Laetitia Plaisance

The Diversity of Coral Reefs: What Are We Missing?

Tropical reefs shelter one quarter to one third of all marine species but one third of the coral species that construct reefs are now at risk of extinction. Because traditional methods for assessing reef diversity are extremely time consuming, taxonomic expertise for many groups is lacking, and marine organisms are thought to be less vulnerable to extinction, most discussions of reef conservation focus on maintenance of ecosystem services rather than biodiversity loss. In this study involving the three major oceans with reef growth, we provide new biodiversity estimates based on quantitative sampling and DNA barcoding. We focus on crustaceans, which are the second most diverse group of marine metazoans. We show exceptionally high numbers of crustacean species associated with coral reefs relative to sampling effort (525 species from a combined, globally distributed sample area of 6.3 m2). The high prevalence of rare species (38% encountered only once), the low level of spatial overlap (81% found in only one locality) and the biogeographic patterns of diversity detected (Indo-West Pacific>Central Pacific>Caribbean) are consistent with results from traditional survey methods, making this approach a reliable and efficient method for assessing and monitoring biodiversity. The finding of such large numbers of species in a small total area suggests that coral reef diversity is seriously under-detected using traditional survey methods, and by implication, underestimated.

Commonness and rarity in the marine biosphere

Significance Tests of biodiversity theory have been controversial partly because alternative formulations of the same theory seemingly yield different conclusions. This has been a particular challenge for neutral theory, which has dominated tests of biodiversity theory over the last decade. Neutral theory attributes differences in species abundances to chance variation in individuals’ fates, rather than differences in species traits. By identifying common features of different neutral models, we conduct a uniquely robust test of neutral theory across a global dataset of marine assemblages. Consistently, abundances vary more among species than neutral theory predicts, challenging the hypothesis that community dynamics are approximately neutral, and implicating species differences as a key driver of community structure in nature. Explaining patterns of commonness and rarity is fundamental for understanding and managing biodiversity. Consequently, a key test of biodiversity theory has been how well ecological models reproduce empirical distributions of species abundances. However, ecological models with very different assumptions can predict similar species abundance distributions, whereas models with similar assumptions may generate very different predictions. This complicates inferring processes driving community structure from model fits to data. Here, we use an approximation that captures common features of “neutral” biodiversity models—which assume ecological equivalence of species—to test whether neutrality is consistent with patterns of commonness and rarity in the marine biosphere. We do this by analyzing 1,185 species abundance distributions from 14 marine ecosystems ranging from intertidal habitats to abyssal depths, and from the tropics to polar regions. Neutrality performs substantially worse than a classical nonneutral alternative: empirical data consistently show greater heterogeneity of species abundances than expected under neutrality. Poor performance of neutral theory is driven by its consistent inability to capture the dominance of the communities’ most-abundant species. Previous tests showing poor performance of a neutral model for a particular system often have been followed by controversy about whether an alternative formulation of neutral theory could explain the data after all. However, our approach focuses on common features of neutral models, revealing discrepancies with a broad range of empirical abundance distributions. These findings highlight the need for biodiversity theory in which ecological differences among species, such as niche differences and demographic trade-offs, play a central role.

Phylogenetic relationships of the Dactylogyridae Bychowsky, 1933 (Monogenea: Dactylogyridea): the need for the systematic revision of the Ancyrocephalinae Bychowsky, 1937

Phylogenetic analyses based on partial 18S rDNA sequences of polyonchoinean monogeneans were conducted in order to investigate the relationships between selected families and subfamilies of the Dactylogyrinea, mainly within the Dactylogyridae. We tested the status of the Ancyrocephalidae sensu Bychowsky & Nagibina (1978) and the Ancyrocephalinae sensu Kritsky & Boeger (1989). Within the Dactylogyrinea, the Diplectanidae and Dactylogyridae are well supported by maximum likelihood and maximum parsimony analyses, but their phylogenetic relationship with the Pseudomurraytrematidae remains unresolved. Phylogenetic relationships between the Pseudodactylogyrinae, Ancyrocephalinae, Ancylodiscoidinae and Dactylogyrinae indicate paraphyly of the Ancyrocephalidae sensu Bychowsky & Nagibina (1978). The group of species recently considered as the Dactylogyridae sensu Kritsky & Boeger (1989) comprises two sister groups. The first group includes the freshwater Ancyrocephalinae and the Ancylodiscoidinae. The second group includes the Pseudodactylogyrinae, Dactylogyrinae and the Ancyrocephalinae from the fish species Siganus doliatus and Tetraodon fluviatilis. The non-monophyly of the Ancyrocephalinae (i.e. the non-monophyly of the group of species recently considered as members of Ancyrocephalinae), previously suggested by Kritsky & Boeger (1989) using the morphological characters, indicates that classification of the Dactylogyridae needs to be revised.

Investigating patterns may reveal processes: evolutionary ecology of ectoparasitic monogeneans.

We reviewed several published and ongoing studies concerning monogenean communities. Patterns of species richness, host specificity, community structure and host--parasite coevolutionary interaction were carefully analysed, and hypotheses of evolutionary processes are proposed. The structuring of monogenean communities seems to be related to both ecological and historical constraints. The database supports an absence of intra- and interspecific competition in monogeneans. Species richness seems to be more due to host characteristics than to parasite interactions. Monogeneans seem to specialise on large hosts, leading to greater species richness on those hosts. The morphometric evolution of attachment and copulatory organs support the hypothesis of a reproductive segregation among conspecifics parasitising the same host(s). It also suggests the existence of concurrent adaptive and non-adaptive processes. The general absence of a coevolutionary pattern between host and parasites also suggests the constraints of history without dismissing the influences of ecological factors in the structuring of the communities. More generally, we strengthen the need to study the structure of communities in a phylogenetic context.

Molecular phylogeny of gill monogeneans (Platyhelminthes, Monogenea, Dactylogyridae) and colonization of Indo-West Pacific butterflyfish hosts (Perciformes, Chaetodontidae)

We investigated the phylogenetic relationships among monogenean parasites of the Chaetodontidae (butterflyfishes) from the Indo‐West Pacific Ocean. Molecular phylogenies of selected taxa within the Dactylogyridae, including the ancyrocephaline parasites of butterflyfishes, based on two nuclear and one mitochondrial gene fragments (complete 18S rDNA, partial 28S rDNA (D1‐D3), and partial 16S rDNA) were reconstructed using parsimony, maximum likelihood and Bayesian inference methods. Our results show the non‐monophyletic nature of the monogenean fauna of butterflyfishes. The group is divided into two independent lineages. The first clade contains species of the genera Aliatrema and Euryhaliotrematoides, which parasitize Chaetodontidae exclusively. The second contains species of Haliotrema, a generalist group of parasites. The positions of several other species of the Ancyrocephalinae, including freshwater species, at the base of the two clades, provide strong evidence that the monogenean fauna did not result from a single colonization event, but rather that they have colonized their butterflyfish hosts independently at least twice.

Description and redescription of Haliotrema species (Monogenoidea: Poloyonchoinea: Dactylogyridae) parasitizing butterfly fishes (Teleostei: Chaetodontidae) in the Indo-West Pacific Ocean

Haliotrema species are described and/or reported from the gills of butterfly fishes (Chaetodontidae) from coral reefs of the Indo-West Pacific islands: Moorea (French Polynesia), Palau (Micronesia), Wallis (Wallis and Futuna), New Caledonia, Lizard Island and Heron Island (Great Barrier Reef, Australia). Haliotrema angelopterum sp. nov., a new species of Monogenoidea parasite from seven species of Chaetodon Linnaeus, 1758 (Chaetodontidae), is described. A new redescription and statute are given for Haliotrema aurigae (Yamaguti, 1968) comb. nov., a parasite from ten species of Chaetodon and one species of Heniochus Cuvier, 1816 (Chaetodontidae). New records of Haliotrema scyphovagina Yamaguti, 1968 are reported from two localities and from several host species belonging to the genera Chaetodon and Forcipiger Jordan and McGregor, 1898 (Chaetodontidae).

Gyrodactylus salaris (Monogenea, Gyrodactylidae) infections on resident Arctic charr (Salvelinus alpinus) in southern Norway

This study surveys the distribution of Gyrodactylus salaris on resident Arctic charr, Salvelinus alpinus, in lakes connected to three south-Norwegian watercourses: Numedalsvassdraget, Skiensvassdraget and Hallingdalsvassdraget. Gyrodactylus salaris infected charr was only recorded in Numedalsvassdraget. The parasites had the same mitochondrial haplotype as those previously reported on charr in Lake Pålsbufjorden, which is part of Numedalsvassdraget. Since the G. salaris-charr association is persistent in Pålsbufjorden and has a wide distribution above the stretches of the watercourse inhabited by anadromous salmonids, this is considered a stable, although perhaps relatively young, host-parasite system. More detailed analyses of these interactions revealed seasonal variations in the parasite population dynamics between late summer and late autumn, with heavier infections occurring in males and older fish in October. This is explained by the combined action of seasonal differences in temperature and physiology and ecology of host cohorts. It is assumed that the occurrence of G. salaris on charr in Pålsbufjorden resulted from a host switch to charr from rainbow trout, Onchorynchus mykiss. Host switches may cause significant expansions of the geographical range of pathogenic variants of G. salaris. Therefore, observations of frequently occurring G. salaris on charr have implications for the diagnosis, management and control of salmonid gyrodactylosis.

Deep COI sequencing of standardized benthic samples unveils overlooked diversity of Jordanian coral reefs in the northern Red Sea.

High-throughput sequencing (HTS) of DNA barcodes (metabarcoding), particularly when combined with standardized sampling protocols, is one of the most promising approaches for censusing overlooked cryptic invertebrate communities. We present biodiversity estimates based on sequencing of the cytochrome c oxidase subunit 1 (COI) gene for coral reefs of the Gulf of Aqaba, a semi-enclosed system in the northern Red Sea. Samples were obtained from standardized sampling devices (Autonomous Reef Monitoring Structures (ARMS)) deployed for 18 months. DNA barcoding of non-sessile specimens >2 mm revealed 83 OTUs in six phyla, of which only 25% matched a reference sequence in public databases. Metabarcoding of the 2 mm - 500 μm and sessile bulk fractions revealed 1197 OTUs in 15 animal phyla, of which only 4.9% matched reference barcodes. These results highlight the scarcity of COI data for cryptobenthic organisms of the Red Sea. Compared with data obtained using similar methods, our results suggest that Gulf of Aqaba reefs are less diverse than two Pacific coral reefs but much more diverse than an Atlantic oyster reef at a similar latitude. The standardized approaches used here show promise for establishing baseline data on biodiversity, monitoring the impacts of environmental change, and quantifying patterns of diversity at regional and global scales.

Mitochondrial DNA variation of a natural population of Gyrodactylus thymalli (Monogenea) from the type locality River Hnilec, Slovakia

The monogenean flatworm Gyrodactylus thymalli (Žitňan, Helminthologia, 2:266–269, 1960) is considered a harmless ectoparasite on grayling (Thymallus thymallus). The species is closely related to G. salaris Malmberg, 1957 that causes severe gyrodactylosis on Atlantic salmon (Salmo salar) in many Norwegian rivers. In this paper, we study the mitochondrial diversity of a G. thymalli population from one of the type localities Hrable on River Hnilec, Slovakia. By sequencing parts of the mitochondrial NADH dehydrogenase subunit 5 gene, we detected three haplotypes that differ from each other by 2.1–4.1%. The haplotype HnilecI was found most common. Our data suggest that River Hnilec has been colonized independently at least three times with G. thymalli.