Observaciones sobre las características reproductoras de tres especies de Eunicidae (Polychaeta) asociadas a praderas de la fanerógama marina Posidonia oceanica en el Mar Mediterráneo

Observations on the reproductive features are provided for three species of Eunicidae (Lysidice ninetta Audouin and Milne Edwards, Lysidice collaris Grube and Nematonereis unicornis (Grube)). They all occur in Posidonia oceanica meadows as borers in the sheaths. The material examined was collected during several studies on P. oceanica meadows conducted at various times of the year and in different years along the coasts of Sardinia and the Ischia islands (Tyrrhenian Sea), and Otranto (Southern Adriatic Sea). All individuals of the three species were measured (width 3rd chaetiger, diameter of eyes), and checked for presence of gametes. In each of the females recognized, egg diameter was measured. To integrate the observations, living specimens were collected in March 2003 and reared in the laboratory until August 2003 to check for gamete maturation; mature males were fixed for analysis of the structure of the spermatozoa by transmission electron microscopy (TEM). All three species studied are gonochoric. For both species of Lysidice gametes occurred in individuals with a width greater than 0.8 mm. The overall scarcity of mature males and females observed with respect to the total number of specimens collected is probably due to the dimensional constraint exerted by the sheaths. In Lysidice spp. specimens with small developing oocytes were observed in January-February and reached their maximum diameter between June and August (157 µm). Gametes were located mainly in the posterior part of the body, and an enlargement of the eyes (almost doubled in size) characterized mature specimens close to spawning. N. unicornis is a smaller species, and it is less frequent in Posidonia sheaths than Lysidice spp.; individuals with gametes had a width greater than 0.55 mm. A few mature specimens were observed between March and May with a maximum egg diameter of about 155 µm. In this species maturation of the gametes is coupled with a huge enlargement of the eyes (ten-times larger than in immature individuals), while the posterior part of the body is swollen and full of mature gametes, indicating reproduction by schizogamy. Analysis of mature spermatozoa of the three eunicids revealed a similar morphology, which is that of an “ect-aquasperm” type, typical of many free-spawning species with external fertilization. The nucleus is round and globose (2.5 µm diameter) and the acrosome, slightly different among the three species, has the general shape of a truncate sub-cone.Se discuten algunas caracteristicas generales de la biología de la reproducción de tres especies de poliquetos Eunicidae (Lysidice ninetta Audouin and Milne- Edwards, Lysidice collaris Grube y Nematonereis unicornis (Grube)). Estas especies fueron obtenidas en praderas de Posidonia oceánica, en donde viven asociadas a las escamas de las hojas. El material examinado fue recolectado en diferentes anos y en praderas de P. oceánica distribuidas en la costa de Cerdeña, de la isla de Ischia (Mar Tirreno), y de Otranto (Mar Adriatico Sur). Todos los individuos fueron medidos (anchura del tercer segmento, diámetro de los ojos), y analizados para observar en ellos la presencia de los gametos. En cada hembra se midió el diámetro de los huevos. El desarrollo de otros individuos fue observado en el laboratorio desde Marzo a Agosto 2003 con la finalidad de estudiar la maduración de los gametos. Los machos maduros fueron fijados para el análisis de la ultra-estructura de los espermatozoos al Microscopio Electrónico. Las tres especies estudiadas son gonocóricas (sexos separados). Para las dos especies del genero Lysidice las hembras con huevos siempre se presentaron en individuos superiores en anchura a 0,8 mm. La escasez de hembras y machos maduros en relación al total de individuos está probablemente relacionado con las limitaciones que suponen las dimensiones y espesor de las escamas de Posidonia. Individuos de Lysidice spp. con huevos pequeños en desarrollo se observaron desde Enero-Febrero; los oocitos alcanzaron el máximo diámetro en Junio y Agosto (157 μm). Los gametos se localizaron preferentemente en la parte posterior del cuerpo, y cuando los individuos alcanzaron la madurez, sus ojos se hicieron más anchos (casi el doble en su diámetro). N. unicornis es una especie más pequeña, y menos frecuente en las escamas de Posidonia que Lysidice spp. Los individuos con gametos presentan anchuras superiores a 0,55 mm. Algunos individuos maduros fue observado desde Marzo a Mayo, con diámetros máximos de los huevos de casi 155 μm. En esta especie la madurez se relaciona con un enorme aumento del diámetro de los ojos (diez veces mas anchos que en individuos inmaduros), y en la dilatación de la parte posterior del cuerpo llena de gametos maduros; esta característica indica una reprodución de tipo eschizogámico. La ultra-estructura de los espermatozoos maduros es muy similares en las tres especies de Eunicidae, de tipo”ect-aquasperm”, típicas des especies con fecundación externa. El núcleo (2,5 μm en diámetro) es redondo y globular, y el acrosoma, que es un poco diferente entre las especies, es de forma general en cono truncado. &nbsp

Spatio-temporal variability of Borer Polychaetes in Posidonia oceanica beds and its relation to meadow structure

Posidonia oceanica forms an extremely productive and complex ecosystem in the coastal Mediterranean Sea providing a suitable habitat for hundreds of plant and animal species. Among motile invertebrates associated to Posidonia meadows, polychaete borers of the plant sheaths represent a unique group which exploit a peculiar microhabitat. They belong to the family Eunicidae with three dominant species, Lysidice collaris, L. ninetta and L. unicornis. Due to their strong association with Posidonia shoots, these animals are particularly suitable to study the plant and animal spatial relationships and their pattern of variability. The aim of this work was to evaluate the frequency of occurrence of these animals (Index of Borer, IB) at different spatial and temporal (summer vs winter) scales in two Posidonia meadows off the Ischia Island (Gulf of Naples, Italy), which are exposed to different degrees of human impact and of hydrological conditions. Results showed IB values of L. collaris (the most abundant species) significantly different between meadows and at scales from 10s to 100s of meters, as well as between summer and winter. The IB of L. ninetta showed significant differences only at scales of 10s of meters while, on the contrary, the IB of L. unicornis (the less abundant species) did not show variability at any spatial and temporal scales. Most of the variance was at the more impacted and less water movement exposed meadow, suggesting higher level of small and intermediate scales of patchiness of borers at this meadow. These variation patterns are discussed in relation to local environmental differences between the studied Posidonia beds

Relationships between Meiofaunal Biodiversity and Prokaryotic Heterotrophic Production in Different Tropical Habitats and Oceanic Regions

Tropical marine ecosystems are among the most diverse of the world oceans, so that assessing the linkages between biodiversity and ecosystem functions (BEF) is a crucial step to predict consequences of biodiversity loss. Most BEF studies in marine ecosystems have been carried out on macrobenthic diversity, whereas the influence of the meiofauna on ecosystem functioning has received much less attention. We compared meiofaunal and nematode biodiversity and prokaryotic heterotrophic production across seagrass, mangrove and reef sediments in the Caribbean, Celebes and Red Seas. For all variables we report the presence of differences among habitats within the same region, and among regions within the same habitat. In all regions, the richness of meiofaunal taxa in reef and seagrass sediments is higher than in mangrove sediments. The sediments of the Celebes Sea show the highest meiofaunal biodiversity. The composition of meiofaunal assemblages varies significantly among habitats in the same region. The nematode beta diversity among habitats within the same region is higher than the beta diversity among regions. Although one site per habitat was considered in each region, these results suggest that the composition of meiofaunal assemblages varies primarily among biogeographic regions, whereas the composition of nematode assemblages varies more considerably among habitats. Meiofauna and nematode biodiversity and prokaryotic heterotrophic production, even after the removal of covariate effects linked with longitude and the quantity and nutritional quality of organic matter, are positively and linearly linked both across regions and within each habitat type. Our results confirm that meiofauna and nematode biodiversity may influence benthic prokaryotic activity, which, in turn, implies that diversity loss could have negative impacts on ecosystem functioning in these systems

Invasions of the non-indigenous red alga Lophocladia lallemandii (Montagne) F. Schmitz off the Island of Ischia (Tyrrhenian Sea, Italy)

This paper describes the distribution and spread of the non-indigenous red alga Lophocladia lallemandii (Montagne) F. Schmitz along the coast of the Island of Ischia (Tyrrhenian Sea, Italy). Lophocladia lallemandii was monitored through surveys from July 2019 to January 2020 at the Capo Sant’Angelo (Ischia), where L. lallemandii was observed, but not reported, in the years preceding the invasion of the upper rocky infralittoral shore reported here. It is noteworthy that a large portion of the study area is included within one of the two “B no-take” zones of the Marine Protected Area of the “Regno di Nettuno” (“Neptune’s Realm”). During the surveys, the alga was first observed in the middle of July 2019 and totally disappeared by the middle of January 2020. Algal cover showed two peaks in August (55%) and November (58.5%). Fertile thalli (tetrasporophytes) of L. lallemandii were observed in all of the analysed samples. Thalli were not always strongly attached to the substrate or other algae and could often be easily detached by strong hydrodynamic conditions. These detached thalli were found laying on the bottom in dense turfs or floating or stranding on the beach. Noteworthy were the macroflora and fauna, the latter essentially composed by mollusks and amphipods, living among the branches of the alga, and various fishes hiding within the thick algal turf. These observations indicate that this alga may be a source of food and refuge for the native animal community of the upper rocky infralittoral zone

Biology and new records of the invasive species Branchiomma bairdi (Annelida: Sabellidae) in the Mediterranean Sea

The first observations on the reproductive biology of the alien polychaete Branchiomma bairdi (McIntosh, 1885) (Sabellidae) in the Mediterranean Sea are provided as well as additional Mediterranean records of the species, which can help to understand its introduction and spreading. Re-examination of the specimens from Miseno harbour (Tyrrhenian Sea, Italy) revealed the presence of B. bairdi in the central-Mediterranean since September 2004. The histological study of individuals collected in Malta revealed that the species is a simultaneous hermaphrodite, developing male and female gametes in the same body segments; embryos are brooded inside the parent tube. However, there is also evidence of asexual reproduction. The species shows a different reproductive pattern from the previously reported population from the eastern-Pacific; this demonstrates its great plasticity and adaptability. Branchiomma bairdi has an invasive behaviour, colonizing large areas in relatively short-time, and reaching relatively high densities (c.a. 50 individuals/m2). Its expansion to several Mediterranean localities is largely a consequence of the high capacity of this species to colonize extremely different habitats and substrates, the occurrence of sexual and asexual reproductive strategies, and the combination of both. Furthermore, B. bairdi appears to be particularly abundant in confined areas and areas degraded due to anthropogenic impacts. Finally, our findings strongly suggest that the pathway of introduction in the Mediterranean, previously hypothesized as the Suez Canal (Lessepsian migration), is most likely via the Strait of Gibraltar

Nematode diversity patterns at different spatial scales in bathyal sediments of the Mediterranean Sea

Understanding biodiversity patterns and how they are driven at different spatial scales is a crucial issue in eco- logical studies. This is particularly evident for the deep sea, the largest biome of the biosphere, where information on the scales of spatial variation is very scant. Here, we investigated deep-sea nematodes species richness, turnover and func- tional diversity, and life strategies at different spatial scales (from local to macro-regional) to identify the factors that shape regional (γ) and macro-regional (ε) deep-sea diver- sity. This study was conducted in several deep-sea habitats (canyons, open slopes, deep-water corals, and bathyal plains) over > 2000 km across the whole Mediterranean Basin, at a bathymetric range comprised between ca. 600 and 1300 m. Our results indicate that the patterns of local (α) diversity across the deep Mediterranean follow the gradients of the trophic conditions, which decrease from the western to the eastern basins. For all of the sites and habitats, the α diversity is generally low. Conversely, the turnover diversity changes significantly among habitats (β diversity) and between re- gions (δ diversity), showing values of dissimilarity (based on species presence/absence matrixes) between 59 and 90 % for β diversity and between 81 and 89 % for δ diversity. This suggests that patterns and values of γ and ε diversities in the deep Mediterranean Sea are related to turnover diversity among habitats and between regions (β and δ diversities), rather than to the local biodiversity (α diversity). These re- sults indicate also that the differences in β and δ diversi- ties are even more important than those in α diversity for the comprehension of the drivers of biodiversity in the deep Mediterranean Sea. We conclude that the presence of differ- ent habitats and gradients in environmental conditions, by promoting a high turnover diversity across the Mediterranean Sea, may play a crucial role in the levels of γ diversity of deep-sea nematodes

USING VOLCANIC MARINE CO2 VENTS TO STUDY THE EFFECTS OF OCEAN ACIDIFICATION ON BENTHIC BIOTA: HIGHLIGHTS FROM CASTELLO ARAGONESE D’ISCHIA (TYRRHENIAN SEA)

Current research into ocean acidification is mainly being carried out using short-term experiments whereby CO2 levels are manipulated in aquaria and enclosures. We have adopted a new approach in our studies of the effects of ocean acidification on Mediterranean marine biodiversity by using volcanic carbon dioxide vent systems as ‘natural laboratories’ as they cause long-term changes in seawater carbonate chemistry. A range of organisms, including macroalgae, seagrasses, invertebrates, and selected scleractinians and bryozoans have now been investigated in a shallow area located off the island of Ischia (Castello Aragonese, Tyrrhenian Sea, Italy). Our in situ observations give support to concerns, based on model predictions and short-term laboratory experiments, that ocean acidification will likely combine with other stressors (e.g., temperature rise) to cause a decrease in Mediterranean marine biodiversity and lead to shifts in ecosystem structure

Macrofaunal communities in the Gioia Canyon (Southern Tyrrhenian Sea, Italy)

Submarine canyons play pivotal roles in the physical, biological and ecological processes of coastal areas, especially in closed or semi-closed basins as the Mediterranean Sea, influencing the biodiversity and the abundance of the benthic fauna. On February 2013, during the Tyrrhenian Gravity Flows (TyGraF) campaign, samples have been collected along the Gioia Canyon Basin (Italy) with the aim to describe the taxonomical composition and the abundances of the macrobenthic assemblages, filling the gap of knowledge in this area. A total of 93 taxa were identified, and the Annelida was the phylum with the highest number of specimens and most diversified (46 taxa). The polychaetes Sternaspis scutata, Prionospio cirrifera and Monticellina sp., the bivalves Thyasira sp.1 and Saccella commutata and the amphipods belonging to the genera Ampelisca and Harpinia showed the highest densities in the studied area; however, results suggest low values of the abundances of the macrobenthos if compared with those generally reported for other canyons, both inside and outside the Mediterranean Sea. The marine biotic index (AMBI) highlights that the canyon system and the surrounded area were slightly disturbed and characterized by a high percentage of tolerant taxa. This study is the first baseline for future analyses of the macrobenthic communities of this area