Disturbance-related patterns in unstable rocky benthic habitats of the north-eastern Baltic coast

Distinct patterns of benthic flora and fauna are produced when unstable rocky substrata are disturbed by water motion. This study investigated occurrence of disturbance-related patterns in benthic boulder habitats on the north-eastern Baltic coast. Sessile assemblages, mostly algae on tops of boulders and barnacles and bryozoans underneath, were found to differ between small (50–150 cm2 upperside surface area) and large (200–800 cm2) boulders. Densities of motile gammaridean amphipods were negatively correlated with boulder size. These patterns may be due to small boulders being displaced by water motion more frequently than large ones. Most of the barnacle shells/tests were remnant empty ones, and the proportion of empty tests and living barnacles was similar underneath small and large boulders, suggesting that degradation/removal of empty tests was not influenced by disturbance associated with boulder size. There was no consistent evidence of algae being affected by boulder size, but the tops of boulders had less algae than the edges, a pattern that is typically associated with high rates of overturning. Confirmation of disturbance as having caused these patterns and thus being an important process for structuring benthic biota in this region could be achieved by further manipulative experimentation

A note on life-history traits and conservation concerns for viviparous Australian seastars (Parvulastra parvivipara and P. vivipara)

The asterinid seastars Parvulastra parvivipara and P. vivipara share atypical viviparous reproductive modes that have made them of interest for research on life-history evolution and population genetics. This article briefly reviews life-history traits of these endemic Australian species and information on distribution and rarity, as well as providing some additional new analysis. Almost exclusive self-fertilisation has led to extreme genetic poverty in both species and viviparity limits dispersal potential causing relatively small geographical ranges. There is some evidence that the number of intertidal boulder-fields harbouring P. parvivipara, and the overall geographical range, may have become reduced in recent years. In addition, approximately 25 % of boulder-fields with P. parvivipara have been colonised by invasive oysters (Magallana gigas). To understand potential effects of oysters on P. parvivipara, we tested for correlations between P. parvivipara abundances and cover of oyster encrustations that included this invader (native + non-native oyster shells were assessed together because they produced similar encrustations and largely could not be differentiated). Linear regression showed no evidence, however, for any correlation. For P. vivipara, population survey data from the mid 1970’s to present shows marked decline in areas of previous abundance. Parallel with this decline, the boulder habitat has experienced infill and siltation and cementing of the substratum by M. gigas, sponges and other encrusters as well as anoxia. Important future research outcomes on consequences of atypical life-history traits may be allowed by continued research on these seastars but only if their populations are able to persist within the small number of boulder-fields where they occur. Current trends may indicate a need for conservation intervention

From ecosystems to socio-economic benefits: A systematic review of coastal ecosystem services in the Baltic Sea

Highlights: • We summarized 20 ecosystem services provided by coastal Baltic ecosystems. • Information on how services translate into socio-economic benefits is lacking. • The deep knowledge gap impairs the sustainable management of the benefits. • We propose a framework with four key measures to close this knowledge gap. • Toxins and Nutrients are the most well-document pressures to these services. Abstract: Seagrass meadows, algal forests and mussel beds are widely regarded as foundation species that support communities providing valuable ecosystem services in many coastal regions; however, quantitative evidence of the relationship is scarce. Using the Baltic Sea as a case study, a region of significant socio-economic importance in the northern hemisphere, we systematically synthesized the primary literature and summarized the current knowledge on ecosystem services derived from seagrass, macroalgae, and mussels (see animated video summary of the manuscript: Video abstract). We found 1740 individual ecosystem service records (ESR), 61% of which were related to macroalgae, 26% to mussel beds and 13% to seagrass meadows. The most frequently reported ecosystem services were raw material (533 ESR), habitat provision (262 ESR) and regulation of pollutants (215 ESR). Toxins (356 ESR) and nutrients (302 ESR) were the most well-documented pressures to services provided by coastal ecosystems. Next, we assessed the current state of knowledge as well as knowledge transfer of ecosystem services to policies through natural, social, human and economic dimensions, using a systematic scoring tool, the Eco-GAME matrix. We found good quantitative information about how ecosystems generated the service but almost no knowledge of how they translate into socio-economic benefits (8 out of 657 papers, 1.2%). While we are aware that research on Baltic Sea socio-economic benefits does exist, the link with ecosystems providing the service is mostly missing. To close this knowledge gap, we need a better analytical framework that is capable of directly linking existing quantitative information about ecosystem service generation with human benefit

Cleaning up seas using blue growth initiatives : Mussel farming for eutrophication control in the Baltic Sea

Eutrophication is a serious threat to aquatic ecosystems globally with pronounced negative effects in the Baltic and other semi-enclosed estuaries and regional seas, where algal growth associated with excess nutrients causes widespread oxygen free “dead zones” and other threats to sustainability. Decades of policy initiatives to reduce external (land-based and atmospheric) nutrient loads have so far failed to control Baltic Sea eutrophication, which is compounded by significant internal release of legacy phosphorus (P) and biological nitrogen (N) fixation. Farming and harvesting of the native mussel species (Mytilus edulis/trossulus) is a promising internal measure for eutrophication control in the brackish Baltic Sea. Mussels from the more saline outer Baltic had higher N and P content than those from either the inner or central Baltic. Despite their relatively low nutrient content, harvesting farmed mussels from the central Baltic can be a cost-effective complement to land-based measures needed to reach eutrophication status targets and is an important contributor to circularity. Cost effectiveness of nutrient removal is more dependent on farm type than mussel nutrient content, suggesting the need for additional development of farm technology. Furthermore, current regulations are not sufficiently conducive to implementation of internal measures, and may constitute a bottleneck for reaching eutrophication status targets in the Baltic Sea and elsewhere. Highlights • Mussel farming is a viable internal measure to address Baltic Sea eutrophication. • Rates of nutrient removal depend on salinity at the regional scale and food availability at the local scale. • Cost effectiveness of nutrient removal by mussel farming depends also on farm type. • Total farm area needed for achieving HELCOM nutrient reduction targets is realistic

Correction: First evidence of biogenic habitat from tubeworms providing a near-absolute habitat requirement for high-intertidal Ulva macroalgae.

[This corrects the article DOI: 10.1371/journal.pone.0176952.]

First evidence of biogenic habitat from tubeworms providing a near-absolute habitat requirement for high-intertidal Ulva macroalgae.

Disturbances in ecological systems can cause new resources to become available and can free the resources held by strongly competitive species. In intertidal boulder fields, wave-action causes disturbance by overturning boulders and freeing space for re-colonisation. In this study, mensurative experiments showed that boulder disturbance may also cause new biogenic-habitat resources to become available, if pre-disturbance boulders originally had tubeworm encrustations on their undersides. On the high-shore of a South Australian rocky coast, a small proportion of boulders had extensive encrustations of serpulid and spirorbid worm-tubes on their uppersides, and were likely to have recently been overturned, as spirorbid tubeworms are almost always only underneath boulders while living. Ulva macroalgae was absent from all boulders, except those with worm-tubes, where up to 61% Ulva cover was observed. Many boulders with tubes did not, however, have much algae, and this was likely caused by grazing. While limpets were seldom observed attached to tube encrustations, snails such as Nerita atramentosa and Bembicium nanum were equally abundant on and off tubes. N. atramentosa was likely the main grazer, as its densities were negatively correlated with Ulva cover. The mechanism causing association of Ulva and worm-tubes is unknown, but may be related to retention of moisture or algal spores within the complex topography of the tubes. Alternatively, some tubes may still have been living and providing nutrients for Ulva from excretory products. This study takes the first step towards understanding a very distinct habitat requirement which allows an important alga to persist in the hostile environment of the rocky-intertidal high shore

Density of the grazer <i>Nerita atramentosa</i> is positively correlated with <i>Ulva</i> algae cover.

<p>Correlation between density of the grazer <i>N</i>. <i>atramentosa</i> and cover of <i>Ulva</i> (arcsine transformed; [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0176952#pone.0176952.ref049" target="_blank">49</a>]) on boulders which had serpulimorph tubes. Linear regression was used to visually represent the result from the permutational ANCOVA. Data were pooled from three random sites; <i>n</i> = 10.</p

First evidence of biogenic habitat from tubeworms providing a near-absolute habitat requirement for high-intertidal <i>Ulva</i> macroalgae

<div><p>Disturbances in ecological systems can cause new resources to become available and can free the resources held by strongly competitive species. In intertidal boulder fields, wave-action causes disturbance by overturning boulders and freeing space for re-colonisation. In this study, mensurative experiments showed that boulder disturbance may also cause new biogenic-habitat resources to become available, if pre-disturbance boulders originally had tubeworm encrustations on their undersides. On the high-shore of a South Australian rocky coast, a small proportion of boulders had extensive encrustations of serpulid and spirorbid worm-tubes on their uppersides, and were likely to have recently been overturned, as spirorbid tubeworms are almost always only underneath boulders while living. <i>Ulva</i> macroalgae was absent from all boulders, except those with worm-tubes, where up to 61% <i>Ulva</i> cover was observed. Many boulders with tubes did not, however, have much algae, and this was likely caused by grazing. While limpets were seldom observed attached to tube encrustations, snails such as <i>Nerita atramentosa</i> and <i>Bembicium nanum</i> were equally abundant on and off tubes. <i>N</i>. <i>atramentosa</i> was likely the main grazer, as its densities were negatively correlated with <i>Ulva</i> cover. The mechanism causing association of <i>Ulva</i> and worm-tubes is unknown, but may be related to retention of moisture or algal spores within the complex topography of the tubes. Alternatively, some tubes may still have been living and providing nutrients for <i>Ulva</i> from excretory products. This study takes the first step towards understanding a very distinct habitat requirement which allows an important alga to persist in the hostile environment of the rocky-intertidal high shore.</p></div

Frequency distribution of percentage covers of algae (filled bars), and tubes of serpulimorph polychaetes (white bars) across the sampled boulders.

<p>Frequency distribution of percentage covers of algae (filled bars), and tubes of serpulimorph polychaetes (white bars) across the sampled boulders.</p

Amounts of <i>Ulva</i> algae differ significantly between boulders with vs without worm-tubes.

<p>Amounts of <i>Ulva</i> algae differ significantly between boulders with vs without worm-tubes.</p