Estuary-associated Species Research Articles

The Vulnerability of South African Estuaries to Climate Change: A Review and Synthesis

This review evaluates the vulnerability of South African estuaries to Climate Change in a data-limited environment. The regional-scale assessment is based on physical characteristics and predicted/measured changes in the abiotic drivers and ecosystem responses. The major Climate Change stressors were identified in order of importance as change in climatic and hydrological processes, ocean circulation and temperature regimes, sea level rise, increase in frequency and intensity of sea storms, and ocean acidification. Flow-related ecosystem responses included changes in mouth state, salinity regimes, biochemical regimes (nutrient fluxes), and floods and related sediment deposition/erosion cycles. The regional vulnerability assessment provides a summary of the key shifts scaled as high, medium, and low in estuary state. Changes in oceanic processes and temperature regimes drive shifts in nearshore temperatures of the transitional zones, with related ecological responses (e.g., range expansion). However, most structural and functional changes are expected along cool temperate and subtropical biogeographical regions, leading to notable shifts in mouth closures and salinity regimes, which in turn will affect estuary function and estuary-associated species. Monitoring and management of resources (e.g., fresh water and fisheries allocations) need to consider this in long-term planning.

A comparative study of Northern Ireland's estuaries based on the results of beam trawl fish surveys

The fish communities of Northern Ireland's estuaries were described and compared using data collected with a modified beam trawl over a six year period from 2009 to 2014. Multivariate analyses identified four estuary groups based on variations in their physico-chemical attributes. These groups broadly corresponded with the distribution and variation of estuary geomorphic types identified around the Irish coast. The dominant fish species captured were also among the main species reported in other North East Atlantic estuaries. A significant link between the estuary types and their fish communities was found; each estuary group contained a somewhat distinctive fish community. The fish communities also showed a significant relationship with the physico-chemical characteristics of the estuaries. Differences in fish species composition are attributed to habitat and environmental preferences of key estuary-associated species.

Effects of climate change on South African estuaries and associated fish species

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 57:233-248 (2013) - DOI: https://doi.org/10.3354/cr01178 REVIEW Effects of climate change on South African estuaries and associated fish species Nicola C. James1,*, Lara van Niekerk2,3, Alan K. Whitfield1, Warren M. Potts4, Albrecht Götz3,5, Angus W. Paterson1 1South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa 2CSIR, Natural Resources and the Environment, PO Box 320, Stellenbosch 7599, South Africa 3Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa 4Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown 6140, South Africa 5Elwandle Node, South African Environmental Observation Network (SAEON), Private Bag 1015, Grahamstown 6140, South Africa *Email: n.james@saiab.ac.za ABSTRACT: Estuaries are dynamic and their physical and chemical characteristics can change over a scale of hours to years. Consequently, estuarine fish assemblages often exhibit large temporal variations in abundance and composition related to changes in a range of parameters such as river flow, estuarine mouth phase, habitat availability, temperature, salinity and turbidity, all of which are likely to be highly affected by climate change. Many organisms become more stressed towards their range boundaries and the distributions of these species can be expected to shift as environmental conditions change. Preliminary studies have highlighted the increased occurrence of tropical fish species in estuaries along the southeast coast of South Africa. Climate change is also predicted to alter precipitation patterns, which will affect the quality, rate, magnitude and timing of freshwater delivery to estuaries, and will potentially exacerbate existing human modifications of these flows. This is likely to result in changes to fish communities, as river flow has been found to have a major impact on the structure and functioning of fish communities in South African estuaries. The predicted increase in the frequency of extreme weather events, together with sea level rise, may result in a loss of estuarine habitat, which will ultimately affect estuarine fish communities and have implications for fisheries targeting estuary-associated species. KEY WORDS: South Africa · Climate · Change · Estuaries · Impacts · Fishes Full text in pdf format PreviousNextCite this article as: James NC, van Niekerk L, Whitfield AK, Potts WM, Götz A, Paterson AW (2013) Effects of climate change on South African estuaries and associated fish species. Clim Res 57:233-248. https://doi.org/10.3354/cr01178 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 57, No. 3. Online publication date: October 28, 2013 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2013 Inter-Research.

Choice chamber experiments to test the attraction of postflexion Rhabdosargus holubi larvae to water of estuarine and riverine origin

Although the recruitment of larvae and juveniles of marine fishes into estuaries has been well documented, little is known about the factors governing the immigration of estuary-associated marine fishes into estuaries. Fishes have a well-developed sense of smell and it has been suggested by several workers that olfactory cues of freshwater or estuarine origin serve as stimuli, attracting larvae and juveniles of estuary-associated species into estuaries. Attraction of postflexion Rhabdosargus holubi larvae to estuary and river water from the Kowie estuarine system, South Africa, was measured using a rectangular choice chamber. In experiments, conducted during peak recruitment periods, larvae selected estuary and river water with a significantly higher frequency than sea water. This study, the first to assess the possible role of olfaction in the recruitment process of an estuary-associated marine fish species, demonstrates that larvae are able to recognise water from different origins, probably based on odour.

Laval and Juvenile Fishes in the Surf Zone Adjacent to the St Lucia Estuary Mouth, KwaZulu-Natal, South Africa

Composition, seasonality and developmental stages of larval and juvenile fish in the surf zone adjacent to the St Lucia Estuary mouth, KwaZulu-Natal, were investigated. Samples were collected monthly, from February 1992 to January 1993, at six stations along the beach north of the estuary mouth. A 24-h study was also undertaken in the surf zone when the estuary mouth was closed. In the 12-month study a total of 2931 larvae, representing 88 taxa and 47 families, was collected. The most abundant families were the Sparidae, Haemulidae, Ambassidae, Tripterygiidae and Chanidae, together comprising 64.2% of the total catch. The most abundant species were Pomadasys olivaceum, Ambassis sp. and Rhabdosargus holubi. In the 24-h study a total of 13731 larvae, representing 43 taxa and 22 families, was collected and was dominated by Ambassis sp., Croilia mossambica and Chanos chanos. Temperature and turbidity were the most important environmental variables related to fish densities of estuary-associated species. Temporal changes in fish densities were most significant for daylnight catches, with densities being significantly higher at night than during the day. Fish species associated with estuaries peaked in abundance in mid autumn and late winter. Spatial trends in fish densities indicated significantly higher densities of estuary-associated species at Stations 2 and 3, with densities decreasing thereafter away from the estuary mouth. Larval stages were predominantly postflexion for all months sampled. The total catch was dominated by marine spawner species, with 36% of all taxa having some degree of estuarine association. Species with some degree of estuarine association dominated the catch in terms of density during both the 12-month study (60%) and the 24-h study (83%). Results from this study indicate that the surf zone adjacent to the St Lucia Estuary functions as a transit route and a nursery habitat for certain estuary- and non-estuary-associated fish species.

Differences in the structures of fish assemblages inThalassia testudinum beds in Guadeloupe, French West Indies, and their ecological significance

The structures of fish assemblages in twoThalassia testudinum beds in Guadeloupe, French West Indies, one adjacent to mangroves and the other adjacent to coral reefs, were compared between January 1983 and May 1984. The aim of the study was to compare the influences of mangroves and coral reefs on the utilization of seagrass beds by fishes through examination of species composition, catch rate, size of fishes and temporal changes. The two fish assemblages were similar in terms of the number of species they had in common (nearly 44% of the total number of species collected) and the great abundance of juveniles. They both comprised species that usually inhabit other habitats, i.e., estuaries, open waters or coral reefs. Estuary-associated species (e.g. Gerreidae) were the most abundant species in the seagrass bed near the mangroves, while small pelagic species (e.g. Clupeidae) were the most abundant species in the seagrass bed near the coral reefs. The seagrass bed near the mangroves was preferentially utilized as a nursery area by small juveniles of various species (e.g. Clupeidae, Sparidae, Gerreidae, and at least one coral reef species,Ocyurus chrysurus). The abundance of these species varied frequently, suggesting successive arrivals and departures of juveniles over time. The seagrass bed near the coral reefs was characteristically utilized by fishes that are more able to avoid predation, i.e., fishes that forage over seagrass beds at night and shelter in or near the coral reefs during the day (large juveniles of coral reef species and adults of schooling pelagic species, respectively). The constant migrations of these fishes between the coral reefs and seagrass beds explained the relative stability of the structure of the fish assemblage in the seagrass bed over time. Thus, the two seagrass beds were not equivalent habitats for fishes. The distinct ecological influences of the mangroves (as a nursery for small juveniles) and coral reefs (as a shelter for larger fishes) on the nearby seagrass beds was clearly reflected by the distinct utilizations of these seagrass beds by fishes.