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INVERTEBRATES
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Aciagrion tillyardi Laidlaw (Odonata: Zygoptera) a damselfly new to Hong Kong |
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Epixanthus or Macromedaeus? Plus a new xanthid for Hong Kong |
Beetles in seaweed in Hong Kong
by Guillaume de Rougemont
In 1980 Lanna Cheng and Dennis Hill published an introductory survey of the "marine" insects of Hong Kong. Although in the concluding chapter the authors make the point that "Perhaps a distinction should be drawn between truly marine insects and seashore insects. For the present we are interpreting 'marine' insects' as species that live in direct contact with seawater, and those whose actual contact might be limited but whose natural distribution is confined to one of the recognised marine littoral habitats.", the definition seems somewhat vague and confusing, and includes categories, such as insects of mangrove foliage, that do not even have "limited" contact, unless it is accidental, with sea water.
Strictly marine species are those that live in sea water, including ones like the Hong Kong staphylinids Bryothinusa that live in the intertidal zone, are active on the substrate at low tides, and are submerged at high tides. Other categories of sea shore insects should more properly be called 'littoral' species, but even these are sometimes not easily defined: for instance certain genera of halophiles ('salt loving' species) that in Europe are confined to the sea shore also occur on salty soils in central Asia. One category of sea shore insects is however unequivocally littoral: those that live and breed in accumulations of seaweed washed up on beaches. "In areas where seaweeds are washed ashore in large quantities, dense populations of seaweed (kelp) flies, reaching 107/km of beach, may create a nuisance, if not a health hazard." (Cheng & Hill, p. 174). "Members of several families of flies, especially the shore flies (Ephydridae) and seaweed flies (Coelopidae), breed in washed up seaweed (wrack) and other forms of flotsam. The larvae usually feed on decomposed vegetable matter and pupate in the sand or under stones. The adults of several ephydrids are generally rather common along most sandy shores." (Cheng & Hill, p. 177). Not surprisingly, the availability in such abundance of a food source has produced the evolution of a range of specialised predators of these flies and especially of their immature stages, including entire genera of beetles that are found nowhere else. However the only three beetles mentioned in this context by Cheng & Hill (p. 177) are not associated with seaweed or seaweed flies: "Beetles of several families also breed in wrack, or are associated with this habitat. Locally common beach beetles include rove beetles of the genus Bryothinusa (Staphylinidae), the darkling beetles. Gonocephalum pseudopubens (Tenebrionidae) and the beach tiger beetle Cicindela anchoralis (Cicindelidae)." Bryothinusa are strictly marine, intertidal beetles. Gonocephalum spp. are often found on beaches, because they prefer arid, light sandy soils, but are equally common inland. Cicindela anchoralis is a true littoral species, actively hunting other insects on beaches by flying or running and pouncing, but is not associated with seaweed.
Yet the specialised predators of seaweed flies do occur in Hong Kong, just as they do in every zoogeographic region. My own prospections on Hong Kong beaches and searches through the drawers of the Natural History Museum, London, have produced the following list of seaweed beetles:
Family Staphylinidae:
Cafius algarum (Sharp); Cafius corallicola Fairmaire; Cafius histrio (Sharp); Cafius nauticus Fairmaire; Cafius rufescens (Sharp); Phucobius tricolor Bernhauer; Aleochara fucicola (Sharp); Aleochara trisulcata Weise; Atheta algarum Pace; Hydrosmecta subalgarum Pace; Myrmecopora chinensis Cameron.
Family Histeridae:
Hypocaccus varians Schmidt; Eopachylopus sp. cf. ripae Lewis.
Two other littoral staphylinid beetles, Medon rubeculus Sharp and a Scopaeus that appears to belong to an undescribed species (Scopaeus sp. 5, Rougemont 2000) were also found on Hong Kong beaches to the exclusion of any other habitat, but in drier jetsam further up the beach, and may not be associated with seaweed flies, but merely confined to sandy soil: like many staphylinids that live in deserts and other sandy habitats, both these species are relatively depigmented. Cafius is a genus of world-wide distribution exclusively confined to seaweed in which both the larvae and adults prey on the larvae and pupae of seaweed flies. Phucobius is a small genus that lives in the same way but is confined to China and Japan. Aleochara of the subgenus Emplonota (including the very common A. fucicola) are parasitoids of Cyclorrapha flies, as is probably the only known member of the subgenus Triochara (A. trisulcata); both these species were hitherto only known from Japan. The smaller Atheta, Hydrosmecta and Myrmecopora probably prey both as larvae and adults on the eggs and younger larvae of seaweed flies; the two former species are so far only known by the type series collected by me in Hong Kong in 1997, while the Myrmecopora, also only known from Hong Kong, has not been recorded since the types were collected in Mirs Bay before the war. The histerids are also predators of these flies.
The fauna associated with seaweed jetsam, and, more broadly, littoral species in general, appears to be less diverse in the tropics and subtropics than in temperate regions (cf. 22 kelp fly predators and 11 marine staphylinids in Japan (Shibata, 1993) compared with 11 and 5 respectively in Hong Kong), and whole genera of littoral species belonging to other families (Carabidae, Scarabaeidae, Tenebrionidae) that are abundant in Europe, especially southern Europe, appear to be absent in the tropics.
Bibliography
Cheng, L. & Hill, D.S., (1980): Marine insects of Hong Kong, pp. 173-183. In Morton, B.S. & Tseng, C.K. (eds). Proceedings of the First International Marine Biological Workshop: The marine fauna and flora of Hong Kong and southern China. Hong Kong University Press.
Rougemont, G. de. (2000). The Staphylinid Beetles of Hong Kong: Annotated check list, historical review, bionomics and faunistics. Mem. Hong Kong Nat. Hist. Sco. 000.
Shibata, Y. (1993). On the Staphylinid beetles living in the seashore. Insects and Nature 28, 11: 23-27. (in Japanese).
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P.6-7 |
Beetle news
by Guillaume de Rougemont
The survey of the staphylinid beetles now Hong Kong announced in 1996 (Porcupine! 15, p. 44) is complete. The checklist of Hong Kong species now includes 423 species (up from 53 species recorded before 1997): read all about it in the Memoirs of the Hong Kong Natural History Society, vol. 24 ! The survey is completed, that is, but certainly not the list of Staphylinidae that actually occur in Hong Kong. Despite traps run continuously for almost two years, new additions to the list accrued almost every week right up to the last samples taken by Stephen Reels in October 1997, and this might have gone on for much longer had collecting for the biodiversity survey continued.
Most of the other beetles collected during the staphylinid survey still await study; others await specialists prepared to take them on. However a few publications have already appeared on the material collected in the course of the biodiversity survey, and I have received some feedback in private communications on three families of beetles given to friends and colleagues:
Subfamily Scaphidiinae
In Porcupine! 15 (p. 12) I gave a list provided by Ivan Löbl (Geneva Museum) of the Scaphidiinae collected in 1996. These beetles, formerly classed as a Family, are now considered to be a subfamily of Staphylinidae, but are not included in my work on the Hong Kong fauna. The "new species" of Baeocera mentioned in 1996 list has since been described as B. cooteri Löbl, after Jonathan Cooter, who also found this species in Zhejiang Province; the unidentified species of Scaphobaeocera has been identified as S. spinigera Löbl, which is widely distributed in Asia.
Family Histeridae
Histerids are very 'beetley' looking beetles, small to medium (1.5 - 10 mm) ovoid or pill-shaped insects with very hard shiny bodies and short stout legs and appendages. I love the name, but the consonance with 'histerics' is inappropriate: unlike my fretful staphs, histerids are rather ponderous, deliberate creatures. When teased they retract their heads and appendages, tortoise fashion, in which posture they become invulnerable to almost anything but a nutcracker, and play possum until the annoyance ceases before resuming their purposeful progress. Most species are to be found in decaying organic material, dung, carrion etc, in which they prey on smaller arthropods, but many are highly specialised: some are flattened dorso-ventrally as an adaptation to living under bark; others are found exclusively in birds' nests in tree hollows, or in seaweed on beaches (see article "Beetles in seaweed in Hong Kong", p. 6 ); a few, usually very rare species, are found only in ant or termite nests. The histerids I collected in 1996-97 have found their way into the hands of Thomas Lackner (Amsterdam), who provided the following information on the only seven species represented in the material:
Species in organic litter: Atholus bifrons Marseul is widely distributed in the oriental region, but new to Hong Kong; Hister sohieri Marseul is common and widely distributed in the oriental region, including China; Margarinotus arrosi Bickhard on the other hand is very rare: it was hitherto known only by the type from "China" and one other specimen, also labelled "China".
Corticolous species: Platyomalus oceanitis Marseul is common and widely distributed in the oriental region and Australia; a Eulomalus sp. cannot be determined until the genus has been revised.
Littoral species: Hypocaccus varians Schmidt, which is occur on beaches throughout the eastern Indian and western Pacific Oceans, and an Eopachys, possibly a new subspecies of E. ripae which is known from Japan and the Russian Far East, were both found in abundance but only at a single locality, on the relatively pristine beach at Tai Long Bay, Sai Kong Peninsula, in March 1997.
Termitophilous or myrmecophilous species: Paratropus new species. This is the most interesting find, because this genus was hitherto only recorded from Africa and India. The flight interception traps and light traps used for the staphylinid survey revealed many termitophilous and myrmecophilous Staphylinidae for the first time from Hong Kong, but despite the activities of the resident termite expert (Mike Crosland) and myrmecologist (John Fellowes), none have so far been found in association with their hosts. Greater efforts required!
Family Leiodidae
All the Leiodidae, including Catopinae and Coloninae that I collected in Hong Kong and elsewhere in China were given to my friend Jonathan Cooter. Members of the Subfamily Leiodinae feed on fungi, many on subterranean fungi, and are therefore often of cryptic habits. So far material of the genus Agathidium has been studied (Angelini & Cooter, 1999), and includes three species from Hong Kong:
Agathidium xianggangense Angelini & Cooter. The type series is of 6 individuals sifted from leaf litter in May 1996 in a particularly interesting patch of woodland at over 800 m on Tai Mo Shan, a locality that produced other new species that have been found nowhere else (see Rougemont, 2000). The flight interception traps at KARC and CUHK yielded two other species, A. venustum Angelini and De Marzo, described from Taiwan and Guangxi, and A. bowringi Angelini & Cooter, known only from Hong Kong. Another species taken by John Fellowes in Guangdong in 1997 has been named A. gutianense Angelini & Cooter. Studies of the other genera of Leiodidae have not yet been published, but the material includes at least two interesting finds:
A large series of a new species of Colonellus Szyczakowski was collected in the flight interception trap at CUHK. The genus was hitherto only known from Sumatra and Ceylon. Six specimens of a new species of Creagrophorus taken in the same trap are an even greater surprise, for this genus of obligate feeders on puffballs was previously thought to be endemic to Central America.
Others
Among the many weird and wonderful creatures that suddenly appeared out of the tropical night to land in our light or flight interception traps in 1997 were two individuals that add two new beetle Families to the known fauna of Hong Kong:
Family Lymexylidae
In early January 1997 Roger Kendrick, with an expression of mild distaste, handed me an insect that had made its way into his Robinson light trap at KARC the night before. Its minute atrophied elytra were the only indication that this weird creature was a beetle, and suggested that it might be one of my jobs. It turned out to be not a staph but a member of the small Family Lymexylidae, a species of Atractocerus Palisot de Beauvois, possibly A. reversus Walker which was described from Ceylon (species of Atractocerus are very variable in size, and some of the species have been redescribed many times under different names).
These beetles were once thought to be among the most primitive of all Coleoptera, their simple wing venation, almost undifferentiated antennae and tarsi and naked abdomen being likened to a supposed neuropteran common ancestor, but later studies in higher phylogeny (Crowson, 1955) showed that they are highly evolved relatives the more 'beetley' cucujids and clerids. Nothing is known of the bionomics of Atractocerus. The larvae of two other genera of lymexylines, Lymexylon and Melittomma, bore galleries in wood and feed on particular species of fungus that grow on the walls of the burrows; Atractocerus may therefore live in a similar way, but the large eyes and very active behaviour of adults is more suggestive of predators than of fungus feeders. Some species appear to mimic Ophion, Provespa and other wasps when they are attracted to light (Kurosawa, p. 111, and my own observations in Africa). Since the great majority of captures have been made at light, these insects may be less rare than they appear to be from collections: few coleopterists regularly use light as a sampling method, and lepidopterists less enlightened than Roger are more likely to treat these arrivals as something nasty and likely to sting or bite, and to squash rather than collect them.
Kurosawa has divided Atractocerus sensu lato into five genera, based entirely on the size of the eyes and consequent modification in the shape of the head. These differences appear to be directly linked to the beetles' habits, according to whether they are diurnal, crepuscular or nocturnal. It is my view that the differences are no more than specific, and that a study taking other characters into account will prove that all the species known at present belong to a single, or at most to two genera.
Family Rhipiphoridae
While sorting the KARC flight interception trap sample for that same week I was about to flick what looked like a midge with large flabellate antennae into the waste paper bin when, again, the sight of a pair of wrinkled atrophied elytra made me realise that this was not a fly but a species of Rhipidius. All rhipiphorid beetles are rare, and as far as is known all are parasitoids of other insects, mainly of wasps and solitary bees. The few species of Rhipidius known from Europe parasitise forest cockroaches: the larvae and the larviform females live in and on their hosts' living bodies. This is, as far as I know, the first occurrence of the genus in China where it presumably lives on one of the local wild cockroaches (how it might thrive in Hong Kong if it could be persuaded to exploit the domestic kinds!).
The Family Rhipiphoridae, notwithstanding the peculiar bionomics, is similar to and closely related to the Mordellidae, the so called "tumbling flower beetles" whose Hong Kong representatives are being studied by Lu Wenhua.
The unique Chinese specimen has unfortunately since been reduced to half a dozen separate fragments by a family cat that leaped from the floor to land, painfully I am glad to say, on the pinned specimens in an open box on my desk. I am now separated from my wife and cat and living in the woods in SW France, so this particular hazard to valuable specimens no longer exists, and material can safely be sent to me for determination.
Bibliography
Angelini, F. & Cooter, J. (1999). The Agathidiini of China with descriptions of twelve new species of Agathidium Panzer (Coleoptera: Leiodidae). Oriental Insects 33: 187-232.
Crowson, R.A. (1955). The natural classification of the families of Coleoptera. Nathaniel Lloyd, London.
Kurosawa, Y. (1985). Revisional notes on the Family Lymexylonidae (Coleoptera) in Eastern and Southeastern Asia. Bull Natn. Sci. Mus. Tokyo, A 11(2): 109-119.
Löbl, I.. (1999) A review of the Scaphidiinae (Coleoptera: Staphylinidae) of the People's Republic of China, I. Revue Suisse de Zoologie 106 (3): 691-744.
Rougemont, G. de. (1996). Scaphidiids in Hong Kong. Porcupine! 15: 12.
Rougemont, G. de. (1996). A madman, a taipan and Hong Kong's staphylinid beetles. Porcupine! 15: 44-45.
Rougemont, G. de. (2000). The Staphylinid Beetles of Hong Kong: Annotated check list, historical review, bionomics and faunistics. Mem. Hong Kong Nat. Hist. Soc. In Press
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P.7-8 |
Aciagrion tillyardi Laidlaw (Odonata: Zygoptera) a damselfly new to Hong Kong
by Keith D. P. Wilson
Introduction
The dragonfly fauna of Hong Kong was comprehensively detailed in Wilson (1997). In this account 107 species were treated. A species of damselfly, Aciagrion tillyardi Laidlaw, discovered at Pat Sing Leng on 21 May 2000, brings the total odonate fauna known from Hong Kong to 108 species. A full description is provided here, with details of material and a full discussion of synonymy.
 Fig. 1 |
 Fig. 2 |
 Fig. 3 |
 Fig. 4 |
Figs 1-4
Aciagrion approximans (not of Selys): Fraser, 1933: 334-335 (key),
342-344, figs 148 (a-b), “Assam, India”.
Aciagrion tillyardi: Laidlaw, 1924: 3-6, pl. 1 (fig. 15), “Assam,
India”; Lieftinck, 1954: 76, “Sumatra”; Lahiri, 1979: 121, “Assam, India”;
Wilson, 1999: 28-30, figs 12-13, “Guangdong and Guangxi”; Hämäläinen &
Pinratana, 1999: 9, 39, “Thailand”. Enallagma assamica Fraser,
1920: 877, 888, “Assam”. Material: 5 males, Pat Sing Leng, 21-V-2000.
Description: A medium-sized Aciagrion with male coloured with violaceous markings on head, thorax and tip of abdomen. Male - Labium pale yellow. Labrum, anteclypeus and frons violaceous. Small dark spot discernible at base of anteclypeus. Postclypeus black. Top of head black with violaceous postocular spots, which are linked by a narrow, violaceous, transverse stripe across the occiput. The head is illustrated in fig. 1. Middle and hind lobes of prothorax black with pale anterior lobe and sides bluish violet or pruninosed white. Thorax black dorsally which extends beyond the humeral suture into the metepisternum. Narrow violaceous antehumeral stripe. The remaining three-quarter of the metepisternum is bluish violet fading to a pale bluish green on the metepimeron. Pale areas of thorax heavily pruninosed. The thorax is illustrated in fig. 2. Legs white with femora broadly striped black on the outer surface. Wings hyaline with greyish pterostigma, which is larger in fore wing than hind wing. Dorsum of abdominal segments 1-7 and 10 black with sides of segments 1-2 and lateral base of 3 pale blue. Segments 8-9 wholly violaceous blue. Dorsal base of segments 3-7 narrowly ringed with pale whitish yellow and black areas are narrowly expanded laterally at apical border. Distal third of segment 7 and segments 8-10 markedly dilated. Length of superior caudal appendages (fig. 3) half their width, when viewed laterally, and slightly longer than the inferior appendages; coloured black. There is a pale distal mark at base of the inferior appendage, which is otherwise black. The penile organ is simple and illustrated in fig. 4.
Female (Guangdong material) - Similar head and thoracic pattern to male but predominant colour is yellow. Abdomen black with tenth abdomen segment blue. Segment 9 with large blue spots laterally at distal margins. Intersegmental membrane between segments 7 - 8 and 8 - 9 blue. Measurements (mm): Male. Abdomen + appendages 22.0 ü 25.0, hind wing 13.5 ü 15.0; female (Guangdong material) abd. + app. 22.0, hw. 14.5. Distribution: China (Guangdong, Guangxi, Hainan and Hong Kong), India, Indonesia (Sumatra) and Thailand.
Discussion
There are some 27 species of Aciagrion known from Africa, Australasia and the Orient. It is a difficult genus, with the dozen or so Oriental species in need of revision. Fraser (1933) synonymised Aciagrion tillyardi Laidlaw with Aciagrion approximans (Selys 1876). However, subsequent authors have discounted this synonymy. In order to avoid any confusion I have provided an explanation below for not accepting Fraser’s synonymy with approximans.
Selys (1876) described Pseudagrion microcephalum ‘approximans’ (as a race of P. microcephalum) on the basis of a single male specimen, which lacked the last abdominal segments and also lacked any locality data. Selys subsequently wrote that he was, “convinced that the specimen comes from Malaysia or elsewhere from tropical Asia”. Later in his Burma publication, Selys (1891: 80) wrote that P. approximans is an Aciagrion that occurs in Khasia Hills, which presumably refers to the Khasi Hills, Shillong, Assam. He stated the anal appendages of approximans resemble those of A. hisopa. However, Selys's identification of the Assamese specimens as being conspecific with the real approximans must be treated as a sup-position, since the holotype lacked anal appendages and the type locality was uncertain. At that time only three species (A. hisopa, A. approximans and A. pallidum) were known in the genus, so his supposition based on colour pattern and venation was understandable. It is now known that these characters are too similar to be used to separate taxa in this species rich genus.
Laidlaw (1924) stated that the last three segments of the type approximans were missing and the female was unknown. He remarked that the type is, “said to have come from the Kjasi Hills”, which is incorrect. Selys (1891) never claimed that the holotype of approximans came from Assam. Laidlaw (1924) indicated his only records and specimens of tillyardi were from Assam. The type of tillyardi comes from the Tura Garo Hills, which are located in west of the Khasi Hill range in Assam. Laidlaw considered his Aciagrion tillyardi was “possibly synonymous” with approximans.
Fraser (1933) supposed that his material from Khasia Hills (Khasi Hills), Assam was approximans and commented it was very common at 5000-6000 feet. In truth, the locality of approximans remains unknown. Fraser’s drawings of the anal appendages of approximans, based on material of tillyardi (Fraser, 1933: 343, fig. 148a-b), are somewhat stylized. He clearly illustrates a lateral view of the inferior appendage with a robust tooth, which he described as, “directed inward and upward”. In Chinese material this tooth is only slightly directed upwards and cannot be seen from the side without displacing or removing the superior appendage, but nevertheless it is clearly present.
The holotype of approximans was apparently destroyed in the Dresden bombings during the war. A future reviser of the genus should suppress the taxon approximans, since its status is uncertain and cannot be verified.
Few records of Aciagrion are known from China. Needham (1930) provides a few records and a description of Aciagrion hisopa Selys from Sichuan, Taiwan and Fujian. However, Lieftinck et al (1984) assigned Needham’s Chinese hisopa records to Aciagrion migratum (Selys, 1891). Sui & Sun (1984) record Aciagrion hisopa (Selys), Aciagrion olympicum Laidlaw and Aciagrion pallidum Selys from China but these records require confirmation. Aciagrion migratum is therefore the only other Aciagrion hitherto recognised from China. Nine species of Aciagrion are known from Indo-China and 13 species in total are known from the oriental region. These are the first Aciagrion tillyardi records from Hong Kong.
There are no common names for Aciagrion that I am aware of. Perhaps this species might be known as the Violet Aciagrion.
Biological notes
Aciagrion tillyardi was found in a hilly wet marsh area at the north side of Hong Kong’s Pat Sing Leng range. Males of tillyardi were perched on vegetation adjacent to small puddled areas of open water. In the same marsh area numerous adult Nannophya pygmaea Rambur, 1842 were present. In Guangxi and Guangdong Nannophya has also been found in company with Aciagrion tillyardi.
Acknowlegements
I am grateful to Dr. Matti Hämäläinen for his helpful advice regarding the taxonomic status of A. tillyardi and A. approximans.
Bibliography
Fraser, F.C. (1920). Indian dragonflies. J. Bombay Nat. Hist. Soc. 26(4): 874-888.
Fraser, F.C. (1933). Fauna of British India, including Ceylon and Burma. Odonata. Vol I, London, Taylor & Francis. xiii + 423 pp, 180 figs, 4 cpl. 1 map.
Hämäläinen, M. and Bro. Amnuay Pinratana (1999). Atlas of the dragonflies of Thailand. Pub. Chok Chai Creation Printing group Co. Ltd., 45 Salapee 1 Rd., Somdej Chao Phraya, Klongsarn, Bangkok.
Lahiri, A.R. (1979). Odonata (Insecta) from different States of North Eastern India. Oriental Insects 13(1-2): 119-132.
Laidlaw, F.F. (1924). Notes on oriental dragonflies of the genus Aciagrion. Proceedings of the U.S. National Museum 66(10)(2547): 1-9.
Lieftinck, M.A. (1954). Handlist of Malaysian Odonata. A catalogue of dragonflies of the Malay Peninsula, Sumatra, Java, and Borneo including adjacent islands. Treubia 22(suppl.): xiii + 202 pp. 1 map.
Lieftinck, M.A., Lien, J.C. & Maa, T.C. (1984). Catalogue of Taiwanese Dragonflies (Insecta: Odonata) Asian Ecological Society, Taichung, Taiwan. 81 pp.
Needham, J.G. (1930). A manual of the dragonflies of China. Zoologia Sinica 11(1): i-xi, 1-344, 2 figs, 20 pls.
Sui, J. Z., & Sun, H. G. (1984). Common species of dragonflies from China. Agric. Pub. House, Beijing, China. pp. 328, pls. 26.
Wilson, K.D.P. (1997). An annotated checklist of the Hong Kong dragonflies with recommendations for their conservation. Mem. Hong Kong Nat. Hist. Soc. 21: 1-68, pl. 1 excl.
Wilson, K.D.P. (1999). Dragonflies (Odonata) of Dinghu Shan Biosphere Reserve, Guangdong Province, China. International Journal of Odonatology 2(1): 23-53.
Wilson, K.D.P. (2001). (in press). Odonata of Hainan. Odonatologica.
Email address of Keith Wilson: wilsonhk@hk.super.net
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P.9-10 |
Winter mortality at Cape d'Aguilar Marine Reserve
by David Y. N. Poon
December, 1999, the last of the millenium, was one of the coldest months
ever recorded in Hong Kong. Life was harsh during that period, with a
minimum air temperature (5.8°C, Hong Kong Observatory) for the year
recorded on December 23. While I was pleased to have extra heavy clothing,
the cold spell must be a nightmare to organisms of the rocky intertidal.
In the afternoon of December 23, I visited Cape d'Aguilar. As usual
I walked along the boulder field of Lobster Bay (mid-low shore), which
was also the study site of my final year project. Again, as usual, I looked
at everything present there and this time I found a Grapsus albolineatus
stranded in a rock pool. On closer examination I could confirm that it
was dead, not the usual empty post-moulting carapace I often see. With
curiosity I began searching for other corpses and soon encountered a dead
juvenile moray eel, Gymnothorax reevesii, under a big boulder.
On the afternoon of the following day, I returned to Lobster Bay to
collect sand and cobbles for my experiment. This time I noted a stranded
crab, a portunid (Charybdis annulata), still alive but barely active.
In a nearby rock pool, I discovered that some Thais clavigera were
clustering around dead fish remains
(most probably the Bathygobius spp.), while another Charybdis
annulata was dead. I again searched for corpses and, this time, upon
lifting a big boulder near the rock pool, I observed that a small grapsid
Gaetice depressus was feeding on dead fish remain.
Later on, I brought the inactive portunid back to the aquarium where
there were signs of recovery. At this point, I began to believe that the
cold spell was responsible for the observed mortalities.
In the early morning of December 25, I began collecting hermit crabs and xanthids for my project. It
was a terribly cold morning with the air temperature below 10°C. While
collecting samples I found two more inactive crabs, both Grapsus albolineatus.
After the sampling work I searched for corpses, and again found aggregations
of Thais on fish remains (possibly gobies) in a low intertidal
rock pool. One blenny (Entomacrodus stellifer) was found stunned
(barely active, very easy to catch). All the stunned animals recovered
soon after I brought them back to the indoor aquarium of SWIMS.
On the afternoon of the next day I extended my search to the western
coastline up to Telegraph Bay. This time an inactive Grapsus albolineatus
was found in a rock pool close to the pumphouse. Later on, in the
journey towards the Telegraph Bay a further two stunned G. albolineatus
and a dead goby were discovered, all found in rock pools (high shore
pools for the crabs).
The effect of low temperature is well documented for local terrestrial
communities, and mortality due to cold stress is known for certain vascular
plants, birds, and insects (Dudgeon & Corlett 1994). While the effect
of heat stress on the local rocky intertidal community is well understood
(e.g. Hodgkiss 1984; Williams & Morritt 1995), there are few documented
works concerning winter mortalities in Hong Kong (but see Maxwell 1997).
The effect of cold stress is well documented for temperate shores (Williams
personal communication) and the tolerance of temperate intertidal communities
to cold stress is well understood (Loomis 1995). Little is known, however,
of cold stress on Hong Kong's intertidal communities. This is certainly
a gap in understanding Hong Kong's coastal ecology.
However, I have to admit that no quantitative measurements were done
for the observations. It is therefore possible that other factors (any
suggestions?) may also have contributed to the outcomes. Certainly follow-up
is needed for the coming cold months to test the hypothesis that cold
stress was causing the mortalities. Finally, I'd like to invite any person
who has made similar observations to send a note to the next issue of
Porcupine!.
Acknowledgements
Thanks to Dr. Williams for discussion on this matter and Andy Cornish
for notification of the Maxwell (1997) literature.
Table 1. List of organisms dead/stunned as a result of the cold stress. The number in the brackets indicate the number of dead/stunned individuals. (D - dead; S - stunned; N/A - data not available)
|
Name |
Fate |
| CRABS | |
| Charybdis annulata (Fabricius, 1798) | D (1) / S (1) |
| Grapsus albolineatus (Lamarck, 1818) | D (1) / S (5) |
| FISHES | |
| Bathygobius spp. | D (N/A) |
| Entomacrodus stellifer (Jordan & Snyder, 1902) | S (1) |
| Gymnothorax reevesii (Richardson, 1845) | D (1) |
Bibliography
Dudgeon, D & Corlett, R. (1994). Hills and Streams: An Ecology of Hong Kong. Hong Kong University Press, Hong Kong.
Hodgkiss, I.J. (1984). Seasonal patterns of intertidal algal distribution in Hong Kong. Asian Marine Biology. 1: 49-57.
Loomis, S.H. (1995). Freezing tolerance of marine invertebrates. Oceanography and Marine Biology: An Annual Review. 33: 337-350.
Maxwell, G.S. (1997). Mullet mortality in the Sai Wan lagoon. Memoirs of the Hong Kong Natural History Society. 21: 223-224
Miyake, S. (1983). Japanese Crustacean Decapods and Stomatopods in Colour Vol. II: Brachyura (Crabs). Hoikusha Publishing, Higashiosaka, Japan (Japanese text).
Williams, G.A. & Morritt, D. (1995). Habitat partitioning and thermal tolerance in a tropical limpet, Cellana grata, on a tropical rocky shores. Marine Ecology Progress Series. 124: 89-103
Internet resources:
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Epixanthus or Macromedaeus? Plus a new xanthid for Hong Kong
by David Y. N. Poon
While lifting a boulder at Lobster bay to search for the cute little
xanthid, I saw an unusual big "Epixanthus" emerging from
the substratum and captured it. On closer examination I found that it
was something new. After checking with the texts of Dai & Yang (1991)
and Miyake (1983), the crab was in fact another species of xanthid called
Medaeops granulosus (Guinot, 1967) which has not been recorded
in Hong Kong before. In addition to the new discovery, I also noticed
that the "Epixanthus frontalis" that I collected was
quite different from the one described in Dai & Yang (1991), and looked
identical to another xanthid Macromedaeus distinguendus (De Haan
1835). Epixanthus or Macromedaeus? The identification of
this species remained unresolved until December 26.
On the afternoon of December 26, I searched for corpses along the western
coastline of Cape d'Aguilar Marine Reserve and finally reached Telegraph
Bay. There, I shifted my target from dead to living organisms -- the crabs
-- in the hope of collecting crab samples for my project. I lifted boulders
in one rock pool and successfully caught a crab. At the first glance it
looked identical to the xanthid samples collected before. Again, on closer
examination I found that it was something different. Without hesitation
I collected a few more crabs from Telegraph Bay and took them back to
the lab. After checking the texts of Dai & Yang (1991), Morton &
Morton (1983) and Wei (1991), the identity of the crab was finally revealed
- it was the real Epixanthus frontalis. Further checking with the
text of Wei also confirmed the identity of the "Epixanthus"
samples collected - they were Macromedaeus distinguendus.
Simple distinguishing features
Macromedeus distinguendus can be easily distinguished from the other two species by the presence
of pubescence at the pterygostomian region. Carapace oval-shaped, with
a convex surface and clearly divided into regions by fine grooves. Chelipeds
asymmetrical, granulated, bearing short hairs on the dorsal surface of
the merus (fourth segment) and inner side of the carpus (third segment).
Fingers armed with teeth of varying sizes. Legs short and depressed, granulated,
with the dorsal margin of the fourth segment (merus) serrated and fringed with hairs.
Epixanthus frontalis can be distinguished from the other two species by having a flat and
almost smooth, oval-shaped carapace, with ill-defined regions and a characteristic
H-shaped groove on the center (gastric-cardiac region). Chelipeds asymmetrical
and smooth, with fingers longer and thinner than the other two species.
Legs are long and slender, depressed and smooth, fringed with short setae
at the distal portion of the first and second segments (dactylus and pro-podus).
Medeaops granulosus can be distinguished from the other two species by the more hexagonal-shaped
carapace, with well-defined regions. Chelipeds asymmetrical, with the
fourth (merus), third (carpus), and the second (manus) segments granulated.
Fingers stout, with pointed tips and varying teeth sizes. Legs not serrated
on the dorsal margin of the fourth segment (merus).
For detailed descriptions interested readers can refer to Dai &
Yang (1991).
Macromedaeus distinguendus may have been misidentified as Epixanthus frontalis for a long
time for several reasons. At first glance M. distinguendus looks
superficially identical to E. frontalis and the former is common
in many local rocky shores (personal observation). Moreover, while checking
the live specimens against materials deposited at the SWIMS
museum, I found that the Macromedaeus specimen there had been misidentified
as "Epixanthus sp.". Furthermore, M. distinguendus
was absent from Morton & Morton (1983) and Morton & Harper (1995).
The latter is especially written for the Marine Reserve, and I found the
illustration of E. frontalis more resembles M. distinguendus!
In Hong Kong, studies of brachyuran fauna have been largely restricted
to the family Grapsidae, in particular the sesarmines (Lai 1999; also
see Lee 1998). Intertidal grapsids have also received considerable attention
and their feeding ecology is well understood (Depledge 1989; Kennish 1997).
The ecology of other local brachyuran fauna, on the other hand, with a
few exceptions, is poorly understood and is largely confined to taxonomic
studies (Davie 1992; George 1980; Hills 1980; Jones & Morton 1994;
Pregenzer & Morton 1990). There is no comprehensive taxonomic checklist
of Hong Kong xanthidsä (but see
Morton & Morton 1983), which are one of the least understood crab
families locally.
Bibliography
Dai, A.Y. & Yang, S.L. (1991). Crabs of the China Seas. China Ocean Press, Beijing.
Davie, P.J.F. (1992). A new species and new records of intertidal crabs (Crustacea: Brachyura) from Hong Kong. In Proceedings of the Fourth International Marine Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 1989 (Ed. B. Morton). Hong Kong University Press, Hong Kong, pp. 345-359.
Depledge, M.H. (1989). Observations on the feeding behaviour of Gaetice depressus (Grapsidae: Varuninae) with special reference to suspension feeding. Marine Biology. 100: 253-259.
George, R.W. (1982). The distribution and evolution of the ghost crabs (Ocypode spp.) of Hong Kong with a description of a new species. In Proceedings of the First International Marine Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 1980 (Eds. B. Morton & C.K. Tseng). Hong Kong University Press, Hong Kong, pp. 185-194.
Hills, D.S. (1982). The Leucosiidae (Crustacea: Decapoda) of Hong Kong. In Proceedings of the First International Marine Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 1980 (Eds. B. Morton & C.K. Tseng). Hong Kong University Press, Hong Kong, pp. 195-205.
Jones, D.S. & Morton, B. (1994). The fiddler crabs (Ocypodidae: Uca) of Hong Kong. Asian Marine Biology. 11: 9-40.
Kennish, R. & Williams, G.A. (1997). Feeding patterns of the herbivourous crab Grapsus albolineatus. Marine Ecology Progress Series. 147: 87-95.
Lai, V.C.S. (1999). A new sesarmine for Hong Kong. Porcupine!. 20: 8-9.
Lee, S.Y. (1998). Ecological role of grapsid crabs in mangrove ecosystems: a review. Marine and Freshwater Research. 49: 335-343.
Miyake, S. (1983). Japanese Crustacean Decapods and Stomatopods in Colour Vol. II: Brachyura (Crabs). Hoikusha Publishing, Higashiosaka, Japan (Japanese text).
Morton, B. & Morton, J. (1983). The Sea Shore Ecology of Hong Kong. Hong Kong University Press, Hong Kong.
Morton, B. & Harper, E. (1995). An Introduction to Cape d'Aguilar Marine Reserve, Hong Kong. Hong Kong University Press, Hong Kong.
Pregenzer, C & Morton, B. (1990). Hong Kong Pinnotheridae: Pinnotherinae (Crustacea: Decapoda). In Proceedings of the Second International Marine Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 1980 (Ed. B. Morton). Hong Kong University Press, Hong Kong, pp. 649-659.
Wei, C. (Ed.). (1991). Fauna of Zhejiang. Crustacea. Zhejiang Science and Technology Publishing House, China (Chinese text).
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