Lithophyllum Incrustans Research Articles

The red coralline alga Hydrolithon onkodes, an attractor of coral larvae, is photosynthetically more susceptible to thermal stress than Lithophyllum incrustans

Abstract. Perrine MJS, Mundil S, Kaullysing D, Bhagooli R. 2023. The red coralline alga Hydrolithon onkodes, an attractor of coral larvae, is photosynthetically more susceptible to thermal stress than Lithophyllum incrustans. Indo Pac J Ocean Life 7: 91-99. Red Coralline Algae (RCAs) are important components of coral reefs and are involved in reef-building via calcification, cementation, the synthesis of anti-fouling compounds and of chemicals to aid recruitment, settlement and metamorphosis of reef species. This study aimed to investigate the distribution of RCAs at four sites around Mauritius Island and the effects of thermal stress on the effective photosynthetic yield of photosystem II (FPSII) of two species of RCA namely, Lithophyllum incrustans (Philippi, 1837) and Hydrolithon onkodes, known to attract coral larvae. Out of the nine RCA species observed, two non-geniculate RCAs, H. onkodes and L. incrustans, were among the most dominant, especially at the lagoonal and reef zones of the four studied sites Flic en Flac, Belle Mare, Trou aux Biches and Flat Island. These two RCAs were collected, acclimated for 24 hours on a 12h:12h dark-light cycle and then exposed to 27°C, 30°C and 33°C for 3 (T3), 6 (T6) and 19 (T19) hours. After 3, 6 and 19 hours, relative change in FPSII compared to initial (T0) was used for comparison among tested species. At 27°C the FPSII did not fluctuate significantly during the experiment for both RCAs. At a temperature 30°C only H. onkodes significantly decreased from 0.541 ± 0.54 at T0 to 0.445 ± 0.116 at T19. At 33°C, L. incrustans showed a significant decline of 24.82 ± 7.4% while H. onkodes decreased by 90 ± 12.6%. Visual observations revealed that H. onkodes changed from the initial healthy-looking color of light grey to pale purple after thermal exposure. These findings indicate that the coral larvae-attracting H. onkodes is more susceptible than the L. incrustans to thermal stress, implying subsequent possible impacts on coral recruitment process especially in the wake of climate change-driven ocean warming.

The Punta de la Mona Rhodolith Bed: Shallow-Water Mediterranean Rhodoliths (Almuñecar, Granada, Southern Spain)

Shallow-water rhodolith beds are rare in the Mediterranean Sea and generally poorly known. The Punta de la Mona rhodolith bed extends for 16,000 square meters in shallow and oligotrophic waters at the southern coast of Spain, off Almuñecar in the Alborán Sea. We present a detailed analysis of the structure (rhodolith cover and density, rhodolith size and shape, sediment granulometry) and morphospecies composition of the bed along a depth gradient. A stratified sampling was carried out at six depths (9, 12, 15, 18, 21, and 24 m), estimating rhodolith cover and abundance; rhodoliths were collected from one 30 by 30 cm quadrat for each transect, resulting in 18 samples and a total of 656 rhodoliths. The collected rhodoliths were measured and the coralline algal components identified morphoanatomically through a stereomicroscope and SEM. Sediment on the seafloor mainly consisted of pebbles and cobbles; the highest rhodolith cover occurred between 15 and 18 m, and the lowest at the shallowest and deepest transects (9 and 24 m). Mean Rhodolith size was similar throughout the depth range (23–35 mm) with a slight increase at 24 m, although the largest rhodoliths occurred at 21 m. In monospecific rhodoliths, size depended more on the forming species than on depth. We found 25 non-geniculate coralline morphospecies, nearly all rhodolith-forming morphospecies reported in the Mediterranean Sea in recent accounts. The highest morphospecies richness (18–19) and proportional abundance were found at intermediate depths (15–18 m), where rhodolith cover is also highest. Lithophyllum incrustans and Lithophyllum dentatum dominated at shallow depths (9–12 m), whereas Lithothamnion valens was the dominant species at intermediate and greater depths. Overall, the latter species was the most common in the rhodolith bed. The shallow-water rhodolith bed in Punta de la Mona is probably the most diverse in the Mediterranean Sea. This highlights the importance of the conservation of this habitat and, in general, emphasizes the role of the Alborán Sea as a diversity center of coralline algae. The Punta de la Mona example contradicts the common assumption in the geological literature that rhodolith beds are indicative of oligophotic environments with high nutrients levels.

Physiology of maerl algae: Comparison of inter- and intraspecies variations.

Free-living red coralline algae play an important role in the carbon and carbonate cycles of coastal environments. In this study, we examined the physiology of free-living coralline algae-forming maerl beds in the Bay of Brest (Brittany, France), where Lithothamnion corallioides is the dominant maerl (i.e., rhodolith) species. Phymatolithon calcareum and Lithophyllum incrustans are also present (in lower abundances) at a specific site in the bay. We aimed to assess how maerl physiology is affected by seasonality and/or local environmental variations at the inter- and intraspecific levels. Physiological measurements (respiration, photosynthetic, and calcification rates) were performed using incubation chambers in winter and summer to compare (1) the dominant maerl species at three sites and (2) three coexisting maerl species at one site. Comparison of the three coexisting maerl species suggests that L.corallioides is the best adapted to the current environmental conditions in the Bay of Brest, because this species is the most robust to dissolution in the dark in winter and has the highest calcification efficiency in the light. Comparisons of L.corallioides metabolic rates between stations showed that morphological variations within this species are the main factor affecting its photosynthetic and calcification rates. Environmental factors such as freshwater inputs also affect its calcification rates in the dark. In addition to interspecies variation in maerl physiology, there were intraspecific variations associated with direct (water physico-chemistry) or indirect (morphology) local environmental conditions. This study demonstrates the plasticity of maerl physiology in response to environmental changes, which is fundamental for maerl persistence.

Combined effects of global climate change and nutrient enrichment on the physiology of three temperate maerl species.

Made up of calcareous coralline algae, maerl beds play a major role as ecosystem engineers in coastal areas throughout the world. They undergo strong anthropogenic pressures, which may threaten their survival. The aim of this study was to gain insight into the future of maerl beds in the context of global and local changes. We examined the effects of rising temperatures (+3°C) and ocean acidification (−0.3 pH units) according to temperature and pH projections (i.e., the RCP 8.5 scenario), and nutrient (N and P) availability on three temperate maerl species (Lithothamnion corallioides, Phymatolithon calcareum, and Lithophyllum incrustans) in the laboratory in winter and summer conditions. Physiological rates of primary production, respiration, and calcification were measured on all three species in each treatment and season. The physiological response of maerl to global climate change was species‐specific and influenced by seawater nutrient concentrations. Future temperature–pH scenario enhanced maximal gross primary production rates in P. calcareum in winter and in L. corallioides in both seasons. Nevertheless, both species suffered an impairment of light harvesting and photoprotective mechanisms in winter. Calcification rates at ambient light intensity were negatively affected by the future temperature–pH scenario in winter, with net dissolution observed in the dark in L. corallioides and P. calcareum under low nutrient concentrations. Nutrient enrichment avoided dissolution under future scenarios in winter and had a positive effect on L. incrustans calcification rate in the dark in summer. In winter conditions, maximal calcification rates were enhanced by the future temperature–pH scenario on the three species, but P. calcareum suffered inhibition at high irradiances. In summer conditions, the maximal calcification rate dropped in L. corallioides under the future global climate change scenario, with a potential negative impact on CaCO3 budget for maerl beds in the Bay of Brest where this species is dominant. Our results highlight how local changes in nutrient availability or irradiance levels impact the response of maerl species to global climate change and thus point out how it is important to consider other abiotic parameters in order to develop management policies capable to increase the resilience of maerl beds under the future global climate change scenario.

Ecological Quality Status of the Algiers coastal waters by using macroalgae assemblages as bioindicators (Algeria, Mediterranean Sea)

Macroalgae assemblages have been used as a quality element for the assessment of the Ecological Status Classes (ESC) of coastal water bodies for the implementation of the European Water Framework Directive (WFD, 2000/60/EC). To assess the suitability of this quality element in Algiers coasts, seven sampling sites with five (5) replications covering a wide range of anthropogenic pressures were studied during spring and summer 2015. Coverage data of macroalgae in each sampling site were analyzed on species, i.e., structural (species number, nMDS, clustering, K-dominance and Simper analysis on Bray–Curtis similarity) and on Ecological Status Groups, i.e., functional (nMDS, clustering, K-dominance, Ecological Evaluation Index/EEI-c) biological levels. Key water variables (temperature, salinity and pH) along with the anthropogenic stress index MALUSI were also estimated. The obtained results revealed a significant effect of anthropogenic stress in the macroalgal assemblages. The structural analysis showed: (1) species richness of 86 taxa in total, (2) dominance of Cystoseira amentacea var. stricta (late-successional) associated by Lithophyllum incrustans, and Jania rubens in non-impacted sites and of Ulva rigida, Ulva intestinalis and Caulerpa cylindracea (opportunistic) species in impacted sites, and (3) record a higher proportion of low abundance of species in polluted communities than in less polluted communities. The functional analysis showed: (1) classification of sites based on multivariate and K-dominance analyses in four groups, three in agreement with water degradation, and one for low salinity influence, (2) classification of sites into “Bad”, ”High”, “Moderate” and “Good” ESC’s by EEI-c index, (3) a strong non-linear relationship (R²=0.85) of EEI-c index with MALUSI index. Therefore, to implement a national monitoring program within the scope WFD in Algeria coasts, the EEI-c index will be a suitable tool.

Modern rhodoliths from the insular shelf of Pico in the Azores (Northeast Atlantic Ocean)

A seabed sediment-sampling survey conducted on the Pico insular shelf found abundant rhodoliths between −64 and −73 m off the south coast of the island. These were small and mainly ellipsoidal in shape with a maximum diameter of 3.75 cm. Granules and small pebbles of eroded basalt were also a typical component of these samples. Thin algal crusts were secreted on basalt pebbles by the coralline red algae Phymatolithon calcareum which, in turn, were covered by Lithophyllum incrustans. Additional samples were collected by snorkelling at Maré (Lajes do Pico), a shallow lagoon (2–4 m in depth) on the south coast. Here, rhodoliths are mostly spheroidal and bigger (maximum diameter of 4.75 cm), formed by thin thalli of P. calcareum. Based on these results (distribution of shapes and species) and previous work on the characteristics of fossil specimens from Neogene deposits on Santa Maria Island (Azores) and other North Atlantic Archipelagos, an empirical depositional model is proposed for the development of rhodoliths on the Pico Island shelf: (1) Nearshore rhodoliths, formed solely by P. calcareum, are subjected to a wide range of currents and waves resulting in their spheroidal shapes. However, those of Maré lagoon are protected from offshore transport and tend to grow larger than deep-water rhodoliths; (2) Although not sampled, there must be middle shelf rhodoliths formed solely by P. calcareum that tend to form more ellipsoidal shapes due to seafloor oscillatory movements caused by waves crossing the shelf; (3) During storms, these middle shelf rhodoliths are then transported to the outer shelf, where L. incrustans overgrows the initial cover of P. calcareum. Shallow associations are normally larger, reflecting therefore, a longer life span than the deeper associations. Transport by storms appears to be an important factor in the formation of some deep-water rhodoliths around volcanic oceanic islands subjected to high-wave energy. However, their exposure to an energetic environment and likely frequent offshore transport does not allow them to grow as large as those from shallow-water.

New Record of Coralline Algae from the Holocene Sediments of Agatti Island, Lakshadweep, India

Abstract: The present paper examines the coralline algal assemblage recovered from the Holocene sediments of Agatti Island, Lakshadweep, India. The assemblage comprises nine species of coralline algae which include Amphiroa fragilisma, Lithophyllum nitorum, Lithophyllum incrustans, Lithoporella melobesioids, Spongites sp., Porolithon craspedium, Aethesolithon problematicum, Clathromorphum parcum, Melobesoideae gen. et spec. indet. Clathromorphum parcumis an endophytic coralline alga reported for the first time from the Indian subcontinent. Out of these, seven species belong to the family Corallinaceae and the two represent the family Hapalidiaceae of the class Rhodophyceae. Coralline algal association of this area is dominated by Lithophylloideae, Melobesioideae and Mastophoroideae which include encrusting to fragmented growth forms. The associated branching corals are well developed and adapted to shallow, warm water, low turbid, protected lagoonal environment.

Current status and multidecadal biogeographical changes in rocky intertidal algal assemblages: The northern Spanish coast

The biogeographic border between the Eastern and the Atlantic subregions of the Lusitanian Province situated on the west coast of Asturias (N. of Spain) has moved westwards in recent years. A comparative study, consisting in a resurvey of 20 shores sampled in 1977, covering 200 km showed a large-scale change affecting the mid and low eulittoral. Cold-temperate canopy species such as kelps (Laminaria hyperborea, Laminaria. ochroleuca and Saccorhiza polyschides), fucoids (Fucus serratus, Fucus vesiculosus and Himanthalia elongata) and Chondrus crispus have almost disappeared and replaced by warm-temperate species such as Cystoseira baccata, Cystoseira tamariscifolia, Bifurcaria bifurcata and coralline algae (Ellisolandia elongata, Lithophyllum incrustans and Mesophyllum lichenoides). The loss of canopy-species can have consequences for the assemblage, especially in the case of fucoid-dominated assemblages.

Sequencing type material resolves the identity and distribution of the generitype Lithophyllum incrustans, and related European species L.hibernicum and L.bathyporum (Corallinales, Rhodophyta).

DNA sequences from type material in the nongeniculate coralline genus Lithophyllum were used to unambiguously link some European species names to field-collected specimens, thus providing a great advance over morpho-anatomical identifi-cation. In particular, sequence comparisons of rbcL, COI and psbA genes from field-collected specimens allowed the following conclusion: the generitype species, L.incrustans, occurs mostly as subtidal rhodoliths and crusts on both Atlantic and Mediterranean coasts, and not as the common, NE Atlantic, epilithic, intertidal crust reported in the literature. The heterotypic type material of L.hibernicum was narrowed to one rhodolith belonging in Lithophyllum. As well as occurring as a subtidal rhodolith, L.hibernicum is a common, epilithic and epizoic crust in the intertidal zone from Ireland south to Mediterranean France. A set of four features distinguished L.incrustans from L.hibernicum, including epithallial cell diameter, pore canal shape of sporangial conceptacles and sporangium height and diameter. An rbcL sequence of the lectotype of Lithophyllum bathyporum, which was recently proposed to accommodate Atlantic intertidal collections of L.incrustans, corresponded to a distinct taxon hitherto known only from Brittany as the subtidal, bisporangial, lectotype, but also occurs intertidally in Atlantic Spain. Specimens from Ireland and France morpho-anatomically identified as L.fasciculatum and a specimen from Cornwall likewise identified as L.duckerae were resolved as L.incrustans and L.hibernicum, respectively.

Physiological responses of three temperate coralline algae from contrasting habitats to near-future ocean acidification

Coralline algae are major calcifiers of significant ecological importance in marine habitats but are among the most sensitive calcifying organisms to ocean acidification. The elevated pCO2 effects were examined in three coralline algal species living in contrasting habitats from intertidal to subtidal zones on the north-western coast of Brittany, France: (i) Corallina elongata, a branched alga found in tidal rock pools, (ii) Lithophyllum incrustans, a crustose coralline alga from the low intertidal zone, and (iii) Lithothamnion corallioides (maerl), a free-living form inhabiting the subtidal zone. Metabolic rates were assessed on specimens grown for one month at varying pCO2: 380 (current pCO2), 550, 750 and 1000μatm (elevated pCO2). There was no pCO2 effect on gross production in C. elongata and L. incrustans but L. incrustans respiration strongly increased with elevated pCO2. L. corallioides gross production slightly increased at 1000μatm, while respiration remained unaffected. Calcification rates decreased with pCO2 in L. incrustans (both in the light and dark) and L. corallioides (only in the light), while C. elongata calcification was unaffected. This was consistent with the lower skeletal mMg/Ca ratio of C. elongata (0.17) relative to the two other species (0.20). L. incrustans had a higher occurrence of bleaching that increased with increasing pCO2. pCO2 could indirectly impact this coralline species physiology making them more sensitive to other stresses such as diseases or pathogens. These results underlined that the physiological response of coralline algae to near-future ocean acidification is species-specific and that species experiencing naturally strong pH variations were not necessarily more resistant to elevated pCO2 than species from more stable environment.

Palaeoenvironmental and stratigraphic significance of Pliocene rhodolith beds and coralline algal bioconstructions from the Carboneras Basin (SE Spain)

Thick rhodolith beds occur in the transgressive and highstand systems tracts of the early Pliocene sequence in the Carboneras Basin in SE Spain. Rhodolith beds accumulated in mid-to-outer ramp settings and in the leeside of a spit platform during the transgressive interval, whereas rhodolith concentrations in the highstand deposits only formed in the mid-to-outer ramp at the southern margin of the basin. The elevation of rhodolith beds compared with coeval shore deposits suggests that the beds developed at water depths of several tens of metres (probably less than 50m). This palaeodepth estimate is consistent with the composition of algal assemblages, which are dominated by melobesioids common in relatively deep platform environments in the modern Mediterranean Sea. Lithothamnion minervae Basso, 1995, L. philippii Foslie, 1909, and Mesophyllum alternans (Foslie) Mendoza & Cabioch, 1998 with subordinate Phymatolithon calcareum (Pallas) Adey & McKibbin, 1970 and M. macroblastum (Foslie) Adey, 1970 and lithophylloids of the Lithophyllum incrustans Philippi, 1837-L. racemus (Lamarck) Foslie, 1901 complex are the most common of a total of 21 recorded species. All the identified algal species are also living in the present-day Mediterranean except for the extinct Lithothamnion ramosissimum (Reuss) Piller, 1994 and for the recent Spongites decipiens (Foslie) Chamberlain, 1993, which has been reported in the Indo-Pacific and South Adantic, but not in the Mediterranean. Moderate energy and low sedimentation rates promoted development of rhodolith beds in the transgressive deposits, but they are not exclusive to the transgressive systems tract as they continued to accumulate at the southern margin during the highstand, beyond the influx of siliciclastics that reduced carbonate production in the rest of the basin. Isolated pillars (up to 90 cm high) or irregular patches (up to 2 m high and 7 m wide) of coralline algal-bryozoan-bivalve bioconstructions occur in outerramp fine-grained calcarenites. Despite their similarities to pillars and low relief buildups constructed by coralline algae (“coralligène de plateau”) in the present-day Mediterranean Sea, these bioconstructions are unique as bryozoans are the main builders and coralline algae (L. philippii and M. lichenoides) play only a secondary role. In contrast with modern Mediterranean coralline algal buildups, the lack of bioclastic debris derived from the build-ups in the surrounding fine-grained sediments and their general morphology suggest that the Pliocene bioconstructions in the Carboneras Basin did not create significant positive relief on the seafloor.

Benthic assemblages of rock pools in northern Portugal: seasonal and between-pool variability

We investigated the seasonal (winter vs summer and within season) and spatial (between-pool) variability of benthic assemblages of rock pools at mid-intertidal level along the shore of Viana do Castelo (North Portugal). Physical traits of rock pools, including size, depth and position along the shore, were also compared between pools. While pools did not differ for any of the examined physical traits, results indicated a clear seasonal difference in the structure of assemblages, including a total of 49 macroalgal and 13 animal taxa. This finding was driven by six taxa that are more abundant in winter (the reef-forming polychaete Sabellaria alveolata , the articulated coralline algae Corallina spp., the brown alga Bifurcaria bifurcata , the encrusting coralline alga Lithophyllum incrustans , the red alga Chondracanthus acicularis and the grazing snails Gibbula spp.) and four algal taxa that are more abundant in summer (the invasive brown Sargassum muticum , the green Ulva spp., the kelp Laminaria ochroleuca and the filamentous red Ceramium spp.). These data provide a new contribution to the knowledge of rock pool systems and have potential implications for monitoring programmes aimed at assessing ecological modifications related to natural and anthropogenic disturbances and for identifying processes responsible for the variability of rock pool assemblages.

Benthic assemblages and temperature effects on Paracentrotus lividus and Arbacia lixula larvae and settlement

Recruitment is a principal controlling factor in population dynamics of marine species. In marine invertebrates with a planktonic larval stage, such as echinoids, recruitment is assured by larval supply, settlement and juvenile survival. Larval supply and juvenile survival are affected by a wide range of factors, including temperature, presence of predators, quality and quantity of food. Echinoid larval settlement is mainly conditioned by the finding of a suitable substrate to metamorphose. The sea urchins Arbacia lixula and Paracentrotus lividus are considered key species of the Mediterranean infralittoral rocky shores. At high densities, the grazing activity of both species can produce and maintain barren grounds, a particular habitat condition characterized by extremely low cover values of erect algae with high presence of naked substrates and encrusting corallinales, poor in biodiversity and ecosystem functions. We tested the role of different settlement substrates on the metamorphosis competent larvae of the two species. Furthermore, from our larval rearing trails we were able to identify strong temperature effects on larval development of the two species. P. lividus and A. lixula larvae have been reared at 18°C but for the second species it was necessary to use higher temperatures (22°C) to perform settlement experiments, as in the 18°C set all larvae died in the first week. Both species larvae have been fed Cricosphaera elongata. Metamorphosis of competent larvae has been induced using different substrates: naked stones, Lithophyllum incrustans, Stypocaulon scoparium, Corallina elongata, turf forming algae and Posidonia oceanica. For each species, two larval batches were used for settlement experiments; for each larval batch two replicates/substrates were set up. No differences in the rate of metamorphosis on any of the tested substrates were observed for P. lividus, while A. lixula showed to prefer naked stones and encrusting coralline algae Considering that A. lixula population growth may trigger barren extension on rocky shores, this may lead to a positive feedback between barren extension and A. lixula population density. Furthermore, our results suggest that the predicted rise in seawater temperature may favor A. lixula larval survival and inhibit P. lividus. Combining information on temperature tolerance with other sources of information for these species in the Mediterranean, it is possible to develop a conceptual model of the interaction between the two species and the alternative state of their habitats.

Type and timing of disturbance modify trajectories of recovery of rockpool assemblages at Aguda (NW Portugal)

Patterns of recovery of rock pool assemblages were experimentally investigated along the rocky shore of Praia da Aguda (NW Portugal). The temporal variance in the structure of whole assemblages and abundance of individual algal and invertebrate organisms was examined after two experimental disturbances differing in intensity, i.e. one able to eliminate all the biota from the substratum, the other able to create a mosaic of bare patches interspersed within the remaining organisms. Two experimental trials were carried out (starting in March 2007 and July 2007, respectively), with a duration of the study of 13 months each. Multivariate results indicated a temporally consistent positive relationship between the intensity of disturbance applied and the temporal variance of the structure of assemblages. A similar response was documented at the univariate level by the encrusting coralline alga Lithophyllum incrustans and the foliose green algae of the genus Ulva, while both experimental disturbances decreased temporal fluctuations of the abundance of mussels, Mytilus galloprovincialis, compared to unmanipulated control. The present study has implications for understanding and predicting responses of intertidal assemblages to natural disturbances whose intensity is predicted to increase in the future, including climate events.

Influence of UV radiation on growth of sporelings of three non-geniculate coralline red algae from Southern Iberian Peninsula

SUMMARY The effects of UV radiation (UVR) on growth of sporelings of Melobesia membranacea (Esper) Lamouroux, Lithophyllum incrustans Philippi and Mesophyllum lichenoides (Ellis) Lemoine, were investigated by culturing the algae under different doses of photosynthetically active radiation (PAR) only and PAR + UVR. Under natural conditions, the light fields occurring in the habitats of the three species differ substantially. Whereas M. lichenoides and L. incrustans inhabit sun-exposed places in the eulittoral and upper part of the sublittoral, M. membranacea grows as an epiphyte in shady crevices in the eulittoral, where irradiance is < 10% of that in sun-exposed places. The relative growth rate (RGR) of sporelings of these non-geniculate coralline algae was affected by the UVR. The extent of harmful UVR effects on growth rate showed a similar increase as a function of the logarithm of the dose in the three species, inferred by a similar slope in all the linear regressions for a given action spectrum. The inhibition of growth under the PAR + UVR showed similar features in the two species of non-geniculate coralline species from sun-exposed places, that is, similar intercepts and slopes in the linear regressions of RGR as a function of the logarithm of the biologically effective dose.

Phylogenetic positions of Lithophyllum incrustans and Titanoderma pustulatum (Corallinaceae, Rhodophyta) based on 18S rRNA gene sequence analyses, with a revised classification of the Lithophylloideae

This study was initiated to reexamine phylogenetic relationships among coralline algae having secondary pit connections and lacking cell fusions. Nuclear small-subunit ribosomal RNA (18S rRNA) gene sequences were determined for the nongeniculate species Lithophyllum incrustans Philippi and Titanoderma pustulatum (Lamouroux) Nägeli and aligned with 18S rRNA sequences for 35 other coralline species. Parsimony and maximum likelihood analyses of these data yielded congruent trees in which four major lineages were resolved. In these trees, geniculate and nongeniculate species having secondary pit connections and lacking cell fusions formed a well-supported clade within the Corallinaceae. Within this clade, the geniculate genera Amphiroa and Lithothrix do not form a monophyletic group. Results suggest that the genicula of Amphiroa and Lithothrix are probably not homologous; these genera are more closely related to nongeniculate species than they are to one another. A close relationship inferred between Amphiroa and Titanoderma was robustly supported in all analyses performed. The molecular data imply that Titanoderma and Lithophyllum are phylogenetically distinct and should be maintained as separate genera. Based on these and other data, a revised classification of the Lithophylloideae is presented and the subfamily is emended. Possible phylogenetic relationships among the Lithophylloideae and other coralline subfamilies are discussed and an overview of genicular evolution within the Corallinales is presented.

Growth rates ofLithophyllum incrustans(Corallinales, Rhodophyta) from South West Wales

Growth rates of Lithophyllum incrustans, a rock-encrusting coralline red alga, have been studied at three sites on the coast of Pembroke, south-west Wales. Horizontal and vertical growth rates and calcium carbonate deposition rates were determined. There are some significant differences between sites, especially in vertical growth rates which include the formation of reproductive tissue. The data indicates that L. incrustans is, on average, 2·25 years old before reproduction is initiated. Growth rates of this alga were found to be similar to other arctic and temperate encrusting red algae, but an order of magnitude less than those in the tropics.

Spore production byLithophyllum incrustans(Corallinales, Rhodophyta) in the British Isles

Spore production in Lithophyllum incrustans, a rock-encrusting coralline red alga, was studied at 12 sites around the coast of Britain. Two types of spore are produced from asexual plants, bispores and tetraspores. The percentage of sexual plants in populations increases from north to south of the country and is strongly correlated with tetraspore production. A study of two populations over the course of one year revealed a seasonality in spore production, with plants being fertile during the winter months. Sexual plants are also fertile over the winter months.

Données preliminaires sur le contenu digestif de l'oursin comestible Paracentrotus lividus (Lamarck) soumis à l'influence d'effluents domestiques

Populations of the sea-urchin Paracentrotus lividus were investigated in an area polluted by domestic wastes from the Marseilles sewarage outfall. The organic carbon content near the outlets us about 10 g C 1−1 in the water column; it corresponds to particles coming from the precipitation and flocculation process, these becoming quickly covered with bacteria. This organic matter provides food for the mussel-beds at 1 to 3 m depth. Sea urchins (mainly below 3 m depth) also feed on this organic deposit falling on Lithophyllum incrustans thallus flourishing down to 15–18 m depth. The sea-urchins ingest small pieces of the algae itself and some of the micro- and meiobenthos assemblage living there. The pellets of the sea-urchin stomach and gut may be divided into four types: (i) Very fine—non-identified—elements mixed with some diatoms and sponge-spicules. (ii) Particles with small mineral fragments—crystalline or amorphous—also associated with diatoms and sponge-spicules. (iii) Lithophyllum fragments, together with many diatoms but few spongespicules. (iv) At station 0 and seldom at station 1. Irregular bulks and entanglements—without any mucoid envelope—of paper-fibres and threads (chiefly of toilet-paper) which apparently cannot be digested before defecated in their original state. Analysis of the constituents in each type of pellet from the four stations investigated reveals that diet is determined by the substrate and the assemblage living within, and not upon the organic matter coming from the outlets. Pollutants from the outfall, at station 0, led to a sea-urchin diet that was higher by 2·1 for Hg, 2·3 for Cu, 2·7 for Pb and 1·6 times for Zn than at station 1, where the population densities were the highest for all investigated stations. This suggests that excessive concentration of some pollutants prevents the sea-urchin from wholly benefiting from the greater food supply available.

Population biology of the crustose red alga Lithophyllum incrustans Phil. 3. The effects of local environmental variables

Populations of the crustose red alga Lithophyllum incrustans were analysed for their age structure and reproductive characteristics. Two different types of age structure were observed, and shown to be associated with different surface area to volume ratios of the rock pools from which the populations were sampled. Geographic clines and surface area to volume ratios of the pools influenced the reproductive effort and the proportion of sexual plants in the populations. The relationship between temperature, salinity, surface area to volume ratio of the pools and the life history of the alga is discussed.