Maria Cristina Gambi

Divergent ecosystem responses within a benthic marine community to ocean acidification

Ocean acidification is predicted to impact all areas of the oceans and affect a diversity of marine organisms. However, the diversity of responses among species prevents clear predictions about the impact of acidification at the ecosystem level. Here, we used shallow water CO2 vents in the Mediterranean Sea as a model system to examine emergent ecosystem responses to ocean acidification in rocky reef communities. We assessed in situ benthic invertebrate communities in three distinct pH zones (ambient, low, and extreme low), which differed in both the mean and variability of seawater pH along a continuous gradient. We found fewer taxa, reduced taxonomic evenness, and lower biomass in the extreme low pH zones. However, the number of individuals did not differ among pH zones, suggesting that there is density compensation through population blooms of small acidification-tolerant taxa. Furthermore, the trophic structure of the invertebrate community shifted to fewer trophic groups and dominance by generalists in extreme low pH, suggesting that there may be a simplification of food webs with ocean acidification. Despite high variation in individual species’ responses, our findings indicate that ocean acidification decreases the diversity, biomass, and trophic complexity of benthic marine communities. These results suggest that a loss of biodiversity and ecosystem function is expected under extreme acidification scenarios.

Benthic associations of the shallow hard bottoms off Terra Nova Bay, Ross Sea: zonation, biomass and population structure

Quantitative and semi-quantitative samples of phyto- and zoobenthic organisms were collected by SCUBA diving at five stations along a depth transect from 0.5–16 m on the shallow hard bottoms off Terra Nova Bay, Ross Sea, Antarctica. The benthic associations were dominated by two macroalgal species ( Iridaea cordata and Phyllophora antarctica ) and by few animal taxa (mainly polychaetes, molluscs and peracarid crustaceans). Distribution at the community and species levels revealed a well-defined zonation pattern as a function of depth, governed mainly by sea ice scouring and melting. Zonation of vagile fauna was also affected by the effects of covering and architecture of the two dominant macroalgae. Species richness and diversity were higher in the Phyllophora -associated community, where habitat complexity and sheltering were higher. The highest faunal abundance (over 82 000 ind.m −2 ) and biomass (macroalgae and fauna wet weight 2392 g m −2 ) were recorded at 2 m depth in association with the Iridaea covering, where the harsher environmental conditions select a few taxa. The biomass values, even if underestimates of the whole community standing crop, are among the highest recorded in shallow austral biotopes. An autoecological and demographic analysis of the most abundant animal species revealed for some species (e.g. Laevilitorina antarctica and Paramoera walkeri ) a quite complex population structure with up to three size classes, including juveniles. In some species, the cohort of juveniles showed a well-defined depth preference probably related to sheltering by the macroalgae. As a whole, the species analyzed showed various and contrasting reproductive strategies, despite the fact that the environmental conditions along the transect were relatively similar and quite selective.

Distribution of Soft-bottom Polychaetes in Two Coastal Areas of the Tyrrhenian Sea (Italy): Structural Analysis

Abstract Multidimensional statistical analysis was used to study the polychaete distribution in soft-bottoms of two coastal areas of the Tyrrhenian Sea (Italy), which are influenced by the discharges of the rivers Tiber and Ombrone. In both areas the distributional patterns of these organisms are determined mainly by sediment types and related factors such as hydrodynamics, river input, and sedimentation. The grain-size gradient from the coast to the open sea affects not only species composition, but also species richness, diversity and abundance. In both areas three main communities have been identified: a sandy biocoenosis, a mixed-sediment biocoenosis and a muddy biocoenosis. The sandy coastal community is characterized by only a few species, while the intermediate zone of sandy-mud sediments presents the highest species richness and diversity. At the mouth of the River Tiber the influence of the river is more evident than at the mouth of the River Ombrone. This is due to the Tibers greater river flow, which determines an environmental uniformity and a ‘cenotic continuum’ from sandy to muddy communities. This does not occur at the mouth of the Ombrone, where the river flow is less important and the polychaete communities are better defined.

Polychaete populations of the shallow soft bottoms off Terra Nova Bay (Ross Sea, Antarctica): distribution, diversity and biomass

Abstract Diversity, distribution and biomass patterns of polychaetes were studied in the shallow soft bottoms off Terra Nova Bay (Ross Sea, Antarctica). Benthic samples, collected in the austral summer 1989–1990, were sampled using a Van Veen grab at 14 stations distributed between 23- and 194-m depth. A total of 5,768 individuals of polychaetes belonging to 77 species were found. The species richness recorded was high, despite the few biotopes investigated at Terra Nova Bay in this study, especially when compared to that recorded from previous investigations in the same area and from the whole Ross Sea (146 species). Despite the high number of species found, only a few species accounted for 76% of the total abundance: Tharyx cincinnatus (27%), Spiophanes tcherniai (23%), Leitoscoloplos mawsoni (18%) and Laonice weddellia (5%) were mainly distributed in the deeper stations (below 100-m depth), while Aglaophamus ornatus (3%) was the only species abundant in the shallowest stations (above 50-m depth), characterized by gravels and coarse sands. Species richness, diversity and evenness showed an increase with depth. Abundances ranged between 40 to over 12,000 ind/m2. Biomass values ranged between 0.9 to 176 g/m2 (wet weight). A trophic-guild classification revealed the occurrence of various feeding categories that were, however, numerically dominated by deposit feeders with both discretely motile epiand endobenthic forms, and sessile ones. Both the Bray-Curtis similarity and Correspondence (C.A.) analyses showed stations ordered according to depth and to the local dominance of some species. Both poorly and well-structured polychaete assemblages occurred and they seemed related to depth-related factors, such as degree of environmental disturbance (shallowest bottoms vs deep ones), heterogeneity of the substrate and habitat complexity (gravel and coarse sands vs mixed sediment. The richest and most diverse assemblages of polychaetes were those occurring below 140-m depth, where the substrate was dominated by medium sands, often mixed with a mosaic of rocks and boulders.

Community dynamics and ecosystem simplification in a high-CO2 ocean

Disturbances are natural features of ecosystems that promote variability in the community and ultimately maintain diversity. Although it is recognized that global change will affect environmental disturbance regimes, our understanding of the community dynamics governing ecosystem recovery and the maintenance of functional diversity in future scenarios is very limited. Here, we use one of the few ecosystems naturally exposed to future scenarios of environmental change to examine disturbance and recovery dynamics. We examine the recovery patterns of marine species from a physical disturbance across different acidification regimes caused by volcanic CO2 vents. Plots of shallow rocky reef were cleared of all species in areas of ambient, low, and extreme low pH that correspond to near-future and extreme scenarios for ocean acidification. Our results illustrate how acidification decreases the variability of communities, resulting in homogenization and reduced functional diversity at a landscape scale. Whereas the recovery trajectories in ambient pH were highly variable and resulted in a diverse range of assemblages, recovery was more predictable with acidification and consistently resulted in very similar algal-dominated assemblages. Furthermore, low pH zones had fewer signs of biological disturbance (primarily sea urchin grazing) and increased recovery rates of the dominant taxa (primarily fleshy algae). Together, our results highlight how environmental change can cause ecosystem simplification via environmentally mediated changes in community dynamics in the near future, with cascading impacts on functional diversity and ecosystem function.

New record of the alien seagrass Halophila stipulacea (Hydrocharitaceae) in the western Mediterranean: a further clue to changing Mediterranean Sea biogeography

The occurrence of the tropical seagrass species Halophila stipulacea (Hydrocharitaceae) is reported within the harbour of Palinuro (Salerno, central Tyrrhenian Sea, Italy). The bottom covered by the seagrass has been evaluated in about 16 m, fragmented in various small patches distributed in a narrow belt between 0.5 and 5 m depth, and all settled on dead matte of the endemic Mediterranean seagrass Posidonia oceanica. Mean density was 10,500 shoots m. This record documents a displacement of about 180 km north of the previously documented limit of Halophila stipulacea in the western Mediterranean, likely mediated by pleasure boat traffic and anchoring, and favoured by climate change. This record illustrates a further example of the changing Mediterranean Sea biogeography: north–south patterns in biotic ranges will probably replace the presently well established west–east patterns in the Mediterranean Sea of tomorrow.

Posidonia oceanica as a biomonitor of trace elements in the Gulf of Naples: temporal trends by lepidochronology.

Levels of Hg, Cd, Pb, Cu, Zn, Fe, and Mn were assessed by using Posidonia oceanica as a bioindicator in the Gulf of Naples (southern Italy). Lepidochronology, which enables retroactive dating of scales and rhizomes of this seagrass, was combined with atomic spectrometry to assess temporal trends of trace elements in dated scales and rhizomes over a 10-year period. Lepidochronology occasionally has been used to monitor Hg in dated scales, but never has been used to determine concentrations of other trace elements in dated rhizomes. Data were compared between various structural parts of seagrass and between sampling sites. Concentrations of some elements found in dated scales or rhizomes showed a similar trend in most of the sites; increasing for Hg and Cu and decreasing for Pb, Fe, and Zn. Contaminant levels indicated by seagrass meadows varied from metal to metal. Concentrations of Hg, Cd, and Pb fell within the ranges measured in other areas considered to have low levels of heavy metal pollution, whereas Cu, Mn, and Zn had higher concentrations only in some years. However, on the basis of other studies, none of the sampling sites are considered to have high contamination levels.

Invertebrate borers in Posidonia oceanica scales: relationship between their distribution and lepidochronological parameters

The occurrence and pattern of distribution of invertebrate borers in the scales (remains of leaf bases still connected to the rhizome) of the seagrass Posidonia oceanica was studied in two meadows of the Mediterranean Sea. At Noli (Ligurian Sea), Posidonia shoots were sampled at 1, 5, 10 and 15 m depths, while at cape Coda Cavallo (Northern Sardinia) samples were collected only at 6 m depth. The lepidochronology technique (based on the annual cycle variation in the scale thickness) was employed in order to study the relationship between plant and borers and to characterize their microhabitat in the stem. Borers belong to Polychaeta and Crustacea Isopoda. Three species of polychaetes belonging to the family Eunicidae (Lysidice ninetta Audouin and M. Edwards, Lvsidice collaris (Grube) and Nematonereis unicornis (Grube)) and one species of isopod of the family Limnoriidae (Limnoria tuberculata (Sowinski)) were responsible for burrowing within Posidonia scales. Estimated density of borers reached in some instances values as high as 278 individuals m 2. Isopods occurred in younger scales, whereas polychaetes inhabited older scales. A positive trend was observed between polychaete width (3rd body segment) and scale thickness; however, both Spearman rank correlation and linear regression coefficients showed quite low significant values. In some instances polychaetes burrowed also into the living tissues of the shoots. Borers have been recorded also in several other Posidonia beds along the Italian

Cladistic relationships within Amphiglena Claparède (Polychaeta: Sabellidae) with a new species and a redescription of A. mediterranea (Leydig)

A new species of Amphiglena Claparede 1864, A. lindae n. sp., is described from Belize having up to five pairs of radioles, eight thoracic chaetigers, and as many as 26 abdominal chaetigers. This species, like other Amphiglena spp., is a simultaneous hermaphrodite with eggs and sperm developing in abdominal chaetigers. However, in A. lindae the gametes are found in the mid-abdominal region rather than the anterior abdomen. It is also unique in having a pair of spermathecae with red pigmentation at the base of the dorsal lips. A redescription of the type species of the genus, A. mediterranea Leydig, 1851, is also provided based on material from Italy. No type material of A. mediterranea was ever deposited but it is thought unnecessary to designate neotypes. The cladistic relationships among the species of Amphiglena are then assessed using an outgroup based on the six genera that are the sister group to the Laonome/Amphiglena clade. Two species of Laonome are included as part of the ingroup. The monophyly ...

To brood or not to brood: Are marine invertebrates that protect their offspring more resilient to ocean acidification?

Anthropogenic atmospheric carbon dioxide (CO2) is being absorbed by seawater resulting in increasingly acidic oceans, a process known as ocean acidification (OA). OA is thought to have largely deleterious effects on marine invertebrates, primarily impacting early life stages and consequently, their recruitment and species’ survival. Most research in this field has been limited to short-term, single-species and single-life stage studies, making it difficult to determine which taxa will be evolutionarily successful under OA conditions. We circumvent these limitations by relating the dominance and distribution of the known polychaete worm species living in a naturally acidic seawater vent system to their life history strategies. These data are coupled with breeding experiments, showing all dominant species in this natural system exhibit parental care. Our results provide evidence supporting the idea that long-term survival of marine species in acidic conditions is related to life history strategies where eggs are kept in protected maternal environments (brooders) or where larvae have no free swimming phases (direct developers). Our findings are the first to formally validate the hypothesis that species with life history strategies linked to parental care are more protected in an acidifying ocean compared to their relatives employing broadcast spawning and pelagic larval development.