Abstract
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.
Highlights
The zooplankton community has been intensively studied in the northern regions of the California Current System (CCS), but off Baja California it has received less attention, in terms of taxa such as the hyperiid amphipods that comprise only a small proportion of the community and are assumed to have minimal ecological importance
This study presents evidence of intermittent occupation by hyperiids of the coastal shelf in the Gulf of Ulloa, Baja California, and possible mechanisms underlying this behavior
The study region is less populated with hyperiid amphipods compared to northern Baja California
Summary
The zooplankton community has been intensively studied in the northern regions of the California Current System (CCS), but off Baja California it has received less attention, in terms of taxa such as the hyperiid amphipods that comprise only a small proportion of the community and are assumed to have minimal ecological importance This perception may be incorrect for oceanic waters, where they are relatively abundant [1,2,3,4] and may represent attractive forage food for predators in the California Current such as small pelagic and myctophid fishes and seabirds [5,6,7]. More studies are required to quantify these crustaceans and their roles more precisely in trophic webs in tropical and subtropical seas
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