Stable isotopes in fish otoliths discriminate between lagoonal and oceanic residents of Taiaro Atoll (Tuamotu Archipelago, French Polynesia)

 The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures, suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work to determine which individuals and species complete their life-cycles in this unusual lagoon. Accepted: 28 August 1997     

Feasible mechanisms for algal digestion in the king angelfish

To determine the ability of the king angelfish Holacanthus passer to digest algae, three algal species were immersed in acidic conditions similar to that found in the stomach of fish. Only one of them was not susceptible to acidic lysis; two were affected after 40 and 60 min at pH 2·0. King angelfish have an expanded region of the intestine called here the hindgut chamber (HC) containing populations of micro-organisms. Some of these micro-organisms have the capacity to grow in cellulose, agar, and alginic acid; the main components of algal cell walls. Micro-organisms grew in carboxymethylcellulose cultures under aerobic and micro-aerobic conditions. The HC is highly vascularized, which could increase absorptive efficiency of material digested in it.     

Mass Coral Reef Bleaching: A Recent Outcome of Increased El Niño Activity?

Coral reefs are generally considered to be the most biologically productive of all marine ecosystems, but in recent times these vulnerable aquatic resources have been subject to unusual degradation. The general decline in reefs has been greatly accelerated by mass bleaching in which corals whiten en masse and often fail to recover. Empirical evidence indicates a coral reef bleaching cycle in which major bleaching episodes are synchronized with El Niño events that occur every 3–4 years on average. By heating vast areas of the Pacific Ocean, and affecting the Indian and Atlantic Oceans as well, El Niño causes widespread damage to reefs largely because corals are very sensitive to temperature changes. However, mass bleaching events were rarely observed before the 1970s and their abrupt appearance two decades ago remains an enigma. Here we propose a new explanation for the sudden occurrence of mass bleaching and show that it may be a response to the relative increase in El Niño experienced over the last two decades.     

PHOTOACCLIMATION IN THE TROPICAL CORALLINE ALGA HYDROLITHON ONKODES (RHODOPHYTA, CORALLINACEAE) FROM A FRENCH POLYNESIAN REEF

Pigment concentration, in vivo absorption, and photosynthetic parameters of the coralline alga Hydrolithon onkodes (Heydrich) Penrose and Woelkerling were compared among samples from a lagoon and from a reef crest of Tahiti Island. Four groups of specimens were considered, differing in their natural exposure to PAR. For specimens collected from the lagoon, the tissues from low-light samples had significantly higher pigment concentration, particularly chl a and phycobilins, compared with the high-light exposed plants that contained more total carotenoids. The in vivo absorption spectra normalized to chl a (called a* values) also revealed differences. The low-light samples had a reduced absorption capacity and a well-marked phycobilin absorption signature, whereas sunlit samples showed a greater absorption at wavelengths absorbed mainly by chl a and carotenoids. The decrease of a* when pigment concentration increased is interpreted as a consequence of the pigment packaging. Significantly lower α (chlorophyll basis) and higher E_k values were found in the shaded plants. The values of P _max for the four groups of specimens were not significantly different. The samples showed various degrees of photoinhibition depending on the light exposure during growth, and this effect was more pronounced in the shaded plants. The specimens from the reef crest deviate from the general model presented for the lagoon samples and show a mix of sun- and shade-exposed characteristics. We have shown that the coralline alga H. onkodes responds to its light environment, probably by acclimation rather than ecotypic genetic variation, by adjusting its physiology, but some morphological differences are also involved. Photoacclimation can explain partly the wide distribution of this species over the reef ecosystem and its major contribution to the building of the reef.     

The goatfish Pseudupeneus maculatus and its follower fishes at an oceanic island in the tropical west Atlantic

The influence of a substratum-disturbing forager, the spotted goatfish Pseudupeneus maculatus on the assemblage of its escorting, opportunistic-feeding fishes was examined at Fernando de Noronha Archipelago (tropical west Atlantic). Followers attracted to spotted goatfish foraging singly differed from followers of spotted goatfish foraging in groups in several characteristics. The larger the nuclear fish group, the greater the species richness and number of individuals of followers. Moreover, groups of foraging spotted goatfish attracted herbivores, not recorded for spotted goatfish foraging singly. The size of follower individuals increased with the size and the number of foraging spotted goatfish. The zoobenthivorous habits of the spotted goatfish and its ability to disturb a variety of soft substrata render it an important nuclear fish for several follower species of the reef fish assemblage at Fernando de Noronha.     

湖南邵东中泥盆统棋梓桥组层孔虫生物群及其生态环境

湖南中部泥盆纪地层和生物礁相当发育。湖南邵东中泥盆世棋梓桥期的泥质石灰岩中层孔虫广泛分布,本文共描述邵东廉桥马鞍山棋梓桥期层孔虫12属18种,其中Stromatopora wenshanensis为一新名,代替1982年根据一个云南标本定名为Stromatopora irregularis的种名。 马鞍山礁是—发育在海底平台上的厚度稍有变化的层状礁,马鞍山礁的沉积相变化过程,是由近岸浅海到展状礁普遍发育的开阔台地,再到封闭或半封闭的泻湖或潮坪环境。生物组合和沉积物也随沉积环境的变化而发生相应的变化。     

Habitat selection and subsequent reproductive success in the beaugregory damselfish

Synopsis Male beaugregory damselfish,Stegastes leucostictus, were provided with three types of artificial breeding structures to determine if they change habitats based on past or future reproductive payoffs. All three site types quickly lured males away from their natural sites. In comparison to those living on natural sites, those using artificial sites were less likely to move to different areas and had a higher reproductive success. When given no choice, male reproductive success was correlated to structural type. A second experiment provided males with an additional structure after using the intermediate quality type for 2 months. Males would often initially use both sites but would eventually shift their spawning activity to the new site if it was of the same quality or better than the old one. However, males would not move if the new site was of inferior quality. When given a new site identical to the initial one, approximately half of the males shifted to the new site. There was no evidence that reproductive performance influenced a male's decision to use a new site.     

Termination of parental care due to small clutch size in the temperate damselfish,Chromis notata

Synopsis Reproductive behavior of the temperate damselfish, Chromis notata, was investigated on the island of Mukaishima, Japan, almost daily during the breeding season in 1982. Both males and females repeated reproductive cycles many times during the breeding season. Females had a strong tendency to spawn a whole clutch on one nest during a few hours. The average number of eggs which a male gained per reproductive cycle was estimated at 38560 (480–131100 eggs). Males ordinarily cared for eggs until just prior to hatching, but abandoned more than half of the nests with the eggs numbering less than 11568. Contribution 207 from the Mukaishima Marine Biological Station.     

Sexual differentiation,gonad development,and spawning seasonality of the Hawaiian butterflyfish,Chaetodon multicinctus

Synopsis The reproductive biology of the coral reef butterflyfish,Chaetodon multicinctus, was investigated by histological examination of gonads sampled over an 18 month period from a shallow inshore population on Oahu, Hawaii. Most gonads developed directly from previously undifferentiated tissue. Ovarian development (the structural formation of lamellae and primary oocytes) was observed in fish ≥44 mm and testicular development (the formation of spermatogenic crypts) in fish ≥62 mm standard length (SL). In addition, testis formation was identified within the ovarian lamellae of several differentiated but immature fish. It is hypothesized that prematurational sex change may facilitate monogamy within the highly competitive social structure of this site attached species. Oocyte development in mature females was marked by distinct phases of primary growth, the formation of yolk vesicles, and vitellogenesis. Spawning activity was histologically identified by the maturation and hydration of fully yolked oocytes, and presence of postovulatory follicles. Recently spawned females from field collections and experimental gonadotropin-treatments exhibited postovulatory follicles that were estimated to persist at least 24 h after ovulation. Atresia of yolked oocytes was classified into four stages of cell degeneration and resorption. Monthly analyses of oocyte development and atresia within the sample population show thatC. multicinctus has a protracted annual spawning season with a major peak during the early spring and evidence of spawning activity among some individuals in the fall. Histological analyses of spawning activity provide more accurate and unambiguous information than do traditional gonadosomatic assays in this and probably other coral reef fishes.     

Improving multispecies rocky reef fish censuses by counting different groups of species using different procedures

Synopsis A number of factors can influence the accuracy and precision of underwater visual transect techniques. Among these are observer swimming speed and, during multispecies surveys, the effect of counting all fishes on estimates of particular species. This paper examines the effect of these factors on population estimates of inconspicuous fishes (defined as Type 1) in a temperate reef fish assemblage near Sydney, Australia. Counting Type 1 fishes with all others yielded significantly lower estimates of species richness and abundance than when counted alone. This suggests that multispecies surveys should be split into 2 or more counts, using a census procedure that is appropriate to the group of species cencused. Further, the effect of counting all other fishes on estimates of Type 1 fishes varied according to the relative abundance of the former: their effect was lowest when abundance of other fishes was lowest. There was a negative relationship between observer speed and estimated abundance for Type 1 fishes. Survey precision of Type 1 fishes was generally improved by surveying at slower observer speeds.