Selection of a spawning aggregation site by Chromis hypsilepis (Pisces: Pomacentridae): habitat structure, transport potential, and food availability

Abstract

Spawning aggregations form when fishes migrate to a site from their normal feeding grounds and form temporary groupings for breeding. Spawning aggregation sites are spatially rare, and demonstrating differences between a spawning aggregation site and unselected sites nearby is the first step towards understanding the benefits provided by the aggregation site. Chromis hypsilepis (Pomacentridae) is a demersally spawning reef fish, one population of which reproduces in a large, single aggregation at a rocky reef off the central coast of New South Wales, Australia. This study compared the habitat structure (rugosity, reef slope, substratum particle size, and abundance of preferred spawning microhabitat) of the spawning aggregation site and several non-spawning sites, and tested the hypotheses that the spawning aggregation site provided greater off-reef larval transport and prey availability for brooding males. Substratum rugosity was significantly greater and the preferred spawning microhabitat was significantly more abundant at the spawning aggregation site. Reef relief and substratum particle size were not significantly different from non-spawning sites. Passively drifting surface current drogues released at the spawning aggregation site were more rapidly transported off the reef, but did not travel further or faster, than drogues released at a nonspawning site over a 12 h period. Biomass of the preferred prey (copepods of 0.441 to 1.49 mm equivalent spherical diameter) was not significantly greater, but was less variable, at the spawning aggregation site.

Reproductive output traits of the simultaneous hermaphrodite <I>Serranus scriba</I> in the western Mediterranean

“…Diel periodicity or time of spawning will affect reproductive success through the probability of fertilization, rates of predation, and dispersion of eggs and larvae (Yamahira 2001, Cowen et al 2006, Gladstone 2007. Assuming eggs are at a neutral buoyancy up to 3 hours after being spawned at sunset, it would take the eggs a maximum of 9.5 h (if spawned at 40 m, the maximum depth for this species) to reach the surface, corresponding to sunrise during the summer period.…”

Non-Consumptive Effects of Predators in Coral Reef Communities and the Indirect Consequences of Marine Protected Areas

“…Inside protected areas there was greater structural complexity, territories were smaller and had food resources with greater nutritional quality relative to unprotected sites. For many coral reef fish, sites with high substratum rugosity are a preferred microhabitat for spawning aggregations (Gladstone 2007), although we could not detect a direct relationship between structural complexity and the frequency of spawning. Furthermore, males may be more likely to encounter and thus spawn with harem females in smaller territories, which we found in protected areas, and greater food quality, which we also found in territories in protected areas, may allow males to meet the energetically expensive demands of spawning.…”

“…This would provide an added benefit for S. aurofrenatum in choosing high complexity regions to establish their territories. Thus, more complex areas are likely more desirable as a feeding and breeding habitat for S. aurofrenatum, as has been demonstrated in other reef fish (Gladstone 2007). As coral cover declines (Gardner et al 2003) and reef complexity is lost ), our data suggests that there also may be an associated loss of key habitat types for territorial species.…”

“…Furthermore, males may be more likely to encounter and thus spawn with harem females in smaller territories, which we found in protected areas, and greater food quality, which we also found in territories in protected areas, may allow males to meet the energetically expensive demands of spawning. Additionally, there are other factors occurring at different spatial and temporal scales that we did not measure that can influence spawning activity of coral reef fish including reef size, the availability of suitable spawning sites, and the potential for successful transport of gametes (Johannes 1978, Warner 1984, Gladstone 2007. These factors likely varied among study sites, individual territories, and sampling days, making it challenging to identify the specific individual drivers of spawning activity.…”

Seasonal changes in size, sex-ratio and body condition of the damselfishChromis chromisin the central Mediterranean Sea

“…Since investing energy in parental care is advantageous for males only when it increases their reproductive success by affording a higher number of hatched eggs (Gladstone, 2007b), when the number of eggs within a nest is low, or when no female lays her eggs in a nest, males may adopt alternative brooding strategies (Taborsky, 1998(Taborsky, , 2001. In this framework, the evaluation of the number of males feeding in the water column may be taken as an instrument to assess the length and the intensity of reproductive activity.…”