Ronald L. Shimek, Ph.D.

Editor's Commentary:

Three different, yet related articles comprise this month's Science Notes & News section. The first, by S. Brooke and C. M. Young, describes the early embryonic development and larval biology of an ahermatypic Caribbean coral. Hobbyists will soon need to spawn and raise their own corals if the hobby is to thrive, and this article gives an indication of what is necessary for such aquaculture.

The second article, by K. Fabricius, is a review article detailing some of the effects of terrestrial runoff on coral reefs. Virtually all coral reefs are degraded, and some of the most profound effects are indirectly caused by terrestrial runoff. This article is a must read for anyone interested in the magnitude of coral reef degradation. Not only is coral care in the hands of local individuals, but it is also affected by the activities of people, such as farmers and foresters, some distance from the seashore.

The final article, by M. Hasan, documents the rapid and complete destruction by overfishing of a population of Red Sea cucumbers. The ecological extinction of such animals may be long-term, persistent, and cause profound effects on a reef, yet may occur exceptionally rapidly. This article describes how one such population was effectively extirpated within a couple of years of the initiation of a fishery. Collection of animals for the aquarium trade could easily cause a similar result; this is yet another reason for hobbyists to attempt to grow their own animals. Not only will they ensure a supply of the animals, but they will be forestalling their extinction in nature.

Brooke, S. and C. M. Young. 2005. Embryogenesis and larval biology of the ahermatypic scleractinian Oculina varicosa. Marine Biology. 146: 665-675.

Abstract:

The ivory tree coral Oculina varicosa (Leseur, 1820) is an ahermatypic branching scleractinian that colonizes limestone ledges at depths of 6-100m along the Atlantic coast of Florida. This paper describes the development of embryos and larvae from shallow-water O. varicosa, collected at 6-8m depth in July 1999 off Fort Pierce, Florida (27º 32.542 N; 79º 58.732 W). The effect of temperature on embryogenesis, larval survival, and larval swimming speed were examined in the laboratory.

Ontogenetic changes in geotaxis and phototaxis were also investigated. Embryos developed via spiral cleavage from small (100 lm), negatively buoyant eggs. Ciliated larvae developed after 6-9 hours at 25º C. Embryogenesis ceased at 10º C, was inhibited at 17º C, and progressed normally at 25º C and 30º C. Larval survival, however, was high across the full range of experimental temperatures (11-31º C), although mortality increased in the warmest treatments (26º C and 31º C). Larval swimming speed was highest at 25º C, and lower at the temperature extremes (5º C and 35º C). An ontogenetic change in geotaxis was observed; newly ciliated larvae swam to the water's surface and remained there for approximately 18 hours, after which they swam briefly throughout the water column, then became demersal. Early larvae showed no response to light stimulation, but at 14 and 23 days larvae appeared to exhibit negatively phototactic behavior. Although low temperatures inhibited the development of O. varicosa embryos, the larvae survived temperature extremes for extended periods of time. Ontogenetic changes in larval behavior may ensure that competent larvae are close to the benthos to facilitate settlement. Previous experiments on survival, swimming speeds, and observations on behavior of O. varicosa larvae from deep-water adults indicate that there is no difference between larvae of the deep and shallow populations.

Fabricius, K. E. 2005. Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis. Marine Pollution Bulletin. 50: 125-146.

Abstract:

This paper reviews and evaluates the current state of knowledge on the direct effects of terrestrial runoff on (1) the growth and survival of hard coral colonies, (2) coral reproduction and recruitment, and (3) organisms that interact with coral populations (coralline algae, bioeroders, macroalgae and heterotrophic filter feeders as space competitors, pathogens, and coral predators). The responses of each of these groups are evaluated separately against the four main water quality parameters: (1) increased dissolved inorganic nutrients, (2) enrichment with particulate organic matter, (3) light reduction from turbidity and (4) increased sedimentation.

This separation facilitates disentangling and understanding the mechanisms leading to changes in the field, where many contaminants and many responses co-occur. The review also summarizes geographic and biological factors that determine local and regional levels of resistance and resilience to degradation. It provides a conceptual aid to assess the kind of change(s) likely to occur in response to changing coastal water quality.

Hasan, M. H. 2005. Destruction of a Holothuria scabra population by overfishing at Abu Rhamada Island in the Red Sea. Marine Environmental Research. 60: 489-511.

Abstract:

Populations of Holothuria scabra at Abu Rhamada Island were investigated during 52 months, from July 1999 to October 2003. During the first 23 months (July, 1999-May, 2001) the Island had a robust population with a tri-modal size frequency distribution curve, very high densities (85.7-95.1 ind./100m² at the sandy habitat), high abundance (3362-3110 individuals) and biomass (46.7-34.3 kg/100m²). Also, during this period most individuals were at depths between 4 and 6m and no individuals were recorded deeper than 15m. The population declined after harvesting began (June, 2001) and by March, 2002 the size frequency distribution showed a bimodal pattern with an obvious decrease in abundance of large individuals. There was also a slight reduction in densities (73.2-60.1 ind./100m² at the sandy habitat), abundance (2292-1682 individuals) and biomass (21.6-11.3 kg/100m²), and a marked shift towards deeper waters. Overfishing reached its maximum during the final 19 months of the study, and by October, 2003, density (30.7- 0.4 ind./100m² at the sandy habitat), abundance (802-10 individuals) and biomass (6.9- 0.1 kg/100m²) were all greatly reduced. The size frequency distribution of the population became unimodal, large animals disappeared and no recruits were seen. During this period, individuals were found at very deep depths (30 to >40m). The study also showed that sandy substrate was the preferred habitat for H. scabra, accommodating the largest number of individuals.

The population of H. scabra at Abu Rhamada Island was found to spawn biannually from 1999 to 2001, then only once during 2002 when high fishing pressure occurred, and ceased completely in 2003. The sex ratio was not significantly different from 1:1 before fishing begun, but shifted to an increasing male bias reaching 93% males by January 2003. None of the small animals remaining after January, 2003 could be sexed. Size at sexual maturity decreased from prefishing (185mm for females and 160mm for males) to 155mm for females and 125 mm for males in January 2003. There was a positive relationship between fecundity and size. And oocyte/female was highest in 1999 (0.73-1.7 million) and 2000 (0.75-1.72 million), decreased during 2001 (0.2-0.85 million) to reach its minimum at 2002 (0.28-0.29 million).