Browsing by Author "Igulu, Mathias"

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    Freshwater Inflows for the Wami River Estuary, Saadani National Park, Tanzania
    (2016-02) Saha, Amartya K.; Kashaigili, Japhet; Mashingia, Fredrick; Kiwango, Halima; Igulu, Mathias; Kimaro, Michael; Hyera, Pendo; Evarist, Roman; Tamatamah, Rashid; Abbott, Vivienne
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    Mangrove Fish Production is Largely Fuelled by External Food Sources: A Stable Isotope Analysis of Fishes at the Individual, Species, and Community Levels from Across the Globe
    (2013) Mgaya, Yunus D.; Van der Velde, Gerard; Nagelkerken, Ivan; Igulu, Mathias
    Coastal ecosystems are energetically connected through passive transport of nutrients but also by migrations of motile organisms. Mangroves are highly productive tropical ecosystems that replenish offshore populations of many species, but we know little about the degree to which this production is fuelled by prey from mangroves, especially in the cases in which mangroves are only accessible at high tide. Different results have been obtained on the importance of mangroves as feeding habitats, confounded by differences in species composition, seascape configuration, and methodology. In the present study, we took a more holistic approach by exploring reliance by fishes on mangroves as a feeding habitat at multiple ecological levels: from individuals to species to communities in mangrove ecosystems from across the globe, using a stable isotope approach. A two end-member mixing model showed a wide range (12–72%) in degree of reliance on mangrove food sources by fishes from different studies across the globe. However, analyzed at the levels of individual fish and species, reliance was low (for example, <25% for 55% of the species worldwide, or <50% for 85% of species, respectively) even though they were collected from sites that differed in geographical location, tidal regime, seascape structure, and species composition. The high fisheries productivity of mangroves appears to be energetically supported largely by food sources from adjacent habitats. In light of the ongoing rapid demise and fragmentation of mangrove and adjacent ecosystems, loss of ecosystem connectivity is likely to affect the productivity and functioning of tropical coastal ecosystems and the services they pro
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    Orientation from open water to settlement habitats by coral reef fish: behavioral flexibility in the use of multiple reliable cues
    (2013) Igulu, Mathias; Nagelkerken, Ivan; van der Beek, M.; Schippers, M.; van Eck, R.; Mgaya, Yunus D.
    Most coastal marine organisms have a dispersive oceanic larval stage, during which they must be able to distinguish and respond to relevant environmental cues when settling into their first benthic habitat. Chemical stimuli emanating from settlement habitats and being dispersed by water plumes could enable long-distance navigation by larval reef fish, but we know little about the cues responsible and their interactive effects. In the present study, we tested this by conducting several ex situ choice experiments in which the response of the coral reef fish Lutjanus fulviflamma towards different chemical cues from coastal habitats was tested close to their settlement stage. Fish preferred seagrass habitat water over that from coral reef and mangrove habitats. Furthermore, fish were attracted to chemical cues from their own species (conspecifics) and other fish species, as well as vegetation of 4 different seagrass species, when offered in isolation (i.e. soaked in neutral water), but a strong response remained only towards cues from conspecifics and seagrass leaves when these cues were mixed with seagrass habitat water that naturally contains other cues. Hierarchical effects were observed as fish preferred chemical cues from seagrass leaves over those from conspecifics when both were offered at the same time. The importance of visual habitat cues only overruled that of chemical cues when it concerned preferred cues (i.e. seagrass as opposed to mangrove cues). Our findings indicate that pelagic fish and settlers possess the ability to use multiple reliable chemical cues to locate suitable early life stage habitats, although the importance of these cues is context-dependent. Nevertheless, this flexibility in choice behavior is probably an adaptive strategy to enhance fitness by increasing successful orientation towards preferred settlement habitats.
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    The potential role of visual cues for microhabitat selection during the early life phase of a coral reef fish (Lutjanus fulviflamma).
    (2011) Mgaya, Yunus D.; Ligtenberg, H.; van Hintum, R.; Fraaije, Rob; Nagelkerken, Ivan; Igulu, Mathias
    Pelagic larvae of various coral reef fish species are known to be active swimmers that can carefully select preferred microhabitat during settlement. Fish larvae may use visual, environmental, or chemical cues to orient and settle in shallow-water habitats such as coral reefs, mangroves, and seagrass beds. In the present study, we investigated in dual-choice laboratory experiments the visual attraction of recent settlers of a reef fish (Lutjanus fulviflamma) towards different microhabitats, conspecifics, and heterospecifics, and the interactive effects among these cues. Fish preferred seagrass and coral above mangrove roots. Fish were more attracted towards a combination of conspecifics or heterospecifics and seagrass microhabitats than to seagrass microhabitats alone, but showed a significantly stronger preference for conspecifics than for heterospecifics when placed in preferred seagrass or non-preferred mangrove microhabitats. However, the preference for conspecifics disappeared when choice was given between conspecifics placed in non-preferred mangrove microhabitat versus heterospecifics placed in preferred seagrass micro habitat. A multiple choice experiment further showed that recent settlers preferred conspecifics of equal or about 1cm larger body size, but not of 2 or 3cm larger body size. The higher attraction towards the combination of seagrass microhabitats and conspecifics/heterospecifics shows an additive effect of the latter, which could be explained by the fact that presence of resident fish in preferred habitat may indicate favorable conditions in the field and may offer an increased safety through schooling. However, (1) attraction towards conspecifics of (nearly) similar body size and not larger, (2) stronger attraction towards conspecifics in a non-preferred than in a preferred microhabitat, and (3) equal attraction towards conspecifics in non-preferred microhabitat vs. heterospecifics in preferred microhabitat all indicate that the importance of schooling with conspecifics is highly context-dependent. This may have significant effects on the habitat selection and distribution of early-stage fish (and thus also on consecutive life stages) in coastal habitats. Our findings point to the potential ecological significance of various visual cues, and their interactive effects, for early juvenile coral reef fishes while settling into shallow-water habitats and/or selecting early post-settlement habitats.