Short-term effects of trampling on intertidal Mytilus galloprovincialis beds.

Human trampling represents one of the main anthropogenic pressures in the rocky intertidal. This habitat includes many ecosystem engineers such as mussels that provide biogenic habitat and multiple services. This research assessed potential impacts of human trampling on beds of the mussel, Mytilus galloprovincialis, on NW shores of Portugal. To test for direct effects of trampling on mussels and indirect effects on the associated assemblages, three treatments were applied: control (untouched beds), low and high intensity of trampling. Effects of trampling were dependent on the taxa. Thus, values of shell length of M. galloprovincialis were greater under the highest intensity of trampling while abundances of Arthropoda, Mollusca and Lasaea rubra showed the opposite pattern. Moreover, total number of taxa and abundances of Nematoda and Annelida showed higher values under low trampling intensity. The implications of these results to manage human use in areas with ecosystem engineers are discussed.

Effects of habitat homogenisation on assemblages associated with mussel clumps.

Biodiversity loss is considered one of the main threats to marine ecosystems. In this framework of biodiversity decline, organisms that provide biogenic habitat play a relevant role by their capacity to structure assemblages and influence ecological processes. The Mediterranean mussel Mytilus galloprovincialis is considered an ecosystem engineer because it alters local environmental conditions maintaining habitat suitability for other organisms, and enhancing local biodiversity. Although it is widely recognized that mussel beds increase diversity, the drivers shaping these assemblages are poorly explored. We investigate whether mussel size homogenisation shapes the abundance, richness and structure of macrobenthic assemblages associated with mussel beds in two shores of the Galician coast (NW Spain). At each shore, two sites, 10 m apart, were selected and at each site, faunal assemblages were compared between mussel clumps showing shells of various sizes (control), and mussel clumps with closely similar-sized mussels, considered as homogenised. Homogenised clumps showed, in general, higher values in total number of individuals and species than control clumps. Regarding the effect of mussel size homogenisation on the multivariate structure of the assemblages, significant differences between control and homogenised clumps were found in three out of the four sites. Most relevant associated species usually reached higher abundances in homogenised clumps than control ones. Therefore, mussel size homogenisation influenced the structure of the macrofaunal assemblages associated with mussel beds but, its effect was context dependent (i.e., varied with sites). Information about the species contribution to dissimilarities among homogenised and control clumps was provided and the potential influence of sediment and algae on mussel clumps was discussed.

Reproductive Cycle of the Seagrass Zostera noltei in the Ria de Aveiro Lagoon.

Sexual reproduction in seagrasses is essential to increase their resilience towards environmental stressors, but its phenology is still unknown in some regions, limiting our knowledge about the recovery capacity of these ecosystems. In this study, the flowering effort, reproductive phenology, seed production and ability of germination of Zostera noltei was studied for the first time in the Ria de Aveiro lagoon, Portugal. Flowering of Z. noltei in the Ria de Aveiro lasts from June to November, reaching a peak between July and August. All the meadows showed similar flowering effort and phenology over time. Comparing with other European populations, the flowering effort of Z. noltei in Ria de Aveiro lasted for a longer period, which could be related with the milder temperatures in summer and autumn and the great anthropogenic stress to which the meadows are subjected in the lagoon. The number of seeds produced and their ability of germination were similar among meadows and sampling periods, reaching levels similar to those of other European regions. Nevertheless, future studies are needed to determine the fate of the produced seeds in the field to have a better understanding about the natural recovery capacity of the species.

Sediment Characteristics Determine the Flowering Effort of Zostera noltei Meadows Inhabiting a Human-Dominated Lagoon.

Recent studies have shown increasing Zostera noltei meadows in areas modified by anthropogenic activities. However, it is not entirely clear whether this trend of expansion could be linked to a greater reproductive effort in the species. Anthropogenic stressors can induce the reproductive effort of seagrass meadows as a response to stress, but other variables, such as seagrass biometrics or environmental factors, can also influence their sexual reproduction. To increase the knowledge regarding this issue, we monitored the flowering effort, seagrass biometrics and abiotic parameters of three Z. noltei meadows in an area that has been highly modified by anthropogenic activities during the past decades. Results showed that silt and clay content in the sediment (strongly correlated with organic matter) and seagrass vertical shoot density explained 54% of the variability in the flowering effort of the meadows. This study suggests that stress-induced flowering of Z. noltei may occur under determinate environmental conditions, such as silty environments with organic enrichment.

Spatial-temporal variability of Mytilus galloprovincialis Lamarck 1819 populations and their accumulated sediment in northern Portugal.

Mytilus galloprovincialis is an ecosystem engineer that provides habitat and generates environmental heterogeneity, increasing local biodiversity. Moreover, it is an economically important species representing 14% of the global production of marine bivalves. Natural drivers and the increase of anthropogenic pressures, such as sediment stress, influence its populations on rocky shores. The objective of this study was to explore the spatial-temporal patterns of different M. galloprovincialis attributes along the north of Portugal. For that purpose, six rocky shores were selected and sampled six times along the year 2019. The percentage of cover, density, spat density, condition index, clump thickness, size classes and clump sediment content were considered. Results showed the lack of seasonality in M. galloprovincialis along the north coast of Portugal. However, density, spat stage, clump thickness, condition index and size classes showed some variability among dates and shores. The percentage cover and sediment content only significantly differed among shores. Our results indicated an absence of seasonality for all the studied variables, probably because temperature was always within the optimum range for this species and the abundance of food supply in the study area independently of the season. The accumulated sediment on mussel clumps did not show any temporal variability with only significant differences among shores. The accumulated sediment was composed mainly by medium and coarse sand and it was correlated with mussel average size, condition index, but especially with the mussel clump thickness.

The role of urbanisation in affecting Mytilus galloprovincialis.

Urbanisation is considered as one of the most critical and widespread threats to coastal marine ecosystems. The aim of this study was to compare the density, percentage cover, thickness of clumps, condition index and size-frequency distribution of Mytilus galloprovincialis between urban and non-urban shores, at nested spatial scales, in the Northern Portuguese coast. M. galloprovincialis was selected as model because it is economically and ecologically relevant. Moreover, the relationship between mussel size and the other variables (i.e. density, percentage cover, thickness and condition index) were investigated. Mussels on urban shores showed a smaller density and a greater frequency of larger individuals. A significant negative correlation between mussel length with density and with thickness of clumps was also found. Our results seem to indicate that recruitment has declined on urban shores and, as a result, intraspecific competition is also smaller, leading to more resources being available for a fewer individuals which can reach larger sizes. As mussel beds support a great biodiversity of invertebrates and provide many ecosystem services, urbanisation may have indirect effects on communities associated with mussels. Understanding the vulnerability of mussel beds to urbanisation could inform management.

Carbon and nitrogen stable isotopes in coastal benthic populations under multiple organic enrichment sources.

In a dispersive coastal area under multiple organic enrichment sources, stable isotopes were used to trace organic sources of carbon and nitrogen in sediments and benthic macrofauna. The Bivalve Abra alba and the Polychaetes Nephtys sp. and Pectinaria (Lagis) koreni were reliable indicators of the input of terrestrial-derived organic matter into this coastal area, either originated in outfall sewage discharges or estuarine outflow. An isotopic depletion was observed up to 250 m from the outfall branches, much stronger in the biota than in the sediments. An enrichment of 2 ‰ in the sediments, and 2-6 ‰ in the species was noticed in sites located farther than 1500 m from the outfall. Depositivores and carnivores/omnivores gave the best picture of the extension of the sewage dispersion and incorporation into the food web.

Coastal sediments under the influence of multiple organic enrichment sources: An evaluation using carbon and nitrogen stable isotopes.

Sediment descriptors (grain size, total volatile solids, redox potential) and stable carbon and nitrogen isotopes were used to trace the origin of organic matter in a coastal area under multiple organic enrichment sources (urban outfall and a major estuary). The sediments fines content and total volatile solids were similar to outfall pre-operation period (1994), but the incorporation of terrestrial organic matter within the sediments located closer to the outfall was diagnosed by depleted (13)C values (-24.2+/-0.38 per thousand) and (15)N values (2.4+/-0.93 per thousand). Data also indicated depleted nitrogen signature at larger distances from the outfall than the carbon signature, due to confounding sediment grain size properties. Analysis in the bivalve Abra alba gave the same results for both isotopes and thus allowed a coherent interpretation of the spatial extent of the organic enrichment, highlighting the importance of bringing a biological element into the environmental assessment.

Estuarine sediment acute toxicity testing with the European amphipod Corophium multisetosum Stock, 1952.

This study assessed the use of the European amphipod Corophium multisetosum Stock [Stock, J.H., 1952. Some notes on the taxonomy, the distribution and the ecology of four species of the genus Corophium (Crustacea, Malacostraca). Beaufortia 21, 1-10] in estuarine sediment acute toxicity testing. The sensitivity of adults to the reference toxicant CdCl(2) was determined in water-only 96 h exposures in salinity 2. LC(50) values ranged from 0.33mgCd(2+)L(-1) at 22 degrees C to 0.57mgCd(2+)L(-1) at 15 degrees C. Adult survival was studied in control sediment with water salinity from 0 to 36 and with fine particles content (<63 microm) from 2% to 97% of total sediment, dry weight. Experiments were conducted at 15, 18 and 22 degrees C and the results indicate that the species can be used under the full salinity range although higher mortality was observed at the lower salinity in the higher water temperature, and at the higher salinity in the lower water temperature. The species also tolerated the studied range of sediment fines content and showed the highest sensitivity at intermediate values of fines, especially at the higher temperature, thus advising that tests which have to accommodate sediments with a wide range in fines content should preferably be conducted at 15 degrees C rather than at 22 degrees C. The response in natural sediments was studied in samples collected yearly from 1997 to 2006, at a site located off the Tagus Estuary, western Portugal. A major flood event in winter 2000-2001 induced detectable alterations in sediment baseline descriptors (grain-size, redox potential and total volatile solids), organic contaminants (PAHs, PCBs, DDT metabolites and gamma-HCH) and the macrofauna benthic community. Mortality of the amphipod diminished significantly from the before to the after flood period, in close agreement with diminishing sediment contamination and increasing benthic fauna diversity, in the same time period. C. multisetosum is suitable to conduct acute sediment toxicity tests and presents good potential for the development of a full life-cycle sediment test, due to its amenability to laboratory culture and high survival in the control sediment.