Marine biology: the role of accommodation in shaping marine biodiversity

A review of evidence from two kinds of studies conducted in the marine environment suggests a species relationship not previously recognized as being consistent and widespread. In the first instance, observations on species invading from a more diverse ecosystem into a less diverse ecosystem indicate that successful colonizations take place because space is yielded by their ecological equivalents. In the second instance, widespread studies show that any community, rich or poor, located in tropical or cold waters, is vulnerable to invasions by species from a larger, more diverse region. Furthermore, the species richness of a community apparently depends upon that of the region to which it belongs. Together, these observations indicate the existence of a general rule which states that if an invader becomes established, it is permitted to do so by an accommodation on the part of the species that occupies the preferred ecological space. Paleontological data on invasions provide evidence of speciation following accommodation. This leads to the recognition of a three-step process: invasion to accommodation to speciation (IAS). This process, which may be called the IAS mechanism, may have contributed to historical rises of global biodiversity.     

Influence of the mineralogical composition on microbial activities in marine sediments: an experimental approach

We investigated the influence of the mineralogical composition of marine sediments on bacterial activity in experimental microcosms. Calcite and quartz were added to natural marine sediments and microbial response in terms of total bacterial abundance and biomass, β-D-glucosidase exo-enzymatic activity and bacterial incorporation of a radio-labelled (³H-leucine) substrate were investigated for a period of one month. We report here that after 15 days the mineralogical composition of the sediment (calcite vs. quartz) had an impact on bacterial abundance and activity (reduced for ca 15% and 56%, respectively). However, such impact was mitigated or even disappeared in high organic nutrient conditions.     

Influence of the mineralogical composition on microbial activities in marine sediments: an experimental approach

We investigated the influence of the mineralogical composition of marine sediments on bacterial activity in experimental microcosms. Calcite and quartz were added to natural marine sediments and microbial response in terms of total bacterial abundance and biomass, β-D-glucosidase exo-enzymatic activity and bacterial incorporation of a radio-labelled (³H-leucine) substrate were investigated for a period of one month. We report here that after 15 days the mineralogical composition of the sediment (calcite vs. quartz) had an impact on bacterial abundance and activity (reduced for ca 15% and 56%, respectively). However, such impact was mitigated or even disappeared in high organic nutrient conditions.     

Protected area planning to conserve biodiversity in an uncertain future

Protected areas are a key instrument for conservation. Despite this, they are vulnerable to risks associated with weak governance, land-use intensification, and climate change. We used a novel hierarchical optimization approach to identify priority areas for expanding the global protected area system that explicitly accounted for such risks while maximizing protection of all known terrestrial vertebrate species. To incorporate risk categories, we built on the minimum set problem, where the objective is to reach species distribution protection targets while accounting for 1 constraint, such as land cost or area. We expanded this approach to include multiple objectives accounting for risk in the problem formulation by treating each risk layer as a separate objective in the problem formulation. Reducing exposure to these risks required expanding the area of the global protected area system by 1.6% while still meeting conservation targets. Incorporating risks from weak governance drove the greatest changes in spatial priorities for protection, and incorporating risks from climate change required the largest increase (2.52%) in global protected area. Conserving wide-ranging species required countries with relatively strong governance to protect more land when they bordered nations with comparatively weak governance. Our results underscore the need for cross-jurisdictional coordination and demonstrate how risk can be efficiently incorporated into conservation planning. Planeación de las áreas protegidas para conservar la biodiversidad en un futuro incierto     

Bioconcentration of Cd and Ni in various tissues of two marine bivalves living in different habitats and exposed to heavily polluted seawater

Two marine bivalves, Mytilus galloprovincialis and Callista chione, were exposed to various concentrations of cadmium and nickel (0.5, 1.0, 2.5 and 20 ppm), for 20 days, plus 10 days’ depuration period, in a laboratory experiment. Animals from each experimental condition were dissected and the bioaccumulation and distribution of Cd and Ni were determined in their gills, mantles and remaining bodies. The concentrations of Fe and Zn were also measured. Heavy metal tolerance, bioconcentration and distribution of heavy metals in tissues were considerably different in M. galloprovincialis and C. chione: (i) both animals were tolerant to Ni pollution, even at the highest concentration used; (ii) C. chione was more tolerant to Cd; (iii) M. galloprovincialis was a better Cd and Ni accumulator, with the exception of the highest Cd concentration tested, where C. chione accumulated more Cd; (iv) Fe and Zn levels were much more affected in M. galloprovincialis; (v) in general, accumulation and distribution of Ni and Cd in the tissues were metal-, species- and time of exposure- dependent; (vi) significant amounts of heavy metals remained in the tissues after 10 days’ depuration. Our results support a hypothesis for a two competing processes mechanism for metal accumulation and detoxification.     

The Mediterranean intertidal habitat as a natural laboratory to study climate change drivers of geographic patterns in marine biodiversity

Nylon bags containing yellow leaves of Rhizophora apiculata and Avicennia marina, were immersed for 80 days from August to October, 1996. the decomposing leaves were collected every 10 days and analysed for dry weight loss and six biochemical parameters: tannins, total amino acids, total sugars, total nitrogen, total lipids and fatty acid profile. the leaf weight initially decreased very rapidly by about 50% of the start in two species of mangroves within 10 days. Similar changes were observed with tannins, total amino acids and sugars. However, the concentration of nitrogen increased significantly with decomposition. There was no significant change in total lipid and fatty acid profile. the highest concentration of fatty acid in the decomposing leaves was palmitic acid (16:0). Unsaturated fatty acids such as, 18:1 w7c and 18:1 w9c were found to be present in decomposing leaves of both species.     

Seagrass mortality due to oversedimentation: an experimental approach

Mortality due to oversedimentation of the Mediterranean seagrassPosidonia oceanica was experimentally evaluated by field manipulations of the sediment level. Increased levels of sediment placed over plant shoots and rhizomes induced significant shoot mortality, even at moderate burial levels (ca. 5 cm). When sediment was added to reach levels 15 cm higher than the initial one, a 100 % mortality was observed after 200–300 days. The response of the plant was independent of site and depth. These results can be used in ecological risk assessment of coastal activities which potentially affect sediment deposition.     

A statistical test to detect vortices in the current fields of bodies of water

Vortices could play an important role in the occurrence of certain biological phenomena, such as the massive proliferation of harmful algae in bodies of water. Many measures exist to detect vortices in fluids, but little is known about the stochastic behavior of these quantities with data that contain statistical noise. Consequently they do not provide control over the probability of false positives and give little information about the risk of false negatives. Obtaining such control requires a statistical testing procedure. In this paper, we develop a test for vortices in random current fields using only the directions of the current observed at points on a regular grid. We construct a change-point test for spatially ordered angular data to detect the presence of a local vortex. A global vortex detection procedure based on this test is developed and applied to a data set from a lagoon located in the south of France. It is shown that this procedure can detect the presence of multiple vortices with good accuracy.     

Small-scale genetic structure in a marine population in relation to water circulation and egg characteristics

Until the last decade it was assumed that most marine species have pronounced gene flow over vast areas, largely because of their potential for dispersal during early life stages. However, recent genetic, modeling, and field studies have shown that marine populations may be structured at scales that are inconsistent with extensive dispersal of eggs and larvae. Such findings have stimulated the birth of new studies explaining the mechanisms that promote population structure and isolation in the oceans, in the face of high potential for dispersal. Here we study the vertical and horizontal distribution of cod (Gadus morhua) eggs in relation to small-scale circulation and water column hydrography in a coastal location of southern Norway. Previous studies conducted in this region have shown that cod populations inhabiting fjord locations, which are on average 30 km apart, are genetically differentiated, a remarkable outcome considering that Atlantic cod have pelagic egg stages and long pelagic larval duration. We document that cod eggs are found in greater abundance in shallow water layers, which on average are flowing up the fjord (away from the open ocean), and in the inner portion of the fjord, which is subject to lower current speeds compared to the outer or mouth of the fjord. Eggs were found to be neutrally buoyant at shallow depths, a trait that also favors local retention, given the local circulation. The same patterns held during two environmentally contrasting years. These results strongly suggest that population structure of Atlantic cod is favored and maintained by a balance between water circulation and egg characteristics.     

Oogenesis in the marine mussel Mytilus edulis: an ultrastructural study

Ultrastructural changes occurring during the course of development in oocytes of Mytilus edulis are described for mussels collected at monthly intervals over a period of one year (September 1981 to October 1982) from a site in Cornwall, England. During early stages of oogenesis the oocyte is surrounded by a small number of follicle cells but, as development proceeds, the follicle cells are restricted to the stalk region which attaches the oocyte to the acinar wall. Contact between the follicle cells and the developing oocyte is maintained by means of desmosomelike gap junctions. Organelles and inclusion bodies present in the ooplasm during oogenesis include rough endoplasmic reticulum (RER), Golgi bodies, mitochondria, free ribosomes, Balbiani's vitelline body, annulate lamellae and yolk and cortical granules. The RER, in particular, varies considerably throughout the course of development. Evidence for uptake of exogenous macromolecules into oocytes by pinocytosis is presented; it occurs in the basal region of previtellogenic oocytes prior to the formation of the vittelline coat. Lipid-yolk granules invariably have mitochondria in close association and, during the winter months, develop in close proximity to small, apparently glycogen-rich vesicles possibly suggesting that conversion of glycogen to lipid takes place in developing oocytes. Oocyte degeneration was commonly observed and involves initial breakdown of the plasma membrane followed by rupture of the vitelline coat. The oocyte contents once released into the acinar lumen are resorbed by the epithelial cells of the gonoducts, which are prevalent throughout the mantle of ripe individuals.     

Laser-induced fluorescence of polycyclic aromatic hydrocarbons: an approach to gas standards

Rapid methods are needed to analyse air pollutants such as polycyclic aromatic hydrocarbons (PAHs). Reliable semi-quantitative gas standards were required for the development of a laser-induced fluorescence (LIF) method for polycyclic aromatic hydrocarbon analysis, based on sampling of air onto multi-channel polydimethylsiloxane rubber traps. Easily constructed diffusion tubes provided naphthalene vapour at ~2 ng s⁻¹. A gas chromatographic fraction collection method for loading less volatile PAHs onto the traps from a flame ionization detector outlet was developed and optimized. The accuracy of the method, which can be further optimized, was sufficient for initial LIF screening tests to flag samples exceeding threshold PAH levels for subsequent quantitative GC–MS analysis.     

Multiscale codependence analysis: an integrated approach to analyze relationships across scales

The spatial and temporal organization of ecological processes and features and the scales at which they occur are central topics to landscape ecology and metapopulation dynamics, and increasingly regarded as a cornerstone paradigm for understanding ecological processes. Hence, there is need for computational approaches which allow the identification of the proper spatial or temporal scales of ecological processes and the explicit integration of that information in models. For that purpose, we propose a new method (multiscale codependence analysis, MCA) to test the statistical significance of the correlations between two variables at particular spatial or temporal scales. Validation of the method (using Monte Carlo simulations) included the study of type I error rate, under five statistical significance thresholds, and of type II error rate and statistical power. The method was found to be valid, in terms of type I error rate, and to have sufficient statistical power to be useful in practice. MCA has assumptions that are met in a wide range of circumstances. When applied to model the river habitat of juvenile Atlantic salmon, MCA revealed that variables describing substrate composition of the river bed were the most influential predictors of parr abundance at 0.4-4.1 km scales whereas mean channel depth was more influential at 200-300 m scales. When properly assessed, the spatial structuring observed in nature may be used purposefully to refine our understanding of natural processes and enhance model representativeness.     

A heuristic approach to predicting water beetle diversity in temporary and fluctuating waters

An understanding of the causal mechanisms and processes that shape macroinvertebrate communities at a local scale has important implications for the management and conservation of freshwater biodiversity. Here we compare the performance of linear and non-linear statistics to explore diversity-environment relationships using data from 76 temporary and fluctuating ponds in two regions of southern England. We focus on aquatic beetle assemblages, which have been shown to be excellent surrogates of wider freshwater macroinvertebrate diversity. Ponds in the region contained a rich coleopteran fauna, totaling 68 species, which provided an excellent model system with which to compare the performance of two non-linear procedures (artificial neural networks—ANNs and generalised additive models—GAMs) and one more traditional linear approach (Multiple linear regression—MLR) to modelling diversity-environment relationships. Of all approaches employed, the best fit was obtained using an ANN model with only four input variables (conductivity, turbidity, magnesium concentration and depth). This model accounted for 82% of the observed variability in Shannon diversity index across ponds. In contrast, the best GAM and MLR models only explained 50% and 14% of this variation, respectively. Contribution profile analysis of conductivity, turbidity, magnesium concentration and depth, obtained from the best fit ANN through a hierarchical cluster analysis, allowed the identification of direct and proxy effects in relation to the environmental variables measured in this study. In each case, distinct clusters of ponds were identified in contribution profile analysis, suggesting that ponds across the two regions fall into a number of discrete groups, whose beetle faunas respond in subtly yet significantly different ways to key environmental variables. Aquatic coleopteran diversity in ponds in the two regions appears to be driven at a local scale by changes in relatively few physicochemical gradients, which are related to diversity in a clearly non-linear manner.     

Going with the flow: using species-discharge relationships to forecast losses in fish biodiversity

In response to the scarcity of tools to make quantitative forecasts of the loss of aquatic species from anthropogenic effects, we present a statistical model that relates fish species richness to river discharge. Fish richness increases logarithmically with discharge, an index of habitat space, similar to a species-area curve in terrestrial systems. We apply the species-discharge model as a forecasting tool to build scenarios of changes in riverine fish richness from climate change, water consumption, and other anthropogenic drivers that reduce river discharge. Using hypothetical reductions in discharges (of magnitudes that have been observed in other rivers), we predict that reductions of 20-90% in discharge would result in losses of 2-38% of the fish species in two biogeographical regions in the United States (Lower Ohio-Upper Mississippi and Southeastern). Additional data on the occurrence of specific species relative to specific discharge regimes suggests that fishes found exclusively in high discharge environments (e.g., Shovelnose sturgeon) would be most vulnerable to reductions in discharge. Lag times in species extinctions after discharge reduction provide a window of opportunity for conservation efforts. Applications of the species-discharge model can help prioritize such management efforts among species and rivers.     

Nephtys hombergii, a free-living predator in marine sediments: energy production under environmental stress

Nephtys hombergii is a free-living, burrowing predator in marine sediments. The worm is, therefore, exposed to various environmental conditions which tube-dwelling polychaetes of the same habitat most likely do not encounter. The worms have to survive periods of severe hypoxia and sulphide exposure, while at the same time, they have to maintain agility in order to feed on other invertebrates. N. hombergii is adapted to these conditions by utilising several strategies. The species has a remarkably high content of phosphagen (phosphoglycocyamine), which is the primary energy source during periods of environmental stress. With increasing hypoxia, energy is also provided via anaerobic glycolysis (pO₂<7 kPa), with strombine as the main end-product. Energy production via the succinate pathway becomes important only under severe hypoxia (<2 kPa), suggesting a biphasic response to low oxygen conditions which probably is related to the worm's mode of life. The presence of sulphide resulted in a higher anaerobic energy flux and a more pronounced energy production via glycolysis than in anoxia alone. Nevertheless, after sulphide exposure under anaerobic conditions of <24 h, N. hombergii is able to recover completely. Although N. hombergii appears to be well adapted to a habitat with short-term fluctuations in oxygen and appearance of hydrogen sulphide, its high energy demand as a predator renders it likely to limit its survival in an environment with longer lasting anoxia and concomitant sulphide exposure. Received: 28 May 1997 / Accepted: 21 June 1997     

Predicting tree distributions in an East African biodiversity hotspot: model selection, data bias and envelope uncertainty

The Eastern Arc Mountains (EAMs) of Tanzania and Kenya support some of the most ancient tropical rainforest on Earth. The forests are a global priority for biodiversity conservation and provide vital resources to the Tanzanian population. Here, we make a first attempt to predict the spatial distribution of 40 EAM tree species, using generalised additive models, plot data and environmental predictor maps at sub 1 km resolution. The results of three modelling experiments are presented, investigating predictions obtained by (1) two different procedures for the stepwise selection of predictors, (2) down-weighting absence data, and (3) incorporating an autocovariate term to describe fine-scale spatial aggregation. In response to recent concerns regarding the extrapolation of model predictions beyond the restricted environmental range of training data, we also demonstrate a novel graphical tool for quantifying envelope uncertainty in restricted range niche-based models (envelope uncertainty maps). We find that even for species with very few documented occurrences useful estimates of distribution can be achieved. Initiating selection with a null model is found to be useful for explanatory purposes, while beginning with a full predictor set can over-fit the data. We show that a simple multimodel average of these two best-model predictions yields a superior compromise between generality and precision (parsimony). Down-weighting absences shifts the balance of errors in favour of higher sensitivity, reducing the number of serious mistakes (i.e., falsely predicted absences); however, response functions are more complex, exacerbating uncertainty in larger models. Spatial autocovariates help describe fine-scale patterns of occurrence and significantly improve explained deviance, though if important environmental constraints are omitted then model stability and explanatory power can be compromised. We conclude that the best modelling practice is contingent both on the intentions of the analyst (explanation or prediction) and on the quality of distribution data; generalised additive models have potential to provide valuable information for conservation in the EAMs, but methods must be carefully considered, particularly if occurrence data are scarce. Full results and details of all species models are supplied in an online Appendix.     

Structural gradients in an intertidal hard-bottom community: examining vertical,horizontal, and taxonomic clines in zoobenthic biodiversity

Measures of biodiversity along environmental gradients have long been the focus of marine ecological research. However, a general lack of comparability between studies and under-appreciation of co-occurring, less obvious clines has often undermined any general conclusions. Latitudinal, vertical, horizontal, and taxonomic gradients in intertidal biodiversity were assessed directly and indirectly using a large data set from one locality in southwest Ireland. A total of 153 epifaunal species, from 106 families and 13 phyla, was recorded from over 200,000 individuals in a sample area of 63 m². Multivariate analysis revealed that the vertical gradient of immersion was the primary structuring factor in the community but that a flow-driven horizontal gradient was also important in structuring low- and mid-shore zones. Crustaceans, annelids, and molluscs were most numerous over the entire site, but bryozoans and sponges may have played the most significant role in driving the horizontal (flow-related) trend in species richness at lower levels on the shore. Comparison of species richness with sites from other locations around the world proved inconclusive in assessing a global trend in richness from the poles to the tropics. However, interpolation of this and similar studies may prove useful in future latitudinal investigations of hard-substratum intertidal biota. Higher-taxon surrogacy for species trends proved significant and useful at the scale investigated here, whereby analysis of data from family or even order level may prove an efficient method of future monitoring. More data are required to assess if the top-down taxonomic approach will sufficiently mirror species trends at larger spatial scales. Overall, the generality of effects of environmental gradients on intertidal organisms may be more conclusive where entire communities are studied and consideration is given to other, less dominant clines.Communicated by J.P. Thorpe, Port Erin     

Rapid assessment of metabolic activity in marine microalgae: application in ecotoxicological tests and evaluation of water quality

A new method for the assessment of the effects of several contaminants on marine microalgae,Tetraselmis suecica (Kyling) Butcher,Skeletonema costatum (Grev.) Cleve, andProrocentrum lima (Ehrenberg) Dodge was developed in 1990. The method is based on the measurement of cell esterase activity using a fluorimetric stain, fluorescein diacetate (FDA), selected from amongst three stains (FDA, Neutral Red, thiazolyl tetrazolium bromure) for its higher sensitivity. Biochemical (K _m,V _max) and physiological (growth, specific activity) aspects of the enzymatic activity as revealed by the FDA method are discussed. Different categories of compounds (weed-killers, insecticides, metals) and some water samples from Seine Bay were tested for their toxic effects on microalgae. Experiments were performed on microplates using a fluorimetric microplate reader. The various steps of the experiments and data-processing were controlled by software. Applications of the system to rapid ecotoxicological tests (determination of the IC₅₀, i.e., the concentration at which 50% inhibition of growth occurs) and to the assessment of environment quality by studying the toxic effect of water samples on microalgae are proposed.