Macroalgal holdfasts and their interaction with environments from the Neoproterozoic Doushantuo Formation in Guizhou, South China

Numerous macro-organisms of the Doushantuo macrobiota, which were found in the black carbonaceous mudstone of the upper Neoproterozoic Ediacraan Doushantuo Formation in Jiangkou County, Guizhou Province, China, are considered to live on sea floor by their holdfasts. The appearance and preserved forms of the macroalgal holdfasts may provide some data to the study of the living and buried environments of macrobiota. They lived in the lower energy and clear environment, and fixed on a soupground with rich water (about 79 water). Currents, possibly ocean currents, could pull out the macroalgal holdfasts from the soupground and break off the macroalgal foliations. After such events, the corpses of macro-organisms would be covered in a reduced environment by the deposits. Afterwards, a new community, including regenerating and undying macro-organisms, lived continuously on a new deposit. __________ Translated from Acta Micropalaeontologica Sinica, 2005, 23(2): 154-C164 [译自: 微体古生物学报]     

黔东北新元古代陡山沱期宏体藻类的固着器特征及其沉积环境意义

产于贵州江口新元古界陡山沱组上部黑色碳质泥岩和硅质泥岩中的宏体生物群,多数为发育固着器的固着底栖生物。宏体藻类固着器的形态和保存方式可提供生物群生活环境和埋藏环境的信息。黔东北陡山沱期宏体生物群生活于相对平静、较为清澈的水体之中,固着基底为富含水份的粥性基底。可能与洋流有关的水流事件将宏体藻类折断或“连根”拔起;水流事件之后,沉积物将宏体藻类的遗体掩埋于还原性较强的环境之中,新生的和水流事件未致死亡的宏体生物在新的沉积物表面上继续生长。     

Ediacaran macroalgal holdfasts and their evolution: a case study from China

A macroalgal holdfast (root-like structure) anchored or grown into sediments is a key trait of metaphytes and eukaryotic algae. Various patterns and taphonomic variants of congeneric holdfasts are preserved on the bedding planes of black shales of the Ediacaran Wenghui biota in South China. The macroalgal holdfast, which commonly consists of a rhizome, rhizoid and pith (perhaps mechanical tissue), can be morphologically classified into ten types within four groups of rhizomes: bare rhizome holdfasts (Grypania, Tongrenphyton and Sectoralga-type holdfasts), canopy rhizome holdfasts (Gemmaphyton, Gesinella, Discusphyton and Baculiphyca-type holdfasts), pithy rhizome holdfasts (Zhongbaodaophyton and pithy-cone-type holdfasts) and differentiated rhizome holdfasts (Wenghuiphyton-type holdfasts). Analysis of the Precambrian macroalgal record indicates that rhizomes played a more important role in the evolution of macroalgal holdfast than rhizoids. The following evolutionary stages of development of macroalgal holdfasts are proposed: (1) growth of the basal thallus into sediments (Grypania-type holdfast); (2) development of a primitive (indistinct) rhizome from the base of a stipe or thallus (Tongrenphyton-type and Sectoralga-type holdfasts); (3) growth of a distinct rhizome with rhizoid (Gemmaphyton-type, Gesinella-type and Discusphyton-type holdfasts); (4) development of a pith in the stipe (Baculiphyca-type holdfast); (5) pith extension into the rhizome (Zhongbaodaophyton-type and pithy-cone-type holdfasts); and (6) rhizome differentiation and development of a complex holdfast system (Wenghuiphyton-type holdfast).     

The ontogeny of habitat associations in the tropical tiger tail seahorse Hippocampus comes Cantor, 1850

This study examined how habitat associations changed with ontogeny in the tiger tail seahorse Hippocampus comes Cantor, 1850, over four reef zones in a coral reef ecosystem. Hippocampus comes showed ontogenetic differences in their use of habitat at the scale of reef zones (macrohabitat) and holdfasts (microhabitat). Across reef zones, juvenile size classes (25–105 mm standard length, L _S) were most abundant in wild macroalgal beds ( Sargassum spp.) (55·7%), while adults (>105 mm L _S) occupied both coral reefs (39·7%) and macroalgal beds (42·7%). Microhabitat use also varied with ontogeny. Juveniles generally used macroalgal holdfasts, while adults >135 mm L _S used a greater diversity of specialized microhabitats that included branching sponges, branching corals and tall seagrass. Ontogenetic changes in habitat association, as well as size-related shifts in crypsis and aggregation, suggest that H. comes experiences fitness trade-offs that vary with size; juveniles may associate with habitat that reduces predation, while larger individuals may use distinct microhabitat in reef zones to optimize reproductive success. Results are discussed in the context of targeted exploitation, expanding artisanal mariculture, habitat damage from illegal fishing and reserve design.     

Variations in holdfast attachment mechanics with developmental stage, substratum-type, season, and wave-exposure for the intertidal kelp species Hedophyllum sessile (C. Agardh) Setchell

Biomechanical models that describe physical and biological interactions on wave-exposed shores typically assume that a species' attachment properties are similar between seasons and sites. We tested this assumption using Hedophyllum sessile to investigate how macroalgal biomechanical attachment properties vary with developmental stage, substratum-type, season, and wave-exposure. Hedophyllum sessile is an intertidal kelp species that is able to survive in wave-exposed areas in the Northeast Pacific. For both juveniles and adults, holdfast attachment force and strength were measured at a wave-exposed and wave-protected site in Barkley Sound, British Columbia, Canada. Substratum and wave-exposure effects on attachment properties were tested in juvenile populations. Adult populations were sampled prior to (in July 1996) and after (in November 1996) a series of storms. Site and seasonal wave-exposure effects on attachment properties were tested in these adult populations. Comparisons to known attachment properties of other temperate macroalgal species were also made. Causes for these patterns are discussed but were not isolated in these studies. Juveniles' attachment properties differed on different substrata types and between wave-exposures, with the highest attachment forces and the most attached juveniles in articulated coralline algal turfs. Adult attachment is firm ( approximately 100 N), but relatively weak ( approximately 0.07 MNm(-2)). Adult attachment did not vary with site wave-exposure, but there was a shift within each site to more resistant holdfasts after a series of early winter storms. Seasonal increases in storm swells correlated to more thallus tattering and selected against large, loose holdfasts. The data presented here suggest that results from holdfast attachment field studies in one season cannot be extrapolated to another due to a complex set of dynamics. This is the first documentation of seasonal patterns in macroalgal attachment properties.     

Range expansion of a habitat-modifying species leads to loss of taxonomic diversity: a new and impoverished reef state

Global climate change is predicted to have major negative impacts on biodiversity, particularly if important habitat-modifying species undergo range shifts. The sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone poleward range expansion to relatively cool, macroalgal dominated rocky reefs of eastern Tasmania (southeast Australia). As in its historic environment, C. rodgersii in the extended range is now found in association with a simplified 'barrens' habitat grazed free of macroalgae. The new and important role of this habitat-modifier on reef structure and associated biodiversity was clearly demonstrated by completely removing C. rodgersii from incipient barrens patches at an eastern Tasmanian site and monitoring the macroalgal response relative to unmanipulated barrens patches. In barrens patches from which C. rodgersii was removed, there was a rapid proliferation of canopy-forming macroalgae (Ecklonia radiata and Phyllospora comosa), and within 24 months the algal community structure had converged with that of adjacent macroalgal beds where C. rodgersii grazing was absent. A notable scarcity of limpets on C. rodgersii barrens in eastern Tasmania (relative to the historic range) likely promotes rapid macroalgal recovery upon removal of the sea urchin. In the recovered macroalgal habitat, faunal composition redeveloped similar to that from adjacent intact macroalgal beds in terms of total numbers of taxa, total individuals and Shannon diversity. In contrast, the faunal community of the barrens habitat is overwhelmingly impoverished. Of 296 individual floral/faunal taxa recorded, only 72 were present within incipient barrens, 253 were present in the recovered patches, and 221 were present within intact macroalgal beds. Grazing activity of C. rodgersii results in an estimated minimum net loss of approximately 150 taxa typically associated with Tasmanian macroalgal beds in this region. Such a disproportionate effect by a single range-expanding species demonstrates that climate change may lead to unexpectedly large impacts on marine biodiversity as key habitat-modifying species undergo range modification.     

Evidence for a complex life cycle and endospore formation in the attached, filamentous, segmented bacterium from murine ileum.

Light and electron microscope observations showed that the filamentous, segmented bacterium commonly found attached to the ileal epithelium of rats and mice undergoes a complex life cycle. Filaments comprising up to 90 segments were attached to the microvillous border of absorptive epithelial cells by a specialized terminal holdfast segment. Starting at the free end of the filament and progressing toward the attached end, undifferentiated segments were converted into reproductive or mother segments. Within each mother cell two new holdfast segments developed. As the holdfasts matured, their mother cells degenerated and released them into the intervillar space where they attached, grew, and divided to produce new segmented filaments. Alternately, in some filaments, newly formed but not yet released holdfasts were converted into endospores, which were released in the same manner as holdfasts, presumably to spread the bacterial colony to other members of the rodent population.     

Crinoid holdfasts from the Silurian of Gotland

Crinoid holdfasts occur throughout the Silurian sequence of Gotland, with a marked concentration to reefs and immediate reef surroundings. Four morphological groups are recognized: (1) Discoid holdfasts. (2) Cirriferous holdfasts, represented by (a) Rhizocrinus -like holdfasts, (b) large radices with stout, often branching cirri, and (c) rhizoid holdfasts, formed by a complicated net of pseudocirri. (3) Creeping stems attached to the substrate by thin strands of stereome. (4) Coiling stems. Discoid attachments, cirriferous holdfasts (types b and c) and coiling stems show little preference to substrate and adapt morphologically to conditions at hand. Rhizoid holdfasts display the greatest variation and apparently occur within many different groups of crinoids. Rhizocrinusttke holdfasts have been found only in quiet-water deposits, while creeping stems were concentrated to more turbulent environments. Coiling stems were epizoic, attached to rugose corals, bryozoans, crinoid stems and similar supports. Growth, mode of life (attached or free), settling and fixation of larvae, and relation to substrate and other organisms ate discussed.     

A common garden experiment with Porphyra umbilicalis (Rhodophyta) evaluates methods to study spatial differences in the macroalgal microbiome

While macroalgal microbiomes are the focus of many recent studies, there is little information about microbial spatial diversity across the thallus. Reliance on field material makes it difficult to discern whether recovered microbiomes belong to the host or its epiphytes, and technical comparisons of macroalgal samples for microbial studies are needed. Here, we use a common garden approach that avoids the problem of epiphytes, particularly at holdfasts, to examine the microbiome of Porphyra umbilicalis (strain Pum1). We used the V6 hypervariable region of the 16S rDNA with Illumina HiSeq sequencing and developed PNA clamps to block recovery of organelle V6 sequences. The common garden approach allowed us to determine differences in the microbiome at the holdfast versus blade margin. We found a notable increase in the relative abundance of Planctomycetes and Alphaproteobacteria at the holdfast, particularly of the possible symbiont Sulfitobacter sp. Nonadjacent 1.5 cm² samples of blade margin had microbiomes that were not statistically different. The most abundant phylum in the overall microbiome was Proteobacteria, followed by Bacteroidetes. Because phycologists often work in remote sites, we compared three stabilization and preparation techniques and found silica gel desiccation/bead‐beating and flash‐freezing/lyophilization/bead‐beating to be interchangeable. Core taxa (≥0.1% of sequences) across treatments were similar and accounted for ≥95% of all sequences. Finally, statistical conclusions for all comparisons were the same, regardless of which microbial community analysis tool was used: mothur or minimum entropy decomposition.     

Characterization of the Adhesive Holdfast of Marine and Freshwater Caulobacters

Caulobacters are prosthecate (stalked) bacteria that elaborate an attachment organelle called a holdfast at the tip of the cellular stalk. We examined the binding of lectins to the holdfasts of 16 marine Caulobacter strains and 10 freshwater species or strains by using a panel of fluorescein-conjugated lectins and fluorescence microscopy. The holdfasts of all the marine isolates bound to only wheat germ agglutinin (WGA) and other lectins that bind N-acetylglucosamine (GlcNac) residues. The freshwater caulobacters showed more variability in holdfast composition. Some bound only to WGA and comparable lectins as the marine strains did. Others bound additional or other lectins, and some did not bind to the lectins tested. The binding of WGA appeared to involve the regions of the holdfast involved with adhesion; a holdfast bound to WGA was significantly less adhesive to glass. Competition experiments with WGA-binding holdfasts and oligomers of GlcNac demonstrated that trimers of GlcNac (the preferred substrate for WGA binding) were more effective than dimers or monomers in preventing WGA binding to holdfasts, suggesting that stretches of contiguous GlcNac residues occur in the WGA-binding holdfasts. In addition, differences between freshwater and marine holdfasts in the strength of WGA binding were noted. The effect of a number of proteolytic and glycolytic enzymes on holdfast integrity was examined; the proteases had no effect for all caulobacters. None of the glycolytic enzymes had an effect on marine caulobacter holdfasts, but chitinase and lysozyme (both attack oligomers of GlcNac) disrupted the holdfasts of those freshwater caulobacters that bound WGA. Despite some similarity to chitin, holdfasts did not bind Calcofluor and no measurable effects on holdfast production were detectable after cell growth in the presence of diflubenzuron or polyoxin D, inhibitors of chitin synthesis in other systems. Finally, the holdfasts of all caulobacters bound to colloidal gold particles, without regard to the coating used to stabilize the gold particles. This binding was stronger or more specific than WGA binding; treatment with colloidal gold particles prevented WGA binding, but the reverse was not the case.     

Seaweed attachment to bedrock: biophysical evidence for a new geophycology paradigm

Seaweeds are amongst the most obvious and ecologically important components of rocky shore communities worldwide but until now little has been known about the processes involved in their attachment. This multidisciplinary study investigated for the first time the interactions between marine macroalgal holdfasts and their underlying substrata, requiring the development of specialized sample preparation techniques to maintain the structural integrity of the holdfast–bedrock interface. Transmitted plane polarized light microscopy, scanning electron microscopy with energy dispersive spectroscopy and structured light illumination microscopy were used in the examination of the interface between Ascophyllum nodosum (Fucales, Heterokontophyta) and crustose red algae Lithothamnion sp. (Corallinales, Rhodophyta) on granite and limestone substrates. The new evidence presented here represents a paradigm shift in the way we view seaweed attachment because results show that the holdfasts exploit the physical characteristics of the rock-forming minerals in order to penetrate the bedrock and thus facilitate the attachment process. Mineral cleavage planes together with intercrystalline and intracrystalline boundaries and fractures provide penetration pathways for the holdfast tissue. This process causes disaggregation of rock-forming minerals to depths <10 mm and therefore assists in the bioerosion of coastal bedrock. It is concluded that seaweeds are able to cause weathering of natural rock and the term 'geophycology' is introduced to describe seaweed–bedrock interactions, including seaweed-induced weathering.     

Herbivory facilitates growth of a key reef‐building Caribbean coral

The decline of reef‐building corals in conjunction with shifts to short‐lived opportunistic species has prompted concerns that Caribbean reef framework‐building capacity has substantially diminished. Restoring herbivore populations may be a potential driver of coral recovery; however, the impact of herbivores on coral calcification has been little studied. We performed an exclusion experiment to evaluate the impact of herbivory on Orbicella faveolata coral growth over 14 months. The experiment consisted of three treatments: full exclusion cages; half cage procedural controls; and uncaged control plates, each with small O. faveolata colonies. We found that herbivorous fish exclusion had a substantial impact on both macroalgal cover and coral growth. Fleshy macroalgae reached 50% cover within some exclusion cages, but were almost absent from uncaged control plates. Critically, O. faveolata calcification rates were suppressed by almost half within exclusion cages, with monthly coral growth negatively related to overgrowth by fleshy macroalgae. These findings highlight the importance of herbivorous fishes for coral growth and the detrimental impact of macroalgal proliferation in the Caribbean. Policy makers and local managers should consider measures to protect herbivorous fishes and reduce macroalgal proliferation to enable coral communities to continue to grow and function.     

WATER MOTION, MARINE MACROALGAL PHYSIOLOGY, AND PRODUCTION

Water motion is a key determinant of marine macroalgal production, influencing directly or indirectly physiological rates and community structure. Our understanding of how marine macroalgae interact with their hydrodynamic environment has increased substantially over the past 20 years, due to the application of tools such as flow visualization to aquatic vegetation, and in situ measurements of seawater velocity and turbulence. This review considers how the hydrodynamic environment in which macroalgae grow influences their ability to acquire essential resources and how macroalgae might respond physiologically to fluctuations in their hydrodynamic regime with a focus on: (1) the biochemical processes occurring within the diffusion boundary layer (DBL) that might reduce rates of macroalgal production; (2) time scales over which measurements of velocity and DBL processes should be made, discussing the likelihood of in situ mass transfer limitation; (3) if and how macroalgal morphology influences resource acquisition in slow flows; and (4) ecobiomechanics and how hydrodynamic drag might influence resource acquisition and allocation. Finally, the concept that macroalgal production is enhanced in wave-exposed versus sheltered habitats is discussed.     

Attachment of the adhesive holdfast organelle to the cellular stalk of Caulobacter crescentus

Caulobacters attach to surfaces in the environment via their holdfasts, attachment organelles located at the base of the flagellum in swarmer cells and later at the end of the cellular stalk in the stalked cells which develop from the swarmer cells. There seems to be little specificity with respect to the types of surfaces to which holdfasts adhere. A notable exception is that the holdfast of one cell does not adhere to the cell surface of another caulobacter, except by joining holdfasts, typically forming "rosettes" of stalked cells. Thus, the localized adhesion of the holdfasts to the cells is in some way a specialized attachment. We investigated this holdfast-cell attachment by developing an adhesion screening assay and analyzing several mutants of Caulobacter crescentus CB2A selected to be defective in adhesion. One class of mutants made a normal holdfast by all available criteria, yet the attachment to the cell was very weak, such that the holdfast was readily shed. Another class of mutants made no holdfast at all, but when mixed with a wild-type strain, a mutant of this class participated in rosette formation. The mutant could also attach to the discarded holdfast produced by a shedding mutant. In addition, when rosettes composed of holdfast-defective and wild-type cells were examined, an increase in the number of holdfast-defective cells was correlated with a decrease in the ability of the holdfast material at the center of the rosette to bind colloidal gold particles. Gold particles are one type of surface to which holdfasts adhere well, suggesting that the stalk end and the colloidal gold particles occupy the same sites on the holdfast substance. Taken together, the data support the interpretation that there is a specialized attachment site for the holdfast at the base of the flagellum which later becomes the end of the stalk, but not a specialized region of the holdfast for attachment to this site. Also, attachment to the cell is accomplished by bond formations that occur not only at the time of holdfast production. Thus, we propose that the attachment of the holdfast to the cell is a true adhesion process and that the stalk tip and base of the flagellum must have compositions distinctly different from that of the remainder of the caulobacter cell surface.     

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.     

Patterns of abundance and assemblage structure of epifauna inhabiting two morphologically different kelp holdfasts

The mobile fauna associated with two sympatric kelp species with different holdfast morphology (Saccorhiza polyschides and Laminaria hyperborea) was compared to test for differences in the assemblage structure of holdfast-associated mobile epifauna. A total of 24,140 epifaunal individuals were counted from 30 holdfasts of each kelp species. Overall epifaunal abundances exceeded faunal abundances previously reported from holdfasts of other kelps. Three taxonomic groups, Amphipoda, Mollusca, and Polychaeta, accounted for ca. 85% of all individuals. Total abundances increased with the amount of habitat available, quantified either as the volume or the area provided by the holdfasts. The multivariate structure of the epifaunal assemblage did not differ between holdfasts of the two kelp species. However, epifaunal assemblages responded differentially to the habitat attributes provided by each type of kelp holdfast: multivariate variation in the assemblage structure of epifauna was mostly explained by holdfast area and volume for L. hyperborea, and by the surface-to-volume ratio for S. polyschides holdfasts. Therefore, the physical attributes of biogenic habitats, here kelp holdfasts that better predict patterns in the assemblage structure of associated fauna can differ according to their different physical morphology, even though the overall assemblage structure of associated fauna was similar.     

Nonlinear multivariate models of successional change in community structure using the von Bertalanffy curve

von Bertalanffy curves were used to describe the nonlinear relationship between assemblages inhabiting holdfasts of the kelp Ecklonia radiata and the volume of the holdfast. This was done using nonlinear canonical analyses of principal coordinates (NCAP). The volume of the holdfast is a proxy for the age of the plant and, thus, the canonical axis is a proxy for succession in the marine invertebrate community inhabiting the holdfast. Analyses were done at several different taxonomic resolutions on the basis of various dissimilarity measures. Assemblages in relatively large holdfasts demonstrated ongoing variation in community structure with increasing volume when the dissimilarity used was independent of sample size. Smaller holdfasts had proportionately greater abundances of ophiuroids and encrusting organisms (bryozoans, sponges, ascidians), while larger holdfasts were characterised by proportionately greater abundances of crustaceans, polychaetes and molluscs. Such linear and nonlinear multivariate models may be applied to analyse system-level responses to the growth of many habitat-forming organisms, such as sponges, coral reefs, coralline algal turf or forest canopies.     

Regional differences in kelp-associated algal assemblages on temperate limestone reefs in south-western Australia

Abstract. Ecklonia radiata (C. Agardh) J. Agardh kelp beds — a characteristic feature of the nearshore environment along the south‐west Australian coastline — contribute significantly to the coastal biodiversity in temperate Australia, yet, little is known about the organization of these macroalgal assemblages. By compiling existing and new data sets from habitat surveys, we have characterized and compared the structure of kelp‐associated macroalgal assemblages in three regions (Marmion Lagoon, Hamelin Bay and the marine environment neighbouring the Fitzgerald River National Park) across more than 1000 kilometres of the south‐west Australian coastline. 152 macroalgal taxa had been recognized within the three regions and this is in the range of species richness reported from other Australian and African kelp beds. The kelp‐associated algal assemblages were regionally distinct, 66% of all taxa were only found in one region and only 17 taxa were found in all three regions. Adjacent regions shared an additional 13–15 taxa. The regional shifts in assemblage structure were evident in species composition of both canopy and understorey. The organization of assemblages followed a spatial hierarchy where differences in assemblage structure were larger among regions (hundreds of kilometres apart) than among sites within regions (kilometres apart) and differences among sites within region were larger than differences among quadrats within sites (metres apart). Despite this hierarchy each level of nesting contributed approximately the same to total variation in assemblage structure and these spatial patterns were stronger than temporal differences from seasons to 2–3 years. Our results suggest that local and small‐scale processes contribute considerably to heterogeneity in macroalgal assemblages throughout south‐western Australia, and, in particular, our results are consistent with E. radiata exerting a strong influence on macroalgal assemblage structure. Further, our study contradicts the existence of a general south‐west Australian kelp assemblage, although a few species may form the core of E. radiata associations across regions.     

Differences in response between haploid and diploid isomorphic phases of Gracilaria verrucosa (Rhodophyta: Gigartinales) exposed to artificial environmental conditions

This study tests the responses of juvenile gametophytes and tetrasporophytes (holdfast stage) of the isomorphic alga Gracilaria verrucosa under different environmental conditions.Estimations of survival and growth of holdfasts of haploid and diploid juvenile individuals were performed in natural sea-water and artificial culture medium, and under stringent conditions using lead as a toxin and ultra violet radiation as a mutagen. Results indicate that (i) holdfasts of haploid juveniles grow better than diploids in non-optimal medium conditions; (ii) holdfasts of diploid juveniles have a better tolerance to lead than haploids; and (iii) slight advantage of holdfasts of diploid juveniles grow better than haploids under U.V. radiation.     

Integration of chlorophyll a fluorescence and photorespirometry techniques to understand production dynamics in macroaglal communities

Global declines of macroalgal beds in coastal waters have prompted a plethora of studies attempting to understand the drivers of change within dynamic nearshore ecosystems. Photosynthetic measurements are good tools for assessing the consequences of numerous stressors of macroalgae, but there is somewhat of a disconnection between studies that focus on organism‐specific ecophysiological responses and those that address causes and consequences of shifts in macroalgal productivity. Our goal is to highlight the applications of two complementary tools for measuring photosynthesis—variable chlorophyll a fluorescence and photorespirometry—and provide guidance for the integration of physiology and ecology to understand the drivers of change in macroalgal communities. Photorespirometry can provide an integrated measure of whole‐community metabolism, including an estimate of the physiological costs associated with stressors, while fluorescence‐based techniques provide point measures of the efficiency of the photosynthetic apparatus within communities. Variable chlorophyll a fluorescence does not provide an estimate of carbon balance or integrated photosynthesis across either whole plants or whole communities but can be used to estimate the contribution of individual community components in the dynamic subcanopy environment to help us understand the mechanisms underlying observed responses. We highlight the importance of the highly dynamic light environment within macroalgal communities and call for better integration of physiological techniques in an ecological context to enhance our understanding of the responses of whole communities to local and global stressors.