Tropical Benthic Communities Research Articles

Distributional range shifts of Western Atlantic benthic Sargassum species (Fucales, Phaeophyceae) under future climate change scenarios

Climate change is altering the world’s marine biota, in particular, their geographic distribution. Sargassum species are foundation species that play critical ecological roles in tropical benthic communities, providing food, habitat heterogeneity and shelter for a wide range of marine organisms. To understand how future changes in abiotic variables could affect the distribution of Sargassum species along the Western Atlantic Ocean, we performed Ecological Niche Models (ENM) for 12 benthic Sargassum species. We projected present and future habitat suitability distributions under the RCP 4.5 and RCP 8.5 IPCC scenarios. We fit ENM and created ensembles from different algorithms. Our results predict changes in species latitudinal range (niche suitability) in the order of 0.5˚ to 8.1˚ northward, and 0˚ to 5.5˚ southward. Six species are likely to reduce their suitability area from 10% to 80%, while other six species are likely to expand their suitability area from 4% to 168%. Overall, changes in suitability area and latitudinal ranges will increase at larger latitudes for most species while suitability areas will decrease at lower latitudes for half of the species. This pattern is consistent with the expected tropicalization of temperate latitudes following global warming. Such changes can produce considerable losses in ecosystem services maintained by healthy Sargassum beds, particularly at lower latitudes. Our findings highlight the need to improve Sargassum conservation policies and management strategies to avoid the negative effects caused by losses in Sargassum forests.

Recruitment and Succession in a Tropical Benthic Community in Response to In-Situ Ocean Acidification.

Ocean acidification is a pervasive threat to coral reef ecosystems, and our understanding of the ecological processes driving patterns in tropical benthic community development in conditions of acidification is limited. We deployed limestone recruitment tiles in low aragonite saturation (Ωarag) waters during an in-situ field experiment at Puerto Morelos, Mexico, and compared them to tiles placed in control zones over a 14-month investigation. The early stages of succession showed relatively little difference in coverage of calcifying organisms between the low Ωarag and control zones. However, after 14 months of development, tiles from the low Ωarag zones had up to 70% less cover of calcifying organisms coincident with 42% more fleshy algae than the controls. The percent cover of biofilm and turf algae was also significantly greater in the low Ωarag zones, while the number of key grazing taxa remained constant. We hypothesize that fleshy algae have a competitive edge over the primary calcified space holders, coralline algae, and that acidification leads to altered competitive dynamics between various taxa. We suggest that as acidification impacts reefs in the future, there will be a shift in community assemblages away from upright and crustose coralline algae toward more fleshy algae and turf, established in the early stages of succession.

An exception to the rule: top-down control of a coral reef macroinvertebrate community by a tropical spiny lobster

In temperate habitats, predation by lobsters creates trophic cascades that reverberate through benthic communities. However, the influence of lobsters on tropical benthic communities is thought to be minimal due to higher prey diversity and the mobility and broad diet of lobsters. We hypothesized that this would not be the case for the spotted spiny lobster (Panulirus guttatus Latreille, 1804), an obligate, philopatric dweller of Caribbean coral reefs. Our study took place in the Florida Keys (USA), where we examined the gut contents of wild lobsters, conducted laboratory experiments on lobster prey selection and foraging effectiveness in rubble, and manipulated lobster density on isolated patch reefs to examine the effects of lobster predation on macroinvertebrate prey over a 3-yr period. We found P. guttatus to be a generalist carnivore that consumed a suite of macroinvertebrates, including important reef herbivores (e.g., herbivorous crabs, gastropods, and urchins) that comprised >60% of its diet. Higher densities of P. guttatus exerted strong top-down control over the abundance and composition of macroinvertebrate prey in rubble substrates on patch reefs, but not prey living in substrates dominated by macroalgae. Lobster foraging success in rubble also depended on rubble size; lobsters extracted prey from and overturned rubble more easily when rubble was smaller. The abundance and high site fidelity of predatory P. guttatus appears to provide the necessary conditions for top-down control of prey in coral reef rubble zones, an effect similar to the powerful influence of lobster predation observed in temperate ecosystems.

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

Summary Top‐down control of benthic communities by fishes in temperate and Neotropical streams has received considerable attention, yet relatively little is known about the occurrence or strength of such top‐down control in tropical Asian streams. We undertook pool‐scale removals of an entire macroconsumer assemblage of fishes and predatory shrimp, as well as its component guilds (algivores versus predators), in three Hong Kong streams during the dry season and monitored the responses of periphyton, benthic macroinvertebrates (predominantly insects) and leaf‐litter breakdown. Pools supported high densities and biomass of predatory macroconsumers. Algivorous balitorid fishes had a mean density of 30.1 indiv m−2 (range: 1.5–58.2 indiv m−2) and a wet‐weight biomass of 20.9 g m−2 (range: 1.6–34.2 g m−2); values for predatory fishes (mainly a nemacheilid and a goby) were 9.4 indiv m−2 (range: 7.3–11.1 indiv m−2) and 29.7 g m−2 (range: 24.1–38.0 g m−2). Densities of predatory palaemonid shrimp were likewise high (mean: 14.0 indiv m−2; range: 8.9–19.0 indiv m−2). Despite high macroconsumer standing stocks, there was little evidence of top‐down control of benthic communities. The removal of algivorous fishes had no effects on algal biomass, periphyton accumulation, silt accrual or abundance of benthic insects. The removal of all predators (fishes and shrimp), as well as the removal of all macroconsumers, was associated with a small increase in the density of insect scrapers (especially baetid mayflies), although no such effect was evident when predatory fishes (but not shrimp) were removed. Apparently, shrimp substituted for the role of predatory fishes by cropping any excess prey. However, the removal of the entire predatory guild or all macroconsumers produced no additional changes in macroinvertebrate assemblages, nor any influence on periphyton or leaf‐litter breakdown. The pool‐scale approach used in this investigation, combined with the inclusion of three study streams, should have provided a realistic picture of the significance of top‐down control of benthic communities by macroconsumers. Statistical power may have been limited by logistical constraints on the number of replicate pools. Localised nutrient limitation caused by the removal of macroconsumers might have contributed to the apparent weakness of top‐down control of benthic communities. However, given the high standing stocks of fishes and shrimps, it is remarkable that experimental manipulations resulted in generally small or negligible effect sizes.

First record of the green alga Halimeda (Bryopsidales: Chlorophyta) at Rocas Atoll—natural dispersion or anthropogenic causes?

Rocas is the only atoll in the south-western Atlantic and comprises a shallow platform area of about 360 km 2 , distant 230 km from the continent and 130 km from Fernando de Noronha Archipelago, in Brazil. Since the 1970s, its marine flora has received the attention of several authors, giving rise to considerable and well-established knowledge about its algal biodiversity, with a total of 143 seaweed species reported for the area. Previous efforts stressed the interesting absence of the green algae Halimeda , usually abundant in tropical reefs and one of the most important seaweed groups in the structure of the tropical benthic community. Herein, we report for the first time the presence of Halimeda opuntia at Rocas, collected during an expedition in January 2012. Based on phylogenetic analysis, was proposed that H. opuntia was originated in the Indo-Pacific Ocean and that its establishment in Brazil was independent from populations of the Caribbean as a whole and the Bahamas in particular. Another hypothesis is the current scenario of increased frequency and intensity of extreme events along the Brazilian coast, which could explain the transport of propagules from adjacent areas towards the atoll.

INDUCTION AND REDUCTION OF ANTI‐HERBIVORE DEFENSES IN BROWN AND RED MACROALGAE OFF THE KENYAN COAST1

Herbivory is particularly intense in tropical benthic communities, suggesting preference of constitutive, rather than inducible, anti‐herbivory defense. The objective of the study was to examine whether anti‐herbivore defenses in the red alga Hypnea pannosa J. Agardh and the brown algae Sargassum asperifolium Hering and G. Martens ex J. Agardh and Cystoseira myrica (S.G. Gmelin) C. Agardh could be induced and subsequently reduced in response to grazing by the amphipod Cymadusa filosa Savigny. During a 14‐day treatment phase, algae were exposed to amphipod grazing or were left ungrazed (control). Subsequently, one subset of algae was used in feeding assays, whereas another was cultivated for additional 14 days without consumers (recovery phase). At the end of each phase, bioassays were conducted to detect defensive traits in terms of differences in consumption rates of grazed and control pieces of live algae and agar‐based food containing nonpolar algal extracts. Consumption of grazed live S. asperifolium and H. pannosa specimens was lower than of control algae. Furthermore, nonpolar extracts of grazed S. asperifolium and C. myrica were less preferred than those from control algae. Defensive responses were exclusively detected after the treatment phase, although strong preference of ungrazed H. pannosa and C. myrica over grazed conspecifics continued throughout the recovery phase. These findings suggest that phenotypic plasticity in anti‐herbivory defense of marine macroalgae 1) might be more common than previously shown, 2) could be switched on and off within 2 weeks, and 3) can be found in nonpolar algal extracts.

Grazing insects reduce algal biomass in a neotropical stream

Herbivorous insects have received relatively little attention in studies of consumer resource interactions in tropical compared to temperate streams. In this study I examined the effects of small, highly mobile, herbivorous insects on epilithic algae in riffle habitats of a stream located on the Pacific coast of Costa Rica. By elevating artificial substrates 20–30 cm off the streambed, while holding other abiotic factors constant, I successfully reduced the densities of grazing insects (primarily mayflies and dipterans) throughout an 8 week experimental period. This manipulation resulted in approximately 30% more algal biomass (measured as AFDM and chlorophyll a) on raised (grazer exclusion) than on control substrates placed directly on the streambed. Observations of the one common epibenthic grazing fish species, Sicydium salvini (Gobiidae), indicated that there were no consistent differences in their visitations to raised and lowered substrates, suggesting that fish grazing pressure did not contribute to observed differences in algal biomass between treatments. These results show that insects can be effective in reducing algal biomass in a tropical stream. While previously neglected, the role of grazing insect in contributing to the regulation of algal resources in tropical benthic communities warrants closer examination.

Benthic fauna in tropical tidal flats of Hinchinbrook Channel, NE Australia: diversity, abundance and their spatial and temporal variation

A survey of the benthic infauna (macro- and mesofauna) in tidalflats of Hinchinbrook Channel, north-east Australia, was carried out toassess the species diversity and individual abundances as well as theirtemporalvariations. Two sites were surveyed at five occassions from November 1988 toOctober 1991. In addition, spatial distributions over the intertidal gradientwere investigated once in May 1990. During the entire survey, over 200 specieswere recorded, with 53 species found on average at each sampling occassion.Species densities ranged from 4.0 to 8.2 species 177cm−2 for macrofauna and from 4.1 to 11.8 species10 cm−2 for mesofauna, but varied little betweensites. The average infaunal diversity (H') was 2.53. Individual abundancesreached median values of 14.0 individuals 177cm−2for macrofauna and 14.5 individuals 10 cm−2 formesofauna. Changes in total abundances were not related to season andinconsistent at the two study sites, with significantly higher abundancesoccurring either at site A or B on single sampling dates. Transects sampled inMay 1990 showed varying species compositions and abundances in the upper, midand lower intertidal, but no defined benthic communities were revealed bymultivariate analyses. Temporal variations in the benthic assemblages of thetwotidal flats in Hinchinbrook Channel were higher than variations between sites,with a separation of assemblages before and after 1989. Problems to assess andinterpret temporal changes in species rich tropical benthic communities arediscussed.

Sponge-mediated nitrification in tropical benthic communities

Sponge-mediated nitrification in tropical benthic communities

Nutrients, Predation and the History of Reef-Building

The trophic structure of modern tropical benthic communities, especially reefs, is profoundly influenced by ambient nutrient levels and resultant predator characteristics. In oligotrophic regimes the presence of abundant specialist grazers promotes succession and yields climax-stage communities. Such communities produce the classic «framework» reef dominated by large, heavily calcified phototrophs and multiserial mixotrophs. These primary producers bear many anti-predator adaptations and have a marked preference for hard-substrates. Increasing nutrient levels favor a transition in the benthos from photo- and mixotrophs via benthic algae to soft-substrate communities of solitary or uniserial heterotrophs feeding on planktonic primary producers

Effects of a crude oil terminal on tropical benthic communities in Brunei

An environmental survey was carried out in May 1981 at the intertidal and subtidal zone of Sungai (River) Bera, where Brunei Shell Petroleum Company discharges wastewater from its operations. Two reference sites, Sungai Lumut and Sungai Tali, situated northeast of Sungai Bera were also studied. In addition to sampling the macrobenthic communities, hydrocarbon, metal levels, and particle size distribution of the sediments were also studied. Populations of intertidal and subtidal macrobenthic organisms at Sungai Bera were very much lower when compared to those at Sungai Tali and Sungai Lumut. The hydrocarbon levels were highest at Sungai Bera, and least at Sungai Lumut. The distribution pattern corresponds well with the levels of hydrocarbons found at the three sites. Hydrocarbons found at the three sites were of petrogenic origin. The effects of the wastewater discharged on the intertidal zone were very localized, confined mainly to Sungai Bera. The hydrocarbon levels at Sungai Tali were almost the same as those at Sungai Lumut. No deleterious effects on the macrobenthic community were detected at these two sites.

Role of competition and predation in determining habitat occupancy of Cerithiidae (Gastropoda: Prosobranchia) on the rocky, intertidal, Red Sea coasts of Sinai

Six cerithiid snail species occur on rocky intertidal flats along the Sinai coasts of the Red Sea: Clypeomorus moniliferum, Cerithium caeruleum, C. scabridum, C. columna, Clypeomorus tuberculatum and Cerithium echinatum. The present study, conducted at 22 stations covering almost the whole length of Sinai, covered the 4 yr period from October 1972 to August 1976, and describes the habitat occupancy of 5 of these species (C. echinatum is excluded for lack of data). Several of these species (sometimes all) often occur together, and in such cases are distincly segregated by habitat. However all species considerably overlap in their distribution along the axes of four major interrelated abiotic gradients, thus excluding the possibility that habitat segregation is determined by larval settlement preferences. Other distributional patterns observed at some sites, such as lack of overlap or contact between belts of the various species and the relative abundance of food available to all species, make postlarval competitive interactions unlikely. The existence and the degree of proximity of a coral reef with its associated predatory fishes, influence the cerithiids' distributional patterns. Differences between the cerithiid species in their vulnerability to fish predation, associated with differences between sites in the abundance and the accessibility of predatory fishes, and in the availability of refuges for each cerithiid species, can satisfactorily explain the observed distributional patterns including co-occurrence with habitat segregation. It is proposed that habitat segregation is caused by predation on young stages by generalist fishes which may totally eliminate a certain species at a given site; the same site may provide refuges for recruits of another species, allowing these to survive to an advanced age. In general, the flat's structural complexity is associated with its diversity of refuges from predation, and hence with the number of co-existing species. This mechanism for co-existence and habitat segregation in tropical Cerithiidae may also be instrumental in maintaining the high species diversity of other tropical benthic communities.

Methane production in shallow-water, tropical marine sediments.

The in situ production of methane was monitored in several types of tropical benthic communities. A bed of Thalassia testudinum located in Caesar Creek (Florida Keys) exhibited the highest methanogenic activity (initial rates = 1.81 to 1.86 mumol CH4/m2 per h) as compared with another seagrass (Syringodium sp., 0.15 to 0.33 mumol/m2 per h) and two coral reef environments (Hydro-Lab, 0.016 to 0.10 mumol/m2 per h; Curacao, 0.14 to 0.47 mumol/m2 per h). The results suggest that a wide variety of benthic metabolic processes (e.g., photosynthetic oxygen production) influences methane production rates.

Methane Production in Shallow-Water, Tropical Marine Sediments1

The in situ production of methane was monitored in several types of tropical benthic communities. A bed of Thalassia testudinum located in Caesar Creek (Florida Keys) exhibited the highest methanogenic activity (initial rates = 1.81 to 1.86 mumol CH4/m2 per h) as compared with another seagrass (Syringodium sp., 0.15 to 0.33 mumol/m2 per h) and two coral reef environments (Hydro-Lab, 0.016 to 0.10 mumol/m2 per h; Curacao, 0.14 to 0.47 mumol/m2 per h). The results suggest that a wide variety of benthic metabolic processes (e.g., photosynthetic oxygen production) influences methane production rates.

A description of a highly diverse soft-bottom community in Kingston Harbour, Jamaica

A highly diverse soft-bottom community in Kingston Harbour, Jamaica is described to provide additional information on the structure of tropical benthic communities. It is shown that the community has a level of diversity unique to stable tropical environments, that dominance by a few species is greatly reduced,and that there are no true parallels to this community in similar environments. The community described seems to fit Sanders' stability-time hypothesis. The density and standing crop of the community are low, and possible explanations for this are discussed. Continuous year-round breeding, short life-spans, and fast turnover rates are suggested as the most important factors regulating biomass in the community described.