Deep-water rhodolith distribution, productivity, and growth history at sites of formation and subsequent degradation

This study provides the first quantitative measures of deep-water (i.e., below scuba depths) rhodolith development, distribution, abundance, and primary productivity at sites of both active formation and breakdown. The 1.27-km² upper platform surface of San Salvador Seamount, Bahamas, ranges in depth from 67 to 91 m and averages 95.8% cover of rhodoliths that contribute an estimated 391 t organic C·yr⁻¹ to deep-sea productivity. The predominant nongeniculate coralline alga of the slope environment has an extremely narrow PI curve (photosynthesis vs. irradiance) of net primary production (0.005) to slightly beyond 0.24 μmol·m⁻²·⁻¹ PAR) suggesting that some deep-water benthic algae may be acclimated to restricted light ranges. Platform areas contain up to fice-deep accumulations (≈45 cm thick) of rhodoliths with their visible, planar (2-D), crustose algal cover (68.5%) composed of 41% Lithophyllum sp., 14.9% average nongeniculate corallines, and 12.6% Peyssonnelia sp. Platform rhodoliths also contain ≈25% average planar cover of the foraminiferan Gypsina sp. overlying the rock-penetrating chlorophyte Ostreobium sp.

On the steep slopes of the seamount, to a depth of 290 m, rhodoliths that have spilled down from the relatively flat platform average 17.4% cover. These nodules tend to be concentrated in fan-shaped deposits that are most prevalent (33.3% cover) on the west side (leeward) of the mount where they are more abundant near the top of the slope than on the other three sides. Cover of living crustose algae on the deeper slope rhodoliths averages only 22.8% and is made up of 14.8% unidentified nongeniculate corallines, 6% Lithophyllum sp., and 2% Peyssonnelia. Gypsina sp. is not an important component of the slope nodules. Biotic overstory on the seamout slopes is greatly reduced relative to the platform, restricted mainly to bedrock, and consists mostly of Halimeda, gorgonians, and sponges along with scattered patches of small frondose algae.

Over platform depths from 67 to 91 m, rhodoliths are fairly uniform in composition and abundance. Ranging from 4 to 15 cm in diameter, with an average of ≈ 9 cm, they are roughly spherical with smooth living surfaces. The rhodoliths spilling down the steep slopes of the seamount to depths below 200 m are characteristically smaller (mean of ≈5 cm diameter), much rougher, and pittend by boring organisms. As shown by cross sections through the centers of the platform nodules, outer, relatively thin (1–3 cm thick), well-preserved envelopes overlie dead laminated crustose layerse. These layers surround much thicker cores of biotically altered carbonate (mostly coralline, foraminiferan, and coral) that have been extensively reworked by boring sponges, algae, polychaetes, and pelecypods. Borings have been infilled with carbonate detritus and are lithified to various degrees ranging from porous to dense and stony.

Radiocarbon dates indicate that the outermost unaltered envelopes that underlie actively growing crusts are 112–880 yr old ( ), while the innermost unaltered layers average 731 ybp (range = 200–1100 ybp). The consistently abrupt transitions from the intact underlying layers of living.     

Sequencing type material resolves the identity and distribution of the generitype Lithophyllum incrustans,and related European species L. hibernicum and L. bathyporum (Corallinales,Rhodophyta)

DNA sequences from type material in the nongeniculate coralline genus Lithophyllum were used to unambiguously link some European species names to field‐collected specimens, thus providing a great advance over morpho‐anatomical identifi‐cation. In particular, sequence comparisons of rbcL, COI and psbA genes from field‐collected specimens allowed the following conclusion: the generitype species, L. incrustans, occurs mostly as subtidal rhodoliths and crusts on both Atlantic and Mediterranean coasts, and not as the common, NE Atlantic, epilithic, intertidal crust reported in the literature. The heterotypic type material of L. hibernicum was narrowed to one rhodolith belonging in Lithophyllum. As well as occurring as a subtidal rhodolith, L. hibernicum is a common, epilithic and epizoic crust in the intertidal zone from Ireland south to Mediterranean France. A set of four features distinguished L. incrustans from L. hibernicum, including epithallial cell diameter, pore canal shape of sporangial conceptacles and sporangium height and diameter. An rbcL sequence of the lectotype of Lithophyllum bathyporum, which was recently proposed to accommodate Atlantic intertidal collections of L. incrustans, corresponded to a distinct taxon hitherto known only from Brittany as the subtidal, bisporangial, lectotype, but also occurs intertidally in Atlantic Spain. Specimens from Ireland and France morpho‐anatomically identified as L. fasciculatum and a specimen from Cornwall likewise identified as L. duckerae were resolved as L. incrustans and L. hibernicum, respectively.     

Phylogenetic analysis of rhodolith formation in the Corallinales (Rhodophyta)

Although the ecological importance of rhodolith (maerl, free-living coralline algae) beds is well-known, rhodolith-forming species have been neglected in molecular phylogenetic studies. This is the first molecular systematic study aimed at understanding whether the rhodolith habit is a fixed feature in lineages and determining the relationship (phylogenetic vs. environmental) between rhodolith and crustose habits. Phylogenetic relationships of rhodolith-forming species and encrusting coralline algae at generic and species levels were analysed using SSU rDNA and psbA sequences. Extensive sampling in the European North Atlantic, Pacific and Caribbean Mexico of Phymatolithon, Lithothamnion, Lithophyllum and Neogoniolithon taxa forming rhodoliths and crusts was accompanied by examination of type or topotype material. Phylogenetic reconstruction showed that Neogoniolithon contained a monophyletic group of rhodolith-forming species whereas other rhodolith-formers were closely related to encrusting forms in the genera Phymatolithon, Lithothamnion, Mesophyllum, Hydrolithon, Spongites and Sporolithon. DNA analysis showed that the crust-forming Lithophyllum cf. incrustans/dentatum also forms rhodoliths with a stone nucleus that occur on rocky shores. In contrast, species that form beds of non-nucleate rhodoliths (e.g. Neogoniolithon spectabile, N. strictum, Lithophyllum cf. incrustans/dentatum or sp. 1 and Phymatolithon calcareum) rarely form crusts. The rhodolith habit cannot be used to delimit species for taxonomic or identification purposes. Extensive taxonomic revision will be required to deal with problems such as the position of specimens identified as Lithophyllum margaritae in two unrelated lineages.     

High CO2 decreases the long‐term resilience of the free‐living coralline algae Phymatolithon lusitanicum

Mäerl/rhodolith beds are protected habitats that may be affected by ocean acidification (OA), but it is still unclear how the availability of CO₂ will affect the metabolism of these organisms. Some of the inconsistencies found among OA experimental studies may be related to experimental exposure time and synergetic effects with other stressors. Here, we investigated the long‐term (up to 20 months) effects of OA on the production and calcification of the most common mäerl species of southern Portugal, Phymatolithon lusitanicum. Both the photosynthetic and calcification rates increased with CO₂ after the first 11 months of the experiment, whereas respiration slightly decreased with CO₂. After 20 months, the pattern was reversed. Acidified algae showed lower photosynthetic and calcification rates, as well as lower accumulated growth than control algae, suggesting that a metabolic threshold was exceeded. Our results indicate that long‐term exposure to high CO₂ will decrease the resilience of Phymatolithon lusitanicum. Our results also show that shallow communities of these rhodoliths may be particularly at risk, while deeper rhodolith beds may become ocean acidification refuges for this biological community.     

Heterozoan carbonate-enriched beach sand and coastal dunes—with particular reference to rhodoliths,Dirk Hartog Island,Shark Bay,Western Australia

This is a preliminary interdisciplinary study on the enrichment of heterozoan carbonates on Dirk Hartog Island, Shark Bay, Western Australia, with particular reference to rhodolith (free-living non-geniculate) coralline algae. The current study aims to investigate the geological impact of shallow-water rhodoliths in Shark Bay, as well as fill critical information gaps on the biogeographical distribution of rhodoliths in Australia. We analyzed the composition of sand from eight sites (totaling 21 beach and sand dune samples) on the eastern (windward) shore of the island, and investigated the origin of the coralline algal grains. Heterozoan carbonates (shell, geniculate coralline algae grains, and rhodolith grains) together comprised 3–84% of the carbonate-enriched beach and dune sand samples. While shell fragments often comprised the highest percentage (up to 73%), rhodolith grains (up to 27%) were found in 12 of 21 samples, with rhodolith grains also occurring in two dune samples. Geologically, the study has shown that rhodoliths and rhodolith beds are important shallow-marine habitats in Shark Bay, with a proven capacity to enrich beach/dune sands in Shark Bay and potentially other areas along the Australian coast. Biogeographically, the study confirmed the presence of a previously undescribed shallow rhodolith bed in Shark Bay (the first bed documented on the Western shore) with the possibility of a third bed near Sandy Point on Dirk Hartog Island. It also confirmed the presence of rhodolith forming Neogoniolithon brassica-florida and Lithophyllum sp. in Shark Bay, and is the first record of Hydrolithon reinboldii rhodoliths in Australia.     

Coralline-algal assemblages of a Burdigalian platform slope: implications for carbonate platform reconstruction (northern Sardinia,western Mediterranean Sea)

The rhodolithic slope deposits of a Burdigalian carbonate platform in Sardinia near Sedini were analyzed to reconstruct facies and palaeobathymetry. There is a distinct red-algal growth zonation along the platform slope. The clinoform rollover area consists of coralline-algal bindstones, which downslope change into a zone where rhodoliths are locally fused by progressive encrustation. Mid-slope rhodoliths are moderately branched, and downslope rhodoliths have fruticose protuberances, resulting in branching rhodolith growth patterns. There is a sharp change from the rhodolitic rudstones to the basinal, bivalve-dominated rudstones at the clinoform bottomsets. Red-algal genera identified include Sporolithon, Lithophyllum, Spongites, Hydrolithon, Mesophyllum, Lithoporella, Neogoniolithon, and other mastophoroids and melobesioids. Genera and subfamilies show a zonation along the clinoforms, allowing palaeobathymetric estimates. The clinoform rollovers formed at a water depth of around 40 m and the bottomsets around 60 m. Results from geometrical reconstruction show that coral reefs in the inner platform formed at water depths of around 20 m. Therefore, the Sedini carbonate platform is an example of a reef-bearing platform in which the edge or the platform-interior reefs do not build up to sea level.     

GENETIC DIFFERENCES BETWEEN TWO GROWTH‐FORMS OF LITHOPHYLLUM MARGARITAE (RHODOPHYTA) IN BAJA CALIFORNIA SUR,MEXICO1

Unattached, nongeniculate, coralline algae or rhodoliths exhibit a range of morphological variability seemingly dependent on environmental factors. Rhodoliths have an extensive fossil record, and environmentally dependent characteristics make them potentially reliable paleoindicators. Species of the rhodolith‐forming genus Lithophyllum Philippi in Baja California Sur, Mexico were recently consolidated into one species. Under the new classification, L. margaritae (Hariot) Heydrich consists of several growth forms presumably reflecting local environmental conditions. We examined the genetic structure of four populations of this species using amplified fragment length polymorphisms (AFLP) to characterize the extent of genetic variation associated with foliose and fruticose growth forms. AFLP band sharing analysis revealed that foliose growth forms exhibited consistently higher intrapopulation similarities (0.75–0.85) than fruticose growth forms (similarity range, 0.55–0.67). This trend was also evident in comparisons of geographically isolated populations. These data indicate that the two morphologies are genetically distinct and that genetic exchange between foliose and fruticose growth forms of L. margaritae may be limited. Consequently, rhodolith growth forms appear to be the result of an interplay between both genetic makeup and environmental conditions.     

Community structure of rhodolith-forming beds on the central Brazilian continental shelf

The community structure of rhodoliths beds in the central Brazilian continental shelf was studied under the hypothesis that nongeniculate coralline algae are the major contributors of the individual rhodoliths. Samples were collected from five localities within a single area at 17–18 m depth. At each locality, rhodoliths were collected in 10 random quadrat samples along a 20-m transect. Our results show that dead cores of rhodoliths were significantly composed by nongeniculate coralline red algae rather than bryozoans, corals, or inorganic material. The live outer layers of the rhodoliths are composed mainly of 7 species of nongeniculate red coralline algae (Lithophyllum coralline, L. johansenii, L. depressum, L. stictaeformis, Neogoniolithon brassica-florida, Spongites fruticosus, and Lithothamnion muellerii) associated with other encrusting organisms such as bryozoans, sponges, corals, barnacles, and Peyssonnelia red algae. Significant differences were found in the proportion of Lithophyllum species in relation to other red coralline algae found in this study. Our results show that on the Brazilian continental shelf, the rhodolith-forming species are quite higher in size than in any other studied areas in the world. There was no difference in the proportion of live-to-dead rhodolith materials, suggesting an old bed deposit. Also, the amount of calcium carbonate material in the specimens is relevant to take in account in terms of the CO₂ balance worldwide.     

TUBE SIZE COMPARISON AND AUTOMATED GROWTH MEASUREMENT IN A TUBULAR REACTOR USING SPIRULINA PLANTENSIS

A tubular photobioreactor for outdoor cultivation of Spirulina platensis was successfully operated for the last two years. The reactor was made of transparent 2.4‐cm diameter tubes with a total length of approximately 101‐m and a volume of 124‐liter. Flow was induced using an airlift pumping system. To optimize the system further, a larger tube diameter was also tested. Preliminary results have suggested that a larger tube diameter might provide increased output with reduced surface area requirements. Results of experiments comparing the productivity of the same culture volume in tubes of 2.4 cm and 5.0 cm will be presented which show a small decrease in productivity by volume, but a large increase in areal productivity. This suggests that the larger tube diameter would be an appropriate choice for larger scale systems. Additionally, data will be presented demonstrating the effectiveness of an on‐line surface scatter turbidimeter for accurate measurement of Spirulina density when correlated to manual dry weight measurements.     

Tree age influences on the development of edible ectomycorrhizal fungi sporocarps in Pinus sylvestris stands

The study of factors influencing the production and development of wild edible mushroom sporocarps is extremely important in the characterization of the fungi life cycle. The main objective of this work is to determine how tree age influences the speed of sporocarp growth of edible ectomycorrhizal fungi Boletus edulis and Lactarius deliciosus in a Pinus sylvestris stand. This study is based on information recorded on a weekly basis every autumn between 1995 and 2008 in a set of permanent plots in Spain. Sporocarps are collected weekly, and as a result, specimens may not have reached their maximum size. The study area is a monospecific P. sylvestris stand. Three age classes were considered: under 30 years, between 31 and 70 years, and over 70 years. Sporocarps of B. edulis and L. deliciosus grow faster in the first age class stands than in the other two, and in the second age class stands, sporocarps are more than 50% smaller. The average weight of the picked B. edulis sporocarps clearly varies in the three age classes considered, with its maximum in the first age class (127 g and 6.8 cm cap diameter), minimum in the second age class (68 g and 4.7 cm cap diameter), and showing a relative maximum in the third (79 g and 4.3 cm cap diameter). L. deliciosus sporocarps are on average larger in the first age class (48 g and 7.4 cm cap diameter), decreasing in the second (20 g and 5.8 cm cap diameter) and also in the third (21 g and 5.3 cm cap diameter). The results show the influence of tree age in speed of sporocarp growth for the two ectomycorrhizal species.     

Rainforest fragmentation and the demography of the economically important palm <Emphasis Type="Italic">Oenocarpus bacaba</Emphasis> in central Amazonia

We summarize a long-term study of the effects of edge creation on establishment of the economically important arboreal palm Oenocarpus bacaba in an experimentally fragmented landscape in central Amazonia. Recruitment and mortality of large individuals (≥10 cm diameter-at-breast-height) were recorded within 21 1-ha plots in fragmented and intact forests for periods of up to 22 years. In addition, 12 small (0.7 × 14 m) sub-plots within each 1-ha plot were used to enumerate the abundance of seedlings and saplings (5–400 cm tall). On average, the recruitment of large trees was over two times faster near forest edges, leading to a sharp (90%) increase in the mean population density of large individuals near forest edges, whereas the density of larger trees remained constant in the forest interior. Overall seedling and sapling density was significantly lower in edge than interior plots, but edge plots had a much higher proportion of larger (>100 cm tall) saplings. Our findings demonstrate that forest edges can have complex effects on tree demography and that one must consider all tree life stages in order to effectively assess their effects on plant populations.     

Contrasting responses of heterotrophic and autotrophic respiration to experimental warming in a winter annual‐dominated prairie

Understanding how soil respiration (Rs) and its source components respond to climate warming is crucial to improve model prediction of climate‐carbon (C) feedback. We conducted a manipulation experiment by warming and clipping in a prairie dominated by invasive winter annual Bromus japonicas in Southern Great Plains, USA. Infrared radiators were used to simulate climate warming by 3 °C and clipping was used to mimic yearly hay mowing. Heterotrophic respiration (Rh) was measured inside deep collars (70 cm deep) that excluded root growth, while total soil respiration (Rs) was measured inside surface collars (2–3 cm deep). Autotrophic respiration (Ra) was calculated by subtracting Rh from Rs. During 3 years of experiment from January 2010 to December 2012, warming had no significant effect on Rs. The neutral response of Rs to warming was due to compensatory effects of warming on Rh and Ra. Warming significantly (P < 0.05) stimulated Rh but decreased Ra. Clipping only marginally (P < 0.1) increased Ra in 2010 but had no effect on Rh. There were no significant interactive effects of warming and clipping on Rs or its components. Warming stimulated annual Rh by 22.0%, but decreased annual Ra by 29.0% across the 3 years. The decreased Ra was primarily associated with the warming‐induced decline of the winter annual productivity. Across the 3 years, warming increased Rh/Rs by 29.1% but clipping did not affect Rh/Rs. Our study highlights that climate warming may have contrasting effects on Rh and Ra in association with responses of plant productivity to warming.     

Reproductive biology of the greyfin croaker <Emphasis Type="Italic">Pennahia anea</Emphasis> in the northern South China Sea

The greyfin croaker Pennahia anea is one of the most common croakers currently on retail sale in Hong Kong, but there are no regional studies on its biology or fishery. The reproductive biology of the species, based on 464 individuals obtained from local wet markets, was studied over 16 months (January 2008–April 2009) using gonadosomatic index (GSI) and gonad histology. Sizes used in this study ranged from 8.0 to 19.0 cm in standard length (SL). Both the larger and smaller size classes were missing from samples, implying that they are infrequently caught in the fishery. Based on GSI data, the approximate minimum sizes for male and female maturation were 12 cm SL. The size at 50% maturity for females was 14.3 cm SL, while all males in the samples were mature. Both GSI and gonad histology suggest that spawning activity occurred from March–April to June, with a peak in May. Since large croakers are declining in the local and regional fisheries, small species such as P. anea are becoming important, although they are mostly taken as bycatch. In view of unmanaged fishing pressure, and given the decline in large croakers and sizes of P. anea presently caught, proper management of the species is suggested.     

Arctic rhodolith beds and their environmental controls (Spitsbergen, Norway)

Coralline algae (Corallinales, Rhodophyta) that form rhodoliths are important ecosystem engineers and carbonate producers in many polar coastal habitats. This study deals with rhodolith communities from Floskjeret (78°18′N), Krossfjorden (79°08′N), and Mosselbukta (79°53′N), off Spitsbergen Island, Svalbard Archipelago, Norway. Strong seasonal variations in temperature, salinity, light regime, sea-ice coverage, and turbidity characterize these localities. The coralline algal flora consists of Lithothamnion glaciale and Phymatolithon tenue. Well-developed rhodoliths were recorded between 27 and 47 m water depth, while coralline algal encrustations on lithoclastic cobbles were detected down to 77 m water depth. At all sites, ambient waters were saturated with respect to both aragonite and calcite, and the rhodolith beds were located predominately at dysphotic water depths. The rhodolith-associated macrobenthic fauna included grazing organisms such as chitons and echinoids. With decreasing water depth, the rhodolith pavements were regularly overgrown by non-calcareous Polysiphonia-like red algae. The corallines are thriving and are highly specialized in their adaptations to the physical environment as well as in their interaction with the associated benthic fauna, which is similar to other polar rhodolith communities. The marine environment of Spitsbergen is already affected by a climate-driven ecological regime shift and will lead to an increased borealization in the near future, with presently unpredictable consequences for coralline red algal communities.     

Cruoriella rhodoliths from shallow-water back reef environments in La Parguera, Puerto Rico (Caribbean Sea)

The occurrence of shallow-water (0.9 to 1.3 m) rhodoliths in back reef environments in southwest Puerto Rico is reported. The rhodoliths were generally cylindrical, discoidal or irregular in shape with an average longest dimension of 7.2 cm. They occurred at a maximum density of 524 m⁻². The rhodoliths were composed of mostly coral nuclei with concentric laminations of aragonite-producing Cruoriella armorica (Peyssonneliaceae, Rhodophyta). Maximum Cruoriella accretion around coral nuclei was 30 mm although accretions of 1 to 20 mm were more common. Based on measurements of Cruoriella accretion, these shallow water rhodoliths are estimated to have minimum ages of 12 to 24 years. It is further estimated that approximately 2% of the rhodoliths are turned over daily. Accepted: 1 October 1999     

Habitat-mediated cannibalism and microhabitat restriction in the stream invertebrate <Emphasis Type="Italic">Gammarus pulex</Emphasis>

In cannibalistic species, small individuals often shift habitats to minimize risk of predation by larger conspecifics. The availability of diverse size-structured habitats may mediate the incidence of cannibalism by larger individuals on smaller individuals and increase fitness of smaller individuals. We tested these hypotheses in a series of laboratory studies with Gammarus pulex, a freshwater amphipod inhabiting substrates with varying interstitial pore space sizes. In the absence of larger, potentially cannibalistic individuals, small Gammarus actively used all pore space sizes offered. They used only substrates containing food and preferred food items that provided cover to food items that did not. In the presence of larger G. pulex, small individuals almost exclusively used smaller pore spaces from which larger individuals were excluded. Small individual survival was significantly lower in the presence of larger Gammarus than in controls without larger individuals regardless of substrate size, but availability of mixed pore sizes significantly increased survival. Food consumption and growth per individual were not affected by the presence of larger individuals or substrate composition. Our results suggest that the distribution and availability of complex and high-quality habitats may affect the occurrence and significance of cannibalism in size-structured populations. Handling editor: K. Martens     

A nested parasite species subset pattern in tropical fish: host as major determinant of parasite infracommunity structure

The number of monogenean gill parasite species associated with fish hosts of different sizes is evaluated for 35 host individuals of the West African cyprinid Labeo coubie. The length of host individuals explains 86% of the total variation in monogenean species richness among individuals. Larger hosts harbour more species than smaller ones. The existence of a hierarchical association of parasite species in individuals of L. coubie is demonstrated. Monogenean infracommunities on larger fish hosts consist of all species found on smaller hosts plus those restricted to the larger size categories, suggesting some degree of compositional persistence among host individuals. The findings provide strong support for an interpretation of the relationship between monogenean parasite species richness and host body size in terms of a nested species subset pattern, thus providing a new record of repetitive structure and predictability for parasite infracommunities of hosts.After 15/01/1995, ORSTOM, BP 165 97323 Cayenne cedex Guyane France     

Physiologic and metagenomic attributes of the rhodoliths forming the largest CaCO3 bed in the South Atlantic Ocean

Rhodoliths are free-living coralline algae (Rhodophyta, Corallinales) that are ecologically important for the functioning of marine environments. They form extensive beds distributed worldwide, providing a habitat and nursery for benthic organisms and space for fisheries, and are an important source of calcium carbonate. The Abrolhos Bank, off eastern Brazil, harbors the world''s largest continuous rhodolith bed (of ∼21 000 km²) and has one of the largest marine CaCO₃ deposits (producing 25 megatons of CaCO₃ per year). Nevertheless, there is a lack of information about the microbial diversity, photosynthetic potential and ecological interactions within the rhodolith holobiont. Herein, we performed an ecophysiologic and metagenomic analysis of the Abrolhos rhodoliths to understand their microbial composition and functional components. Rhodoliths contained a specific microbiome that displayed a significant enrichment in aerobic ammonia-oxidizing betaproteobacteria and dissimilative sulfate-reducing deltaproteobacteria. We also observed a significant contribution of bacterial guilds (that is, photolithoautotrophs, anaerobic heterotrophs, sulfide oxidizers, anoxygenic phototrophs and methanogens) in the rhodolith metagenome, suggested to have important roles in biomineralization. The increased hits in aromatic compounds, fatty acid and secondary metabolism subsystems hint at an important chemically mediated interaction in which a functional job partition among eukaryal, archaeal and bacterial groups allows the rhodolith holobiont to thrive in the global ocean. High rates of photosynthesis were measured for Abrolhos rhodoliths (52.16 μmol carbon m⁻²s⁻¹), allowing the entire Abrolhos rhodolith bed to produce 5.65 × 10⁵ tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean.     

Effects of group size and group density on trade-offs in resource selection by a group-territorial central-place foraging woodpecker

Trade-offs in resource selection by central-place foragers are driven by the need to balance the benefits of selecting resources against the costs of travel from the central place. For group-territorial central-place foraging birds, trade-offs in resource selection are likely to be complicated by a competitive advantage for larger groups at high group density that may limit accessibility of high-quality distant resources to small groups. We used the group-territorial, central-place foraging Red-cockaded Woodpecker Leuconotopicus borealis (RCW) as a case study to test predictions that increases in group density lead to differences in foraging distances and resource selection for groups of different sizes. We used GPS tracking and LiDAR-derived habitat data to model effects of group size on foraging distances and selection for high-quality pines (≥ 35.6 cm diameter at breast height (dbh)) and lower quality pines (25.4–35.6 cm dbh) by RCW groups across low (n = 14), moderate (n = 10) and high group density (n = 10) conditions. At low and moderate group density, all RCW groups selected distant high-quality pines in addition to those near the central place because competition for resources was low. In contrast, at high group density, larger groups travelled further to select high-quality pines, whereas smaller groups selected high-quality pines only when they were close to the central place and, conversely, were more likely to select lower quality pines at greater distances from the central place. Selection for high-quality pines only when close to the cavity tree cluster at high group density is important to long-term fitness of small RCW groups because it allows them to maximize benefits from both territorial defence and selecting high-quality resources while minimizing costs of competition. These relationships suggest that intraspecific competition at high group density entails substantive costs to smaller groups of territorial central-place foragers by limiting accessibility of distant high-quality foraging resources.