Increasing nutrient concentrations and the rise and fall of a coastal fishery; a review of data from the Nile Delta,Egypt

There is a conceptual basis, and some empirical evidence, that increasing nutrient loads to coastal waterbodies will initially increase ecosystem productivity up to a threshold, beyond which secondary productivity and fishery yields will decline. Here we have compiled data from the Egyptian and international literature for fish landings and inorganic nutrient (nitrogen and phosphorus) data from four large coastal lagoons (63–500 km²) on Egypt's Nile Delta to provide evidence for the initially positive, but then negative, response of fishery yields to increased nutrient supply across a very wide range of enrichment (up to 1 mM dissolved organic nitrogen, DIN). Taking the data from the four lagoons as an aggregate, fish landings increase with increased nutrients up to a peak in landings at approximately 100 μM DIN, beyond which there was an exponential decline in landings. It appears that pesticide and heavy metal contamination and overfishing played only minor roles in the lowered fishery yield at highest DIN concentrations. We do not have sufficient evidence about the specific mechanisms that led to the decline of the fishery, but suspect that some feature of eutrophication—low oxygen, for example, may have been involved.     

Zonation and Ecology of Epiphytic Hydroids in a Mediterranean Coastal Lagoon: The 'Stagnone' of Marsala (North-West Sicily)

Abstract. Distribution patterns of epiphytic hydroids of seagrass ( Posidonia occanica and Cymodocea nodosa ) beds were studied in the 'Stagnone', a moderately hypcrhaline lagoon in Sicily. The role of water movement in determining the spatial and temporal zonation of epiphytic hydroids and their morpho-physiological variations is evaluated. Remarks on systematics arc also included.     

Longitudinal transport in a coastal lagoon

A two-dimensional, finite difference numerical model is used to describe longitudinal transport through a transverse cross section into and out of the northern segment of Indian River lagoon, along the Atlantic coast of Florida. The model uses four layers to represent the Atlantic Intracoastal Waterway, and two layers in the shallow waters east and west of the waterway to quantify transport. Simulations during a 161-day period from late June through late November 1983 include a seasonal shift in the longitudinal component of the wind. Transport is in the same sense throughout the cross section 32% of the time. Relatively subtle lateral shear, however, has a profound effect on long-term net transport. For most of the study, cumulative net transport in the shallow areas on either side of the waterway follows the cumulative along-channel windstress, but it is directed upwind in the lower half of the Intracoastal Waterway. Four numerical experiments examine the relative importance of terms in the momentum equation and components of the database. Results suggest that time-varying baroclinic forcing is an important component of the pressure gradient. Simulations which ignore water-level variations at the open end of the model differ substantially from those which incorporate water-level fluctuations.     

Effect of changes in water salinity on ammonium, calcium, dissolved inorganic carbon and influence on water/sediment dynamics

The effect of a sudden increase in salinity from 10 to 37 in porewater concentration and the benthic fluxes of ammonium, calcium and dissolved inorganic carbon were studied in sediments of a small coastal lagoon, the Albufera d'Es Grau (Minorca Island, Spain). The temporal effects of the changes in salinity were examined over 17 days using a single diffusion-reaction model and a mass-balance approach. After the salinity change, NH₄⁺-flux to the water and Ca-flux toward sediments increased (NH₄⁺-flux: 5000–3000 μmol m⁻² d⁻¹ in seawater and 600/250 μmol m⁻² d⁻¹ in brackish water; Ca-flux: −40/−76 meq m⁻² d⁻¹ at S=37 and −13/−10 meq m⁻² d⁻¹ at S=10); however, later NH₄⁺-flux decreased in seawater, reaching values lower than in brackish water. In contrast, Ca-flux presented similar values in both conditions. The fluxes of dissolved inorganic carbon, which were constant at S=10 (55/45 mmol m⁻² d⁻¹), increased during the experiment at S=37 (from 30 mmol m⁻² d⁻¹ immediately after salinity increase to 60 mmol m⁻² d⁻¹ after 17 days).In brackish conditions, NH₄⁺ and Ca²⁺ fluxes were consistent with a single diffusion-reaction model that assumes a zero-order reaction for NH₄⁺ production and a first-order reaction for Ca²⁺ production. In seawater, this model explained the Ca-flux observed, but did not account for the high initial flux of NH₄⁺.The mass balance for 17 days indicated a higher retention of NH₄⁺ in porewater in the littoral station in seawater conditions (9.5 mmol m⁻² at S=37 and 1.6 mmol m⁻² at S=10) and a significant reduction in the water consumption at both sites (5 mmol m⁻² at S=37; 35/23 mmol m⁻² at S=10). In contrast, accumulation of dissolved inorganic carbon in porewater was lower in seawater incubations (−10/−1 meq m⁻² at S=37; 50/90 meq m⁻² at S=10) and was linked to a higher efflux of CO₂ to the atmosphere, because of calcium carbonate precipitation in water (675/500 meq m⁻²). These results indicate that increased salinity in shallow coastal waters could play a major role in the global carbon cycle.     

Variability and fluxes of nitrogen and organic carbon at the mouth of a coastal lagoon

This work examines the tidal exchanges of heat, inorganic nitrogenous nutrients and various forms of organic matter at the mouth of San Quintin Bay, Baja California, Mexico. It also attempts to elucidate the main factors responsible for the short-term fluctuations of these seawater properties. To accomplish this, a time series sampling was carried out at the mouth of the bay from 25 June to 5 July, 1979. The bay systematically exported heat, with an average of 1·2×10¹⁰ kcal per half tidal cycle during the sampling period. Inputs of nitrite and nitrate during upwelling were of major importance to the productivity of the lagoon. During non-upwelling conditions the trend was toward a dynamic equilibrium in the oxidized inorganic nutrient fluxes. There were significant exports of ammonia. These ammonia exports were, on average, about 20% of the nitrate plus nitrite imports. Ammonia concentrations were related to metabolic and mixing processes. Ammonia might be an important export product throughout the year, as a result of the reduced state of the sediments. During the sampling, there were imports of particulate organic carbon and nitrogen. The C/N ratio suggests that the main origin of organic detritus was other than the breakdown of eelgrass in the bay. There were mostly imports of diatom carbon, but fluxes of dinoflagellate carbon were always near equilibrium. Zooplankton showed both exports and imports. Variability in the zooplankton carbon was mostly related to diel vertical migration. There were no significant exports of floating seagrass, not even during spring tides.     

Alongshore distribution and abundance of fish larvae off the coast of Kenya

Knowledge is limited on the fish larval assemblage in shallow lagoonal reefs along the Kenyan coast. Fish larvae from five lagoons, spanning 120 km on the Kenyan coast, were sampled in March 2007 and April 2008 to compare interannual spatial variations in species composition, abundance and diversity along the coast. In all, 2 644 fish larvae were sampled, comprising 26 families and 37 species in 2007 and 43 families and 73 species in 2008. The larval assemblage was dominated by Gobiidae, Blenniidae, Pomacentridae and Gerreidae during both years. Larvae hatched from non-pelagic mode of spawning constituting 92% of total numbers. Mean larval abundance (no. 100 m^?3 ± SE) along the coast ranged from 5.0 ± 1.0 to 414 ± 226, with highest densities occurring on the northern sites of Watamu (414 ± 226) and Malindi (31 ± 10). Interannual variation in larval abundance between 2007 (2.17 ± 0.3) and 2008 (2.16 ± 0.1) was not significant (p > 0.05). Shannon-Wiener species diversities between sites ranged from 1.2 ± 0.4 to 2.3 ± 0.3, with highest diversities occurring in Mombasa (2.2 ± 0.5) and Nyali (2.3 ± 0.3). In 2007, the occurrence of preflexion larvae increased northwards from Mombasa (18.2%) to Watamu (86.4%), whereas in 2008, the reverse was the case with the incidence of preflexion larvae reducing northwards from Mombasa Marine Park (76%) to Watamu Marine Park (2%). These trends indicate interannual variation in larval source sites for fish species. Correspondence analysis revealed distinct larval assemblages at sites along the coast, which varied between years.     

Fish fauna recovery in a newly re-flooded Mediterranean coastal lagoon

Drana Lagoon, located at the NW site of Evros River Delta, was drained in 1987 and re-flooded in 2004 within the framework of an integrated wetland restoration project. This study presents the results of a monitoring program of the lagoon's oceanographic, water quality and fish fauna characteristics, during the pre- and post-restoration period. Results depict the presence of high salinity water (up to 41) due to seawater intrusion, strong evaporation in its interior and inadequate freshwater inflows. Overall, nutrient levels were low depicting local changes. Tidal variability at the mouth was approximately 0.2 m, producing high velocity tidal currents (up to 0.75 m/s). Eleven fish fauna species were collected; seven species were caught in both the inlet channel and the lagoon during the pre-restoration period and nine species in the post-restoration period. Atherina boyeri (37.6%) and Pomatoschistus marmoratus (31.7%) dominated the lagoon during the post-restoration period. Most of the A. boyeri specimens (88.5%) were caught inside the lagoon, while P. marmoratus had an almost equal distribution in the inlet channel and the lagoon (56.3% and 43.7% respectively). The presence of species of the Mugilidae family (5.2% total average catches after lagoon re-flooding) was mainly in the inlet channel (12.6% of the average catches) and not inside the lagoon (only 1.3% of the average catches). The small number of fish species inhabiting the lagoon might be the result of the recent restoration or it could be related with the increased water flow observed at the lagoon mouth during the flood and ebb tidal phases, and also in the presence of a smooth bank in the concrete waterspout that connects the entrance channel with the lagoon. The limited presence of the Mugilidae juveniles inside the lagoon could be related to the prevailing tidal inlet dynamics (i.e. strong ebb flow at lagoon inlet), thus preventing the species to enter the lagoon. In order to restore the lagoon environment, careful and gradual steps should be undertaken under the basis of continuous monitoring of hydrologic, environmental and fisheries system's status.     

Hydraulic zonation of the lagoons of Marano and Grado,Italy. A modelling approach

The hydraulic regime-based zonation scheme of the Lagoons of Marano and Grado (Italy) has been derived by means of numerical models. A finite element modelling system has been used to describe the water circulation taking in account different forces such as tide, wind and rivers. The model has been validated by comparing the simulation results against measured water levels, salinity and water temperature data collected in several stations inside the lagoons. The analysis of water circulation, salinity and spatial distribution of passive tracers released at the inlets, led to a physically-based division of the lagoons system into six subbasins. The derived classification scheme is of crucial value for understanding the renewal capacity and pollutants distribution patterns in the lagoon.     

Three main stressors acting on the Ria Formosa lagoonal system (Southern Portugal): Physical stress, organic matter pollution and the land–ocean gradient

During the last 15 years of the 20th century, several researchers carried out extensive sampling of benthic macrofauna communities in the Ria Formosa lagoon. The main objective of this paper is to discern the main communities of benthic fauna of the Ria Formosa and the leading stressors that limit them based on this large data set.The high species richness and high diversity values observed at most of the stations or groups of stations indicate a good ecological status, with the exception of the sewage-impacted areas and the physically stressed areas. It was possible to define three main stressors acting on the Ria Formosa. The most important is the physical stress imposed by the limited water renewal in some areas of the Ria Formosa. The second is the nutrient and organic matter pollution that is limited to the vicinity of the sewage outfall stations and to some locations of the Ria Formosa. This is due to the dual effects of the low residence time of water, but also due to a degradation of water quality in places of relatively restricted water circulation but with high primary production, symptoms of eutrophication. The third stressor is the natural land–ocean gradient, denoting the influence of seawater exchanges and emersion time, attenuated by the high water exchange rates of Ria Formosa.It was possible to differentiate the anthropogenic stress from the natural physical stress through the application of multivariate analysis. However, both structural (species richness and diversity indices) and functional indicators (trophic composition) indicate the same trend – low species richness, low diversity indices, and a community dominated by detritivores species at the locations characterized by high anthropogenic impact or by physical stress. The physically stressed areas were dominated by chironomid larvae and hydrobiid gastropods and the most polluted areas were dominated by oligochaetes, mainly tubificids.     

New Zealand coastal system boundaries, connections and management

Abstract:    Understanding coastal boundaries, connections and drivers of landscape change is integral to effective coastal planning and management. This concept is explored here through case studies representing two very different New Zealand systems: embayed sand beaches in eastern and western open-coast settings; and mixed sand and gravel coast river-mouth lagoons. When framed within a resource and environmental management context these studies indicate that national recognition of the dynamic and interactive nature of coastal environments is a relatively new and amorphous phenomenon in New Zealand and, as such, has been ineffective in driving integrated regional management practices and sustainable coastal outcomes.