Reef-building Polychaete Research Articles

Double-phased controlled and influenced biomineralization in marine invertebrates: The example of Miocene to recent reef-building polychaete cirratulids from southern Peru

Carbonate biomineralization normally occurs in three distinct types: controlled, induced and influenced, each with its peculiar characteristics. Building-reef species within the family Cirratulidae (Annelida, Polychaeta) constitute the first known example of “double-phased” biomineralization among marine invertebrates, as they combine controlled and influenced biomineralization types in the process of developing carbonate tube aggregates. The ultrastructure of the tubes, composed of thin calcareous lamellae with a spherulitic prismatic ultrastructure, as well as lamellae with a homogeneous structure, is produced directly by the worms living inside them and clearly indicates a controlled biomineralization, while the calcareous matrix with agglutinated xenolithic granules that fills the areas between the tubes of the same aggregate is the product of an influenced biomineralization.The reason why this biomineralization process occurs is yet unknown. This study is therefore aimed at describing in detail for the first time the biomineralization of Miocene (Diplochaetetes) and Recent (Dodecaceria) tubes of cirratulid aggregates from southern Peru via optical microscopy, epifluorescence, SEM and EDS analyses. Furthermore, a detailed morphometric and compositional study of tubes was performed and results were statistically evaluated. The comparison with recent cirratulids allowed the recognition of the double-phased biomineralized skeletons in the fossil specimens, despite the different degree of recrystallization which affected the studied Peruvian bioconstructions. This observation suggests that this type of biomineralization has not changed over the course of the entire Cenozoic and can be considered a unique evolutionary character which probably was developed by these polychaetes to be safer from predators, as well as generally more stable and more resistant to environmental stressing factors.

Body traits variation of a reef building polychaete across a latitudinal gradient

Body size is considered the most important trait in ecology, and as such, helps to understand the species-environment interactions. We explored the relationship between body traits and environmental variables along a gradient range using the polychaete Phragmatopoma caudata, with well-defined and diversified morphological structures. Measurements of five traits (body length, opercular crown, branchiae, tentacles and building organ sizes) were taken at nine sites along the Southwestern Atlantic coast and their relationships to temperature, salinity, tidal range, waves height, and dissolved oxygen were assessed. Our results demonstrate that traits were influenced by the environmental gradient and temperature was the main factor that drives this variation in body traits, while the other variables showed a minor influence on this. The approach showed patterns of variation of body traits in a macroscale context, increasing the understanding of its relationships with environmental variables and eventual shifts in the distribution in the future climate scenarios.

First report of the mitogenome of the invasive reef-building polychaete Ficopomatus enigmaticus (Annelida: Serpulidae) and a cryptic lineage from the Japanese Archipelago.

The mitochondrial genomes (mitogenomes) of the family Serpulidae are characterized by a high nucleotide sequence divergence and a significant number of gene order rearrangements compared with other families within the phylum Annelida. However, only two of 50 genera of serpulids have mitogenomes already sequenced. In this study, we report the first sequencing and assembly of the complete mitogenome of Ficopomatus, thus providing further knowledge on mitochondrial gene sequences of Serpulidae. A mitogenome of the invasive reef-building polychaete Ficopomatus enigmaticus was amplified by long PCR and sequenced using the Illumina MiSeq System. It comprised 15,853bp and consisted of 12 protein-coding genes(atp8was not found), 23 tRNA, and two rRNA genes. The AT and GC skew values were infrequent when compared to annelid mitogenomes but similar to other serpulids sequenced to date (i.e., Spirobranchus and Hydroides). The mitochondrial gene order of F. enigmaticus was highly rearranged compared to other serpulids. To amplify 16S rRNA gene sequences, we developed a 16S rRNA primer set by modifying the universal primer set 16SarL/16SbrH. We detected the 16S rRNA sequence of F. enigmaticus deposited in GenBank erroneously characterized as of serpulid origin. We reported for the first time the presence of two lineages of F. enigmaticus in Japan, which have already been identified in California, Australia, and the Mediterranean. The first mitochondrial genome of F. enigmaticus showed a unique gene order rearrangement, corroborating the remarkable diversity in the previously reported mitogenomes of other serpulid species. The presence of the two lineages of F. enigmaticus identified for the first time in Japan represents another case of cryptic invasion. The first 16S rRNA gene sequences of F. enigmaticus obtained in the present study can be used as reference sequences in future DNA metabarcoding studies.

Abundance of microplastic in different coastal areas using Phragmatopoma caudata (Kroyer in Morch, 1863) (Polychaeta: Sabelariidae) as an indicator

Plastic debris has been reported in the marine environment since the '70s. These plastic materials are introduced into the marine environment in several sizes, one of them microplastics (MP), and they have drawn great interest and concern in the past decades. Consumption of MP can cause weight loss, feeding rate decrease, reproductive activity decrease, and several other negative effects. Ingestion of MPs has already been reported for some species of polychaetes but the use of these annelids in MP studies is still poorly reported. Costa et al. (2021) was the first study to investigate the capability of the reef-building polychaete Phragmatopoma caudata to incorporate microplastic in its colony's structures. This makes the colonies a reservoir of MP and thus they reflect the environment's quality regarding MP presence. Consequently, this specie becomes an important asset to MP pollution investigation in coastal areas. Therefore, this work aims to investigate the abundance of MPs on the coastline of Espírito Santo using P. caudata as an indicator of MP presence. For this, we collected samples of P. caudata colonies in 12 sampling sites along the Espírito Santo coast (three replicates at each site). These colony samples were processed to extract the MPs particles from the colony surface, its inner structure, and tissues from the individuals. These MPs were counted using a stereomicroscope and sorted according to their color and type (filament, fragment, and other). Statistical analysis was performed using GraphPad Prism 9.3.0. Significant values followed p < 0.05. We found MP particles in all 12 sampled beaches, configuring a pollution rate of 100 %. The number of filaments was notably greater than the number of fragments and others. The most impacted beaches were found inside the metropolitan region of the state. Finally, P. caudata is an efficient and trustable indicator of microplastic in coastal areas.

Temporal dynamics of a Sabellaria wilsoni (Sabellariidae: Polychaeta) reef on the Brazilian Amazon Coast

Polychaetes of the family Sabellariidae build extensive reefs in many coastal regions worldwide. These structures are dynamic systems that undergo a natural cycle of growth and destruction provoked by fluctuations in hydrodynamic conditions and biological factors. Here, we monitored a Sabellaria wilsoni reef over an annual cycle on Algodoal-Maiandeua Island on the Brazilian Amazon coast. We studied the impact of temporal variations in local environmental characteristics on the structure of the reef and the reef-building polychaete population. Metrics included the local climate (temperature, rainfall, and winds), hydrological variables (suspended particulate matter and salinity), and the output of a numerical model of the local hydrodynamics. There was increased hydrodynamic stress in the dry season due to changes in the direction and intensity of the wind and stronger waves. This in turn led to an accentuated decrease in sabellariid density, and the eventual erosion of the reef, which lost &gt;80% of its original area. The reduction in the hydrodynamic energy at the end of the rainy season favoured the mass recruitment of sabellariids as well as the subsequent growth and recuperation of the reef. Oligohaline conditions also contributed to a reduction in worm density, but not to any loss in reef structure. These findings provide important insights into the thresholds of energy and salinity tolerated by the reef-building polychaete S. wilsoni and offer a useful baseline for future research on the ecology of this species and the monitoring of this important marine habitat.

Sabellaria alveolata (Annelida, Polychaeta) bioconstructions and associated macroalgal community from Portopalo di Capo Passero (SE Sicily)

The shallow-water reef building polychaete Sabellaria alveolata is recorded from a new locality in the southeastern corner of Sicily, off Portopalo di Capo Passero. Here, a particular habitat is formed on upper infralittoral rocky bottoms beaten by waves, with S. alveolata developing as veneer-like bioconstructions interspersed/covered with a dense macroalgal community including alien Caulerpa taxa and dominated by Ericaria giacconei. First insights about the development of this particular habitat, as well as observations on possible relationships between Sabellaria and the associated algae, are presented.

Looking for diversity in all the right places? Genetic diversity is highest in peripheral populations of the reef-building polychaete Sabellaria alveolata

Species distributions have been profoundly affected by past climate change, and are expected to change considerably in response to future environmental change. To better apprehend how future climate change is likely to affect genetic diversity in marine populations, it is essential to first evaluate the processes that have shaped the current distribution of genetic diversity in the sea. The honeycomb worm is a reef-building polychaete that hosts high biodiversity. Here we show that the genetic diversity in populations of S. alveolata is highest towards the edges of the current species range and lowest at its center. Pleistocene glacial cycles likely led to extirpations of S. alveolata from central populations in the Bay of Biscay, with coalescent-based estimates of post-glacial colonization dating to the beginning of the Holocene interglacial, from 10,000 to 14,000 years ago. Meanwhile, populations in the Irish Sea and English Channel likely persisted in glacial refugia since the Eemian interglacial, 120,000 years ago. Northern populations host at least two sets of divergent haplotypes, indicating that two refugia possibly existed in the north, with Ireland being a likely second refugium. Within biogeographic regions, populations were overall well-connected, but strong genetic differentiation suggests that little exchange occurs between regions. These two unexpected reservoirs of genetic diversity at the range edges deserve greater attention as warming temperatures threaten trailing edge populations, while greater climatic variability threatens leading edge populations.

Influence of complexity and habitat heterogeneity on macrofaunal assemblages provided by an invasive ecosystem engineer in Mar Chiquita coastal lagoon

Invasive ecosystem engineers change habitat attributes and species abundance, affecting the structure of invaded communities. In the Mar Chiquita coastal lagoon (37° 40′S, 57° 23°W), the invasive reef-building polychaete Ficopomatus enigmaticus (Fauvel, 1823) generates a heterogeneous environment with habitats of variable complexity: the reefs themselves (high complexity), the sediment surrounding the reefs (low complexity), and the substrate from the areas without reefs (intermediate complexity). Our objective was to compare the macrofaunal assemblages along the whole complexity gradient. We hypothesized that individuals' abundance, diversity, species richness, and evenness of the macrofaunal assemblages increase with habitat complexity, since more complex habitats may represent greater availability of suitable spaces. The composition of the species assemblage was compared through monthly field samplings in each of the three habitats. Results showed that individuals' abundance increased with habitat complexity. In addition, amphipods were the most abundant group in the reefs, while ostracods were the most abundant group in the sediment surrounding the reefs and that from reef-free areas. However, community parameters were occasionally similar between the reefs and the sediment from reef-free areas, depending on the month considered. Our study suggests that the invasion of F. enigmaticus changed the macrofaunal assemblages and the individuals' abundances by providing a high complexity substrate, but also, and less predictably, by increasing habitat heterogeneity, highlighting the importance of including both dimensions of habitat structure in the study of invasions by ecosystem engineers.

Seascape genomics reveals population isolation in the reef-building honeycomb worm, Sabellaria alveolata (L.)

BackgroundUnder the threat of climate change populations can disperse, acclimatise or evolve in order to avoid fitness loss. In light of this, it is important to understand neutral gene flow patterns as a measure of dispersal potential, but also adaptive genetic variation as a measure of evolutionary potential. In order to assess genetic variation and how this relates to environment in the honeycomb worm (Sabellaria alveolata (L.)), a reef-building polychaete that supports high biodiversity, we carried out RAD sequencing using individuals from along its complete latitudinal range. Patterns of neutral population genetic structure were compared to larval dispersal as predicted by ocean circulation modelling, and outlier analyses and genotype-environment association tests were used to attempt to identify loci under selection in relation to local temperature data.ResultsWe genotyped 482 filtered SNPs, from 68 individuals across nine sites, 27 of which were identified as outliers using BAYESCAN and ARLEQUIN. All outlier loci were potentially under balancing selection, despite previous evidence of local adaptation in the system. Limited gene flow was observed among reef-sites (FST = 0.28 ± 0.10), in line with the low dispersal potential identified by the larval dispersal models. The North Atlantic reef emerged as a distinct population and this was linked to high local larval retention and the effect of the North Atlantic Current on dispersal.ConclusionsAs an isolated population, with limited potential for natural genetic or demographic augmentation from other reefs, the North Atlantic site warrants conservation attention in order to preserve not only this species, but above all the crucial functional ecological roles that are associated with their bioconstructions. Our study highlights the utility of using seascape genomics to identify populations of conservation concern.

Linking multiple facets of biodiversity and ecosystem functions in a coastal reef habitat

Reef-building species play key roles in promoting local species richness and regulating ecosystem functions like biogeochemical fluxes. We evaluated the functioning of a habitat engineered by the reef-building polychaete Sabellaria alveolata, by measuring oxygen and nutrient fluxes in the reef structures and in the soft-sediments nearby. Then, we investigated the relative importance of temperature, the engineer S. alveolata, and different facets of macrofauna diversity (taxonomic, functional diversity and identity), on the reef biogeochemical fluxes using multiple linear regressions and effect sizes. The reef fluxes were more intense than the soft-sediment fluxes and mainly driven by the engineer biomass and abundance, stressing the importance of these biogenic structures. Higher water temperatures and an intermediate level of associated macrofauna functional dispersion weighted only by abundance (i.e. intermediate biological trait variability) maximized the reef’s global biogeochemical functioning. Ultimately, the physical degradation of the reefs could lead to lower levels of functioning.

Genetic variation of reef-building polychaete Sabellaria chandraae in the south-eastern Arabian Sea based on mitochondrial COI gene sequences

The honeycomb worm Sabellaria chandraae is the most common reef-building polychaete in the intertidal area along the south-eastern Arabian Sea. We used the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene to examine the levels of genetic variation the population. The samples were collected from seven intertidal areas along the south-eastern Arabian Sea. The hierarchical Analysis of Molecular Variance (AMOVA) and conventional population statistics (FST) showed a low level of genetic differentiation (FST = 0.0864, p < .05), indicating no geographical patterning among seven populations. The present results were able to provide a reference for the single stock population along the south-eastern Arabian Sea.

You are not always what you eat-Fatty acid bioconversion and lipid homeostasis in the larvae of the sand mason worm Lanice conchilega.

The meroplanktonic larvae of benthic organisms are an important seasonal component of the zooplankton in temperate coastal waters. The larvae of the reef-building polychaete Lanice conchilega contribute up to 15% of the summer zooplankton biomass in the North Sea. Despite their importance for reef maintenance (which positively affects the benthic community), little is known about the trophic ecology of this meroplanktonic larva. Qualitative and quantitative estimates of carbon (C) transfer between trophic levels and of fatty acid (FA)—specific assimilation, biosynthesis, and bioconversion can be obtained by compound-specific stable isotope analysis of FA. The present work tested the hypothesis that the concept of fatty acid trophic markers (FATM), widely used for studies on holoplankton with intermediate to high lipid contents, is also applicable to lipid-poor organisms such as meroplanktonic larvae. The incorporation of isotopically-enriched dietary C by L. conchilega larvae was traced, and lipid assimilation did not follow FA-specific relative availabilities in the diet. Furthermore, FAs that were unavailable in the diet, such as 22:5(n-3), were recorded in L. conchilega, suggesting their bioconversion by the larvae. The results indicate that L. conchilega larvae preferentially assimilate certain FAs and regulate their FA composition (lipid homeostasis) independently of that of their diet. Their quasi-homeostatic response to dietary FA availability could imply that the concept of FATM has limited application in lipid-poor organisms such as L. conchilega larvae.

Presence of microplastics in the tube structure of the reef-building polychaete Gunnarea gaimardi (Quatrefages 1848)

The prevalence of microplastics in the marine environment has resulted in a need to understand their association with various fauna. The aim of this study was to assess whether microplastic particles are present in the tube structure of the indigenous reef-building polychaete Gunnarea gaimardi, which occurs along the coast of South Africa. Sampling was conducted at nine stations along the west and southeast coastlines of South Africa, in July 2016 and April/May 2017. Microplastic particles were recorded in all tube structures of G. gaimardi, with the density ranging between 0.056 and 1.113 microplastic particles g–1 dry weight (dwt). There were no significant differences between sites (p > 0.05), resulting in an overall average of 0.275 (SD 0.215) microplastic particles g–1 (dwt). To the authors’ knowledge, this is the first study to show that synthetic polymers are found in the tubes of reef-building polychaetes along the coast of South Africa.

Invasión de un poliqueto nativo en una isla del Pacífico Oriental Tropical

Fluctuations in population dynamics, like demographic expansions and invasions, are relatively common in ecosystems, and in certain cases may affect biodiversity and a suite of other ecological attributes. In this paper, we report the appearance and population explosion of the reef-building polychaete (Sabellariidae) Idanthyrsus cf. cretus in Gorgona Island (Eastern Tropical Pacific), describing some ecological characteristics (abundance and coverage). The survey was carried out in three study areas of Gorgona Island, located in the Colombian Pacific. Sampling was performed randomly at low, mid and high intertidal levels, in order to measure density and coverage. Density was measured randomly in three study areas at low, mid and high intertidal levels collecting samples (N=37) of 100 cm2 from the colony. Coverage was measured using random transects (N=21) per locality and intertidal levels (20 m length × 1 m width). A total of 1,904 I. cf. cretus were collected with a mean density of 73 ind./100 cm2. Coverage was statistically different between intertidal zones, with the highest values in the mid-intertidal level (11%). Differences in coverage of I. cf. cretus colonies among study areas are probably due to differing intertidal physical characteristics: the availability of adequate substrate and building materials in the study areas sediments, which in turn might affect abundance and colony size. Suitable substrate and construction material might have favored the rapid spreading and local invasion of this species.

Lipid remodelling in the reef-building honeycomb worm, Sabellaria alveolata, reflects acclimation and local adaptation to temperature.

Acclimation and adaptation, which are key to species survival in a changing climate, can be observed in terms of membrane lipid composition. Remodelling membrane lipids, via homeoviscous adaptation (HVA), counteracts membrane dysfunction due to temperature in poikilotherms. In order to assess the potential for acclimation and adaptation in the honeycomb worm, Sabellaria alveolata, a reef-building polychaete that supports high biodiversity, we carried out common-garden experiments using individuals from along its latitudinal range. Individuals were exposed to a stepwise temperature increase from 15 °C to 25 °C and membrane lipid composition assessed. Our results suggest that S. alveolata was able to acclimate to higher temperatures, as observed by a decrease in unsaturation index and 20:5n-3. However, over the long-term at 25 °C, lipid composition patterns are not consistent with HVA expectations and suggest a stress response. Furthermore, unsaturation index of individuals from the two coldest sites were higher than those from the two warmest sites, with individuals from the thermally intermediate site being in-between, likely reflecting local adaptation to temperature. Therefore, lipid remodelling appears limited at the highest temperatures in S. alveolata, suggesting that individuals inhabiting warm environments may be close to their upper thermal tolerance limits and at risk in a changing climate.

Top-Down Effects of an Exotic Serpulid Polychaete on Natural Plankton Assemblage of Estuarine and Brackish Systems in the SW Atlantic

ABSTRACT Pan, J. and Marcoval, M.A., 2014. Top-down effects of an exotic serpulid polychaete on natural plankton assemblage of estuarine and brackish systems in the SW Atlantic. The invasive reef-building polychaete Ficopomatus enigmaticus (Fauvel, 1923) has become well-established in many temperate brackish waters. To analyze preferences for different planktonic food sources, short-term (∼1.5 h), grazing microcosm experiments were performed in situ (n = 3), at two water bodies, a coastal lagoon (Mar Chiquita, MC) and the mixohaline stretches of a coastal creek (La Tigra, LT), Argentina, in January 2007. Relative clearance rates of phytoplankton were assessed for chlorophyll a size-fractions and for different groups of nanoplanktonic and microplanktonic protists. The two locations showed significant differences in plankton community structure. Nanoeukaryotes were the dominant group at both locations; the second most-abundant groups were diatoms at MC and ciliates at LT. There were significant differences ...

Effects of macroalgae on the recruitment, growth, and body condition of an invasive reef forming polychaete in a south-western Atlantic coastal lagoon

Species interactions could mediate species invasive processes. In Mar Chiquita coastal lagoon (37° 40′S, 57° 23´W, Argentine), the invasive reef building polychaete Ficopomatus enigmaticus (Fauvel 1923) enhances the biomass of the red alga Polysiphonia subtilissima Montagne 1840 on reef surfaces, and excludes green macroalgae (mainly Cladophora sp. Kützing, 1843) from sediment between reefs. In turn, macroalgae could have several community structuring effects (e.g., as food or by competing for space). Therefore, macroalgae may affect F. enigmaticus. To evaluate this hypothesis we studied (1) the interaction between macroalgae and F. enigmaticus during the colonization of new substrates and (2) the effects of macroalgae on the recruitment, growth, and body condition of F. enigmaticus. Field sampling and experiments suggested a lack of competition on new substrates. However, there was a positive effect of macroalgae on F. enigmaticus during the warm season, since its recruitment, tube length, and body condition were higher in areas with macroalgae on reef surfaces. Considering that previous studies showed that reefs positively affect macroalgae, our results suggest that there is a positive feedback on F. enigmaticus created by macroalgae on established reefs and during the reefs' growing season. This interaction may contribute to the maintenance and growth of established reefs.

Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small, urban estuary

Two of the greatest threats to native biodiversity are the construction of artificial structures in natural environments and the introduction of invasive species. As the development and urbanisation of estuaries continues at an increasing rate worldwide, these environments are being simultaneously affected by these threats. This study quantifies the spread of an invasive reef-building polychaete, Ficopomatus enigmaticus, in a small, highly manipulated urban estuary in South Africa and investigates its role as an ecosystem engineer. Anthropogenic changes to the Zandvlei Estuary, including construction of a rubble weir and canalisation near the estuary mouth, construction of an extensive marina development and hardening of the banks with concrete, have facilitated the expansion of F. enigmaticus. The standing stock of F. enigmaticus increased from 13.69 t, as measured in 1986, to 50.03 t in 2012, due both to increase in the total area colonised and standing stock per m2. Since F. enigmaticus reefs support a greater biomass of infauna than adjacent sandy areas, total invertebrate biomass in the estuary is estimated to have increased from less than 0.30 t in 1942, to over 56.80 t in 2012, due mainly to hardening of banks in parts of the main estuary with concrete and construction of a marina system. A positive correlation between reef mass and infaunal biomass, density and diversity was also found.

Factors controlling macroalgae assemblages in a Southwest Atlantic coastal lagoon modified by an invading reef forming polychaete

In the Mar Chiquita coastal lagoon (37° 40′S, 57° 23°W, Argentina), the invasive reef building polychaete Ficopomatus enigmaticus, change the composition and abundance of macroalgae by providing habitat to some species and by excluding others. The magnitude of these effects may be regulated by consumers and nutrients availability. Here we evaluate the relative importance of consumers and nutrients in controlling macroalgae development on the reefs, and on the sediment in areas without reefs. Experiments showed that: (1) large consumers (birds, fishes and crabs) had no effect on red (Polysiphonia subtilissima) and green (Cladophora sp.) macroalgae on reefs; (2) large consumers had positive effect on green macroalgae development on the sediment of areas without reefs, probably by enhancing the availability of bivalve shells for macroalgae attachment; (3) small consumers (amphipods, hydrobiid snails and crabs) had negative effect on green macroalgae development, probably by direct consumption; (4) small consumers had positive effect on the biomass of the red macroalga P. subtilissima; and (5) nutrient had no effect on macroalgae. These interactions would determine the abundance and the spatial distribution of macroalgae (e.g., patchiness). Consequently, the effect of an invader ecosystem engineer in the composition of species assemblages may be mediated by other community structuring forces, which in turn may have different effects according to their interaction with the invader.

Effects of an invasive reef-building polychaete on the biomass and composition of estuarine macroalgal assemblages

Invasive species can transform ecological communities. Their profound effects may alter the sources and pathways of primary production. We investigated the effects of the reef forming polychaete Ficopomatus enigmaticus invasion on the biomass and distribution of estuarine macroalgae in a SW Atlantic coastal lagoon (Mar Chiquita, 37° 40′S, 57° 23′W, Argentina). Reefs built by this species serve as substrates for macroalgal development and furnish structures that modify physical and biological conditions for the surrounding benthos. We showed that (1) the red macroalga Polysiphonia subtilissima settles and grows almost exclusively on the surface of the reef, (2) the green macroalgae Cladophora sp. and Enteromorpha intestinalis are found almost exclusively in areas without reefs attached to mollusk shells and, (3) no macroalgae occur in the sediment between reefs. Manipulative experiments show that reefs provide a complex substrate for settlement and survival and therefore benefit red macroalga. These experiments also show that the invasive reef builder has negative indirect effects on green macroalgae by increasing grazing and probably by increased sedimentation between reefs. Via these direct and indirect effects, reefs change the relative biomass contribution of each macroalgal species to the overall production in the lagoon. Knowledge of these processes is important not only for predicting net effects on primary production but also because changes in macroalgal species composition may produce effects that cascade through the food web.