Larval Fish Assemblage Structure at Coastal Fronts and the Influence of Environmental Variability

Abstract

Within the coastal zone, oceanographic features, such as fronts, can have major effects on the abundance and distribution of larval fish. We investigated the effects of fronts on larval fish assemblages by jointly collecting physical (ADCP and CTD) and biological (larvae) data in the nearshore waters of the south coast of South Africa, on four separate neap-tide occasions. Accumulation of fish larvae at predominantly internal wave-associated fronts was observed, with higher larval densities inshore of and within the front than farther offshore. On each occasion, larvae of coastal species with pelagic eggs (Mugillidae and Sparidae) were numerically dominant at the front itself, while inshore of the front, larvae of coastal species with benthic eggs (Gobiesocidae and Gobiidae) were more abundant. Offshore catches mainly comprised Engraulidae (pelagic species with pelagic eggs) larvae, which were generally restricted to the bottom, where current velocities were onshore on each occasion. On the occasion when fast (>100 cm/s) currents prevailed, however, accumulation of the larvae of coastal species occurred offshore of the front, and larvae were mixed throughout the water column. Thus, larval occurrence at these coastal frontal systems was strongly affected by the degree of mixing by currents, which on most occasions resulted in onshore retention. The results underline the importance of frontal systems in determining the nearshore distributions of fish larvae, particularly by retaining coastal fish species in the inshore region. The environmental variability observed at these frontal systems has potential implications for larval connectivity of fish populations.

Lateral Border of a Small River Plume: Salinity Structure, Instabilities and Mass Transport

“…The interactions between river plumes and ambient sea are important for understanding land-ocean fluxes of fluvial water and river-borne dissolved and suspended matter. Structure and circulation at the plume border play an important role in transport of fine terrigenous sediments [7][8][9][10][11][12][13] and floating matter, including river-borne marine litter and microplastic [14][15][16][17], fish larvae [18][19][20][21], etc. However, many processes at the plume-sea interface remain understudied, especially those with small spatial and temporal scales.…”

Assessing the Conservation Value of Artificial and Natural Reefs via Ichthyoplankton Spatio-Temporal Dynamics

“…To surmise the fish species, the study reefs were used as breeding grounds, and fish eggs were quantified based on 11 stages of embryonic development [46]: early development (stages 1-5), medium development (stages 6-8), and late development (9)(10)(11). Fish larvae were classified according to the development of the notochord in stages of yolk-sac, preflexion, flexion, and post-flexion [47,48].…”

Environmental Heterogeneity Determines Diatom Colonisation on Artificial Substrata: Implications for Biomonitoring in Coastal Marine Waters

“…Triplicate (500 ml) water samples were collected at the same depth as the cages for inorganic nutrient determinations. The water samples were gravity-filtered through Whatman R GF/F filters (47-mm diameter, 0.7-µm pore size) in the laboratory, the filters and filtrates were immediately frozen at −20 Bate and Heelas (1975) and Parsons et al (1984). Water column chlorophyll-a (Chl-a-used as proxy for phytoplankton biomass) was extracted from the GF/F filters using 10 ml of 95% ethanol (Merck R 4111) for 24 h at ∼2 • C in the dark.…”