Habitat provision of barnacle tests for overcrowded periwinkles

In habitats where competition for space is a shaping force of animal distribution such as in the intertidal rocky ecosystem, new habitats are readily taken by colonising species. We examined the importance of empty Chthamalus spp. tests as a habitat for the intertidal common periwinkle Melaraphe neritoides on Portuguese rocky shores. The role played by the space between neighbouring barnacles as a habitat for other species has been largely studied with regard to how an ecosystem functions, whereas the equivalent role of empty barnacle tests remains largely unknown. The small periwinkle is one of the most abundant snails in European rocky shores and is an important prey for key mobile predators. Biological facilitation is common in the rocky intertidal zone, where biological structures often potentiate the abundance of other species. The role played by barnacles as biological facilitators through habitat provision is not fully understood. In this study, the abundance and morphometric features of empty barnacle tests and their occupants were examined across shore levels and shores with differing exposures, as these are important gradients explaining barnacle distribution. The availability of empty barnacle tests was also experimentally manipulated to examine the percentage, time and length of occupation. Empty barnacles were more abundant on the midshore of sheltered shores and barnacle tests were wider on the upper shore but taller on the midshore. The minimum barnacle test occupation rate by the periwinkle was 70%. Barnacle shell height was an important factor determining snail occupation, where taller barnacles harboured significantly more, but not necessarily larger, snails. Snails outside the barnacle tests were significantly larger than those found within, suggesting that this crustacean group has an increased importance as a habitat for juvenile snails, thus potentially influencing the population dynamics of M. neritoides. We found that occupation of experimentally created empty barnacles was extremely high (70%) on the day after, and remained at 100% after 3 months of monitoring. Our study is the first of its kind to focus on the features of barnacle tests that snails occupy and their occupying snail traits. According to our results, it is clear that barnacles have an important role in providing additional habitat for young gastropods. The small periwinkle is an important grazer and prey for intertidal and subtidal foraging predators; hence, the potential refuge role of barnacle tests for juvenile M. neritoides may be important in the dynamics of intertidal communities.     

Temporal and spatial biomonitoring of heavy metals in eastern Aegean coastal waters using Amphibalanus amphitrite

This biomonitoring study presents the spatial and temporal distributions of heavy metals in the soft tissues of a major fouling species Amphibalanus amphitrite living on hard substrate at different sites along the eastern Aegean coast. A. amphitrite has been chosen as a strong candidate for monitoring heavy metals. Sediment and seawater samples were also collected to detect their metal contents in order to gain more information on the environmental conditions and possible bioaccumulation patterns. The physico-chemical characteristics of sampling stations have been measured in order to characterize the sampling area. The order of metal concentrations in barnacles, sediment and seawater decreased in the following order Cu > Fe > Zn > Mn > Cd > Cr > Pb > Hg, Fe > Mn > Zn > Cu > Pb > Cr > Hg > Cd and Fe > Zn > Mn > Cu > Pb > Cr > Cd > Hg, respectively. These results showed that barnacles accumulate Cu in a higher degree than both sediment and seawater. Moreover, metal concentrations in barnacle have the potential for use in any future regulatory framework monitoring and eventually controlling ambient metal pollution levels.     

Vertical distribution of barnacle larvae at a fixed nearshore station in southern California: Stage-specific and diel patterns

Patterns of vertical distribution in marine invertebrate larvae interact with coastal hydrodynamics to determine cross-shore distributions, dispersal ranges, and scales of connectivity among populations. We present observations on the vertical distribution of barnacle larvae from southern California, collected from 3 depth intervals every 2 h and over a 48-h period at a fixed nearshore station. Larvae were identified to species and stage of development, and their vertical distributions were tested for day/night and between-stage differences within each species, as well as for correlations with environmental variability. Stage-specific patterns of vertical distribution were distinct and consistent across species. Nauplii were most abundant near the surface at all times, and were numerically dominated by Chthamalus spp. (78% of N_n = 1835). Cyprids were substantially less abundant than nauplii in our samples (N_c = 146) and corresponded mostly to the subtidal barnacle Balanus nubilus (84%). Despite the lower counts and different species composition, our data suggest that cyprids remain within the mid-depth and bottom layers, and that changes in their mean depth of distribution (MDD) may track changes in pycnocline depth. Temporal changes in nauplii MDD were not correlated with water-column variability, wind forcing, or tidal height. The apparent vertical segregation of nauplii and cyprids may be related to previously documented differences in the cross-shore distribution of these stages.     

Different crab species influence feeding of the snail Nucella lapillus through trait‐mediated indirect interactions

Indirect interactions are among the many important factors that influence the community structure of the rocky intertidal zone. Trait‐mediated indirect interactions, in which the presence of a predator or competitor can influence the relationship between two other species, have emerged as vital for understanding community dynamics. This study examined the effect of different crab species on the feeding habits of an intertidal snail, Nucella lapillus. Crab species were defined as being sympatric predatory (Carcinus maenas and Cancer irroratus), sympatric non‐predatory (Uca pugnax and Pagurus longicarpus), or allopatric predatory (Mithrax sculptus and Percnon gibbesi). Nucella lapillus were potentially exposed to risk cues from each of the crab species. Crabs were kept in perforated boxes, which allowed any chemical cues to be emitted but prevented direct contact. Nucella lapillus had significantly lower feeding rates in the presence of sympatric predatory crab species than N. lapillus exposed to either sympatric non‐predatory crabs or allopatric predatory crabs. There was no difference in feeding rate between N. lapillus exposed to the sympatric non‐predatory crabs and to the allopatric predatory crabs. Nucella lapillus in the presence of sympatric predatory crabs had a feeding rate of only 0.07 barnacles per snail per day, whereas N. lapillus housed with non‐predatory crabs and allopatric predatory crabs had rates of 0.11 and 0.12, respectively, suggesting that N. lapillus alter their behavior in response to chemical risk cues from local predators. These results suggest that the ability to detect and respond to risk cues is a selectively evolved trait.     

Assessment of organotin (butyltin species) contamination in marine biota from the Eastern Aegean Sea, Turkey

The marine environment continues to be adversely affected by tributyltin (TBT) release from maritime traffic. Therefore the concentrations of TBT, dibutyltin (DBT) and monobutyltin (MBT) were measured in barnacles, mussels and fish along the Eastern Aegean coastline. The average concentrations of TBT ng Sn g⁻¹ were found to be 235 in fish, 116 in mussels and 635 in barnacles. The highest concentrations of TBT, DBT and MBT were observed in the barnacles which had been sampled in marinas and harbors. All mussels sampled showed values of TBT + DBT, which were below the “tolerable average residue level (TARL)” as currently accepted. This indicates a lack of risk to the consumer. However, 7 out of the 15 fish sampled displayed TBT + DBT levels above the TARL, which indicates that a fish consumer group may be at risk. Barnacles have high potential as biomonitors for the presence of organotin in the Aegean Sea.     

Epibiotic community on the acorn barnacle (Balanus amphitrite) from a monsoon‐influenced tropical estuary

The epibiotic communities (diatoms and metazoans) on the outer surfaces of the shell of the barnacle Balanus amphitrite (BSh) and its opercular valves (the scutum and tergum; BST) were investigated on a monthly basis for 1 year in a tropical monsoon‐influenced estuary and compared with that of the surrounding rock biofilm. BSh and BST were rich in the diatoms Achnanthes longipes and Melosira nummuloides and amongst the invertebrates, nematodes and tardigrades were abundant. To the best of our knowledge, this is the first report of epibiosis on the acorn barnacle. Diatom abundance was at its maximum during the monsoon season on all the inter‐tidal substrata i.e. BSh, BST and rock. A significant correlation was found between the density of diatoms and invertebrates associated with the BSh and BST, possibly because of the trophic relationship between them or the suitability of the physical environment. The possible role of these epibionts on the settlement of this barnacle species is currently unknown and needs further investigation.     

Toxic effects of copper on larval development of the barnacle Balanus amphitrite

Experiments were conducted to assess the effects of copper on larval development in the barnacle Balanus amphitrite. In the first experiment, we compared the sensitivity of three naupliar stages to copper stress. Molting inhibition occurred at copper concentrations ranging from 32 μg l⁻¹ in nauplius II to 128 g l⁻¹ in nauplius VI. EC₅₀ for molting ranged from 97 μg l⁻¹ in nauplius II to 129 g l⁻¹ in nauplius VI. Decreased survival occurred at 128 μg Cu l⁻¹ in all of the naupliar stages tested, with LC₅₀ ranging from 145 in nauplius II to 213 μg l⁻¹ in nauplius VI. In the second experiment, we examined effects of copper on the development from nauplius II to cyprid. The larvae reached cypris stage only in treatments of 16 μg Cu l⁻¹. Our study therefore showed that molting was a more sensitive endpoint than survival, nauplius II was the most sensitive naupliar stage, and that whole larval development assay was more sensitive than assays using a particular larval stage. The results were discussed with respect to the use of this species in toxicity tests.