The Atlantidae are holoplanktonic gastropods with aragonitic shells that inhabit the epipelagic habitat primarily in tropical and subtropical oceans, as well as in certain transitional and temperate regions, such as the California Current System. However, there is limited knowledge about how their diversity, distribution, and abundance respond to environmental changes over different time scales. The strongest seasonal changes of zooplankton species composition and environmental conditions in the southern California Current System occur between winter and spring. El Niño Southern Oscillation and marine heat waves are two additional environmental change drivers of interannual scale. Our aim was to infer the effect of the seasonal (winter-spring) and interannual (2012–2016) environmental variability on the diversity, distribution, and abundance of the Atlantidae species assemblage along the Pacific coast off the Baja California peninsula, Mexico. Atlantidae diversity was higher during winters than during springs. Their horizontal distribution recorded during winter was statistically correlated with temperature, salinity, and the seawater masses distribution, and during spring was correlated with the depth of hypoxic conditions (<60 μmol O2/kg oxyline) and the depth of Ω aragonite saturation horizon. Atlanta californiensis was the most abundant species, mainly during spring and its relative abundance decreased during anomalously warm periods, while tropical/subtropical species showed an opposite abundance pattern. The maximum species richness was associated with the 2013–2015 marine heat wave and El Niño 2015–2016 events, when tropical species were observed in the study area. Differences in the species community structure, their response to Ω aragonite undersaturated waters and hypoxia, and their seawater mass affinity showed that atlantids are useful biological indicators of environmental changes, ocean acidification, and deoxygenation conditions.

The spinetail devil ray Mobula mobular is a data-poor species of global conservation concern with distribution and movement patterns that are linked to dynamic oceanographic processes. While some conservation measures to protect this species from diverse human threats have been implemented, the potential impacts of climate variability on this species and its main prey Nyctiphanes simplex have not yet been fully considered. We used boosted regression tree models to predict the habitat suitability and niche overlap (Schoener's D index) of predator and prey in northwestern Mexico during 2005-2015. This period included anomalously warm (El Ni & ntilde;o) and cold (La Ni & ntilde;a) years, allowing us to predict habitat preferences for both species under contrasting ENSO environmental conditions. Our model predicts that M. mobular and N. simplex distributions are associated with productive waters along the coast and with considerably less probability offshore of northwest Mexico. We found strong spatial relationships between the habitat suitability of M. mobular and its prey, with high distributional overlap inside the Gulf of California during the warm season. During the 2010 La Ni & ntilde;a event, environmental conditions resulted in particularly high habitat suitability and overlap for both species inside the Gulf during August and September, while during the 2015 El Ni & ntilde;o event, habitat suitability and overlap were higher on the west coast of the Gulf of California. We demonstrate how predicting distribution patterns of data-poor species provides vital information for marine resource managers to develop effective protection strategies for species of conservation concern, like M. mobular.

Bahía de Los Ángeles (BLA) is located on the peninsular coast of the Gulf of California, near to the midriff islands. It is a greatly diverse ecosystem and a marine protected area due to its importance for whale sharks, turtles, and reef fishes. The bay also supports commercial fisheries that require ecological information for the integrated management of resources. Zooplankton studies are required as is an essential link in the trophic webs. There are few zooplankton studies in BLA focused mainly on the major taxa and species of copepods and cladocerans. Only one study addressed the seasonal variation in zooplankton but with gaps in the sampling. Here, we report the monthly changes in the zooplankton abundance and the composition of the major groups and cladoceran species. Eighty-one samples were collected between September 2017 and January 2019. The holoplankton taxa identified numbered 17, which accounts for 93% of the mean abundance (range 71–100%), with copepods and cladocerans being dominant. The meroplankton consisted of 15 taxa with a greater presence during the warm months (summer–autumn), dominated by the larval stages of bivalves, gastropods, and barnacles. In contrast, many copepod nauplii were found in January associated with low temperatures. Only cladacerans were identified to the species level. They showed strong seasonal fluctuations, reaching a third of the total zooplankton from spring to autumn, with Penilia avirostris being the most abundant species. These results are compared with other temperate and tropical coastal locations of the eastern Pacific.

2022 marked the third consecutive La Niña and extended the longest consecutive stretch of negative Oceanic Niño Index since 1998-2001. While physical and biological conditions in winter and spring largely adhered to prior La Niña conditions, summer and fall were very different. Similar to past La Niña events, in winter and spring coastal upwelling was either average or above average, temperature average or below average, salinity generally above average. In summer and fall, however, upwelling and temperature were generally average or slightly below average, salinity was close to average and chlorophyll a was close to average. Again, as during prior La Niña events, biomass of northern/southern copepods was above/below average off Oregon in winter, and body size of North Pacific krill in northern California was above average in winter. By contrast, later in the year the abundance of northern krill dropped off Oregon while southern copepods increased and body sizes of North Pacific krill fell in northern California. Off Oregon and Washington abundances of market squid and Pacific pompano (indicators of warm, non-typical La Niña conditions) were high. In the 20th century, Northern anchovy recruitment tended to be high during cold conditions, but despite mostly warm conditions from 2015-2021 anchovy populations boomed and remained high in 2022. Resident seabird reproductive success, which tended in the past to increase during productive La Niña conditions was highly variable throughout the system as common murre and pelagic cormorant, experienced complete reproductive failure at Yaquina Head, Oregon while Brandt’s cormorant reproduction was average. At three sampling locations off central California, however, common murre reproduction was close to or above average while both pelagic and Brandt’s cormorant were above average. California sealion reproduction has been above average each year since 2016, and pup weight was also above average in 2022, likely in response not to La Niña or El Niño but continuous high abundance of anchovy. The highly variable and often unpredictable physical and biological conditions in 2022 highlight a growing recognition of disconnects between basin-scale indices and local conditions in the CCE. “July-December 2022 is the biggest outlier from individual “strong” La Niña (events) ever going back to the 50s.” – Nate Mantua

The episodic stranding of millions of pelagic red crabs ( Pleuroncodes planipes ) along California beaches is a striking and puzzling phenomenon. Pleuroncodes planipes are usually abundant off Baja California, Mexico, and their appearance in central California is thought to coincide with anomalously warm waters and northward advection related to El Niño. This anecdotal association has stimulated many hypotheses, but no hypothesis has gained clear and convincing support. Motivated by an unprecedented number of P. planipes strandings and at‐sea observations in 2015–2019, we compiled 10 P. planipes datasets spanning 1950–2019, tested the anomalous advection hypothesis using a transport analysis from 1981 to 2010, and explored other compelling hypotheses. We found P. planipes presence off central California was related to anomalous advection of waters from Mexico, sometimes but not always associated with El Niño events, with P. planipes likely remaining residents of northern waters for several years without additional anomalous transport but potentially facilitated by warm waters. By identifying a mechanism behind episodic P. planipes range expansions, we show that a source water index could provide an early indicator for anomalous events in the future.

Ecologically similar species partition their use of resources and habitats and thus coexist due to ecological segregation in space, time, or diet. In seabirds, this segregation may differ over the annual cycle or vary inter-annually. We evaluated niche segregation in 3 sympatric storm-petrel species (Hydrobates melania, H. leucorhous, and H. microsoma) from the San Benito Islands, Mexico, during 2012 and 2013. We used diet samples and carbon (δ13C) and nitrogen (δ15N) isotopic values obtained from egg membranes, blood, feathers, and prey. We used krill samples to delineate marine δ13C and δ15N isoscapes for the Baja California Peninsula. During the breeding season, storm-petrels segregated regarding diet composition, stable isotope values, and isotopic niches. H. melania consumed higher trophic-position prey from neritic waters, while H. leucorhous and H. microsoma foraged on lower-trophic position prey from oceanic waters. Isotopic niches among species did not overlap in 2013, whereas those of H. microsoma and H. leucorhous overlapped in 2012. The feeding strategies of H. melania varied among breeding phases, and adults consumed different prey items from different areas compared to those of their offspring. H. microsoma adults and their chicks consumed the same prey items but from different habitats. During the non-breeding period, niche segregation between species persisted, except for H. microsoma and H. leucorhous during the molt of primary (P1) and undertail cover feathers. These 3 sympatric species coexist through niche segregation based on prey items and foraging areas that vary seasonally and year-round, probably due to changes in oceanographic conditions and the distribution and availability of prey.

The California Current System (CCS) has experienced large fluctuations in environmental conditions in recent years that have dramatically affected the biological community. Here we synthesize remotely sensed, hydrographic, and biological survey data from throughout the CCS in 2019–2020 to evaluate how recent changes in environmental conditions have affected community dynamics at multiple trophic levels. A marine heatwave formed in the north Pacific in 2019 and reached the second greatest area ever recorded by the end of summer 2020. However, high atmospheric pressure in early 2020 drove relatively strong Ekman-driven coastal upwelling in the northern portion of the CCS and warm temperature anomalies remained far offshore. Upwelling and cooler temperatures in the northern CCS created relatively productive conditions in which the biomass of lipid-rich copepod species increased, adult krill size increased, and several seabird species experienced positive reproductive success. Despite these conditions, the composition of the fish community in the northern CCS remained a mixture of both warm- and cool-water-associated species. In the southern CCS, ocean temperatures remained above average for the seventh consecutive year. Abundances of juvenile fish species associated with productive conditions were relatively low, and the ichthyoplankton community was dominated by a mixture of oceanic warm-water and cosmopolitan species. Seabird species associated with warm water also occurred at greater densities than cool-water species in the southern CCS. The population of northern anchovy, which has been resurgent since 2017, continued to provide an important forage base for piscivorous fishes, offshore colonies of seabirds, and marine mammals throughout the CCS. Coastal upwelling in the north, and a longer-term trend in warming in the south, appeared to be controlling the community to a much greater extent than the marine heatwave itself.

Hyperiid amphipod species from the Gulf of Ulloa, Baja California, and the adjacent region (from shelf break to 200 km offshore) were analyzed in order to evaluate diversity and abundances in this productive area that supports small-scale commercial fisheries such as barred sand bass ( Paralabrax nebulifer ), California spiny lobster ( Panulirus interruptus ), abalones, clams, and others. Strong coastal upwelling events were observed during summer seasons of the period 2002-2008 between Punta Eugenia and Punta Abreojos. The upwelling plumes at Punta Abreojos are projected southward in slope waters bordering the coastal shelf of the Gulf of Ulloa, contributing to the separation of coastal and oceanic regions, and explain differences in amphipod diversity and abundances. In the offshore region, the most abundant species were Vibilia armata, Lestrigonus schizogeneios, Primno brevidens , and Eupronoe minuta , similar to previous findings in northern regions of Baja California and southern California. However, their abundances were lower (between 10 and 30 individuals/1000 m3), only reaching 20-50% of abundance levels reported off northern Baja California. In the coastal shelf of the Gulf of Ulloa, amphipods were virtually absent during 2002, 2003 and 2006. However, during 2004 and 2005, abundances of P. brevidens increased (54 and 20 ind/1000 m3, respectively). Moreover, during 2007, abundances of L. schizogeneios, P. brevidens, Lycaea nasuta, Lycaea pulex , and Simorhynchotus antennarius increased considerably (261, 39, 31, 68, 416 ind/1000 m3, respectively), indicating occasional utilization of the coastal shelf by pelagic amphipods. Gelatinous organisms paralleled changes in hyperiid populations and were particularly abundant in 2007 in the coastal shelf. Significant correlations of 17 amphipod species with gelatinous taxa, which are often used as host organisms by hyperiid amphipods, suggest that those organisms enhanced hyperiid abundance and promoted the progression onto the coastal shelf during some years of the 2002-2008 period.

Hyperiid amphipod species from the Gulf of Ulloa, Baja California, and the adjacent region (from the shelf break to 200 km offshore) were analyzed to evaluate diversity and abundances. This productive area supports small-scale commercial fisheries, including sand bass (Paralabrax nebulifer), California spiny lobster (Panulirus interruptus), abalones, clams, and others. Strong coastal upwelling events were observed during summer seasons of the period 2002-2008 between Punta Eugenia and Punta Abreojos. The upwelling plumes at Punta Abreojos are transported southward in slope waters bordering the coastal shelf of the Gulf of Ulloa, contributing to the separation of coastal and oceanic regions, and explain differences in amphipod diversity and abundances between both regions. In the offshore region, the most abundant species were Vibilia armata, Lestrigonus schizogeneios, Primno brevidens, and Eupronoe minuta, similar to previous findings in northern regions of Baja California and southern California. However, abundances of these species were lower (10-30 individuals/1000 m3), only reaching 20-50% of abundance levels reported off northern Baja California. In the coastal shelf of the Gulf of Ulloa, amphipods were virtually absent during 2002, 2003 and 2006. However, during 2004 and 2005, abundances of P. brevidens increased (54 and 20 ind/1000 m3, respectively). Moreover, during the late summer of 2007, abundances of L. schizogeneios, P. brevidens, Lycaea nasuta, Lycaea pulex, and Simorhynchotus antennarius increased considerably (261, 39, 31, 68, 416 ind/1000 m3, respectively), indicating occasional utilization of the coastal shelf by pelagic amphipods. Changes in gelatinous populations (medusae, siphonophores, ctenophores, doliolids, and salps) paralleled changes in hyperiid populations, with highest abundances in 2005-2008 in the coastal shelf. Significant correlations of 17 amphipod species with gelatinous taxa, which are often used as host organisms by hyperiid amphipods, suggest that gelatinous presence enhanced hyperiid abundance and promoted the progression of hyperiid amphipods onto the coastal shelf during parts of the 2002-2008 period.

Euphausiids represent a significant part of the total zooplankton biomass and are a key link in the trophic web of the California Current System (CCS). During 2014-2016, the northeast Pacific experienced warming caused by two successive events, the Blob and the 2015-2016 El Nino, which affected the whole ecosystem. Here we present evidence for a strong impact of the 2014-2016 warm events on euphausiids in the Baja California region, namely two species (Euphausia pacifica and Nematoscelis difficilis) that are dominant in the CCS transition zone. Both species decreased approximately 95% in relation to the previous years (1999-2010). A similar decrease was observed for E. pacifica during the 1997-1998 El Nino, but the decrease in N. difficilis was higher in 2014-2016 and unprecedented during the 1997-2016 period. Biomass of the coastal species Nyctiphanes simplex showed negative anomalies during the Blob but not during the 2015-2016 El Nino. The tropical species Euphausia eximia and Euphausia recurva increased in biomass during the Blob in 2014 relative to the previous years, and even more during the 2015-2016 El Nino. The strong increase of E. eximia, E. recurva, and N. simplex during El Nino may have been due to upwelling activity in winter 2015-2016. Canonical correspondence analysis (CCA) was performed to assess the relation between the euphausiid community and environmental variables. The most influential variables were temperature and chlorophyll, and to a lesser extent salinity. The subarctic E. pacifica showed covariance with chlorophyll while a set of tropical species did with thermohaline conditions. However, the variance accounted for was low (20% taking the first three axis). N. difficilis did not show significant scores in the CCA suggesting that other variables such as availability of prey could be important for this carnivore species.

The California Current Ecosystem (CCE) has been in a primarily warm state since 2014, and this pattern largely continued into 2019. The CCE experienced a mild El Nino from late 2018 into 2019, and basin-scale indicators reflected this condition (elevated Oceanic Nitio Index and Pacific Decadal Oscillation; table 1). Despite the El Nino, spring upwelling was above average between southern California and Washington but below average in Baja California. Sea surface temperature (SST) was mostly near the long-term average between Washington and southern California, while surface chlorophyll a was above average in Oregon/Washington and slightly below average in most of California in spring/early summer 2019. SST changed dramatically by fall 2019, however, as a marine heat wave (MHW) that formed in May 2019 in the Gulf of Alaska impinged upon the West Coast of the United States. The expansion of the 2019 MHW followed a similar pattern to the 2014-15 MHW. Off Oregon, the zooplankton assemblage was in a mixed state as southern copepods were close to average while northern copepod abundances were positively anomalous in 2019. Off northern California, Euphausia pacifica body size was smaller than average. Euphausid abundances were well below average in both central and southern California in 2019. In the north, winter 2019 larval fish abundances were high and dominated by offshore taxa that are associated with warm conditions; spring larval and post-larval biomass were close to average; and spring surface trawls observed record-high market squid (Doryteuthis opalescens) abundances. The single most important finding in 2019 was that northern anchovy (Engraulis tnordax) adults and larvae were at record-high abundances in central and southern California. In central California, market squid and Pacific sardine (Sardinops sagax) were also abundant. In southern California warm-water mesopelagic fishes have been very abundant since 2014, and this trend continued into 2019. Indicators for future salmon returns were mixed in 2019. The abundance of northern copepods, which correlate positively with returns, was high. However, abundances of yearling Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch), which also correlate positively with returns, were slightly below average. Winter ichthyoplankton was comprised mostly of southern or offshore taxa, which bodes poorly for future salmon returns. Seabird (common murre [Urfa aalge]; Brandt's cormorant [Phalacrocorax penidllatus]; and pelagic cormorant [Phalacrocorax pelagicus]) productivity off Oregon was the highest in years in both 2018 and 2019. In 2018, common murre chicks in Oregon consumed large amounts of young-of-the-year flatfish, a prey item known to be conducive to chick survival. Despite the prevalence of northern anchovy in central California, common murre and Brand's cormorant production was low in Southeast Farallon Island as these birds were unable to feed optimally on northern anchovy, and there was a scarcity of more appropriate prey such as young-of-the-year flat-fishes or rockfishes. California sea lions (Zalophus californianus), by contrast, benefitted greatly from the large northern anchovy forage base. In 2018, live pup count, weight, and growth rate were anomalously high, and northern anchovy remains occurred in >85% of scat samples. Humpback whale (Megaptera novaeangliae) sightings were also very high in 2019, likely because humpback whales congregated near shore to feed on northern anchovy.

In order to understand how the structure and composition of euphausiid assemblages are affected by changes in environmental conditions caused by El Niño and La Niña events in the Colombian Pacific, euphausiids present in zooplankton samples obtained during Estudio Regional del Fenómeno El Niño – Cuenca Pacífica Colombiana (ERFEN-CPC) cruises, in September 2009 (El Niño), October 2011 (La Niña) and September 2012 (Neutral) were analyzed. Fifteen species (5 genera) were identified, of which Euphausia diomedeae was the most abundant during El Niño and Euphausia distinguenda was the most abundant during La Niña and the Neutral condition. In addition, considering all euphausiid species found in this study; under La Niña and Neutral conditions, juveniles were the most abundant phase; while during El Niño, furcilia larvae were the most abundant. During the Neutral condition, the total abundance of euphausiids was significantly higher than during El Niño and La Niña, suggesting that the environmental changes caused by these anomalous conditions would affect abundance due to possible movements of the species towards more favourable conditions. Finally, during El Niño, the euphausiid assemblage was significantly different from the other two conditions, suggesting that the increase in temperature produced by this condition affect the structure and composition of euphausiids assemblage in the Colombian Pacific.

Euphausiids are a major component of the zooplankton biomass due to their large size, contributing with high carbon content to other trophic levels in the pelagic ecosystem. We analyzed the summer interannual variability in euphausiid species composition based on carbon mass of the Baja California oceanic domain during 1998-2008. Selection of one exclusive season allowed the emphasis of interannual changes in order to research possible biological impacts. During the period 1998-2008 prevailed intense interannual activity, with four El Nino events, two of them (1997-1998 and 2006-2007) with SST anomalies propagating toward the eastern Pacific (EP-El Nino), while the other two (2002-2003 and 2004-2005) had SST anomalies limited to the central Pacific (CP-El Nino). There were also La Nina events in 1998-2000 and 2007-2008. The species with higher biomass contribution off Baja California were Nematoscelis difficilis, Euphausia gibboides, Thysanoessa gregaria, Euphausia eximia, Nyctiphanes simplex, and Euphausia pacifica, with a global geometric mean of 156, 66, 38, 30, 21, and 13 mu g Cm-3 respectively. N. difficilis and E. pacifica were dominant in the northern area (29.5-32 degrees N), N. difficilis and E. gibboides in the central area (27-29.5 N), and E. eximia dominated in the southern area (24.5-27 N). 1998-2008 biomass anomalies showed a variety of patterns by species with the clearest footprint, in most of the species, during the strong EP-E1 Nino 1997-1998. CP-E1 Nini events also left a footprint in the biomass of some species but this was not always by anomalies of the same nature as EP-E1 Nino. The best examples were N. difficilis and N. simplex, which presented lightly positive anomalies during July 1998 but were strongly negative in the summer of 2003 and 2004. The opposite was observed in E. recurva, with a negative anomaly in July 1998 but positive in 2004 and 2005. The biophysical coupling between the species assemblage and environmental variables, using canonical correspondence analysis (CCA), explained 22% of the biomass variability. The first axis was responsible for thermal conditions in the upper layer (temperature at 10 m, 50 m, and the gradient between 10 and 100 m depth), while the second axis concentrated the oxygen gradient, oxygen and salinity at 50 m depth, and 200 m temperature. A large group of tropical-subtropical species showed covariance with axis-1, while E. pacifica and T. spinifera had art inverse covariance. The equatorial species E. distinguenda and E. lamelligera were close to axis-2, though the stations were limited to slope water where intense upwelling bring oxygen depleted deep water. Transition zone species (E. gibboides, N. difficilis, T. gregaria, and N. simplex) were relatively inert to both axes. Their response to climatic variability was less predictable and new variables should be explored, including bottom-up and top-down mechanisms.

Following the marine heat wave of 2014-16, the California Current System (CCS) trended towards more typical conditions north of Point Conception, California, from mid-2017 to mid-2018, but became highly abnormal in the south by mid-2018.Two basinscale indices (Pacific Decadal Oscillation and Oceanic Nino Index) were close to neutral, but the North Pacific Gyre Oscillation was extremely low at the end of 2017 and beginning of 2018. Regional analyses demonstrated that upwelling was close to normal throughout most of the CCS with the exception of high upwelling from northern California to Washington in summer and fall of 2017. Sea surface temperature was close to normal throughout most of the CCS but warmed to record levels in summer 2018 in southern California and northern Baja California. In spring 2018, surface chlorophyll a was negatively anomalous throughout most of the US West Coast with localized hot spots around the Columbia River, in the Gulf of Farallones, and Monterey Bay. Lipid-rich copepod densities and sizes returned to normal levels in the northern CCS, and euphausiid abundances were above average in central California but below average in southern California in spring 2018. Abundances of 7 zooplankton taxa were slightly to well above average off of northern Baja California in late 2017. Pyrosomes, which are associated with warm water, were found throughout the CCS. The fish assemblage off Oregon and Washington was comprised of both northern and southern/offshore species. In the central region (near Monterey Bay) most fishes were close to long-term mean abundances; however, adult northern anchovy (Engraulis mordax) abundance was the highest on record. The ichthyoplankton assemblage off southern California had a tropical signal similar to 2014-15 as warm-water associated mesopelagic abundances were close to record highs and cold water mesopelagics abundances were very low.Anchovy larvae abundances in southern California were the highest since the 1960s. Indicators that can affect salmon survival were mixed in 2018. On the one hand, several indices forecast high salmon return (moderate-high salmon yearling abundance, high larval fish (salmon prey) abundance, normal lipid-rich copepod abundances). On the other hand, low survival was predicted by high fall PDO, high abundances of offshore larval fishes, and above average abundance of lipid-poor copepods.This unusual mix of indicators makes it difficult to forecast salmon returns in upcoming years. Common murre (Urfa aalge) reproduction was historically low in the northern CCS in 2017 as colonies experienced complete reproductive failure both at Yaquina Head, Oregon, and Castle Rock, California. In both cases, forage was scarce, birds conducted long foraging excursions which left eggs unattended for extended periods, and many eggs were consumed by avian predators. Brandt's (Phalacrocorax peniscillatus) and pelagic (P. pelagicus) cormorants had above average reproductive success in 2017 at Yaquina Head, but Brandt's cormorant also had total reproductive failure in 2017 at Castle Rock. At Southeast Farallon Island murre, Brandt's cormorant, and pelagic cormorant productivity was close to average in 2017, and Brandt's cormorant and murre were slightly above average in 2018. Preliminary 2018 results fromYaquina Head also indicated that murre successfully produced chicks for the first time since 2014. At-sea bird surveys in the north demonstrated that sooty shearwater and common murre abundances were historically low in 2017, but increased to some of the highest values on record in 2018. By contrast, the at-sea surveys off central California found that murre densities were anomalously high in 2017 but fell to an average level in 2018. Improving California sea lion (Zalophus californianus) pup condition continued from 2016 into 2017 as live pup counts, pup weight, and rate of growth were above average. Augmented pup conditions in 2016-17 was likely driven by increased availability of anchovy, as anchovy remains were found in nearly 100% of sea lion scat. There were record high encounters with Humpback whales (Megaptera novaeangliae) off central California in 2018. Overall, much of the CCS was in more of a normal state through mid-2018 relative to the past 5 years. However, remnants of the 2014-16 marine heat wave were still resonating in the north, and another highly anomalously warm water event affected the southern part of the CCS in summer 2018. Thus, while the CCS was returning to typical conditions in the north, it was anything but normal in the south in 2018.

There are few studies on pelagic mollusks from the California Current, despite their ecological importance and vulnerability to climate change (e.g., ocean acidification and hypoxia). We analyzed abundances of holoplanktonic mollusks during three years (2006-2008) along a transect-line parallel to the Baja California coast. The main differences in physical factors were increasing temperature and salinity from north to south, and lower dissolved oxygen concentration south of Punta Eugenia (28 degrees N). The lowest oxygen concentrations occurred in summer, with hypoxic conditions (< 0.5 ml.L-1) in the upper 100 m depth at some locations. Planktonic mollusk abundance did not differ along the latitudinal gradient, excepting Desmopterus pacificus Essenberg, 1919 and individuals from the genus Pterotrachea Forskal, 1775. In contrast, the temporal variability was high, mainly in a seasonal scale but also among years. The influence of El Nino 2006-2007 and La Nina 2007-2008 were evident by a sharp increase of Corolla spectabilis Dall, 1871 in April 2007 during the El Nino-La Nina transition. During 2008, pelagic mollusks remained with moderate abundance in winter-spring despite the high chlorophyll concentrations recorded (up to 3.26 mg.m(-3)). Subsequently, during the relaxation of a first pulse of La Nina in July 2008, there was a rebound in the abundance of the heteropod Atlanta Lesueur, 1817. and individuals in the Order Gymnosomata. The oxygen gradient inversely influenced mollusk abundance in most of the genera (Clio Linnaeus, 1767, Limacina Bosc, 1817, Atlanta, and Firoloida Lesueur, 1817) and the order Gymnosomata, but for Cavolinia Abildgaard, 1791, Creseis Rang, 1828, Desmopterus, and Pterotrachea, the salinity gradient was more influential. Therefore, holoplanktonic mollusks genera were useful indicators of climatic variability.

The seasonal succession of species community structure, abundance and carbon biomass of five zooplankton taxa (Copepoda, Euphausiacea, Chaetognatha, Amphipoda and fish larvae) and their variability during different oceanographic conditions was investigated on the continental shelf of the central Mexican Pacific (19 degrees N, 105 degrees W) during a monthly time-series (1996-1998). These zooplanktonic taxa included 291 species, with maximum species richness during El Nino 1997-98, when 54 tropical oceanic species invaded the continental shelf. This typical offshore community was advected onshore by the anomalous intrusion of Subsurface Equatorial water mass which caused + 7 degrees C temperature anomalies. Nineteen species comprised the bulk of the abundance (91%) and biomass (87%) of the five zooplankton taxa. Multivariate statistical analysis revealed four species assemblages associated with distinct oceanographic conditions: (1) mixed water column period (upwelling; February-June, non-El Nino period) characterized by high abundance and carbon biomass of omnivorous zooplankters (copepods Subeucalanus subcrassus, Centropages furcatus, Canthocalanus pauper, Temora discaudata, and Subeucalanus subtenuis, euphausiid Euphausia distingtienda, and fish larvae Bregmaceros bathymaster); (2) stratified water column period (July-January, non-El Nino period) with low-moderate abundance and biomass of the predominant species of the first group plus the euphausiid E. lamelligera, the chaetognaths Flaccisagitta enflata and Zonosagitta bedoti, and the tropical amphipod Hyperfoides sibaginis; and (3 and 4) two highly diverse assemblages associated with El Nino-stratified conditions and post El Nino (July 1997-December 1998). These last two assemblages were distinguished by a high numerical dominance of carnivores (F. enflata, Z. bedoti, and H. sibaginis) and a pronounced decline of abundances of omnivore copepods, euphausiids, and fish larvae. Both the seasonal upwelling dynamics and the interannual-scale El Nino events shaped the tropical zooplankton community structure succession of this neritic ecosystem. The local community structure modulates the function and productivity of this ecosystem, which sustains regional fisheries and ecotouristic activities. More frequent, intense or even longer El Nino events may significantly decrease zooplanktonic carbon biomass and trophic transfer through the neritic epipelagic food web, resulting in impoverishment of the shelf biota with negative economic implications.

BEDOLLA-GUZMÁN Y., MASELLO J.F., AGUIRRE-MUÑOZ, A., LAVANIEGOS, B.E. & QUILLFELDT, P. 2017. Breeding biology, chick growth, and diet of the Least Storm-Petrel Oceanodroma microsoma on Islas San Benito, Mexico. Marine Ornithology 45: 129–138 The Least Storm-Petrel Oceanodroma microsoma is endemic to islands on both coasts of Baja California, in Mexico. It is the smallest seabird species and one of the least studied of the order Procellariiformes. We present a detailed account of its breeding success, chick growth, and diet at Islas San Benito, Baja California, during three consecutive breeding seasons (2013 to 2015) and of sex differences in adult morphology, a study conducted in 2012. Eggs hatched between late July and mid-September, and the fledging period started in mid-October. The timing of breeding varied from year to year: the hatching period began earlier in 2013 than in 2015 and was longer in 2014, while the fledging period started later in 2014 than in 2013. Hatching success (around 80%) and fledging success (about 90%) were consistently high in all three years. Nevertheless, nestlings fledged with longer wings, tails, and bills in 2015. Four species of euphausiids, two species of larval fish, and one species of squid were identified in food samples. Differences in the timing of breeding and chick growth during the period of this study may reflect a variation in food supply associated with anomalous climate conditions recorded in 2014 and 2015.