Daniel B. Lluch-Cota

Sea surface temperature variability in coastal areas of the northeastern Pacific related to the El Niño‐Southern Oscillation and the Pacific Decadal Oscillation

We examined monthly time-series (1950 to 1999) of sea surface temperature (SST) anomalies in 47 quadrants (2° × 2°) along the coast of North America and their relation to the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). We used the Multivariate ENSO Index (MEI) and the PDO Index (PDOI) and assumed a linear interaction of the mechanisms behind their interannual variations. Then, we examined SST anomalies as functions of MEI and PDOI using multiple linear regression (MLR). On average, ENSO influence decreases poleward but is still dominant at 31°N. Northward, the PDO signal dominates. MLR was also applied to selected sea level height (SLH) series. ENSO effects on SLH were clear up to 48°N, while PDO showed a weak effect only in the Gulf of Alaska. This suggests that, poleward of Southern California, ENSO effects may be largely restricted to the inshore coastal environment.

Baja California's biological transition zones: Refuges for the California sardine

The information on the transitional areas between the temperate and tropical domains at the southern extent of the California Current System is reviewed and described, particularly searching for the relative isolation or interchange between the western coast of the Baja California peninsula and the Gulf of California, as well as mechanisms that permit the existence of sizeable stocks of California sardine. Biological Action Centers that have high productivity throughout the year, as opposed to the rest of the coastal area, are found in both the western coast of the peninsula at the Sebastián Vizcaíno—Punta Eugenia region and in the Ballenas Channel inside the gulf; these features support large biomasses of sardine throughout the full year and serve as long term refuges during adverse periods. The role of the Sebastián Vizcaino sardine stock as the primary group for expansion is examined.

Shell Shape Differences between Two Panopea Species and Phenotypic Variation Among P. Globosa at Different Sites using two Geometric Morphometrics Approaches

ABSTRACT Most previous studies identifying Panopea generosa and P. globose have used non-rigorous visual methods as well as older shell measurement techniques. Newer mathematical methods based on shell shape variation allow for more accurate identification of clam species, as well as modeling of phenotypic differences due to environmental effects in populations in different sites. Interspecific shell morphology for two Mexican geoduck clam species was analyzed from a total of five sites off both coasts of the Baja California peninsula. In addition, intraspecific analyses of shell morphology were conducted for one of the species, P. globosa, at four sites along its reported distribution. Two approaches were employed for the analyses: a novel approach based on radiating lines to characterize shell outlines, and a more traditional approach using internal shell landmarks. In general, the novel approach afforded greater fidelity in distinguishing inter- and intraspecific variation. Our results from both methods agree with original species descriptions, and showed that Bahía Magdalena geoducks are P. globosa, thus revealing a wider distribution than previous reports for this species. The outline and internal scars were highly discriminant between the two species. Shell shape of P. generosa was also less variable than that of P. globosa. Intraspecific analyses of P. globosa shell shape suggest an adaptive or phenotypic response to environmental conditions at each site. Our results may also be indicative of reproductive isolation between Pacific P. globosa at Bahía Magdalena and conspecifics in the Gulf of California.

Distribution Limits of the Geoduck Clams Panopea generosa and P. globosa on the Pacific Coast Of Mexico

ABSTRACT Two species of geoduck clams, Panopea, are known from the Pacific coast of Mexico: P. generosa, also present in the temperate areas along the western coast of North America, and P. globosa, originally considered endemic to the Gulf of California. Often regarded as a temperate and a tropical species, their respective distributions were assumed to be clearly separate. However, commercial interests recently found populations in the temperate-tropical transition zone, thus raising doubts regarding their taxonomic identity and the distribution limits of each species. Discriminant function analysis was used to examine the morphological characteristics of the shells of individuals from nine locations to identify their species and to re-examine the distribution limits of Panopea spp. in this region. Results show that the tropical limit in the distribution of P. generosa is the western coast of the Baja California Peninsula, south to at least Punta Canoas (29°43′N). It was found that the distribution of P. globosa not only includes the Gulf of California but extends to at least Bahía Magdalena (24°38′N) on the western coast of the peninsula. This is the first report of P. globosa outside of the Gulf of California, thus extending its distribution to more temperate areas.

Recent trends in sea surface temperature off Mexico

Changes in global mean sea surface temperature may have potential negative implications for natural and socioeconomic systems; however, measurements to predict trends in different regions have been limited and sometimes contradictory. In this study, an assessment of sea surface temperature change signals in the seas off Mexico is presented and compared to other regions and the world ocean, and to selected basin scale climatic indices of the North Pacific, the Atlantic and the tropical Pacific variability. We identified eight regions with different exposure to climate variability: In the Pacific, the west coast of the Baja California peninsula with mostly no trend, the Gulf of California with a modest cooling trend during the last 20 to 25 years, the oceanic area with the most intense recent cooling trend, the southern part showing an intense warming trend, and a band of no trend setting the boundary between North-Pacific and tropical-Pacific variability patterns; in the Atlantic, the northeast Gulf of Mexico shows cooling, while the western Gulf of Mexico and the Caribbean have been warming for more than three decades. Potential interactions with fisheries and coastal sensitive ecosystems are discussed.

Modeling Geoduck Growth: Multimodel Inference in Panopea globosa from the Southwestern Baja California Peninsula, Mexico

ABSTRACT Studies about individual growth for geoducks are relevant because they allow an understanding of biomass production and its maintenance in the population. This study presents the first growth curves for Panopea globosa from the southwestern Baja California Peninsula. Geoduck samples were collected from November 2006 to October 2007 in Bahía Magdalena (n = 392). The morphological data for live individuals were obtained and their ages were estimated from the right shell by counting band growth from a thin section cut from the hinge plate region. The length-at-age data were fitted to six growth models—Gompertz, Johnson, von Bertalanffy growth model (VBGM), generalized VBGM, Richards, and Schnute—using a negative log-likelihood function. The models were analyzed using multimodel inference to select the best candidate growth model based on the Akaike information criterion. The results indicate the size structure from Bahía Magdalena has a unimodal shape and shows negative allometric growth in the relationship between shell length and total weight (b = 2.4). Shell lengths varied from 93–206 mm and total weight ranged from 332–2824 g. Age validation was based on the marginal increment ratio, and suggested the growth line and band were deposited annually. Growth line formation occurred annually between January and April, and the growth band was deposited from June to December. A dominance of older year classes, from 13–22 y, was noted along with an estimated maximum age of 47 y. Based on multimodel inference, the Gompertz growth model was the best candidate for estimating growth for P. globosa. The estimated parameters included an asymptotic size of 167.51 mm, the rate at which the asymptotic size was reached was 0.218, and the age at size 0 was 0.003. These growth parameters for P. globosa from the southwestern of the Baja California Peninsula show the length at age in this region is greater than in the central Gulf of California, suggesting that management rules must be based regionally.

Trophic spectrum and feeding pattern of cannonball jellyfish Stomolophus meleagris (Agassiz, 1862) from central Gulf of California

The diet and feeding pattern of scyphomedusa Stomolophus meleagris (Rhizostomeae) was studied, by comparing stomach samples from different developmental stages and environmental zooplankton with the aim to determine diet composition, trophic niche breadth, selectivity and feeding overlap of this edible jellyfish species. Samplings were performed during April and December 2010 and in January 2011, in the coastal lagoon Las Guasimas (27°49′–27°54′N 110°40′–110°35′W), central Gulf of California, which consisted of zooplankton tows and jellyfish collections for stomach content. More than 39 prey items were identified in the gut contents (N = 69), from which eight taxa formed over 90% of the total. Fish eggs were considered main prey (58.6%), copepods (10.8%), veliger larvae of gastropod (13.0%) and bivalve (12.7%) were secondary prey while cirriped and decapod larvae were incidental prey ( S. meleagris is a specialist predator and Pearres index showed positive selection of fish eggs, gastropods, bivalves and cirripeds while selectivity was negative for copepods and appendicularians. The relative timing of these changes suggests that ontogenetic processes are closely related with shift in the diet, which indicates increasing predation pressure during development of the medusoid stage of this species, thus emphasizing their ecological importance in coastal ecosystems.

Genetic Structure of the Cortes Geoduck Panopea globosa Dall, 1898, from the Mexican Northwest

ABSTRACT The geoduck Panopea globosa is found on the Pacific coast of Baja California south of Bahia Magdalena Bay and throughout the Gulf of California, and sustains a vibrant and growing fishery. Despite morphometric analyses that suggest populations from the Pacific are distinct from those inside the Gulf of California, it is unclear whether populations are connected via larval dispersal and gene flow throughout its range. Thirteen microsatellite loci were used to estimate levels of genetic diversity and to evaluate genetic connectivity patterns among four exploited populations, including clams from the Pacific (Bahia Magdalena) and the Gulf of California (San Felipe, Puerto Peñasco, and Guaymas). Geoducks from Bahia Magdalena showed significant genetic differentiation from populations inside the Gulf of California, particularly when compared with San Felipe and Puerto Peñasco. Gene flow and inferred larval dispersal were found to be predominantly unidirectional, and followed the typical anticyclonic (clockwise) circulation of the northern Gulf of California during late fall and winter when geoducks spawn. San Felipe is located upstream relative to the oceanographic flow and has the largest effective population size. This population also showed evidence of local retention of larvae and may serve as the main source of larvae to downstream populations that show a gradient of reduced diversity and population size along the direction of the prevailing flow. The asymmetry found in connectivity patterns has implications for distributing the fishery effort and no-take zones in the Gulf of California to increase sustainability.

Geoduck Panopea generosa Growth at Its Southern Distribution Limit in North America using a Multimodel Inference Approach

ABSTRACT The Pacific geoduck Panopea generosa is distributed throughout the North Pacific temperate zone from Alaska to Baja California and is described as a species that reaches large sizes, has prolonged longevity, and exhibits slow growth. This study assessed the individual growth and population structure of the P. generosa population located at its southernmost geographic distribution limit. Shell length and total weight data were obtained from a commercial fishery established on Punta Canoas, Baja California. Individual age was determined by counting growth lines for 243 organisms. The results revealed the following averages: shell length (SL), 113.5 mm; total weight, 511.8 g; age, 12.5 y. The relationship of SL to total weight showed negative allometric growth (b = 2.16). Size-at-age data were adjusted to von Bertalanffy, Gompertz, logistic, Johnson, and Schnute growth models according to the multimodel inference (MMI) approach. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Schwartz—Bayesian criterion (SBC). The AIC indicated that the Schnute growth model was the best candidate growth model, whereas the SBC showed the Johnson growth model was best. These growth models indicate that between 7 y and 8 y of age, organisms reach 75% of their estimated asymptotic length (SL, ∼103 mm), and although the growth rate decreases subsequently, growth continues up to 25 y (maximum age observed). The MMI approach applied to the analysis of growth in Panopea species identified particular population attributes that are not observable via the von Bertalanffy model. The population of P. generosa from Punta Canoas exhibited smaller mean SL, lower mean weight, an age structure with fewer age classes, and slower growth when compared with northern populations in Washington state and British Columbia, Canada.

Satellite measured interannual variability of coastal phytoplankton pigment in the tropical and subtropical eastern Pacific

Abstract Interannual variability of phytoplankton biomass, measured as phytoplankton pigment concentrations (PPC) by the Coastal Zone Color Scanner (CZCS), was compared for eight selected, productive areas along the Pacific coast of Central America, Mexico, and California for 1980–1986. Monthly anomalies series were analyzed by means of principal components analysis (PCA) followed by varimax rotation, to identify spatially coherent variability between areas as indicative of El Nino forcing. PPC decreased during the 1982–1983 El Nino in all areas; however, there were regional differences in variability between the southern (tropical) areas and the northern (subtropical). In the southern areas the decrease occurred during 1982, but for the northern areas this was not observed until mid-1983. Results suggest the recovery of phytoplankton to pre-El Nino was larger and occurred earlier in the south as compared to the north. The same analysis was used for comparing sea surface temperature and sea level height series from the same areas, resulting in regional differences that were related to the two regional modes of chlorophyll variability. These were also investigated in relation to wind-driven upwelling (WDU). Unlike the other physical variables, upwelling showed little coherent variability between areas and was not clearly related to the major interannual changes of phytoplankton biomass during the period.