Colonization patterns of the date mussel Lithophaga lithophaga (L., 1758) on limestone breakwater boulders of a marina

Background and Purpose: The European date mussel (Lithophaga lithophaga) is widespread along the whole Mediterranean rocky coastline where it is frequently but illegally harvested. It is well known that the growth of the date mussel is very slow; however, patterns of recolonization of exploited surfaces have been scarcely investigated. The objective of this study is to assess colonization patterns of the date mussel on limestone boulders which have been in the sea for 19 years. These results could be useful in predicting the reconstitution of natural populations of the date mussel after harvesting. Materials and Methods: Limestone breakwater boulders were placed along the dike of the Marina of Rovinj (northern Adriatic, Istrian peninsula, Croatia) in 1984. Sampling was carried out in summer 2003 by SCUBA diving from six habitats of different inclination and topography: horizontal, inclined, vertical, sheltered, vaults, and whole stones. The abundance and biomass of L. lithophaga at the Marina were compared with those in natural control locations. Results: At the Marina, no date mussels were found on the horizontal and inclined sides of the boulders, and very few date mussels were found on the vertical side. On the contrary, sheltered and vault sides of boulders and whole stones were intensively colonized by L. lithophaga. In vaults, the abundance was similar to that in nature. In these habitats, L. lithophaga biomasswas generally lower than in nature. However, large date mussels, of lengths from 50 to 70 mm, were already present on boulders of theMarina. They amounted to 35% in the sheltered habitat, 24% in vaults, and 3% of the total number in whole stones. Conclusions: An unexpected high colonization rate and growth of date mussels was detected in certain unexposed rocky habitats at the boulders of the Marina. However, on the natural rocky Istrian coast, the date mussel was mostly collected on exposed inclined and vertical rocky surfaces where repopulation after harvesting may require very long periods

Preliminarno istraživanje raznolikosti bezkralježnjaka unutar naselja alge Corallina officinalis na području južne Istre

Red coralligenous algae Corallina officinalis provides shelter to many invertebrate species from wave actions, predation and desiccation stress in the intertidal area. Physical structure and complexity of the habitat have a major influence on biodiversity of this community. The aim of this preliminary study was to examine the diversity of invertebrate assemblages inside the red algae C. officinalis turf. Three sampling locations were chosen where algal cover range was above 90%. On each location sampling was done quantitatively by scraping off within 3 replicate quadrats 20 x 20 cm in size. A total of 30,518 specimens were isolated from all sampling locations. The prevalent groups were amphipod crustaceans, polychaetes, bivalves and gastropods that made a total of 86% of all macrofaunal groups associated with algal turfs. The most abundant group were amphipods that made 42% of the total separated individual invertebrates. Our study demonstrated that C. offic-inalis is a very important habitat with high abundance and diversity of invertebrate assemblages.Crvena inkrustirajuća alga Corallina officinalis pruža zaklon mnogim beskralješnjacima u području mediolitorala od djelovanja valova, predacije i isušivanja. Karakteristična struktura i složenost staništa imaju veliki utjecaj na bioraznolikost ove zajednice. Cilj ovog rada bio je istražiti raznolikost faune beskralješnjaka unutar naselja crvene alge C. officinalis. Tri lokacije uzorkovanja odabrane su na području gdje je pokrivenost algom bila veća od 90%. Na svakoj lokaciji uzorko-vanje je provedeno kvantitativno u 3 replikata, struganjem unutar kvadrata veličine 20 x 20 cm. Ukupno je izolirano 30.518 jedinki, a dominantne skupine bile su amfipodni rakovi, mnogočetinaši, školjkaši i puževi. Ovi taksoni su činili ukupno 86% svih beskralješnjaka pronađenih unutar staništa alge. Naj-brojnija skupina su amfipodni rakovi koji su činili 42% ukupnih izoliranih beskralježnjaka. Naše je istraživanje pokazalo da je naselje alge C. officinalis vrlo važno stanište s visokom brojnošću i raznolikošću beskralješnjaka

Promjene sastava masnih kiselina u algi Fucus virsoides J. Agardh na različitim podlogama

The effect of the substratum type (natural, limestone, or artificial, concrete) on the fatty acid composition of Fucus virsoides in six habitats around the harbours and beaches of the Istrian coast (northern Adriatic Sea) was investigated during the summer, the period of maximum development. All habitats of F. virsoides were regulated by very similar environmental factors and were exposed to moderate anthropogenic influences. F. virsoides growing on artificial substrata was characterised by lower concentrations of fatty acids, lower proportions of fatty acids among total lipids, higher C16:0/18:1 ratios (FA: 6.7±0.6 mg g-1 d.w.; FA/TL: 22%; 16:0/18:1: 0.57±0.08) and an overall increase in saturation in comparison to communities growing on natural substrata (FA: 10.2±2.9–12.5±3.4 mg g-1 d.w.; FA/TL: 30.8–33.7%; 16:0/18:1: 0.34±0.11–0.45±0.13). These results likely reflect the less favourable conditions for F. virsoides development on artificial substrates relative to natural substrates. The physiological processes of the algae growing on artificial substrata were more impaired with increasing age (FA: 1.9±0.6 mg g-1d.w.; FA/TL: 18.2%; 16:0/18:1: 0.68±0.08).U proljeće tijekom maksimuma vegetacijskog razvoja smeđe alge Fucus virsoides istražen je učinak podloge (prirodna, vapnenac ili umjetna, beton) na sastav masnih kiselina u algi. Uzorkovano je na šest staništa, uključujući luke i plaže, duž istarske obale (sjeverni Jadran). Sva staništa su bila pod utjecajem vrlo sličnih okolišnih čimbenika, i izložena umjerenom antropogenom utjecaju. Za vrstu F. virsoides na umjetnoj podlozi karakteristična je niža koncentracija masnih kiselina (MK), njihov niži udio u ukupnim lipidima (UL), povišeni C16:0/18:1 omjeri (MK: 6.7±0.6 mg g -1 s.t.; MK/UL: 22%; 16:0/18:1: 0.57±0.08) te veća zasićenost u usporedbi sa zajednicama na prirodnoj podlozi (MK: 10.2±2.9–12.5±3.4 mg g-1s.t.; MK/UL: 30.8–33.7%; 16:0/18:1: 0.34±0.11–0.45±0.13). Dobiveni rezultati odražavaju nepovoljne uvjete za rast i razvoj vrste F. virsoidesna umjetnoj podlozi u odnosu na prirodnu. Na umjetnoj podlozi je utvrđeno lošije fiziološko stanje u starijim primjercima alge (MK: 1.9±0.6 mg g-1 s.t.; MK/UL: 18.2%; 16:0/18:1: 0.68±0.08)

Promjene sastava masnih kiselina u algi Fucus virsoides J. Agardh na različitim podlogama

The effect of the substratum type (natural, limestone, or artificial, concrete) on the fatty acid composition of Fucus virsoides in six habitats around the harbours and beaches of the Istrian coast (northern Adriatic Sea) was investigated during the summer, the period of maximum development. All habitats of F. virsoides were regulated by very similar environmental factors and were exposed to moderate anthropogenic influences. F. virsoides growing on artificial substrata was characterised by lower concentrations of fatty acids, lower proportions of fatty acids among total lipids, higher C16:0/18:1 ratios (FA: 6.7±0.6 mg g-1 d.w.; FA/TL: 22%; 16:0/18:1: 0.57±0.08) and an overall increase in saturation in comparison to communities growing on natural substrata (FA: 10.2±2.9–12.5±3.4 mg g-1 d.w.; FA/TL: 30.8–33.7%; 16:0/18:1: 0.34±0.11–0.45±0.13). These results likely reflect the less favourable conditions for F. virsoides development on artificial substrates relative to natural substrates. The physiological processes of the algae growing on artificial substrata were more impaired with increasing age (FA: 1.9±0.6 mg g-1d.w.; FA/TL: 18.2%; 16:0/18:1: 0.68±0.08).U proljeće tijekom maksimuma vegetacijskog razvoja smeđe alge Fucus virsoides istražen je učinak podloge (prirodna, vapnenac ili umjetna, beton) na sastav masnih kiselina u algi. Uzorkovano je na šest staništa, uključujući luke i plaže, duž istarske obale (sjeverni Jadran). Sva staništa su bila pod utjecajem vrlo sličnih okolišnih čimbenika, i izložena umjerenom antropogenom utjecaju. Za vrstu F. virsoides na umjetnoj podlozi karakteristična je niža koncentracija masnih kiselina (MK), njihov niži udio u ukupnim lipidima (UL), povišeni C16:0/18:1 omjeri (MK: 6.7±0.6 mg g -1 s.t.; MK/UL: 22%; 16:0/18:1: 0.57±0.08) te veća zasićenost u usporedbi sa zajednicama na prirodnoj podlozi (MK: 10.2±2.9–12.5±3.4 mg g-1s.t.; MK/UL: 30.8–33.7%; 16:0/18:1: 0.34±0.11–0.45±0.13). Dobiveni rezultati odražavaju nepovoljne uvjete za rast i razvoj vrste F. virsoidesna umjetnoj podlozi u odnosu na prirodnu. Na umjetnoj podlozi je utvrđeno lošije fiziološko stanje u starijim primjercima alge (MK: 1.9±0.6 mg g-1 s.t.; MK/UL: 18.2%; 16:0/18:1: 0.68±0.08)

Diversity and Distribution Patterns of Hard Bottom Polychaete Assemblages in the North Adriatic Sea (Mediterranean)

The knowledge on the hard bottom polychaete assemblages in the Northern Adriatic Sea, a Mediterranean region strongly affected by environmental pressures, is scarce and outdated. The objective of this paper was to update the information on polychaete diversity and depict their patterns of natural spatial variation, in relation to changes in algal coverage at increasing depth. Hard bottom benthos was quantitatively sampled by scraping off the substrate from three stations at Sveti Ivan Island (North Adriatic) at three depths (1.5 m, 5 m and 25 m). Polychaete fauna comprised 107 taxa (the majority of them identified at species level) belonging to 22 families, with the family Syllidae ranking first in terms of number of species, followed by Sabellidae, Nereididae, Eunicidae and Serpulidae. Considering the number of polychaete species and their identity, the present data differed considerably from previous studies carried out in the area. Two alien species, Lepidonotus tenuisetosus, which represented a new record for the Adriatic Sea, and Nereis persica, were recorded. The highest mean abundance, species diversity and internal structural similarity of polychaete assemblages were found at 5 m depth, characterised by complex and heterogeneous algal habitat. The DISTLM forward analysis revealed that the distribution of several algal taxa as well as some algal functional-morphological groups significantly explained the observed distribution patterns of abundance and diversity of polychaete assemblages. The diversity of the North Adriatic hard bottom polychaete fauna is largely underestimated and needs regular updating in order to detect and monitor changes of benthic communities in the area

The effects of an invasive seaweed on native communities vary along a gradient of land-based human impacts

The difficulty in teasing apart the effects of biological invasions from those of other anthropogenic perturbations has hampered our understanding of the mechanisms underpinning the global biodiversity crisis. The recent elaboration of global-scale maps of cumulative human impacts provides a unique opportunity to assess how the impact of invaders varies among areas exposed to different anthropogenic activities. A recent meta-analysis has shown that the effects of invasive seaweeds on native biota tend to be more negative in relatively pristine than in human-impacted environments. Here, we tested this hypothesis through the experimental removal of the invasive green seaweed, Caulerpa cylindracea, from rocky reefs across the Mediterranean Sea. More specifically, we assessed which out of land-based and sea-based cumulative impact scores was a better predictor of the direction and magnitude of the effects of this seaweed on extant and recovering native assemblages. Approximately 15 months after the start of the experiment, the removal of C. cylindracea from extant assemblages enhanced the cover of canopy-forming macroalgae at relatively pristine sites. This did not, however, result in major changes in total cover or species richness of native assemblages. Preventing C. cylindracea re-invasion of cleared plots at pristine sites promoted the recovery of canopyforming and encrusting macroalgae and hampered that of algal turfs, ultimately resulting in increased species richness. These effects weakened progressively with increasing levels of land-based human impacts and, indeed, shifted in sign at the upper end of the gradient investigated. Thus, at sites exposed to intense disturbance from land-based human activities, the removal of C. cylindracea fostered the cover of algal turfs and decreased that of encrusting algae, with no net effect on species richness. Our results suggests that competition from C. cylindracea is an important determinant of benthic assemblage diversity in pristine environments, but less so in species-poor assemblages found at sites exposed to intense disturbance from landbased human activities, where either adverse physical factors or lack of propagules may constrain the number of potential native colonizers. Implementing measures to reduce the establishment and spread of C. cylindracea in areas little impacted by land-based human activities should be considered a priority for preserving the biodiversity of Mediterranean shallow rocky reefs