Genomic Characterization of the Barnacle Balanus improvisus Reveals Extreme Nucleotide Diversity in Coding Regions

Barnacles are key marine crustaceans in several habitats, and they constitute a common practical problem by causing biofouling on man-made marine constructions and ships. Despite causing considerable ecological and economic impacts, there is a surprising void of basic genomic knowledge, and a barnacle reference genome is lacking. We here set out to characterize the genome of the bay barnacle Balanus improvisus (= Amphibalanus improvisus) based on short-read whole-genome sequencing and experimental genome size estimation. We show both experimentally (DNA staining and flow cytometry) and computationally (k-mer analysis) that B. improvisus has a haploid genome size of ~ 740 Mbp. A pilot genome assembly rendered a total assembly size of ~ 600 Mbp and was highly fragmented with an N50 of only 2.2 kbp. Further assembly-based and assembly-free analyses revealed that the very limited assembly contiguity is due to the B. improvisus genome having an extremely high nucleotide diversity (π) in coding regions (average π ≈ 5% and average π in fourfold degenerate sites ≈ 20%), and an overall high repeat content (at least 40%). We also report on high variation in the α-octopamine receptor OctA (average π = 3.6%), which might increase the risk that barnacle populations evolve resistance toward antifouling agents. The genomic features described here can help in planning for a future high-quality reference genome, which is urgently needed to properly explore and understand proteins of interest in barnacle biology and marine biotechnology and for developing better antifouling strategies.

Simulated diurnal pH fluctuations radically increase variance in—but not the mean of—growth in the barnacle Balanus improvisus

Shallow coastal waters are characterized by substantial diurnal fluctuations in pH, especially in nearshore environments. The biological effects of ocean acidification in combination with these natural fluctuations have received relatively little attention to date. We exposed multiple batches (≈ different genotypes) of newly settled barnacles, Balanus improvisus, to constant pH under “control” (pH = 8.1) or “stable acidified” (pH = 7.7) conditions, as well as a treatment that simulated the maximum diurnal pH fluctuations seen in the nearshore habitats where this barnacle lives (±0.2 pH units), superimposed on the stable acidified treatment (“fluctuating acidified”; 7.5 ≤ pH ≤ 7.9). We found that fluctuating acidification had no effect on mean response in growth and shell mineralogy, but caused an ∼20-fold increase in variance of responses, compared with stable acidification. In contrast to these results, we found no effect of fluctuating acidification on variances of response ratios for barnacle survival and shell strength. Similarly, mean survival did not vary significantly with pH. However, we observed a strong negative effect of stable and fluctuating acidification on mean shell strength. Our finding that barnacles respond differently to fluctuating pH than to stable low pH indicate the importance of including fluctuating acidification treatments when studying species that live in variable environments. Importantly, because phenotypic variance is the raw material for natural selection, and thus lays at the heart of evolutionary responses to environmental variability and change, our findings also highlight the need to study changes in variance of—as well as mean—responses to changing ocean climates.

Possible effect of Balanus improvisus on Cerastoderma glaucum distribution in the south-western Caspian Sea

We studied the communities of the invasive Balanus improvisus and native Cerastoderma glaucum populations in the south-western Caspian Sea. The massive movement of live Bivalvia attached to Cirripedia colonies along the studied coastline strengthens the hypotheses asserting the possible negative effects of exotic species on endemic species. Different live stages of both animals including meroplankton and macro-invertebrates were considered in the analysis. Bivalvia larvae showed a downward trend in population, in contrast with an upward trend of Cirripedia larvae from 1996 to 2013. The abundance of C. glaucum decreased west to east along the sea shore in contrast with increasing biomass of B. improvisus. Both Bivalvia and Cirripedia larvae did not show any overlapping temporal abundance. The Cirripedia larvae showed its highest abundance in winter while the bloom of Bivalvia larvae occurred in April and May during 2004–2013. The biomass of B. improvisus reported in this study was higher than those reported for the northern parts and for the middle parts. Distribution patterns of both species were described based on temperature, salinity gradient and local nutrient content. A non-linear growth model of Bivalvia showed the short-term effects of Cirripedia on Bivalvia growth. The controversy between the effects of Cirripedia on the movement of two different Cardiidae (C. glaucum, which is affected by the presence of B. improvisus, and Adacna vitrea with no attached Cirripedia) highlights the contributing role of several other factors including ecosystem degradation.

Species Composition of the Benthic Macroinvertebrates on the Coastline Vegetated Rocky Substrates of the Southern Caspian Sea

For studying benthic macrofaunal composition associated with seagrass rocky beds of the southern Caspian Sea, two time samplings were carried out along the coast line in the winter and summer of 2013. In total, 1,286 specimens of the five species were identified: Pontogammarus maeoticus, Balanus improvisus, Mytilaster lineatus, Palaemon elegans and Alitta succinea. The total recorded abundance was 5,675 and 755 ind./m2, with a biomass of 147,271 and 31,238 mg/m2 in the winter and summer respectively. The collected species in this study are generally non-indigenous (except P. maeoticus) and could potentially have an effect on native benthic fauna, as an additional food source could facilitate the commercially exploited fish stocks. Thus further studies are required to monitor their potential interactions on the Caspian Sea fauna