Do species display characteristic intraspecific levels of patchiness in a given habitat type? The case of intertidal seagrass macrobenthos

AbstractIntertidal macrobenthic assemblages associated with monospecific stands of Zostera muelleri, Cymodocea serratula, Halodule uninervis and Halophila ovalis seagrasses are known to display uniform spatial patchiness on the Moreton Bay coast of North Stradbroke Island, Queensland, as do those in Z. capensis in the Knysna estuarine bay, South Africa. Thirty-seven historical datasets of these macrobenthic assemblages were re-analysed to assess variation of local patchiness in each of the 18 most common individual assemblage components at each of these localities in terms of three metrics: overall patchiness (Lloyd's index of patchiness), levels of unoccupancy, and variation in abundance across occupied samples (Lloyd's index of mean crowding). Within-site patchiness was not caused by a restriction of individual species to specific subareas but by variation in their local density, particularly by the extent of unoccupied ‘interstitial’ spaces within patches. Especially in the more uniform Queensland conditions, the more common species occurred relatively widely across the whole locality; individual samples from which a given species was absent never themselves formed patches, the number of such samples conforming to points on truncated normal curves of the frequency of occurrence. Of the 36 species investigated, the two most abundant and widespread both in Queensland and in South Africa displayed significant or near-significant uniformity of levels of local patchiness, whilst five showed significantly uniform mean crowding and ten significantly uniform unoccupancy. This is the first demonstration that some species may display a characteristic level of patchiness in a given habitat type.</jats:p

Interspecific relationship of patchiness to occupancy and abundance, as exemplified by seagrass macrobenthos

The macroecological abundance-occupancy relationship is well known; not so the potential one of patchiness with either or both. Following earlier work on the intertidal seagrass Zostera capensis in South Africa, interspecific macrofaunal patchiness-occupancy and patchiness-abundance relationships were investigated within each of a number of other seagrass systems (intertidal Cymodocea serratula, Halodule uninervis, Halophila ovalis, Zostera muelleri and Z. noltei, and subtidal Z. capensis) where faunal assemblages were markedly different in their overall abundance and species richness, and where the beds differed in their latitude, longitude, and other variables, including one in an artificial canal in a residential marina. Notwithstanding these differences, in all cases the more abundant and widespread the macrobenthic species, the less was its Lloyd's I patchiness, the more clearly so in respect of occupancy than of abundance. Correlation of I and mean crowding (I ) values was relatively poor, and often not significant. This suggests that patchiness of a species is more influenced by unoccupancy levels than by even marked variation in abundance at occupied sites (e.g. I values of 380). Indeed, values of I were closely correlated with the expression [a.unoccupancy + (1−a).I ], where a is >0.80. In all cases, component macrofaunal species displayed a significant or near significant negative patchiness-occupancy relationship in the form of a power-law with a mean scaling coefficient across sites of −0.76, although data points appeared highly scattered. There was little uniformity amongst the component species in the life-style of the most patchy, most widespread or most abundant. p p c c p

Horizontal patterns of water temperature and salinity in an estuarine tidal channel: Ria de Aveiro

This work presents results from two complementary and interconnected approaches to study water temperature and salinity patterns in an estuarine tidal channel. This channel is one of the four main branches of the Ria de Aveiro, a shallow lagoon located in the Northwest coast of the Iberian Peninsula. Longitudinal and cross-sectional fields of water temperature and salinity were determined by spatial interpolation of field measurements. A numerical model (Mohid) was used in a 2D depth-integrated mode in order to compute water temperature and salinity patterns. The main purpose of this work was to determine the horizontal patterns of water temperature and salinity in the study area, evaluating the effects of the main forcing factors. The field results were depth-integrated and compared to numerical model results. These results obtained using extreme tidal and river runoff forcing, are also presented. The field results reveal that, when the river flow is weak, the tidal intrusion is the main forcing mechanism, generating saline and thermal fronts which migrate with the neap/spring tidal cycle. When the river flow increases, the influence of the freshwater extends almost as far as the mouth of the lagoon and vertical stratification is established. Results of numerical modelling reveal that the implemented model reproduces quite well the observed horizontal patterns. The model was also used to study the hydrology of the study area under extreme forcing conditions. When the model is forced with a low river flow (1 m3 s−1) the results confirm that the hydrology is tidally dominated. When the model is forced with a high river flow (1,000 m3 s−1) the hydrology is dominated by freshwater, as would be expected in such an area

Tree thinking cannot taken for granted: challenges for teaching phylogenetics

Tree thinking is an integral part of modern evolutionary biology, and a necessary precondition for phylogenetics and comparative analyses. Tree thinking has during the 20th century largely replaced group thinking, developmental thinking and anthropocentricism in biology. Unfortunately, however, this does not imply that tree thinking can be taken for granted. The findings reported here indicate that tree thinking is very much an acquired ability which needs extensive training. I tested a sample of undergraduate and graduate students of biology by means of questionnaires. Not a single student was able to correctly interpret a simple tree drawing. Several other findings demonstrate that tree thinking is virtually absent in students unless they are explicitly taught how to read evolutionary trees. Possible causes and implications of this mental bias are discussed. It seems that biological textbooks can be an important source of confusion for students. While group and developmental thinking have disappeared from most textual representations of evolution, they have survived in the evolutionary tree drawings of many textbooks. It is quite common for students to encounter anthropocentric trees and even trees containing stem groups and paraphyla. While these biases originate from the unconscious philosophical assumptions made by authors, the findings suggest that presenting unbiased evolutionary trees in biological publications is not merely a philosophical virtue but has also clear practical implications

Stable Photosymbiotic Relationship under CO2-Induced Acidification in the Acoel Worm Symsagittifera Roscoffensis

As a consequence of anthropogenic CO2 emissions, oceans are becoming more acidic, a phenomenon known as ocean acidification. Many marine species predicted to be sensitive to this stressor are photosymbiotic, including corals and foraminifera. However, the direct impact of ocean acidification on the relationship between the photosynthetic and nonphotosynthetic organism remains unclear and is complicated by other physiological processes known to be sensitive to ocean acidification (e.g. calcification and feeding). We have studied the impact of extreme pH decrease/pCO2 increase on the complete life cycle of the photosymbiotic, non-calcifying and pure autotrophic acoel worm, Symsagittifera roscoffensis. Our results show that this species is resistant to high pCO2 with no negative or even positive effects on fitness (survival, growth, fertility) and/or photosymbiotic relationship till pCO2 up to 54 K µatm. Some sub-lethal bleaching is only observed at pCO2 up to 270 K µatm when seawater is saturated by CO2. This indicates that photosymbiosis can be resistant to high pCO2. If such a finding would be confirmed in other photosymbiotic species, we could then hypothesize that negative impact of high pCO2 observed on other photosymbiotic species such as corals and foraminifera could occur through indirect impacts at other levels (calcification, feeding)

Trace Elements and Carbon and Nitrogen Stable Isotopes in Organisms from a Tropical Coastal Lagoon

Trace elements (Fe, Mn, Al, Zn, Cr, Cu, Ni, Pb, Cd, Hg, and As) and stable isotope ratios (δ13C and δ15N) were analyzed in sediments, invertebrates, and fishes from a tropical coastal lagoon influenced by iron ore mining and processing activities to assess the differences in trace element accumulation patterns among species and to investigate relations with trophic levels of the organisms involved. Overall significant negative relations between trophic level (given by 15N) and trace element concentrations in gastropods and crustaceans showed differences in internal controls of trace element accumulation among the species of different trophic positions, leading to trace element dilution. Generally, no significant relation between δ15N and trace element concentrations was observed among fish species, probably due to omnivory in a number of species as well as fast growth. Trace element accumulation was observed in the fish tissues, with higher levels of most trace elements found in liver compared with muscle and gill. Levels of Fe, Mn, Al, and Hg in invertebrates, and Fe and Cu in fish livers, were comparable with levels in organisms and tissues from other contaminated areas. Trace element levels in fish muscle were below the international safety baseline standards for human consumption

A qualitative and quantitative model for climate-driven lake formation on carbonate platforms based on examples from the Bahamian archipelago

Lakes on carbonate platform islands such as the Bahamas display wide variability in morphometry, chemistry, and fauna. These parameters are ultimately driven by climate, sea level, and carbonate accumulation and dissolution. The authors propose a model that integrates climatological, geomorphological, and stratigraphic frameworks to understand processes of carbonate-hosted lake formation and limnological characteristics in modern day environments, with applications to carbonate lake sedimentary records. Fifty-two lakes from San Salvador Island and Eleuthera, Bahamas, were examined for water chemistry, basin morphology, conduit development, conductivity, and major ions. Using non-metric, multi-dimensional scaling ordination methods, the authors derived a model dividing lakes into either constructional or destructional formational modes. Constructional lakes were further divided into pre-highstand and highstand types based on whether their formation occurred during a marine regressive or transgressive phase. Destructional lakes are created continually by dissolution of bedrock at fresh/saline water interfaces and their formation is therefore related to changing climate and sea level. This model shows that lake formation is influenced by the hydrologic balance associated with climatic conditions that drives karst dissolution as well as the deposition of aeolian dune ridges that isolate basins due to sea-level fluctuations. It allows for testing and examining the climatic and hydrologic regime as related to carbonate accumulation and dissolution through time, and for an improved understanding of lake sensitivity and response to climate as preserved in the lacustrine sedimentary record

Intron analyses reveal multiple calmodulin copies in Littorina

Intron three and the flanking exons of the calmodulin gene have been amplified, cloned and sequenced from 18 members of the gastropod genus Littorina. From the 48 sequences, at least five different gene copies have been identified and their functionality characterized using a strategy based upon the potential protein product predicted from flanking exon data. The functionality analyses suggest that four of the genes code for functional copies of calmodulin. All five copies have been identified across a wide range of littorinid species although not ubiquitously. Using this novel approach based on intron sequences, we have identified an unprecedented number of potential calmodulin copies in Littorina, exceeding that reported for any other invertebrate. This suggests a higher number of, and more ancient, gene duplications than previously detected in a single genus