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Coral reefs experience numerous natural and anthropogenic environmental gradients that alter biophysical conditions and affect biodiversity. While many studies have focused on drivers of reef biodiversity using traditional diversity metrics (e.g., species richness, diversity, evenness), less is known about how environmental variability may influence functional diversity. In this study, we tested the impact of submarine groundwater discharge (SGD) on taxonomic and functional diversity metrics in Mo‘orea, French Polynesia. SGD is the expulsion of terrestrial fresh or recirculated seawater into marine environments and is associated with reduced temperatures, pH, and salinity and elevated nutrient levels. Using a regression approach along the SGD gradient, we found that taxon and functional-entity richness displayed unimodal relationships to SGD parameters, primarily nitrate + nitrite and phosphate variability, with peak richness at moderate SGD for stony coral and the full benthic community. Macroalgae showed this unimodal pattern for functional-entity but not taxonomic richness. Functional community composition (presence and abundance of functional entities) increased along the gradient, while taxonomic composition showed a nonlinear relationship to SGD-related parameters. SGD is a common feature of many coastal ecosystems globally and therefore may be more important to structuring benthic functional diversity than previously thought. Further, studying community shifts through a functional-trait lens may provide important insights into the roles of community functions on ecosystem processes and stability, leading to improved management strategies. 

Coral reefs experience numerous environmental gradients affecting organismal physiology and species biodiversity, which ultimately impact community metabolism. This study shows that submarine groundwater discharge (SGD), a common natural environmental gradient in coastal ecosystems associated with decreasing temperatures, salinity and pH with increasing nutrients, has both direct and indirect effects on coral reef community metabolism by altering individual growth rates and community composition. Our data revealed that SGD exposure hindered the growth of two algae,Halimeda opuntiaandValonia fastigiata,by 67 and 200%, respectively, and one coral,Porites rus,by 20%. Community metabolic rates showed altered community production, respiration and calcification between naturally high and low exposure areas mostly due to differences in community identity (i.e. species composition), rather than a direct effect of SGD on physiology. Production and calcification were 1.5 and 6.5 times lower in assemblages representing high SGD communities regardless of environment. However, the compounding effect of community identity and SGD exposure on respiration resulted in the low SGD community exhibiting the highest respiration rates under higher SGD exposure. By demonstrating SGD’s role in altering community composition and metabolism, this research highlights the critical need to consider compounding environmental gradients (i.e. nutrients, salinity and temperature) in the broader context of ecosystem functions. 

Abstract Marine organisms are increasingly recognized as both responding to and driving biogeochemical changes in their environment. The addition of exogenous resources to the ocean, such as nutrients, that alter organismal physiology can lead to biogeochemical cascades wherein these solutes both alter water chemistry directly and indirectly by changing biological processes that influence water chemistry. To quantify how allochthonous nutrients drive biogeochemical cascades, we measured a suite of biogeochemical parameters during synoptic spatial surveys across two reefs in Mo’orea, French Polynesia conducted day and night at both low and high tide in two different seasons. These data were used to build a model that demonstrates how inputs of nutrients to coral reefs via submarine groundwater discharge directly alter reef metabolism with cascading effects on the cycling of dissolved organic and inorganic carbon that regulate productivity, calcification, and the microbial loop. 

Abstract Manipulation of host phenotypes by parasites is hypothesized to be an adaptive strategy enhancing parasite transmission across hosts and generations. Characterizing the molecular mechanisms of manipulation is important to advance our understanding of host–parasite coevolution. The trematode (Levinseniella byrdi) is known to alter the colour and behaviour of its amphipod host (Orchestia grillus) presumably increasing predation of amphipods which enhances trematode transmission through its life cycle. We sampled 24 infected and 24 uninfected amphipods from a salt marsh in Massachusetts to perform differential gene expression analysis. In addition, we constructed novel genomic tools forO. grillusincluding a de novo genome and transcriptome. We discovered that trematode infection results in upregulation of amphipod transcripts associated with pigmentation and detection of external stimuli, and downregulation of multiple amphipod transcripts implicated in invertebrate immune responses, such as vacuolar ATPase genes. We hypothesize that suppression of immune genes and the altered expression of genes associated with coloration and behaviour may allow the trematode to persist in the amphipod and engage in further biochemical manipulation that promotes transmission. The genomic tools and transcriptomic analyses reported provide new opportunities to discover how parasites alter diverse pathways underlying host phenotypic changes in natural populations.