Intertidal Region Research Articles

Maintenance of ionic gradients and tissue hydration in the intertidal sea cucumberHolothuria griseaunder hypo- and hyper-salinity challenges

Echinoderms are exclusively marine, osmoconformer invertebrates. Their distribution patterns are strongly influenced by salinity. Nevertheless, several species of the phylum inhabit the challenging intertidal zone, characterized by steep and fast salinity fluctuations. This study evaluated the response of coelomic fluid ionic concentrations (sodium, chloride, magnesium and potassium) of the intertidal sea cucumberHolothuria griseato hypo- and hypersaline challenges. A stepwise protocol was performed for the whole animal exposure to both anisosmotic conditions: from 35 to 15 psu along 8 h, and from 35 to 45 psu along 6 h, to simulate intertidal conditions. Tissue water regulation by the longitudinal muscle, oesophagus and posterior intestine was also evaluated, upon hypo- and hyper-osmotic shocks of 20 and 50% of intensity with respect to the isosmotic control. Ionic gradients were observed between coelomic fluid and external water, mainly for potassium and magnesium, but also sodium, and in a greater extent under hyposaline conditions than under hypersaline exposure. Consistently,H. griseashows retracted tube feet in 15 psu, but a more relaxed appearance and exposed tube feet in 45 psu. In addition,H. griseashowed greater capacity for tissue water maintenance during hyper- than in hyposmotic conditions.Holothuria griseashows an avoidance behaviour in low salinity (thus sustaining ionic gradients), preventing its tissues from intense swelling. This strategy allows it to dwell in the intertidal region.

Assessment of mangroves from Goa, west coast India using DNA barcode.

Mangroves are salt-tolerant forest ecosystems of tropical and subtropical intertidal regions. They are among most productive, diverse, biologically important ecosystem and inclined toward threatened system. Identification of mangrove species is of critical importance in conserving and utilizing biodiversity, which apparently hindered by a lack of taxonomic expertise. In recent years, DNA barcoding using plastid markers rbcL and matK has been suggested as an effective method to enrich traditional taxonomic expertise for rapid species identification and biodiversity inventories. In the present study, we performed assessment of available 14 mangrove species of Goa, west coast India based on core DNA barcode markers, rbcL and matK. PCR amplification success rate, intra- and inter-specific genetic distance variation and the correct identification percentage were taken into account to assess candidate barcode regions. PCR and sequence success rate were high in rbcL (97.7 %) and matK (95.5 %) region. The two candidate chloroplast barcoding regions (rbcL, matK) yielded barcode gaps. Our results clearly demonstrated that matK locus assigned highest correct identification rates (72.09 %) based on TaxonDNA Best Match criteria. The concatenated rbcL + matK loci were able to adequately discriminate all mangrove genera and species to some extent except those in Rhizophora, Sonneratia and Avicennia. Our study provides the first endorsement of the species resolution among mangroves using plastid genes with few exceptions. Our future work will be focused on evaluation of other barcode markers to delineate complete resolution of mangrove species and identification of putative hybrids.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-3191-4) contains supplementary material, which is available to authorized users.

Phylogenetic Placement of a Schistosome from an Unusual Marine Snail Host, the False Limpet (Siphonaria lessoni) and Gulls (Larus dominicanus) from Argentina with a Brief Review of Marine Schistosomes from Snails

In the blood fluke family Schistosomatidae, marine snails are well known as intermediate hosts. Eight families of marine snails have thus far been reported to host schistosomes across the world, most of which have been implicated in human cercarial dermatitis (HCD) outbreaks. As part of our larger effort to define the species diversity and biology of schistosomes in Argentina, in particular their role in causing HCD, we searched in the marine pulmonate snail (Siphonaria lessoni) for a schistosome species described previously from S. lessoni from southern Argentina. Additionally, gulls (Larus dominicanus) collected from a different project locality (inland) were examined, because they are known to spend time in the intertidal regions. Schistosome sporocysts were found in S. lessoni, and a small worm fragment was retrieved from a gull. Molecular phylogenies for 28S, ITS1-5.8S-ITS2, and cox1 genes revealed that the specimens from the gull and S. lessoni grouped closely together, suggesting they are conspecifics. Also, ITS1-5.8S-ITS2 sequences suggested one of the schistosomes from S. lessoni and a schistosome from a South African penguin were also conspecifics. Further study is needed to verify if these specimens comprise a distinct marine clade within the larger avian schistosome clade that is comprised mostly of species using freshwater snail hosts. Thus far, it appears this group of marine schistosomes may be more likely found in the southern hemisphere. It is unclear if the observed distribution pattern of schistosomes in Siphonaria is a result of sampling bias and/or indicative of a specific bird-snail-schistosome association. It is clear they are sharply differentiated from the basal marine clade of avian schistosomes that includes Austrobilharzia.

Biotic hotspots in mangrove-dominated estuaries: macro-invertebrate aggregation in unvegetated lower intertidal flats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 556:31-43 (2016) - DOI: https://doi.org/10.3354/meps11860 Biotic hotspots in mangrove-dominated estuaries: macro-invertebrate aggregation in unvegetated lower intertidal flats Marcus Sheaves, Liliana Dingle, Carlo Mattone* Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), Estuary and Coastal Wetland Ecosystem Research Group, College of Marine and Environmental Sciences, James Cook University, Queensland 4811, Australia *Corresponding author: carlo.mattone@my.jcu.edu.au ABSTRACT: Macro-benthic invertebrates are important components of estuarine communities providing links between primary producers and higher trophic levels. In temperate regions, abundance and biomass peak in the mid-intertidal, giving this zone substantial functional importance. In tropical estuaries, the higher intertidal is generally occupied by mangrove forests, potentially influencing the way intertidal invertebrate assemblages are structured. We investigated the distribution and richness of benthic invertebrates across intertidal sand- and mud-flats seaward of mangrove forest to quantify the extent and location of areas of high benthic richness, abundance and biomass. Four estuaries in tropical north Queensland and 2 habitat types, sand and mud, were sampled using a van Veen grab. Macro-invertebrate richness, abundance and biomass peaked with a ‘hotspot’ in the lower low-intertidal, with patterns of distribution similar among substrate types. However, substantial differences in biotic and abiotic contexts between tropical estuaries and the temperate systems, where models of intertidal macro-invertebrate distribution were developed, mean that the variables influencing tropical macro-invertebrate hotspots are likely to differ from those that operate in temperate regions. The high concentration of benthic biomass in the lower low-intertidal means this zone probably regulates many of the ecological processes occurring in the intertidal regions of tropical estuaries. Consequently, any damage or modification to this zone is likely to severely impact estuarine function. KEY WORDS: Benthos · Tropical estuary · Nutrients · Invertebrate distribution Full text in pdf format Supplementary material PreviousNextCite this article as: Sheaves M, Dingle L, Mattone C (2016) Biotic hotspots in mangrove-dominated estuaries: macro-invertebrate aggregation in unvegetated lower intertidal flats. Mar Ecol Prog Ser 556:31-43. https://doi.org/10.3354/meps11860 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 556. Online publication date: September 08, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Volume regulation of intestinal cells of echinoderms: Putative role of ion transporters (Na+/K+-ATPase and NKCC)

Echinoderms are exclusively marine osmoconformer invertebrates. Some species occupy the challenging intertidal region. Upon salinity changes, the extracellular osmotic concentration of these animals also varies, exposing tissues and cells to osmotic challenges. Cells and tissues may then respond with volume regulation mechanisms, which involve transport of ions and water into and/or out of the cells, through ion transporters, such as the Na+/K+-ATPase and NKCC. The goal of this study was to relate the cell volume regulation capacity of echinoderm intestinal cells Na+/K+-ATPase and NKCC activities, in three echinoderm species: Holothuria grisea, Arbacia lixula, and Echinometra lucunter. Isolated cells of these species displayed some control of their cell volume upon exposure to anisosmotic media (isolated intestinal cells, calcein fluorescence as indicator of volume change), with a distinct higher capacity shown by H. grisea, which did not swell even upon 50% hyposmotic shock. The holothuroid cells showed indirect evidence (effect of furosemide) of the participation of NKCC in this process, with a secretory function, and of a secondary role by the NKA (effect of ouabain). Other mechanisms are probably responsible for this function in the urchins. Variable expression of these transporters, and others not examined here, may to some extent account for the variability in cell volume regulation capacity in echinoderm cells.

Geochemical assessment and fractionation of trace metals in estuarine sedimentary sub-environments, in Mumbai, India

The distribution and concentrations of selected metals (Fe, Mn, Cu, Pb, Co, Zn and Cr) in intertidal regions (mudflat and mangrove) of Ulhas estuary, located in Mumbai, India were studied. The sediment metal contamination was assessed by applying Enrichment Factor (EF), Anthropogenic factor (AF), Contamination factor (CF) and Pollution load Index (PLI). Also, Sediment Quality Guidelines (SQGs) by Environmental Protection Agency was used to determine the risk of increased metal levels to biota. Amongst the two sub-environments studied, the mudflat region exhibited higher metal contamination than the mangrove region necessitating fractionation analysis of the core. The geochemical fractionation analysis showed higher metal percentage in the residual fraction, except for Mn and Zn. The fractionation results, in general, indicated that contamination due to the metals- Mn and Zn might pose a potential risk to the estuarine system if the sediment gets disturbed with time.

Differences in the oxidative stress and antioxidant responses of three marine macroalgal species upon UV exposure

Differences in the oxidative stress and antioxidant responses of three marine algal species, i.e., Ulva pertusa (a chlorophyte), Laminaria japonica (a phaeophyte), and Grateleoupia lanceolata (a rhodophyte), collected from intertidal region of Korea, upon exposure to UVA and UVB were investigated. The U. pertusa exhibited a strong adaptive antioxidant response to UV radiation as manifested by the decrease in lipid peroxidation and the reduction of cellular glutathione, i.e., increase in the ratio of reduced to oxidized glutathione, which showed clear correlations with increases in glutathione-metabolizing and ROS-scavenging enzyme activities. In contrast, the L. japonica and the G. lanceolata exhibited significant susceptibilities to UV radiation as manifested by the increase in lipid peroxidation and the decrease in glutathione content, which correlated with the decreases in antioxidant enzyme activities. The efficient UV-adaptive response of U. pertusa may be attributed to acclimation to their habitat and environment, the shallow intertidal zone.

Use of Polymerase Chain Reaction for Bivalve Pathogen Surveillance in the Yellow Clam Mesodesma mactroides.

The yellow clam Mesodesma mactroides is a valuable shellfish occurring from the southeastern coast of Brazil to the northern coast of Argentina. Populations of yellow clams are disappearing from their entire range, and the cause is still unknown. The objective of this paper was to search for World Organisation for Animal Health (OIE)-listed pathogens and their relatives in the genera Marteilia, Bonamia, and Perkinsus as well as Mikrocytos mackini and the virus OsHV-1 μ var the yellow clam population in southern Brazil using molecular techniques and classic histology protocols. A total of 180 clams were manually collected in the intertidal region at six sampling points covering the entire coast of Rio Grande do Sul State (length, 622 km) in 2013. Tissue samples were tested by OIE-recommended single-step conventional polymerase chain reaction assays. The screening showed no evidence of the specific sequences of the protistan parasites and viral pathogens at any site within the six zones under study. We recommend continuous monitoring of the mollusks in the region. Received July 3, 2015; accepted February 3, 2016.

Effects of Ocean Acidification and Temperature Increases on the Photosynthesis of Tropical Reef Calcified Macroalgae.

Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO2-driven ocean acidification and temperature rises on the photosynthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3, -0.6, -0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.

TIDAL PERIODICITY IN MICROGROWTH BANDS OF BLOOD CLAM Anadara indica (Bivalvia: Arcidae): A POSSIBLE ENVIRONMENTAL SCLEROCHRONOMETER IN THE TROPICS

This study examining the microgrowth periodicity of wild type Anadara indica (Gmelin, 1791) being submerged for 29 d in the cage and field plot. Individual clams showed daily increment growth that conforms to semilunar tidal cycle of 14.8 d. The shell therefore provided record about the absolute growth history of the organism, presumably including the environmental conditions under which shell deposition took place. Shell accretion decreased in rhythm to the gonad development and spawning measured as Condition Index. The significantly departed sex ration to 0.25:1 in favour of > 35 mm shell length females indicating the occurrence of male to female sex reversal, likewise its con-specific A. granosa (Linne, 1758) and A. antiquata (Linnaeus, 1758). It is thought that habitat overlap between A. granosa and A. indica, combined with irresponsible fisheries of the local people which commercially caught small size male clams caused the shift in population dominance among these two species, i.e., from A. granosa to A. indica. However, this study showed that A. indica might as well thrive in areas close to intertidal region likewise A. granosa, where tidal periodicity role as a forcing function to the environment.

Numerical model simulations for optimisation of tidal lagoon schemes

This study considers environmental impacts and the power production potential of a number of coastally attached tidal lagoons, proposed along the North Wales coast, UK. Initially, the impoundment shape, turbine and sluice gate locations were modified according to the regional bathymetric data. A refined 0-Dimensional approach was implemented to optimise the lagoon operation, based on given turbine and sluice gate specifications. In turn, a two-dimensional numerical model, based on an unstructured triangular mesh, has been refined to simulate the hydrodynamic processes, initially without and subsequently in the presence of the lagoons. The hydrodynamic model adopts a TVD finite volume method to solve the 2D shallow water equations, based on a second-order accurate spatial and temporal numerical scheme. An encouraging performance is apparent in reproducing the established conditions encountered in the region through comparisons against available data. The incorporation of tidal lagoons in the model appears to have a considerable effect on the flow structure in the region, by inducing high velocity accelerations near the sluices and turbines, depending on the stage of the tidal cycle. Considering a two-way generation regime, it is outlined that the loss of intertidal regions can be minimised, which is a major source of concern with regards to the environmental impact of such schemes through an ebb-generation operation. Particular focus is directed towards the comparisons between the 0-D and 2-D modelling results, an aspect which has not been reported previously. Predictions of the models diverge as the scale of the lagoon project increases, but it is highlighted that the 0-D methodology can be utilised for the optimisation of the processes in the initial stages of design before proceeding to more sophisticated numerical model simulations.

An ex situ and in vitro approach to delineate pennate diatom species with bioindicator potentials in a well mixed tropical estuarine ecosystem

An experiment was performed on selected pennate diatom species collected from the well mixed waters of the Hooghly Estuary with the aim of distinguishing the ones with qualities to be employed as monitors of their ecosystem. The Hooghly Estuary is enriched with domestic, sewage and agricultural effluents and coastal upwelling along with tide-mediated advective circulation from the mangrove forests ensure concomitant nutrient pool replenishment in this ecoregion. There have been several attempts to establish certain centric diatom species as bioindicators in various parts of the world owing to their better responsiveness to sudden shifts in stoichiometry but hardly any with pennate diatoms. Pennate diatoms are typical benthic mat formers in the intertidal regions, on submerged surfaces and thus bear greater feasibility to be employed as accurate pointers to long term deviations in their respective ecosystems, in spite of the greater sensitivity of the centric diatoms. The study was carried out in laboratory controlled environment to minimize the interference from other extrinsic factors compromising the outcome and also due to the fact that such studies to be performed in natural conditions require a decent financial support and time to conclusively arrive upon the objectives. From the present endeavour it was inferred that Nitzschia sigmoidea, Pleurosigma angulatum and Ulnaria oxyrhyncus (formerly Synedra ulna var. oxyrhyncus) stood a good chance of being recruited as bioindicators to eutrophic well mixed estuaries, similar to the one they had been sampled from.

Trailing the Spawning Horseshoe Crab Tachypleus Gigas (Müller, 1785) at Designated Natal Beaches on the East Coast of Peninsular Malaysia

Due to limited availability of literature on the spawning activity of Malaysian horseshoe crab, Tachypleus gigas (Muller, 1785), the reproduction behaviour and biology of this arthropod remains poorly understood. Hence, an investigation was carried out from April-July to trail spawning horseshoe crab amplexus at Balok and Cherating, the only known T. gigas spawning grounds on the east coast of Peninsular Malaysia. Through visual tracking during daytime full moon spring tides, the release of air bubbles indicate nest digging by female crabs. While air bubble formation aggravated, flagged aluminium poles were carefully driven into the sediment to mark the nest. Out of the 13 spawning T. gigas amplexus tracked, only one pair was able to dig up to 12 nests and release up to 2,575 eggs within the 2.5 hour spawning period. The female crabs dug nests at the intertidal regions, ranging 1.3-43.2 m from the highest tide marking on the beach. Interestingly after spawning, the horseshoe crabs returned to high seas during the residing tides as amplexus because the male crabs remained clinging onto the female crab’s opisthosoma. The incidence of recapturing a tagged female crab with different attached male crab at Cherating indicates this spawning ground as natal beach. In addition, the presence of 8 horseshoe crab amplexus at Balok compared to only 5 amplexus at Cherating highlight preferable beach settings for spawning and/or the presence of larger spawning crab assemblages at the former beach. Since only 13 spawning horseshoe crab pairs were witnessed at Balok and Cherating, identification of factors that alter beach sediment composition and water chemistry as well as gender-specific poaching and excessive boating activities should be regulated to restore wild T. gigas populations.

Using Numerical Bifurcation Analysis to Study Pattern Formation in Mussel Beds

Soft-bottomed mussel beds provide an important example of ecosystem-scale self-organisation. Field data from some intertidal regions shows banded patterns of mussels, running parallel to the shore. This paper demonstrates the use of numerical bifurcation methods to investigate in detail the predictions made by mathematical models concerning these patterns. The paper focusses on the “sediment accumulation model” proposed by Liu et al (Proc. R. Soc. Lond. B 14 (2012), 20120157). The author calculates the parameter region in which patterns exist, and the sub-region in which these patterns are stable as solutions of the original model. He then shows how his results can be used to explain numerical observations of history-dependent wavelength selection as parameters are varied slowly.

State of the art of the meiofauna of Brazilian Sandy Beaches

Abstract In Brazil, meiofauna studies began in the middle of last century, but they adopted a purely taxonomical approach, describing species from various zoological groups. After this first step, this benthic group was largely neglected until the end of the 20th century when ecological studies began. We here provide a brief review of present knowledge of the meiofauna found on Brazilian sandy beaches to provide information for ReBentos (Coastal Benthic Habitats Monitoring Network). Our methodology consisted of a bibliographic survey undertaken using different datasets (Web of ScienceTM, SCOPUS, Google Scholar and Lattes Plataform). For the survey, we considered only those studies published till early 2015. Our analysis showed that the number of meiofauna studies has increased over the last two decades, though they are mainly still concentrated on the Southeast of Brazil. These studies aim to explain the distribution pattern of the meiofauna of the intertidal region of sandy beaches. Based on the results, we presented a discussion of three main topics, i.e., (a) current knowledge of Brazilian sandy beach meiofauna, (b) sampling strategies for monitoring of the meiofauna, and (c) use of the meiofauna as a tool to assess climate change. We trust that this brief review will be useful as a starting point for the delineation of further climate change investigations into sandy beach meiofauna.

A temporal waterline approach to mapping intertidal areas using X-band marine radar

Mapping the morphology of intertidal areas is a logistically challenging, time consuming and expensive task due to their large expanse and difficulties associated with access. A technique is presented here that uses standard marine navigational radar operating at X-band frequency. The method uses a series of time-exposure radar images over the course of a two-week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images, thereby building up a morphological map of the target intertidal area. This “Temporal Waterline” method is applied to a dataset acquired from Hilbre Island at the mouth of the Dee Estuary, UK, spanning March 2006 to January 2007. The radar gathered data with a radial range of 4km and the resulting elevation maps describe the intertidal regions of that area. The results are compared with airborne LiDAR data surveyed over the same area and within the radar survey time period. The residual differences show good agreement across large areas of beach and sandbanks, with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water. This paper presents the theoretical framework of the method and demonstrates its stability and accuracy. The Temporal Waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines.

Preliminary Evidence for the Amplification of Global Warming in Shallow, Intertidal Estuarine Waters.

Over the past 50 years, mean annual water temperature in northeastern U.S. estuaries has increased by approximately 1.2°C, with most of the warming recorded in the winter and early spring. A recent survey and synthesis of data from four locations in Southern Rhode Island has led us to hypothesize that this warming may be amplified in the shallow (<1 m), nearshore portions of these estuaries. While intertidal areas are not typically selected as locations for long-term monitoring, we compiled data from published literature, theses, and reports that suggest that enhanced warming may be occurring, perhaps at rates three times higher than deeper estuarine waters. Warmer spring waters may be one of the factors influencing biota residing in intertidal regions both in general as well as at our specific sites. We observed greater abundance of fish, and size of Menidia sp., in recent (2010–2012) seine surveys compared to similar collections in 1962. While any linkages are speculative and data are preliminary, taken together they suggest that shallow intertidal portions of estuaries may be important places to look for the effects of climate change.

Diversity of Ascidians from the Great Nicobar Biosphere Reserve (GNBR), India

The Great Nicobar Biosphere Reserve nurtures a diverse amount of life and is very important to the biological diversity of India. Ascidians diversity has been recorded for the first time from the Great Nicobar Biosphere Reserve. In the present study, 15 species of ascidians were noticed in both intertidal and sub-tidal regions of GNBR, belonging to two orders, three suborders, six families and ten genera (Didemnum fulgens, Didemnum vexillum, Didemnum granulatum, Didemnum albidum, Didemnum candidum, Trididemnum cyanophorum, Diplosoma simile, Diplosoma spongiforme, Clavelina oblonga, Aplidium fuscum, Synoicum castellatum, Pycnoclavella diminuta, Ascidia virginea, Ascidiella aspersa and Styela sp.) during the year 2013-2014 of which, the Didemnidae family was recorded with the high diversity of 15 species. Species richness were highly recorded in Bquary Beach and lowly recorded from Campbell Bay. The present data suggests that GNBR coast offers a unique opportunity for future research on the ascidians diversity and ecology assessment. Keywords: Ascidians, Biodiversity, GNBR

Influence of spatial competitor on the growth and regeneration of the marine sponge Cinachyrella cf. cavernosa (Porifera, Demospongiae)

Availability of suitable substratum is often a limiting factor for sessile organisms. We studied growth and regeneration of golf ball sponge Cinachyrella cf. cavernosa with and without its aggressive neighbour, soft coral (Zoanthus sansibaricus) in rocky intertidal area of Anjuna (Goa), India to understand impact of spatial competition on these life-history processes. Specific growth rate of C. cf. cavernosa ranged from 3.38 ± 0.47 to 24.57 ± 1.99% year−1. A wound-healing experiment demonstrated 50–100 times faster regeneration, compared to their average growth rate. Both growth and regeneration decreased as sponge size increased. The sponges exhibited 36–69% higher growth and 30–76% faster regeneration rate in the absence of the competitor species, Z. sansibaricus. The protein synthesis ability (RNA to DNA ratio), which is an index for physiological activity was adversely affected by sponge size and competitor abundance. Results suggest that in a space-limited region, the presence of an aggressive neighbour acts as one of the crucial factors affecting the primary functions (such as growth and regeneration) of the sponge. This study also highlights the remarkable regenerative ability of the slow growing sponge C. cf. cavernosa which aids in maintaining its abundance under stressful conditions of rocky intertidal region.

The role of patellid limpets as omnivorous grazers: a new insight into intertidal ecology

Although patellid limpets are influential grazers on many shores, few studies have characterised their diets in detail. These key species can be found as dominant grazers on rocky shores, but this ecosystem is being transformed due to the increase in infrastructures such as jetties, breakwaters or seawalls by commercial, residential and tourist activities. Increasing knowledge about the ecological effects of these artificial substrates on marine environments is available, and many papers have reported that urban infrastructures support different biota and assemblages and do not act as a surrogate for natural rocky shores. However, little is known about the effect of artificial substrata on marine trophic ecology. The aim of the study was to explore the influence of artificial substrata (breakwaters) on the dietary composition of the common grazer Patella caerulea, to provide data about food resource availability, and its influence on the trophic ecology of limpets. A nested design was used to explore potential differences between natural and artificial shores in Algeciras Bay (Strait of Gibraltar). Additionally, the dietary composition of the endangered limpets Cymbula safiana and Patella ferruginea was studied in a single site. Analyses of the chlorophyll a concentration of the substrate did not show differences between substrata. The analysis of the rock surface by SEM indicated a general prevalence of diatoms and cyanoprokaryotes on all of the substrata. P. caerulea specimens collected from artificial substrata showed a lower number of consumed taxa than those collected from natural rocky shores, whereas the assemblages found in the gut contents also differed between artificial and natural substrata. The diet richness of the three species might be due to the differences in the position of the species on the shore. Our results suggest that limpets are a key group in the top-down control of meiofaunal and macrofaunal populations, due to the presence of several animal taxa in their gut contents in this study, despite the fact that they have traditionally been considered herbivorous grazers that regulate only algal populations in the intertidal regions.