Publications

Patterns in primary production and carbon export from the euphotic zone suggest that the relative contribution of planktonic heterotrophs to community biomass should decline along gradients of phytoplankton biomass and primary production. Here, we use an extensive literature data survey to test the hypothesis that the ratio of total heterotrophic (bacteria + protozoa + mesozooplankton) biomass to total autotrophic biomass (H : A ratio) is not constant in marine plankton communities but rather tends to decline with increasing phytoplankton biomass and primary production. Our results show that the plankton of unproductive regions are characterized by very high relative heterotrophic biomasses resulting in inverted biomass pyramids, whereas the plankton of productive areas are characterized by a smaller contribution of heterotrophs to community biomass and a normal biomass pyramid with a broad autotrophic base. Moreover, open‐ocean communities support significantly more heterotrophic biomass in the upper layers than do coastal communities for a given autotrophic biomass. These differences in the biomass structure of the community could be explained by the changes in the biomass‐specific rates of phytoplankton production that seem to occur from ultraoligotrophic to eutrophic marine regions, but other factors could also generate them. The patterns described suggest a rather systematic shift from consumer control of primary production and phytoplankton biomass in open ocean to resource control in upwelling and coastal areas.

A theoretical and quantitative framework of first principles would benefit estuarine and coastal ecologists in search of predictions to enhance our understanding and management of marine resources. The Metabolic Theory of Ecology describes a possible unifying theory for ecology, including mechanistically derived equations that predict scaling exponents observed in empirical, allometric relationships from individuals to ecosystems. The controversy surrounding this theory should stimulate our exploration of its potential use in the coastal realm, where questions specific to an applied science may suggest new refinements and derivations, contributing to the overall progress of ecology.

The Mediterranean Sea is a vulnerable region for climate change, warming at higher rates compare to the global ocean. Warming leads to increased stratification of the water column and enhanced the oligotrophic nature of the Mediterranean Sea. The oligotrophic waters are already highly transparent, however, exposure of Mediterranean plankton to ultraviolet radiation (UV-B and UV-A) may increase further if the waters become more oligotrophic, thereby, allowing a deeper UV radiation penetration and likely enhancing impacts to biota. Here we experimentally elucidate the cumulative effects of warming and natural UV-B radiation on the net community production (NCP) of plankton communities. We conducted five experiments at monthly intervals, from June to October 2013, and evaluated the responses of NCP to ambient UV-B radiation and warming (+3ºC), alone and in combination, in a coastal area of the northwest Mediterranean Sea. UV-B radiation and warming lead to reduced net community production and resulted in a heterotrophic (NCP<0) metabolic balance. Both UV-B radiation and temperature, showed a significant individual effect in NCP across treatments and time. However, their joint effect showed to be synergistic as the interaction between them (UV x Temp) was statistically significant in most of the experiments performed. Our results showed that both drivers, would affect the gas exchange of CO2-O2 from and to the atmosphere and the role of plankton communities in the Mediterranean carbon cycle

Abstract. The relationship between the partial pressure of carbon dioxide (pCO2) and dissolved organic carbon (DOC) concentration in Brazilian lakes, encompassing 225 samples across a wide latitudinal range in the tropics, was tested. Unlike the positive relationship reported for lake waters, which was largely based on temperate lakes, we found no significant relationship for tropical and subtropical Brazilian lakes, despite very broad ranges in both pCO2 and DOC. Closer examination showed that the strength of pCO2 vs. DOC relationships declines with increasing water temperature, suggesting substantial differences in carbon cycling in warm lakes, which must be considered when upscaling limnetic carbon cycling to global scales.

Abstract In this article, we review evidence of how climate change has already resulted in clearly discernable changes in marine Arctic ecosystems. After defining the term ‘footprint’ and evaluating the availability of reliable baseline information we review the published literature to synthesize the footprints of climate change impacts in marine Arctic ecosystems reported as of mid‐2009. We found a total of 51 reports of documented changes in Arctic marine biota in response to climate change. Among the responses evaluated were range shifts and changes in abundance, growth/condition, behaviour/phenology and community/regime shifts. Most reports concerned marine mammals, particularly polar bears, and fish. The number of well‐documented changes in planktonic and benthic systems was surprisingly low. Evident losses of endemic species in the Arctic Ocean, and in ice algae production and associated community remained difficult to evaluate due to the lack of quantitative reports of its abundance and distribution. Very few footprints of climate change were reported in the literature from regions such as the wide Siberian shelf and the central Arctic Ocean due to the limited research effort made in these ecosystems. Despite the alarming nature of warming and its strong potential effects in the Arctic Ocean the research effort evaluating the impacts of climate change in this region is rather limited.

Seagrasses cover about 0.1–0.2% of the global ocean, and develop highly productive ecosystems which fulfil a key role in the coastal ecosystem. Widespread seagrass loss results from direct human impacts, including mechanical damage (by dredging, fishing, and anchoring), eutrophication, aquaculture, siltation, effects of coastal constructions, and food web alterations; and indirect human impacts, including negative effects of climate change (erosion by rising sea level, increased storms, increased ultraviolet irradiance), as well as from natural causes, such as cyclones and floods. The present review summarizes such threats and trends and considers likely changes to the 2025 time horizon. Present losses are expected to accelerate, particularly in South-east Asia and the Caribbean, as human pressure on the coastal zone grows. Positive human effects include increased legislation to protect seagrass, increased protection of coastal ecosystems, and enhanced efforts to monitor and restore the marine ecosystem. However, these positive effects are unlikely to balance the negative impacts, which are expected to be particularly prominent in developing tropical regions, where the capacity to implement conservation policies is limited. Uncertainties as to the present loss rate, derived from the paucity of coherent monitoring programmes, and the present inability to formulate reliable predictions as to the future rate of loss, represent a major barrier to the formulation of global conservation policies. Three key actions are needed to ensure the effective conservation of seagrass ecosystems: (1) the development of a coherent worldwide monitoring network, (2) the development of quantitative models predicting the responses of seagrasses to disturbance, and (3) the education of the public on the functions of seagrass meadows and the impacts of human activity.

Abstract. The direct CO2 released by respiration of humans and domesticated animals, as well as CO2 derived from the decomposition of their resulting wastes was calculated in order to ascertain the direct and indirect metabolic contribution of humanity to CO2 release. Human respiration was estimated to release 0.6 Gt C year−1 and that of their associated domestic animals was estimated to release 1.5 Gt C year−1, to which an indirect release of 1.0 Gt C year−1, derived from decomposition of the organic waste and garbage produced by humans and their domestic animals, must be added. These combined direct and indirect metabolic sources, estimated at 3.1 Gt C year−1, have increased 7 fold since pre-industrial times and are predicted to continue to rise over the 21st century.

The planktonic metabolic balance that is the balance between gross primary production (GPP) and community respiration (CR) was determined in Matilda Bay (estuarine) and Woodman Point (coastal) in Perth, Western Australia. The rates of net community production (NCP = GPP - CR) and the ratio between GPP and CR (P/R) were assessed to evaluate whether the metabolic balance in the two coastal locations tends to be net autotrophic (production exceeding community respiration) or net heterotrophic (respiration exceeding production). We also analyzed environmental variability by measuring temperature, salinity, and nutrients and chlorophyll a concentration. Samples were collected biweekly from March 2014 to March 2015. During the study period the metabolic rates were three times higher in Matilda Bay than in Woodman Point. The predominant metabolism was net autotrophic at both sites with P/R ratios >1 in the majority of the sampling dates. In Matilda Bay, the metabolic rates were negatively correlated with salinity denoting river dynamics influence, and positively with chlorophyll a. In Woodman Point only the GPP was positively correlated with chlorophyll a. The positive correlation between P/R ratio and GPP in Matilda Bay and the positive correlations between the metabolic rates and chlorophyll a suggest that factors controlling autotrophic processes are modulating the planktonic metabolic balance in the coastal marine ecosystem in Perth. Significant correlations were found between CR and GPP-standardized to chlorophyll a and water temperature. The net autotrophic metabolic balance indicates that in both ecosystems planktonic communities are acting as a sink of CO2 and as a source of organic matter and oxygen to the system and are able to export organic matter to other ecosystems.

Study of 2 diatom species, Leptocylindrus danicus and Skeletonema costatum, growing in a n enclosed plankton community showed that most of the variability in the extent of epialgal colonization (i.e.bacteria algal cell-') was attributable to differences within species, compared to small among-species and temporal vanability.Within-species variability was related to the populahon dynamics of the diatom species examined, because the extent of colonization increased with the time algal cells had been exposed to colonization.Thus, modelling of algal colonization by bacteria requlres both consideration of encounter probabilities and phytoplankton demography.