The invasion of the intertidal canopy-forming alga Fucus serratus L. to southwestern Iceland: Possible community effects

The intertidal serrated wrack, Fucus serratus L. (Fucales: Phaeophyceae), has become an abundant canopy-forming alga along a ca. 100 km stretch of shore in southwestern Iceland in the last century. Its distribution has not changed noticeably since a survey in 1975/1976. Many experimental studies have shown that canopy-forming algae can have profound effects on the community structure. Although such experiments involving F. serratus are few it was decided to test predictions from these experiments on a geographical scale by comparing community compositions within the area where F. serratus is a dominant algae (since at least 1975/1976) with an adjacent area of similar size where F. serratus is absent (with a single exception without consequences). The work is based on measurements on some 372 stations in the F. serratus area, termed region A, and 227 stations from the F. serratus-free area, termed region B. Percentage cover of algae and sessile invertebrates was estimated on 2 m² on each station and animals collected from 800 cm² from each station. The vertical distribution of F. serratus was most similar to that of Fucus distichus and the two species often grew intermingled on the lower part of the shore. F. serratus appeared to have reduced the cover of F. distichus in the lowermost part of the shore, while having little or no effect on other canopy-forming species. The low abundance of Semibalanus balanoides in the F. serratus area (region A) is in line with experiments showing detrimental effect on this barnacle by whiplash of F. serratus. In general algal grazers were more abundant in region A, consistent with the greater attractiveness of F. serratus than other canopy-forming species to grazers, although this may be partly explained by the abundance of understorey algae in region A.     

Effects of temporal variation of the seaweed Caulerpa prolifera cover on the associated crustacean community

The aim of this study was to establish the effect of temporal variation of the alga Caulerpa prolifera cover on the composition and stability of the associated crustacean community. Forty‐five crustacean species were found, amphipods and tanaidaceans being the most abundant groups. The stations were grouped mainly based on the gradient of algal cover, independently of location or sampling period (MDS analyses). Considering separately epifaunal and infaunal species, the epifauna occurred mainly at high cover (HC) and medium–low cover (MLC) stations, while the infauna occurred at MLC and unvegetated (UV) stations. Infaunal species were predominant in all stations and sampling periods, and the abundance and numbers of epifaunal species showed a clear dependence of algal cover. To quantify the loss of biodiversity due to the plant cover variations, we applied the average and variation in taxonomic distinctness (Δ⁺ and Λ⁺, respectively). The HC stations, especially those with fewer algal cover variations along the study period, showed few fluctuations of Δ⁺,and Λ⁺ was usually located near mean; however, UV stations tended to fall in the area where the statistical power of the test is reduced and showed more oscillations of Λ⁺. The ability of these indices to test the fauna composition in function of the alga presence is discussed.     

The effect of dissolved copper on the increase in length of four species of intertidal fucoid algae

The growth of Pelvetia canaliculata (L.) Dec. et Thur., Fucus spiralis L., Fucus vesiculosus L. and Fucus serratus L. is measured in various concentrations of copper (12–970 μg/litre) during a period of ten days. Significant reductions in growth were observed at 12 μg/litre of copper added for P. canaliculata and F. spiralis, at 25 μg/litre for F. serratus and at 50 μg/litre for F. vesiculosus. There is a linear relationship between the percentage reduction (z) in growth rate and the product of time (x) and concentration (y), giving the equation z = kx × xy. The constant k is specific and may be used as a measure of resistance capacity to copper exposure. When previous data on Ascophyllum nodosum (L.) Le Jolis are included the five large Fucoids in the intertidal area may be ranked as follows according to their resistance capacity: $\text{A. nodosum > F. vesiculosus > P. canaliculata ? F. spiralis > F. serratus}$.     

Seasonal variation of molluscan assemblages in different strata of photophilous algae in the Alboran Sea (western Mediterranean)

The seasonal dynamics of molluscan assemblages inhabiting the algal fronds and the underlying sediment of photophilous algae were analyzed in NW Alboran Sea between July 2007 and April 2008. Molluscs were sampled using SCUBA in two different algal stands (7 km apart) dominated by the brown algae Stypocaulon scoparium, and following an inter-strata sampling protocol consisting in first sampling the algal fronds and then the underlying substratum. The studied algal stands harbored a highly biodiverse malacofauna, with 193 species identified. Assemblages on algal fronds and sediment displayed significant seasonal variations, being more apparent on the fronds, with maximum species richness, abundance and Shannon–Wiener diversity values in summer in both strata. The between-strata differences were also observed in the trophic structure of the assemblages: algal fronds were quantitatively dominated by microalgae or periphyton grazers and the sediment by detritivores and plankton and seston feeders. The high dominance of some species resulted in lower values of diversity and evenness in autumn in the sediment (e.g. Nodulus contortus and Bittium reticulatum) and in spring on the fronds (e.g. Rissoa guerinii and Musculus costulatus). The seasonal variability of the assemblages was mainly related to the population dynamics of dominant species (22 spp. displaying dominance values > 1%) (i.e. recruitment events, high mortality rates of juveniles and/or migrations among habitats). Other factors analyzed were (1) the vegetative cycle of algae, which played an important role in the abundance of some dominant epifaunal grazers, with high abundance and species richness values coinciding with high biomass of algae; and (2) the percentage of organic matter in the sediment, which was related to the abundance changes of some depositivores species. Further conservation strategies for macroalgal stands should be taken into consideration, as this type of photophilous habitat harbors rich associated faunistic communities and it is not generally considered in conservation lists of habitats to be protected.     

Release and transformations of inorganic iodine by marine macroalgae

A number of field and laboratory studies on the impact of marine macroalgae on dissolved inorganic iodine speciation are presented. Within tidally isolated rock pools, the brown macroalga Fucus serratus was found to both release stored iodide and to facilitate the reduction of iodate to iodide. In contrast, no discernible changes in iodine speciation were observed in rock pools containing green macroalgae of the genus Ulva. Incubation experiments confirmed that the macroalgae Laminaria digitata, F. serratus and Kallymenia antarctica release iodide, though the rate of release varied between species and between specimens of the same species. Application of oxidative stress by treatment with cell wall derived oligoguluronate elicitors increased the efflux of iodide by L. digitata approximately 20-fold. The release of iodide by macroalgae may impact upon the formation of volatile iodine species (molecular iodine and iodocarbons) that are of importance in the coastal atmosphere.     

Spatial patterns of epifaunal communities in San Francisco Bay eelgrass (Zostera marina) beds

Epifaunal invertebrate species, such as amphipods and isopods, have been shown to play key but varying roles in the functioning of seagrass habitats. In this study, we characterized patterns in the poorly known epifaunal communities in eelgrass (Zostera marina) beds in San Francisco Bay as a first step in understanding the individual and collective importance of these species, while testing predictions on spatial patterns derived from previous studies in other regions. Surveys conducted at five beds across multiple time periods (April, June, August and October 2007) showed that San Francisco Bay eelgrass beds varied strongly in epifaunal community composition, total, and relative abundance, and that abundance differed markedly among time periods. In contrast to findings by others, morphologically complex flowering shoots frequently harbored greater numbers of epifauna (>2× and up to 10× more individuals) than vegetative shoots, but not different species assemblages. Similar to previous studies, several abiotic factors did not explain patterns in distribution and abundance among beds. The proportion of introduced species was very high (>90% of all individuals), a finding unique among seagrass epifaunal studies to date. Defining numerical patterns in epifaunal communities will inform related efforts to understand effects of epifaunal species and assemblages on eelgrass growth dynamics, seed production, and higher order trophic interactions over space and time.     

The introduction of Sargassum muticum modifies epifaunal patterns in a Moroccan seagrass meadow

Marine macrophytes sustain valuable epiphytic biodiversity. Nonindigenous macroalgae may induce changes in composition and structure of epifaunal assemblages and therefore support different assemblages from those associated with native species. In this study, differences in faunal community structure between the introduced fucoid Sargassum muticum and the native seagrass Cymodocea nodosa were tested over a year on an intertidal shallow sandy bottom at the southern introduction front, the El Jadida coastline (NW Morocco). Epifaunal community structure consistently differed between macrophytes through seasons, with more species‐rich assemblages associated with S. muticum than C. nodosa despite comparable abundances. The significantly greater epifauna diversity on S. muticum may be related to its structural complexity. However, the species contributing most to differences in assemblages between both macrophytes, such as Steromphala umbilicalis and S. pennanti, were found on both habitats with temporally varying abundances. Some species‐specific affinities were detected (Stenosoma cf. acuminatum, Elasmopus vachoni, Chauvetia brunnea). Nitrogen, dissolved oxygen, suspended matter and temperature were identified as the best explanatory variables contributing to the observed macroepifaunal patterns. This study provides evidence that S. muticum acts as a favourable and additional habitat for epifaunal species and supports a more diverse epifaunal assemblage in this Moroccan seagrass meadow.     

Macroalgal associations of motile epifaunal invertebrate communities on coral reefs

Small grazing motile epifaunal invertebrates play an important ecosystem role on coral reefs, influencing both the abundance and composition of macroalgal communities and acting as a key food source for a range of predatory fishes. The first aim of this study was to investigate the associations between motile epifaunal communities and four common macroalgal species (Lobophora variegata, Dictyota divaricata, Microdictyon marinum and Halimeda opuntia) on fore‐reef environments in the Exuma Cays (Bahamas, wider Caribbean). Secondly, we investigated the implications of the well documented rise of Caribbean macroalgal cover on invertebrate densities by surveying sites inside and outside the Exuma Cays Land and Sea Park (ECLSP), where increases in parrotfish grazing intensity inside the marine reserves have led to reductions in macroalgal cover. Therefore, surveys compared similar reefs with significantly different macrolagal cover. Comparisons between macroalgal species revealed a four to fivefold difference in motile epifaunal densities per unit volume of macroalgae. Post‐hoc tests revealed that this difference was significant only for Lobophora, with no difference observed among the other species. As macroalgae provide both a refuge from predation and a food source for grazing epifauna, the higher densities of epifauna observed in Lobophora may be attributed to either refuge from visual predators through morphological features (high cover of overlapping blades close to the substrate) or lack of palatability for parrotfish grazing, providing a more stable refuge. Our results revealed no significant differences in diversity, density or community structure of motile epifauna per unit volume of macroalgae between sites inside and outside the ECLSP. Since canopy height and invertivore biomass did not vary systematically across reserve boundaries, this suggests that algal cover does not affect the density of epifaunal invertebrates. However, areal cover was consistently higher for all macroalgal species at sites outside the ECLSP than those inside the reserve. Therefore, when scaled by aerial cover of macroalgae, total abundance of epifauna was twofold higher outside the ECLSP. We suggest that the increasing abundance of macroalgae on Caribbean reefs may be having dramatic effects on epifaunal invertebrate populations and potentially their ecological functions.     

Experimental evidence of habitat provision by aggregations of Riftia pachyptila at hydrothermal vents on the East Pacific Rise

Habitat created or modified by the physical architecture of large or spatially dominant species plays an important role in structuring communities in a variety of terrestrial, aquatic, and marine habitats. At hydrothermal vents, the giant tubeworm Riftia pachyptila forms large and dense aggregations in a spatially and temporally variable environment. The density and diversity of smaller invertebrates is higher in association with aggregations of R. pachyptila than on the surrounding basalt rock seafloor. Artificial substrata designed to mimic R. pachyptila aggregations were deployed along a gradient of productivity to test the hypothesis that high local species diversity is maintained by the provision of complex physical structure in areas of diffuse hydrothermal flow. After 1 year, species assemblages were compared among artificial aggregations in low‐, intermediate‐, and high‐productivity zones and compared to natural aggregations of R. pachyptila from the same site. Hydrothermal vent fauna colonized every artificial aggregation, and both epifaunal density and species richness were highest in areas of high chemosynthetic primary production. The species richness was also similar between natural aggregations of R. pachyptila and artificial aggregations in intermediate‐ and high‐productivity zones, suggesting that complex physical structure alone can support local species diversity in areas of chemosynthetic primary production. Differences in the community composition between natural and artificial aggregations reflect the variability in microhabitat conditions and biological interactions associated with hydrothermal fluid flux at low‐temperature hydrothermal vents. Moreover, these local ecological factors may further contribute to the maintenance of regional species diversity in hydrothermal vent communities on the East Pacific Rise.     

RELATIONSHIP BETWEEN PHOTOSYNTHESIS OR RESPIRATION OF SOME SEAWEEDS AND TEMPERATURE OR SALINITY

The effect of temperature and salinity on the photosynthetic and respiratory rates of some seaweeds are reported. The regression equations for the seaweeds and their correlograms are discussed and compared.The results indicate that the photosynthetic rate of E. binghamiae fronds shows a significant negative linear correlation (p<0.01) with changing of temperature (20-35℃), the optimum temperature being 20℃, while for the others there is a conic correlation between photosynthetic rate and temperature.The optimum temperature for photosynthesis is 23-25℃ for two species of Porphyra fronds, 25-28℃ for Gracilaria sp. thalli and 23-30℃ for V. conglobata and S. hemiphyllum fronds, separately. The rates of respiration for all the studied species increase linearly with increasing temperature from 18 to 35℃. The optimum salinities for photosynthesis range from 26 to 32 for two species of Gracilaria, whose respiratory rates decrease gradually with increasing salinity.     

Benthic foraminifera as bioindicator for cold-water coral reef ecosystems along the Irish margin

Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, >63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species (Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting.     

Trace metal concentrations in brown seaweeds, Cardigan Bay, Wales

Concentrations of zinc, cadmium, copper, manganese, iron, cobalt, nickel and molybdenum are examined in brown algae, Fucus serratus and F. vesiculosus, from Cardigan Bay, Irish Sea, Great Britain. In both species a seasonal variation in metal content was observed. Zinc, cadmium, copper, iron nickel and cobalt concentrations were highest in the spring and lowest in the autumn, probably reflecting levels of metabolic activity and climatic factors. All the studied elements, except nickel, reached highest concentrations in harbour specimens from Aberystwyth and Aberaeron where rivers draining mineralized areas enter the sea. Outside harbours, marked regional variations were observed in most of the studied elements. Zinc values were highest in the Aberystwyth area while copper and manganese were highest in the northeast part of the bay.Trace-element concentrations varied among different species from the same locality and also varied according to position on the shore.Marine algae may be used to monitor coastal-water trace-metal concentrations, provided a careful sampling procedure is adopted.     

A comparative study of the photosynthetic activity among three temperate seagrass species in Northern Japan

The photosynthetic activity of Zostera marina, Zostera asiatica and Phyllospadix iwatensis shoots from populations of Hokkaido (Northern Japan) was determined using the pulse amplitude modulated (PAM) fluorometer. Several fluorescence parameters were measured as a function of irradiance and leaf age: electron transport rate (ETR), quantum yield, photochemical quenching (qP) and non‐photochemical quenching (NPQ). The leaf age determined by the leaf position in the shoot bundle strongly influenced the photosynthetic activity of Z. marina, Z. asiatica and P. iwatensis. Young leaves had the maximum electron transport rate (Zm: Leaf 1 = 15.7, Leaf 2 = 16.3; Za: Leaf 1 = 13.0, Leaf 2 = 12.2; and Pi: Leaf 1 = 12.5, Leaf 2 = 11.7) and showed higher photoprotection (NPQ) than old leaves. Among the studied seagrass species, Z. marina had the highest photosynthetic activity (ETR_max = 15.3), in accordance with the highest production in the field in comparison with the other two seagrass species. The PAM fluorometry technique showed to be effective in determining intraspecific (among‐leaves) and interspecific (among‐species) variation in seagrass photosynthetic activity.     

Geographical ecology of the symbiotic crabs Libinia ferreirae and Libinia spinosa: Distributional patterns in south and south-eastern coast of Brazil

The Brazilian coast is home to two species of Majoid crabs: Libinia ferreirae and Libinia spinosa, with similar habits, as they live in symbiosis with the jellyfish Lychnorhiza lucerna during their juvenile stage and dwell on the bottom of the ocean near the coast when adults. This study investigated the spatial and temporal distribution of L. ferreirae and L. spinosa during different ontogenic phases on the south and south-eastern coast of Brazil, between latitudes 22º and 27ºS. Our results showed that both species have different distributions during their development in the three studied regions. Libinia ferreirae were more abundant associated with jellyfish, and L. spinosa were more abundant in the free-living phase. Environmental factors, especially temperature and salinity, for associated and free-living crabs, respectively, are the main factors that need to be supported for the establishment of these specimens. We were able to identify that the presence or absence of hosts (given the ecological interactions between the species) is determinant in finding the associated crabs. Geographical variations (morphology of the regions, marine currents and the strength of the tide) are linked directly to the movement of the jellyfish hosts to the coast, influencing the abundance of L. fereirae and L. spinosa populations and affecting their distribution patterns. We can infer that both species are connected with other populations because of the association with the jellyfish, crabs could be passively transported along the south and south-eastern coast of Brazil, maintaining the connection between metapopulations.     

Spatial and diurnal distribution of invertebrate and fish fauna of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA)

Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and fish were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m⁻². Abundance and species number of fish were greater at night than during the day and greater in eelgrass beds (Z. marina) than in unvegetated habitats. Daytime fish collections were dominated by Atlantic silversides (Medinia medinia), while juvenile winter flounder (Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were significantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only five occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were significantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values (H′) were relatively low but fit well in the general pattern of decreasing diversity towards northern latitudes.     

Photoacclimation of the invasive alga Caulerpa racemosa var. cylindracea to depth and daylight patterns and a putative new role for siphonaxanthin

The introduced green alga Caulerpa racemosa var. cylindracea grows along a broad depth range (from very shallow to 60 m depth) in the Mediterranean basin. In the present work, the photoacclimation capacity of this invasive variety was investigated in summer, the season of its maximum spread. Natural populations from the Gulf of Naples (Italy) were analyzed for photoresponse on two scales of light variability: a spatial scale (at three stations along a depth gradient, from 0.3 to 20 m depth) and a temporal scale (on the shallowest meadow, from sunrise to sunset). These responses were studied through pigment analysis (with HPLC), and in situ measurements of photosynthetic parameters (with a Diving‐PAM fluorometer). Electron transport rate (ETR)–irradiance curve parameters showed acclimation along environmental gradients dominated by variation in irradiance. In the shallowest plants, the lack of a midday depression in both the maximum relative ETRs and the photosynthetic efficiency at sub‐saturating irradiance (α) pointed to a maintenance of energy conversion levels despite the protective lowering of light‐harvesting efficiency revealed by the trend in F_v/F_m. On the other side, variation of photosynthetic efficiency occurred with depth and buffered the effect of decreasing light on maximum photosynthetic rates. A previously undescribed xanthophyll cycle centred on lutein‐siphonaxanthin interconversion appeared to operate in the shallowest populations in addition to the violaxanthin/antheraxanthin/zeaxanthin cycle commonly occurring in Chlorophyta; this would further enhance phototolerance of the alga. A further role of siphonaxanthin is in the acclimation to low light of deep environments as indicated by its stronger increase from the surface to the deepest station with respect to siphonein and chlorophyll b.     

浙江三门湾海域主要底上动物生态位及种间联结性

大型底上动物参与海洋生态系统中的物理、化学和生物过程,具有极高的研究价值。浙江三门湾是天然的半封闭海湾,也是海洋生物重要的栖息、觅食和育幼的场所。为探究三门湾海域物种间的资源利用情况及生态关系,在该海域进行了底拖网生物调查。根据2017年和2018年夏季在三门湾海域进行的大型底上生物研究结果,运用优势度(Y)、生态位宽度、生态位重叠、方差比率法(VR)、χ²检验、联结系数(AC)、共同出现百分率(PC)对生态位和种间联结性进行了研究。结果表明: 2017~2018年间三门湾海域共捕获大型底上动物53种,包括两年共有种,即主要底上动物22种。其中优势种3种,包括哈氏仿对虾(Mierspenaeopsis hardwickii)、中华栉孔虾虎鱼(Ctenotrypauchen chinensis)和棒锥螺(Turritella terebra),这三个物种属中生态位种;三门湾主要底上动物依据生态位宽度值划分为3组,即广生态位种、中生态位种和窄生态位种;种对间生态位重叠值总体差异性较大,其与种对的食性、栖息环境密切相关;根据总体联结性分析得主要底上动物总体呈显著正关联,群落结构较为稳定; χ²检验、联结系数(AC)和共同出现百分率(PC)表明种对间联结性较弱,趋近于相互独立。三门湾大型底上动物的群落结构比较稳定,但种对间的关联性在逐渐下降。     

The mutagenicity of acid digests from several common marine macroalgae (Fucus serratus,Porphyra umbilicalis,Enteromorpha spp.)

Acid digests of three common marine macroalgae (Fucus serratus, Enteromorpha spp., Porphyra umbilicalis) exhibit substantial mutagenic activity for Salmonella typhimurium strains TA98 and TA100 in the microtire fluctuation test. Although these algae are known to concentrate heavy metals, the mutagen(s) is probably an organic compound(s).Collections of these three marine macroalgae were made along the Gower coast of Wales, Great Britain, at distances between 8·0 and 32·0 km from the industrial center of Swansea-Port Talbot. When tested for mutagenicity with TA98, the acid digests of F. serratus and Enteromorpha spp. showed an inverse relationship between activity and distance from Swansea-Port Talbot. This relationship was not observed with P. umbilicalis or with any of the digests when tested with TA100.These data are consistent with the hypothesis that Swansea-Port Talbot is a point emitter for contaminants which are mutagenic for TA98 and are accumulated by Enteromorpha and Fucus.     

Acute toxicity of a used chrome lignosulphonate drilling mud to several species of marine invertebrate

The acute toxicity of a used seawater chrome lignosulphonate drilling mud to several species of marine annelids, crustaceans and molluscs was evaluated. The medium density mud (13·4 lb/gal, 1·57 kg/litre) was composed primarily of seawater, bentonite clay, chrome lignosulphonate, lignite, sodium hydroxide and barium sulphate. The toxicity of four mud/seawater preparations was determined. These were the layered solids phase (LSP), the suspended solids phase (SSP), the unfiltered mud aqueous fraction (MAF) and the filtered mud aqueous fraction (FMAF). Four species each of marine annelids and bivalve molluscs and five species of marine crustaceans were evaluated. The median lethal concentration of the MAF (96-h LC₅₀) varied from 32 to > 100% MAF for the different species. The FMAF was slightly less toxic than the MAF. Adult polychaetes, Neanthes arenaceodentata and Ctenodrilus serratus, one-day old juveniles of opossum shrimp, Mysidopsis almyra, and four day zoeae of grass shrimp, Palaemonetes pugio, were the most sensitive to the MAF. Juvenile N. arenaceodentata, adult polychaetes, Ophryotrocha labronica, and three bivalve molluscs were highly tolerant to the MAF. The SSP preparation at concentrations of 10-20 ml/litre was toxic to post-larvae and juveniles of the commercial shrimp, Penaeus duorarum and P. aztecus, respectively. Exposure to the LSP preparation caused greater than 50% mortality amongst adult N. arenaceodentata, juvenile and adult coquina clams, Donax variabilis texasiana and adult scallops, Aequipecten amplicostatus. Other species tested were quite tolerant. A sublethal response observed was the inhibition of reproduction in the marine annelids, Dinophilus sp. and Ctenodrilus serratus. Toxicity of the mud aqueous fractions appeared to be due primarily to volatile soluble organic materials in the extract, whilst that of the SSP and LSP preparations appeared to be due to the smothering action of fine particulates in the mud. Based on the results of this investigation and published observations of solids concentrations in the water column during drilling mud discharge, it is concluded that discharge of a used chrome lignosulphonate drilling mud, such as that used in the present investigation, from offshore platforms is not likely to cause measureable damage to benthic, demersal or pelagic marine animals.