Rapid Effects of Marine Reserves via Larval Dispersal

Marine reserves have been advocated worldwide as conservation and fishery management tools. It is argued that they can protect ecosystems and also benefit fisheries via density-dependent spillover of adults and enhanced larval dispersal into fishing areas. However, while evidence has shown that marine reserves can meet conservation targets, their effects on fisheries are less understood. In particular, the basic question of if and over what temporal and spatial scales reserves can benefit fished populations via larval dispersal remains unanswered. We tested predictions of a larval transport model for a marine reserve network in the Gulf of California, Mexico, via field oceanography and repeated density counts of recently settled juvenile commercial mollusks before and after reserve establishment. We show that local retention of larvae within a reserve network can take place with enhanced, but spatially-explicit, recruitment to local fisheries. Enhancement occurred rapidly (2 yrs), with up to a three-fold increase in density of juveniles found in fished areas at the downstream edge of the reserve network, but other fishing areas within the network were unaffected. These findings were consistent with our model predictions. Our findings underscore the potential benefits of protecting larval sources and show that enhancement in recruitment can be manifested rapidly. However, benefits can be markedly variable within a local seascape. Hence, effects of marine reserve networks, positive or negative, may be overlooked when only focusing on overall responses and not considering finer spatially-explicit responses within a reserve network and its adjacent fishing grounds. Our results therefore call for future research on marine reserves that addresses this variability in order to help frame appropriate scenarios for the spatial management scales of interest

Influence of topography on tide propagation and amplification in semi-enclosed basins

An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when\ud the length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential to reproduce semi-diurnal and diurnal\ud tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf

Quantifying the Spatial Ecology of Wide-Ranging Marine Species in the Gulf of California: Implications for Marine Conservation Planning

There is growing interest in systematic establishment of marine protected area (MPA) networks and representative conservation sites. This movement toward networks of no-take zones requires that reserves are deliberately and adequately spaced for connectivity. Here, we test the network functionality of an ecoregional assessment configuration of marine conservation areas by evaluating the habitat protection and connectivity offered to wide-ranging fauna in the Gulf of California (GOC, Mexico). We first use expert opinion to identify representative species of wide-ranging fauna of the GOC. These include leopard grouper, hammerhead sharks, California brown pelicans and green sea turtles. Analyzing habitat models with both structural and functional connectivity indexes, our results indicate that the configuration includes large proportions of biologically important habitat for the four species considered (25–40%), particularly, the best quality habitats (46–57%). Our results also show that connectivity levels offered by the conservation area design for these four species may be similar to connectivity levels offered by the entire Gulf of California, thus indicating that connectivity offered by the areas may resemble natural connectivity. The selected focal species comprise different life histories among marine or marine-related vertebrates and are associated with those habitats holding the most biodiversity values (i.e. coastal habitats); our results thus suggest that the proposed configuration may function as a network for connectivity and may adequately represent the marine megafauna in the GOC, including the potential connectivity among habitat patches. This work highlights the range of approaches that can be used to quantify habitat protection and connectivity for wide-ranging marine species in marine reserve networks

Tidal currents in the Gulf of California: intercomparisons among two- and three-dimensional models with observations

Two three-dimensional and one two-dimensional models are used to simulate the tides (heights and currents) in the Gulf of California. One of the three-dimensional models uses sigma coordinates and the other uses fixed vertical levels. The results of the models are compared to observations by means of harmonic constants. It is found that tidal heights are better modelled with a simple two-dimensional model, while tidal currents are better modelled with the three-dimensional model with fixed vertical levels

Modeling of residual currents in the Gulf of California using different grid sizes

The effect of the mesh size resolution to model residual currents produced by the tides (M2) in the Gulf of California was studied. The grid sizes used range from 14 x 14 to 2 x 2 km. The results show consistent tidal and residual currents among the different grids. In the northern gulf, a well-defined circulation pattern, aligned with the isobaths, emerged. In the archipelago area, an anticyclonic eddy was found northwest of Tiburón Island. The rest of the gulf showed no appreciable residual circulation. Maximum modeled velocities of ~18 cm s–1 were found in the archipelago; the northern gulf velocities were of the order of 1 cm s–1. The 3 x 3 km grid was considered suitable to model the residual currents in the northern gulf

Tidal dynamics and energy budget in the Gulf of California

The dynamics and energetic behavior of the tides in the Gulf of California were studied with their principal constituents. Three cases were chosen: the first included the M2 constituent; the second, the two principal semidiurnal constituents; and the third, the seven most important tidal constituents in the gulf. The results show that the tide was successfully modeled for all constituents and for all cases. It was proved that small changes in the friction coefficient produce important errors in the tidal adjustment. The dynamics and energetic behavior of the tides did not change while varying the friction coefficient, even when more constituents were included. The most important forces that maintain the momentum balance in the gulf are the pressure gradient, Coriolis and friction. In the northern gulf the most important forces are the pressure gradient and friction, while in the southern gulf the most important forces are in geostrophic balance. Advection is also important in the northern gulf and in the archipelago of the large islands. The regions where most of the tidal energy is dissipated are the northern gulf and the archipelago, especially in the Upper Gulf, Adair Bay, Ballenas Channel, and San Lorenzo and San Esteban sills. The inclusion of more constituents introduced more momentum and energy to the gulf, and part of this momentum and energy was transferred to the mean field and part to the low-frequency field. The results show that changes in the friction coefficient did not affect the tidal behavior in the gulf; nevertheless, the tidal energy dissipation estimated inside the gulf was affected

Evolution and extension of the Santa Ana winds of February 2002 over the ocean, off California and the Baja California Peninsula

The evolution and extension of Santa Ana winds over the Pacific Ocean, off the coasts of California and the Baja California Peninsula, is documented from QuikScat satellite observations. The typical wind pattern in this region is towards the southeast, but between 9 and 12 February 2002 it was modified by Santa Ana winds, changing in direction towards the south, southwest and west. The changes were notable at first in southern California, but the largest indices of variation occurred between 26ºN and 28ºN off the Baja California Peninsula, with maxima in the Gulf of California, mainly in the northern part. The maximum extension of the winds to the west of the coast was on 11 February, reaching 32ºN and 125ºW, or ~700 km; however, towards the southwest the winds extended to 25ºN and 124ºW, or ~1000 km. The topography of the peninsula plays an important role in controlling the winds passing from the Gulf of California to the Pacific, causing plumes of sand and dust in several locations over the ocean

Effect of the spatial and temporal variability of winds on the circulation in the Gulf of California

A numerical model of the Gulf of California is used to study and compare the circulation due to a spatially homogeneous and time symmetric wind (VI) and one derived from QuikScat data (VO). The mean and seasonal evolution of the currents are presented for both cases, as well as their associated fields of kinetic energy, vorticity and horizontal divergence. On average, the currents generated by VI are weaker than those of VO and with a simpler spatial structure: anticyclonic circulation in the south and irregular in the north. In both cases, variability is larger on the continental coast in shallow waters but differs in the duration of the cyclonic/anticyclonic gyre in the northern basin. The magnitude of the currents also shows differences between the experiments because of stronger winds from autumn to winter for VO and during summer for VI. The average of the kinetic energy is greater for both experiments on the continental side. High relative vorticity cores are present along the gulf for VO. Close to the coast, the divergence and convergence is large in both cases, and large only for VO far from the coast. The temporal evolution of the kinetic energy, vorticity and divergence is more irregular for VO. Vorticity and divergence is generated only on the coasts and for strong winds for VI, whereas for VO it is also produced as a result of the wind stress curl

Time and spatial variability of sea surface temperature in the Gulf of California

Fourteen years of satellite images (1983–1996) are used to examine the variability of sea surface temperature (SST) in the Gulf of California. The study focussed on the semiannual, annual and interannual scales and on the average. On average, SST decreases from the mouth to the head and its variability increases. The annual scale is responsible for most of the temporal variability, which oscillates in phase with minor north-south variations. The northern gulf shows the formation of warm anticyclonic eddies during winter and cold cyclonic eddies during summer. The spring transition shows a cyclonic eddy closer to the mainland side of the gulf; the autumn transition shows a not well-defined anticyclonic eddy. The SST around the island region is always colder than the rest of the gulf. The lateral variability in the central and southern regions is associated with upwelling phenomena. The semiannual and annual amplitudes increase to the north by a factor of two with respect to the southern region. On the interannual scale, the 1988–1989 and 1992–1993 events reach all the gulf. Both events appear first in the south and island regions, and the signals are more intense at the islands than the rest of the gulf. This behavior has not been reported before. The 1985, 1987 and 1990 events show a "normal" evolution, i.e., the warm waters appear in the south and gradually progress into the gulf