The recent colonization of south Brazil by the Azores chromis Chromis limbata

The damselfish Chromis limbata is native to the Macaronesian Archipelagos (Azores, Madeira and Canaries) and the western coast of Africa between Senegal and Angola. During the austral summers of 2008 and 2009 the species was recorded for the first time in the south‐western Atlantic Ocean around Campeche and Xavier Islands, in Florianópolis, Santa Catarina State, Brazil. Here, the progression of C. limbata in southern Brazilian waters is described using visual counts and genetic surveys and changes in the density of the native congener Chromis multilineata were also investigated. Underwater visual censuses of both Chromis species were carried out from 2009 to 2014. Chromis limbata tissue samples were collected and the mtDNA control region was sequenced and compared with mtDNA haplotypes from the natural range to confirm species identity, compare genetic diversity and to infer connectivity between newly established Brazilian populations. The Brazilian population of C. limbata increased significantly over the past 5 years and the effect on C. multilineata is still an open question, longer time‐series data will be necessary to clarify possible interactions. The molecular analyses confirmed species identity, revealed strong haplotype connectivity among Brazilian study sites and showed a low genetic diversity in Brazil when compared with the native populations, suggesting few individuals started the invasion. Four hypotheses could explain this colonizing event: C. limbata was released by aquarium fish keepers; larvae or juveniles were transported via ship ballast water; the species has rafted alongside oil rigs; they crossed the Atlantic Ocean through normal larval dispersal or naturally rafting alongside drifting objects. The rafting hypotheses are favoured, but all four possibilities are plausible and could have happened in combination.     

Siliciclastic‐carbonate ramp,a hostile world for carbonate shelf fauna? The example of the Givetian Ardenne Platform

The Givetian platform of the Ardennes Massif records several alternations between a siliciclastic‐carbonate ramp and a carbonate shelf. Usually these depositional contexts are considered as a major disruption implying a perturbation of many ecological parameters. We established the impact of these variations on the biodiversity structure through the study of the trophic organisation. Thanks to a previous microfacies analysis, 550 levels of the Mont d'Haurs section in Givet and ten associated environments were precisely defined. Seven palaeotrophic levels are recognized from micropalaeontological data, including benthic, planktonic, heterotroph and autotroph organisms. The spatial and temporal distributions of these levels have been analysed through means of multivariate analyses. The statistic results show that the distribution of the palaeotrophic levels during periods characterized by a mixed ramp is not significantly different than during carbonate shelf influences. These environmental modifications do not affect the community‐type. These results support recent studies performed on different benthic communities occurring in the Givetian of the Ardennes Massif. Indeed, trilobite and ostracod faunas of this period appear more affected by global environmental changes as the Ka?ák (uppermost Eifelian) and Taghanic (late middle Givetian) events. Moreover, along the proximal‐distal transect on the platform, the reef constitutes the most singular environment. However, contrary with the Frasnian reefs of the Ardennes Massif, which consist of carbonate mud mounds laying on a deep mixed ramp, there is no trilobite community that appears restricted to Givetian reefs. Thus global bioevents during the Middle Devonian have a more important control on the biodiversity than the platform morphology. These results support the view that at wide scales (spatial and temporal), the biodiversity responds more positively to ecological disturbances.     

青岛崂山湾人工鱼礁区底层游泳动物群落结构特征

基于2015年5月至2016年1月在青岛崂山湾人工鱼礁区的调查数据, 采用Margalef种类丰富度指数(d)、Shannon-Wiener多样性指数(H')、Pielou均匀度指数(J)、丰度/生物量曲线、等级聚类分析、SIMPER相似性百分比分析和非度量多维尺度排序(NMDS)分析, 对底层游泳动物群落结构和多样性进行研究。调查期间共捕获游泳动物61种, 隶属34科, 其中鱼类36种, 甲壳类22种, 头足类3种。优势种为日本蟳(Charybdis japonica)、许氏平鲉(Sebastes schlegelii)、大泷六线鱼(Hexagrammus otakii)、斑头鱼(H. agrammus)和星康吉鳗(Conger myriaster), 其中日本蟳(26.91%)和许氏平鲉(26.74%)的生物量占绝对优势。礁区游泳动物的渔获量和渔获种类数均多于对照区, 月平均单位捕捞努力量渔获量(CPUE)最高值出现在5月, 达到735.74 ± 316.59 g·net^-1·d^-1。游泳动物群落组成的特征值上, 7、8月的多样性指数较高, 但鱼礁区和对照区无显著差异(P>0.05)。丰度/生物量曲线表明, 5、6月游泳动物群落处于严重受干扰状态, 11月和次年1月群落处于相对稳定状态。聚类分析表明, 除1月外, 各月份不同区域的样方相似性都较高, 5、6月三亩前礁区的相似性最高, 达到86.21%。     

Coral reef crisis in deep and shallow reefs: 30 years of constancy and change in reefs of Curacao and Bonaire

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zooxanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non-agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environment with extremely low temperatures possibly related to deep-reef bleaching. An erratum to this article can be found at     

Benthic cyanobacterial bloom impacts the reefs of South Florida (Broward County, USA)

Benthic cyanobacteria of the genus Lyngbya can form prominent mats and blooms in tropical and subtropical coral reef and seagrass habitats worldwide. A Lyngbya bloom on the reef tract offshore of Broward County, Florida, was first noted in 2002, and although it is seasonally variable in its distribution and abundance, it has persisted and spread over the past 3 years. In this study, the most abundant species of Lyngbya found in the blooms have been identified and compared to other species of Lyngbya by morphological and molecular methods. The most common species of Lyngbya is consistent with the properties of Lyngbya confervoides C. Agardh. The 16S ribosomal DNA sequence shares 88–92% identity with other known Lyngbya sequences, suggesting that this bloom consists primarily of a new, previously unsequenced species of Lyngbya. The second most common Lyngbya in the bloom is consistent with Lyngbya polychroa. This persistent bloom is a concern because it smothers octocorals and other invertebrates and negatively impacts these southeastern Florida reefs.     

Size-spectra as indicators of the effects of fishing on coral reef fish assemblages

The data requirements and resources needed to develop multispecies indicators of fishing impacts are often lacking and this is particularly true for coral reef fisheries. Size-spectra, relationships between abundance and body-size class, regardless of taxonomy, can be calculated from simple sizeabundance data. Both the slope and the mid-point height of the relationship can be compared at different fishing intensities. Here, we develop size-spectra for reef fish assemblages using body size- abundance data collected by underwater visual census in each of ten fishing grounds across a known gradient of fishing intensity in the Kadavu Island group, Fiji. Slopes of the size-spectra became steeper (F_9,69=3.20, p<0.01) and the height declined (F_9,69=15.78, p<0.001) with increasing fishing intensity. Regressions of numbers of individuals per size class across grounds were negative for all size classes, although the slope was almost zero for the smallest size class. Response to exploitation of each size class category was greatest for larger fish. Steepening of the slope with increasing fishing intensity largely resulted from reductions in the relative abundance of large fish and not from the ecological release of small fish following depletion of their predators. The slope and height of the size-spectrum appear to be good indicators of fishing effects on reef fish assemblages.     

Resilience of predators to fishing pressure on coral patch reefs

Numbers and biomass of piscivorous fish and their predation on other fish may often be high in undisturbed coral reef communities. The effects of such predation have sometimes been studied by removal of piscivores (either experimentally or by fishermen). Such perturbations have usually involved removal of large, highly vulnerable, mobile piscivores that are often actively sought in fisheries. The effects of fishing on smaller, demersal, semi-resident piscivores have been little studied. We studied such effects on the fish communities of patch reefs at Midway atoll by experimentally removing major resident, demersal, piscivorous fishes. First, four control reefs and four experimental reefs were selected, their dimensions and habitats mapped, and their visible fish communities censused repeatedly over 1 year. Census of all control and experimental reefs was continued for the following 39 months, during which known piscivores were collected repeatedly by hand spearing. Records were kept of catch and effort to calculate CPUE as an index of predator density. Spearfishing on the experimental reefs removed 2504 piscivorous fish from 12 families and 43 taxa (mostly species). The species richness of the catch did not show an overall change over the duration of the experiment. Spearman rank correlation analysis showed some unexpected positive correlations for density in numbers and biomass of major fished piscivorous groups (especially lizardfish) over the experiment. Only two relatively minor fished piscivorous taxa declined in abundance over the experiment, while the overall abundance of piscivores increased. Visual censuses of fish on the experimental reefs also failed to show reduction of total piscivores over the full experimental period. No significant trend in the abundance of lizardfish censused over the full period was apparent on any of the control reefs. The high resilience of piscivores on these experimental reefs to relatively intense fishing pressure could result from their protracted recruitment seasons, high immigration rates, cryptic habits, or naturally high abundances. A major factor was the high immigration rates of lizardfish, replacing lizardfish and other less mobile piscivores removed from the reefs by spearing. On the fished reefs, the removed lizardfish population replaced itself >20 times during the experiment; other piscivorous taxa replaced themselves only 5 times.     

Reef fish assemblage structure affected by small-scale spacing and size variations of artificial patch reefs

To examine how varying the distance between patch reefs affects reef fish assemblage structure, replicate concrete reef modules (∼ 1 m³ each) were deployed on sand bottom at 8 m depth off Ft. Lauderdale, Florida, USA (26°07N, 80°05W). Modules were positioned at the apices of one of four differently sized equilateral triangles. Triangular configurations had side lengths of: 25 m, 15 m, 5 m, and 0.33 m; each treatment with two replicates. Two additional configurations: (1) a solitary module (Single) and (2) two modules side by side (Double), also with two replicates, were deployed in order to examine the interaction of reef size with fish assemblages. SCUBA divers censused fishes monthly, for 2 years, recording the species present, their abundance and sizes (TL). Fishes were assigned to one of five length categories: < 2 cm, > 2-5 cm, > 5-10 cm, > 10-20 cm, and > 20 cm. In general and excluding the smallest three-module spacing treatment (0.33 m treatment), which may have provided unique treatment-specific refuge, total fish abundance and richness were shown to increase when isolation distance increased. However, there were also species-specific and size class differences in response to isolation distance. The second part of this study indicated varying reef size, by doubling and tripling the number of reef modules, increased total fish abundance and species richness. Nevertheless, fish abundance and species richness did not change by an identical multiplier (e.g., doubling modules ≠ double abundance). These results suggest that scientists and marine managers alike should consider reef size and isolation as habitat attributes capable of altering the structure and dynamics of reef fish assemblages.     

Effects of territorial damselfish on cryptic bioeroding organisms on dead Acropora formosa

Many damselfishes exclude other grazers from their territories and “farm” filamentous algae within their territories. In this study the indirect effect of damselfish territories on faunal composition and abundance of internal bioeroders of dead Acropora formosa (Dana, 1846) was investigated in territories of two damselfish species, Stegastes nigricans (Lacepède, 1802) and Plectroglyphidodon lacrymatus (Quoy and Gaimard, 1825). S. nigricans tends to be more protective and defend their territories more aggressively than P. lacrymatus. Newly killed branches of A. formosa were placed inside and outside damselfish territories, for 1 or 2 years, at a coral reef near Zanzibar, Tanzania. As predicted, the coral branches became covered with more filamentous algae in the S. nigricans territories than in the controls, with intermediate levels in the P. lacrymatus territories. Among the internal bioeroding fauna, polychaetes were by far the most common group. In total, there were significantly more borers in the first year than the second, which was mainly due to a high abundance of sabellids. Furthermore, sabellids were significantly more abundant in control areas and in the P. lacrymatus territories compared to the S. nigricans territories. However, many other genera showed the opposite pattern, with more polychaetes in the fish territories compared to the controls. There was also a clear difference in assemblage structure between S. nigricans territories and controls. Thus, we found strong effects of whether a piece of coral was placed inside or outside a damselfish territory on the abundance of many of the bioeroding taxa. We discuss multiple reasons for these indirect effects of the territories, including that deposit feeding bioeroders may benefit from the dense algal turf found inside the territories whereas suspension feeding bioeroders may benefit from substrate with less filamentous algae found outside territories. Considering our results in the context of the large areas of coral reefs that typically are defended as territories by damselfishes, these fish are likely to have a considerable impact on the boring community of a coral reef.     

Spatial structure of coral reef fish communities at Kudaka Island (Ryukyu Archipelago), Japan

The present study aimed to investigate the spatial structure of fish communities at juvenile and adult stages on coral reefs at Kudaka Island (Ryukyu Archipelago, Japan) and to relate spatial patterns in the structure of the fish communities to gradients in environmental variables. Diurnal visual censuses allowed us to record 2,602 juveniles belonging to 60 species and 1,543 adults belonging to 53 species from October to December 2005. The distribution of species highlighted that the juvenile community was organised into three distinct assemblages, rather than exhibiting gradual change in community structure along the cross-reef gradient. Correlations between spatial patterns of juvenile community and environmental variables revealed that the most significant factors explaining variation in community structure were coral rubble and coral slab. In contrast, the adult community was organised into one assemblage, and the most significant variation factors in community structure were depth, live coral in massive form, live coral in branched form, dead coral and sand. Overall, the present study showed that most juvenile and adult coral reef fish at Kudaka Island exhibited striking patterns in their distribution and depth and some biological factors (e.g., abundance of live coral, dead coral and coral rubble) might exert considerable influence on the distribution of fishes.