Spawning and nursery areas of Sardinops sagax (Pacific sardine) and Engraulis mordax (northern anchovy) were characterized during early winter in the Gulf of California, using near-surface horizontal and oblique Bongo tows. The main spawning area for anchovy was located near the islands of Tiburón and Ángel de la Guarda and for sardine near both coasts on either side of the central region of the gulf. A hydroacoustic survey showed a close spatial overlap between the distribution of small pelagic fish schools, their spawning areas and areas with the highest zooplankton biomass. Distribution and abundance of eggs and distinct larval stages showed that the nursery area is considerably larger than the spawning area. Sardines and anchovies had distinct inter-specific larval drift patterns, mostly caused by differences in the spawning locations that were influenced by regionally distinct advection caused by coastal upwelling, filaments and eddies. Abundance of eggs and early larvae of both species were closely associated with higher abundance of fucoxanthin and chlorophyll a, zooplankton biomass and the small copepod Acartia clausi. Older larvae were mostly associated with abiotic environmental variables and large-sized copepods, such as Centropages furcatus and Calanus pacificus. These results suggest the importance of sequential spatial overlap of larvae with food availability as they drift in the Gulf of California.

This study analyzed seasonal and interannual variations in larval fish abundance in Cabo Pulmo National Park (CPNP) from January 2015 to November 2017, encompassing the 2015–2016 El Niño and subsequent thermal relaxation, to examine the impacts of climate-driven events on larval fish abundance, diversity, and species richness in a no-take marine protected area. A total of 166 larval fish taxa were identified, spanning 59 families, 94 genera and 98 species. Dactyloscopidae spp. (relative frequency: 41.7%; abundance: 9.9%), Auxis spp. (32.3%, 7.3%), Abudefduf troschelii (24%, 4.7%), Syacium spp. (17.7%, 3.9%) and Tripterygiidae spp. (12.5%, 2.8%) were the most frequent and numerically dominant taxa, after excluding 13 mesopelagic and bathypelagic species not typically found in CPNP’s shallow waters as adults. Although larval fish assemblages responded to short-term seasonal fluctuations (quarterly and semi-annual), we found that fish larvae abundance, diversity and species richness (independently of their biogeographic and habitat affinity) declined during the 2015–2016 El Niño compared to both the period before El Niño and the subsequent thermal relaxation (June 2016–November 2017). These findings highlight their vulnerability to El Niño-driven oceanographic changes, with implications for the resilience of these populations in the context of a changing climate.

The distribution of fish eggs and larvae (ichthyoplankton) reflects spawning and nursery areas as well as dispersal routes. This study’s goal is to demonstrate how the identification of ichthyoplankton species and stages and their spatial distribution among natural reefs (NRs) and artificial reefs (ARs) may serve as decision-making tools in conservation and fishery management. Natural reefs exhibited an eight-times higher abundance of eggs, as well as the highest abundance of larvae in the yolk-sac and preflexion phases. In contrast, ARs had the highest abundance of larvae in the flexion and postflexion phases. Natural reefs may serve as breeding grounds for Scaridae, Labridae, and Mugilidae; whereas, ARs may serve as breeding sites for Lutjanidae, Synodontidae, Carangidae, Fistularidae, and Haemulidae. Our study revealed differences between ARs and NRs, which demonstrate the potential of artificial reefs to expand the supply and settlement options of reef fishes and consequently can lead to increased fish production with potential benefits to adjacent fishing areas through connectivity. Thus, ARs as no-take sites can be effective tools for both fishery management and biodiversity conservation. The findings highlight the potential use of ichthyoplankton tools and the importance of considering both types of reefs in marine conservation and management efforts.

<!--Galleys --> <!--Full Text:--> PDF <!--END GALLEYS---> Abstract In fish, the larval stage constitutes the most vulnerable phase in the life cycle and reveals important ecological and evolutive information of fish and fundamental data to manage marine ecosystems. However, their identity is one of the biggest gaps in knowledge, particularly for the Microgobius genus, where only three of 15 species have been described. In this study, the larval development of Microgobius tabogensis was described based on 116 specimens (2.75-14.20 mm standard length) from Ensenada de La Paz, Mexico. The typical gobiid body shape characterized larvae, a well-developed dorsally pigmented gas bladder, a curve at the hindgut, and 27 myomeres. The pigmentation pattern in M. tabogensis consisted of a series of melanophores along the ventral postanal midline, increasing from three to seven during the preflexion stage and up to 16 in the postflexion stage. It had three to five melanophores on the ventral preanal midline, one at the jaw angle and one on the dorsal postanal midline. Through all stages, one of the ventral melanophores was normally stellate, bigger than the others, and extended between the myomeres. A dorsal melanophore was located near the end of the intestine in the preflexion stage but disappeared with growth. Notochord flexion started at approximately 4.3 mm and ended at 5.1 mm. Anal fin development started at the beginning of the flexion stage, followed by the dorsal fin. All elements of the fins were formed by the late postflexion stage (14.2 mm).

The development of Opistognathus rosenblatti from larvae to juveniles is described using 60 specimens (3.6-47.0 mm LP). Adults were captured in the Loreto Bay Marine Park, Gulf of California, Mexico. They were conditioned and bred in captivity. Changes from larva to juvenile in morphological, meristic, and pigmentation pattern characters were described from specimens preserved in formalin solution (4%). Meristic data of larvae and juveniles were 27-29 total myomeres, XI, 13 dorsal fin, II, 13 anal fin, 8+7-9 caudal fin, and 5 hypural bones. The pigmentation pattern of the larvae from preflexion to postflexion stage consisted of: A cephalic region with small melanophores on the dorsal surface of the brain, on the lower margin of the nasal capsule, on the lateral surface of the lower and upper jaws, on the nape, and the gular region; abdominal region with a series of melanophores on the intestinal sac margins, including the swim bladder; the trunk region with few melanophores in the last myomeres; caudal region with three series of stellate melanophores on the dorsal, ventral margins and medial-lateral section between myomeres 1-14. Other stellate melanophores were present throughout this section, which interlaced towards all margins, providing a very light brown coloration on this section of the body. The juvenile is yellow-orange, with small punctate melanophores that extend across its entire body surface. It also exhibits four discontinuous series of brown spots (circular to oval) extending from the ventral-posterior margin of the eye to the height of the tips of the bases of the dorsal and anal fins. The conjunction of pigmentation patterns, myomeres count, and fin meristics is a distinctive identifier for O. rosenblatti larvae and juveniles, as it is not observed in the larvae of other fish species.