaceans.
Plenum Press, New York, Pp. 55-56.
7. Nagasawa, S., R.W. Holmes, and T. Nemoto. 1989. Occurrence of
cetacean diatoms in the sediments of Otsuchi Bay, Iwate, Japan. Proceedings of the Japanese
Academy, 65, Ser. B Pp. 80-83.
8. Nagasawa, S., R.W. Holmes, and T. Nemoto. 1990. The morphology
of the cetacean diatom genus Plum sigma nemoto. Sci. Rep. Cetacean Res., No. 1. pp.
85-91.
9. Nagasawa, S. 1993. Cetacean diatoms from sediments at Otsuchi,
Iwate-ken, Japan. Bulletin of the National Science Museum, Tokyo, Ser. C, 19(3): 91-97.
10. Nemoto, T., R.L. Brownell, Jr., and T. Ishimaru. 1977. Cocconeis
diatom on the skin of franciscana. Sci. Rep. Whales Res. Inst., No. 29. pp. 101-105.
11. Nemoto, T., P.B. Best, K. Ishimaru, and H. Takano. 1980. Diatom films
on whales in South African waters. Sci. Rep. Whales Res. Inst., No. 32. pp. 97-103.
12. Omura, H. 1950. Diatom infection on Blue and Fin whales in the
Antarctic whaling area V (the Ross sea area). Sci. Rep. Whales Res. Inst. No. 4. pp. 14-26.
13. Van der Werff, A. 1950. On a characteristic diatom from the skin film
of whales. The Amsterdam Naturalist. Vol I. No. 3. pp. 91-93.