Gradients in coral reef fish density and size across the Barbados Marine Reserve boundary: effects of reserve protection and habitat characteristics
MR Chapman, DL Kramer 1999 Marine Ecology Progress Series. PDF “ABSTRACT: Reductions in fishing mortality within no-take coral reef marine reserves can produce gradients in the density and size of fishes across reserve boundaries. Such gradients may be affected by other factors, however, including differences in habitat quality between reserve and non-reserve areas and the movement of fish across reserve boundaries. To examine the effects of protection from fishing mortality and of habitat quality on an assemblage of exploited reef fishes, we measured the spatial patterns of fish density and size on fringing reefs near the boundary of the Barbados Marine Reserve (Barbados, West Indies) and statistically controlled for habitat correlates of fish density and size. Reserve sites supported a higher total density and size of fishes than non-reserve sites. Most species had a non-significantly higher mean density and size at reserve sites. The density and/or size of many species were correlated with the depth, rugosity, and/or substrate composition of sites. After statistically controlling for the effects of habitat correlates, the difference in total density between reserve and non-reserve sites remained significant, and the mean density and size of most species remained non-significantly higher at reserve sites. Neither the mobility of species nor their vulnerability to capture by Antillean fish traps was correlated with their relative difference in density or size between reserve and non-reserve sites. Spearfishing target species had a significantly higher relative difference in size between reserve and non-reserve sites than non-target species. Protection from fishing mortality and higher habitat quality appear to contribute to the increased density and size of fishes on study reefs in the Barbados Marine Reserve, and this difference is not compromised by emigration from the reserve.”
Indirect effects of overfishing on Caribbean reefs: sponges overgrow reef-building corals
Loh et al., 2015 in peerJ “..Here, we show an explicit indirect effect of overfishing on competition between sponges and reef-building corals from surveys of 69 sites across the Caribbean…Leveraging the large-scale, long-term removal of sponge predators, we selected overfished sites where intensive methods, primarily fish-trapping, have been employed for decades or more, and compared them to sites in remote or marine protected areas (MPAs) with variable levels of enforcement. Sponge-eating fishes (angelfishes and parrotfishes) were counted at each site, and the benthos surveyed, with coral colonies scored for interaction with sponges. Overfished sites had >3 fold more overgrowth of corals by sponges, and mean coral contact with sponges was 25.6%, compared with 12.0% at less-fished sites…These results validate the top-down conceptual model of sponge community ecology for Caribbean reefs, as well as provide an unambiguous justification for MPAs to protect threatened reef-building corals. ..An unanticipated outcome of the benthic survey component of this study was that overfished sites had lower mean macroalgal cover (23.1% vs. 38.1% for less-fished sites), a result that is contrary to prevailing assumptions about seaweed control by herbivorous fishes.
Effects of trap fishing on reef fish communities
Julie P. Hawkins et al., 2006. “Trap fishing is widespread on coral reefs but the sustainability of this practice is causing concern because it is efficient and unselective. The effects of trap fishing were investigated by comparing fish assemblages among six Caribbean islands subject to different trapping pressures. These ranged from none in Bonaire and Saba increasing through Puerto Rico, St Lucia, Dominica and Jamaica respectively.Fish were censused at depths of 5 m and 15 m on fore-reef slopes…
The Tetraodontiformes, which include many non-target species, were particularly susceptible to trapping in both countries. Their abundance in the six islands censused was inversely related to trap fishing pressure, as was that of two other non-target families, butterflyfish (Chaetodontidae) and angelfish (Pomacanthidae)…In conclusion, at the intensities seen in this study, trap fisheries cause serious over-fishing, reduce biodiversity, and alter ecosystem structure. While commonly perceived as low impact, coral reef trap fisheries in the Caribbean and further afield, need tighter regulation and control.
Overfishing and the ecological impacts of extirpating large parrotfish from Caribbean coral reefs
Andrew A. Shantz et al., 2019 in Ecological Monographs “..we combine survey data from 282 sites across the Caribbean with a field experiment to investigate how altering the size structure of parrotfish populations impacts coral reef communities. We show that Caribbean-wide, parrotfish populations are skewed toward smaller individuals, with fishes <11 cm in length comprising nearly 70% of the population in the most heavily fished locations vs. ~25% at minimally fished sites. Despite these differences in size structure, sites had similar overall parrotfish biomass. As a result, algal cover was unrelated to parrotfish biomass and instead, was negatively correlated with the density of large parrotfishes… Unexpectedly, branching corals benefited from excluding large parrotfishes whereas the growth of mounding coral species was impaired. Similarly, removing large parrotfishes led to unexpected increases in coral recruitment that were absent when both large and medium bodied fishes were excluded. Our data highlight the unique roles of large parrotfishes in driving benthic dynamics on coral reefs and suggests that diversity of size is an important component of how herbivore diversity impacts ecosystem function on reefs. ”
Benthic and fish population monitoring associated with a marine protected area in the nearshore waters of Grenada, Eastern Caribbean
Anderson et al., 2012 in Revista de Biología Tropical vol.60 suppl.1 “.. Relative abundance of fishes along 30x2m belt transects did not vary significantly among years however density of fishes decreased significantly across years for most major groups. Chromis spp. dominated the survey sites at 65.2% in 2008 and 49.8% in 2010, followed by territorial damselfish,11.1% and 15.5%, wrasse increased from 7.3% to 15.5%. Both the substrate cover and fish survey data analyses indicated a stable but degraded community.”
Chapter Twelve – The timing and causality of ecological shifts on Caribbean reefs
Precht et al. 2020 in Advances in Marine Biology/Book on “Population Dynamics of the Reef Crisis”. “Caribbean reefs have experienced unprecedented changes in the past four decades. Of great concern is the perceived widespread shift from coral to macroalgal dominance and the question of whether it represents a new, stable equilibrium for coral-reef communities.”
Caribbean reefs of the Anthropocene: Variance in ecosystem metrics indicates bright spots on coral depauperate reefs
Sarah E. Lester et al., 2020 in Global Change Biology “Dramatic coral loss has significantly altered many Caribbean reefs, with potentially important consequences for the ecological functions and ecosystem services provided by reef systems. Many studies examine coral loss and its causes—and often presume a universal decline of ecosystem services with coral loss—rather than evaluating the range of possible outcomes for a diversity of ecosystem functions and services at reefs varying in coral cover. We evaluate 10 key ecosystem metrics, relating to a variety of different reef ecosystem functions and services, on 328 Caribbean reefs varying in coral cover. We focus on the range and variability of these metrics rather than on mean responses. In contrast to a prevailing paradigm, we document high variability for a variety of metrics, and for many the range of outcomes is not related to coral cover. We find numerous “bright spots,” where herbivorous fish biomass, density of large fishes, fishery value, and/or fish species richness are high, despite low coral cover. Although it remains critical to protect and restore corals, understanding variability in ecosystem metrics among low-coral reefs can facilitate the maintenance of reefs with sustained functions and services as we work to restore degraded systems. This framework can be applied to other ecosystems in the Anthropocene to better understand variance in ecosystem service outcomes and identify where and why bright spots exist.”