Increasing ocean temperatures allow tropical fishes to survive overwinter in temperate waters

The southeast coast of Australia is a global hotspot for increasing ocean temperatures due to climate change. The temperate incursion of the East Australian Current (EAC) is increasing, affording increased connectivity with the Great Barrier Reef. The survival of tropically sourced juveniles over the winter is a significant stumbling block to poleward range shifts of marine organisms in this region. Here we examine the dependence of overwintering on winter severity and prewinter recruitment for eight species of juvenile coral reef fishes which are carried into temperate SE Australia (30–37 °S) by the EAC during the austral summer. The probability of persistence was most strongly influenced by average winter temperature and there was no effect of recruitment strength. Long‐term (138 years) data indicate that winter water temperatures throughout this region are increasing at a rate above the global average and predictions indicate a further warming of >2 °C by the end of the century. Rising ocean temperatures are resulting in a higher frequency of winter temperatures above survival thresholds. Current warming trajectories predict 100% of winters will be survivable by at least five of the study species as far south as Sydney (34 °S) by 2080. The implications for range expansions of these and other species of coral reef fish are discussed.     

Foraging plasticity in obligate corallivorous Melon butterflyfish across three recently bleached reefs

Because obligate corallivorous butterflyfish feed exclusively on coral polyps, they are particularly sensitive to changes in coral cover and its spatial distribution. To understand how such differences in coral cover influence obligate corallivores, we examined the densities and foraging behavior of Melon butterflyfish Chaetodon trifasciatus across three reefs in the Lakshadweep archipelago. These reefs suffered differential bleaching mortality after the 2010 El Niño Southern Oscillation, resulting in wide variation in coral cover and community composition. Despite these differences, C. trifasciatus were able to persist at similar densities across reefs. However, our analysis of high‐resolution video recordings of multiple focal fish revealed that time budgets, bite rates, and diet selectivity differed significantly. Fish in resource‐poor reefs spent more time moving between coral patches and less time foraging than ones in relatively resource‐rich reefs. We also found that fish in resource‐poor reefs had higher bite rates and were less selective in their foraging. Our results provide novel insights into how obligate corallivores cope with even large differences in resource availability. At a time when we are rapidly losing corals to repeated climate‐induced bleaching events, this flexibility may represent a critical mechanism that enables persistence of obligate corallivores in resource‐poor reefs, even if it does not guarantee longer‐term survival.     

Spermatogenesis in the inseminating African butterflyfish Pantodon buchholzi (Teleostei: Osteoglossiformes: Pantodontidae) with the revision of residual bodies formation

The aim of this study was to analyse spermatogenesis in the African butterflyfish, Pantodon buchholzi, using transmission electron microscopy and scanning electron microscopy. P. buchholzi is the most basal teleost that exhibits insemination and produces a highly complex introsperm with the most elongate midpiece known in teleost fishes. Their early stages (spermatogonia and spermatocytes) do not differ greatly from those of other fishes, with the exception of Golgi apparatus degradation appearing as spindle-shaped bodies (SSBs). In round, early spermatids, the development of the flagellum begins after the migration of the centriolar complex towards the nucleus. Later, the elongation of the midpiece coincides with the displacement of the mitochondria and their fusion to produce nine mitochondrial derivatives (MDs). In these spermatids, the nucleus is situated laterally to the midpiece, with condensing chromatin in the centre of the nucleus. Within the midpiece, the flagellum is located within a cytoplasmic canal and is surrounded by a cytoplasmic sleeve containing fibres, MDs and a great amount of cytoplasm located on one side. During the next phase, nuclear rotation, the highly condensed chromatin is displaced to a position above the centriolar apparatus, whereas chromatin-free nucleoplasm is transferred to the cytoplasm. Later, this nucleoplasm, still surrounded by the nuclear membrane, is eliminated into the cyst lumen as the nucleoplasmic packet. Within the highly elongate spermatids, other excess organelles (SSBs, endoplasmic reticulum and mitochondria) are eliminated as residual bodies (RBs). Fully developed spermatozoa, which contain conical-shaped nuclei, eventually coalesce to form unencapsulated sperm packets (spermatozeugmata) that are surrounded by RBs at the level of the extremely elongate midpieces. Later, RBs are removed at the periphery of the cyst by means of phagocytosis by Sertoli cells.     

Development of DNA microsatellite markers in the multiband butterflyfish (Chaetodon multicinctus)

Twelve polymorphic microsatellite loci were developed in the multiband (pebbled) butterflyfish Chaetodon multicinctus. The loci were scored in 45 individuals from Hawaii. There were five to 21 alleles per locus with observed heterozygosity ranging from 0.419 to 0.883. Four of the primer sets also reliably amplified polymorphic loci in Chaetodon quadrimaculatus. We expect these markers to be useful for studies of genetic population structure and kinship, for example to determine whether new recruits settling onto reefs are related.     

Effects of anemonefish on giant sea anemones: expansion behavior,growth, and survival

The symbiosis between giant sea anemones and anemonefish on coral reefs is well known, but little information exists on impacts of this interaction on the sea anemone host. On a coral reef at Eilat, northern Red Sea, individuals of the sea anemone Entacmaea quadricolor that possessed endemic anemonefish Amphiprion bicinctus expanded their tentacles significantly more frequently than did those lacking anemonefish. When anemonefish were experimentally removed, sea anemone hosts contracted partially. Within 1–4 h in most cases, individuals of the butterflyfish Chaetodon fasciatus arrived and attacked the sea anemones, causing them to contract completely into reef holes. Upon the experimental return of anemonefish, the anemone hosts re-expanded. The long-term growth rate and survival of the sea anemones depended on the size and number of their anemonefish. Over several years, sea anemones possessing small or no fish exhibited negative growth (shrinkage) and eventually disappeared, while those with at least one large fish survived and grew. We conclude that host sea anemones sense the presence of symbiotic anemonefish via chemical and/or mechanical cues, and react by altering their expansion behavior. Host sea anemones that lack anemonefish large enough to defend them against predation may remain contracted in reef holes, unable to feed or expose their tentacles for photosynthesis, resulting in their shrinkage and eventual death.     

Does client size affect cleaner fish choice of client? An empirical test using client fish models

To determine whether the choice of client fishes in the cleaner fish Labroides dimidiatus was influenced by client size, cleaner fish were given a choice of equal amount of food spread on large and small client redfin butterflyfish Chaetodon trifasciatus models. All large models received bites from cleaners compared to 27% for small models. Seventy‐nine per cent of cleaners took their first bite from the large fish model. The results suggest that client size may affect cleaner fish choice.     

The laterophysic connection and swim bladder of butterflyfishes in the genus Chaetodon (Perciformes: Chaetodontidae)

The laterophysic connection (LC) is an association between bilaterally paired, anterior swim bladder extensions (horns) and medial openings in the supracleithral lateral line canals that diagnoses butterflyfishes in the genus Chaetodon. It has been hypothesized that the LC makes the lateral line system sensitive to sound pressure stimuli that are transmitted by the swim bladder horns and converted to fluid flow into the lateral line system via a laterophysic tympanum. The purpose of this study was to define variation in the morphology of the LC, swim bladder and swim bladder horns among 41 Chaetodon species from all 11 Chaetodon subgenera and a species from each of four non-Chaetodon genera using gross dissection, histological analysis as well as 2D or 3D CT (computed tomographic) imaging of live, anesthetized fishes. Our results demonstrate that the lateral line system appears rather unspecialized with well-ossified narrow canals in all species examined. Two LC types (direct and indirect), defined by whether or not the paired anterior swim bladder horns are in direct contact with a medial opening in the supracleithral lateral line canal, are found among species examined. Two variants on a direct LC and four variants of an indirect LC are defined by combinations of soft tissue anatomy (horn length [long/short] and width [wide/narrow], number of swim bladder chambers [one/two], and presence/absence of mucoid connective tissue in the medial opening in the supracleithrum). The combination of features defining each LC variant is predicted to have functional consequences for the bioacoustics of the system. These findings are consistent with the recent discovery that Chaetodon produce sounds during social interactions. The data presented here provide the comparative morphological context for the functional analysis of this novel swim bladder-lateral line connection.     

Long-term monitoring of the coral reef fish communities around a nuclear power plant

Over the past 21 years (1979–1999) we have observed temporal changes in the fish communities on a coral reef around a nuclear power plant in southern Taiwan. Data used for analyses were collected bimonthly by scuba-diving ichthyologists at four sub-tidal stations (Stations A, B, D, E). The commercial operation of the nuclear power plant was launched in the summer of 1984. During the study period the number of fish species varies, with the coefficient of variation (CV) ranging from 19.0% (Station A) to 25.2% (Station D). Nevertheless, the sequential data on number of species follow a random trend in terms of runs up and down at all four stations. This characteristic persists both before and after the initiation of power plant operation. Dendrograms drawn using UPGMA (unweighted pair-group method using arithmetic averages) on the dissimilarity coefficients between yearly fish occurrences show that the years 1980–1984 are more closely grouped than any other years. This phenomenon prevails at all stations, indicating that wide-scale change occurred between 1984 and 1985. After the power plant began operation, changes in water temperature were minute at these sub-tidal stations. Impacts from other sources such as chlorine release and fish impingement seem remote. We believe temporal variations in the studied fish communities can be better explained as arising from natural fluctuations of environmental factors as well as physical disturbance caused by typhoons. The latter factor is also thought to account for the major faunal change between 1984 and 1985.