Hydroid assemblages from Mar del Plata, Argentina, at depths between 0 and 500 m. Distribution and biological substrata

The first studies on hydroids of the subantarctic region (SW Atlantic Ocean) were based on samples from expeditions to the Antarctic at the end of the 19th and beginning of the 20th centuries. In spite of these works, hydroids from the northern Argentine continental shelf remained unknown until the 1960s. In coastal waters off Mar del Plata, studies on hydroids have been few in number and limited to species described from preserved material. Even rudimentary ecological information is lacking in these reports. Over the past few decades, samples from oceanographic expeditions, and specimens collected directly from the intertidal rocky shore or by means of scuba diving and snorkeling, have provided heretofore unpublished information on hydropolyps of the Mar del Plata region. The goal of this work is to analyze the hydroid fauna of the Mar del Plata coast, including bathymetric distributions, frequencies of occurrence, and biological substrata. A total of 36 species were included. Most were found at depths shallower than 8 m, where hard substrates predominated. Numbers of species decreased markedly below 80 m. The shallow-water hydroid fauna of Mar del Plata comprises a large number of cosmopolitan or widely distributed species. In deeper zones, species with subantarctic or south hemisphere distributions predominated. Hard bottom outcrops were surrounded by extensive areas of sand. Although such substrata are unfavorable for most hydroids, many species were found in soft bottom areas on polychaete tubes. Stems of hydroids provided the greatest number of epizoic species (18), followed by polychaete tubes (16 species) and sponges (15 species). Hydroids, bivalve mollusks, and sponges were the most frequent substrates. Colonies grew less frequently on bryozoans and tunicates. This general scheme changed at greater depths, where the most frequent substrates were polychaete tubes and sponges.Les premières études sur les faunes hydraires de la région subantarctique (Atlantique sud-occidental) ont été basées sur les échantillons récoltés par les expéditions antarctiques de la fin du XIXe siècle et du début du XXe siècle. Cependant, les hydraires du nord de la plateforme continentale Argentine ont été ignorés jusque vers les années 60. Dans la zone côtière de Mar del Plata, il y a peu d’études relatives aux hydropolypes ; les espèces ont été décrites à partir de matériel préservé, sans aucune information écologique. Les échantillons des expéditions océanographiques et les spécimens collectés sur la côte rocheuse ou par plongeurs ont apporté beaucoup d’informations sur les hydraires de Mar del Plata. Aujourd’hui, une information considérable sur ces espèces est disponible. Le présent travail étudie la faune des hydraires de la zone côtière de Mar del Plata avec sa distribution bathymétrique, sa fréquence et les substrats biologiques. Un total de 36 espèces sont étudiées. Le plus grand nombre d’espèces est trouvé à des profondeurs inférieures à 8 m où les substrats durs sont abondants ; ce nombre diminue à partir de 80 m de profondeur. La faune hydraire de faible profondeur à Mar del Plata comprend un grand nombre d’espèces cosmopolites. À plus grande profondeur, le nombre d’espèces subantarctiques ou de l’hémisphère Sud augmente. Les fonds durs sont entourés de grandes étendues de sable. Ces substrats sont défavorables à la majorité des hydraires ; cependant, certaines espèces ont été trouvées sur ces fonds meubles mais vivant sur les tubes de polychètes. Les caules des hydropolypes apportent le nombre le plus important d’espèces epizoïques (18), suivie par les tubes de polychètes (16 espèces epizoïques) et les spongiaires (15 espèces epizoïques). Les hydraires, les bivalves et les spongiaires sont des substrats très abondants. Les colonies se situent plus rarement sur des bryozoaires ou des tunicates. Ce schéma change à grande profondeur où les substrats dominants sont les tubes de polychètes et les spongiaires

Natural history of Bimeria vestita Wright, 1859 (Hydrozoa, Bougainvilliidae) in the rocky intertidal of Mar del Plata (Argentina)

The population dynamics, reproductive period and substrate preference of the hydroid Bimeria vestita Wright, 1859 were analyzed from October 1990 to February 1992 in the rocky intertidal zone of Mar del Plata (Argentina). Colonies were found year-round, with maximun abundances in summer and autumn (60% of the colonies). During these periods the colonies produce gonophores. Bimeria vestita is more frequently found on colonies of the hydroids Sertularella mediterranea Hartlaub, 1901 (58.1%) and Tubularia crocea (Agassiz, 1862) (37.5%) than on other substrates (4.4%). Seasonal differences in substrate preferences were observed. Tubularia crocea was the most preferred substrate in spring and summer (75–80%), while S. mediterranea was preferred in autumn and winter (70–80%). Stolonial growth of B. vestita suggests a "guerrilla" strategy to avoid competition in the basal zones of the substrates

Frequency of study and diversity of benthic hydrozoa of the argentine continental shelf

The Argentine continental shelf was divided into 12 sectors every two degrees of latitude. All the bibliographical records and hydropolyp species found in each section were registered. The Hydrozoa of southern sections of the Magellanic zoogeographical province have been investigated since the nineteenth century, while in northern sections of this province and in the Bonaerensian zoogeographical province studies began in the early 1960s. The north section of the Magellanic zoogeographical province is the least known and shows less diversity. A total of 116 species were found. They are distributed among the families Sertulariidae (32.8%) Syntheciidae (1.7%), Campanulariidae (26.7%), Lafoeidae (10.3%) Plumulariidae (8.6%), Haleciidae (5.2%) Campanuliniidae (4.3%) Tubulariidae (2.6%), Bougainvilliidae (2.6%) Hydractiniidae (1.7%), Eudendriidae (1.7%), Corynidae (0.9%) and Clavidae (0.9%). Endemism was rare (8.5%) but 49.6% of the species have an austral distribution and 41.9% are cosmopolitan species. There are differences between the two zoogeographical provinces analyzed; the Magellanic zoogeographical province shows higher diversity (94 species), with 71 exclusive species, while the Bonaerensian zoogeographical province shows 48 species, 25 exclusive. Only 23 species were found in both provinces

Two new records of Pycnogonids on the Uruguayan coast

The Pycnogonida from Uruguayan waters are scarcely known, and their reports are markedly discontinuous. In this paper, several individuals of two previously unrecorded Pycnogonids at the shallow rocky subtidal and lower intertidal fringes of Cerro Verde (Rocha, Uruguay) are reported. The specimens were assigned to Pycnogonum pamphorum Marcus, 1940 and Anoplodactylus petiolatus (Kroyer, 1844). This is the first record of these species on the Uruguayan coast and the southernmost record of P. pamphorum, previously recorded only in Santos, Brazil (type locality)