Search

Competition for resources, which often results in resource tradeoffs, is intense among sessile benthic organisms. In this investigation, we tested the tradeoffs between the primary and secondary functions by studying the influence of spatial competitor Zoanthus sansibaricus on the reproductive outcome of the sponge Cinachyrella cf. cavernosa. Field studies were carried out at a rocky intertidal beach at Anjuna, Goa, India, from October 2013 to September 2015. C. cf. cavernosa reproduces asexually via ‘budding’ that comprises three stages (Stage I–III) with distinctive morphological and skeletal characteristics. The budding frequency was positively regulated by temperature of the rock pool water and negatively by the substrate cover of Z. sansibaricus. In the absence of the spatial competitor Z. sansibaricus, there was a significant increase in budding frequency (10–30%), bud count per sponge (45–60%), bud settlement probability (60–80%) and physiological activity (RNA/DNA ratio) of buds (10–35%). Over-expression (75–80%) of heat shock protein 70 (stress response) was observed in the sponge during the competitive interaction. This investigation shows that spatial competition adversely affects asexual reproduction of C. cf. cavernosa, and it supports the earlier observations of tradeoffs between the primary and secondary functions. [ABSTRACT FROM AUTHOR]

The effect on bottom organisms of periodic freezing of the upper layer of intertidal sediments during abnormal cold winters has been studied for a long time in seas of a moderate climatic zone. However, the effect of ice cover every year on intertidal communities in polar seas is still poorly investigated. Seasonal and long-term variation in the structure of intertidal soft-bottom communities in two small bights in the White Sea with annual ice cover was studied for over two decades. Sampling was carried out four times a year, in the hydrological spring, summer, autumn, and winter. It was found that bottom macrobenthic communities at upper and lower horizons of the intertidal distinctly differed in the studied sites. Periodic changes caused by the effect of abnormal ice conditions, including the partial removal by ice of sediment with in situ organisms, were discovered. Recovery of communities after disturbance normally took less than half a year. Communities at the lower and upper horizons of the intertidal zone were more stable than intermediate communities, which led to periodic shifts of the biological border between lower and upper intertidal assemblages. [ABSTRACT FROM AUTHOR]

The level of fluctuating asymmetry (FA), which is defined as random deviations from perfect bilateral symmetry in the morphological traits of an organism, increases with increasing developmental instability, and it may be used as an indicator of environmental and/or genetic stresses. This study attempted to relate FA levels in the opercular plates of the barnacle Amphibalanus ( Balanus) amphitrite with shore height and body trace metal concentrations. Barnacles were collected from both low and mid shores at six coastal locations with various degrees of marine pollution in Hong Kong. Four opercular traits, namely scutum length, tergum length, scutum width, tergum width were measured in the specimen while concentrations of five common trace metals (Cd, Cu, Cr, Mn and Zn) were determined in their body tissues using inductively coupled plasma-atomic emission spectrophotometry. Among the four traits, only tergum length and scutum width fulfilled the assumption of FA while their measurement errors were low. Across all sites, mid-shore A. amphitrite consistently exhibited a significantly higher FA level in scutum width than that in low-shore barnacles, but FA levels in tergum length were similar between the two shore heights. These results suggested that FA was trait-dependent, and mid-shore barnacles were possibly under high physical stress, such as desiccation and high temperature, leading to high developmental instability. Although no positive association was observed between FA and metal contamination in low-shore A. amphitrite, FA level in tergum length significantly increased with decreasing body concentration of manganese (Mn) in these barnacles. Such a negative relationship may be explained by the mechanism of bioaccumulation and physiological role of Mn in A. amphitrite with respect to the formation of barnacle shell plates. [ABSTRACT FROM AUTHOR]

In situ measurements of both community metabolism (primary production and respiration) and PAM fluorometry were conducted during emersion on intertidal sediments in the Mont Saint-Michel Bay, in areas where oysters and mussels were cultivated. Results highlighted a low benthic metabolism compared to other intertidal areas previously investigated with the same methods. Comparisons between gross community primary production and relative electron transport rates confirmed this statement. More specifically, primary productivity remained very low all over the year, whereas the associated microalgal biomass was estimated to be high. We suggest that the microphytobenthic community studied was characterized by a self-limitation of its primary productivity by its own biomass, as previously shown in Marennes-Oléron Bay for example. The almost permanent high biomass would represent a limiting factor for micromigration processes within the first millimetres of the sediment. This could be explained by very low resuspension processes occurring in the western part of the bay, enhanced by the occurrence of numerous aquaculture structures that could decrease tidal currents in the benthic boundary layer. [ABSTRACT FROM AUTHOR]

The dwarf seagrass Zostera noltii is an important primary producer in Atlantic coastal ecosystems from Mauritania to southern Norway and the Mediterranean Sea. Sessile intertidal organisms existing at the interface between marine and terrestrial environments may be particularly vulnerable to environmental change. In this study, we asked how near to thermal tolerance limits natural populations of Z. noltii are in the Ria Formosa coastal lagoon system in southern Portugal. We recorded the maximum temperatures in the Ria Formosa during the 2007 summer, and conducted experiments to determine the sub-lethal temperature of Z. noltii shoots sampled at two sites located at different tidal heights. Mortality rates and photosynthetic performance were recorded within a range of heat shock temperatures between 35 and 41°C. Survival was recorded ≤37°C, while higher temperatures led to a sudden drop in photosynthetic capacity followed by mortality (shoot loss) that occurred more rapidly with increasing temperatures. At 39°C and above, the rate of shoot mortality in both sites was close to 100%, occurring between 5 and 13 days after the heat shock. Survival was ca. 95 and 90% at 35 and 37°C, respectively. From these results for Z. noltii populations in the Ria Formosa we estimated sub-lethal temperature to be approximately 38°C for Z. noltii, close to the maximum of 36°C recorded in the summer 2007. Considering predicted trajectories in the coming decades, these results raise concern as to the future viability of intertidal Z. noltii populations near the southernmost edge of their distribution. [ABSTRACT FROM AUTHOR]

On NW Atlantic rocky shores, the main basal organisms in intertidal communities are seaweeds ( Ascophyllum nodosum, Fucus spp. and Chondrus crispus) and filter feeders (barnacles, Semibalanus balanoides, and mussels, Mytilus spp.). Their ecology has been extensively studied in New England (United States), but knowledge gaps exist for northern shores, which are subjected to stronger environmental stress. Therefore, we studied the above organisms on Canadian shores. We quantified the summer abundance of these seaweeds and filter feeders across full vertical (intertidal elevation) and horizontal (wave exposure and winter ice scour) environmental gradients on the Gulf of St. Lawrence and open Atlantic coasts of Nova Scotia. At the regional scale along the open Atlantic coast, seaweeds showed similar abundances in Nova Scotia than values reported for New England. However, both filter feeders were considerably less abundant in Nova Scotia. At the local scale in Nova Scotia, intense winter ice scour (which only occurs on the Gulf of St. Lawrence coast) was associated with a very low abundance of all species except barnacles. Spatial trends in Nova Scotia were similar to patterns known for certain species elsewhere, such as A. nodosum being almost restricted to sheltered habitats, regardless of elevation, and C. crispus being almost restricted to low elevations, regardless of exposure. Other trends were, however, characteristic of Nova Scotia, such as C. crispus being frequent at low elevations in exposed habitats, unlike in New England, where mussels often predominate there because of competitive advantages. In Nova Scotia, mussels were always restricted to cracks and crevices, unlike in New England, where they form extensive intertidal beds on exposed shores. The direct effects of increased environmental stress and indirect effects through altered interspecific interactions might explain the regional differences in local species distribution, which will require experimental validation. [ABSTRACT FROM AUTHOR]

We describe the spatial distribution patterns of rocky intertidal Patella spp. limpets (heavily collected by shellfishers) and top-shell snails belonging to the genus Osilinus (comparatively slightly harvested) through a multiscaled sampling design spanning five orders of magnitude of spatial variability (from 10s of m to 100s of km) throughout the Canarian Archipelago (eastern Atlantic); where rocky intertidal assemblages on opposite sides of the Archipelago (western vs. eastern islands) are subjected to different regimes of bottom-up effects, as large spatial variation in oceanographic conditions is recorded across an east–west gradient. We tested the hypothesis that the response of rocky intertidal populations to mesoscale oceanographic bottom-up variability (quantified using differences in Chlorophyll- a concentration among islands as an approximation to bottom-up effects) depends on the exploitation status of coastal resources, by means of a correlative approach. Our study represent another case in which mesoscale shore-associated physical processes seem to be correlated to large-scale differences (variability among islands, 10s to 100s of km apart) in the abundance of slightly harvested intertidal grazers (topshell snails). In contrast, we did not observe large-scale spatial differences for heavily collected grazers (limpets). In conclusion, our study suggests that the signal of bottom-up processes in coastal populations may be difficult to demonstrate under intense human exploitation. [ABSTRACT FROM AUTHOR]