Tropical Indo-West Pacific Region Research Articles

Atmospheric bias teleconnections in boreal winter associated with systematic sea surface temperature errors in the tropical Indian Ocean

Abstract. Coupled climate models suffer from significant sea surface temperature (SST) biases in the tropical Indian Ocean (TIO), leading to errors in global climate predictions. In this study, we investigate the local and remote effects of the TIO SST bias on the simulated atmospheric circulation and spatio-temporal variability – bias teleconnections. A set of century-long simulations forced by idealized SST perturbations, which resemble various (monopolar or dipolar, positive or negative) TIO SST biases in coupled climate models, are conducted with an intermediate-complexity atmospheric model. Bias teleconnections with a focus on boreal wintertime are analysed using the normal-mode function (NMF) decomposition, which can differentiate between balanced and unbalanced flows across spatial scales. The results show that the atmospheric circulation biases caused by the TIO SST bias have the Gill–Matsuno-type pattern in the tropics and Rossby-wave-train structure in the extratropics, similar to the steady-state response to tropical heating perturbations. The teleconnections between the tropical and extratropical biases are set up by Rossby wave activity flux emanating from the subtropics. Over 90 % of the bias variance (i.e. the square of the bias amplitude) is contained in zonal wavenumbers k≤5. The northward shift of the SST bias away from the Equator weakens the amplitude but does not change the spatial structure of the atmospheric response. Besides, the positive SST bias produces stronger bias teleconnections than the negative one of the same size and magnitude. In the NMF framework, the change in the spatial variance of the time-mean state (i.e. energy) is equal to the sum of the bias variance and the covariance between the circulation bias and the reference state (i.e. bias covariance). Due to the TIO SST biases, the global unbalanced zonal-mean (k=0) flow energy decreases, whereas its balanced counterpart increases. These changes primarily arise from the strong bias covariance. For k>0, both the global unbalanced and the tropical balanced energies increase in the case of a monopolar SST bias and decrease in the case of a dipolar SST bias. The increase appears mainly as the bias variance, whereas the decrease is associated with a strong negative bias covariance at k=1 and 2. In contrast, the extratropical balanced wave energy decreases (increases) when the TIO SST bias is positive (negative), which is mainly associated with the bias covariance at k=1. The change in the interannual variance (IAV) is contingent upon the sign of the TIO SST bias. A positive bias reduces, whereas a negative one increases, the IAV in both balanced and unbalanced flows. Geographically, large IAV changes are observed in the tropical Indo-West Pacific region, Australia, South and Northeast Asia, the Pacific-North America region, and Europe, where the background IAVs are strong.

Morphological and molecular analysis of the tropical hermit crab Calcinus vachoni (Decapoda, Diogenidae) and its potential association with colonial anemone.

Calcinus is the colorful hermit crab genus belonging to the family Diogenidae and is often found in coral reefs of the tropical Indo-West Pacific region, including southern Honshu, Japan, which is the northern limit of their occurrence. In the present study, we found C. vachoni for the first time in the intertidal zone of Jeju Island-the southernmost island of South Korea. We examined their morphology and provided a diagnosis of their morphological details with illustrations. In addition, the Korean Calcinus population was genetically characterized using mtDNA cox1 sequences and by placing them into three previously reported regional haplogroups. The phylogenetic tree from maximum likelihood analysis revealed that Korean C. vachoni is assigned to the C. vachoni haplogroups exclusively, one of the three well-supported mitochondrial haplogroups with distinct geographic ranges (i.e., C. vachoni, C. aff. vachoni Cooks, and C. aff. vachoni Mascarenes). This result provides new information on the species distribution of C.vachoni, extending their geographic range further north into the southern coast of Korea. In this study, we also first report the potential association of C. vachoni with their co-occurring colonial anemone species Palythoa aff. mutuki and dead coral head of Pocillopora species based on our on-site observation and a public coral collection database of Calcinus species. However, their ecological association with co-occurring coral species is putatively assumed for now and therefore has to be validated by compelling evidence from further field observation and experimental studies (i.e., whether the presence/absence of colonial anemones affects the behavior and survival of the hermit crabs).

Comparative Analysis of Complete Mitogenomes of Two Oxyurichthys Gobies and Their Phylogenetic Implication.

Oxyurichthys is a genus of goby that is widespread in the tropical Indo-West Pacific region. Oxyurichthys species are usually found in estuarine and coastal marine habitats. In Southeast Asia, they are commercial fishes and often collected by trawling to serve the market's demand. The mitogenome serves as a good marker for investigating the systematics and evolution of fishes, but the mitogenome of Oxyurichthys species remains unknown. In this study, mitogenomes of two Oxyurichthys gobies, O. ophthalmonema and O. microlepis, were characterized and compared. The sizes of the mitogenomes were 16,504 bp and 16,506 bp for O. ophthalmonema and O. microlepis, respectively. Mitogenomes of these two species were similar in gene content and structure. Both included 37 genes and a control region. The two Oxyurichthys mitogenomes shared similar gene features and base composition with other recorded gobies. Typical conserved blocks (CSB-1, CSB-2, CSB-3 and CSB-D) were found in the control region of both species. Phylogenetic analyses based on concatenation of 13 protein-coding genes and 2 rRNAs revealed that the two Oxyurichthys species clustered together and were sister to species of the genera Sicydium, Sicyopterus and Stiphodon. The findings of the present study support previous evolutionary studies of gobies using other molecular markers.

Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands.

Forty-two species of hydroids, excluding stylasterids, are reported in the present collection from the Northwestern Hawaiian Islands. Of these, four are anthoathecates and 38 are leptothecates. Among the latter, Sertularella affinicostata and Monotheca gibbosa are described as new species. The binomen Halopteris longibrachia is proposed as a new replacement name for Plumularia polymorpha var. sibogae Billard, 1913, an invalid junior primary homonym of P. sibogae Billard, 1911. Based largely on evidence from earlier molecular phylogenies, the genus Disertasia Neppi, 1917 is resurrected to accommodate species including Dynamena crisioides Lamouroux, 1824, Sertularia disticha Bosc, 1802, and Sia. moluccana Pictet, 1893. Sertularella robusta Coughtrey, 1876 is an invalid junior primary homonym of Sla. gayi var. robusta Allman, 1874a, and has been replaced here by the binomen Sla. quasiplana Trebilcock, 1928, originally described as Sla. robusta var. quasiplana Trebilcock, 1928. Clytia hummelincki (Leloup, 1935) is referred to the synonymy of its senior subjective synonym, C. brevithecata (Thornely, 1900). Following Reversal of Precedence provisions in the International Code of Zoological Nomenclature to preserve prevailing usage of binomena, the familiar names Sia. disticha Bosc, 1802 (also known as Dynamena disticha) and Lytocarpia phyteuma (Stechow, 1919b) are designated nomena protecta and assigned precedence over their virtually unknown senior synonyms Hydra quinternana Bosc, 1797 and Aglaophenia clavicula Whitelegge, 1899, respectively, names now reduced to the status of nomena oblita. Twenty species are reported for the first time from Hawaii [Eudendrium merulum Watson, 1985, Phialellidae (undetermined), Hebella sp., Hebellopsis scandens (Bale, 1888), H. sibogae Billard, 1942, Clytia brevithecata, C. linearis (Thornely, 1900), C. cf. noliformis (McCrady, 1859), Halecium sp., Sla. affinicostata, Sla. angulosa Bale, 1894, Pasya heterodonta (Jarvis, 1922), Tridentata orthogonalis (Gibbons Ryland, 1989), Pycnotheca producta (Bale, 1881), Monotheca gibbosa, H. longibrachia, A. postdentata Billard, 1913, A. suensonii Jderholm, 1896, A. whiteleggei Bale, 1888, and L. flexuosa (Lamouroux, 1816)]. Sertularia orthogonalis, reported for only the third time worldwide, is assigned to the genus Tridentata Stechow, 1920. Hydroids of the NOWRAMP 2002 collection consisted largely of presumptive widespread species, with over 75% of them having been reported elsewhere in the tropical Indo-west Pacific region.

British Naturalist Laura Roscoe Thornely (1860–1951), Taxonomist of Hydroids and Bryozoans

Laura Roscoe Thornely was born on 6 March 1860 in Blundellsands, Lancashire, England. On approaching age 30, in the late 1880s, she became interested in the taxonomy of hydroids and bryozoans under Prof. W.A. Herdman at University College, Liverpool. Her studies during much of the 1890s were based largely on the relatively well-known fauna of the boreal northeastern North Atlantic Ocean. Around the turn of the century, however, her focus shifted to collections from the species-rich tropical Indo-West Pacific region, the hydroids and bryozoans of which were then little-known. The publications by Thornely on hydroids from the tropical western Pacific, from Sri Lanka, and from the Sudanese Red Sea, the most noteworthy of her works on the group, are still frequently cited. Concurrently, papers were published on the Bryozoa from Northern Ireland, the Indian Ocean, and Antarctica. Overall, she described 70 new species, with 26 of them based on hydroids and 44 on bryozoans; one hydroid species was assigned by her to a new genus. A person of affluent means, the motivation for her research appears to have been pure academic interest; she never held a university appointment or degree. Thornely died on 18 July 1951 at age 91 in Troutbeck, Westmorland, England.

Mycale species of the tropical Indo-West Pacific (Porifera, Demospongiae, Poecilosclerida).

The species of the cosmopolitan sponge genus Mycale occurring in the tropical Indo-West Pacific region and adjacent subtropical waters are reviewed taxonomically. Specimens incorporated in the collections of the Naturalis Biodiversity Center form the basis of this comprehensive study, supplemented by (type) specimens borrowed from or examined in other institutions. Specimens available numbered 351, belonging to 44 species, including 14 species new to science, Mycale (Aegogropila) prognatha sp.nov., Mycale (Carmia) amiri sp.nov., Mycale (Carmia) fungiaphila sp.nov., Mycale (Carmia) monomicrosclera sp.nov., Mycale (Carmia) tenuichela sp.nov., Mycale (Carmia) tubiporicola sp.nov., Mycale (Carmia) tydemani sp.nov., Mycale (Mycale) asigmata sp.nov., Mycale (Mycale) grandoides sp.nov., Mycale (Mycale) sundaminorensis sp.nov., Mycale (Naviculina) mascarenensis sp.nov., Mycale (Paresperella) sceptroides sp.nov., Mycale (Paresperella) seychellensis sp.nov., Mycale (Zygomycale) sibogae sp.nov. Three species, indicated by the designation 'aff.', were not definitely assigned to known or new species due to uncertainty of their identity. The genus Kerasemna, previously considered a junior synonym of Mycale, was revived as an additional subgenus Mycale (Kerasemna). One species, previously assigned to the genus Desmacella as D. lampra De Laubenfels is here reassigned to Mycale, subgenus at present undecided. Additionally, species previously reported from the region but not represented in our collections are briefly characterized and discussed. We propose new names Mycale (Mycale) mauricei nom.nov. for Mycale macrochela Burton (junior primary homonym of Mycale fistulata var. macrochela Hentschel) and Mycale (Mycale) bouryesnaultae nom.nov. for Mycale (Mycale) fibrosa Boury-Esnault Van Beveren (junior primary homonym of Mycale (Aegogropila) adhaerens subsp. fibrosa Koltun). Keys to the species of each subgenus occurring in the region are provided. The opportunity of having studied this comprehensive set of species and specimens from the tropical Indo-West Pacific is taken to review and discuss the morphological and biogeographical data gathered so far on the genus Mycale. The genus currently comprises approximately 255 accepted species, with highest diversity focused in tropical Atlantic and Indo-West Pacific regions as well as in warm-temperate Mediterranean-Atlantic regions.

Transcriptomic Analysis of Gill and Kidney from Asian Seabass (Lates calcarifer) Acclimated to Different Salinities Reveals Pathways Involved with Euryhalinity

Asian seabass (or commonly known as barramundi), Lates calcarifer, is a bony euryhaline teleost from the Family Latidae, inhabiting nearshore, estuarine, and marine connected freshwaters throughout the tropical Indo-West Pacific region. The species is catadromous, whereby adults spawn in salinities between 28 and 34 ppt at the mouth of estuaries, with resultant juveniles usually moving into brackish and freshwater systems to mature, before returning to the sea to spawn again as adults. The species lives in both marine and freshwater habitats and can move quickly between the two; thus, the species’ ability to tolerate changes in salinity makes it a good candidate for studying the salinity acclimation response in teleosts. In this study, the transcriptome of two major osmoregulatory organs (gills and kidneys) of young juvenile Asian seabass reared in freshwater and seawater were compared. The euryhaline nature of Asian seabass was found to be highly pliable and the moldability of the trait was further confirmed by histological analyses of gills and kidneys. Differences in major expression pathways were observed, with differentially expressed genes including those related to osmoregulation, tissue/organ morphogenesis, and cell volume regulation as central to the osmo-adaptive response. Additionally, genes coding for mucins were upregulated specifically under saline conditions, whereas several genes important for growth and development, as well as circadian entrainment were specifically enriched in fish reared in freshwater. Routing of the circadian rhythm mediated by salinity changes could be the initial step in salinity acclimation and possibly migration in euryhaline fish species such as the Asian seabass.

The identities of three species of Parahelice Sakai, Türkay amp; Yang, 2006 (Crustacea: Brachyura: Varunidae) from the western Pacific, based on morphological and molecular evidence.

Species of the varunid genus Parahelice Sakai, Türkay Yang, 2006, inhabit high intertidal areas of oceanic islands of the tropical Indo-West Pacific region. As several species of Parahelice and Pseudohelice subquadrata (Dana, 1851) were found to be sympatric in some places, and their morphological differences are minor, especially in females, the misidentification of species is not uncommon in the literature. In this study, the DNA barcoding marker, mitochondrial cytochrome c oxidase subunit I (COI), was applied to confirm species identities and this was correlated with the specific characters of males and females. Distributions of three species of Parahelice were also updated, with Par. daviei (Sakai, Türkay Yang, 2006), Par. pilimana (A. Milne-Edwards, 1873), and Par. pilosa (Sakai, Türkay Yang, 2006) being new records to Taiwan, and Par. pilosa new to Bali, Indonesia.

B Chromosomes of the Asian Seabass (Lates calcarifer) Contribute to Genome Variations at the Level of Individuals and Populations.

The Asian seabass (Lates calcarifer) is a bony fish from the Latidae family, which is widely distributed in the tropical Indo-West Pacific region. The karyotype of the Asian seabass contains 24 pairs of A chromosomes and a variable number of AT- and GC-rich B chromosomes (Bchrs or Bs). Dot-like shaped and nucleolus-associated AT-rich Bs were microdissected and sequenced earlier. Here we analyzed DNA fragments from Bs to determine their repeat and gene contents using the Asian seabass genome as a reference. Fragments of 75 genes, including an 18S rRNA gene, were found in the Bs; repeats represented 2% of the Bchr assembly. The 18S rDNA of the standard genome and Bs were similar and enriched with fragments of transposable elements. A higher nuclei DNA content in the male gonad and somatic tissue, compared to the female gonad, was demonstrated by flow cytometry. This variation in DNA content could be associated with the intra-individual variation in the number of Bs. A comparison between the copy number variation among the B-related fragments from whole genome resequencing data of Asian seabass individuals identified similar profiles between those from the South-East Asian/Philippines and Indian region but not the Australian ones. Our results suggest that Bs might cause variations in the genome among the individuals and populations of Asian seabass. A personalized copy number approach for segmental duplication detection offers a suitable tool for population-level analysis across specimens with low coverage genome sequencing.

Non-indigenous species (NIS) of polychaetes (Annelida: Polychaeta) from the Atlantic and Mediterranean coasts of the Iberian Peninsula: an annotated checklist

This study provides an updated catalogue of non-indigenous species (NIS) of polychaetes reported from the continental coasts of the Iberian Peninsula based on the available literature. A list of 23 introduced species were regarded as established and other 11 were reported as casual, with 11 established and nine casual NIS in the Atlantic coast of the studied area and 14 established species and seven casual ones in the Mediterranean side. The most frequent way of transport was shipping (ballast water or hull fouling), which according to literature likely accounted for the introductions of 14 established species and for the presence of another casual one. To a much lesser extent aquaculture (three established and two casual species) and bait importation (one established species) were also recorded, but for a large number of species the translocation pathway was unknown. About 25% of the reported NIS originated in the Warm Western Atlantic region, followed by the Tropical Indo West-Pacific region (18%) and the Warm Eastern Atlantic (12%). In the Mediterranean coast of the Iberian Peninsula, nearly all the reported NIS originated from warm or tropical regions, but less than half of the species recorded from the Atlantic side were native of these areas. The effects of these introductions in native marine fauna are largely unknown, except for one species (Ficopomatus enigmaticus) which was reported to cause serious environmental impacts. In other cases, the displacement of native species or economic damages are suspected.

Did biogeographical processes shape the monogenean community of butterflyfishes in the tropical Indo-west Pacific region?

Geographical distribution of parasite species can provide insights into the evolution and diversity of parasitic communities. Biogeography of marine parasites is poorly known, especially because it requires an understanding of host-parasite interactions, information that is rare, especially over large spatial scales. Here, we have studied the biogeographical patterns of dactylogyrid parasites of chaetodontids, one of the most well-studied fish families, in the tropical Indo-west Pacific region. Dactylogyrid parasites were collected from gills of 34 butterflyfish species (n=560) at nine localities within an approximate area of 62millionkm2. Thirteen dactylogyrid species were identified, with richness ranging from 6 to 12 species at individual localities. Most dactylogyrid communities were dominated by Haliotrema angelopterum or Haliotrema aurigae, for which relative abundance was negatively correlated (ρ=−0.59). Parasite richness and diversity were highest in French Polynesia and the Great Barrier Reef (Australia) and lowest in Palau. Three biogeographic regions were identified based on dactylogyrid dissimilarities: French Polynesia, characterised by the dominance of H. angelopterum, the western Pacific region dominated by H. aurigae, and Ningaloo Reef (Australia), dominated by Euryhaliotrema berenguelae. Structure of host assemblages was the main factor explaining the dissimilarity (turnover and nestedness components of the Bray-Curtis dissimilarity and overall Bray-Curtis dissimilarity) of parasite communities between localities, while environment was only significant in the turnover of parasite communities and overall dissimilarity. Spatial structure of localities explained only 10% of the turnover of parasite communities. The interaction of the three factors (host assemblages, environment and spatial structure), however, explained the highest amounts of variance of the dactylogyrid communities, indicating a strong colinearity between the factors. Our findings show that spatial arrangement of chaetodontid dactylogyrids in the tropical Indo-west Pacific is primarily characterised by the turnover of the main Haliotrema spp., which is mainly explained by the structure of host assemblages.

Narcine baliensis, a new species of electric ray from southeast Asia(Chondrichthyes: Torpediniformes).

A new species of numbfish, Narcine baliensis, sp. nov., is described from the tropical eastern Indian Ocean from Indonesia. It is superficially similar to N. brevilabiata and N. atzi in aspects of its color pattern, but is distinguished from both congeners in details of its color pattern, in tooth band morphology, and in proportions of its dorsal fins, among other features. Narcine baliensis, sp. nov., is unique in having a dorsal color pattern composed of large, circular, ovoid or elongate dark brown spots or blotches on dorsal disc along with more numerous small (about eye-sized or slightly greater) brownish, subcircular spots, with large blotches and small spots surrounded by a very slender creamy-white pattern, as well as in having broadly circular upper and lower tooth bands of about the same width and shape. The genus Narcine is now composed of 20 valid species, but uncertainty remains concerning the identification and morphological variation of some of its species in the tropical Indo-West Pacific region.

The genus Pirenella Gray, 1847 (= Cerithideopsilla Thiele, 1929) (Gastropoda: Potamididae) in the Indo-West Pacific region and Mediterranean Sea.

Members of the genus Pirenella are abundant inhabitants of intertidal sedimentary shores, often found in association with mangroves, on the continental margins of the western Pacific and Indian Oceans, and eastern Mediterranean Sea. Until recently, four morphological species were recognised in the tropical Indo-West Pacific region and classified in the genus Cerithideopsilla, while another species occupying the Mediterranean and Indian Ocean was classified as Pirenella conica. Molecular phylogenetic analysis has demonstrated that all these species are congeneric and here it is shown that the valid name for the genus is Pirenella. A recently published molecular study recognised a total of 16 species and the present work is a systematic account of these species. Of the 16, nine are described as new. Other significant nomenclatural acts are: fixation of type species of Pirenella as Pirenella mammillata J.E. Gray, 1847; designation of neotypes for Cerithium alatum Philippi, 1849, Cerithium microptera Kiener, 1841, Cerithium conicum Blainville, 1829, Pirenella mammillata J.E. Gray, 1847 and Murex cingulatus Gmelin, 1791; designation of lectotype for Cerithium retiferum G.B. Sowerby II, 1855. The species accounts include full synonymies, detailed descriptions of shells (based on 831 museum samples), distribution records and maps, reviews of life history, of habitat and of ecology, and some images of radulae. Details of shell sculpture are adequate for the diagnosis of most species. Distorted shells are common in some populations and are suggested to represent parasitised individuals. Some species are pests of fishponds in Southeast Asia and P. conica is the intermediate host of a trematode responsible for the human disease heterophyiasis, while others are threatened by habitat destruction.

After the gold rush: population structure of spiny lobsters in Hawaii following a fishery closure and the implications for contemporary spatial management

We compared mitochondrial genetic data for two spiny lobsters in Hawaii with different geographic ranges and histories of fishing pressure. Panulirus marginatus (Quoy and Gaimard, 1825) is endemic to Hawaii, and experienced a short, intense fishery in the Northwestern Hawaiian Islands (NWHI) and long-term, less intense exploitation in the Main Hawaiian Islands (MHI). Populations show significant overall structure (F ST = 0.0037, P = 0.007; D est_Chao = 0.137), with regional differentiation (F CT = 0.002, P = 0.047) between the MHI and the NWHI. Haplotype diversity did not differ significantly between regions (F2, 8 = 3.740, P = 0.071); however, nucleotide diversity is significantly higher at the primary NWHI fishery banks (0.030) than in the MHI (0.026, Tukey's P = 0.013). In contrast, Panulirus penicillatus (Olivier, 1791), found across the tropical Indo-West Pacific region, was not targeted by the NWHI fishery, but has experienced long-term exploitation in the MHI. Panulirus penicillatus has no significant overall population structure in Hawaii (F ST = 0.0083, P = 0.063; D est_Chao = 0.278), although regional differentiation (F CT = 0.0076, P = 0.0083) between the MHI and the NHWI is significant. Neither haplotype nor nucleotide diversity differed significantly between regions for P. penicillatus While neither species has suffered a loss of genetic diversity from fishing, our results highlight that only by incorporating knowledge of fishing history with genetic connectivity data can we understand the most beneficial management strategy for each species. Neither exemplar species nor specific suites of traits are reliable predictors of the spatial scales of management.

Additional records of the pagurid hermit crab genus Trichopagurus de Saint Laurent, 1968 (Crustacea: Decapoda: Anomura), with description of a new species from the Philippines

The pagurid hermit crab genus Trichopagurus de Saint Laurent, 1968 is currently represented by three shallow water spe- cies from the tropical Indo-West Pacific region. In this paper, three species of the genus, including one new species, are reported. Trichopagurus tenuidactylus n. sp. is described on the basis of a single ovigerous female from the Bohol Sea, the Philippines, and compared with two close relatives, T. asper Komai & Poupin, 2012 and T. macrochela Komai & Os- awa, 2005. New locality records are provided for T. macrochela (the Philippines) and T. trichophthalinus (Forest, 1954) (Taiwan and Marianas). An identification key to the four species of the genus is presented.

Revision of the Octopus horridus species-group, including erection of a new subgenus and description of two member species from the Great Barrier Reef, Australia

The tropical Indo-West Pacific region contains a distinctive group of small to moderate-sized octopuses referred to in the past as the Octopus horridus species-group. Member species are found primarily on intertidal reef flats. They possess small bodies, long arms and complex skin sculpture and body patterns enabling excellent camouflage. When attacked, these octopuses are capable of autotomising their arms at the base: the writhing severed arm acting as a decoy to predators and aiding escape. Lost arms regenerate within 2–3 months. Attributes of this group of octopuses are described and the subgenus Abdopus, subgen. nov. is here coined to define this group. Historically, many members of this subgenus have been incorrectly identified as Octopus horridus, a distinct large-egg species known only from the Red Sea and the northwest Indian Ocean. Seven species are here recognised as belonging in Abdopus, subgen. nov. Two member species from Great Barrier Reef waters (Octopus aculeatus d’Orbigny, 1834 and Octopus capricornicus, sp. nov.) are described. A number of additional, as yet undescribed, species occur throughout the Indo-West Pacific region. Certain earlier works have linked other octopus genera and species with members of this subgenus on the grounds of long arms and arm autotomy. Significant differences occur in the morphologies of these taxa and the nature of the arm autotomy processes. It is proposed that these groups have evolved independently and that arm autotomy has arisen more than once amongst the octopuses. The restriction of the subgenus Abdopus to the tropical Indo-West Pacific region suggests relatively recent origins and radiation.

Sabiaon shells: A specialized Pacific-type commensalism in the Caribbean Neogene

In the Recent biota, species of the hipponicid gastropod genusSabiathat excavate characteristic pits on the outer surfaces of shells of reef-dwelling gastropods and hermit crabs occur only in the tropical Indo-West Pacific region and in adjacent warm-temperate parts of Japan and Australia. I report the discovery ofSabiapits in reef-associated gastropod shells from the Cercado (late Miocene) and Gurabo (early Pliocene) Formations of the Dominican Republic. The likely culprit wasHipponix otiosaPilsbry and Johnson, 1917, a species here reassigned toSabiaGray, 1840. Pliocene extinction, which was far more severe in the Caribbean and elsewhere in the western Atlantic than in the Indo-West Pacific, selectively eliminatedSabiaand its commensalism from Atlantic reef ecosystems. This case is one of several examples indicating the vulnerability of specialized associations to extinction-causing disturbances.

Microhabitat Resource Use, Activity Patterns, and Episodic Catastrophe: Conus on Tropical Intertidal Reef Rock Benches

Low species richness (five to nine species) and high population density (means of 0.2—8.6 individuals per square metre) characterize Conus assemblages on intertidal benches throughout the tropical Indo—West Pacific region. Data from 16 such habitats in Hawaii, Marshall Islands, Australia, Maldives, and Seychelles indicate that similarity of microhabitats between species is equal to or greater than random expectation. Significant between—species differences in zonation pattern occur across benches at a given time and place. The peak of C. ebraeus abundance typically occurs closest to shore; C. chaldaeus and C. sponsalis are usually most distant from shore. However, we found about as man significant within—species differences between censuses made at different times on the same bench as between—species differences within censuses. Co—occurring species thus tend not to use microhabitat resources differentially. Physical environmental variables including tide level, strength of water flow and time of day determine refuging and foraging activity patterns, and all species appear to respond similarly to these factors. The data thus do not support the hypothesis of temporal resource partitioning. We found evidence neither for homing, as mark—recapture results suggested that individuals occupy any convenient refuge after foraging, nor for interference competition for protected sites among Conus. species diversity is significantly correlated with (1) substrate topographic diversity measured either independently or as the diversity of microhabitats utilized by all species together, and (2) the proportion of individuals occupying protected sites. Where refuges (potholes and crevices) comprise only 2—9% of bench surface area, an average of 63% of Conus individuals occupy them, indicating strong selection for protected microhabitats. The presence and quality of these physical refuges are less important on benches with thick mats of algal turf binding sand. The gastropods burrow in these mats during periods of stress. A catastrophic rainstorm coinciding with low tide caused high mortality in an inner bench population at Enewetak, but more C. ebraeus survived (30%) than other species (8%). Tolerance to such unpredictable physical stress may explain the observed patterns of zonation of Conus of different species and sizes across benches.