RQ of benthic marine invertebrates

This study investigated an incubation method which employed simultaneous measurement of CO₂ production and O₂ consumption rates to calculate the RQ (respiratory quotient; CO₂ production rate: O₂ consumption rate) of individual benthic marine invertebrates. Carbon dioxide production rates were calculated from changes in CO₂ concentration determined using seawater pH. O₂ consumption rates were calculated from changes in O₂ concentration with a correction applied for O₂ flux across the air/water interface due to gaseous exchange. Species examined were Triphyllozoon sp. cf. moniliferum (MacGillivray 1860), a bryozoan; Herdmania momus (Savigny), a solitary ascidian; Poneroplax albida (Blainville 1825), a chiton; and Haliotis roei (Gray 1826), an abalone. Six individuals of each were collected on 14 November 1985 from the limestone walls of a cave in a nearshore reef off Marmion, Western Australia. After acclimation for 6 h in experimental conditions, rates of CO₂ production and O₂ consumption were measured. A minimum period of 4 h was required to obtain consistent RQ values for each species. The standard error (SE) of the (calculated) RQ ratio was 14 to 33% of the mean in incubations of 4 h, and less than 14% in incubations of 4 to 12 h. The RQ is commonly used as an indicator of unknown catabolic substrates by comparing it with biochemically determined limits for known substrates. This study provides a strong argument against using the RQ of individual animals to draw any conclusions about catabolic substrates. Unexplained variation in the components of the RQ of an individual, measured over short time periods, and the potential involvement of stored reserves in catabolism, over longer time periods, obscure the relationship between the RQ of individual animals and the ratio's biochemically determined limits.     

Community recruitment: Settlement and juvenile survival of seven co-occurring species of sessile marine invertebrates

Recruitment of a group of co-occurring sessile invertebrates (a serpulid polychaete, an oyster, a bryozoan, and several colonial and one solitary ascidian) that encrust floating docks in Pearl Harbor, Hawaii, was studied in August 1985. Daily photographs were taken of acrylic settling plates over a 14 d period, and daily settlement and juvenile mortality were measured. Settlement rates were compared between species and days, while juvenile mortalities were compared between species, days, juvenile ages and densities of juveniles on the plates. Species differed in abundance of both settlers and juveniles, and in rate and pattern of juvenile mortality. Settlement intensity varied between days for some species. Significant juvenile mortality occurred during the 14 d for most species; it appeared to be caused by fish predation. For two species, mortality varied with juvenile age, with older individuals suffering higher mortality. Mortality was density-dependent for some species, increasing with numbers of juveniles on the plates. Mortality patterns varied even within the colonial species. Assessing larval settlement and juvenile mortality for a single species or type of organism in a community thus may not indicate that similar patterns exist for co-occurring species.     

On predation of pelagic larvae and early juveniles of marine bottom invertebrates by adult benthic invertebrates and their passing alive through their predators

The dynamic quantitative balance between prey and predator invertebrate species inhabiting the same shallow-shelf (sublittoral level bottom) benthic communities was first discussed by Thorson (1953). Thorson considered the exact timing of larval settlement of prey and predator species possessing pelagic development and temporal supression of the adult predators' feeding activities during reproduction at the time of the preys' settlement to constitute the major factors which facilitate survival of the prey species in such communities. However, information obtained demonstrates that Thorson's “mechanism of balance between predator and prey species of benthic communities” is not always effective in securing survival from predation not only of the prey's spat but even sometimes of the predator's spat also. Because of this, the “mechanism” can not be rated as universally effective in all situations. Analysis of the data so far published demonstrates that, in marine benthic communities, especially in shallow-shelf waters, it is not uncommon for gametes, larvae, or early juveniles of different prey species to pass alive through suspension (filter)-feeding and deposit-feeding adult invertebrates preying on them. Sometimes development can even continue after excretion by predators. The hypothesis of Voskresensky (1948) and Goycher (1949) of the importance of this phenomenon for the maintenance and recruitment of the mussel Mytilus edulis and other filter-feeding lamellibranchs of nearshore waters preying on their own and other lamellibranch pelagic larvae must be rejected on the basis of accumulated data on their feeding and general biology and on the adverse influence of the mucous of their faecal pellets and pseudofaeces on the larvae excreted by them alive. The data considered here demonstrate that, although the passing alive of larvae and spat of benthic invertebrates through benthic predators is not uncommon in shallow-shelf bottom-communities, it plays no important role in the processes of maintenance and recruitment of the species and communities involved nor of the marine benthos as a whole. The actual ecological significance of predation on pelagic larvae and bottom spat of benthic invertebrate prey species by all three main trophic groups of marine benthos (suspension or filter-feeders, deposit-feeders, carnivores) and its importance to predator-prey dynamics in marine benthic communities remains open to debate until more reliable quantitative data become available.     

Responses of marine benthic microalgae to elevated CO2

Increasing anthropogenic CO₂ emissions to the atmosphere are causing a rise in pCO₂ concentrations in the ocean surface and lowering pH. To predict the effects of these changes, we need to improve our understanding of the responses of marine primary producers since these drive biogeochemical cycles and profoundly affect the structure and function of benthic habitats. The effects of increasing CO₂ levels on the colonisation of artificial substrata by microalgal assemblages (periphyton) were examined across a CO₂ gradient off the volcanic island of Vulcano (NE Sicily). We show that periphyton communities altered significantly as CO₂ concentrations increased. CO₂ enrichment caused significant increases in chlorophyll a concentrations and in diatom abundance although we did not detect any changes in cyanobacteria. SEM analysis revealed major shifts in diatom assemblage composition as CO₂ levels increased. The responses of benthic microalgae to rising anthropogenic CO₂ emissions are likely to have significant ecological ramifications for coastal systems.     

Nitrogen and phosphorus turnover in some benthic marine invertebrates: implications for the use of C:N ratios to assess food quality

The present study was designed to measure the relative turnover of nitrogen and phosphorus during a standard period of metabolism among several co-occurring species of benthic invertebrates: chitons (Poneroplax albida Blainville 1825); albalones (Haliotis roei Gray, 1826); gastropods [Turbo (ninella) torquatus Gmelin, 1791]; ascidians [Herdmania momus (Savigny)]; and sponges (Aplysina sp. and Iotrochata baculifera Ridley, 1884). Five of the six species (collected at Wreck Rock, Western Australia in 1985) exhibited a high turnover of phosphorus (P) relative to nitrogen (N). In contrast to N, P turnover was related to the concentration of P in body tissues. A relatively high demand for P in the diet is required to support the observed rapid turnover of P with respect to N. This observation suggests that the evaluation of potential foods would be better accomplished by the measurement of the C:P or the N:P ratio, rather than the commonly used C:N ratio.     

High pressure effects on marine invertebrates and fishes

A survey of literature and of new information from the author's laboratory is presented concerning the comparative pressure physiology of marine invertebrates and fishes. Short term experiments on littoral marine animals have revealed that the taxonomic groups exhibiting the greatest resistance to high pressures are those with the greatest vertical distributions in the deep sea, namely, echinoderms, molluscs, amphipods, isopods and polychaetes. Shallow water species which possess high thermal and osmotic resistance also show an exceptionally high degree of pressure resistance. The relative differences in genetic pressure resistance of lower marine invertebrates are the same in whole, intact animals and in isolated, surviving tissue pieces. Adaptation of nonregulating euryoecous invertebrates to higher temperatures, higher osmotic concentrations and higher calcium contents of the tissues results in increased pressure resistance. Under pressure, the optimum cellular pH shifts downward to a lower pH range.Lecture presented on October 23, 1967 at Duke University, Marine Laboratory, Beaufort (USA); on November 6, 1967 at the Instituto di Biologia Marinha of the University of São Paulo (Brasil); and on November 8, 1967 at the Institute of Marine Science of the University of Miami (USA).     

Studies on the resistance of marine bottom invertebrates to oxygen-deficiency and hydrogen sulphide

Oxygen-deficient and H₂S-containing marine areas are characterized by a decline in the number of species. In laboratory experiments with bottom invertebrates from various biotopes of the North Sea and the Baltic, comparative measurements of the resistance to oxygen-deficiency alone, and to the simultaneous presence of H₂S, were carried out. The resistance values obtained show relations to the substratum on which the species naturally occur. The resistance to H₂S is greater in those macrofauna species which show higher survival rates under oxygen-deficiency. Further experiments with isolated tissues demonstrate that the species specific differences in resistance occurring in whole animals are already based on the cell metabolism. In general, oxygen-deficiency and simultaneous presence of H₂S were endured better in cold than in warmth, and at somewhat reduced pH-values (around 7). The dependence of this resistance on the salinity was only minimal in euryhaline species.     

Global biodiversity patterns of benthic marine algae

Species richness patterns are remarkably similar across many marine taxa, yet explanations of how such patterns are generated and maintained are conflicting. I use published occurrence data to identify previously masked latitudinal and longitudinal diversity gradients for all genera of benthic marine macroalgae and for species in the Order Bryopsidales. I also quantify the size, location, and overlap of macroalgal geographic ranges to determine how the observed richness patterns are generated. Algal genera exhibit an inverse latitudinal gradient, with biodiversity hotspots in temperate regions, while bryopsidalean species reach peak diversity in the tropics. The geographic distribution of range locations results in distinct clusters of range mid-points. In particular, widespread taxa are centered within tight latitudinal and longitudinal bands in the middle of the Indo-Pacific and Atlantic Oceans while small-ranged taxa are clustered in peripheral locations, suggesting that variation in speciation and extinction are important drivers of algal diversity patterns. Hypotheses about factors that regulate diversity contain underlying assumptions about the size and location of geographic ranges, in addition to predictions as to why species numbers will differ among regions. Yet these assumptions are rarely considered in assessing the validity of the prevailing hypotheses. I assess a suite of hypotheses, suggested to explain patterns of marine diversity, by comparing algal-richness patterns in combination with the size and location of algal geographic ranges, to the richness and range locations predicted by these hypotheses. In particular, the results implicate habitat areas and ocean currents as the most plausible drivers of observed diversity patterns.     

Fish feeding on mobile benthic invertebrates: influence of spatial variability in habitat associations

Patterns of habitat association and foraging were examined for a group of tropical goatfishes (family Mullidae) that feed on mobile benthic invertebrates at Lizard Island (Great Barrier Reef). All goatfish possess barbels that disturb the substratum during feeding. Foraging methods were examined for the six most common species and used in conjunction with data on habitat associations to estimate the distribution and potential impact on the benthic invertebrate assemblage of foraging-related disturbance. Particular species exhibited broad habitat associations which differed little over two surveys (January 1989, January 1990). All species showed different preferences for the substrata they foraged. Preferences for substrata exhibited by the most common reef-associated species, Parupeneus multifasciatus, differed among locations separated by 1 km, between sites 150 m apart, and between depths (shallow and deep). Habitat preferences changed with ontogeny. Based on their habitat associations and foraging preferences, species were divided into habitat generalists and specialists. Specialists associated primarily with soft sediments. Habitat generalists, such as P. multifasciatus and P. cyclostomus, are likely to have an impact on their mobile invertebrate prey that is localised, diffuse and transitory, making any experimental analysis difficult and expensive. Habitat specialists form a guild of fishes with complementary feeding modes that efficiently exploit soft sediments and are more amenable to experimental manipulation. Experiments designed to detect the impact of foraging by these fishes must be repeated at different locations and times and must account for depth differences in foraging pressure.     

Temperature effects on behavior and survival of marine invertebrates exposed to variations in hydrostatic pressure

Investigation into the pressure resistance of 8 intertidal species belonging to the genera, Uca, Sesurma, Talorchestia and Littorina from the Northern Gulf of Mexico and Panama sheds light on the relationships between temperature and hydrostatic-pressure resistance. Generally, increasing temperature increases the pressure required to elicit reversible reactions such as increased activity and tetany, or paralysis, wheroas increasing temperature generally evokes the irreversible response of death (LD₅₀) at a decreasing pressure. Tropical stenotherms tend to be more sensitive to hydrostatic pressure than eurythermal-temperate species at the same or similar temperatures.     

Influence of environmental factors on selenium flux in two marine invertebrates

The influence of certain environmental factors on the flux of selenium through marine biota has been studied, using Mytilus galloprovincialis and Lysmata seticaudata as test organisms of commercial interest. Over a selenium concentration range in sea water spanning 3 orders of magnitude, bioaccumulation of selenium by mussels was strongly dependent upon the ambient selenium concentration in sea water. Mussels accumulated Se (+4) to a much greater extent than Se (+6) and bioaccumulation was dependent upon temperature and mussel size. The presence of varying amounts of mercury did not significantly alter selenium uptake kinetics in mussels. Shrimp accumulated selenium to a lesser degree than mussels, the difference in concentration factors being due to the large amount of sorbed isotope lost with shrimp molts. Once incorporated, selenium was lost more rapidly from shrimp than from mussels. Temperature influenced selenium loss from mussels but did not alter the elimination rate in shrimp. Neither the chemical form of selenium nor mercury concentration in the organism affected loss of selenium from mussels. Elimination of selenium from shrimp was dependent upon the route of uptake; more rapid loss was noted from individuals which had absorbed the isotope directly from water than from those which had accumulated selenium via the food chain. In general, long-term selenium turnover rates were quite similar for both species; biological half-times ranged from 58 to 60 days for shrimp and 63 to 81 days for mussels. In the case of mussels, turnover rates measured in animals maintained in the laboratory differed somewhat from those determined from individuals held in field enclosures. Observed variations in flux rate may have been due to differences in food availability in the two experimental systems.Based on a communication given at the International Symposium on Interaction Between Water and Living Matter, Odessa, USSR, 6–10 October, 1975.     

Man-made structures on marine sediments: Effects on adjacent benthic communities

This study (1975–1977) examines the effect of man-made structures on natural sand bottom communities in shallow water in San Diego County, southern California, USA. While there were shallow scour effects to 15 m around some artificial reefs, the reefs had no measurable effect on sand ripple patterns, grain size, organic carbon or infauna beyond the scoured areas. Foraging by reef-associated fishes produced profound alterations in the epifauna populations of the sea pen Stylatula elongata. The sea pen densities were 4 to 10 m^-2 before the reefs were established, but within 5 mo were eliminated from distances greater than 200 m around the reefs. On the other hand, densities of the tube-building polychaetes Diopatra spp. seemed to be enhanced in the immediate vicinity of the artificial reef. Oil platforms and bridge pilings seem to have much more profound effects on the nearby sand communities than do the relatively small artificial reefs. In addition to the elimination of sea pens, Diopatra spp. densities increased from <1.0 m^-2 in control areas to as many as 73 m^-2 in the vicinity of oil platforms. Grain size and infauna were strongly affected by the oil platform.     

The effects of chlorination of wastewater on fertilization in some marine invertebrates

Unchlorinated domestic sewage was found to be a relatively weak inhibitor of external fertilization in 3 marine invertebrates. Chlorinated sewage was a potent spermicide, active in inhibiting fertilization in concentrations of available chlorine as low as 0.05 ppm. Sodium hypochlorite in seawater duplicated the effect, and excess sodium thiosulfate terminated it. The possibility of chlorine disinfection affecting reproductive success in the vicinity of outfalls is discussed.     

Structural and functional vulnerability to elevated pCO2 in marine benthic communities

The effect of elevated pCO₂/low pH on marine invertebrate benthic biodiversity, community structure and selected functional responses which underpin ecosystem services (such as community production and calcification) was tested in a medium-term (30 days) mesocosm experiment in June 2010. Standardised intertidal macrobenthic communities, collected (50.3567°N, 4.1277°W) using artificial substrate units (ASUs), were exposed to one of seven pH treatments (8.05, 7.8. 7.6, 7.4, 7.2, 6.8 and 6.0). Community net calcification/dissolution rates, as well as changes in biomass, community structure and diversity, were measured at the end of the experimental period. Communities showed significant changes in structure and reduced diversity in response to reduced pH: shifting from a community dominated by calcareous organisms to one dominated by non-calcareous organisms around either pH 7.2 (number of individuals and species) or pH 7.8 (biomass). These results were supported by a reduced total weight of CaCO₃ structures in all major taxa at lowered pH and a switch from net calcification to net dissolution around pH 7.4 (Ω_calc = 0.78, Ω_ara = 0.5). Overall community soft tissue biomass did not change with pH and high mortality was observed only at pH 6.0, although molluscs and arthropods showed significant decreases in soft tissue. This study supports and refines previous findings on how elevated pCO₂ can induce changes in marine biodiversity, underlined by differential vulnerability of different phyla. In addition, it shows significant elevated pCO₂-/low pH-dependent changes in fundamental community functional responses underpinning changes in ecosystem services.     

Assessing the effectiveness of marine reserves on unsustainably harvested long-lived sessile invertebrates

Although the rapid recovery of fishes after establishment of a marine reserve is well known, much less is known about the response of long-lived, sessile, benthic organisms to establishment of such reserves. Since antiquity, Mediterranean red coral (Corallium rubrum) has been harvested intensively for use in jewelry, and its distribution is currently smaller than its historical size throughout the Mediterranean Sea. To assess whether establishment of marine reserves is associated with a change in the size and number of red coral colonies that historically were not harvested sustainably, we analyzed temporal changes in mean colony diameter and density from 1992 to 2005 within red coral populations at different study sites in the Medes Islands Marine Reserve (established in 1992) and in adjacent unprotected areas. Moreover, we compared colony size in the Medes Islands Marine Reserve, where recreational diving is allowed and poaching has been observed after reserve establishment, with colony size in three other marine protected areas (Banyuls, Carry-le-Rouet, and Scandola) with the enforced prohibition of fishing and diving. At the end of the study, the size of red coral colonies at all sampling sites in the Medes Islands was significantly smaller than predicted by growth models and smaller than those in marine protected areas without fishing and diving. The annual number of recreational dives and the percent change in the basal diameter of red coral colonies were negatively correlated, which suggests that abrasion by divers may increase the mortality rates of the largest red coral colonies within this reserve . Our study is the first quantitative assessment of a poaching event, which was detected during our monitoring in 2002, inside the marine reserve. Poaching was associated with a loss of approximately 60% of the biomass of red coral colonies.     

Effects of enhanced UVB radiation on a marine benthic diatom mat

In order to study the ecophysiological response of a natural diatom-dominated microbial mat to an enhanced level of ultraviolet-B radiation (UVBR), intact sediment cores from a shallow microtidal bay on the Swedish west coast were incubated in an outdoor flow-through system and exposed to either no UVBR or to an artificially enhanced level of UVBR. The microbial mat was cohesive and dominated by the large (≈ 400 μm) motile diatom Gyrosigma balticum. Functional response to UVBR was assessed by measuring carbon fixation (¹⁴C) and allocation of photosynthetic products. Sediment oxygen microprofiles were measured as indicators of the balance between the photosynthetic and respiratory activity of the community. Structural variables included biomass and composition of microalgae, pigment composition (HPLC), content of UV-absorbing compounds, and composition of fatty acids. An enhanced level of UVBR resulted in significant functional changes in the microalgal community. Significantly decreased carbon fixation and lower net oxygen production (as calculated from oxygen microprofiles) suggest that primary productivity in the type of microbial mat studied is potentially sensitive to an enhanced level of UVBR. The pattern of carbon allocation hinted a change as to the photosynthetically active part of the community when exposed to UVBR, indicating a differential sensitivity among algal cells. Despite significant functional effects, pigment or algal composition were not significantly affected by enhanced UVBR. The concentration of UV-absorbing compounds was low and did not increase at UVBR exposure. Due to the short duration of the experiment (4 d), a change in algal biomass or composition was not to be expected. Moreover, the thickness of the sampled sediment layer, may have contributed to the lack of observed structural effects of enhanced UVBR. Visual observations suggested that UVBR affected the motility of G. balticum. This study, as well as other experiments with a similar diatom mat, suggest that vertical migration is a key mechanism to be further studied in relation to UVBR exposure of diatom-dominated microbial mats. Received: 7 September 1996 / Accepted: 8 October 1996     

Long-term variability in the structure of subtidal benthic communities in Puget Sound,Washington, USA

Data on benthic infauna from 4 permanent stations in Puget Sound off Seattle, USA, collected during 1963–1964, 1967, and 1969, revealed considerable stability in numbers of species and specimens and in diversity within stations among sampling dates. The species composition of the faunal assemblages also remained rather constant during the period of investigation, but the relative dominance among the numerically important species varied somewhat. Biomass data did not differ significantly in 1964 and 1969, but the 1967 data were considerably lower at all stations.     

Larvae of benthic invertebrates in hydrothermal vent plumes over Juan de Fuca Ridge

Larvae of benthic invertebrates collected in the water column above Juan de Fuca Ridge show distinct variations in abundance and composition in, and away from, the neutrally-buoyant hydrothermal plume emanating from underlying vents. Larvae of vent gastropods (Lepetodrilus sp. and two peltospirid species) occur in significantly higher abundances in the plume than away from it (mean abundance=21.0 individuals 1000 m^?3 vs 1.4 individuals 1000 m^?3), and larvae of vent bivalves (Calyptogena? sp.) occur exclusively in the plume (mean abundance=0.5 individuals 1000 m^?3). Larvae from other benthic taxa known not to be endemic to Juan de Fuca vent communities, such as anthozoans, pholad clams, bryozoans and echinoderms, are less abundant in the plume than away (mean abundance=47.5 vs 16.9 individuals 1000 m^?3) at comparable depths and heights above the bottom. These results support the hypothesis that larvae of vent species are entrained into buoyant hydrothermal plumes and transported at the level of lateral spreading several hundred meters above the seafloor. The discovery of vent-associated larvae in the plume suggests that models used to predict hydrodynamic processes in the plume will also be useful for modeling larval dispersal. Advanced imaging and new molecular-based approaches will be required to resolve taxonomic uncertainties in some larval groups (e.g. certain polychaete families) in order to distinguish vent species and make comprehensive flux estimates of all vent larvae in the neutrally-buoyant plume.     

Contrasting effects of variable species recruitment on marine sessile communities

The species composition, density, and frequency of recruitment into any given habitat are highly variable in most biological systems that rely on dispersive propagules (larvae, seeds, spores, etc.). There are few direct experimental studies of how recruitment variation between single species influences the composition and assembly of whole communities in many of these systems. We manipulated recruitment of a variety of single taxa and followed their effects on the subsequent development of hard-substrate communities of sessile animals living in temperate marine waters. The effects of recruitment on communities were complex. Patterns of recruitment of individual species influenced community structure, but these effects varied greatly depending on the identity of species recruits, the time of community development, and location across three different sites. Variable recruitment of arborescent bryozoans and didemnid ascidians had little effect on community structure. At one site, recruitment of the colonial ascidian Botryllus schlosseri had short-lived effects on community structure, while barnacles had more persistent effects. At another site, recruitment of B. schlosseri and the bryozoan Watersipora subtorquata had strong persistent effects on community structure, dominating space where they recruited and influencing the abundances of a variety of different taxa. Differences in the effects of species recruitment on communities appear to be caused by differences between the ecology and life history of recruiting species as well as differences in background processes between sites. These results demonstrate that discrete recruitment events that vary between single species can be important drivers of community composition but are likely to be heavily influenced by the local environment, even within a single species.