Within-species relationship of patchiness to both abundance and occupancy, as exemplified by seagrass macrobenthos.

For the first time, intraspecific relationships between the macroecological metrics patchiness (P) and both abundance (A) and occupancy (O) were investigated in a faunal assemblage. As a companion study to recent work on interspecific P, A and O patterns at the same localities, intraspecific patterns were documented within each of the more dominant invertebrates forming the seagrass macrobenthos of warm-temperate Knysna estuarine bay (South Africa) and of sub-tropical Moreton Bay (Australia). As displayed interspecifically, individual species showed strong A-O patterns (mean scaling coefficient - 0.76 and mean R2 > 0.8). All P-O relations were negative and most (67%) were statistically significant, although weaker (mean R2 0.5) than A-O ones; most P-A ones were also negative but fewer (43%) achieved significance, and were even weaker (mean R2 0.4); 33% of species showed no significant interrelations of either O or A with P. No species showed only a significant P-A relationship. Compared with interspecific P-A-O data from the same assemblages, power-law scaling exponents were equivalent, but R2 values were larger. Larviparous species comprised 70% of the total studied, but 94% of those displaying significant patchiness interrelationships; 5 of the 9 showing no P-A or P-O relationships, however, were also larviparous. At Knysna, though not in Moreton Bay, larviparous species also showed higher levels of occupancy than non-larviparous ones, whilst non-larviparous species showed higher levels of patchiness. Dominant Moreton Bay species, but not those at Knysna, exhibited homogeneously sloped P-O relationships.

Uca cryptica Naderloo, Türkay & Chen, 2010 (Crustacea: Brachyura:Ocypodidae) is no longer cryptic.

Uca cryptica Naderloo, Türkay & Chen, 2010, was originally described from four male specimens found in museum collections without any information regarding the site of collection. We present the first recorded field observations of this species and new morphological features. Specimens were observed and collected in the Wakatobi National Park, on the island of Kaledupa, Sulawesi Tenggara, Indonesia. Colouration of both males and females is described and ecology and distribution are noted. Uca cryptica has been seen coexisting with nine other species; one of the highest recorded numbers of Uca species living in sympatry.

Microscale dispersion of intertidal seagrass macrofauna.

Previous studies of dispersion of intertidal seagrass-associated macrobenthos in subtropical Moreton Bay, Queensland, showed that patchiness characterised its assemblage abundance with scale-invariant magnitude across areas ranging from >8000 to 0.1 m2. Those studies were here continued across the smaller scales (down to 0.014 m2) arguably more relevant to the dominant 2-10 mm long animals, using 16 replicate blocks of 5x5 contiguous 0.0024 m2 cores nested within the previously studied site. At microscales ≥0.09 m2, the earlier congruence of conclusions derived from patchiness indices and spatial autocorrelation broke down. At >0.014 m2, adjacent points (cores) no longer together formed larger spatial units of related abundance (i.e. showed no autocorrelation), but point abundances were still highly disparate (as reflected in patchiness indices). Congruent indications of patchiness only manifested at 0.014 m2 spatial scales. Assemblage dispersion pattern was partly consequent on one microgastropod (Pseudoliotia) occurring superabundantly in scattered 0.0024 m2 hotspots.

Seagrass macrobenthic biodiversity does not vary in conformity with a leaky-lagoonal confinement gradient.

Coastal lagoon ecology often changes on progression from the open, well-flushed mouth region to the depositional zone furthest from the open sea. This is generally considered consequent on increasing 'confinement' and associated features, rather than on the often co-occurringly decreasing salinity. The 12 km Rainbow Channel connecting part of Moreton Bay, a microtidal leaky lagoon, to the adjacent Pacific provides a gradient of increasing confinement without any significant salinity change, i.e. a tenfold increase in water residence time for a salinity decrease of <1. Macrobenthic faunal assemblages characterising intertidal Zostera seagrass at strategic points along its length were compared to test whether their nature changed in conformity with confinement models. Results suggest that it does not; faunal abundance, species richness, evenness and composition remaining effectively unchanged along the gradient. Seagrass systems may constitute a special case because they decouple renewal times of the overlying water and local organic enrichment/decomposition; as may leaky lagoons because of their high tidal velocities.

Interspecific abundance-occupancy relations along estuarine gradients.

Do interspecific abundance-occupancy (A-O) relationships vary systematically along environmental gradients? A-O relationships of macrobenthic assemblages of seagrass and adjacent bare-sediment were compared at series of sites along two types of estuarine gradient; the longitudinal one of the main axial channel, and a transverse one from that channel into progressively smaller channels and creeks enclosed within fringing saltmarsh. Three general features emerged: A-O regression slopes were remarkably uniform across all the disparate assemblages and sites (1.04 ± 0.08); values of R2 were very high (≈0.96); and where small but significant differences between sites occurred, they were associated with the stronger gradients (i.e. those with the larger differentials in abundance and smaller compositional similarities). In two such cases, slope values were correlated with position along the gradient (although only at the margin of statistical significance). Variation in A-O relationships along estuarine gradients does clearly occur, but their constancy leaves the stronger impression.

What does measuring species diversity in estuarine seagrass systems actually assess?

Relationships between species diversity and other species-density and species-richness metrics were investigated in the seagrass macrobenthos of Knysna estuarine bay, South Africa. Although a wide range of species density occurred across sites, neither Hill-Shannon nor Hill-Simpson diversity showed any significant relationship with it, although they did with species richness. Instead species diversity was very closely related to relative evenness, and (negatively) to overall assemblage abundance. No significant relationship was found between species density and evenness. Whilst there was a clear and marked decrease in species density upstream along the main estuarine channel, only one of the species-diversity indices (the Hill-Shannon) showed a significant equivalent decrease. Relationships depended on how 'species richness' was assessed, and were very strongly influenced by the superabundant local occurrence of a few individual faunal components (three gastropod and one tanaid species). Species-diversity analysis contributes nothing new in such estuarine seagrass meadows and seems best avoided.

Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics.

Ten species of fiddler crab are reported inhabiting the intertidal zone of a shore on Kaledupa Island, Indonesia. This is one of the highest recorded numbers of fiddler crab species living in sympatry, equating to over two-thirds of those known from the Wallacea biogeographic region and more than half of all those recorded from Indonesia. The descriptions to identify and distinguish these ten species are provided using a suite of characters e.g., carapace, major cheliped, male gonopods, gastric mills, life colouration in males and females, and notes on their ecology and distribution. Specimens were observed and collected in the Wakatobi National Park, near the village of Ambeua on Kaledupa island, Sulawesi Tenggara, Indonesia. Gastric mills are described for the first time for Gelasimus jocelynae, Paraleptuca crassipes, Tubuca coarctata, T. demani and T. dussumieri. A tabulation of anatomical features and colouration for all species in this study is provided as a support for field studies. It identifies features that support the recently proposed taxonomic revision of fiddler crabs by Shih et al. (2016).

Do different sympatric seagrasses support macrobenthic faunas of differing composition, abundance, biodiversity or patchiness?

Intertidal macrobenthic assemblages associated with monospecific areas of different sympatric though not syntopic seagrasses [Cymodocea, Halodule, Zostera and Halophila] were investigated in Moreton Bay across a continuous <0.12 ha seagrass area with minimal potentially-confounding environmental variables. Results indicated patterns of unchanging faunal metrics across seagrass types (abundance, richness, diversity, evenness, taxonomic distinctness, and patchiness) but variation in relative proportions of dominant taxa, particularly microgastropods (abundant in Zostera, insignificant in Cymodocea and Halodule). Although assemblage composition varied, faunal dissimilarities (except with Zostera) were very low and of similar magnitudes within and between different 'host' seagrasses. This suggests that such macroecological faunal characteristics are not consequent on the precise local ecosystem engineer but largely reflect those of a common pool of locally available species, so that the differences in animal abundance and biodiversity described in some studies relate not directly to features inherent in the different seagrasses, but to associated habitat variables.

Local patchiness of macrobenthic faunal abundance displays homogeneity across the disparate seagrass systems of an estuarine bay.

Spatial variation in the degree of local patchiness of macrobenthic assemblage abundance was assessed across the 16 km2 warm-temperate Knysna estuarine bay (South Africa) where the seagrass Zostera (Zosterella) capensis grows under a broad spectrum of environmental conditions and supports invertebrate assemblages at a wide range of local density (<2000->320000 ind. m-2). Macrobenthic assemblage abundance at all 27 representative sites examined displayed low-level but highly-significant spatial patchiness (mean Lloyd's index, IP = 1.148). Except at high tidal levels, however, the magnitude of this local patchiness did not vary statistically across the system (CV 4.3%) regardless of assemblage abundance, location or species composition. Patchinesses well within ±1 standard deviation of Knysna's value also characterise an equivalent Z. (Zosterella) capricorni assemblage in subtropical Queensland (IP 1.169) and another, Z. (Zosterella) noltei, assemblage in cool-temperate England (IP 1.135), suggesting that at local scales intertidal dwarf-eelgrass macrobenthic abundance displays a characteristic level of patchiness.

Isometric scaling of faunal patchiness: Seagrass macrobenthic abundance across small spatial scales.

Following earlier studies across 2115 → 33 m2 scales (Barnes and Laurie, 2018), patchiness of macrobenthic abundance in intertidal Queensland seagrass was assessed by dispersion indices, spatial autocorrelation and hotspot analysis across a hierarchically-nested series of smaller scales (5.75 → 0.09 m2). Overall patterns of distribution and abundance over larger extents and with greater lag were mirrored across these smaller ones. Assemblage abundance per station varied by a factor of >10, but all three approaches showed effective constancy of total assemblage patchiness across all sub-2115 m2 scales (across-scales-mean Lloyd's IP of 1.06 and global Moran's I of 0.13). Equivalent constancy was also shown by most numerically-dominant species (scaling exponent ß = 0.93-1.15). Decreasing patchiness of some species with decreasing scale, however, resulted in two no longer being patchily dispersed across small scales. Significant hotspots of abundance occurred at a constant proportion of stations across scales, against a background of randomly scattered peak-abundance points.

Seagrass macrofaunal abundance shows both multifractality and scale-invariant patchiness.

Spatial patterns of abundance of the whole macrobenthic assemblage and of its 10 most numerous species were examined across hierarchically nested scales within a 0.85 ha area of intertidal seagrass in subtropical Moreton Bay, Queensland. Multifractality characterised the assemblage and all ten dominant species across those scales (c. 33, 130, 530 & 2115 m2), with patchiness of assemblage numbers and those of at least some dominants exhibiting scale-invariance. The system displayed several abundance peaks, 12% of stations accounting for 88% of total variance, with many individual dominants showing a series of non-overlapping 'hot-spots'. Scale invariance and multifractality occurred notwithstanding low levels of species interaction consequent on maintenance at very low density. This suggests that critical self-organisation cannot be responsible for such patterning. Contrary to received wisdom, coefficient ß of Taylor's power-law cannot form an index of aggregation, although it does indicate direction of change in dispersion pattern with changing numbers.

First record of the genus Eriopisella Chevreux, 1920 (Crustacea, Amphipoda, Senticaudata, Eriopisidae) from Australia, with the description of a new species, Eriopisella moretoni sp. nov.

The genus Eriopisella is recorded for the first time from Australia. Material from Moreton Bay, Queensland, proved to be an undescribed species and is here fully described and figured under the name E. moretoni sp. nov. An identification key to the nine known world species of Eriopisella is provided.

Are seaward pneumatophore fringes transitional between mangrove and lower-shore system compartments?

Work in temperate New Zealand has concluded that seaward fringes of Avicennia pneumatophores (P) form an 'important ecological transitional environment' between seagrass (Z) and mangrove (M), supporting intermediate macrofaunal numbers and biodiversity (Alfaro, 2006). This study re-examined that hypothesis in subtropical Moreton Bay, Queensland, and investigated its dependence on the nature of the lower-shore habitat; i.e. whether seagrass or sandflat (S). Adjacent macrobenthic assemblages across 45 m deep Z:P:M and S:P:M interfaces were compared uni- and multivariately and via various assemblage metrics. Here, system compartment P was not intermediate. In Z:P:M interfaces it was essentially an extension of the lower-shore assemblage and supported peak biodiversity. In contrast, P in S:P:M interfaces was partly an extension of the upper-shore assemblage with unchanged biodiversity but minimum abundance. Several species spanned the whole interface zone, and assemblage structure and several metrics remained unchanged across it. These findings are discussed in relation to ecotones in general. Like other such zones the characteristics of pneumatophore-fringe ecotones are context dependent.

Spatial homogeneity of benthic macrofaunal biodiversity across small spatial scales.

Spatial heterogeneity of biodiversity has been extensively researched, but its spatial homogeneity is virtually unstudied. An intertidal seagrass system at Knysna (South Africa) known to display spatially homogeneous macrobenthic species density at scales ≥0.0275 m2 was re-investigated at four smaller spatial grains (0.0015 m2 - 0.0095 m2) via a lattice of 8 × 8 stations within a 0.2 ha area. The aim was to investigate the null hypothesis that spatial homogeneity of species density is not a fixed emergent assemblage property but breaks down at small spatial grains within given spatial extents. Although assemblage abundance was significantly heterogeneous at all spatial grains investigated, both species density and functional-group density were significantly homogeneous across those same scales; observed densities not departing from those expected on the basis of independent assortment. Spatial homogeneity is therefore an emergent assemblage property within given spatial extents at Knysna and probably at equivalent sites elsewhere. Equivalent species density in South Africa, Australia and the UK at spatial grains <0.03 m2, however, is a scale-related sampling artefact, as may be temporal homogeneity of species density at Knysna over a 3 year period, but close similarity in shape of their species occupancy distributions remains unexplained.

Uniform functional structure across spatial scales in an intertidal benthic assemblage.

To investigate the causes of the remarkable similarity of emergent assemblage properties that has been demonstrated across disparate intertidal seagrass sites and assemblages, this study examined whether their emergent functional-group metrics are scale related by testing the null hypothesis that functional diversity and the suite of dominant functional groups in seagrass-associated macrofauna are robust structural features of such assemblages and do not vary spatially across nested scales within a 0.4 ha area. This was carried out via a lattice of 64 spatially referenced stations. Although densities of individual components were patchily dispersed across the locality, rank orders of importance of the 14 functional groups present, their overall functional diversity and evenness, and the proportions of the total individuals contained within each showed, in contrast, statistically significant spatial uniformity, even at areal scales <2 m(2). Analysis of the proportional importance of the functional groups in their geospatial context also revealed weaker than expected levels of spatial autocorrelation, and then only at the smaller scales and amongst the most dominant groups, and only a small number of negative correlations occurred between the proportional importances of the individual groups. In effect, such patterning was a surface veneer overlying remarkable stability of assemblage functional composition across all spatial scales. Although assemblage species composition is known to be homogeneous in some soft-sediment marine systems over equivalent scales, this combination of patchy individual components yet basically constant functional-group structure seems as yet unreported.

Biodiversity differentials between the numerically-dominant macrobenthos of seagrass and adjacent unvegetated sediment in the absence of sandflat bioturbation.

Species composition, abundance and biodiversity of the South African estuarine invertebrate fauna are known to show marked differentials between seagrass beds and adjacent unvegetated sands in enclosed estuarine/marine bays. Such differentials were investigated at four disparate localities in a bay lacking the callianassid bioturbation of other local sites. Here there were no such marked or consistent differences: <50% of differentials were statistically significant, with seagrass showing the lower, not higher, level in half of those. Overall, faunal abundance was lower in seagrass in the ratio of 0.64 : 1, whilst species density was higher but only by 1.13 to 1. Seagrass assemblages at a given locality were more similar to those of the adjacent bare sand than they were to seagrass assemblages at other localities, and likewise in respect of those in the bare sand. This suggests that marked differentials, where they occur, may result not from any supposed favourability of seagrass as a habitat but from the operation of processes within the unvegetated-sediment compartment of the system.