The targets of management rules for marine mammal populations require justification: A reply to

The management of anthropogenic impacts on marine mammal populations involves the setting of targets that are built on assumptions and choices. Scientific methods can be used to investigate the implications of management actions, but the choice of overall objectives and priorities lies outside science. A recent paper (Potential biological removal and other currently used management rules for marine mammal populations: A comparison in Marine Policy), summarised the characteristics of the main approaches currently used to set conservation management targets for marine mammal populations in order to provide a basis for discussion of the targets they contain. Cooke et al. (Management rules for marine mammal populations: A response to Lonergan in Marine Policy) responded, giving some important additional information about these management rules. However most of that paper's criticisms were incorrect or misplaced. Specifically, it erroneously treated an example of how PBR could be reworked, to make its abundance explicit, as a proposal to ignore uncertainty in managing populations. This paper addresses Cooke's main criticisms, and suggests that explicit justifications should be an important part of the process of setting targets for the management of marine mammal populations.     

Swimming with whales in Tonga: Sustainable use or threatening process?

The Oceania population of humpback whales (Megaptera novaeangliae) using Tongan waters is a listed Endangered subpopulation that supports a large swim-with whale industry focussed primarily on mothers and calves. This raises concerns about the industry's potential to impact on the subpopulation's breeding success and recovery. This study investigated whether whales responded differently to approaches by swimmers from boats than to boat approaches alone and whether different types of swimming (quiet approach, loud splashing or diving following a quiet approach) induced different avoidance responses. An avoidance response was defined as whales moving away from boats or swimmers and the strength of the response was defined by how far the whales moved away and whether there was an increase in surface activity. Animals responded more quickly to a loud splashing approach than to quiet approaches. There were no significant differences in measures relating to the strength of the response caused by swim type, however closer approaches by a boat did significantly increase the level of whale activity. These results suggest that managing swimmer behaviour around whales, particularly ensuring quiet approaches, will contribute to the ability of the industry to minimise disturbance of the animals and support the industry's sustainability.     

The precautionary approach to non-native fisheries—The case of striped bass in Texas

Fisheries managers have long relied on non-native fish to improve, sustain, or create recreational fishing opportunities, often without adequate consideration of potentially negative ecological consequences. There is growing advocacy for using the precautionary approach to avoid potentially serious or irreversible harm to the environment in the face of scientific uncertainty. This paper uses striped bass (Morone saxitilis) in Texas to examine possible effects that might have resulted had the precautionary approach been applied before stocking began in the 1960s when the species was considered non-native to Texas. The current range of reproducing striped bass populations extends from the North Atlantic Ocean to the U.S.–Mexico border. However, the western extent of the species current range beyond Louisiana is probably the result of stocking begun in 1965 that continues today. The historic range is yet unresolved. The best available information suggests that striped bass are not native to Texas, fish stocking has resulted in beneficial economic impacts, and any negative effects (i.e., harm) are currently unknown. It seems unlikely that application of the precautionary approach would have led to different outcomes in Texas than currently exist. However, the complete striped bass story has yet to be written.     

Experimental catches and the precautionary approach: the Southern Bluefin Tuna dispute

Southern Bluefin Tuna (SBT) is a depleted stock with a rebuilding target and timeframe defined by the responsible management body (CCSBT). All recent stock assessments have found that the stock is depleted but large differences exist in estimates of recovery probabilities under current catches. In 1996, CCSBT adopted a set of principles and a process for considering experimental fishing, which are fundamentally consistent with an actively adaptive management policy. Substantial efforts to develop a program in line with these principles did not succeed, partially due to the lack of a decision-making framework. In 1998 and 1999, Japan conducted unilateral experimental fishing arguing that the additional substantial catches could reduce uncertainty in stock assessments and thus were justified. This led to international legal proceedings under UNCLOS, in which preliminary measures were issued preventing further unilateral experimental fishing (these were later rescinded when an UNCLOS arbitral tribunal found that it lacked jurisdiction in the dispute). This decision has been cited as a possible manifestation of industry's “worst fear with the implementation of the precautionary approach”. This paper examines the SBT dispute in relationship to adaptive management and the precautionary approach, Results of recent stock assessments indicate that the Japanese experimental fishing, even if successful, was unlikely to resolve the disparity in estimates of the recovery probabilities or provide an improved basis for management decision making. In this context, it is the absence of a management framework, rather than a fundamental problem with adaptive management, that challenges the compatibility of these experimental fishing catches and the precautionary approach. The real issue in the SBT situation is the standards and burden of proof required if experimental fishing is to be considered.     

Institutionalizing environmental reform with sense-making: West and Central Africa ports and the ‘green port’ phenomenon

Harmonizing economic activities with environmental considerations has emerged as a new globalizing phenomenon for ports. The phenomenon is labelled as ‘green port’. There is however no canonical way of turning green port into business reality. Some advanced ports have adapted it and African ports are also beginning to follow. The Freeport of Monrovia in West and Central Africa had its process of incorporating environmental considerations into its operational practices in an environmental reform labelled as ‘going green’, akin to the green port phenomenon. The process interrupted routinized port activities and behavior. Employees of Freeport of Monrovia and stakeholders could not foresee the meaning and consequences of such reform. The uncertainty triggered a process for employees and stakeholders to collectively make sense of and react to their new situation. This paper integrates Weick's sense-making properties with Weber and Glynn's institutional mechanisms affiliated to sense-making as a conceptual tool to analyze and understand the process by which meaning was assigned to Freeport of Monrovia's environmental reform and also how it became institutionalized. The analysis is based on hands-on empirical research on an environmental capacity strengthening project executed in 2013 in the Freeport of Monrovia as part of its institutional reform from a service port into landlord port. Findings bring to light the dynamic interplay of institutions and sense-making in the greening of Freeport of Monrovia.     

Development of Bayesian stock assessment methods for Namibian orange roughy Hoplostethus atlanticus

Bayesian methods are useful in fisheries stock assessment because they provide a conceptually elegant and statistically rigorous approach to making decisions under uncertainty. The application of Bayesian stock assessment methods in the management of Namibian orange roughy Hoplosthethus atlanticus within the 200 mile EEZ of Namibia is reviewed. Time-series of relative abundance are short and their reliability in indicating abundance trends is uncertain. The development of informative prior probability density functions (pdfs) for the constants of proportionality (q) for hydro-acoustic, commercial trawl swept area, and research trawl swept area indices produced statistically consistent prior estimates of absolute abundance for each of the three grounds where more than one index of abundance was available. The posterior pdfs for stock assessment model parameters were used to account for uncertainty in evaluations of the potential consequences of alternative harvesting policies under a stock reduction model in which catch removals were assumed to account for any declines. It appears that all orange roughy stocks off Namibia have been depleted below the limit reference point (50% of long-term unfished biomass). However, the stock reduction model could not easily account for the large declines in indices on the four fishing grounds over the period from 1995 until 1999 when the informative priors for q were applied. In the 2000 stock assessment, the Bayesian procedure was updated to account formally for uncertainty in model structures that could explain the decline in abundance. The possibility of very low stock abundance could still not be discounted when these uncertainties were accounted for. Although this most recent methodology applies more statistical rigour, its complexity has hindered its acceptance in Namibia. However, if it is worth quantifying risks and uncertainties in future stock assessments for the provision of precautionary management advice, it is proposed that the assessment protocols adopted be probabilistic to account for uncertainty in model parameters, that careful attention be given to subjective judgements about their inputs and the representation of uncertainty within them, and that, where appropriate, alternative hypotheses about stock abundance and mechanisms for catchability and stock decline be taken into account.     

Horizontal distribution of particulate matter and its characterization using phosphorus as an indicator in surface coastal water,Harima-Nada,the Seto Inland Sea,Japan

To study the horizontal distribution and characterization of suspended particulate matter (SPM) in the coastal environment, the distribution and seasonal variation of particulate phosphorus (PP), divided as organic (POP) and inorganic (PIP) fractions with POC, PON, and Chl.a, in 4 seasons throughout Harima-Nada of the Seto Inland Sea, Japan, were investigated. A high concentration of PIP was observed not only in the northern coastal area, which received much freshwater discharge, but also in the channel parts. In winter, when Δσt was low, the difference between surface and bottom σt, resuspension of sinking particles or/and surface sediment which has a high PIP/PP ratio seems to have occurred, and then a high concentration of PIP in surface water was observed. In spring and summer, PIP/PP ratios (0.24) of surface waters were close to those of phytoplankton (0.1–0.2). On the other hand, PIP/PP ratios in autumn and winter, when Δσt was low, were similar to those of surface sediment in Harima-Nada (0.32–0.39). SPM in Harima-Nada showed higher PP contents than other coastal environments, and its mean value of 9.10 mg P/g was close to the phytoplankton P content of 9.75 mg P/g. This suggests that SPM in Harima-Nada was strongly affected by phytoplankton. The C/N ratio in Harima-Nada in spring was high (11), although high Chl.a and low PIP/PP were observed, possibly resulting from preferential decomposition of nitrogen in comparison with carbon. We consider that the PIP/PP ratio is a good indicator to characterize SPM and to predict its origin as well as the C/N.     

Establishment and closure of the directed Florida whiting (Menticirrhus americanus) fishery and implications for North Atlantic right whale (Eubalaena glacialis) conservation and management

Today, ocean and coastal marine resource management is extremely complex. Marine resource managers are charged with conserving and managing many diverse species. Southern kingfish (Menticirrhus americanus), commonly known as whiting, are found from southern New England to Florida. During the fall through winter, western North Atlantic right whales (Eubalaena glacialis) are primarily found in the coastal nearshore waters off South Carolina, Georgia, and Florida, overlapping the whiting's range and habitat.     

Dialectics of nature: The emergence of policy on the management of commercial fisheries in english European Marine Sites

European Marine Sites (EMS), designated under either the Habitats or Birds Directives, protect the biodiversity of the European Union (EU) and contribute to the implementation of the 1992 UN Convention on Biological Diversity [1]. The introduction of this form of marine protected area (MPA), as a consequence of EU conservation directives, introduced new legal obligations in waters long exploited by inshore fishing communities. Although the Habitats and Birds Directive have been in place since 1992 and 1979 respectively (the 1979 Directive updated in 2009), it has not been until more recently (2014) that ongoing inshore fisheries activities in England, which predate designation of sites, have been systematically assessed and managed, for their impact in protected sites. In practice it was assumed by many MPA practitioners that at the time of designation of EMS, ongoing activities would be compatible with the conservation objectives of these sites. This paper illustrates the introduction of a general and systematic “revised approach” to managing fisheries in all English EMSs, and how this represented a change in government policy which can be traced directly to a legal campaign between 2008 and 2012 by two UK environmental Non-Governmental Organisations (eNGOs). The paper elucidates this iterative marine policy process analysing the dialogue between government bodies and eNGOs and show how the resulting interpretation of conservation law, has sought to resolve the tensions between the precautionary approach as emphasised by the eNGOs and the Government's desire for proportionality of response.     

Joint modelling of wave spectral parameters for extreme sea states

Characterising the dependence between extremes of wave spectral parameters such as significant wave height (H_S) and spectral peak period (T_P) is important in understanding extreme ocean environments and in the design and assessment of marine structures. For example, it is known that mean values of wave periods tend to increase with increasing storm intensity. Here we seek to characterise joint dependence in a straightforward manner, accessible to the ocean engineering community, using a statistically sound approach.Many methods of multivariate extreme value analyses are based on models which assume implicitly that in some joint tail region each parameter is either independent of or asymptotically dependent on other parameters; yet in reality the dependence structure in general is neither of these. The underpinning assumption of multivariate regular variation restricts these methods to estimation of joint regions in which all parameters are extreme; but regions where only a subset of parameters are extreme can be equally important for design. The conditional approach of Heffernan and Tawn (2004), similar in spirit to that of Haver (1985) but with better theoretical foundation, overcomes these difficulties.We use the conditional approach to characterise the dependence structure of H_S and T_P. The key elements of the procedure are: (1) marginal modelling for all parameters, (2) transformation of data to a common standard Gumbel marginal form, (3) modelling dependence between data for extremes of pairs of parameters using a form of regression, (4) simulation of long return periods to estimate joint extremes. We demonstrate the approach in application to measured and hindcast data from the Northern North Sea, the Gulf of Mexico and the North West Shelf of Australia. We also illustrate the use of data re-sampling techniques such as bootstrapping to estimate the uncertainty in marginal and dependence models and accommodate this uncertainty in extreme quantile estimation.We discuss the current approach in the context of other approaches to multivariate extreme value estimation popular in the ocean engineering community.     

Picophytoplankton: A major contributor to planktonic biomass and primary production in a eutrophic,river-dominated estuary

Biomass and primary productivity of picophytoplankton (PP; phytoplankton <3 μm) and larger phytoplankton (>3 μm) were determined during an annual cycle along the salinity gradient in North Carolina’s Neuse River Estuary (NRE), a eutrophic, microtidal estuary. The PP were a major component of total phytoplankton biomass and productivity, contributing ∼35–44% of the total chlorophyll a (Chl a) and 42–55% of the total primary productivity. Chl a and productivity of PP decreased from the upper to lower estuary, although the PP contribution relative to larger phytoplankton remained nearly constant. Significant PP growth occurred in the spring, but PP productivity and biomass were maximal in summer. PP productivity and biomass were positively correlated with temperature and dissolved inorganic phosphorus concentrations, which were maximal in summer due to release from sediments. Biomass and productivity of PP and >3 μm phytoplankton were also positively correlated, suggesting that growth conditions favoring the onset of blooms of larger phytoplankton species will similarly affect PP. High PP productivity and biomass in the NRE support the notion that PP play an important role in the production and eutrophication potentials of this estuary. High PP productivity and biomass have been noted in several other temperate estuaries, all sharing a common feature with the NRE—long residence time. These findings challenge the assumption that PP relative importance should be minimal in eutrophic systems.     

Changes in fisheries management in Mexico: Effects of increasing scientific input and public participation

In this article, we analyze a change in the role of federal institutions in charge of managing Mexican fisheries during the mid-1990s. During 30 years, the fishery policy in Mexico began by promoting an accelerated fishing effort. This worked through 1981, when the country recorded its highest landings (1.6 million metric tons), but landings have not increased subsequently whereas the number of fishermen has continued to increase. In 1995, the federal administration acknowledged the problems: biological over-exploitation; over-capitalization; monopoly in commercialization; failures in loan payments; failures in controlling effort; obsolete vessels and equipment; and social conflicts for the resources. In an attempt to resolve some of these problems, the administration implemented structural changes in management, science and enforcement institutions. This arrangement established goals and introduced instruments in fisheries management: it determined the biological status of most of the fisheries; applied the precautionary approach for those fully exploited or over-exploited fisheries; gave scientific advice an important role in decision making; and involved the users in decision making. This article evaluates these changes in management policy by document review, participation and interviewing management and scientists who participated in this process. We analyze, in particular, the use of science-based categorization of fisheries status, and the introduction of public participation. The interview data demonstrate that sustainable Mexican fisheries require an evolution to a more public participatory policy, in order to strengthen local institutions and fishermen over federal institutions, which should lead to a re-definition of regulation of fisheries resources.     

Uncovering governance mechanisms surrounding harbour porpoise conservation in the Danish Skagerrak Sea

The harbour porpoise (Phocoena phocoena) is the focus of a range of conservation efforts and policies, including the Habitats Directive, aimed at reducing the bycatch of non-target species in gillnet fisheries. This paper describes the governance process and analyses the governance mechanisms and conflicts surrounding ongoing fisheries management planning with a focus on two Natura 2000 sites in the Danish part of the Skagerrak Sea designated to protect harbour porpoises. Responsibility for developing fisheries management for Natura 2000 sites is solely the remit of the fisheries agency, including mechanisms related to stakeholder involvement. This approach fuels the efficiency of the decision making process, while full transparency and/or co-decision becomes less of a given within a ministry for an economic sector compared with the environment ministry. In relation to porpoises, conflicts are driven mainly by the economy and the varying perceptions of the bycatch issue, with great differences between government, NGO's and fishers. Interviews with fishers and fishing effort data reveal intra-sectoral conflicts pertaining to the incompatibility of active trawling and passive gillnetting in the areas. The paper questions the overall approach to managing the harbour porpoise bycatch issue in light of Natura 2000 and discusses the role of science and its high level of influence in this planning process.     

Coastal biodiversity management in Japanese satoumi

Evidence accumulates that better management of coastal biodiversity outside of protected areas will be necessary to halt current trends of depletion. Japanese satoumis are human-influenced coastal seas that are both productive and rich in biodiversity. Satoumi has gained interest within and outside Japan as a field-tested approach to conciliate sustainable ecosystem use and conservation of biodiversity. This paper provides a review of new reports on field implementation of satoumi in Japan. An analysis identifying key institutional features that foster satoumi is provided as well. A great variety of active conservation measures that do not rely on the exclusion of human influence to manage biodiversity are being assessed. Some are centuries-old, such as river basin forestry, some more recent such as seagrass transplants or artificial tidal flats. Crucial to their success are the involvement of local communities and the voluntary contribution of significant labour by ecosystem users, mostly fishers. These contributions from fishers’ communities are an internalisation of the costs of conservation by the economic activity that benefits from it. Rather than a cultural specificity, the latter appears to rest essentially on collective ownership of territorial use-rights, strong local collective structures that enforce the community's interest, and the availability of active conservation measures as options to contribute to biodiversity management through manual work in the ecosystem. It is argued that as the effectiveness of these approaches becomes demonstrated, they should be adequately accounted for in international agreements and targets for biodiversity conservation.     

An oceanic general circulation model framed in hybrid isopycnic-Cartesian coordinates

A newly developed hybrid-coordinate ocean circulation model is documented and tested. Coordinate surfaces in this model adhere to isopycnals wherever this does not violate minimum layer thickness requirements; elsewhere, coordinate surfaces are geometrically constrained. The intent of this approach, some of whose features are reminiscent of the Arbitrary Lagrangian–Eulerian (ALE) technique, is to combine the best features of isopycnic-coordinate and fixed-grid circulation models within a single framework. The hybrid model is an offshoot of the Miami Isopycnic Coordinate Ocean Model whose solutions, obtained under identical geographic and forcing conditions, serve as reference. Century-scale simulations on a coarse-mesh near-global domain show considerable similarities in the modeled thermohaline-forced circulation. Certain architectural details, such as the choice of prognostic thermodynamic variables (ρ,S versus T,S) and the algorithm for moving coordinate surfaces toward their reference isopycnals, are found to only have a minor impact on the solution. Emphasis in this article is on the numerical resiliency of the hybrid coordinate approach. Exploitation of the model's flexible coordinate layout in areas of ocean physics where pure isopycnic coordinate models only have limited options, such as mixed-layer turbulence parameterization, will be the subject of forthcoming articles.     

Assessment of carbon- and fluorescence-based primary productivity in Ariake Bay,southwestern Japan

A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by ¹³C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r² > 0.90) and daily (r² = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. ¹³C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to ¹³C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate (P^B) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR–P^B relationship) was found to be linear for FRRF and curvilinear for ¹³C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR–P^B relationships, a combined and/or instantaneous PAR–P^B relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF.     

Historical abundance of juvenile commercial fish in coastal habitats: Implications for fish habitat management in Canada

An important component of science-based fisheries policy is the provision of habitat adequate for population renewal. In Canada, the Fisheries Act pays little attention to managing fish habitat, and was further weakened by changes enacted in 2012. Specifically, determining the role of fish habitat in contributing to fisheries and fish stock recovery is challenging when many stocks have severely declined and no longer occupy former habitats. This study compared the abundance of juvenile fish in coastal vegetated habitats before and after collapse or decline of groundfish stocks in Atlantic Canada. This comparison was done by compiling past studies that surveyed juvenile Atlantic cod (Gadus morhua) and pollock (Pollachius virens) in vegetated habitats across three provinces. Two studies were repeated, and one that already had post-collapse data was analyzed to quantify long-term changes in juvenile abundance. In all three cases substantial reduction in juvenile abundance coincided with declines in adult stocks. However, juvenile fish still occur in coastal habitats and could aid in adult stock recovery. The current version of the Canadian Fisheries Act requires presence of an ongoing fishery to trigger habitat protection. This is problematic as low fish abundance may lead to lowered habitat protection and potentially habitat degradation, with less or lesser-quality habitat for fish in the future. Thus, recommendations are made to repeal the 2012 Fisheries Act changes and enhance current fish habitat legislation. Using a precautionary approach for coastal fish habitat management, particularly in valuing its potential for fish stock recovery, would strengthen Canadian fisheries management.     

Fishing industry and related perspectives on the issues raised by no-take marine protected area proposals

In the face of growing calls for no-take marine protected areas (NTMPAs), the views of fishing industry representatives in south-west (SW) England on related issues are analysed. Only 23% thought NTMPAs were the way forward and a range of concerns were expressed, e.g. that the ‘terrestrial’ protected areas approach and related biodiversity conservation objectives will be extended to the seas, and that fish yield reductions from the loss of access to NTMPAs are very unlikely to be compensated for through spillover/export. Some interesting approaches to ameliorating these concerns emerged, such as being open and honest that NTMPAs are primarily intended to achieve biodiversity conservation benefits, reducing uncertainty concerning the potential for any secondary fisheries spillover/export benefits, justifying NTMPAs on an objective, rational basis rather than on a subjective, precautionary basis, and the quid pro quo streamlining of wider fisheries management approaches. This research reveals a more diverse range of perspectives amongst fishing industry representatives on the issues raised by NTMPA proposals than is often assumed.     

When regulation fails: vendace fishery in the Gulf of Bothnia

The fishing of vendace (Coregonus albula), in the Gulf of Bothnia, is a good illustration of the presumption that institutional arrangements that are too inflexible to cope with changing ecological conditions, are unlikely to prosper. Although the vendace fishing is regulated by the State, catches have decreased dramatically, and there is a considerable fear that the resource is about to be depleted. This article discusses how the present institutional arrangement affects collective action and why political solutions seem to have failed. The vendace case illustrates that even a rather limited resource concentrated in a limited area is unlikely to be sustainably managed by top-down regulation performed by the State. It is concluded that changes in management practices that are obvious from the perspective of ecosystem management might turn out to be unfeasible, given the multi-stakeholder character of the management system. From this article it can also be concluded that resilience theory and experiences from long-enduring CPRs correspond very well with each other. Finally, it is discussed whether it is meaningful to talk about institutional, or managerial, resilience uncoupled from the ecosystem it is supposed to be managed. If an ecosystem, like the vendace, that is subject to human activity loses its resilience this would automatically indicate the socio-economic system, as manifested in management practices, has already lost its ability to adapt. Thus, social and ecological resilience are communicating vessels but not perhaps as the concept might be understood according to a popular call for increased institutional resilience in natural resource management.     

Influence of allochthonous input on autotrophic–heterotrophic switch-over in shallow waters of a tropical estuary (Cochin Estuary), India

Bacterial productivity (BP) and respiration (BR) were examined in relation to primary productivity (PP) for the first time in a shallow tropical ecosystem (Cochin Estuary), India. The degree of dependence of BP (6.3–199.7 μg C L⁻¹ d⁻¹) and BR (6.6–430.4 μg C L⁻¹ d⁻¹) on PP (2.1–608.0 μg C L⁻¹ d⁻¹) was found to be extremely weak. The BP/PP (0.05–8.5) and PP/BR (0.02–7.9) ratios widely varied in the estuary depending on the season and location. There was a seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter input through rivers which enhanced the bacterial heterotrophic activity and very high pCO₂ (106–6001 μatm) levels. The heterotrophic zones were characterized by low PP but high bacterial production and respiration leading to oxygen undersaturation and exceptionally high pCO₂. We propose that the CO₂ supersaturation caused by increased bacterial respiration (in excess of PP) was a result of bacterial degradation of allochthonous organic matter. This indicates that sources other than planktonic compartment need to be explored to understand the C-cycling in this estuary. These results are of particular relevance to tropical ecosystems in general, where the bulk of world's river discharges occur.