Changes in amphipod (Crustacea) assemblages associated with shallow-water algal habitats invaded by Caulerpa racemosa var. cylindracea in the western Mediterranean Sea

Two better than one: The complementary of different types of artificial substrates on benthic marine macrofauna studies

Non-destructive methodologies based on the use of artificial substrates (AS) for quantitative sampling of macrofauna have been used to solve sampling problems in complex benthic environment, such as rocky reefs. The macrofauna assemblages of two different types of AS (dendritic and crevice), at two different locations were studied. The main goal was to evaluate the complementarity of dendritic and crevice AS when sampling the macrofauna associated with rocky environments, in two scenarios: within the same location and between locations. With this approach, we intend to contribute to the development of a non-destructive sampling methodology based on AS. The hypotheses tested were that i) the assemblages associated with each type of AS would differ between them and, ii) regardless of AS type, assemblages would differ between locations. Our results revealed significant differences after three months between the macrofauna assemblages from dendritic and crevice substrates in both locations and differences between locations irrespective of the AS type used. Hence, due to the high number of species that only were attracted by each type of AS and the species settlement preferences, our findings have shown the complementarity of the two types of AS (dendritic and crevice). This suggests that the mixed use of AS could be the best approach to non-destructive standard monitoring programs based on benthic marine macrofauna.

The distribution of benthic amphipod crustaceans in Indonesian seas

Amphipod crustaceans are an essential component of tropical marine biodiversity. However, their distribution and biogeography have not been analysed in one of the world’s largest tropical countries nested in the Coral Triangle, Indonesia. We collected and identified amphipod crustaceans from eight sites in Indonesian waters and combined the results with data from 32 additional sites in the literature. We analysed the geographic distribution of 147 benthic amphipod crustaceans using cluster analysis and the ‘Bioregions Infomaps’ neural network method of biogeographic discrimination. We found five groups of benthic amphipod crustaceans which show relationships with sampling methods, depth, and substrata. Neural network biogeographic analysis indicated there was only one biogeographic region that matched with the global amphipod regions and marine biogeographic realms defined for all marine taxa. There was no support for Wallaces or other lines being marine biogeographic boundaries in the region. Species richness was lower than expected considering the region is within the Coral Triangle. We hypothesise that this low richness might be due to the intense fish predation which may have limited amphipod diversification. The results indicated that habitat rather than biogeography determines amphipod distribution in Indonesia. Therefore, future research needs to sample more habitats, and consider habitat in conservation planning.

Potentially combined effect of the invasive seaweed Caulerpa cylindracea (Sonder) and sediment deposition rates on organic matter and meiofaunal assemblages

The seaweed Caulerpa cylindracea (Sonder) is one of the most successful marine bioinvaders worldwide. Caulerpa cylindracea can influence the quantity and biochemical composition of sedimentary organic matter (OM). However, it is still unknown if the effects of C. cylindracea on both OM and small metazoans (i.e. meiofauna) can change according to different sediment deposition rates. To provide insights on this, we investigated the biochemical composition of sediments along with the abundance and composition of meiofaunal assemblages in sediments colonized and not-colonized by the seaweed C. cylindracea under different regimes of sediment deposition. Our results show that the presence of the invasive alga C. cylindracea could alter quantity, biochemical composition, and nutritional quality of organic detritus and influence the overall functioning of the benthic system, but also that the observed effects could be context-dependent. In particular, we show that the presence of C. cylindracea could have a positive effect on meiofaunal abundance wherever the sediment deposition rates are low, whereas the contextual presence of high to medium sedimentation rates can provoke an accumulation of sedimentary organic matter, less favourable bioavailability of food for the benthos, and consequent negative effects on meiofauna.

High Nitrogen and Phosphorous Acquisition by Belowground Parts of Caulerpa prolifera (Chlorophyta) Contribute to the Species' Rapid Spread in Ria Formosa Lagoon, Southern Portugal

Despite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids, and phosphate through the fronds and rhizoids + stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpa prolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of ¹⁵ N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas ¹⁵ N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C. prolifera was 689 μmol · m^-2 · h^-1 , whereas the total nitrogen requirement for growth was 672 μmol · m^-2  · h^-1 . The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C. prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.

A new record of the invasive seaweed Caulerpa cylindracea Sonder in the South Adriatic Sea

The green alga Caulerpa cylindracea Sonder is one of the most infamous and threatening invasive species in the Mediterranean Sea. Since 1985, it started rapidly spreading to all Mediterranean regions causing many ecological changes on natural communities. In the present study, we present an example of this proliferation with the first record in the Marine Protected Area of Tremiti Island (MPATI) in the South Adriatic Sea. Fifteen sites along the coast and 5 different depths have been investigated. Our results provide eveidence of a wide invasion of this pest in three islands, San Domino, San Nicola and Capraia. This study fills a particular data gap in the ongoing biomonitoring of invasive seaweeds in the Mediterranean Sea representing a base line of this invasive species for the MPATI.

Fish nursery value of algae habitats in temperate coastal reefs

The nursery function of coastal habitats is one of the most frequently mentioned and recognized ecosystem services in the valuation of coastal ecosystems. Despite its importance our understanding of the precise habitat parameters and mechanisms that make a habitat important as a nursery area is still limited for many species. The study aimed to establish the importance of different algae morphotypes in providing shelter and food for juvenile coastal fish during the main settlement peaks, in early spring and late summer, in littoral rocky reef systems in the Northwestern Mediterranean. The results of our study showed strong seasonal differences in algae cover, composition and height between the two sampling periods. Overall, during spring the algae were well developed, while in late summer, both density and height, of most algae decreased considerably. Equally, prey biomass, in form of suitable sized invertebrate fauna associated to the algae, decreased. Accordingly, the shelter and food for the fish settling in this habitat during late summer were less abundant, indicating a mismatch between the observed presence of juvenile fish and optimal habitat conditions. Differences in prey densities were detected between algae morphotypes, with structurally more complex algae, such as Cystoseira spp. and Halopteris spp. consistently containing more prey, independent of season, compared to simpler structured morphotypes such as Dictoytales. The study furthermore related juvenile fish density to habitats dominated by different algae morphotypes. Out of the three-study species (Diplodus vulgaris, Symphodus ocellatus, Coris julis) only S. ocellatus showed a significant association with an algae habitat. S. ocellatus related positively to habitats dominated by Dictoytales which provided the highest cover during late summer but had the lowest prey densities. A strong association of this species with Cystoseira, as reported by other studies, could not be confirmed. Cystoseira was abundant within the study area but in a state of dieback, showing loss and reduced height of foliage, typical for the time of year within the study area. It is therefore likely that algae-fish associations are context-dependent and that several algae species may fulfil similar functions. We also discovered that prey biomass did not appear to have an important effect on juvenile abundances. Nevertheless, the availability of prey may influence juvenile fish condition, growth performance and ultimately long-term survival. We therefore suggest that future studies on habitat quality should also include, besides abundance, indicators related to the condition and growth of juveniles.

Meiofauna communities, nematode diversity and C degradation rates in seagrass (Posidonia oceanica L.) and unvegetated sediments invaded by the algae Caulerpa cylindracea (Sonder)

We investigated meiofauna and sedimentary C cycling in seagrass (Posidonia oceanica) and unvegetated sediments invaded and not invaded by the non-indigenous tropical algae Caulerpa cylindracea. In both habitats, invaded sediments were characterized by higher organic matter contents. No effect was observed for prokaryotes and C degradation rates. In seagrass sediments, C turnover in invaded beds was about half that in not invaded ones. Meiofaunal communities varied significantly among invaded and not invaded grounds only in bare sediments. In both habitats, nematode species richness and assemblage composition were not affected by the algae. The effect of C. cylindracea on the turnover and nestedness components of the Jaccard dissimilarity varied between the two habitats. We show that the presence of C. cylindracea gives rise to variable consequences on meiofauna biodiversity and C cycling in different habitats. We conclude that further studies across different habitats and ecological components are needed to ultimately understand and predict the consequences of C. cylindracea invasion in shallow Mediterranean ecosystems.

Long-Term Field Study Reveals Subtle Effects of the Invasive Alga Sargassum muticum upon the Epibiota of Zostera marina

Invasive species can alter coastal ecosystems both directly, e.g. through competition for substratum and nutrients, and indirectly. Indirect effects may be mediated by creation of dissimilar or inimical habitats, changes in predator and/or prey assemblages, alterations in associated biota, and perturbations of water movement and thermal regimes. Previous studies have shown that invasive algae can modify native habitat architecture, disrupt intricately linked food webs and alter epibiotic assemblages. In the UK, the seagrass Zostera marina supports a diverse epibiotic assemblage, influencing key factors such as sediment dynamics, depositional regime and trophic linkages. Increasing encroachment of the invasive alga Sargassum muticum into seagrass meadows changes the physical and chemical characteristics of the local environment and creates the potential for changes in the epibionts associated with the seagrass blades, threatening the integrity of the seagrass ecosystem. We investigated the effects of S. muticum invasion upon the epibiota of Z. marina in a drowned river valley in SW England seasonally from spring to autumn over four years in an in-situ manipulative experiment, comparing permanent quadrats with and without artificially introduced S. muticum. Epibiota were weighed, identified to the most detailed operational taxonomic unit (OTU) possible, and unitary organisms were enumerated. Multivariate PERMANOVA+ analysis revealed significant differences in epibiont assemblages between Sargassum treatments. Linear mixed effects models indicated that differences in epibiota assemblage composition were not reflected as significant differences in mean biomass per sample, or number of epibiont OTUs per sample. We conclude that S. muticum invasion into Z. marina meadows may significantly alter the species composition and abundance distribution of epibiotic assemblages found on the blades of the seagrass. Thus S. muticum invasion could have more wide-reaching effects on processes within coastal ecosystems than predicted purely by direct effects.

Beyond the border: effects of an expanding algal habitat on the fauna of neighbouring habitats

The impacts of novel habitat-forming organisms on associated fauna have been difficult to predict, and may affect the fauna of neighbouring habitats due to changes in the spatial configuration of habitat patches of differing quality. Here, we test whether the localised expansion of a native habitat-forming macroalga, Caulerpa filiformis, on subtidal reefs can affect the abundance of fauna associated with a neighbouring macroalgal habitat. C. filiformis was a functionally distinct habitat for fauna, and the total abundance of epifauna associated with the resident alga, Sargassum linearifolium, was reduced at some sites when in close proximity to or surrounded by C. filiformis. Experimental manipulation of habitat configuration demonstrated that the low abundance of gastropods on S. linearifolium when surrounded by C. filiformis was likely explained by C. filiformis acting as a physical dispersal barrier for mobile fauna. Changes to the spatial configuration of novel and resident habitats can thus affect the abundance of fauna in addition to the direct replacement of habitats by species undergoing range expansions or increasing in abundance.

Abundance and diversity of amphipods (Crustacea: Peracarida) on shallow algae and seagrass in lagoonal ecosystem of the Mediterranean Tunisian coast

BACKGROUND

Bizerte lagoon is a semi-enclosed marine ecosystem, where various types of human activities have been developed. To investigate the distribution and temporal variation of amphipod assemblage, monthly sampling was conducted at the Menzel Jemil site from October 2009 to September 2010.

RESULTS

Atotal number of 3,620 specimens were collected from floating algae and seagrass allowing the identification of 10 amphipod species. Moreover, several indices, species richness, dominance, mean density, and diversity index were estimated to characterize the amphipode assemblage. Gammarusaequicauda wasthe most dominant species in all seasons. In addition, the minimum and maximum values of species richness of amphipod were observed in January (3 species) and April (8 species), respectively. The mean density and species richness were negatively correlated with plant biomass. Mean Shannon index (H')and evenness (J')were 1.62 ± 0.34 and 0.67 ± 0.16, respectively. Non-metric multidimensional scaling (MDS) analysis based on the mean species density showed three seasonal groups of samples. Therefore, canonical correspondence analysis (CCA) made it possible to summarize the overall situation for the species, monthly sampling, and environmental parameters on a single graph.

CONCLUSIONS

Thus, the temperature, turbidity, and chlorophyll a content are the most often reported factors for the distribution and structure of amphipods in the Bizerte lagoon.

Subtle effects of biological invasions: cellular and physiological responses of fish eating the exotic pest Caulerpa racemosa

The green alga Caulerpa racemosa var. cylindracea has invaded Mediterranean seabed including marine reserves, modifying the structure of habitats and altering the distributional patterns of associated organisms. However, the understanding of how such invasion can potentially affect functional properties of Mediterranean subtidal systems is yet to be determined. In this study, we show that C. racemosa changes foraging habit of the native white seabream, Diplodus sargus. In invaded areas, we found a high frequency of occurrence of C. racemosa in the stomach contents of this omnivorous fish (72.7 and 85.7%), while the alga was not detected in fish from a control area. We also found a significant accumulation of caulerpin, one of the main secondary metabolites of C. racemosa, in fish tissues. The level of caulerpin in fish tissues was used here as an indicator of the trophic exposure to the invasive pest and related with observed cellular and physiological alterations. Such effects included activation of some enzymatic pathways (catalase, glutathione peroxidases, glutathione S-transferases, total glutathione and the total oxyradical scavenging capacity, 7-ethoxy resorufin O-deethylase), the inhibition of others (acetylcholinesterase and acylCoA oxidase), an increase of hepatosomatic index and decrease of gonadosomatic index. The observed alterations might lead to a detrimental health status and altered behaviours, potentially preventing the reproductive success of fish populations. Results of this study revealed that the entering of alien species in subtidal systems can alter trophic webs and can represent an important, indirect mechanism which might contribute to influence fluctuations of fish stocks and, also, the effectiveness of protection regimes.

The non-native seaweed Asparagopsis armata supports a diverse crustacean assemblage

This is the first study describing the crustacean fauna associated to Asparagopsis armata, a non-native, red seaweed widely distributed along western Mediterranean coasts. First found in Australia and New Zealand, it was introduced naturally through the Strait of Gibraltar and rapidly spread out. A one-year spatio-temporal study (Feb 08-Feb 09) was carried out in the Strait of Gibraltar to characterize the spatio-temporal patterns of the associated crustacean fauna. Maximum biomass of A. armata was measured during April-June, whereas the maximum crustacean abundances were registered from June-October. In total 41 crustacean species were identified. The caprellid Caprella penantis, traditionally associated to non-polluted areas, was more abundant on Tarifa Island (higher values of dissolved oxygen and pH) than in Algeciras (lower oxygen and pH). The gammarid Podocerus variegatus was dominant in Algeciras Bay while Hyale schmidti and Apherusa mediterranea were the most abundant on Tarifa Island. Among isopods, Synisoma nadejda was only found on Tarifa Island. When compared with literature of native algae of the intertidal and shallow sublittoral, the species richness of associated crustaceans was similar in A. armata and the natives. Very little is known about the influence of this algae on altering marine communities, so complete faunistic studies dealing with other groups such as polychaetes or molluscs are necessary to properly address biogeographical, ecological and management programmes dealing with this non-native species.