Role of environmental seasonality in the turnover of a cetacean community in the southwestern Gulf of California

Abstract

La Paz Bay is a distinct region within the Gulf of California whose rich cetacean community exhibits an intense annual overturn. We studied the environmental conditions that could drive this change over the course of a year. Cetacean biomass was estimated from monthly surveys, with concurrent collection of water-column measurements of temperature, salinity, nutrients, chlorophyll a (chl a), and biogenic matter fluxes. The water-column structure showed 3 major conditions: deep mixing during winter, stratified isopycnal shoaling in spring and early summer, and deep stratification during late summer and autumn. Chl a and relative fluxes of biogenic silica and calcium carbonate indicated a seasonal succession of primary producers in response to the observed evolution of hydrography. During the periods of mixing and isopycnal shoaling, the bay provided suitable habitat for blue whales, bottlenose dolphins, and common dolphins, while fin whales, Bryde's whales, and short-finned pilot whales were numerically dominant during the period of stratification. To provide a regional context to the observed seasonality, we fitted temporal least-squares to an 11 yr monthly time series of satellite-derived wind, sea surface temperature (SST), and chlorophyll concentration (CHL). Within the bay, the SST followed the annual monsoonal shift in the wind, whereas CHL showed a bi-modal pattern, with a main peak occurring under mixing conditions in winter and a second peak under isopycnal shoaling in spring/early summer. The regional fitting suggested that the latter period was driven by a localized intraseasonal phenomenon that could be responsible for the higher biological richness of the bay compared to the surrounding gulf.KEY WORDS: Ecological succession · Seasonal variability · Nutrient supply · Stratification · Biogenic matter fluxes · Trophic levels · Marine hotspots 487: 245-260, 2013 prey for large fauna (e.g. Wingfield et al. 2011). Although these hotspots are often detectable through remote sensing of the ocean's surface, other areas that appear oligotrophic and devoid of dynamic features at the surface may also attract large feeding predators and even influence their migration patterns (e.g. Domeier et al. 2012). In such areas, the biological production maxima may be in the subsurface in the presence of a deep/sharp thermocline, underscoring the importance of measuring hydrographic and biological parameters, both at the surface and in the water column, for the characterization of biological hotspots. Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Biophysical coupling of marine hotspots' FREE REE ACCESS CCESSMar Ecol Prog SerThe most productive areas of the Gulf of California (hereafter 'the gulf'; Fig. 1) are located along its eastern (continental) side and in the northern region due to winter upwelling and tidal mixing, respectively (Lluch-Cota 2000). The southwestern gulf (peninsular side) is comparatively less produc tive, except for La Paz B...

Estimating blue whale skin isotopic incorporation rates and baleen growth rates: Implications for assessing diet and movement patterns in mysticetes

“…It is possible that the observed variation in skin incorporation rates among zones could be influenced by water temperature [10,96–100], with higher rates in the warmer waters of GC in comparison to the CCS (Table 3). In cold waters, marine mammals reduce peripheral blood flow to maintain a constant internal body temperature, which results in a decrease of epidermal metabolism [101–103].…”

Scales and mechanisms of marine hotspot formation

“…Aggregations of mid-trophic species can be important hotspots for top predators that migrate large distances to optimize foraging opportunities (Cotte & Simard 2005, Bailey et al 2010). The mechanisms underlying trophic hotspots can include island/ seamount wake effects (Johnston & Read 2007, Morato et al 2010, up welling shadows (Nur et al 2011, Wingfield et al 2011, Pardo et al 2013, this Theme Section), wind or eddy-driven upwelling (Croll et al 2005, Atwood et al 2010, Thorne & Read 2013, this Theme Section), or bathymetric features (Croll et al 2005, Gende & Sigler 2006. Fundamentally, changes in these hotspots may have indirect consequences on ecosystem functioning that cascade through to top predators.…”

“…The decline in foraging habitat months after Hurricane Katrina suggests some hotspots, such as seagrass beds, may have been lost or disrupted by the hurricane. Pardo et al (2013) studied the role of environmental seasonality in a cetacean community within a small bay in the Gulf of California. Different species used the bay as the season progressed; periods of mixing and pycnocline shoaling resulted in increased habitat for blue whales and 2 dolphin species, while other whales were more common during periods of stratification.…”

Seasonal acoustic behavior of blue whales (Balaenoptera musculus) in the Gulf of California, Mexico

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