Fabián H. Acuña

Importance of Nematocysts in Taxonomy of Acontiarian Sea Anemones (Cnidaria, Actiniaria): A Statistical Comparative Study

Abstract Many papers describe the cnidae from acontiarian sea anemone species, but comparative studies involving significant data amounts, combined with adequate statistical treatment have not been realized. The aim of the present paper is to carry out a comparative study of acontian cnidae from the species Haliplanella lineata (Verrill, 1869), Tricnidactis errans Pires, 1988 (Haliplanellidae) and Anthothoe chilensis (Lesson, 1830) (Sagartiidae). Five living specimens of each species were used; the length of 50 unfired capsules was measured and taken randomly from the following nematocyst categories: b-rhabdoids, p-rhabdoids B1b, p-rhabdoids B2a. A total of 2,000 measurements was done. The data were analyzed with descriptive statistics (mean, standard deviation, median, maximum, minimum, and semiinterquartile range) and Shapiro-Wilks test, Box-Cox transformation, Kruskal-Wallis test and single factor ANOVA. The normal distribution of the dataset must be tested for each nematocyst type in any quantitative study of the cnidae. We conclude that variation in nematocyst size should not be used as an element of conclusive value in the diagnosis of species of acontiarian sea anemones. For these purposes, other characters have to be used to define precisely each taxon, including qualitative variation of the cnidae.

Hydroid populations from sublittoral outcrops off Mar Del Plata, Argentina: Abundance, seasonality and reproductive periodicity

Abstract An analysis is given of the frequency, abundance, seasonality, and reproductive periods of hydroids from sublittoral rocky outcrops in coastal waters off Mar del Plata, Argentina. A total of 13 hydroid species belonging to 8 families were found, 12 of them referable to the subclass Leptothecatae. Species were grouped into three categories based on their occurrence and frequency during the year. Amphisbetia operculata, Sertularella mediterranea and Plumularia setacea were the most abundant hydropolyps in the study area. They occur as distinct clumps in patches having a contagious distribution, although the exact patterns vary considerably. Colonies of A. operculata were observed throughout the year, with gonothecae present between May and January and a reproductive peak at the end of winter. The seasonality of S. mediterranea, with a peak of reproductive activity during the cold period, was similar to that of colonies of the species from the intertidal zone studied previously. Conversely, differences were noted in seasonal patterns of P. setacea between the two zones. Intertidally, this species was found only during the warm season, as small clumps (not more than 35 mm high). In contrast, sub-littoral colonies were larger (up to 130 mm high) and three overlapping generations each year were observed. Comparisons with intertidal hydroid communities are made.

Species richness, endemicity and distribution patterns of South African sea anemones (Cnidaria : Actiniaria & Corallimorpharia)

A revised and updated list of South African sea anemones is compiled and the distribution pattern and endemicity of each determined from museum and literature records. Forty nine valid species are recognized. Species richness appears fairly uniform around the coast, although marked peaks occur at Cape Town, False Bay and Durban almost certainly the result of disproportionately intense sampling effort at these locations. Forty nine per cent of species are endemic, slightly above the average for the South African marine fauna (31%), but well within the range shown by component taxa. Endemics are absent in the northwest, but otherwise comprise a fairly consistent proportion of species in each region. The fact that existing records are strongly biased towards a few centres of high sampling activity, indicates a pressing need for additional systematic collection of this group in under represented areas.

Characterization of Aulactinia (Actiniaria: Actiniidae) species from Mar del Plata (Argentina) using morphological and molecular data

This study performs a morphological and molecular characterization of the species belonging to the genus Aulactinia from Mar del Plata (Argentina), previously identified as A. marplatensis and A. reynaudi. The great similarity in the natural history of these species, and our results on external and internal anatomy, clearly suggests that the sea anemones of the genus Aulactinia inhabiting the studied areas must be considered a single species, A. marplatensis. The molecular data provided here further support this assertion: all the individuals of A. marplatensis and A. reynaudi appear together intermixed in a monophyletic group clearly distinct from the outgroup species A. incubans and A. verrucosa. We have also completed the description of A. marplatensis, adding more anatomical features based mainly on internal anatomy and cnidae.

Composition, biometry and statistical relationships between the cnidom and body size in the sea anemone Oulactis muscosa (Cnidaria : Actiniaria)

This study analyses the possible relationships between body size and length of cnidae from different tissues of the sea anemone Oulactis muscosa . We describe the cnidom, providing new qualitative and quantitative data. Our description adds spirocysts for tentacles and acrorhagi, and is more precise about the ranges and types of basitrichs, microbasic b -mastigophores, and holotrichs. We distinguish two types of holotrichs in the acrorhagi, and differentiate between microbasic b -mastigophores and basitrichs in the actinopharynx and mesenterial filaments. A relationship between cnida length and body weight was not demonstrated. The results are based on a complete account of cnida types from all tissues, and considering the great number of capsules measured (5400) and the modern statistical tools employed, we think that a normal distribution of cnida lengths is uncommon, perhaps refuted. This finding is very important when a quantitative analysis of cnidae is necessary and an adequate statistical tool must be used. We have shown that generalized linear models are an alternative and therefore analyses can be done with parametric methods despite the non-normal distribution of cnida size. The use of these statistical tools should be generalized since appropriate package for analyses (like the R package) are available from the web and the obtained results are robust and powerful.

Hydroid colonies as primary substrata for recruits of the mussel Mytilus edulis platensis front off Mar Del Plata, Argentina

Abstract Due to the sparse presence of algae, hydroid clumps appear as the main primary substrata for the settlement of epizoical mussels in Buenos Aires province (Argentina). The settlement and growth of Mytilus edulis platensis on Amphisbetia operculata and Plumularia setacea colonies during their first life stages was analyzed throughout the year and the double settling larvae phenomenon is discussed. Colonies of both species were frequently colonized by numerous spat, which reached a maximum density of 1370 and 1450 individuals g-1 of colony, respectively. Settlement of Mytilus larvae on the hydroids occurred mainly in November, decreasing in December and January. The plantigrades biomass on A. operculata increased from December until April in spite of a decrease in the number of individuals. In constrast in P. setacea both plantigrade numbers and biomass decreased from December and no individuals were found in February. The major abundance and permanency of plantigrades on A. operculata could be explained by its bigger size and more profuse branching in comparison with P. setacea. The competent Mytilus larvae also settle on mussel beds, but only the filamentous substrata seem to ensure a high probability of survival during the early benthic stages, because it provides protection from predators (sea urchins and sea stars).

First record and redescription of the introduced sea anemone Sagartia ornata (Holdsworth, 1855) (Cnidaria: Actiniaria: Sagartiidae) from South Africa

The brooding sea anemone Sagartia ornata is reported from South Africa for the first time and is redescribed. The species is abundant intertidally in Langebaan Lagoon, where it attaches to stones shal lowly buried in sediment. It is probably a recent intro duction from Europe.

Diet of the sea anemone Anthopleura nigrescens: composition and variation between daytime and nighttime high tides

BackgroundThe diverse feeding habits of sea anemones have led them to be classified as opportunistic polyphagous predators. However, most studies have focused on the diet of temperate sea anemones, and little is known about the trophic ecology of tropical species and their role in tropical ecosystems. We studied the diet of the intertidal sea anemone Anthopleura nigrescens by examining the gut contents of specimens collected at two sites on Costa Rica’s Pacific coast, testing for differences in prey items captured between daytime and nighttime high tides.ResultsWe found 25 prey items including: mollusks, crustaceans, annelids, insects and eggs. Juvenile bivalves, barnacle cyprids, and copepods were the main prey items. The anemones at Playa Dominical captured significantly more juvenile bivalves during nighttime high tides, and those at Mata de Limón captured more cyprids during daytime high tides.ConclusionsThis study shows that A. nigrescens is an opportunistic polyphagous predator, like most of its temperate counterparts.

New records of sea anemones (Cnidaria: Anthozoa) from Costa Rica

Despite being important components in coastal marine systems, sea anemones have been poorly studied on both coasts of Costa Rica. In this paper new records of sea anemones are mentioned for the Caribbean and Pacific coasts of Costa Rica and the Isla del Coco National Park. Additionally, the presence of other species previously recorded in Costa Rica based on single observations or photos, is reconfirmed. An updated inventory of these cnidarians is provided, and with the corallimorpharians, comprises of 16 species (10 in the Caribbean and 6 in the Pacific and Coco Island). A comparison with the sea anemone fauna of Panama is added.

Hierarchical biogeographical processes largely explain the genomic divergence pattern in a species complex of sea anemones (Metridioidea: Sagartiidae: Anthothoe)

The phylogenetic resolution provided by genome-wide data has demonstrated the usefulness of RAD sequencing to tackle long-standing taxonomic questions. Cnidarians have recently become a model group in this regard, yet species delimitation analyses have been mostly performed in octocorals. In this study, we used RAD sequencing to test the species hypotheses in a wide-spread complex of sea anemones (genus Anthothoe), contrasting this new line of evidence with their current classification. The alternative hypotheses were tested using a Bayes Factors delimitation method, and the most probable species tree was then evaluated under different biogeographic scenarios. Our results decisively rejected the current morphology-informed delimitation model and infer the presence of several cryptic species associated with distinct marine ecoregions. This spatial pattern was remarkably consistent throughout the study, highlighting the role of geographic distribution as a powerful explanatory variable of lineages diversification. The southern Gondwana pattern with episodic, jump dispersal events is the biogeographic historical representation that best fits the Anthothoe species tree. The high population differentiation possibly amplified by the occurrence of asexual reproduction makes it difficult to identify genes responsible for local adaptation, however, these seem to be mainly associated with cellular and metabolic processes. We propose a new set of species hypotheses for the Southern Hemispheric Anthothoe clade, based on the pronounced genomic divergence observed among lineages. Although the link between the genetic and phenotypic differentiation remains elusive, newer sequencing technologies are bringing us closer to understanding the evolution of sea anemone diversity and, therefore, how to appropriately classify them.